ENGINEERING 
 LIBRARY 
 
 x^ 
 
 
 
 *'^- 
 
 ;^^ 
 
 APPLIED 
 AERONAUTICS 
 
 — THE AIRPLANE — 
 
 i. 
 
 PUBLISHED BY 
 
 AIRPLANE ENGINEERING DEPARTMENT 
 
 McCOOK FIELD, DAYTON, OHIO 
 
 U. S, A, 
 
 . iiijii | i»iii 1 1 m i l ji i j i I I. imi.» I.. 
 
 -j^!iB|!|l!'?^!.J-'
 
 THE LIBRARY 
 
 OF 
 
 THE UNIVERSITY 
 
 OF CALIFORNIA 
 
 LOS ANGELES 
 
 GIFT OF 
 
 BALDWIN M.WOODS
 
 i
 
 APPLIED AERONAUTICS 
 
 — THE AIRPLANE —
 
 APPLIED 
 AERONAUTICS 
 
 — THE AIRPLANE — 
 
 First Edition 
 1918 
 
 Published by 
 
 Airplane Engineering Department 
 
 McCook Field, Dayton, Ohio 
 
 U. S. A.
 
 ll.n^in> ermg 
 Cv libraiy 
 
 PREFACE 
 
 TODAY the subject of aeronautics appeals to nearly everyone, due 
 largely to the wonderful progress which has been made in the de- 
 velopment and utility of the airplane since the beginning of the war. 
 
 Although the airplane is among the most important features of 
 modern warfare, yet there are comparatively few comprehensive texts 
 which the beginner in aviation can readily understand. In many cases 
 the student aviator and the aero mechanic have had but a limited tech- 
 nical training nor have many of them been specially trained in nuithe- 
 matics, particularly in the higher branches. Therefore, many of the 
 present-day text-books on aeronautics, which the aeronautical engineer 
 would consider quite elementary, are very difficult for the beginner. 
 
 Realizing the difficulty under which the beginner labors, the Airplane 
 Engineering Department felt that an elementary course in applied aero- 
 nautics and practical aviation was needed, and has brought forth this 
 volume with the hope of filling this need, primarily for the instruction 
 of the men at McCook Field. This book, however, is not intended as a 
 text on the design of airplanes, but was written solely with the thought 
 of imparting a clear idea of the principles of flight, together with such 
 other practical information as can be applied readily by the man in the 
 shop or in the air. 
 
 The text is base<l primarily upon lectures given at the U. S. Army 
 School of Military Aeronautics, Ohio State University. The Technical 
 Publications Department at McCook Field, however, has rearranged, re- 
 classified and rewritten a great deal of the text matter contained in these 
 lectures in order to make the book as clear and instructive as possible. 
 Some of the lectures as given by the instructors have been split up into 
 several chapters, and, where it was felt that certain parts of these lec- 
 tures could be enlarged upon, the Technical Publications Depai'tment 
 has taken the liberty of making such changes as were thought advisable. 
 A number of illustrations and diagrams have been added to those used 
 by the instructors. 
 
 The Airplane Engineering Department therefore gratefully acknowl- 
 edges its obligations to Mr. H. C. Lord for various sections in the first 
 chapter on the theory of flight, and jointly to ^fr. Lord and IMr. O. T. 
 Stankard for a large part of the chapters on instruments. It also wishes 
 
 527090
 
 Preface 
 
 to express its thanks to Mr. ^\. A. Kiiiiilit for the information furnished 
 by him on riggino- and alignment of ])lanes. These men are instructors 
 in the U. S. Army School of Military Aeronautics, Ohio State University. 
 
 It is hoped that this book will assist the student aviator and the aero 
 mechanic in getting one step nearer their goals as efficient and experi- 
 enced units in the U. S. Air Service, and if it accomplishes this result the 
 Airplane Engineering Depai-tment will feel amply repaid for its efforts 
 in bringing it forth. 
 
 Dayton, Ohio, IT. S. A., July 1, 1918.
 
 CONTENTS 
 
 PU(JC 
 Chapter 1 
 
 Theory of FVujht 11 
 
 Investigating wind action — Constant values — Studying action of 
 wind — Streamline shapes — Head resistance — Lift, drift and angle 
 of attack — Suction on top of plane — Center of pressure — Cambered 
 planes — Horizontal flight — Engine power — Power to climb — 
 Stability. 
 
 Chapter 2 
 Types of Machines ------- 37 
 
 General divisions — Dirigibles and balloons — Heavier-than-air craft 
 — Training machines, primary and secondary — Pursuit planes — 
 Reconnoissance machines — Bombing and raiding machines, day 
 and night. 
 
 Chapter 3 
 Hhippiufi, ruJodding (uid AssciiihJi)ifi - - - 41 
 
 Shipping instructions — Marking boxes — Methods of shipping — 
 Railroad cars used — Unloading — Method of loading on truck — 
 Tools required — Unloading from truck — Unloading uncrated ma- 
 chines — Opening boxes — Assembling — Fuselage and landing gear 
 — Center panel and wings. 
 
 Chapter 4 
 Rif/giug -------- 44 
 
 Fuselage — Construction — Longerons — Struts — Fuselage covering 
 — Monocoque — Landing gear — Struts — Bridge — Axle box or saddle 
 — Axle and casing — Wheels — Tail skid — Shock absorber — Wing 
 skids — Pontoons on sea planes— Flying-boat hull — Wing construc- 
 tion — Front and rear spars — Ribs — Cap strip — Nose strip — 
 Stringers — Sidewalk — Struts — Wire bracing — Wing covering — 
 Dope — Inspection windows — Stay Avires and terminal splices — 
 Aircraft wire — Strand — Aircraft cord or cable — Terminals and 
 splices — Soldering — Turnbuckles — Locking devices. 
 
 Chapter 5 
 
 Alignment -------- 58 
 
 Fuselage alignment — Horizontal and vertical stabilizers — Landing 
 gear or under-carriage — Center wing section — Wings — Lateral di- 
 hedral angle — Table for lateral dihedral— Stagger — Overhang — 
 Rigger's angle of incidence — Wash-out and wash-in — Overall meas- 
 urements — Aileron controls — Elevator controls — Rudder controls 
 — Notes on aligning board.
 
 Contents 
 
 Page 
 
 Chapter 6 
 
 (.'are and Inspection - - . - - - - 70 
 
 Cleanliness — Control cables and wires — Locking devices — Struts 
 and sockets — Special inspection — Lubrication — Adjustment — Vet- 
 ting or sighting by eye — Mishandling on the ground — Airplane 
 shed or hangar — Estimating time — Weekly inspection card form. 
 
 Chapter 7 
 
 Minor Repairs -...--- 76 
 
 Patching holes in wings — Doping patches — Terminal loops in 
 solid wire — Terminal splices in strand or cable — Soldering and 
 related processes — Soft soldering — Hard soldering — Brazing- — 
 Sweating — General procedure in soldering — Fluxes — Melting 
 points of solders. 
 
 Chapter 8 
 
 Instruments ........ SO 
 
 Compass — Magnetic error — Variation — Deviation • — Correction — 
 Napier diagram — Heeling errors — Magnetic clouds — Aneroid 
 barometer — Errors — Uses — Altimeter — Errors — Banking meter — 
 Air speed indicator — Incidence indicator — Sperry clinometer — 
 Automatic drift set — Bourdon gauge — Radiator thermometer. 
 
 Properties of Varioii.^ Woods . . . . 103 
 
 Chapter 9 
 
 Nomenclature for Aeronautics . . . . 104 
 
 Based on official nomenclature recommended by the National Ad- 
 visory Committee for Aeronautics and definitions used and 
 standardized by the U. S. Army School of Military Aeronautics at 
 Ohio State University.
 
 APPLIED AERONAUTICS 
 
 — THE AIRPLANE — 
 Chapter 1 
 
 THEORY OF FLIGHT 
 
 Investigating wind action — Constant values — Studying action of wind — Streamline 
 sliapes — Head resistance — Lift, drift and angle of attack — Suction on top of plane 
 — Center of pressure — Cambered planes — Horizontal flight — Engine power — Power 
 to climb — Stability. 
 
 IN THIS age of mechanical flight everyone is interested in airplanes. 
 But very few people, however, clearly grasp the underlying principles. 
 The theory involved, nevertheless, may be demonstrated by simple exi)eri- 
 ments, so that the reader with only an elementary knowledge of mathe- 
 matics and mechanics can understand. 
 
 The simplest principle of airplane flight may be demonstrated by 
 plunging the hand in water and trying to move it horizontally, after 
 first slightly inclining the palm so as to meet, or attack, the fluid at a 
 small angle. It will be noticed at once that although the hand renmins 
 very nearly horizontal, and though it is moved horizontally, the water 
 exerts upon it a certain amount of pressure directed nearly vertically 
 upwards and tending to lift the hand. This is a fair analogy to the prin- 
 ciple underlying the flight of an airplane. The wings of the plane are 
 set at a small angle, and the plane is pushed or pulled through the air 
 by the propeller, which receives its power from the engine. Tlie action 
 of the air on the wings, inclined at an angle, tends to lift the plane just 
 as the action of the water on the hand, inclined at a small angle, has a 
 tendency to raise the hand out of the water. 
 
 Investigating Wind Action 
 
 A rough form of apparatus for studying laws of wind resistance is 
 shown in Fig. 1. The arm E hinged at C carries a rectangular plaiu^ B. 
 The adjustable weight D, supported by the arm F, is used to balance 
 the pressure of the wind from the blower A. The pressure exerted on the 
 plane B can then be measured by moving the weight D along the arm V 
 until B floats with the wind. 
 
 Professor Langley, in another experiment, proved that we can inves- 
 tigate the action of the wind upon various forms of surfaces as well by 
 directing a current of air of known velocity against the surface held in 
 position, and weighing the reactions, as we can by forcing the plane itself
 
 12 
 
 APPLIED AERONAUTICS 
 
 throTigli still air. The special apparatus used was mounted on the end of 
 a revolvinii arm driven by a steam engine as is shown in Fi.c 2. The 
 chronograph, a recording instrument, was used to measure the velocity' 
 or number of revolutions of the table in a given time. 
 
 By such a method as that shown in Fig. 1, and that of Professor 
 Langley, it is easy to see that the laws of pressure and velocity can be 
 determined readily. Methods such as these have been -used in determin- 
 ing that the rvind resistance varies as the square of the velocity. 
 
 In other words, if the velocity is doubled it follows that the resist- 
 ance is increased four times, or if velocity is five times as great, the wind 
 resistance is twenty-five times as large. 
 
 Constant Values 
 
 It would therefore seem to need no experimentation to prove that if 
 we increase the surface B (Fig. 1) we would increase the pressure in 
 direct proportion to the increase in surface area. Now if we were to 
 increase both the velocity and the area of surface, we would increase the 
 pressure proportionally to the product of the square of the velocity and 
 the area of the surface. Thus if we were to raise the velocity of the air 
 three times, the resistance would be increased nine times, and if we 
 then doubled the surface we would double the resistance, which has 
 alreadv been increased nine times, making a total increase of eighteen- 
 fold. 
 
 Fig. 1 — Elementary apparatus for studying huts of wind resistance
 
 THEORY OF FLIGHT 
 
 13 
 
 3/c/e £'/e\/'af''/b/7 of ^/7/r//h^ >^r/?7 
 
 Fig. 2 — Prof. Langlei/'.'^ ajtimratus for inrcs!ti(i<itniii irintl action on 
 various forms of surfaces
 
 14 APPLIED AERONAUTICS 
 
 There is still another factor to take into consideration in calculating 
 wind pressures, and that is the shape of the surface. To take that into 
 account we must use what is called a constant, the value of which is 
 determined by experiments for each particular shape of surface. 
 
 The following explanation will enable one to see very clearly the 
 meaning of the term constant and how its value is determined. First let 
 us explain the term formula which is merely a sentence tersely ex- 
 pressed. To attempt to make a study of flight without formulae would 
 make it necessary to express relations between quantities in long para- 
 graphs of words that could more readily be stated in simple equations. 
 Thus if it were desired to state the rule that the quantity A multiplied 
 by twice the quantity B is equal to C, the formula representing this 
 
 would be : 
 
 A X 2B = C 
 
 Each letter or symbol in a formula represents some factor that is sub- 
 stituted when its value is known. If A == 16, and B = 4, then C = 128, 
 since the rule interpreted reads : 16 X 8 = 128. 
 
 Derived and empirical equations. — The term equation simply means 
 that the quantities on one side of the equal sign are equivalent or equal 
 to the quantities on the other side. Equations are of two kinds, derived 
 and empirical. A derived equation is susceptible to proof, by use of 
 mathematical processes , An empirical equation is neither derived nor 
 proven. It is merely a statement of the results of experiment regardless 
 of mathematical proof. 
 
 In many branches of engineering, empirical formulie are constantly 
 used, and in aviation the lack of a satisfactory basic theory of air flow 
 makes empirical formulae based on experiment most necessary. Empir- 
 ical formuhe are really experimental averages. 
 
 The term constant can now be fully explained and it will be seen 
 how beautifully it works out in a formula. It is often found necessary, 
 
 PROJECTED 
 
 Fig. 3 — IUustratin(j ntcanhig of term "projected area"'' 
 
 especially in an experimental field, to introduce numerical constants to 
 balance the two sides of an equation. For example, the pressure on a 
 surface, as we have already learned, is equal to a constant times the pro- 
 jected area of the surface (see Fig. 3) times velocity squared, or express- 
 ing the same quantities in a formula, 
 
 p = KSV= 
 
 where P = Pressure S = Projected surface area 
 
 K = Constant Y' = Velocity squared
 
 THEORY OF FLIGHT 
 
 15 
 
 The exact value of the constant K for any surface is determined 
 experinientally by wind tunnel tests. So valuable have wind tunnels 
 proven for such determinations that several of the larj-e airplane build- 
 ers now have installed them in their plants. 
 
 In solving- a i)roblem it mi^ht be known that the pressure P varies 
 as the area of the surface and the velocity scjuared, but we could not 
 express this relation in an equation capable of solution until a numerical 
 value for K is determined for the particular shape subjected to the wind 
 pressure, such as the shape illustrated in Fig-. 3. Each different shai)e 
 of surface requires a different value for K, which can be determined 
 experimentally. 
 
 From Loening's Military Aeroplanes 
 
 Fifj. 4 — HliowiiKj forms of eddies set up bij various shaped surfaces in 
 
 air currents 
 
 The majority of formula" for air pressures involve constants, and 
 the great advance in desig-ning during the past two years may be traced 
 directly to the determinations by the aerodynamic laboratories, of bet- 
 ter values of these constants, for use in empirical formulje. So when 
 M, Eiffel, or other men of authority, inform us that the constant K for 
 a flat shape is .003, we accept the value just as we do the report of a 
 chemist who tells us the composition of an alloy. 
 
 Studying Action ot Wind 
 
 A study will now be made of the action of the wind ui)on various 
 surfaces. Fig. i sho^vs what would be seen if the air were filled with 
 smoke or other particles and blown from the blower in Fig. 1 past the 
 surface, and then an instantaneous photograjjh made. You will note how 
 in the first picture the air is piled up in front of the surface and how it 
 eddies and whirls behind it, thus showing that the disturbance extends 
 far beyond the actual obstruction itself. Note the decrease in the eddies 
 in the cases of the other shapes in Fig. 4.
 
 16 
 
 APPLIED AERONAUTICS 
 
 The sphere offers less obstruction than the flat plane, and the two 
 peculiar shapes at the bottom offer still less. Such bodies are said to be 
 streamline. The bii^- end is the advancing end. An old rule for the de- 
 sign of a whaling ship was that "it should have the head of a cod and the 
 tail of a mackerel." With such streamline shapes, K is much smaller in 
 value than for a flat square plane. 
 
 Parasite Resistance 
 
 A picture of a typical airplane is shown in Fig. (J. Notice that all 
 the struts, wires, landing wheels and the fuselage or body offer resistance 
 to passage through the air — a resistance which must be overcome by the 
 engine. The sum total of the separate resistances of all these parts is 
 called the paraf^ite resistance. This wastes power and so all such parts 
 are carefully streamlined wherever possible. 
 
 Fig. 5 — Ejcperiment shoicinfj lift of inclined surface in air current 
 
 Xote the wings or aerofoils, two on each side, one above and one 
 
 below, and at the rear a vertical rudder K in front of which is a vertical 
 
 fin V, and the horizontal fin H, the back part of which can be turned up 
 
 or down by the pilot. The effect of this is to cause the macliine to point 
 
 up or doAvn and thus change the angle at which the relative wind strikes 
 
 the aerofoils. This change, as we will see, has much to do with the flying 
 
 of the machine. 
 
 Lift, Drift and Angle of Attack 
 
 Thus far we have found a lot of things about an airi)lane which 
 would tend to prevent its flying. XoSv let us study Fig. 5. Here Ave 
 haA^e a plane B fastened so that it makes a small angle with the direction 
 of the wind from the blower A. The arm is hinged at C, and balanced by 
 the weight D, so that Avhen the movable weight W is pushed back to C 
 the plane B will be slightly too heavy. When the blower A is started
 
 THEORY OF FLIGHT 
 
 17 
 
 N
 
 18 
 
 APPLIED AERONAUTICS 
 
 the plane B instantly lifts and the aniomit oi" this lift may he measured 
 by the movable weight W. If Ave replaced this model by one exacth' like 
 it except that the plane B makes a much smaller angle with the relative 
 wind we would find that the movable weight W would have to be much 
 nearer C than before. This simple experiment proves the existence of a 
 force which tends to lift the plane and further that this force is greater 
 as the angle is increased. This angle is called the angle of uttack that 
 the plane B makes with the air stream. The force which tends to raise 
 the plane is called the lift, and evidently its value mUvSt depend upon the 
 profile of the plane, the velocity squared, and the angle of attack. 
 
 Besides the lift, there is another force which is due to the plane's 
 velocity through the air, called the drift. This force is due to the fact 
 that the plane itself offers resistance to forward motion through the air. 
 In Fig. 7. A represents a bubble of air, BC a plane moving in the direc- 
 tion of the arrows. Xow evidently one of two things must happen. 
 Either the plane must force the bubble of air down or the bubble of air 
 must force the plane up. This resistance that the bubble of air offers 
 to being displaced, as we have seen, depends upon the square of the veloc- 
 ity with which it is forced out of the way. The total resistance offered 
 by the bubble to the movement of the plane may be represented by the 
 force P acting at right angles to the surface of the plane. The horizontal 
 and vertical components of P are represented by D and L, respectively. 
 
 
 Fif/. 7 — Illustrating how 
 lift and drift result from the 
 moving of an inclined surface 
 in direction of arrows 
 
 If we were to let the air force on the surface have its way, it would 
 push the surface upwards in the direction of L and backwards in the 
 direction of D at the same time. 
 
 So we put weight on the surface, enough to overcome the force L, 
 and then quite logically call this force the lift. And for D, we push 
 against it, with the thrust from a propeller, and we call D the drift.
 
 THEORY OF FLIGHT 
 
 19 
 
 This simple exjdanalioii enables us at once t(t state the reason wiiy 
 flight in heavier-than-air niaehines is possible. By pushing the inclined 
 surface into the air with a horizcuital force D, we create a pressure on 
 the surface equal to P, the force of which I) is the horizontal component. 
 But by doing so we have also created the other component L, which is a 
 lifting- force, capable of carrying weights into the air. 
 
 Consideration of this resolution into lift and drift at once indicates 
 that the characteristics to be sought for in a surface are great lift with 
 a very small drift, so that for a minimtim expenditure of jiower a max- 
 imum load carrying capacity is obtained. 
 
 Apparatus used to prove existence of lift and drift. — An apparatus 
 used to demonstrate the existence of these forces is shown in Fig. 8. The 
 inclined plane B is fastened to the arm S hinged to the carriage C 
 
 Fif/. 8 — Apparatus provintj c.fistence of hoth lift and drift 
 
 at the point F. The carriage rests on a glass plate D and is shielded 
 from the wind from the blower H by the screen E. It is found that when 
 the blower is started the plane B will lift and the carriage C moves 
 slowly backward carrying the plane with it, thus jtroving the existence 
 of lift and drift. The screen E is then removed and it is found that the 
 carriage moves away very rapidly thus showing the effect of the added 
 head resistance due to the carriage itself. 
 
 Suction on Top of Plane 
 
 The flat surface is seldom used for the aerofoils of an airplane. The 
 f(»llowing illustrations and explanation will help to show the reasons for 
 not using it. 
 
 The plane P (Fig. 9) has an opening at O connected to manometer 
 ^I. while on the under side is a similai- o]iening connected to the man-
 
 20 
 
 APPLIED AERONAUTICS 
 
 Fig. 9 — Dcrice for ntea.siiriiu/ coin ituratirc air pressures on upper and 
 lower surfaees of an inclined plane 
 
 ometer N tli rough the rubber tube T. Wheu the blower is started the uiau- 
 ometer M shows suetiou at the poiut O on the ui»i)er side of the i)lane aud 
 N shows pressure on the under side of tlie phine. In other words, the 
 plane is not only bh)wn up, but it is sucked up as well. 
 
 This is very effectively illustrated by a still simpler experiment. 
 Fii>'. 10 sho^^•s; the plane AB of heavy cardboard to which is fastened a 
 light strip of paper at the ptunt A and left free at the point C. When 
 the plane is placed in a wind blowing in the direction of the arrows the 
 paper is seen to be drawn up to the position AC a>\ay from the i)lane AB. 
 
 Fi(j. 10 — Hhon-i)i<j suetion on top of ineJiiied plane irhe)i e-rposed to n-ind 
 current in direction of arrows
 
 THEORY OF FLIGHT 
 
 21 
 
 From Loening's Military Aeroplanes 
 
 Fifj. 11 — CoiHifdndiie rt-sislaitcc to a<1ranccmcnt of a fhit ]tjnn<' at 
 carious aufjles of attack 
 
 Fig. 11 represents smoke pictures of a flat plane in fonr different 
 positions. The lower right hand one shows the plane at a very small 
 angle of attack. The existence of tlie vacnnni at the npper front edge 
 of the plane is very evident. 
 
 E.r peri incuts at Eiffel Lahoratorji. — Fig. 12 sliows the result of accu- 
 rate measurements by M. Eiffel of the suction on top of a plane and the 
 
 F^ressure Curve for 
 Upper \5i/rfc;cG 
 
 /fe/af/ve Mnd 
 
 /^ressure Curve for 
 L o wer •3urface 
 
 Fig. 12 — Prc.ssiti-e diat/raiu of iip/K-r and loa'cr .surfaces of iiicliunl plane
 
 22 
 
 APPLIED AERONAUTICS 
 
 Fifj. 13 — In a flat plane, center of pressure C moves toward the Jeadinfj 
 edge A as the angle of incidence becomes smaller 
 
 pressure underneath. Furthermore. Eiffel has shown bv recent experi- 
 ments that when the angle of incidence of a flat plane is low, the value of 
 the suction on the upper surface is considerably more than that of tlie 
 pressure on the under surface. Thus in this case it is the upper side of 
 the plane which contribiTtes most towards the creation of the lift, a 
 function increasing as the angle grows smaller. This fact shows that the 
 profile of the upper surface of a plane has as much, if not more, impor- 
 tance from the standpoint of the value of lift than that of the under 
 surface. 
 
 Center of Pressure 
 
 In Fig. 1, it is evident that the wind's force on the plane B could be 
 entirely replaced by a single force acting at the center of the plane. The 
 fact that this point would be the center of the plane is due to the fact 
 that the wind strikes the ]»lane aV)solnte]y symmetrically. On an inclined 
 
 Fig. 14 — Location of center of pressure on flal .surface for rarious angles 
 
 of attacl:
 
 THEORY OF FLIGHT 
 
 23 
 
 plane, however, the aetiou of the wind on tlie front or advancing- edge of 
 the plane is different from that on the reai- or trailing edge of the plane, 
 hence, we can no longer say that the center of pressnre is at the geomet- 
 rical center of the plane. 
 
 The resnlt of the double action of the air-cui-rent with pressnre below 
 and suction above, both unecjually distributed, is that the total reaction 
 on the plane is applied at a point C (Fig. 13) nearer to the leading 
 edge A than to the trailing edge B. This point C is called the center of 
 pressure of the plane. In a flat plane, C moves toward the forward edge 
 as the angle of incidence becomes smaller, until when the angle is zero 
 it reaches the point A. 
 
 Tlie curve. Fig. 14, shows the position of the center of pressnre on a 
 flat plane for different angles of attack. It will be noticed that from 
 15 deg. to deg. the center of pressure moves very rapidly towards the 
 front of the plane A. Tlie wind is supposed to be blowing from the right 
 in a direction perpendicular to AB. Airplanes almost never fly with an 
 angle of attack greater than 15 deg. This change in position of the center 
 of pressure very easily can lie pro^•eu hy a well-known and very simjile 
 
 ^ 
 
 c 
 
 B 
 
 C 
 
 Fig. 15 — Center of pressure locatet] close to foncard echje of canlhonnl 
 strip used in simple experiment 
 
 experiment. If we take a strip of light cardboard about 8 in. long by 1^ 
 in. wide we know that the center of gravity will pass through the geo- 
 metrical center. Now if we were to project this through the air in a hor- 
 izontal position with the long side forward, the center of pressure being 
 at the front end and acting upwards, while the weight at the center of 
 gravity acts downwards, a couple would be produced causing the plane to 
 rotate with the advancing edge going up. This shows that the center of 
 pressure is near the front edge. 
 
 We cannot change the center of pressnre but we can change the po- 
 sition of the center of gravity by placing a small lead weight on the 
 front edge. Then if the corners at A and B, Fig. 15, are turned slightly 
 upwards while the whole is given a lateral dihedral angle as shown in 
 the lower iiart of Fig. 15. the plane on being projected in the air is seen 
 to glide almost perfectly. A little practice is necessary in adjusting the 
 weight.
 
 24 
 
 APPLIED AERONAUTICS 
 
 F'reS'Sore Curve for 
 Upper 3urfacG 
 
 D/ reef /on of 
 
 Re/afive Wind 
 
 pressure 
 
 Anc^le of Incidence 
 
 F'ressure Curve for 
 Lower Surface 
 
 Fig. 1(3 — Pressure diagraiii for upper and loirer fares of curved surface 
 u-'ttJi inclined chord. ('oiiip(rre witJt Fig. 12 
 
 of 
 6 en ^er of f^ressurG 
 
 D/recfon of 
 f^e/afve W/nd 
 
 Fig. 17 — Location of center of pressure on a curved surface at various 
 angles of attack, (.'oiujiare irittt Fig. 11
 
 THEORY OF FLIGHT 
 
 ^:5 
 
 Figs. 1(5 and 17 show pressures and the path of the center of pressure 
 for a curved surface. It will be noted first how greatly the suction effect 
 on the tojj of the plane has been increased, and that from zero to 15 deg. 
 (see Fig. 17) the center of pressure moves in exactly the reverse direction 
 from the way it does in a flat plane. This latter effect has a very im- 
 portant bearing when we come to stability. 
 
 Cambered Planes 
 
 Fig. 18 is a rough sketch of what one might call a typical wing sec- 
 tion. Note the <lifference in ])rofile between the top and bottom surfaces. 
 The chord may be defined as the straight line which is tangent to the 
 under surface of the aerofoil section, front and rear, and the miglc of 
 attdcl- as the angle between the relative wind and the chord of the aero- 
 foil. We may write the following simple expression for the lift and 
 the drift : 
 
 The Lift (L) = K^y^ 
 The Drift (D) = L/r. 
 
 l/f/ 
 
 Dnff / Tro///n^ ^doe- 
 
 '/eofAffoc/i 
 
 Fig. IS — Sl'ctch of a typical wing section icith avronuutical terms 
 
 indicated 
 
 The coefficient kj^ depends upon the shape of the aerofoil and the angle of 
 attack and must be determined experimentally. The quantity r, also 
 determined experimentally, is called the lift-drift ratio and measures 
 the efficiency of the aerofoil. 
 
 Fig. 19, gives two curves for an aerofoil of the section shown. The 
 first curve gives the values of the quantity kL for different angles of at- 
 tack, while the second cur^ e gives the values of the lift-drift ratio. 
 
 For example, suppose that an airplane with aerofoils of the ty])e 
 shown, lifting surface 60 s<|. ft., is flying at an angle of attack of 11 deg.. 
 and with a velocity of 70 m.p.h. What will be the lift and the drift? 
 
 Fr(mi the chart. Fig. 19, we find that for this type of plane and 
 angle of attack kj^ = 0.0028 and r =:- 11, hence, 
 
 L = ki.SV- = 0.002S X 60 X (70)= = 823 lbs. 
 
 D 
 
 823 
 
 = 75 lbs. 
 
 11
 
 26 
 
 APPLIED AERONAUTICS 
 
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 0° r a° 3°-^" .5"" e^ 7°a° &" /(r/r/2''/3r/^r/sve''/T/8''/9''2o'' 
 
 A NGLE or /rs/C/OBNCE OF W/As/G CHORD 
 
 Fig. 19 — Curves slioir'nif/ values of Ul and Lift/Drift ratio for a fypieal 
 
 icing section
 
 THEORY OF FLIGHT 27 
 
 Tf now wi' cliaiiue the angle of attack to 3i dei''., keeping the surface 
 and vt'kK'ity the same, we find from the chart that k^ = 0.0014 and 
 r = 13.5, hence, 
 
 L = kLSV= = 0.0014 X 60 X (70)= = 412 lbs. 
 
 L 412 
 
 D = = = 30 lbs. 
 
 r 13.5 
 
 Horizontal Flight 
 
 For horizontal flight the lift produced by the machine's velocity 
 must at all times exactly equal its weight. For if the lift were less than 
 the weight of the plane would fall, while if the lift were greater than 
 the weight the machine would begin to climb. We therefore can replace 
 the lift by the weight W. Then we would have for horizontal flight : 
 
 Weight (W) = kLSV- 
 and the drift (D) = W/r. 
 
 For example, a given airplane weighs I with load) 1800 lbs. Its aero- 
 foils are of the type illustrated and the lifting surface is 120 sq. ft. 
 What will be its velocity for horizontal flight at an angle of attack of 
 12deg.? 
 
 From the chart, Fig. 10, we find that for this type of plane and angle 
 of attack, kL = 0.0029, whence, 
 
 L = W = kLSV^ or 1800 = 0.0029 X 120 X V- 
 
 1800 
 
 transposing, V^ =-- = 5172 
 
 .0029 X 120 
 
 hence, V = >/5172 = 72 m.p.h. 
 
 If now we reduce the angle of attack to 5 deg., the chart. Fig. 19, 
 shows that kL becomes 0.00175, whence, 
 
 1800 = 0.00175 X 120 X V= 
 
 1800 
 
 transposing, V- = = 8572 
 
 0.00175 X 120 
 
 hence, V = yy8572 or 92+ m.p.h. 
 
 The above example illustrates this important priuci])le that, since 
 a machine in horizontal flight, except for a slight loss due to consump- 
 tion of gasoline, maintains a constant weight and a constant surface and 
 since k^ for a given plane de])ends solely upon tlic angle of attack, the 
 V'elocity for horizontal flight is completely determiued Avheu we know 
 the angle of attack. Xow since the pilot can control the auglf of attack 
 by means of his elevators he can control the velocity for horiz(Uital fliglit.
 
 28 
 
 APPLIED AERONAUTICS 
 
 Fig. 20 shows four different positions of the plane corresponding- 
 to four different angles of attack. In each case the machine is flving 
 horizontally, though at first sight one might think that in position 4 the 
 machine was climbing. 
 
 Fig. 20 
 
 FOUR POSITIONS FOR FLIGHT 
 
 (1) Minimum angle. — This is the smallest angle at which horizontal flight can be 
 maintained for a given power, area of surface, and total weight. The minimum angle 
 gives the maximum horizontal flight velocity at low altitude. Note that the propeller 
 axis is inclined slightly downwards when flying at this angle. 
 
 (2) Optimum atngle. — This is the angle at which the lift-drift ratio is highest. In 
 modern airplanes the propeller axis is generally horizontal at the optimum angle, as 
 shown at (2) in the above figure. Note that in the position shown the velocity of the 
 airplane will be less than when flying at the minimum angle. The effective area of 
 wings and angle of incidence for the optimum angle are such as to secure a slight climb- 
 ing tendency at low altitude 
 
 (3) Best climbing angle. — This angle is a compromise between the optimum and 
 maximum angles. Modern airplanes are designed with a compromise between climb 
 and horizontal velocity. At this angle the difference between the power developed and 
 the power required is a maximum, hence the best climb is obtained at this angle. 
 See Fig. 22. 
 
 (4) Maximum angle. — This is the greatest angle at which horizontal flight can be 
 maintained for a given power, area of surface and total weight. If the angle is in- 
 creased over this maximum, the lift diminishes and the machine falls. 
 
 It would seem at first that we have entirely neglected the engine, 
 especially as there is a general impression that the yelocity of a machine 
 depends upon the power of the engine, while as a matter of fact the form 
 of wing sections together with the plane's dimensions are equally, If not 
 more, important. In tlie preceding discussion we have simply assumed
 
 THEORY OF FLIGHT 
 
 29 
 
 that tlie eii.uiiic liad tlic necessary powci- t(» iiiaiiitaiii the ]»hiiie at sucli a 
 vehx-ity as was (h'teniiined l)y that aiiule of attack at wiiicli the i»ih>t 
 drives the maeliiue. 
 
 Engine Power 
 
 The power of any enjiiue is measured by the velocity at which it can 
 move a body against a ^ven resistance, and its nnit. the horsepower, may 
 be define<l as the power re(|nired to lift one pound ;j8,(MI() ft. in one min- 
 ute or 375 miles in one lionr, or the powei- i-ecpiired to lift 375 ponnds 
 one mile in one lionr. 
 
 We must therefore multiply the total resistam-e offered to the air- 
 plane, which consists of the drift plus the jtarasite resistance multiplied 
 by the velocity of the machine, and divide the result by 375 to get the 
 horsepower required. Or. written as a formula : 
 
 (Drift + Parasite Resistance) X Velocity 
 
 Horsepower. 
 
 From the above expression for horsepower, it will l)e noted that since 
 the drift for a given machine depends solely upon the angle of attack, 
 and the parasite resistance depends upon the square of the velocity, which 
 
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 FUl. 'll—Yulue of kj^ <ind Lift Drift ratio for <i f/ircn iiidrhinc
 
 30 
 
 APPLIED AERONAUTICS 
 
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 \3pee d /n m/7e>s per hour 
 
 Fig. 22 — Shoiving poioer required at different angles, 
 also power delivered 
 
 in turn depends upon the angle of attack, we may state that for a given 
 machine with its load, the horsepower is completel}^ determined when we 
 know the angle of attack at which the machine flies. 
 
 Fig. 21 corresponds for the entire machine to Fig. 19 for the aerofoil 
 itself and gives the value of k^ for a given machine, as well as the lift- 
 drift ratio. 
 
 Fig. 22 gives in the heavy curve the power required to drive the 
 machine at the angles of attack marked on the curve, which correspond 
 to the speed in miles per hour given at the bottom. The other set of 
 curves, four of them dashed and one a light line, give the power delivered 
 to the machine by the engine through the propeller. The latter would 
 be straight horizontal lines were it not for the fact that the efficiency 
 of the propeller varies Avith the velocity of the airplane. The ordinates 
 as shown on the left side of the diagrajn correspond to horsepower. 
 
 Let us consider the case where the engine is making 1200 r.p.m. It 
 will be seen that if the pilot changes his elevators so as to fly with an 
 angle of attack of a little less than 1 deg., or of a velocity of about 82.5 
 m.p.h., he will be using every particle of power that his engine can de-
 
 THEORY OF FLIGHT 
 
 31 
 
 liver at that speed. Any slight decrease in the angle of attack will ( jiiisc 
 him to go down probably in a nose dive. As he increases the angle of 
 attack we come to a point where the distance between the two curves, 
 power delivered and power required, is the gi'eatest. Here we will have 
 
 (2*120"^ 21'" SZ'T^ 23"^ 24f" 25"^ 26^ 27"^ 26^ 29'" 30"^ 
 F\(j. I'o — ^<Jioiciiig rapid cliaiif/cs in ici)id vclocit// i)i sitort sixiccs of time 
 
 the greatest excess of po\\er over that used for horizont^il flight, all of 
 which can be nseil in climbing. Hence that ]H)int will be the position 
 for maximum rate of climb. It is indicated by the vertical dash line 
 marked maximum climb at an anjile of attack of a little less than 6 deg.
 
 12 
 
 APPLIED AERONAUTICS 
 
 or a velocity of a little over 55 m.p.li. Increasing his angle of attack 
 still further, or at about 8 (leg., which is the lowest point on the curve, 
 where the horsepower required for horizontal flight is only 30, we get 
 a point of most economical flight. Tlien. as we decrease the angle of 
 attack, the power required rises rapidly until at 40 m.p.h. the two curves 
 cross again and any increase in the angle of attack would cause the ma- 
 chine to stall in the sense of going down, which might take the form of 
 either a nose dive or tail slip. It is well to compare this with Fig. 20. 
 
 F'kj. 24 — Calculation of power required to rVunb 
 
 It is also interesting to compare this with Fig. 23, taken from 
 Langley's The Stored Euergi/ of the Wind, and which illustrates the 
 rapid changes in the velocity of the wind occurring in short intervals of 
 time. The vertical lines represent spaces of one minute and the horizon- 
 tal lines wind speeds differing by 4 m.p.h. It will be noticed that between 
 32 and 24 min. the wind fell from about 37 m.p.h. to 12 m.i).h. and rose 
 again to 38 m.p.h. On account of the momentum of the airplane it would 
 be practically impossible for its actual velocity to change with anything 
 like that rapidity, and as the lift depends upon the square of the velocity 
 it is evident that the pilot would experience a series of ''bumps" when 
 the velocity increased, and momentary drops when the velocity decreased. 
 The feeling has been likened to a motor boat driving rapidly through a 
 choppy sea. 
 
 Power to Climb 
 
 Suppose the center of gravity of a machine be moving in the direc- 
 tion AB, Fig. 24, with a velocity of V miles per hour. The horsepower 
 will then be the sum of two components, viz., that necessary to overcome 
 the wind resistance, as already given for horizontal flight and that neces- 
 sary to lift the machine through the distance CB in the time required for 
 the machine to travel fiom A to B. Now if AB be taken to represent the 
 distance the machine travels in an liour, BC would then represent the 
 velocity of climb. The power consumed in climbing is equal to the 
 product of the weight of the machine in pounds by the velocity of climb 
 in miles per hour divided by 375. Let us call AB/BC the climbing ratio 
 R which gives us BC = AB/ K = V/R. We will have then the i>ower 
 expended in the climb alone equal to WV/R, and the total horsepower 
 becomes :
 
 THEORY OF FLIGHT 
 
 33 
 
 m) 
 
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 ^0 45 50 55 60 65 70 75 QO 65 
 ^peed in rr)/7csper/iour 
 
 Fifi. 25 — SJi(nr'uif/ Jioir drift, ixtraxiic resistance and </Jidiii(/ motion 
 depend npon amjle of attack 
 
 (drift + parasite resistance )V WV 
 
 Horsepower = + 
 
 375 R 
 
 The case of special interest is where the horsepower becomes zero. 
 This is the condition when the engine is shnt off on a glide. 
 When, 
 
 (drift + parasite resistance )V WV 
 
 h = 0, this reduces to 
 
 375 375 R 
 
 W 
 
 R = — 
 
 (drift + parasite resistance) 
 
 It should be noted that the value of R is negative, due to the fact 
 that the machine is gliding toward the earth. Now since both drift and 
 parasite resistance depend upon the angle of attack, the gliding velocity 
 and slope depend upon the angle of attack, and are under the control 
 of the ]>il(>t. This is illustrated in Fig. 25. 
 
 Stability 
 
 One of the most important considerations in an airplane is stabiliiv. 
 which is generally considered under three headings, viz.. longitudinal, 
 lateral and directional.
 
 34 
 
 APPLIED AERONAUTICS 
 
 Para//e/ to Chore/ 
 'of Lokver H^/r?^ 
 
 1 
 
 /Jspecf /^ah'o =3- =3 
 /J spec/- /Pa//o ='-§=j-^ 
 
 ASPECT PATJO 
 
 -3fag(jer 
 STAGGER onc/DECALAGE 
 
 GAP 
 
 LA TERAL D/HEDRA L anc/ SPAN 
 
 ^ r-A/ig/i? o/'/nc/c/ence 
 
 D/hec/ro/ 
 
 LONG/TUD/NAL D/HEDPAL 
 
 Fif/. 2(J — niiistnit'tiH/ iiictiiiiii;/ of .some (icntiKniticul fcfmH
 
 THEORY OF FLIGHT 
 
 35 
 
 \ CenferofFre^^ure 
 
 Center cfn-e^ure 
 
 Ceo^rof/^re^3e/rc 
 
 Cenferof 
 
 FUj. -7 — llic center of pressure of u flat phiiie mores forintnl as the 
 angle of incidence is decreased 
 
 Center of Pre^ssure 
 
 Center of/^re&surc 
 
 Center 
 of Pre-ssure 
 
 Fi(j. 28 — T'/ze center of pressure of a ciirred surface mores foru-ard uitJi 
 decreasiuf/ (uu/Jes of iucidence up to aJtout 12 deg. Below this <iii(/Je it 
 reverses uud uiores toward the center Uf/ain 
 
 Ano/e of Incidence 6 Deoree^ '•'^z:Ay/eof/nc/dencG 2 Decrees 
 Main Surface 
 
 D/recfion of Mof/on -^ 
 
 Angle of /ncfder>ce reduced 
 /Deqree to / Dearee — 
 
 f5tabiliz/ng 
 Surface 
 
 "D/recf/on of 
 Mot/on 
 
 ~Anole of Incidence reduced 
 /De^ee to ^ Degrees 
 
 "^D/recfion ofMof/on 
 
 Fi<j. 21) — Jllusfratiuf/ hou' the rear surface Jias its auiiJe of incidence 
 reduced in f/reater proportion than does the front surface ndien the com- 
 hi nation is tipped dou-uirard
 
 36 
 
 APPLIED AERONAUTICS 
 
 Loii(/itii(Jin<iJ siaJ/ilitji. — Tliis stability is needed to keep the airplane 
 from pitching nose downward or tipping backward, nose up and tail 
 (h)wn, whenever a gust or eddy is encountered. 
 
 Flat surfaces are longitudinally stable because, as shown in Fig. 14, 
 the center of pressure moves toward the leading edge as the angle of 
 incidence is decreased. Fig. 27 sIionms four positions of a flat surface 
 moving from right to left. Gloving horizontally as in posithm A the cen- 
 ter of pressure is at the leading edge, and when in the vertical position I) 
 the center of pressure coincides with the transverse center line of the 
 surface. However, suppose the surface to be moving as at C and a sudden 
 gust of wind tips it into position B with a lesser angle of incidence. Then 
 the center of pressure moves forward, introducing a greater moment and 
 tending to force the plane back into its original position (\ On the 
 other hand, if the surface assumes too great an angle, the center of pres- 
 sure moves back and tlie rear is forced up, causing the surface again to 
 
 NORMAL POS/T/ON 
 
 A equa/s 8 
 
 T/PPED POS/T/ON 
 
 A qrea/er /h^r? 3 
 
 F'kj. 30 
 
 resume its original position C. Thus, if it were not for the fact that the 
 flat surface has a very poor ratio of lift to drift, it could be used in air- 
 planes to advantage, due to this inherent longitudinal stability. 
 
 Next consider Fig. 28, giving three positions of a cambered surface, 
 which has a much greater lifting etticienc^- than a flat surface. It is also 
 supposed to be moving from right to left. In position C the center of 
 pressure coincides with the transverse center line. Supposing this sur- 
 face to be moving in attitude V> with the center of pressure at approx- 
 imately the position indicated. If it is suddenly tipped into jtositiou A, 
 it will be seen that the front part has a negative angle of incidence, 
 which results in a do\\nward i)ressure on this portion. The center of 
 pressure of the surface being the resultant of all forces acting, it is obvi- 
 ously affected l)y this action at the front, and moves backwards. If 
 the surface is tipped still further, the backward nunemeut of the center 
 of pressure is increased and therefore there is still less tendency to push 
 the front up, Avhen such a tendency would l»e utost desirable. On the 
 other hand if the auule of iuci<leu<'e becomes suddeulv ureater than the
 
 THEORY OF FLIGHT 
 
 Z7 
 
 iioniml position li, the pressure on the front ed-c decreases and the re- 
 sultant center of j)ressure moves forwai'd, thus tendinj> to push the front 
 up and .i;ive the surface a still <>reater an^le of incidence. 
 
 Therefore, it is necessary to have some way of compensating; foi- this 
 instability of cambered surfaces, and this is done by the use of 'an auxil- 
 iary stabilizing; surface somt^ distance back from the main surface and 
 set at a lesser anj>le of incidence than the main surface. Such a stabilizer 
 is a necessary feature of all modern airplanes. Fi"-. 29 shows two such 
 surfaces in tandem, thus formiui- an elementary aiiplane. (\>nsider the 
 airplane to be traveling; horizontally with the an^le of incidence of the 
 
 ■T^erf/cc?/ Ax/s 
 
 W/hc/ 
 
 Verf/ca/ /y'n 
 
 Fifj. 30A — Diafjnnii to show action of fcrticd] fin in preserrinr/ 
 
 directional stafiilitij 
 
 main surfaces (> deo-. and the lear one-third of this, or 2 de.u. Xow sup- 
 posing a sudden gust pitches the plane into some such position as shown 
 in the lower part of the diagra.m. The angle of incidence of both surfaces 
 is now reduced say 1 deg., the main surface being at a 5 deg. angle 
 and the rear surface at 1 deg. In other words, the main surface has lost 
 only about IT percent of its angle of incidence, whereas the stabilizer 
 has lost 50 percent, ronsecjuently the stabilizer has lost more of its lift 
 than the main surface, and it therefore must fall relative to the position 
 of the main surface, bringing the combination back into normal position 
 again. On the other hand, if the front of the ])lane is suddenly forced up, 
 the stabilizing surface receives a relatively greater increase in angle of
 
 38 APPLIED AERONAUTICS 
 
 iucidence than the main surface, lienee relatively greater increase in lift, 
 causing- the hack, end of the plane to be brought up until the combination 
 again is normal. 
 
 Lateral stahUity. — This stability is necessary to prevent the machine 
 from rolling about its horizontal axis. It is difficult to secure, but is 
 often promoted by having a slight lateral dihedral angle between the 
 upper wing surfaces, as shown in Fig. 30. Should the airplane suddenly 
 be tipped to one side, in the position shown to the right of the diagram, 
 the planes on the dov.n side become more nearly horizontal, whereas, 
 those on the other side assume an angle still greater than they had when 
 flying normally. Thus, the effective projected lifting surface on the 
 side A is increased and that on side B is decreased, briugiug the i)lane 
 back to its normal lateral position. Other features are introduced to aid 
 lateral stfll)ility, such as "wash in" on the left side to give this side 
 slightly more lifting ability to compensate for the torque of the propeller. 
 
 Directional stahUltji. — Sucli stal)ility aids in keeping the plane on 
 its course. In order to prevent ya^^■ing with every gust of wind, the 
 vertical tail fins present on nearly all modern ])lanes are used. Kefer- 
 ring to Fig. 30 A, suppose a sudden gust of wind to deflect the airplane 
 from its normal course A so that the nose points off the course to the 
 pilot's left, as indicated by the dotted lines in position B. This swings 
 the tail around to the right so that the right side of the vertical fin pre- 
 sents a flat surface to the wind pressure resulting from the tendency of 
 the machine still to move forward in the direction A, due to its inertia, 
 even though it is temporarily pointing in direction B. A moment with 
 arm r is thus set up, which tends to swing the plane back on its vertical 
 axis until the fin is again parallel to the direction of the relative wind. 
 The action is similar to that of a wind vane, the vertical fin of which 
 always keei>s it pointing in the direction of the wind.
 
 Chapter 2 
 
 TYPES OF MACHINES 
 
 General divisions — Dirigibles and balloons — Heavier-than-air craft — Training machines, 
 primary and secondary — Pursuit planes — Reconnoissance machines — Bombing and 
 raiding machines, day and night. 
 
 ALL aircraft arc divided into two iicneral classes: heavier tlian air 
 and lighter than air. In tlie li.uliter-than-air class ( which <-onsists 
 of aircraft snpported in the air Ity the Itno.vancy of a ii'as, li.uhter than 
 the ail- it displaces, contained in a jias l)aii <»f some convenient fornii. a 
 further snh-divisiou may he made into diriiiihles, or craft e(|uipped 
 with a power plant, propeller and vertical and horizontal rn<lders. so 
 that they can he operated and steered at the will of the pilot, and hal- 
 loons, or craft not fitted with any means of propulsion or steei-in<>-, 
 and which therefore drift with the wind unless held captive hy means of 
 a cahle anchorinii' them firmly to a point on the liround. 
 
 Diriiiihles are further divided into three types, the rijiid, the semi- 
 rigid and the non-riiiid, all three of which are being- used to a consider- 
 al)Ie extent in the present war. The Z(^])i>elin. which has ])roven such a 
 costly failure for Germany, is the outstanding example of the rigid con- 
 struction. The Blimp as used so successfully by the British in coast- 
 guard observation and anti-submai-ine work, and as being made in this 
 country, is a good example of the non-rigid type. There are several ex- 
 anijiles of the semi-rigid construction, such as the German Parseval and 
 others. 
 
 In the balloon, or non-dirigible class, the captive observation balloon 
 and particularly the kite type balloon are being employed to a consider- 
 able extent, even though they may fall an easy prey to enemy airi)lanes 
 unless strongly protected, ^^'ith improved methods of i)rotection, by 
 means of anti-aircraft barrage, the employment of winches which rapidly 
 pull the captive balloon to cover, and a thorough protective patrol by 
 scouting airplanes, the balloon as a means of reconnoissance and for long 
 distance artillery observation has come into increased favor. Important 
 improvements are also being attempted by using non-inflammable gas 
 in the balloon, or by fitting a protective housing consisting of an outer 
 baa' containinu' an inert "as such as nitronen.
 
 40 APPLIED AERONAUTICS 
 
 In any case the observer in a captive balloon is always equipped 
 with a parachute ready for immediate use in case the balloon should be 
 destroyed by the enemy by any means before it could be pulled down. 
 
 Aircraft Heavier Than Air 
 
 There are four types of heavier-tlian-air machines: airplanes, kites, 
 helicopters and ornithopters. Only one of these, the airplane, for prac- 
 tical reasons is worth considering at this time. This type, bein<>- of gi'eat- 
 est importance will be studied botli from the standpoint of its uses and 
 its constructional features. 
 
 Airplanes for military use are divided into five i>eueral types: train- 
 ini>-, pursuit, combat, reconnoissance and bond)ino or raiding-. 
 
 Traiuuu) machines are either primary or secondary. The former is 
 used in elementary training and is generally of the dual control type, 
 so as to allow the instructor to control the machine until the pupil be- 
 comes accustomed to the "feel" of it, under the guidance of an experi- 
 enced pilot, then take over the control gradually, and to allow the in- 
 structor to correct mistakes of the pupil before they can have serious 
 consequences. Machines called "rollers"' or "penguins," having curtailed 
 wings to prevent them actually rising off the ground, are also used in 
 primary instruction. Secondary school machines are generally similar 
 to those used for actual fighting work ; this being particularly true of 
 scout or pursuit nmchines for "stunt'' flying. Training machines should 
 be easily handled, should possess marked inherent stability and should 
 have a fairl}^ slow get-away speed. A familiar machine used in this 
 country has the following characteristics : 
 
 Tractor biplane 
 Two seater 
 
 Horsepower — 80 to 120. 
 Radius of flight— 200 mi. 
 Rate of climb — 300 ft. per min. 
 Minimum flying speed — 45 m.p.h. 
 Maximum speed — 75 m.p.h. 
 
 In France and England, quite a number of Farman and B. E. 
 pusher machines are used for training, and for advanced work the Nieu- 
 port Scout, the Bleriot monoplane and similar machines are used, espe- 
 cially in French schools. 
 
 Pmsiiit planes. — This class comprises the fastest and most easily 
 handled machines that it is possible to produce. Their offense depends 
 on speed and their defense on ability to maneuver. Due to the great 
 strains imposed in "stunt" flying, the monoplane has lost favor on ac- 
 count of structural weakness. The ^lorane monoplane which is still in 
 use is, however, an exception. The Nieuport one-and-one-half plane, — 
 probably the most successful pursuit machine — the Spad, the English 
 Bristol and the Sopwith scouts are all popular with Allied aviators. The
 
 TYPES OF MACHINES 41 
 
 prime requisites for scouts are speed, ability to climb ami power to ma- 
 neuver. Scouts may be either sinjile or two-seaters. They always carry 
 one <»un either fixed and firin*; tlirouj^h the propeller or on tlie upper 
 plane. Other gun mountings may be used, however, especially when an 
 extra passenger is carried. The princiijal characteristics of scouting 
 machines are : 
 
 Tractor biplane 
 
 Horsepower — above 150 
 
 One or two-seater 
 
 Kadius of fligiit— 300 mi. 
 
 Kate of cliud> — over 800 ft. per min. 
 
 Minimum flying speed — 50 m.p.h. 
 
 Maximum speed — 150 m.p.h. 
 
 Ceiling— 20,000 ft. 
 
 Combat itKicliiiirs. — Airplanes of the combat type are used exten- 
 sively for strictly fighting i)urposes, and are essentially the same as the 
 reconnaissance type machines except that they are stripped of wireless 
 equipment, photographic apparatus and other accessories not essential 
 for fighting purposes. The combat machine is a two-seater and carries 
 four guns, two in the observer's cockpit, and movable on a circular track 
 surrounding the cockpit, and the other two fixetl and synchronizi^l to 
 fire between the propeller blades and operated by the pilot. These ma- 
 chines usually have a ceiling of between 20,000 and 23,000 ft. and carry 
 oxygen tanks for the passengers. They are of the tractor biplane type, 
 and considering their weight and fighting ability, have .remarkable 
 maneuverability. The principal features of combat planes are : 
 
 Tractor biplane 
 Horsepower — 250 or more 
 Two passengers 
 
 IJadius of flight — 300 miles or more 
 Kate of flying— 10,000 ft. in 10 min. 
 31inimum speed — 50 m.p.h. 
 ^Maximum speed — 150 m.p.h. or over 
 Ceiling— 20,000 to 23,000 ft. 
 
 The recoil nois.w nee machine. — This type, usually carrying an ob- 
 server, wireless, photographic apparatus and sometimes a number of 
 light bondis is usually armed with one or two machine guns. The pur- 
 pose of this type is to do various forms of scout and observation work 
 both above and behind the lines, and also contact patrol work. These 
 machines fly at altitudes of from 2,000 to 0,000 feet and usually rely 
 on the pursuit machines for ju'otection. This class of machines is one 
 which comprises a large assortment of constructions. They are gener- 
 ally biplanes, pusher or tractor, and quite often with single, double or 
 triple motors. The armament consists generally of two machine guns.
 
 42 APPLIED AERONAUTICS 
 
 one mounted fixed and firing ahead, tlie other niovahh^ and operated by 
 the observer. The general (jualities of these phxues are as f oUows : 
 
 Biplanes — tractor, pusher or combination 
 Two passenger or more 
 Horsepower — 200 or over 
 IJadius of flight — 300 mi. or over 
 Kate of clind) — 200 ft. per min. or over 
 Mininmm flying s])eed — 50 m.i).li. 
 ^Maximum speed — 110 m.p.li. or over 
 
 BomhiiKi or r(ti<1iii(/. — These machines are large, slow, weight-carry- 
 ing planes. In order to get the latter quality, a biplane, triplane or even 
 a multiplane construction is necessary since there is a limit to the span 
 of wings. Parasite resistance is high and horsepower must necessarily be 
 large. This form of machine is rather new and has been developed dur- 
 ing the i-ecent war, because of its wonderful possibilities, and it is only 
 reasonable to suppose that very nuirked improvements will conu^ in the 
 future. The larger Handley-Page (British) bombers, and tlie Italian 
 Caproni triplanes are an indicarion of what developments are being made 
 in raiding machines. If the Allies are successful in clearing the air of 
 German j)lanes, any destruction or offensive operations must be accom- 
 plished by the bomber. The extent of damage which might be inflicted 
 in this way is limited only by the nuudter of machines and the amount of 
 bombs dropped. These planes rely on the accompanying pursuit planes 
 for protection. Paiding or bombing exj)editious are always carried out 
 in fornuition and the number taking part is unlimited. The character- 
 istics likewise are without limit. 
 
 The principal features of the large boud)ing planes are as follows: 
 
 Biplane, Triplane 
 
 Horsepower — no upper limit. (As many as five 
 
 engines are being used. ) 
 Xund)er of passengers — from two up 
 Kange of action — over 300 mi. 
 Weight carried — above 1000 lbs. 
 Bate of climl) — 250 ft. per min. and over 
 ^lininnnn flying speed — 45 m.p.h. 
 Maximum speed-— up to 85 m.p.h. 
 Ceiling— 10,000 ft. 
 
 A further classification of day and night bombers is made. Night 
 work is dependent on suitable lighting signaling arrangements, proper 
 landing signals and the ability to reckon position in the dark. The Ger- 
 mans have given considerable attention to this branch and it is also bfeing 
 practiced by the Allies.
 
 Chapter 3 
 
 SHIPPING, UNLOADING AND ASSEMBLING 
 
 Shipping instructions — Marking boxes — Methods of shipping^ — Railroad cars used — Un- 
 loading — Method of loading on truck — Tools required — Unloading from truck — 
 Unloading uncrated machines — Opening boxes — Assembling — Fuselage and landing 
 gear — Center panel and wings. 
 
 ^HJPPIXG iii-sf ructions. — Boxes in \vlii<h airplanes or parts tliere<jf 
 ^ are sliijjped should l)e marked with the followinji': 
 
 Destination, or name and address of eonsiijnee in full. 
 
 Sender's name. 
 
 Weiulit of l)ox (<»TOSs, net and tare). 
 
 ('nl>i(' contents (or lenj>th, widtli and heiiiiht). 
 
 Box and shipment nnmlier. 
 
 Hoistiiiii' center. 
 
 "This side np." 
 
 }f('tliO(]s of sJtipiiiii!/ iiHtcliiiK's. — Machines are shipped cither hy 
 loadinu in a railroad car withont cratini*, or by crating in two boxes. 
 In the latter case the win^s, center section panel, tail snrfaces, landinii 
 geiu' and propeller are removed from the fnselaije, and the fnselai»e, land- 
 iiii» j.iear, propeller and radiator are packed securely in the fnselaiie box. 
 The other parts are packed in the panel box. All aerofoil sections are 
 stood on their enterin<»- edi^es and secnrely padded to protect their cover- 
 ing's. Stmts are stood on end. 
 
 If the machine is not to be crated only the followiiiii i)arts are re- 
 moved — winii's, center section panel, tail surfaces and jn'opcllcr. The 
 fnselai>e is loaded into the railroad car and allowed to rest on the landiuj; 
 ijear. The latter should be blocked np, however, to take the l<»ad off the 
 tires of the iandinu _i;var wheels and off the shock absorl)ers. The fiisel- 
 aiie iiinst of course be secnrely fastened in the car to ])revent movement 
 in any direction. The win«is and other separate ])arts are crated aiiainsr 
 the sides (►f the car. The win<is are secnre«l with their entering; wedues 
 down and carefully padded to prevent damajie. 
 
 Railroad ears asnl for tniiisporfatioii. — If i)ossible o]»en end or aut(>- 
 mobile cars are used for transportation of airi»lanes. Sometimes with 
 crated machines sondola cars are used, and with uncrated machines.
 
 44 APPLIED AERONAUTICS 
 
 ordinary box ears having no end doors. In the hitter ease, however, it 
 is necessary that the side doors of the railroad car be as wide as possible, 
 to allow working the fuselage in and out without damage. 
 
 For transporting machines (either crated or uncrated) from the 
 railroad, a flat top truck is used. If the truck is short it will be necessary 
 to use a trailer to support the overhang of the boxes. 
 
 Unloading 
 
 Metliod of Joadiny on truck. — Before unloading a machine, every- 
 thing in the railroad car should be inspected for loss or damage. If 
 everything is O. K. proceed with the unloading, but if any loss or damage 
 is discovered report fully at once to the receiving officer and await his 
 instructions before doing anything further. 
 
 The tools required for removal <»f airplane boxes from the railroad 
 car are : 1 axe or hatchet, 2 crow bars, 6 or 8 rollers and 100 ft. of 1 in. 
 rope. 
 
 The cleats holding the boxes to the car floor are first removed with 
 the axe and crow bars, and the panel box removed from the car. If the 
 fuselage box is not marked to show which is the front end it should be 
 lifted slightly, if possible, first at one end and then at the other, to de- 
 termine which is the engine end. This end, being the heavier, should 
 come out first if possible. 
 
 The truck is backed up to the door of the car, rollers are placed 
 under the fuselage box and it is then rolled out onto the truck. The rope 
 is now used to fasten the box to the truck. After this is done the truck 
 is moved forward slowly and the box is thus pulled out of the car. If a 
 trailer is to be used it should be placed under the box before the latter 
 is taken all the way out of the car. 
 
 When taking the fuselage out tail end first, the same methods are 
 used, except that the light end is blocked up ^^ilen removed from the car 
 and a truck is put under the heavy end. 
 
 When moving along roads care should be taken to go slowly over 
 rough places, tracks and bad crossings. It is also a good policy to have 
 a man on each side of the box to watch the lashings and see that nothing 
 comes loose. 
 
 Panel Box 
 
 The wing box (or panel box) is removed from the car in the same 
 manner as the fuselage box. 
 
 Unloading ho.res from triicl\ — For this work 2 planks about 2 in. x 
 12 in. X 12 ft. long should be used. These should be fastened to the end 
 of the truck with one end resting on the ground, so that they will act as 
 skids. The tail end of the fuselage box is depressed until it rests on the 
 ground, then by moving the truck forward carefully the box will slide 
 down the planks onto the ground. 
 
 Unloadinf/ uncrated machines. — In this case all of the smaller parts 
 should be removed first. Then the cleats and ropes are removed which
 
 SHIPPING, UNLOADING AND ASSEMBLING 45 
 
 hold the inachiiie in the oar. Two lon^ plauks are placed from the door 
 of the car dowu to the j^roimd and are used to roll the machine ont of 
 the car. 
 
 Open ill (J })().i-es. — A screw driver and bit brace should be used to re- 
 move the screws in the top, sides and ends of the box. The top is re- 
 moved first, then one side. All smaller parts of the machine should be 
 taken out, after which the remaining- side of the box is removed, and 
 lastly the ends. 
 
 Asseiiihliitfj a machine. — The landing gear should be put on first. 
 To do this the fuselage must be raised by one of two methods. The first 
 is by chain falls or l)lock and tackle. The rope sling should be passed 
 under the engine sill just to the rear of the nose plate. The tail of the 
 machine is allowed to rest on the tail skid while the nose is raised. The 
 second method is by shims and blocking. This latter method is the most 
 common because chain falls are not always available. Enough blocks 
 should be secured to raise the fuselage high enough to slip the landing 
 gear underneath. The tail is first raised l)y 2 men and blocks are i^laced 
 under Station 5 or the rear wing section strut. The blocking must be 
 directly below the strut and must have padding upon it. Then the tail 
 is depressed and another block is put under the forward wing strut. This 
 operation is then repeated until the fuselage is high enough for the land- 
 ing gear when the nmchiue is blocked under nose and tail and the other 
 l)locks are removed. Three or four men are all that should l)e required 
 for this second method. 
 
 Assembling Wings 
 
 After the landing geiir is assembled the center section panel should 
 be attached and approximately lined up. Then the wings are assembled. 
 There are two methods for doing this; one is to put on the top i)lanes, 
 place supports under the outer edges, then put in struts and lower planes 
 and connect up the wires. The other method is to assemble the wings 
 completely while on the ground. Wings are stood on their entering 
 edge, struts are put in and wires tightened up to hold the wing sections 
 together. Then the wings are attached to fuselage by turning them over 
 and attaching the top wing first, then the lower wing. One side of the 
 machine must be supported until the opposite set of wings is attache<l. 
 After wings are all attached, then the tail surfaces should be assembled 
 to the body. The horizontal stal»ilizer should go on first, then the ver- 
 tical fin. rudder and elevators in the order named. On some nuichines 
 the elevators will have to l)e put on liefore the rudder. After everything 
 is assembled the machine is put in alignment.
 
 Chapter 4 
 
 RIGGING 
 
 Fuselage — Construction — Longerons — Struts — Fuselage covering — Monocoque— Landing 
 gear — Struts — Bridge — Axle box or saddle — Axle and casing — Wheels — Tail skid — 
 Shock absorber — Wing skids — Pontoons on seaplanes — Flying boat hull — Wing 
 construction — Front and rear spars — Ribs — Cap strip — Nose strip — Stringers — 
 Sidewalk — Struts — Wire Bracing — Wing covering — Dope — Inspection windows — 
 Stay wires and terminal splices — Aircraft wire — Strand — Aircraft cord or cable — 
 Terminals and splices — Soldering — Turnbuckles — Locking devices. 
 
 "O IGGING deals with the erection, alignment, adjustment, repair and 
 ■■■^ care of airplanes. 
 
 Airplanes are of liiiht skeleton construction with parts largely held 
 together with adjustable tie wires, hence they easily can be distorted or 
 their adjustment ruined by careless or improper rigging. The eflficiency, 
 controllaltility, general airwortliiness and safety of machine and pilot 
 therefore depend very largely upon the skill and conscientiousness of the 
 rigger. 
 
 For purposes of description the airplane may be divided roughly 
 into three parts ( exclusive of the power plant ) . These are the body or 
 fuselage, the wings or aerofoils and the landing gear. 
 
 The fuselage is the main structural unit of the airplane. It provides 
 a support and housing for the power plant, contains the cockpit for the 
 pilot, and the instruments and control mechanism. The rear end of the 
 fuselage carries the rudder, elevators, stabilizing fins and the tail skid. 
 The wings or aerofoils are attached to the fuselage through suitable 
 hinged connections or brackets and the fuselage is supported by the 
 wings when the machine is in the air. Conversely the wings are sup- 
 ported from the fuselage when the airplane is on the ground, as in that 
 case the Mdiole weight of the machine is supported by the landing gear 
 and the tail skid, liotli of which are attached under the fuselage. 
 
 The body or fuselage is of trussed construction, a form which gives 
 great strength and rigidity for a given weight of material. Parts as- 
 sembled together in the form of a truss are spoken of as members. Those 
 which take a thrust only are called compression members, while those 
 resisting a pull are known as tension mend)ers. 
 
 Other members may be either tension or compression members, de- 
 pending on how the load or force is applied to them at any given time. 
 There are also members subject to a shearing stress and others to cross- 
 bending or compound stresses.
 
 RIGGING 47 
 
 The fuselage is usually coustnieted with four main louiiitudiiial 
 iiieiiibers inniiing the full length. These are called longerons. Thev are 
 ,sei)arated at intervals by (•oiu})ression niend)ers termed stmts. The whole 
 structure is in turn tied together and braced by means of diagonal wires, 
 fitted with turnbuckles for adjustment, which go under the geiUMal name 
 of wire bracing or- stay wires. 
 
 Stay wires in certain parts of an airplane are designated as flying, 
 ground, drift, anti-drift, etc. These will be considered later. 
 
 That part of the surface of the fuselage which is bounded l)y two 
 struts and two of the longerons is known as a panel. The points at which 
 the struts join the longerons are calh'd ])anel points or stations. The 
 cubical space enclosed by eight struts and the four longerons is called a 
 bay. Some makers, Curtiss for instance, number the stations in the 
 fuselage from front to rear calling the extreme front station No. 1. Oth- 
 ers, such as the Standard, nundier these stations from the rear toward 
 the front, calling the tail post zero. 
 
 The longerons are made of well-seasoned, straight-grained ash. They 
 are curved inward toward the front end and usually terminate in a 
 stamped steel nose plate. This is true particularly of airplanes ecjuipped 
 with engines of the revolving cylinder type. The nose plate is stamped 
 from plate steel about .10 in. in thickness. This plate not only ties the 
 longerons together at the front end of the fuselage, but supports one end 
 of the sills on which the engine rests. In some types of planes it also 
 forms a bracket for sui)porting the radiator. In other types of air])lanes 
 the longerons may terminate at the front end of the fuselage in an o])en 
 frame which forms the supx^ort for the radiator and also supports the 
 front ends of the engine bearers or sills. The two upper and the two 
 lower longerons are brought together in pairs one al>ove the other at 
 the rear end of the fuselage, and are joined to the tail post or vertical 
 hinge post on which the rudder is mounted. 
 
 Lightened Construction 
 
 In order to lighten the construction of the fuselage as much as pos- 
 sible, the rear portions of the longerons are often cut out to an I section 
 and spruce is often substituted for ash for the rear half, suitable splices 
 .strengthened with fish plates being used wherever joints are nmde in 
 the longerons. It is possible to lighten the rear portion of the fuselage 
 in this way for the reason that this part of the body does not support as 
 much weight or undergo as severe stresses as the forward portion. 
 
 In a machine of neutral tail lift (one in which the rear horizontal 
 stabilizers are set at such an angle that they barely sustain the weight 
 of the rear portion of the machine when flying horizontally in the air I 
 the stresses in the longerons are exactly the opposite when the machine 
 is in the air to those obtaining on the ground. When the machine is at 
 rest on the ground it is supported near the front and i-ear ends of the 
 fuselage by the landing gear and the tail skid. Tliis metliod of su])port 
 produces tension in the lower longerons and compression in the u])per.
 
 48 APPLIED AERONAUTICS 
 
 When in the air the machine is supported by the wings which are attached 
 to the fuselage at the center wing- section. The system of supports, trusses 
 and stay wires between the upper and lower wings transfers most of the 
 support from the wings to the center panel section of the upper wing. This 
 results in tension in the upper longerons and compression in the lower. 
 The fuselage struts are usually made of spruce, although ash is some- 
 times used. The struts are joine<l to the longerons by means of metal 
 clips. The construction of the clips, which are usually bent in U shape, 
 is such that each forms a partial socket for receiving the end of a strut 
 or struts. In general, struts are subjected to compression only. For this 
 reason spruce is the favorite wood for struts as it is very strong along the 
 grain in tension or compression. The strength of steel, weight for 
 weight, would have to be 180,000 ll)s. per scpiare inch to ecpial spruce for 
 this purpose. Spruce is not, however, very strong across the grain and 
 splits readily, hence it is not a great favorite for parts subject to shearing 
 or cross-l)ending stresses. On account of the liability of spruce to split- 
 ting, the ends of the struts are sometimes encased in copper ferrules or 
 bands. This prevents crushing, splitting and chafing. 
 
 Compression Struts 
 
 When a member is subjected to a compression force it tends to bend 
 or buckle in the center. To resist this tendency, struts subject to com- 
 pression stress are umde larger in the center than at the ends. 
 
 Ash is selected for the longerons because it is strong for its weight 
 (about 38 lbs. per cu. ft.), very elastic and can be obtained in long, 
 straight-grained pieces free from defects. It is strong across the grain 
 so that it is able to resist the compression due to clips and struts at- 
 tached at various points on the longerons. 
 
 The metal clips in which the ends of the struts are mounted ase 
 punched from sheet steel then pressed to form. They are frequently nmde 
 of two or three separate pieces which are then electrically spot-welded 
 together. They are made of .28 to .30 percent carbon steel. 
 
 The lower cr<)ss-meml)ers of the fuselage at stations 3 and 4, num- 
 bered from the front, terminate in a half hinge to which the lower wing- 
 sections are attached on either side of the fuselage. These cross-members 
 serve as compression members when a machine is on the grcmnd, but when 
 it is in the air they become tension members. 
 
 Engine Bearers 
 
 The engine bearers are nmde of spruce with a strip of ash glued on 
 top and bottom. They are further protected against crushing, at points 
 where the engine supporting arms rest on the sills or stringers, by melius 
 of a copper band. 
 
 There is usually a fire screen between the engine space and the cock- 
 pit. This is to prevent injury to the pilot so far as possible in case of 
 a back fii'e or fire in the engine space.
 
 '1 

 
 ■ Ce^/ff/»- /Sv7ff/ 
 
 
 Fig. 31 — Hhomnij principal parts of fiisehi
 
 RIGGING 49 
 
 Tlie seat rails are sliort loiiiiitndinal iiicniltcrs forjiiiii^ siippoi-ts for 
 tlie pilot's and observer's seats. These rails, which are mounted on either 
 side of the fuselage, are attached to adjacent vertical struts at the proper 
 distance above the lower longerons. 
 
 The rudder bar is a cross bar pivoted at its center and mounted a 
 short distance above the floor of the fuselage. It is used to control the 
 vertical rudder and is operated by the pilot's feet. Ordinarily the ends 
 of the rudder bar project through the sides of the fuselage, working in 
 suitable slots cut for them, and the rudder wires are attached to the 
 ends of the rudder bar outside of the fuselage. In machines fitted with 
 dual controls there are, of course, two rudder bars and these are fastened 
 together by means of wires connecting their outer ends. The rear of the 
 two rudder bars is then connected to the vertical rudder in the usual way. 
 
 Wing section struts are vertical or diagonal struts mounted above 
 the fuselage and attached b}^ means of strut sockets to the upper longer- 
 ons. The wing section struts are used to support the center wing panel 
 when the machine is on the ground and when in the air they help to 
 support the fuselage from the center panel, the latter being supported 
 partly by the upper wing sections which are attached on either side of 
 it and partly by the lower wing sections which are braced to the upper 
 sections and also attached on either side of the fuselage as previously 
 described. 
 
 The strut sockets in which the lower ends of the wing section struts 
 are mounted consist of U-shaped steel plates firmly attached to the upper 
 longeron. The wing section struts are mounted between the side walls 
 of the socket, usually by means of a heavy through-bolt. 
 
 Standard Fuselage Construction 
 
 The type of fuselage just described, which is of wood and metal con- 
 struction, may be said to represent standard practice in this ccumtry 
 at the present time. There are, however, other types of construction, 
 such as the all-steel fuselage. In this the shape of the members and the 
 methods of joining them follow closely standard methods in structural 
 steel work. It is claimed for the all steel construction that it is lighter 
 for a given size machine than the wood and metal or composite con- 
 struction. 
 
 The fuselage is usually covered either with canvas or linen material 
 similar to that used for wing coverings or else with very thin panels of 
 veneered wood. In the former case the longerons, struts and braces must 
 carry all the weight and take up all the stresses to which the fuselage is 
 subjected, but when a veneered wood covering is used, it contributes 
 materially to the strength of the fuselage, consequently the framework of 
 the latter may be made lighter. 
 
 There are also fuselages of the monocoque type in which the strength 
 is obtained not by a truss construction, but by the form and nature of the 
 outer shell itself, this being made up of alternate layers of thin wood 
 veneering and cloth until the desired thickness and streugtii are obtained.
 
 50 APPLIED AERONAUTICS 
 
 The various layers of wood veneering are laid with the grain running in 
 different directions in the different layers. This type of shell or body, 
 which is usually somewhat fish-shaped, possesses the necessary strength 
 and elasticity without the system of struts and tie wires common to the 
 ordinary or trussed type of fuselage. The monocoque construction pos- 
 sesses one marked disadvantage, however, and that is that it is veiy hard 
 to repair in case of slight damage. 
 
 It may be added that the monocoque or laminated wood construction 
 is far more common in foreign countries, particularly France and Ger- 
 many, than in the United States. 
 
 Landing Gear 
 
 The landing gear is an assembly of struts, fittings, axle, wheels, 
 shock absorbers and bracing wires whose function is to enable the ma- 
 chine to rise from and land on the ground and to furnish the main sup- 
 port of the machine when resting on the ground. 
 
 The struts of the landing gear are of streamline shape to reduce the 
 resistance when flying. They are usually made of well-seasoned, 
 straight-grained ash or sj>ruce. Very often they are further strength- 
 ened by several Avrappings of linen twine. The struts with their fit- 
 tings constitute important members and should be carefully examined 
 at frequent intervals. Failure or collapse of these struts would be almost 
 certain to cause a serious accident when landing. 
 
 These struts are attached to the lower side of the fuselage, usually 
 to the lower longerons themselves by means of metal socket fittings. The 
 lower ends of the struts on each side of the landing gear are joined to- 
 gether by a metal bridge. This bridge not only serves to tie the lower 
 ends of the struts together, but it also forms a yoke or housing in which 
 the axle box plays up and down. The bridge is made of a steel stamping 
 or drop forging. 
 
 The axle box may be in the form of a whole box or a half box. When 
 it is in the form of a half box it is generally called a saddle. Its purpose 
 is to support the axle and to guide its vertical motion in the bridge. The 
 saddle may be either of bronze or aluminum. It is held in its place in 
 the bridge by a Avrapping of elastic cord, which consists of a number of 
 strands or bands of rubber bunched together and enclosed in a loosely- 
 braided covering. 
 
 The assembly of the saddle, bridge and elastic cords is called the 
 shock absorber. 
 
 The axle is made of steel tubing and is enclosed, between the bridges 
 connecting the pairs of struts, in an axle casing. This is made of wood, 
 or sheet metal, built around the axle itself and is of streamline shape or 
 section to reduce air resistance. 
 
 The wheels are the ordinary type of wire wheels of rather small 
 diameter and usually fitted with pneumatic tires. They do not, how- 
 ever, ordinarily run on ball bearings, as a slight amount of friction in 
 the wheel bearings is of little or no conseciuence Avhen leaving the ground
 
 RIGGING 51 
 
 at the eoinineueeiuoiil of a flij;lit, aud it assists soiiicw hat in briii^iiii^- the 
 machine to a stop without going too far after aligliting. The sides of the 
 wheels are covered with linen cloth discs to decrease air resistance. 
 
 Not all landing gears are like the one described, but this may be 
 taken as standard practice. Some are provided with a skid or a single 
 wheel projecting ahead of and above the main wheels for the purpose of 
 preventing the machine from taking a header or nosing into the ground 
 on landing, in case it strikes the ground at too sharp an angle. Other 
 minor details of construction will be noted, too, on different types of 
 nmchines, particularly in the construction of the shock absorbers. 
 
 The tail skid is a skid or arm projecting below the fuselage near- its 
 rear end. The purpose of the tail skid is twofold; first, to support the 
 rear end of the airplane when on the ground or in landing and prevent 
 damage to the rudder and elevators and their controls, and secondly, to 
 act as a drag or brake to assist in bringing the machine to a stop when 
 landing. The tail skid is frequently hinged or pivoted where it is at- 
 tached to the lower longerons and its upper end, extending above the 
 pivotal point, fitted with rubber cords similar to those used in the shock 
 absorbers on the axle of the landing gear. This construction acts the 
 same way as the shock absorber and prevents damage to the empaunage 
 and rear portion of the fuselage when landing. 
 
 Airplanes are often fitted with wing skids which consist of small 
 auxiliary skids under the outer ends of each lower wing. These skids 
 ordinarih' do not come into action and are only provided to prevent dam- 
 age to the outer wings in alighting on rough ground or in case a sudden 
 side gust of wind should tend to upset the machine when alighting or 
 rising. 
 
 Landing Gear of Seaplanes 
 
 Seaplanes and flying boats are of course fitted with entirely dif- 
 ferent types of landing gear from that described. Seaplanes are fitted 
 with pontoons or floats suitable for arising from and alighting on the 
 water. Usually tliere are one or two main pontoons under the forward 
 section of the fuselage, these corresponding roughly to the main landing- 
 gear of the airplane. There is also a smaller pontoon mounted under the 
 rear end of the fuselage and one under the outer end of each wing to 
 prevent the wings dipping or the whole machine upsetting in rough 
 water. The flying boat is so constructed that the whole fuselage is in 
 the shape of a boat and the whole macliine is therefore supported on 
 tlie fuselage when resting on the water and when alighting and rising 
 from the water. The flying boat is also usually fitted with small auxil- 
 iary pontoons under the outer end of the wings to keep the machine 
 steady in rough water. 
 
 The main members running the full length of the wing are called 
 the spars. They are usually spoken of as front and rear spars. Some- 
 times the front spar is called the main spar. 
 
 The cross members joining the spars together are called ribs. There 
 are two kinds of these, compression ribs and the web ribs. The function
 
 S2 
 
 APPLIED AERONAUTICS
 
 RIGGING 53 
 
 vi the web ribs is merely to siippoit the linen covering of the wings and 
 to resist the lifting force of the air, due to the forward motion of the air- 
 plane. 'I'here is not much end pressure against these ribs, therefore, the 
 central portion is cut out for the sake of lightening them. The function 
 of the compression ribs is not only to resist the lifting force of the air, but 
 also to take the thrust due to the stay wires. 
 
 The ribs are not continuous, that is, they do not pass through 
 the spars. The ribs are made in three sections, the nose section, center 
 section and tail section. 'J'he nose section of a rib is the section which 
 projects for\\ard of the front or main spai*. The center section is the 
 section between the front and rear spars. The tail section of the rib is 
 that which projects to the rear of the rear spar. The nose sections and 
 tail sections are sometimes called nose ribs and tail ribs and are also 
 frequently spoken of as nose webs and tail webs, because they are cut 
 out to a Aveb form. These rib sections are not, of course, called upon to 
 stand compression stresses, as these stresses are all centered in or taken 
 through the front and rear spars. 
 
 A thin strip of wood running from the nose web across the spars to 
 the rear end of the tail webs (lengthwise of the airplane itself) and 
 serving to bind all the wing parts or ribs together, is called the cap strip. 
 There is a top cap strip and a bottom cap strip on each set of ribs. 
 
 Entering and Trailing Edges 
 
 The front edge of the wing section which is the part carrying the 
 nose webs or nose ribs is called the entering edge of the wing. The rear 
 edge of the wing is known as the trailing edge. 
 
 The nose webs are tied together by a strip of spruce running full 
 length of the wing or crosswise of the airplane itself. This strip forms 
 the leading edge of the wing and is called the nose strip. From the nose 
 strip to the front or main spar, on the upper side of the wing, there is 
 a covering of thin laminated wood colled the nose covering. Its pur- 
 pose is to reinforce the covering fabric as it is at this point that the 
 effect of wind pressure due to velocity is most severe. 
 
 t^econdary nose ribs are placed between each pair of full ribs to 
 give additional support to the nose covering. 
 
 There are usually two rod-like members running from end to end of 
 the wing through the central part of the ribs. These are called stringers 
 and are used for the purpose of giving lateral stiffness to the ribs. 
 
 The trailing edge of the Aviiig is made of thin flattened steel tubing 
 attached to the tail webs by metal clips. 
 
 The spars are continuous throughout their length. Furthermore, 
 they have reinforcements of wood at the points where the interplane 
 struts connecting the upper and lower wings are attached. Steel bearing- 
 plates are bolted to the Aving spars at these points. The bolts attaching 
 these bearing plates to the wing spars do not pass through the spars 
 themselves, but through the reinforcements. This is to avoid weakening 
 the spars.
 
 54 APPLIED AERONAUTICS 
 
 Nearly all wood used in wing construction is spruce, with the ex- 
 ception of the nose covering which is made of birch or gum wood, the 
 web ribs, which are made of laminated wood, and small quantities of pine 
 or other woods in the sidewalk and other unimportant places. 
 
 The sidewalk is a boxed-in or wood-covered portion of the inner end 
 of the lower wing. It furnishes a solid footing for the pilot or observer 
 when entering or leaving the cockpit and for mechanics working around 
 the engine, guns, instruments, control mechanism, etc. 
 
 Steel hinge pieces are bolted to the inner ends of the wing spars 
 and serve as a means of connecting the lower wings to the fuselage and 
 the upper wings to the center wing panel. 
 
 Interplane struts are vertical or inclined wooden struts of stream- 
 line section used to transfer compression stresses from the lower wings 
 to the upper wings when the machine is in flight. These struts are used 
 in conjunction with diagonal stay wires which serve to transfer the load 
 towards the center of the machine when in flight. 
 
 The stay wires are divided into two general groups, those which take 
 the drift load or fore-and-aft stresses due to the forward motion of the 
 airplane, and those which take the lift load or vertical load due to the 
 weight of the machine itself and the vertical resistance when in the 
 air. The lift wires are again divided into those which take the load when 
 the machine is flying and those which take it when on the ground. The 
 wires which take the lift load when the nuichine is in the air are called 
 the flying wires, and those which take the load when on the ground are 
 called ground or landing wires. 
 
 Drift and Anti-Drift Wires 
 
 The set of wires in the wings which carry the drift load when flying- 
 are called the flying drift wires, or drift wires for short. There is no 
 reversal of load in these wires when the machine is on the ground, but 
 opposition wires are necessary to maintain structural symmetry. These 
 latter are called the anti-drift wires. 
 
 When the wing frames are covered it is of course impossible to in- 
 spect the internal stay wires of the wings, hence every precaution must 
 be taken to guard against corrosion. The wire used at this point is tin 
 coated before assembling, the steel parts of the turnbuckles and other 
 fittings are copper plated and when completely assembled, all the metal 
 parts are given a coat of enamel paint. All screws, tacks and brads are 
 of brass or copper. 
 
 Wings are covered with a closely woven fabric. At present un- 
 bleached linen seems to give the best satisfaction. Owing to its scarcity, 
 ho^^ever, a satisfactory substitute is being sought for. A cloth made of 
 long fibre sea island cotton is used to some extent and makes a fairly 
 satisfactory substitute. 
 
 Linen fabric weighs 3^ to 4f oz. per sq. yd. and has a strength 
 of GO to 100 lbs. per in. of width. Its strength is increased 25 to 30
 
 RIGGING 55 
 
 perceut by d(>i»iii;^, liowevei'. The weight of cotton faln'ie iw 2 to 4 o/>. per 
 sq. yd., its strength 30 to 60 lbs. per in. of width, and its strength is in- 
 creased 20 to 25 jK'rceut by the ap]tlicatioii of dojM'. 
 
 The cloth surfaces or wing coverings nnist be taut, otherwise on pass- 
 ing through the air they would vibrate or whip. This would not only 
 increase the resistance to a great extent, Itut soon would lead to the de- 
 struction of the fabric. A preparation called dope is used to tighten 
 up the fabric and give a smooth, taut surface. It also tends to make the 
 cloth weather-proof. 
 
 Dope should be easy of applicati(jn, durable, fire resisting and have 
 a preserving effect on the cloth. Dopes at present are divided into two 
 classes or chemical groups, those which are made from a base of cellulose 
 nitrate or pyroxylin and those made from a cellulose acetate base. The 
 base is dissolved in a suitable solvent, such as acetone for instance, and 
 sometimes other substances are added to preserve flexibility or prevent 
 drying out and cracking and checking or to modify shrinkage. 
 
 The greatest difference between these two dopes is in their relative 
 inflammability. The acetate dope makes the fabric not fireproof, but 
 slow burning. A cloth treated with this dope will shrivel and char l)efore 
 burning, but one treated with nitrate do])e will burst into flame immedi- 
 ately on the application of a lighted match or when exposed to a strong 
 spark or punctured by a flaming bullet, etc. See "Airplane Dopes," by 
 Gustavus J. Esselen, Jr., in Aviation, July 5, 1917. 
 
 Inspection windows are often inserted in wing sections over and 
 under certain control joints where the latter are carried inside the wing 
 section itself. For instance, the aileron control cables are frequently 
 run inside the lower wing sections to a jJuUey attached to the front or 
 main spar opposite the middle of the aileron, the cable then passing down 
 at a slight angle and through a thimble or sleeve in the lower covering 
 of the wing section to the point \A'here the cable is attached to the aileron 
 control mast. With this construction inspection windows would be set 
 in the upper and lower coverings of the lower wing immediately above 
 and below the pulley ovjer which the control cable passes. The inspec- 
 tion windows are usually of celluloid or other transparent material 
 firmly sewn into the wing covering material. 
 
 Stay Wires and Splices 
 
 Stay wires and cables are used extensiveh^ in airplane construction. 
 Much of the safety of the nmchine and pilot depends upon the quality of 
 the material in the stay wires, the care used in adjusting them and on 
 the character of the terminal splices. 
 
 Three kinds of materials are used for stay wires: solid or aircraft 
 wire, stranded wire or aircraft strand, and a number of strands twisted 
 together to form a cable and known as aircraft cord. Aircraft wire is a 
 hard drawn carbon steel wire coated with tin to protect it against cor- 
 rosion. Its strength runs from 200,000 to .SOO.OOO llis. per sq. in., 
 depending upon how small it is drawn. Drawing increases both the
 
 56 
 
 APPLIED AERONAUTICS 
 
 strengtli and hardness of this type of wire, but if drawn until too hard it 
 cannot be bent with safety. The aim is to produce a wire of maximum 
 strength, yet with sufficient toughness to allow it to bend without frac- 
 ture. A standard test for bending is to grip the wire in a vice whose jaAvs 
 have been rounded off to 3/16 in. radius, and bend the wire back and 
 forth through an angle of 180 deg. Each bend of 90 deg. counts as one 
 bend. The minimum number of bends for various sizes of aircraft wires 
 should be as follows : 
 
 For wire of B. 
 For wire of B. 
 For wire of B. 
 For wire of B. 
 For wire of B. 
 For wire of B. 
 
 & S. gauge Xo. 6- 
 & S. aauae Xo. 8- 
 
 5 bends without fracture. 
 8 bends without fracture. 
 
 & S. gauge No. 10 — 11 bends without fracture. 
 & S. gauge No. 12 — 17 bends without fracture. 
 & S. gauge No. 11 — 25 bends witliout fracture. 
 & S. gauge No. 10 — 31 bends without fracture. 
 
 Aircraft strand is composed of a number of small wires, usually 19, 
 twisted together. The individual wires of the strand are galvanized or 
 zinc coated before being twisted into the strand. The complete strand 
 
 /s/. 
 
 o 
 
 13 
 
 117 
 
 2/?c/. 
 
 3rd. 
 
 4/k 
 
 VX^ 
 
 F'kj. 33 — ^tcps ill rnal'iiuj an cud .splice in solid icire 
 
 is more flexible than a solid wire of the same diameter and is therefore 
 more suitable for stay wires that are subject to vibration. 
 
 The stay wires of the fuselage at the engine and wing panels are of 
 aircraft strand or cord, but for the remaining stay wires of the fuselage 
 aircraft Avire is ordinarily used. 
 
 Aircraft cord is much more flexible than the strand. It is used 
 for control cables where these must pass over comparatively small pul-
 
 RIGGING 57 
 
 leys. Tlie usual iMdistnutiou of niiTi-alt cord is 7 strands of I'J wires 
 each tAvisted together to form a cable. This specification is known as 
 7 X 10 aircraft cord. The individual wires of the cord are very small and 
 are tin-plated before being stranded. 
 
 For a given diameter, the solid wire is stronger than either the 
 strand or cord. Weight f(»i- weight, however, the cord is a little stronger 
 than the wire, as shown l»y the following tabh'. 
 
 Weight Strength for a Strength for a 
 
 per 100 ft. given diameter given weight 
 
 Wire 8.84 lbs. 5500 lbs. 5500 lbs. 
 
 (;ord 0.47 lbs. 4200 lbs. 5000 11)S. 
 
 A wire or cord is no stronger than its terminal splice. The splice 
 may be formed in a variety of ways. For solid wire the formation of 
 the eye is important. An eye in which the reverse curve has the same 
 radius as the eye proper is called a perfect eye and is the one recom- 
 mended. The inside diameter of the eye should be about three times the 
 diameter of the wire itself. 
 
 After the eye is formed a flattened wrapped wire ferrule, somewhat 
 like a coiled spring flattened to eliptical section, is slipped over the wire 
 and the free end. The latter is then bent back over the ferrule. Such a 
 terminal will have an efficiency of 60 to 05 percent of the strength of 
 the Avire itself. When this tyjte of terminal fails it is usually by slipping. 
 If the free end of the wire is tied doAvn, after being bent back over the 
 ferrule, with an additional wrapping of wire, the efficiency of the termi- 
 nal as a whole will be increased to 80 percent of the strength of the 
 wire. If the whole terminal is soldered the efficiency will be increased 
 to 100 percent according to static tests. This is misleading, however, as 
 such tests take no account of live load stresses or vibration. 
 
 Another form of terminal is made by substituting a thin metal fer- 
 rule or section of flattened tul)e for the wrapped wire ferrule. It can be 
 made secure either by soldering or twisting after being put in place. This 
 terminal for live or vibrational loads is superior to the wrapped wire 
 terminal as there is not so much difference in mass between the wire and 
 the ferrule. 
 
 Aircraft Strand Terminals 
 
 The terminal eye of the aircraft strand is formed around a thimble. 
 The free end of the strand is In-ought around the thimble and either 
 wrapped to the main strand with small wires and soldered, or the free 
 end is spliced into the main strand. Before bending around the thimble, 
 the strand is wrapped with fine wire in order to prevent flattening oi- 
 caging of the strand. 
 
 The terminal eye of the airci'aft cord is always made by splicing the 
 free end of the cord into the main strands after wrap]iing the cord around 
 a thimble. Sometimes the splice is soldered but more often it is wrapped
 
 58 APPLIED AERONAUTICS 
 
 with harness twine. Foreign engineers are opposed to soldering, claim- 
 ing that the disadvantages in the way of corrosion and overheating of 
 the wire outweigh the advantages of the stronger terminals. 
 
 The theory of the splice is simple. A strand or wire of the free end 
 is wrapped around a strand or wire of the main cord, care being taken 
 to have the lay of the wires the same. Three to five complete turns are 
 given, three for the first and four to five for the last weaves of the splice 
 in order to taper the splice gradually. 
 
 Objections to soldering. — The most serious objections to soldering 
 are : a. overheating ; b. corrosive action of fluxes. It is very easy to over- 
 heat and soften the wire and this is all the more serious because the 
 softening takes place at a point where the wire is enlarged by the joint. 
 The stress is naturally localized at this point. 
 
 Some of the so-called non-corrosive fluxes will upon application be 
 found to be more or less corrosive. Even with strictly non-corrosive 
 fluxes, there is a carbonaceous residue, due to heat, driven into the inter- 
 stices between the wires of strands or cords. This serves as a holder for 
 moisture and will in time cause corrosion. 
 
 The corrosive effects of acid fluxes can be neutralized by the appli- 
 cation of an alkaline solution, such as soda water. Washing the soldered 
 splice of a solid wire with such a solution is very effective, but with 
 strands and cords, where the acid is driven into the interior through the 
 application of heat, it is questionable whether any system of washing 
 will eliminate or neutralize the acid. Corrosion of the interior wires of 
 a strand or cord may be concealed by a perfectly good exterior, giving 
 an entirely false appearance of security. 
 
 Turnbuckles 
 
 Turnbuckles are made of three parts, the ferrule or sleeve, and the 
 two ends. To distinguish the ends, they are called the yoke and eye ends, 
 or the male and female. 
 
 Great care should be exercised when tightening or loosening 
 turnbuckles that the cables are not untwisted or frayed. If the cables 
 are untwisted a caging of the strands results which greatly weakens 
 the cable. Cable that has been caged should be replaced. No pliers 
 should be used when tightening or loosening turnbuckles. The correct 
 method is to use two drift pins or nails, one through the terminal eye 
 of the cable to prevent the end of the cable twisting, the other through 
 the hole in the barrel of the turnbuckle. Pliers will scar the wires, 
 which is objectionable for three reasons, the first two of which may lead 
 to serious consequences. These reasons are : First, breaking the pro- 
 tective coating given to guard against corrosion. Second, a nick or scar 
 in a wire or cable which would weaken it considerably. The wire or cable 
 may not show much reduction of strength under a static load or test, but 
 with a live or vibrational load the strength is greatlv reduced and a
 
 RIGGING 59 
 
 slight nick will determine the point of fracture. Third, disfiguration of 
 the parts is offensive to the eye and bespeaks slouchy or careless work- 
 manship. 
 
 Locking Devices 
 
 A fair proportion of accidents occurs to moving mechanism through 
 nuts or other tlireaded fastenings working loose. It is safe to say that 
 several hundred patents have been taken out for nut-locking devices, but 
 of this great number, a few only are of practical value and used to any 
 extent. The castellated nut and cotter pin used of course with a drilled 
 bolt or stud is one of the few devices that finds large application. It is 
 generally used in automobile and airplane work. The spring locking 
 washer is another good device. This is used where the fastening is of a 
 permanent or semi-permanent character. Another method is to batter 
 or hammer down the end of a bolt a little. This should be practiced only 
 as a last resort or as an absolutely permanent job and must be carefully 
 done, otherwise serious damage will result to the bolt and nut. It is suf- 
 ficient to close one thread on the bolt for part of the circumference only. 
 
 Turnbuckles are secured against turning or loosening by running 
 a wire through the adjusting hole in the turnbuckle sleeve and carrying 
 the vdre back and binding it around the ends of the turnbuckle. See 
 Fig. 41.
 
 Chapter 5 
 
 ALIGNMENT 
 
 Fuselage alignment — Horizontal and vertical stabilizers — Landing gear or under-carriage 
 — Center wing section — Wings — Lateral dihedral angle — Table for lateral dihedral 
 — Stagger — Overhang — Rigger's angle of incidence — Wash-out and wash-in — Over- 
 all measurements — Aileron controls — Elevator controls — Rudder control — Notes on 
 aligning boards. 
 
 BY the term airplaue aligmneut is meaut the art of triiiug up an air- 
 plane, and adjusting the parts in their proper relation to each other 
 as designated in the airplane's specifications. The inherent stability, the 
 speed, the rate of climb, the efficiency, in short the air\yorthiness of an 
 aircraft depend in large measni'e on its correct alignment. For this 
 reason the importance of careful and correct alignment cannot be oyer- 
 estimated. 
 
 The instructions as giyen in this chapter are not intended to lie a 
 comiDlete and exhaustiye treatise on the Ayhole subject of airplane align- 
 ment, but are designed rather to giye the beginner a. good general idea 
 of how the work is done. Thus with these instructions as a ground work 
 he can become proficient in the work after having had good practical 
 experience in the hangars. 
 
 The work of aligning an airplane divides naturally into several dis- 
 tinct and separate groups or divisions — a. fuselage, b. horizontal and 
 vertical stabilizers, c. landing gear, d. center wing section, e. wings, f. 
 controls. 
 
 Alif/iiiitent of fiischuje. — The fuselage is aligned before leaving the 
 airplane factory and normally this alignment will last for some time. 
 Tlie fuselage alignment should be checked over carefully, however, after 
 an airplane has been shipped in disassembled condition. Strains on the 
 fuselage caused by rough handling, bad landings, etc., will make it nec- 
 essary to re-align it. 
 
 Before attempting to align any part of an airplane the erection draw- 
 ings should be referred to if available, and the directions furnished by 
 the makers should be followed carefully unless the operator has had a 
 great deal of previous experience upon the particular type of airplane to 
 be aligned, and is familiar with better methods of procedure than those 
 recommended bv the maker.
 
 ALIGNMENT 61 
 
 In general the procedni'e in aligning a fuselage will lie about as fol- 
 lows: A horizontal reference plane is nsnally specified by the makers in 
 connection with the fuselage. Sometiuies the top longerons are taken 
 as this reference plane, in which case they are to be aligned horizontally, 
 laterally, and longitudinally from a specified station to the tail post. 
 Sometimes horizontal lines are drawn on the vertical fuselage struts, and 
 the fuselage is so aligned that these lines all fall in the same horizontal 
 plane. 
 
 Alignment of Longerons 
 
 In the first case, after the fuselage has been placed in a flying posi- 
 tion, the top longerons are aligned for straightness, using a straight edge 
 and a spirit level to aid in finally placing them laterally and longitudi- 
 nally in a liorizontal plane. 
 
 The longerons are next aligned symmetrically with respect to the 
 imaginai'y vertical plane of symmetry through the fore-and-aft axis of 
 the fuselage. There are two general methods of doing this, as follows : 
 
 First Method — The center points are mai'ked on all horizontal 
 fuselage struts. A small, stout cord is stretched from the center of the 
 fuselage nose to the tail post and the horizontal bracing wires adjusted 
 until the centers of the horizontal struts fall beneath this line. A small 
 surveyor's plumb bob is held at different points so that the suspending 
 cord just touches the fore-and-aft aligning cord. The centers of the 
 bottom horizontal struts should fall directly below the bob. 
 
 Second Method — A plumb line is dropped from the center of the 
 propeller and from the tail post and a string is stretched on the ground 
 or floor between these two points. Plumb bobs dropped from the centers 
 of the horizontal struts must point to this line. 
 
 The whole fuselage alignment is checked to make sure that it agrees 
 with the specifications. If the airplane has a nou-liftiug tail, it would 
 be advisable as the next step to support the fuselage in such a way that 
 the rear part (about two-thirds of the total fuselage length) remains un- 
 supported, and then re-check tlie fuselage alignment once more. 
 
 All turnbuckles should then be securely locked and the fuselage 
 carefully inspected. 
 
 Horizontal and Vertical Stabilizers 
 
 The vertical stabilizer is examined to see that tlie bolts holding it in 
 place are properly drilled and cotter-pinned, also to see that it is set 
 parallel or dead on to the direction of motion. It is trued up vertically 
 by the turnbuckles on the tie wires or brace wires connected to it. These 
 turnbuckles are then properly safetied. 
 
 The horizontal stabilizer usually is braced with tie wires fitted with 
 turnbuckles. By means of these its trailing edge should be made straight 
 and at right angles to the horizontal center line of the fuselage. All 
 bolts fastening the horizontal stabilizer to the fuselage should be in- 
 spected to make sure they are properly drilled and cotter-pinned. All 
 turnbuckles should be safetied, as shown iu Fig. 41.
 
 62 APPLIED AERONAUTICS 
 
 Alignment of laiidiiuj gear or under-carriage. — In assembling an 
 airplane which has been completely dismantled, the landing gear should 
 be assembled to the fuselage and aligned with it before the wings 
 are attached. In assembling and aligning the landing gear, the fuselage 
 should be so supported that the landing gear hangs free and the wheels 
 do not touch the ground. 
 
 The fuselage is placed in the flying position, or at least in such a 
 position that the lateral axis is horizontal. There are three general 
 methods of aligning the landing gear, as follows : 
 
 First Method — A small plumb bob is dropped from a point on the 
 fore-and-aft center line of the fuselage above the axle of the landing gear. 
 A tack is placed in the exact center of the axle casing or a scratch is made 
 on the axle at its center. The transverse tie wires are then adjusted until 
 the tack or center line mark falls exactly below the plumb bob. The wires 
 are made moderately tight. The exact degree of tautness required can- 
 not very well be described; it is a matter of experience or personal in- 
 struction. All turnbuckles are safetied and the landing gear inspected 
 carefully. The strut fittings and the elastic shock absorbers should be 
 inspected very carefully. 
 
 Second IMethod — The two forward transverse tie wires are adjusted 
 until equal in leng^th, then the rear transverse tie wires are similarly 
 adjusted until they also are equal in length. All transverse tie wires are 
 tightened equally and the turnbuckles safetied. The landing gear is 
 then given a final inspection. 
 
 Third Method — The transverse tie wires are adjusted until the axle 
 is horizontal as shown by a spirit level. This adjustment is made with 
 the fuselage in the flying position or with the lateral axis horizontal. 
 The transverse tie wires are tightened equally to the correct tautness, the 
 turnbuckles safetied, and the landing gear inspected as before. 
 
 Center Wing Section 
 
 Alignment of center luing section. — The fuselage is first placed in 
 the flying position, and the center wing section adjusted symmetrically 
 about the fore-and-aft center line of the fuselage in plan. A tack driven 
 in the middle of the leading edge of the center panel will then be directly 
 above the center line of the fuselage. This is tested with a small plumb 
 bob and checked by measuring each pair of transverse tie wires to see if 
 the two wires of each pair are equal in length. 
 
 The alignment for stagger is made by adjusting the stagger or drift 
 wires in the fore-and-aft direction until the leading edge of the center 
 panel projects the required distance ahead of the leading edge of the 
 lower plane as given in the airplane specifications. This align- 
 ment is checked by dropping a plumb bob from the leading edge of the 
 center panel and measuring forward in a horizontal plane from the lead- 
 ing edge of the lower plane to the plumb line. The adjustment for stag- 
 ger fixes the rigger's angle of incidence. All turnbuckles are safetied 
 and the alignment re-checked.
 
 ALIGNMENT 63 
 
 Aliy II incut of icings. — Before any attempt is made to align the wings 
 the fuselage should be carefully inspected to make sure that it is properly 
 rigged and in proper alignment. Failure to do this ma}' cause much 
 delay and waste ot time in aligning the wings. 
 
 The next step is to make a general inspection of the wings, noting 
 if all bolts and clevis pins are properly cotter-pinned. Note particularly 
 the clevis pins where the interplane brace wires are fastened to the upper 
 plane fittings. One of the largest airplane makers in this country puts 
 these clevis pins in head down. In this position if the pins are not prop- 
 erly cottered, there is great danger of their working loose and dropping 
 out, disconnecting the wires. Such matters are more easily remedied 
 before the wings are aligned than afterwards. 
 
 Loosen all wires between the planes including flying wires, ground 
 wires, stagger wires and external drift wires. Examine the turnbuckles to 
 see that the same number of threads show at both ends. If not, take the 
 turnbuckle apart and remedy this. It will mean a saving of time in the 
 end if these matters are looked after before the actual truing up of the 
 wings is begun. 
 
 Flying Position 
 
 Place the fuselage in the flying position as defined in the airplane's 
 erection drawings. This may mean aligning the top longerons or the 
 engine bed or other specified parts laterally and longitudinally horizon- 
 tal. This must be done carefull}', using a good spirit level, because the 
 wings are aligned from the fuselage upon the assumption that this flj^ing 
 position is correct. If it is necessary to get into the cockpit or in any 
 other way disturb the fuselage during the alignment of the wings, make 
 sure that the fuselage is still in the correct flying position before pro- 
 ceeding further. 
 
 Lateral dihedral angle. — There are thi'ee common methods of ad- 
 justing for lateral dihedral : 
 
 Aligning Board 
 
 First Method — Aligning Board.* If an aligning board is available 
 its use saves considerable time due to the fact that the rigger secures 
 the lateral dihedral angle, straightness of wing spars, and correct angle 
 of incidence near the wing tips all at the same time. The protractor level 
 should read directly in degrees. Set this instrument at the number of 
 degrees dihedral stated in the airplane's specifications. Place the align- 
 ing board parallel to the front spar (by measuring back from the strut 
 fittings) and, keeping the flying and stagger wires loose, pull up on the 
 ground wires until the bubble on the protractor level reads almost level. 
 Since the aligning board is a straight edge it is easy to keep the front spar 
 perfectly straight by glancing beneath the aligning board occasionally. 
 It should rest on at least three ribs, one near each end and one near the 
 middle. The space between the other ribs and the aligning board should 
 be slicrht. 
 
 *See note on aligning boards at end of this chapter.
 
 64 
 
 APPLIED AERONAUTICS 
 
 Spiht Lei/el 
 
 Dihedral Board 
 
 F'kj. 34 — Metliod of ni<in<i short dllietlnd hoard 
 
 Place the aliiiniDg board in front of and parallel to the rear spar. 
 Adjust the ground wires until the rear spar is straight and the dihedral 
 is slightly greater than called for in the maker's specifications. Check 
 at the front spar. It will now be the same as the rear. If not make it so. 
 
 Now tighten down on all flying wires except those to the overhang, 
 if there is overhang. Test each pair of flying wires for equal tautness 
 by striking with the edge of the hand and watching their vibration. 
 The loose wire has the greatest amplitude of vibration. The lateral 
 <lihedral should now be exactly as called for in the specifications. 
 
 After aligning both wings for dihedral as stated above, both wings 
 will be the same height if the fuselage is level laterally. Check the height 
 of the wings by making the distance BA (see Fig. 35) equal to DC meas- 
 ured from the longerons opposite the butt ends of the front spars on the 
 lower wing panels. V is a tack in the middle of the leading edge of the 
 
 F'kj. 35 — Points of measurement for icing alignment
 
 ALIGNMENT 
 
 65 
 
 center section panel. ^Vitll a steel tape measure the distance VA and VC. 
 These distances slioiikl be equal. 
 
 Equally good results ma^' be obtained by using- a protract<jr spirit 
 level in conjunction with an accurate straight edge. 
 
 Second ^letliod — If a good aligning board is not available the string 
 method may be used. Fig. 3(1 sliows the arrangement of the string which 
 should be small, smooth and tightly drawn. 
 
 Keep the stagger wires, flying Avires and nose drift wires loose as in 
 the first method. Increase the dihedral angle by tightening the ground 
 wires, keeping the panels straight by sighting. The greater the dihedral 
 angle the greater the distance Y (see Fig. 36). The tal)le below shows 
 the variation for customarv range of lateral dihedral : 
 
 ^ 
 
 Sfn'njf 
 
 string 
 
 Mast W/'re- 
 
 '^^ 
 
 rfc^ 
 
 F'lfj. ^6~AIteruatirc method of aligning for dihedral 
 
 Table for Lateral Dihedral Angles 
 
 
 X 
 
 Y 
 
 
 Inches Distance from 
 
 Inches Distance from 
 
 Degrees 
 
 point of support of string 
 
 end of spar vertically up 
 
 
 to end of spar. 
 
 to the horizontal string. 
 
 
 
 100 
 
 
 
 1 
 
 100 
 
 1% 
 
 2 
 
 100 
 
 3V2 
 
 3 
 
 100 
 
 sy* 
 
 4 
 
 100 
 
 7 
 
 5 
 
 100 
 
 m 
 
 6 
 
 100 
 
 lO/iT 
 
 7 
 
 100 
 
 12^^ 
 
 8 
 
 100 
 
 13ii 
 
 3 
 
 100 
 
 15% 
 
 10 
 
 100 
 
 17%
 
 66 
 
 APPLIED AERONAUTICS 
 
 The distance X will probably not be exactly 100 in. as given in the 
 table, but since X and Y increase in the same proportion this is very 
 simple. For example, the distance X (convenient to measure) on a bi- 
 plane having a 3 deg. lateral dihedral angle may be, say 12 ft. 6 in., or 
 150 in., which is one and one-half times 100 in. 
 
 The table gives Y equal to 5^ in. for 3 deg. Our X is one and one- 
 half times the X in the table. Then our Y must be one and one-half times 
 5^ in. (the Y given in the table), which equals 7^ in., which is the proper 
 distance up to the string when the wing has the correct lateral dihedral. 
 
 In determining the distance Y, always measure the vertical distance 
 up to the string from near the inner edge of the wing panel, not from the 
 center section panel. The correct lateral dihedral angle having been 
 obtained- proceed further as in the first method. 
 
 Third Method — On airplanes having sweep-back the string method 
 is rather difficult to apply. If an aligning board such as used in the first 
 method is not available, then a short dihedral board may be made wihich 
 will serve. Fig. 37 shows the construction and Fig. 34 the method of 
 
 Hhort dihedral hoard 
 
 using such a board. It is plain that a separate board must be made for 
 each airplane having a different dihedral from the others at a flying 
 field. Another disadvantage of this board is the fact that it must be used 
 between struts on the spars and is so short that it is apt to be affected 
 greatly by unequal rib heights and any lack of straightness in the spars. 
 
 After obtaining the correct dihedral proceed as in the first method. 
 
 Stagger is usually given in airplane specifications as a linear meas- 
 urement in inches. The specifications will tell whether it is to be meas- 
 ured on a projection of the chord or as a horizontal distance. (See 
 Fig. 38.) It is important to measure the stagger in the manner directed. 
 
 The stagger of the wings is fixed at the fuselage by the stagger of the 
 center wing section. Align for stagger by adjusting the stagger wires 
 between interplane struts. Slight adjustments only should be necessary. 
 Fig. 38 shows the method. 
 
 In exceptional cases the flying and ground wires, front and rear, 
 nearest the fuselage, are used in adjusting the stagger, which is usually 
 found to be correct however after slight adjustments of the stagger wires.
 
 ALIGNMENT 
 
 67 
 
 Stagger is sometimes given as an angle of stagger in degrees. This 
 can be converted into inches by the use of the lateral dihedral table on 
 page 65. In this case AB in Fig. 38 corresponds to X in the table, and Y 
 in Fig. 38 will be proportional to Y in the table. For instance if AB in 
 Fig. 38 is 50 in. in a given airplane, or one-half of X in the table, and the 
 stagger is given in the airplane's specifications as 7 deg., then the 
 amount of stagger Y (Fig. 38) would be one-half of the 12 ^/jg in. given 
 in column Y in the table opposite 7 deg. 
 
 Overhang. — If an airplane has much overhang it is usually supported 
 by mast wires above and flying wires below. See that the flying wires 
 are loose. Tightening one set of wires against an opposing set throws 
 
 Ang/e ojT 
 
 \ 
 
 C or H {k^/j/c/iet/ef method of measuring 
 the specf/tcof/oiis Co// fofj is /he ^fo^geK 
 
 Fig. 38 — Methods of measuring stagger 
 
 undue stress in members. Tighten up on the mast wires until the over- 
 hang inclines very slightly upward. Now tighten up on the flying wires 
 below until the spars are straight. 
 
 The leading and trailing edges of all wing panels should now be 
 straight. In case there should be small local bows in the spars, with a 
 little careful adjusting of wires these can usually be distributed equally 
 between the upper and lower wing panels so that their effect will be les- 
 sened. Fixing the lateral dihedral or the angle of incidence for either 
 upper or lower plane automatically adjusts it for the other plane. 
 
 Rigger's angle of incidence. — Check the lateral dihedral to make sure 
 that it has not been altered in making other adjustments. If it is cor-
 
 68 
 
 APPLIED AERONAUTICS 
 
 Spirit Level 
 
 A B 
 
 Sfraiyht £</ye 
 
 Fig. 39 — Measuring angle of incidence icith straight-edge and spirit level 
 
 rect, front and rear, and the spars are straight, then the angle of inci- 
 dence should be correct all along the wing. Figs. 39 and 40 show two 
 methods of testing this. If the set measurements A or B are known, 
 the first method (Fig. 39) can be used. If the angle AOB is given in the 
 specifications then the second method (Fig. 40) can be employed. Test 
 the angle of incidence near the fuselage and beneath the interplane struts. 
 Wash-out and toash-in. — Due to the reaction from the torque of the 
 propeller the airplane tends to rotate about its longitudinal axis. To 
 counteract this the wing which tends to go down (sometimes referred to 
 as the "heavy" wing) is drawn down slightly at its trailing edge towards 
 its outer end, or in other words it is given a slight additional droop at this 
 point. This is usually referred to as a "wash-in." The wing on the 
 other side of the machine is given a slight upward twist, or "wash-out" 
 at a corresponding point. In single-engined, right-hand tractors wash- 
 
 ySptrif Level ^Oe^rees 
 
 ' ^ yaafBoorJ L 
 
 straight Ed^e 
 
 Fig. 40 — Another method of measuring angle of incidence. It can also 
 be done advantageouslg by vsing a straight edge in conjunction with 
 a protractor spirit level
 
 ALIGNMENT 
 
 69 
 
 in is given to tlie left Avini> ;nnl Avash-ont to tlie riulit. To increase the 
 angle of incidence the rear spar must be warped down hv slackening all 
 the wires connected to the bottom of the strut and tightening all which 
 are connected to the toj) of the struts, until the desired amount of wash- 
 in is secured. This process is reversed to secure wash-out. 
 
 For purposes of increased stability wash-out is sometimes given both 
 wings although of course some lift is lost by doing this. If it is still de- 
 sired to compensate for the reaction due to the propeller toriiue, more 
 wash-out is given on one side than on the other. The side having the least 
 wash-out then has wash-in relative to the other side. 
 
 Fig. 41 — The proper way to lock a iurnhuckle 
 
 Over-all measurements. — Tighten the external drift wires only mod- 
 erately tight. The following over-all measurements should now be taken, 
 using a steel tape (see Fig. 35) : Make BA = DC and LH = MX. Then 
 OA should equal OC and HE should equal EX. These measurements 
 should be made at points on the upper wing panels as well as the lower, 
 making eight check measurements in all. 
 
 Fi<j. 42 — Individual method of connect in (j aileron controls
 
 70 APPLIED AERONAUTICS 
 
 All tiirnhucklcs are now safetied (Fig. 41). Make a fjeneral final 
 inspection of the mings to make sure that nothing has been overlooked. 
 It must he renicinhered that in making one adjustment other adjustments 
 made preriouslg mag he tJiroicn sligJttlg off, so that when the wings are 
 finally aligned it is a good plan to check the lateral dihedral, stagger, 
 angle of incidence, etc., to make sure that all are correct. 
 
 Controls-Ailerons. — Fasten the hand wheel, stick, or shoulder yoke 
 controlling the ailerons in its central position. If the ailerons have brace 
 wires on each side (see Fig. 42 ) and these wires are supplied with turn- 
 buckles, straighten up the trailing edge by adjusting these wires. If the 
 ailerons are connected as in Fig. 43 the trailing edges must be straight- 
 ened as the ailerons are aligned on the airplane. 
 
 There is difference of opinion about drooping the trailing edge of 
 ailerons below the trailing edge of the plane to which they are fastened. 
 At some fields the turnbuckles on the aileron control cables are so ad- 
 jiLSted that the trailing edge of the aileron lines up with the trailing edge 
 
 To/} /^//eron Wire 
 
 Aileron ConrtecZ/'n^ W/res 
 
 ^/^n/'no Board 
 
 ^"^^ ioi/^er Ai/eton 
 
 Fig. 43 — Showing series method of connecting ailerons in pairs 
 
 of the wing panel to which it is hinged. At other fields, from 1/8 in. to 
 3/4 in. of droop is given the trailing edge of the aileron, because it forms 
 a part of a lifting surface and it is reasoned that slack will be taken out 
 of the lower control cables when the machine gets into the air. Unless 
 directed otherwise it perhaps is advisalde to give little or no droop. 
 
 The ailerons should work freely and respond quickly with no feeling 
 of drag when the hand wheel is turned or the stick moved even very 
 
 Profracfor Leve/-^ Sfra/^hf Edge 
 
 Te<sf fof Sfroiphfness 
 
 Fig. 44 — Trying an aligning hoard for straightness
 
 ALIGNMENT 
 
 71 
 
 Test of Pf^oftvcfor Lek'e/ 
 
 Fig. 45 — Aligning board used iritJi table for lateral dihedral angles 
 
 slightly. Improper coiling of cables when a machine is dismantled will 
 ruin this condition about as (juirkly as anytliing could. Care must be 
 taken not to put too much tension on the cables. The pulleys around 
 which they run are light, and not always so strong as they might be. 
 Cracked pulleys may sometimes be found on old machines. 
 
 Interplane ailerons are adjusted so that both are in the same plane 
 when control is neutral. The angle at which they are set must be given 
 by the makers or determined by experiment and experience. 
 
 Elerators. — Fasten the bridge or stick control in its central position. 
 Adjust the turnbuckles on the control cables until the elevators are in 
 their neutral position and both are in the same plane. Tighten the con- 
 trol cables enough to remove lost motion. 
 
 Rudders. — Fasten the rudder footbar in its mid-position and adjust 
 the turnbuckles until the rudder is in the neutral position, and the cables 
 are tight enough to remove lost motion. 
 
 Both elevators and rudders usually carry brace wires witli turn- 
 buckles which can be used in straightening their trailing edges. 
 
 Notes on Aligning Boards 
 
 To be useful an aligning board first of all must be true. Fig. 44 
 shows a method of testing such a board for straightness. ( See A and B, 
 Fig. 44.) Also by supporting the board as shown and setting the pro- 
 tractor level at different degrees the protractor can be tried out. Ref- 
 erence to the table for lateral dihedral on page 65 shows the differ- 
 ence in thickness of the blocks for the different angles. The zero point 
 may be tested by setting the instrument at zero and supporting the align- 
 ing board on some surface known to be level. 
 
 The inclination for the board used in the third method of aligning 
 for lateral dihedral can be determined from the lateral dihedral table. 
 Fifty inches make a convenient length for such a board in which case 
 the Y (see Fig. 45) is just half of that given in the table for lateral 
 dihedral ansles.
 
 Chapter 6 
 
 CARE AND INSPECTION 
 
 Cleanliness — Control cables and wires — Locking devices — Struts and sockets — Special 
 inspection — Lubrication — Adjustments — Vetting or sighting by eye — Mishandling 
 on the ground — Airplane shed or hangar • — Estimating time — Weekly inspection 
 card form. 
 
 CLEANLI]\TES8. — One of the most important items is cleanliness of 
 all parts of the plane. After every flight the machine should be 
 thoroughly cleaned. To remove grease and oil from the wings and covered 
 surfaces, use either gasoline, acetone or castile soap and. water. If castile 
 soap cannot be obtained, be sure the soap used contains no alkali or it 
 will injure the dope. In using the gasoline or acetone, do not use too 
 much or it will also take off the dope. A good way to use the latter is 
 to soak a piece of waste or rng and rub over the grease or oil, then wipe 
 off with a piece of dry waste. When using soap and water be careful 
 not to get any inside the wing as it is liable to warp the ribs or rust the 
 wires. 
 
 When mud. is to be removed from the surfaces it should never be 
 taken off while dry, but should, be moistened with water and then 
 removed. 
 
 Other parts of the nmchine should be kept thoroughly clean to keep 
 down the friction. 
 
 Control cables and wires. — All cables and wires should be inspected 
 by the rigger to see that they are at the correct tension. Also see that 
 there are no kinks or broken strands in any of the cables or strands. 
 Do not forget the aileron balance cable on top of the wings. When a 
 wire is found to be slack do not tighten it at once but examine the op- 
 posing wire to see if it is too tight. If so the machine is probably not 
 resting naturally. If the opposing wire is not over-tight then tighten 
 the slack wire. 
 
 All cables and strands and external wires should be cleaned and 
 re-oiled about every two weeks. The oil should be very thin so that it 
 will penetrate between the strands. 
 
 LocJxing devices. — All threaded fastenings and pins should be in- 
 spected very frequently to see that there is no danger of anything com- 
 ing loose. 
 
 Struts and sockets. — Since the struts are compression members, 
 largely, they should be examined on the ends for crushing and in the 
 middle for bending and cracking.
 
 CARE AND INSPECTION 71 
 
 ^^pccidl ins[)crtioiL — A detailed inspecticm of all parts of the inaeliine 
 should be made ouce every Aveek. Usually there is an inspection sheet 
 provided for this purpose. If no sheet is obtainable, then one should be 
 made before the inspection is started. ^Make a list of all the parts to be 
 inspected, starting- at a certain point on the machine, and following 
 around until that point is reached again. When each part or detail is 
 inspected it should be checked on the sheet as defective or O. K. 
 
 A good weekly inspection card form is given on pages 74 to 77. 
 
 Luhrication. — Always see that all moving parts are working freely 
 before a flight is made. This includes undercarriage wheels, pulleys, 
 control levers, hinges, etc. 
 
 Adjustments. — The angle of incidence, dihedral angle, stagger and 
 position of the controlling surfaces should be checked as often as possi- 
 ble so that everything will be all right at all times. Alignment of the 
 undercarriage should be made so that it will not be twisted and thus cut 
 down the speed of the machine. 
 
 Yetting or sighting hy eye. — This should be practiced at all times. 
 "NThen the machine is properly lined up, look at it and get a picture in 
 your mind of just how it looks. Then when anything becomes out of line 
 it can be easily detected without using any tools. See that the struts are 
 in the same plane when looking at the front or side of the machine. The 
 dihedral angle also can be checked by this method of sighting. Some 
 flyers become so expert that they can check the alignment of the whole 
 machine by eye. 
 
 Distortion 
 
 Always be on the lookout for dislocation of any of the parts. If any 
 distortions cannot be corrected by adjustment of the wires, then the part 
 should be replaced. 
 
 MishandUng on the ground. — Great care should always be taken not 
 to overstress any part of the machine. Members are usually designed 
 for a certain kind of stress and if any other kind is put upon them, some 
 damage is likely to occur. When pulling an airplane along the ground, 
 the rope should be fastened to the top of the undercarriage struts. If 
 this cannot be done, then fasten the rope to the interplane struts as 
 low down as possible. 
 
 Never lay covered parts down on the floor but stand them on their 
 entering edges with some padding underneath. Struts should be stood 
 on end where they cannot fall down. 
 
 Hangar. — The hangar at all times should be kept in the best possible 
 condition. Never have oily waste or rags lying around on the floor or 
 benches, as these are liable to catch fire. No smoking should be allowed 
 in or near the building. Do not have oily saw dust spread around on the 
 floor to catch the oil but have pans for this purpose. 
 
 In making replacements of defective parts, have a place for the old 
 pieces. Never allow them to be put where they will be mistaken for 
 new parts.
 
 74 APPLIED AERONAUTICS 
 
 Each tool should be kept in a certain designated place and when 
 anybody borrows a tool, be sure that he puts it back where it belongs. 
 
 Estimating time. — When any repairs are to be made, learn to esti- 
 mate the time required for the job. With a little practice this can be 
 done very accurately. It may help some time in making a report to an 
 officer in charge as to when an airplane will be ready to go out again. 
 
 Weekly Airplane Inspection Card 
 
 Date 191 
 
 Airplane No Make Model 
 
 Engine No Make Model 
 
 Note : This card must be made out by Field Inspector for every machine 
 under his charge, signed by him, and must be turned over to the Chief In- 
 spector as soon as made out. 
 
 I.,anding gear: 
 
 Wire tension 
 
 Wire terminals 
 
 Strut sockets (nuts, bolts) 
 
 Loose spokes 
 
 Axles greased 
 
 Security of wheels to axle 
 
 Shock absorber rubbers 
 
 Tire inflation 
 
 Propeller : 
 
 Condition of blades 
 
 Hub assembly (bolts, washers, cotters) 
 
 Security to shaft 
 
 Thrust 
 
 Fuselage nose : 
 
 Tension fuselage bracing 
 
 Tension and terminals wing drag bracing 
 
 Engine bed and bolts 
 
 Water system: 
 
 Leakage 
 
 Radiator full 
 
 Engine : 
 
 Valves — 
 
 Intake clearance 
 
 Exhaust clearance 
 
 Spark plugs — 
 
 Clean 
 
 Gap 
 
 Carburetor — 
 
 Security to manifold 
 
 Bracing 
 
 Manifold joints
 
 CARE AND INSPECTION 75 
 
 Oil system : 
 
 Leakage 
 
 Oil (grade) 
 
 Oil reservoir full 
 
 Magneto : 
 
 Mounting 
 
 Distributor board 
 
 Breaker point clearance 
 
 Transmission (drive) wear 
 
 Throttle control: 
 
 Pulleys 
 
 Wiring 
 
 Bell cranks and connections 
 
 Gasoline system: 
 
 Tank 
 
 Gasoline leads and connections 
 
 Pump 
 
 Gasoline in tank full 
 
 Wing joints : 
 
 Lower wing — right 
 
 Lower wing — left 
 
 Upper wing — right 
 
 Upper wing — left 
 
 Wing wires: (tension, terminals, clevis pins, cotters, safety wires) 
 
 Flying wires — right wing 
 
 Flying wires — left wing 
 
 Landing wires — right wing 
 
 Landing wires — left wing 
 
 Wires, fittings, turnbuckles, cleaned and greased 
 
 Wing fittings : (bolts, nuts, cotters) 
 
 Right wing, upper lower 
 
 Left wing, upper lower 
 
 Struts : 
 
 Sockets, bolts, cotters 
 
 Straightness 
 
 Right wing 
 
 Left wing 
 
 Ailerons : 
 
 Straightness 
 
 Hinge assembly (lubricate with graphite grease). 
 
 Security 
 
 Wear 
 
 Hinge pins and cotters 
 
 Control wire, connection (mast) 
 
 Frayed control wire (wheel ) 
 
 (pulleys and guides)
 
 76 APPLIED AERONAUTICS 
 
 Note : Control wires frayed at any part of their length must be re- 
 placed at once. 
 
 Pulleys 
 
 Greased 
 
 Free running 
 
 Right ailerons, upper lower 
 
 Left ailerons, upper lower 
 
 Fuselage rear interior : 
 
 Wire tensions 
 
 Longerons 
 
 Fittings 
 
 Alignment 
 
 Stabilizer : 
 
 Bolts, nuts, cotters, braces 
 
 Vertical fin : 
 
 Bolts, nuts, cotters, braces 
 
 Rudder : 
 
 Hinge assembly 
 
 Security 
 
 Wear 
 
 Hinge pins and cotters 
 
 Control wire connections 
 
 Mast 
 
 Footbar 
 
 Frayed control wire 
 
 Note : Control wires frayed at any point of their length must be re- 
 placed at once. 
 Pulleys 
 
 Greased 
 
 Free running 
 
 Elevators : 
 
 Hinge assembly 
 
 Security 
 
 Wear 
 
 Hinge pins and cotters 
 
 Control wire connections — Mast 
 
 Control wire connections — post 
 
 Frayed control wire 
 
 Note : Control wires frayed at any point of their length must be re- 
 placed at once. 
 
 Pulleys 
 
 Greased 
 
 Free running 
 
 Right elevator 
 
 Left elevator
 
 CARE AND INSPECTION 77 
 
 Tail skid : 
 
 Skid 
 
 Fittings 
 
 Shock absorber 
 
 Controls : 
 
 Free and proj^er operation (lubricate with graphite grease) - 
 
 Elevator 
 
 Rudder 
 
 Aileron 
 
 Alignment of entire machine: 
 
 (Signed) Field Inspector.
 
 Chapter 7 
 
 MINOR REPAIRS 
 
 Patching holes in wings — Doping patches — Terminal loops in solid wire — Terminal splices 
 in strand or cable — Soldering and related processes — Soft soldering — Hard solder- 
 ing — Brazing — Sweating — General procedure in soldering — Fluxes — Melting points 
 of solders. 
 
 THE materials used in patching holes in linen-covered surfaces is 
 unbleached Irish linen, the same kind as used in covering the Avings. 
 The material must be unbleached or it will not shrink the required 
 amount. Generally the kind of dope used is Emaillite dope, although 
 the acetate or nitrate dopes could be used. The dope should be applied 
 in a very dry atmosphere or on a sunshiny day at a temperature not less 
 than 65 deg. F. A brush or a piece of svaste may be used to apply the dope. 
 
 In patching a hole the first thing to be done is to clean the surface 
 of the old dope. To do this, fine sand paper may be used or acetone, 
 gasoline or dope. In using the sand paper, care should be taken not to 
 injure the covering. When using the acetone or gasoline, it should be 
 put on the surface, allowed to stand for a while to soak up the old dope, 
 then scraped off. The same method is applied when using dope to clean 
 the surface. 
 
 After the surface is cleaned, the edges of the hole should be sewed 
 if it is of any considerable size. To do this sewing linen thread and a 
 curved needle are used. The stitches should not be closer together than 
 1 in. and far enough back from the edge so that there is no danger of 
 their tearing out. With a small hole, such as a bullet hole for instance, 
 it is not necessary to do any sewing. When the hole is several inches 
 square, a piece of unbleached linen should be sewed in to give a body for 
 the top patch so that it will not be hollow in the center after it is dry. 
 The sewing up of holes should be done after the surface is cleaned so that 
 any slackness may be taken up before the patch is applied. 
 
 After sewing is finished the patch is cut. It should be made about 
 1 to 2 in. larger on each side than the hole. The edges of the patch must 
 be frayed for about ^ in., this being done to prevent them from tearing 
 easily. 
 
 Dope should now be applied to the wing. Generally several coats 
 are put on so that there will be a sufficient amount to make the patch 
 stick well. After the last coat is applied the patch should be put in place
 
 MINOR REPAIRS 79 
 
 immediately before the dope has a chance to dry. Any air bubbles and 
 wrinkles should now be worked from under the patch by rubbing with 
 the fingers, and more dope put on top of the patch. Usually there are 
 six or seven coats of dope applied on top of the patch, allowing time for 
 each coat to dry before another is applied. 
 
 Any small amount of slackness in the patch will probably be taken 
 out as the linen shrinks. If the patch is hollow after the dope is thor- 
 oughly dry, however, it is not a good patch and should be removed. A 
 good patch should be tight around the edges as well as in the center over 
 the hole and should contain no creases or air bubbles. 
 
 Terminal Splices 
 
 A loop or splice must be formed in the end of every brace wire or 
 control cable where it is attached to a strut socket, turnbuckle, control 
 mast, or other form of terminal attachment. The manner of making 
 the loop or splice in the wire w ill vary according to the type of wire or 
 cable used. The terminal in the end of a solid wire is made in the man- 
 ner shown in Fig. 33. 
 
 There are several points to be observed in making this type of 
 terminal splice, as follows: (a) The size of the loop should be as small 
 as possible within reason, as a large loop tends to elongate, thus spoiling 
 the adjustment of the wires. On the other hand, the loop should not be 
 so small as to cause danger of the wire breaking, due to too sharp a bend, 
 (b) The inner diameter of the loop should be about three times the diam- 
 eter of the wire, and the reverse curve at the shoulders of the loop should 
 be of the same radius as the loop itself. The shape of the loop should be 
 symmetrical. If the shoulders are made to the proper radius there will 
 be no danger of the ferrule slipping up towards the loop, (c) When 
 the loop is finished it should not be damaged anywhere. If made with 
 pliers there will be a likelihood of scratching or scoring the wire, which 
 would weaken it greatly. Any break or score in the surface coating of 
 a wire destroys the protective covering at that particular point and 
 the wire will soon be weakened by exposure. A deep nick or score would 
 greatly weaken the wire and eventually result in breakage at that point. 
 
 Splicing a strand or cable. — The splice in the end of a strand or 
 cable is entirely different from the terminal of a solid wire. The end of 
 the strand is led around a thimble and the free end spliced into the body 
 of the strand or cable just below the point of the thimble. Such a splice 
 is afterward served with twine, but the serving should not be done until 
 the splice has been inspected by whoever is in charge of the workshop. 
 The serving might cover bad workmanship in the splice. 
 
 Soldering. — Terminal loops or splices in solid wire and also splices 
 in the ends of strand or cord are sometimes soldered after being formed. 
 There are some objections to soldering at these points, however, as out- 
 lined on page 58. The ensuing instructions for soldering work will 
 prove valuable in cases where this method of securing a terminal splice 
 is considered desirable.
 
 80 APPLIED AERONAUTICS 
 
 Joininf/ of metals hi/ soldering and related jyrocesses. — There are sev- 
 eral methods of joining metals together by allovs which melt at a lower 
 temperature thau the metals to be joined. These processes differ in tlie 
 alloys used and in tlieir melting temperatures. They are divided into 
 four classes, as follows : 
 
 (1) Soft soldering. — This method is the one used in tin-smithing 
 generally, where the solder is melted by means of a hot soldering copper 
 over the surfaces to be joined. The solder used in this process has a low 
 melting point. 
 
 (2) Hard soldering. — This method is usually used in jewelry work 
 and in the arts, where a higher temperature must be withstood. The 
 joining metal in this case has a much higher melting point than soft 
 solder, and must be heated with a blow-torch to make it flow. 
 
 (3) Brazing. — This process differs from hard soldering onh- in the 
 fact that the joining metal has a still higher melting point. It is used 
 principally in motorcycle, bicycle and automobile construction, where 
 greater strength is required. 
 
 (4) Sweating. — This is a process used where the pieces to be joined 
 can first be fitted together, then individually coated with solder, then 
 clamped together and heated until the solder flows, and cements them 
 solidly together. This method allows for a more perfect joint being 
 made. The more accurately the parts are fitted together the stronger 
 the union will be. Also, the thinner the coat of soldering material, within 
 reasonable limits, the stronger the joint. 
 
 All of the above methods are used more or less in airplane con- 
 struction and maintenance, but the one that is most generally used is 
 the first, or soft-soldering method. 
 
 Cleanliness is of prime importance in making joints or fastening 
 by any of these methods. In soldering, the first step is to see that the 
 soldering copper is clean and well tinned, for this may determine the suc- 
 cess or failure of the job. There are several ways of cleaning and tinning 
 the soldering copper, but the one recommended is to heat the copper to 
 about 600 deg. F., then dip the point quickly into a cup or jar containing 
 ammonium chloride (NH4 CI) and granular tin or small pieces of solder. 
 If any considerable amount of work is to be done, an earthen jar or a 
 teacup can be used, and kept partly filled with this mixture. 
 
 Tinning Soldering Coppers 
 
 Another way of tinning the soldering copper is to make a depression 
 in a piece of sheet tin and place in it a small quantity of soldering flux 
 together with a piece of solder. File the copper until bright, heat it to 
 about 600 deg. F., and then move it around, while hot, in the depression 
 in the tin until it becomes coated with molten solder. It will now be 
 ready to use. 
 
 The next step is to clean thoroughly the parts to be joined, using 
 fine emery cloth, sandpaper or a scraper. If the parts are of raw ma- 
 terial, sandpaper will do, but if they are old parts which previously have
 
 MINOR REPAIRS 81 
 
 been exposed, or if a heavy oxide has formed, the surfaces to be soldered 
 should be filed or scraped until perfectly bright and clean. The cleaned 
 surface should then be covered with soldering fluid or one of the luanj- 
 soldering pastes. 
 
 Heat the soldering copper to about 600 dog. F., and touch it to the 
 solder, being careful to get only a small amount of solder on the copper. 
 Rub the copper over the surfaces to be joined until a bright, even coating 
 of solder clings to the surfaces. Place the pieces together and heat until 
 the solder flows, using the hot copper to furnish the necessary heat and 
 adding more solder as needed. Care must be taken not to overheat the 
 pieces at the joint, as this has a tendency to weaken the metal at that 
 point and may cause trouble. 
 
 The same general procedure as the above is followed for hard solder- 
 ing, -uith the exception that a higher temperature must be applied. 
 
 Fluxes 
 
 Fluxes are used in soldering to prevent, so far as possible, the forma- 
 tion of oxides on the heated surfaces, and to flux off those that may have 
 formed. Acid fluxes are the most effective and on iron or steel are prac- 
 tically necessary. The objection to their use is that unless the parts are 
 thoroughly cleaned after soldering the acid in the flux attacks and cor- 
 rodes them. 
 
 In the case of stranded wires or cables the flux will penetrate into 
 the minute spaces betw^een the strands and will be extremely difficult to 
 remove or neutralize, even when the cable or wire is washed with or 
 dipped in an alkaline solution, such as soap or soda water. 
 
 Some of the fluxes in general use are : 
 Zinc chloride (Zn CI), corrosive. 
 Dilute muriatic acid ( H CI ) , corrosive. 
 
 Resin, non-corrosive. This is satisfactory for tin. but will not 
 work on galvanizing. 
 
 Resin and sperm candle melted together make a fair non-corrosive 
 paste. For either tin or galvanizing use three parts resin to one part 
 sperm candle. Sometimes better results are obtained on dirty surfaces 
 by adding one part alcohol to this mixture. 
 
 Melting points of solders. — The melting points of solders composed 
 of tin and lead in various proportions are as follows : 
 
 Proportion 
 
 Melting 
 
 Tin 
 
 Lead 
 
 Point 
 
 1 part 
 
 
 
 25 parts 
 
 558 deg. F. 
 
 1 part 
 
 
 
 5 parts 
 
 511 deg. F. 
 
 1 part 
 
 
 
 1 part 
 
 370 deg. F. 
 
 11 parts 
 
 
 
 1 part 
 
 340 deg. F. 
 
 5 parts 
 
 
 
 1 part 
 
 278 deg. F. 
 
 A composition of 1 to 1 is most commonly used for tin-smithing. 
 For electrical work where the solder is used in the form of wire, a pro- 
 portion of li to 1 or 2 to 1 is used.
 
 Chapter 8 
 
 INSTRUMENTS 
 
 Compass — Magnetic errors — Variation — Deviation — Corrections — Napier diagram — Heel- 
 ing errors — Magnetic clouds — Aneroid barometer — Errors — Uses — Altimeter — Er- 
 rors — Banking meter — Air speed indicator — Incidence indicator — Sperry Clinom- 
 eter — Automatic drift set — Bourdon gauge — Radiator thermometer. 
 
 T TXDOUBTEDLY the compass is one of the most important instru- 
 ^^ ments on an airplane and a tliorongh knoAvledj»e of its construc- 
 tion, operation and theory are absolutely essential to enable the student 
 to become a successful pilot. 
 
 Theoretically, a compass is a permanently magnetized needle swing- 
 ing freely in a horizontal plane on a pivoted point and indicating a north 
 and south direction, due to the attraction of the earth's magnetic north 
 pole for the north pole of the compass needle, and the repulsion of the 
 magnetic pole for the south pole of the compass needle. As is the case 
 with all mechanisms, this theory has been cimibined with modern refine- 
 ments, until we find in jjractice at the present time two main types of 
 compass, viz., the dry card compass and the liquid compass. 
 
 The dry card compass consists of a graduated card over which the 
 magnetized needle swings freely. The accompanying cut (Fig. 47) il- 
 lustrates such a graduated card, which, in a much smaller form, is in use 
 as a pocket compass. It can readily be seen that such an instrument is 
 very easily disturbed, the slightest jar starting it dancing. Gun fire 
 would, of course, render it useless. Another very prominent defect is its 
 inability to come to a complete rest without considerable oscillation. To 
 overcome these mechanical errors the U. S. Xavy produced the liquid 
 compass now used on all vessels, and. in a more perfected form, on air- 
 planes. 
 
 The construction is somewhat more complex as illustrated by Fig. 46, 
 which is a cross-section of a Creagh Osborne standard airplane compass. 
 Instead of a needle swinging over a graduated card, this compass has a 
 graduated card swinging past a certain point or line marked on the in- 
 side of the compass case, called the "lubber line," the entire mechanism 
 being immersed in an airtight bowl of liquid. 
 
 In detail the construction is as follows : M is a pivot supporting the 
 graduated dial P, the latter being made of tinned brass -and graduated 
 in quarter points and half degrees. This dial is hollow and airtight, 
 having in the center a spheroidal air chamber Q to buoy up the weight
 
 INSTRUMENTS 
 
 83 
 
 of the card and iiiauiicts ( ). allowinu a pressure of between 60 and 90 
 grains on the pivot at r>0 de*i. F. The ])iv()t rests in a socket whose bot- 
 tom X is a sappliire jewel to form a bearin<i. At the base of tlie column 
 is a telescopic sprinn' T to ease the jars on this jewel. The magnets O 
 consist of four highly magnetized bundles of steel wires contained in a 
 sealed cylindrical case, the magnets i)laced parallel to the north and 
 south line of the card, and so aligned that their entire directive force 
 will cause the north point of the card to point to magnetic north. The 
 card is mounted in a cast bronze bowl I) which is entirely filled with 
 liquid — 45 percent alcohol and 55 percent distilled water. Beneath the 
 bowl is a self-adjusting expansion chamber K of elastic metal, arranged 
 with a small hole L. to permit circulation of the liquid between the bowl 
 and expansion chamber. The expansi<m chamber is so designed as to 
 expand Avith a rise in temperature and counteract the expansion of the 
 liquid in the bowl, thus keeping the bowl free from bubbles. At one side 
 is a filling screw through which the air bubbles, which are bound to 
 appear, may be removed, and additional liquid added. 
 
 Fi<j. 46 — Details of the CreayJi Osborne air plane compass
 
 84 
 
 APPLIED AERONAUTICS 
 
 The graduations on the card are marked every 20 degrees, the being 
 dropped to avoid crowding. These markings are insoluble in the liquid 
 and are visible at night. The compass bowl sets in an outer bowl B of 
 the same material. It rests on rubber supports, and between the two 
 bowls is a packing of horsehair for absorbing shock. Beneath the com- 
 pass are the corrections for various magnetic effects which will be dis- 
 cussed later. 
 
 It will be recalled that the dry card compass was subject to oscilla- 
 tion and was easily disturbed. It is obvious that in the liquid compass 
 both these errors are materially reduced, the liquid tending to dampen 
 
 Fig. 47 — Standard compass card 
 
 the oscillatory motion, or magnetic moment, as it is called, and also pre- 
 venting the needle from dancing about the x)ivot point. In addition, the 
 combined effect of the small but powerfully magnetized wires is to give 
 the system a greater sensibility or directive force. 
 
 Magnetic Errors 
 
 Variation. — The errors previously discussed have been mechanical 
 in nature and within the compass itself. There is another class of errors, 
 affecting compasses of all types, which are clue to external influences, 
 and a thorough knowledge of their various actions is absolutely essential 
 to the use of the instrument. 
 
 These may be called ''magnetic" errors, inasmuch as they are due 
 either directlv or indirectlv to the magnetic influence of the earth itself.
 
 INSTRUMENTS 85 
 
 Consider the earth as a huge magnet having a north and soutli magnetic 
 pole. The north magnetic pole and the north geogi-aphical pole do not 
 coincide in location. Tlie true north or geographic north is Avhat we call 
 the north pole and is the northernmost point on the earth's surface. The 
 magnetic north pole is located near the northern part of the Hudson Baj 
 region, and is so called because the earth's magnetic influences in the 
 northern hemisphere reach a maximum at this point. Inasmuch as the 
 north-seeking end of the compass needle points to this point, it can readily 
 be seen that there is an error between the true nortli and the compass 
 reading. This error is called the variation and is known and tabulated 
 for all points on the earth's surface. It changes slightly from year to 
 year, but for air work we can consider it as constant for any point, and, 
 as the compass cannot be mechanically corrected for it, the variation 
 must always be included in the calculation of bearings. 
 
 Depends on Locality 
 
 Variation may be either easterly or westerly, depending on the loca- 
 tion on the earth's surface; if easterly, it is given a positive sign, if west- 
 erly it is considered negative in sign. These signs or directions are de- 
 termined by the observer who is considered as being at the center of the 
 compass and facing the point under consideration. It must of course 
 be understood that all conditions are reversed in the southern hemi- 
 sphere. In this connection it might be interesting to note that the vari- 
 ation in Flanders amounts to about 14 deg. and is westerly. Hence to fly 
 true north from any point in that region the compass will read 14 deg. 
 [3G0 deg. - (-11 deg.)]. The compass being graduated from zero to 
 3G0 deg., the following rule may be formulated for finding the compass 
 course from the true course: "Always subtract the variation (neglecting 
 sign) if easterly, and add it, if westerly, from the true course, in order 
 to get the compass course." 
 
 Deviation. — Again let us consider the earth as a huge magnet with 
 lines of force flowing between the poles like invisible rubber bands. If 
 an iron rod is held parallel to these lines of force, i. e., approximately 
 north and south, and then struck two or three sharp blows, it will be 
 found by bringing it to a compass needle, that one end either attracts or 
 repels the needle, thereby indicating that the rod has become magnetized. 
 Xow, if the rod be reversed, end for end, and the experiment repeated, 
 it will be found that the magnetism has become reversed. In other words, 
 there has been induced into an iron rod, a certain amount of magnetism, 
 which is called "induced magnetism." If the rod is of hard iron it will 
 remain a permanent magnet, but if it is of soft iron it will lose the mag- 
 netism as soon as the inducing influence is removed. It readily can be 
 seen from the above exjjeriment that in the construction of an airplane 
 there is a certain amount of magnetism induced into the iron and steel 
 parts of the engine, beams, wires, etc., due to hammering. Such a mag- 
 netism is knoAvn as "residual" or "sub-permanent" magnetism, and the 
 error which it produces in the compass is called "deviation."
 
 86 
 
 APPLIED AERONAUTICS 
 
 Correction for suh-periiifiiieiif iiKifincflHui. — There are two methods 
 of correction for sub-permanent maj^uetism, both of which are rather 
 teclinical in theory, but sinij)le in practice. The first is by means of small 
 "adjustino- magnets," and the second is ''Napier's diagram." No at- 
 tempt will be made to explain the theory of either method, but simply 
 liow they operate in actual practice. It should be added that Napier's 
 
 Fig. 48 — Model sJiOic'ni;/ Jiow corrections are made for residual or sub- 
 
 pernianeiit uia</netisiii 
 
 diagram is a simple method of finding a talde of corrections rather than 
 elimination of the deyiation. 
 
 Fig. 48 is a model \yhicli seryes to illustrate the method of correc- 
 tion for sub-permanent magnetism by means of small adjusting mag- 
 nets. AiV represents a ship which can be rotated in a horizontal plane 
 aboye the axis B and so placed that the center line of the ship has the 
 true magnetic bearing indicated by the dial D. The compass is fastened 
 to the block which rotates with the ship AA. The sub-permanent mag-
 
 INSTRUMENTS 
 
 87 
 
 iietism is roin-escnted by tlio iiiaunots MM which can l»t^ i)laocd in any 
 position. Practice lias sliown, however, that one magnet is better than 
 two. These magnets are used merely to illustrate the method. In 
 actual jn-actice tlie metal i)arts of the shij) or airplane take their place. 
 Small correcting magnets s and t are held by the standard S over 
 the vertical axis of the compass. Their distance can be varied by means 
 
 Fig. 49 — Mariner's coiiipass 
 
 of the small holes as shown. These small magnets may be placed either 
 above or below the compass as long as they are in the plane of its vertical 
 axis. The compass is then corrected by raising or lowering these mag- 
 nets. The following directions explain in detail how an airplane com- 
 pass is corrected :
 
 88 APPLIED AERONAUTICS 
 
 1. Place the airplane in the true magnetic north and south flying 
 position (almost every airdrome has some cement cross or stakes to 
 mark these positions). 
 
 2. Bring down one of the small adjusting magnets over the compass 
 in an east or west position. If deviation increases reverse the magnet 
 end for end and again lower it over the compass until the deviation is zero. 
 
 3. Fix the magnet at that height above the compass at which devi- 
 ation is zero. 
 
 4. Turn the plane to a true magnetic east and west flying position. 
 
 5. Repeat 2 and 3, using another adjusting magnet and being sure 
 to apply it in an east and west position. 
 
 6. Check on other magnetic bearings. 
 
 In summarizing this method there are a few salient facts to be em- 
 phasized. The adjusting magnets must always be applied in an east 
 and west position regardless of the heading of the ship or plane. After 
 the position of a correcting magnet has been determined it can be turned 
 in any direction simultaneously with the compass without destroying its 
 effect. In actual practice the corrections are usually placed below the 
 compass in receptacles arranged for that purpose. This is shown in 
 Pig. 49, which is an illustration of a mariner's compass, or by referring 
 back to Fig. 46, F. The correction is not a permanent one, and from 
 time to time should be checked. 
 
 ^ Napier Diagram 
 
 Najner diagram. — The second method of correcting for sub-perma- 
 nent magnetism is by means of Napier's diagram, an illustration of which 
 is shown on page 87. The diagram is nothing more or less than a gTad- 
 uated compass card straightened out into a straight line. This method 
 does away with the small iron correctors. Referring back to Fig. 48, 
 assume an airplane AA rotating in a horizontal plane. The magnets 
 MM represent the sub-permanent magnetism causing deviation of the 
 compass; in practice the metal parts of the engine and plane have 
 the same effect. 
 
 To plot deviations on the Napier diagram. — Obtain the compass 
 reading for the true magnetic course at each of the cardinal points of 
 the compass. If the reading is greater than the true course the devi- 
 ation should be plotted on the left side of the chart. If the reading is 
 less than the true course, plot the deviation on the right side of the chart. 
 Mark on the center scale of the diagram the compass reading for a given 
 true magnetic course, north or for instance, then draw a line, paral- 
 leling the dotted lines, from the compass reading to the solid line from 
 the corresponding true magnetic course. Follow the same procedure 
 for each of the cardinal points of the compass for which readings were 
 taken, then draw a curve through the points at which the dotted lines 
 projected from the compass readings intersect the solid lines from the 
 corresponding true magnetic courses. From this ciTrve the deviation 
 for any course can be plotted.
 
 INSTRUMENTS 
 
 89 
 
 To ohtaiii course to he steered for a given 
 trite magnetic course. — From the point ou 
 the center scale representing the true mag- 
 netic course desired project a line parallel 
 to the solid lines until it intersects tlie 
 curve already plotted. From this point 
 project another line parallel to the dotted 
 lines back to the center scale. The point 
 at which this last line intersects the center 
 scale gives tlie course to be steered. 
 
 A homely, but easily remembered rule 
 for the use of a Napier diagram is given 
 below : 
 
 Sh/p's 
 
 H&acf 
 
 Compass- 
 Degrees 
 
 Dei^/a//on- 
 
 Magnetic 
 
 De^re^S 
 
 
 N 
 
 
 
 28 -^ 
 
 ^'28 
 
 N.E. 
 
 45 
 
 80 ^ 
 
 -35-^^ 
 
 £. 
 
 90 
 
 1/8 '-^^ 
 
 '28 ^ 
 
 S.£ 
 
 /35 
 
 /45 -- 
 
 ^^-/O 
 
 S 
 
 /do 
 
 /7/ — 
 
 -^^i^ 
 
 3.h< 
 
 225 
 
 /99 — 
 
 —*26 
 
 IV. 
 
 270 
 
 236 -~~~~ 
 
 _jfj<? 
 
 MH< 
 
 3/5 
 
 289 -\ 
 
 *2e 
 
 N. 
 
 360 
 
 388 ^ 
 
 ^^-28 
 
 \ 
 
 "If you wish to steer the course allotted. 
 Depart by plain, return by dotted; 
 From compass course, magnetic to gain, 
 Depart by dotted, return by plain." 
 
 Fig. 50 — Najner diagrarii shoming method of 
 plotting deviation curve
 
 90 
 
 APPLIED AERONAUTICS 
 
 A Napier diagram is shown in Fig. 50 togetlier with a sample table 
 jjiving assumed compass readings for the cardinal compass points, and 
 showing how the curve is plotted from these compass readings. 
 
 HeeJinq error. — In all previous discussions the force of sub-perma- 
 nent magnetism has been considered as acting only in a horizontal plane. 
 It can readily be seen from the accompanying sketch that, when the ves- 
 sel heels to port or starboard the horizontal and vertical components 
 
 it 
 
 y 
 
 Ship heoding North. 
 
 » 
 
 ® 
 
 Hee/ed to Pori: U^nc^ht Heeled fo Storboard. 
 
 On even 
 
 Heeled 
 
 Heeled 
 
 ® 
 
 Heel. 
 
 to Port 
 
 to Storboord. 
 
 Ship heoding East. 
 Fig. 51 — ^lioicing compass error due to heeVuig of ship when headed 
 
 north or south
 
 INSTRUMENTS 
 
 91 
 
 change jjosition to a cei-tain extent, piodiicinii- a resultant force which 
 acts on the needle. This is the "heeling;" error and as the illustration 
 shows, it is a maximum when the ship is heading north or south and zero 
 when east or west. Being due to vertical forces it is corrected by a single 
 vertical magnet placed directly in the vertical axis of an<l at a certain 
 distance below the compass while the airplane is ui)right. This is illus- 
 trated by H in Fig. 46. Tn the northern hemisphere the noith })olc of 
 this magnet will be up. 
 
 Magnetic clouds. — A third form of error, more or less mechanical, 
 should also be mentioned. It is based on the erroneous supposition that 
 the clouds exert a nuignetic influence on the compass needle, due to the 
 fact that on entering a cloud, the card may be observed to turn of its 
 own accord. The theory that clouds exert a magnetic influence has been 
 put forth in explanation. Ordinary clouds are not magnetic — only 
 thunder clouds — and the aviator does not usuallv flv in thunderstorms. 
 
 Fig. 52 — Standard form of airplane compass 
 
 The magnetism of the earth causes the north end of the needle or 
 card to dip in the northern hemisphere, the angle varying from deg. at 
 the equator to 90 deg. at the magnetic north pole. To offset this, the 
 south pole of the compass is weighted slightly. If a machine be flying 
 north, and turns to right or left, centrifugal force acts on the needle, 
 causing the southern end to swing out an<l the northern end to swing in, 
 \\hen exactly the reverse should take ])lace. If a pilot is unaware of this 
 action, he is verv liable to increase his turn still more, thercbv increasing
 
 92 
 
 APPLIED AERONAUTICS 
 
 liis error. lu time tlie inomeutnni may cause the card to swing com- 
 pletely around, as is often the case. If the aviator has any point to steer 
 by he can hold the machine steady until the card has settled down. The 
 only way to correct this error is to make the needle a Tery weak magnet, 
 thus requiring a very small weight on the south end to offset the dip. 
 
 The aviator should examine his compass with a view to finding out 
 if it is subject to this error. Compasses with a short period of vibration 
 are likely to be wrong ; those with a long period are usually right. 
 
 Summary. — This completes the discussion of the main errors of the 
 compass. There remain a few forms of error which are to be studied 
 only in the case of the mariner's compass, and which are too delicate to 
 be considered in aerial work. The student should acquire the habit of 
 constantly checking the instrument when in flight by bearings or rivers, 
 roads, bridges, towns, etc., over which he passes. This cannot be too 
 strongly emphasized. 
 
 Figs. 52 and 53 are illustrations of two forms of compass now 
 in use on airplanes, the latter being a Creagli Osborne type, a cross 
 section of which is shown in Fig. 46. 
 
 The Aneroid Barometer 
 
 Fundamental principles of air pressure. — If a glass tube sealed at one 
 end and completely filled with mercury is inverted into a boAvl of the same 
 liquid and allowed to run out, it will be found that the mercury in the 
 
 r 
 
 ~\ 
 
 
 /^ 
 
 ^^Kfk 
 
 *^€^^ 
 
 Aw 
 
 ^ ' ,. j^Pl 
 
 B'^'^'IIh 
 
 a m 
 
 / ^^Pi^ 
 
 s M^l 
 
 Iv 
 
 '^H^^- 
 
 ^#H 
 
 ^ 
 
 
 W\ 
 
 mt.. 
 
 
 \ 
 
 
 Fig. 53 — Creagli Osborne type of airplane compass
 
 INSTRUMENTS 
 
 93 
 
 Fig. 54 — Ane7^oid barometer with cover reinoced 
 
 tube drops a total of approximately 30 in. This experiment indicates 
 that the air has Axeight, this weight exerting a pressure sufficient to 
 maintain the column of mercury in the tube up to about 30 in. from the 
 top. Calculation shows that the pressure amounts to about 14.7 lbs. 
 per square inch at sea level. This experiment also illustrates in a simple 
 way the theory and construction of the mercurial barometer, Avhicli is 
 used in all measurements of atmospheric pressure. At the same time it 
 readily can be seen that such an instrument would be entirely imprac- 
 ticable for use on an airplane. Hence for use in aerial work there is 
 used what is known as the aneroid barometer, an illustration of whicL 
 is shown in Fig. 54. 
 
 Construction of aneroid barometer. — The aneroid barometer receives 
 its name from the word "aneroid" which means "without fluid." Its con- 
 struction is very simple, and in detail is as follows : In place of the col- 
 umn of mercury there is a German silver corrugated expansion chamber 
 M (see Fig. 54) connected by a post P to a steel leaf spring S which in 
 turn is connected to a pivot A. The spring is also connected b}' a lever 
 arm L and a system of levers IJ to a post supported by a table T. This has 
 a chain gear mechanism at C operating the indicator G. A hair spring H 
 is fitted which serves to take up any slight shock due to loose connections. 
 Any elevation or depression of the expansion chamber due to change in 
 barometric pressure raises or lowers the leaf spring, which in turn com- 
 uiunicates this action by means of the lever arm and system of levers to 
 tlie indicator. The leaf spring also serves the purpose of maintaining a 
 constant tension upon the expansion chamber and the indicator. 
 
 Errors. — The aneroid is not an absolutely accurate measurement of 
 air pressure. It does not permit of the numerous refinements of mech-
 
 94 APPLIED AERONAUTICS 
 
 aiiisni necessary to coiupeiisate for the various conditions that must be 
 taken into consideration in atmospheric measurements. It is absolutely 
 necessary that the entire system be rigidly connected, otherwise any 
 small change in the expansion chamber Avould mereh' serve to overcome 
 the slack in the mechanism. In otlier words there must be a perfect 
 balance of the system. For this reason sudden changes in temperature 
 affect it verj seriously, bringing about looseness in the joints, and in- 
 creases in friction. As it is not designed to compensate for these changes, 
 the readings may often be in error. By tapping the aneroid at different 
 points, errors due to slack or lack of balance, may be detected. 
 
 Uses of the aneroid haroiiieter. — The most common use of the aneroid 
 in aviation is for determining changes in elevation, in which use it gen- 
 erally appears as a pocket aneroid. It is very frequently used in con- 
 nection with sounding balloons for determining atmospheric conditions 
 at higher levels, Such aneroids are self-recording and are known as 
 barographs. 
 
 The Altimeter 
 
 The theorj^, construction, and operation of the altimeter are practi- 
 cally the same as the aneroid barometer. It is primarily an instrument 
 for measurement of altitude and is very often combined with the aneroid 
 in which case it is known as the aneroid altimeter. There are, however, 
 certain conditions that must be considered in the graduations of the 
 altimeter that are not considered with the aneroid. It was shown that 
 the atmosphere exerts a pressure of approximately 14.7 lbs. per square 
 inch at sea level. Observation has proven that this pressure does not 
 vary directly with the altitude. In fact, half the earth's atmosphere is 
 included in the first three and one-half miles above the earth's surface, 
 and it is assumed that traces of our atmosphere can be found even as high 
 as two hundred miles. From this it readily can be seen that at an alti- 
 tude of two miles the pressure will not be one-half as much as at one 
 mile. The pocket aneroid altimeter is accordingly graduated to meet 
 these conditions, smaller graduations occurring at the higher altitudes. 
 
 The altimeter in general use in aerial work is graduated as in Fig. 
 55, Note that the graduations are equal. This is compensated for by a 
 somewhat complicated system of levers within the instrument itself. The 
 altimeter is so constructed that it may be adjusted for any elevation 
 above sea-level at which the pilot may be, this being done by rotating 
 the dial until the zero and needle are coincident. This adjustment is 
 provided to enable the pilot to tell at a glance his actual altitude above 
 the ground, without having to make allowances for the height of the 
 ground above sea-level. This latter might be a very few feet or several 
 thousand, depending on the locality. 
 
 Errors of the altimeter. — The altimeter is subject to the same eiTors 
 as the aneroid but it is highly important that these errors be taken into 
 consideration far more carefully than in the latter instrument. Tempera- 
 ture changes will affect the looseness in the links thereb}^ destroying the 
 balance of the instrument. Sudden changes are even more injurious.
 
 INSTRUMENTS 
 
 95 
 
 Changes in barometric pressure after the pilot has started must be 
 taken into consideration and no altimeter yet has been designed which 
 will do tliis. If during the course of a fliiilit the aviator sliouhl pass from 
 a region of high barometric pressure to one of low pressure without 
 changing his altitude, he would find that his instrument was registering 
 an increased heiglit. This is due, of course, to atmospheric conditions, of 
 which the aviator must be a student in order to be on guard for such er- 
 rors. Weather maps for the region in which he is operating will give him 
 some idea of the location of regions of high or low barometric pressure. 
 
 Another very important error over which the altimeter has no con- 
 trol originates from the topography of the ground over which the machine 
 
 Fig. 55 — Altimeter as used on airplanes 
 
 is flying. For the sake of illustration we will assume that an aviator 
 leaves Onmha, which has an elevation of 3000 ft. aI)ove sea-level, and 
 flies to Pike's Peak. He will set his instrument at zero at Omaha, and 
 on alighting on Pike's Peak, which is about 14,000 ft. above sea-level, 
 will find that his altimeter reads in the neighborhood of 11,000 ft. That 
 is, he is 11,000 ft. above Omaha but not above Pike's Peak. In other 
 words, the altimeter does not take into consideration changes of elevation 
 in the territory over which a plane flies. From this it can l)e seen that a 
 thorough knowledge of the topography of the region in wliich the pilot 
 is operating is verv essential in aerial Avork.
 
 96 APPLIED AERONAUTICS 
 
 There is a fourth form of error which is mechanical and is due to 
 the lag of the instrument. It occurs especiall}' in connection with the 
 nose dive, and may be the cause \)f a very serious accident. The aviator 
 in dropping from an altitude of 10,000 ft. to 1,000 ft., for instance, will 
 reach the lower elevation before his instrument can record the change. 
 The danger lies in the fact that if he depends entirely upon his altimeter, 
 he may not realize until too late that he is much closer to the ground 
 than the altimeter indicated. This error will probably' never be entirely 
 eliminated, but it gradually is being reduced with increasing perfection 
 in construction. 
 
 This practically covers the main errors of the instrument, all of 
 which are due to external influences. Mechanical errors can be detected 
 either by comparing the instrument with a standard barometer or by 
 tapping it to discover slack. In fact, the instrument frequently should 
 be compared with a standard mercurial barometer, merely as a check 
 on its accuracy. 
 
 It should be added that since hot air weighs less than cold air, the 
 readings of an altimeter for the same height will vary with the tempera- 
 ture of the air. Obviously it is impossible to obtain this temperature at 
 all times, hence this factor must be neglected, thus introducing an error 
 which may reach as high as ten per cent. 
 
 Banking Meter 
 
 As its name indicates the banking meter, or banking indicator as it 
 is sometimes called, is used to show the amount of bank which the pilot 
 is making and guard him against skidding or side-slipping. 
 
 There are two forms in use at the present time. One form of this 
 meter is constructed on the same principle as the ordinary spirit level 
 such as is in use on carpenter's levels, transits, etc. It consists essen- 
 tially of a small glass tube nearly filled with liquid, leaving a small 
 bubble. When the tube and its mounting are horizontal the bubble will 
 come to rest in the center of the length of the tube. Any slight inequality 
 in the surface beino; tested is sufficient to send the bubble to the end of 
 
 Fig. 56 — A form of hanking meter patterned after the spirit level
 
 INSTRUMENTS 
 
 97 
 
 Fig. 57 — TJir needle or bar, pirated in ihe eeiiter ejf this hanking indicator, 
 is actuated hg a plninh hob as the plane banks 
 
 the tube. Such an iiistrnment would be impracticable in an airplane, 
 hence a cnrved tube is used. The fanlt of this instrument lies in the 
 fact that it does not indicate the amount of bank correctly as a rule. 
 
 Tlie Sperrv Gyroscope Co. has perfected a bankinii indicator, an 
 illustration of which is shown in Fig. 57. It is based on the principle 
 of the plumb bob. The upper framework shown on the dial indicates the 
 position of the airplane relative to the horizontal and the lower indicator 
 (the horizontal bar pivoted at its center) tells the pilot whether he has 
 banked liis machine sufficiently to meet the centrifugal force due to a 
 turn. The dials are painted with radiolite and are visible at night. 
 
 The inclinometer, which may be used to indicate the longitudinal 
 or lateral inclination of the plane, is ])ractically the same in i)rin(iple as 
 the first form of banking meter described and merely serves as a general 
 check on the attitude of the machine in flight. Instruments based on the 
 ]>rinciple of the spirit level are very inaccurate, being subject to error 
 due to acceleration. Fig. 5(1 is an illustration of the airplane incli- 
 nometer. (See also incidence indicator and clinometer.) 
 
 Air Speed Indicator 
 
 The construction of this instrument is l>ased on the theory of a i^poed 
 measuring device known, after its inventor, as a Pitot tube. Such an 
 instrument contains two essential elements; tlic first is the dvnamic
 
 98 
 
 APPLIED AERONAUTICS 
 
 opeuing or mouth of the impact tube. (See Fig. 58.) It points directly 
 against the current of gas or liquid in which the speed is to be measured 
 and receives the full impact of the current. The second is a static open- 
 ing for obtaining the so-called static pressure of the moving fluid, that 
 is, the pressure that would be indicated by a pressure gauge moving with 
 the current and not subject to impact. To avoid the influence of impact 
 the static opening is placed at right angles to the dynamic opening. If 
 the two pressure heads are connected to the opening of a U tube partly 
 filled with liquid, and a current of air generated against the mouth of 
 the impact tube it will be seen that the liquid will indicate a difference 
 in pressure between the two openings. Starting with the formula 
 V = V2gh where h is the difference in elevation between the levels, and 
 g the measure of acceleration due to gravity, a measurement can be ob- 
 tained of the velocity of the air current by measuring the difference in 
 pressure between the two openings. Fig. 58 is a cross section of the 
 opening in a Pitot tube. While the dynamic pressure can be accurately 
 determined, the static pressure is very uncertain, as the air rushing by 
 the static opening is apt to cause suction. The instrument should there- 
 fore be calibrated. 
 
 P/tof Head Venfun Meter 
 
 Fig. 58 — Shoiving operating principles of two forms of air speed meters 
 
 Another form of air speedometer, also shown in Fig. 58, is based on 
 the principle of a venturi tube. This tube consists of a short converging 
 inlet folloAved by a long diverging cone. The opening is placed at right 
 angles to the air current and a measurement is made of the difference in 
 pressure existing between the oj)ening diameter and the smallest diameter 
 of the throat. This measurement is based on the ratio of entrance to 
 throat area, these being the names of the opening and of the smallest 
 area. The tube is provided with connections to a differential gauge by 
 which this difference in pressure is measured. 
 
 The Incidence Indicator 
 
 The incidence indicator, as its name suggests, is used to measure the 
 angle of attack. For this purpose an instrument, if possible, should be 
 "dead beat," or in other words, free from any tendency to swing, and it 
 must actually register any change in the direction of the flow of air to 
 the supporting wings or surfaces.
 
 INSTRUMENTS 
 
 99 
 
 Fig. 59 — Incidence indivator mounted on one of the forward struts. 
 It operates colored lights in the dial shoim in Fig. 60 
 
 Fig. 59 illustrates a form of indicator which is attached to one of the 
 forward struts of an airplane at a point where it will be entirely free 
 from any influence of the propeller. AB is a vertical strut on the air- 
 plane, to which is attached a wind vane CD, revolving about an axis EF, 
 and actuating a dial K. This wind vane CD is horizontal and always 
 points in the direction of the relative wind, in other words the airplane 
 revolves about the axis EF, as the angle of attack changes. This device 
 is then wired to an electric lamp box indicator similar to the sketch in 
 Fig. 60. 
 
 Fastened to the shaft EF (Fig, 59) is a commutator which closes 
 the contact at certain points, and completes the circuit to the different 
 
 Fig. 60 — Indicating dial connected to incidence indicator sthou-n in Fig. 59
 
 100 
 
 APPLIED AERONAUTICS 
 
 Fuj. 61 — Hitcrrij clinometer 
 
 lamps shown in Fi.j;. (>U. When the airplane is in danger of stalling the 
 proper light flashes the information to the pilot. The same is true of the 
 other two lights. 
 
 The Sperry clinometer is designed \\\i\\ the idea of telling the pilot 
 the inclination of the axis of the airplane. Fig. 01 is an illustration of 
 such an instrument. 
 
 Fig. 02 is a cross-section of the same instrument, showing its con- 
 struction, which, it will he noted, is based on the principle of the plund)- 
 bol). The scale S is mounted on the periphery of a wheel W, which is 
 damped by floating in a liquid. The base of the wheel has a small weight 
 X to maintain it constantly in a vertical condition. There is also an 
 expansion chamber and a filling screw similar to the liquid compass. It 
 is to be noted that this and similar instruments are subject to an error 
 due to lag, caused by the inertia of the wheel for an al)rupt change of 
 direction. The clinometer is usually mounted in the cockpit where it 
 can be seen at all times. Skillful pilots pay very little attention to in- 
 struments of this kind, however, relying almost entirely on instinct. 
 
 The Automatic Drift Set 
 
 Before explaining the operation of this instrument, it might be well 
 to include a word in connection Avith the term "drift," as here used. An 
 aviator, desiring to fly to a point due north of his starting point, with a 
 west wind blowing, will find at the end of a certain length of time that 
 he is considerablv to the eastward of his destination, having been blown
 
 INSTRUMENTS 
 
 101 
 
 from his course. To .miaid aiiniiist this, two forms of drift indicators 
 are in use. The first is very simple and consists of an eyepiece, contain- 
 inii' cross-hairs similar to a surveyor's transit. Uy lookiuii directly at the 
 ground, the ai>]>ar('nt motion of surface olijects can he (dtsei'ved and made 
 to coincide with the cross-hairs (»f the eyei)iece. Tliis is done hy rotating 
 the eyepiece about the axis of tlu' teh'scope, and tlie anuuint of this 
 rotation, read from a graduated circle, gives the drift angle directly. The 
 pilot then steers "off his course" an amount eijual to this angle of drift 
 but in the opposite direction, 
 
 A more improved type of this instrument is the Autonmtic Drift Set 
 sho^^■n in Fig. 03. As before, an eyepiece is used to determine the angle 
 of drift as observed from the apparent motion of objects on the ground. 
 As the eyepiece turns to coincide with this line of motion, the connecting- 
 cables shown turn the compass case, so that the "lul»l»er line" of the 
 compass is turned automatically in the opposite direction to the drift, 
 and to an equal amount. The pilot then simply steers his predetermined 
 course on the shifted lubber line. 
 
 The Bourdon Gauge 
 
 This is an instrument for measuring the pressure exerted by a gas 
 or liquid, and is the type used in nearly all steam gauges. It is used on 
 airplanes for registering circulating oil pressure, the pressure of air in 
 
 Fi(j. U2 — Cross-section of Spcrnj cliitonietcr
 
 102 
 
 APPLIED AERONAUTICS 
 
 F'hi. 63 — ^ perry Aiitoinatic Drift Set^ consisting of a small revolving 
 telescope which is connected to compass case in such a way that compass 
 case icith luhher line is automatically turned to compensate for side drift 
 when sighting telescope is turned to line up cross-hairs u'ith apparent 
 motion of plane over ground 
 
 I
 
 INSTRUMENTS 
 
 103 
 
 the fuel tank, etc. It depends for its action upon the principle that a 
 bent tube if subjected to internal pressure tends to straighten out. Its 
 action can be seen in Fig. 64. A is a tank of air which can be compressed 
 to any desired pressure, as indicated by the pressure gauge C. D is a 
 piece of rubber tube with the outer end closed, and E is a steam gauge 
 from which the dial and covering have been removed. By opening the 
 valve V a pressure is exerted internally in the rubber tube D, tending to 
 straighten it out. The same principle is involved in the metal tube E 
 
 Fig. 64 — Test outfit showing principle of operation of Bourdon gauge 
 such as used for indicating steam pressure. This principle is also used 
 in radiator thermometers, air and oil pressure gauges, etc.
 
 104 
 
 APPLIED AERONAUTICS 
 
 A AfoB full of liquid 
 
 Bourdon Gauge 
 
 Fig. (Jo — l>>liowiii</ Jioir a Bourdon (jamjp, connected to a hnlh half 
 fiiU of liquid, is used for a distance thermometer. This device is used in 
 airplanes for indicating radiator temperatures. 
 
 which also tends to straighten out. This tube is flattened to increase its 
 sensitiveness, and is connected through a nuignifying device to the 
 pointer, Avhich moves in front of a graduated dial. 
 
 The Radiator Thermometer 
 
 By connecting a Bourdon gauge with a tube of small bore wliich 
 ends In a chainber or bulb, and then filling the system of gauge and tube 
 with a liquid until the bulb becomes about half full (as shown in Fig. 65) 
 a distance thermometer is obtained, the dial of which can be placed at 
 a point some distance away from the controlling bulb. This type of gauge 
 is used to indicate the temperature of the water in the radiator, so as to 
 guard against overheating or freezing. 
 
 As the temperature of the radiator, in which the bulb is placed, rises, 
 more and more of the liquid in the bulb will be changed to vapor, and its 
 ])ressure will increase accordingly causing the pointer in the Bourdon 
 gauge to move. By properly calibrating the dial the readings can be 
 shown in degrees of temperature in i)lace of pounds of pressure.
 
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 Chapter 9 
 
 NOMENCLATURE FOR AERONAUTICS 
 
 Based on official nomenclature recommended by the National Advisory Committee for 
 Aeronautics and definitions used and standardized by the U. S. Army School of 
 Military Aeronautics at Ohio State University. 
 
 AERODYNAMICS — The science which treats of the air or other gaseous 
 bodies under the action of forces and of their mechanical effects. 
 AEROFOIL — A thin wing-Hke structure, flat or curved, designed to obtain 
 reaction upon its surfaces from the air through which it moves. 
 AERONAUTICS — That branch of engineering Avliich deals with the design, 
 construction and operation of aircraft. 
 
 AILERON — A movable auxiliary surface used for the control of rolling mo- 
 tion of an airplane, i. e., rotation about its fore and aft axis. 
 AIRCRAFT — Any form of craft designed for the navigation of the air; air- 
 planes, balloons, dirigibles, helicopters, kites, kite balloons, ornithopters, glid- 
 ers, etc. ; ; *«*l^ 
 AIRDROME — The name usually applied to a ground and buildings used 
 for aviation. 
 
 AIRPLANE — A form of aircraft heavier than air, which has wing surfaces 
 for sustentation, stabilizing surfaces, rudders for steering, power plant for 
 propulsion through the air and some form of landing gear ; either a gear suit- 
 able for rising from or alighting on the ground, or pontoons or floats suitable 
 for alighting on or rising from water. In the latter case, the term "Seaplane" 
 is commonly used. (See definition.) 
 
 Pusher — A type of airplane with the propeller or propellers in the rear of 
 
 the wings. 
 
 Tractor — A type of airplane with the propeller or propellers in front 
 
 of the wings. 
 
 Monoplane — A form of airplane whose main supporting surface is dis- 
 posed as a single wing extending equally on each side of the body. 
 
 Biplane — A form of airplane in which the main supporting surface is 
 
 divided into two parts, one above the other. 
 
 Triplane^ — A form of airplane whose main supporting surface is divided 
 
 into three parts, superimposed.
 
 NOMENCLATURE FOR AERONAUTICS 107 
 
 Multiplane — An airplane the main lifting surface of which consists of 
 numerous surfaces or pairs of superimposed wings. 
 
 One and One-Half Plane — A biplane in which the span of the lower 
 plane is decidedly shorter than that of the upper plane. 
 Flying Boat — An airplane fitted with a boat-like hull suitable for naviga- 
 tion and arising from or alighting on water. 
 
 Seaplane — An airplane fitted with pontoons or floats suitable for alight- 
 ing on or rising from the water. 
 AIR POCKET — A local movement or condition of the air causing an airplane 
 to drop or lose its correct attitvide. 
 
 AIR SPEED METER — An instrument designed to measure the velocity of 
 an aircraft with reference to the air through which it is moving. 
 ALTIMETER — An instrument mounted on an aircraft to continuously indi- 
 cate its height above the surface of the earth. 
 
 ANEMOMETER — An instrument for measuring the velocity of the wind or 
 air currents with reference to the earth or some fixed body. 
 ANGLE OF ATTACK — The acute angle betvvcen the direction of relative 
 wind and the chord of an aerofoil, i. e., the angle between the chord of an 
 aerofoil and its motion relative to the air. (This definition may be extended 
 to any body having an axis.) 
 
 Best Climbing — ^The angle of attack at which an airplane ascends fastest. 
 An angle about half way between the maximum and optimum angle. 
 Critical — The angle of attack at which the lift is a maximum, or at which 
 the lift curve has its first maximum ; sometimes referred to as the "burble 
 point." (If the lift curve has more than one maximum, this refers to 
 the first one.) 
 
 Gliding — The angle the flight path makes with the horizontal when 
 flying in still air under the influence of gravity alone, i. e., without power 
 from the engine. 
 
 Maximum — The greatest angle of attack at which, for a given power, 
 surface and weight, horizontal flight can be maintained. 
 Minimum — The smallest angle of attack at which, for a given power, 
 surface and w^eight, horizontal flight can be maintained. 
 Optimum — The angle of attack at which the lift-drift ratio is the highest. 
 ANGLE OF INCIDENCE (Rigger's Angle)--The angle between the longi- 
 tudinal axis of the airplane and the chord of an aerofoil. 
 
 APPENDIX — The hose at the bottom of a balloon used for inflation. In the 
 case of a spherical balloon it also serves for equalization of pressure. 
 ASPECT RATIO — The ratio of span to chord of an aerofoil. 
 
 AVIATOR — The operator or pilot of heavier-than-air craft. This term is 
 applied regardless of the sex of the operator. 
 AVION — Tlie official French term for military airplanes only. 
 AXES OF AN AIRCRAFT— The three fixed lines of reference ; usually pass- 
 ing through the center of gravity and mutually rectangular. The principal 
 axis in a fore and aft direction, usually parallel to the axis of the propeller and 
 in the plane of symmetry, is the Longitudinal Axis or the Fore-and-Aft Axis.
 
 108 APPLIED AERONAUTICS 
 
 The axis perpendicular to this and in the plane of symmetry is the Vertical 
 Axis ; the third axis perpendicular to the other two is the Lateral Axis, also 
 called the Transverse Axis or the Athwartship i\xis. In mathematical dis- 
 cussion the first of these axes, drawn from front to rear is called the X Axis ; 
 the second. dra\\ n upward ; the Z Axis ; and the third, forming a "left-handed" 
 system, the Y Axis. 
 
 BALANCED CONTROL SURFACE— A type of surface secured by adding 
 area forward of the axis of rotation. In an airstream a force is exerted on this 
 added area, tending to aid in the movement about the axis. 
 BALANCING FLAPS— (See AILERON.) 
 
 BALLONET — A small balloon within the interior of a balloon or dirigible 
 for the purpose of controlling the ascent or descent, and for maintaining pres- 
 sure on the outer envelope so as to prevent deformation. The ballonet is kept 
 inflated with air at the required pressure, under the control of a blower and 
 valves. 
 
 BALLOON — A form of aircraft comprising a gas bag and a basket and sup- 
 ported in the air by the buoyancy of the gas contained in the gas bag, which 
 is lighter than the amount of air it displaces ; the form of the gas bag is main- 
 tained by the pressure of the contained gas. 
 
 Barrage — A small spherical captive balloon, raised as a protection 
 against attacks by airplanes. 
 
 Captive — A balloon restrained from free flight by means of a cable at- 
 taching it to the earth. 
 
 Kite — An elongated form of captive balloon, fitted with tail appendages 
 to keep it headed into the wind, and deriving increased lift due to its axis 
 being inclined to the wind. 
 
 Pilot — A small spherical balloon sent up to show the direction of the 
 wind. 
 
 Sounding — A small spherical balloon sent aloft, without passengers, but 
 with registering meterological instruments for recording atmospheric 
 conditions at high altitudes. 
 BALLOON— DIRIGIBLE— A form of balloon the outer envelope of which 
 is of elongated horizontal form, provided with a car, propelling system, rud- 
 ders and stabilizing surfaces. Dirigibles are divided into three classes : Rigid, 
 Semi-rigid and Non-rigid. In the Rigid type the outer covering is held in 
 place and form by a rigid internal frame work and the shape is maintained in- 
 dependently of the contained gas. The shape and form of the Semi-rigid type 
 is maintained partly by an inner framework and partly by the contained gas. 
 The Non-rigid type is held to form entirely by the pressure of the con- 
 tained gas. 
 
 BALLOON BED — A mooring place on the ground for a cai)tiv,e balloon. 
 BALLOON CLOTH— The cloth, usually cotton, of which balloon fabrics 
 are made. 
 
 BALLOON FABRIC— The finished material, usually rubberized, of which 
 balloon envelopes are made.
 
 NOMENCLATURE FOR AERONAUTICS 109 
 
 BANK — To incline an airplane laterally, i. e., to rotate it abont the fore-and- 
 aft axis when making a turn. Right bank is to incline the air])lane with the 
 right wing down. Also used as a noun to describe the position of an airplane 
 when its lateral axis is inclined to the horizontal. 
 
 BAROGRAPH — An instrument for recording variations in barometric pres- 
 sure. In aeronautics the charts on which the records are made are prepared 
 to indicate altitudes directly instead of barometric pressure, inasmuch as the 
 atmospheric pressure \aries almost directly with the altitude. 
 BAROMETER — An instrument for measuring the pressure of the atmos- 
 phere. 
 
 BASKET — The car suspended beneath the balloon for passengers, ballast, etc. 
 BIPLANE— (See AIRPLANE.) 
 
 BODY (OF AN AIRPLANE)— A structure, usually enclosed, which contains 
 in a streamline housing the power plant, fuel, passengers, etc. 
 
 Fuselage — A type of body of streamline shape carrying the empannage 
 and usually forming the main structural unit of an airplane. 
 Monocoque — A special type of fuselage constructed of metal sheeting or 
 laminated wood. A monocoque is generally of circular or elliptical cross- 
 section. 
 
 Nacelle — A type of body shorter than a fuselage. It does not carry the 
 empannage, but acts more as a streamline housing. Usually used on a 
 pusher type of machine. 
 
 Hull — A boat-like structure which forms the body of a flying-boat. 
 BONNET — The appliance, having the form of a parasol, which protects the 
 valve of a spherical balloon against rain. 
 BOOM— (See OUTRIGGER.) 
 
 BOWDEN WIRE — A stiff control wire enclosed in a tube used for light con- 
 trol work where the strain is comparatively light, as for instance throttle and 
 spark controls, etc. 
 
 BOWDEN WIRE GUIDE— A close wound, spring-like, flexible guide for 
 Bowden wire controls. 
 
 BRIDLED — The system of attachment of cables to a balloon, including lines 
 to the suspension band. 
 
 BULLS EYES — Small rings of wood, metal, etc., forming i)art of balloon 
 rigging, used for connection or adjustment of ropes. 
 BURBLE POINT— (See ANGLE— CRITICAL. ) 
 
 CABANE (OR CABANE STRUT)— In a monoplane, the strut or pyramidal 
 frame work projecting above the body and wings and to which the stays, 
 ground wires, braces, etc., for the wing are attached. 
 
 In a biplane, the compression member of an auxiliary truss, serving to 
 support the overhang of the upper wing. 
 
 CAMBER — The convexity or rise of the curve of an aerofoil from its chord, 
 usually expressed as the ratio of the maximum departure of the curve from 
 the chord as a fraction thereof. Top Camber refers to the top surface and 
 Bottom Camber to the bottom surface of an aerofoil. Mean Camber is the 
 mean of these two.
 
 no APPLIED AERONAUTICS 
 
 CAPACITY-CARRYING— The excess of the total lifting capacity over the 
 dead load of an aircraft. The latter includes structure, power plant and essen- 
 tial accessories. Gasoline and oil are not considered essential accessories. 
 
 The cubic contents of a balloon. 
 CAPACITY-LIFTING— (See LOAD)— The maximum flying load of an 
 aircraft. 
 
 CATHEDRAL — A negative dihedral. 
 
 CEILING — The maximum possible altitude to which a given airplane can 
 climb. 
 
 CENTER — The point in which a set of effects is assumed to be accumulated, 
 producing the same effect as if all were centered at this point. 
 
 There are five main centers in an airplane— Center of Lift, Center of 
 Gravity, Center of Thrust, Center of Drag and Center of Keelplane Area. 
 The latter is also called the Directional Center. The stability, controllability 
 and general air worthiness of an airplane depend largely on the proper posi- 
 tioning of these centers. 
 
 CENTER OF PRESSURE OF AN AEROFOIL— The point in the plane 
 of the chords of an aerofoil, prolonged if necessary, through which at any 
 given attitude the line of action of the resultant air force passes. (This defi- 
 nition may be extended to any body.) 
 
 CENTER PANEL — The central part of the upper wing (of a biplane) above 
 the fuselage. The upper wings are attached to this on either side. 
 CHORD — (Of an aerofoil section.) A straight line tangent to the under 
 curve of the aerofoil section, front and rear. 
 
 CHORD LENGTH— (Or length of Chord.)— The length of an aerofoil sec- 
 tion projected on the chord, extended if necessary. 
 CLINOMETER— (See INCLINOMETER.) 
 
 CLOCHE — The bell-shaped construction which forms the lower part of the 
 pilot's control lever in the Bleriot control and to which the control cables are 
 attached. 
 
 COCKPIT — The space in an aircraft body occupied by pilots or passengers. 
 CONCENTRATION RING— The hoop to which are attached the ropes sus- 
 pending the basket (of a balloon). 
 
 CONTROLS — A general term applied to the mechanism used to control the 
 speed, direction of flight and altitude of an aircraft. 
 
 Bridge (Deperdussin-"Dep" Control) — An inverted "U" frame pivoted 
 near its lower points, by wdiich the motion of the elevators is controlled. 
 The ailerons are controlled by a wheel mounted on the upper center of 
 this bridge. 
 
 Dual — Two sets of inter-connected controls allowing the machine to be 
 operated by one or two pilots. 
 
 Shoulder — A yoke fitting around the shoulders of the pilot by means of 
 which the ailerons are operated (by the natural side movement of the 
 pilot's body) to cause the proper amount of banking when making a 
 turn or to correct excessive bank. (Used on early Curtiss planes.) 
 Stick (Joy-stick) — A vertical lever pivoted near its lower end and used 
 to operate the elevators and ailerons.
 
 NOMENCLATURE FOR AERONAUTICS 111 
 
 COWLS — The metal covering enclosing the engine section of the fuselage. 
 CROW'S FOOT — A system of diverging short ropes for distributing the pull 
 of a single rope. (Used principally on balloon nets.) 
 
 DECALAGE — The difference in the angular setting of the chord of the upper 
 wing of a biplane with reference to the chord of the lower wing. 
 DIHEDRAL (In an airplane) — The angle included at the intersection of the 
 imaginary surfaces containing the chords of the right and left wings (con- 
 tinued to the plane of symmetry if necessary). This angle is measured in a 
 plane perpendicular to that intersection. The measure of the dihedral is taken 
 as 90 deg. minus one-half of this angle as defined. 
 
 The dihedral of the upper wing may and frequently does differ from that 
 of the lower wing in a biplane. 
 
 Lateral — An airplane is said to have lateral dihedral when the wings 
 slope downward from the tips toward the fuselage. 
 
 Longitudinal — The angular difference between the angle of incidence of 
 the main planes and the angle of incidence of the horizontal stabilizer. 
 DIRIGIBLE — A form of balloon, the outer envelope of which is of elongated 
 horizontal form, provided with a propelling system, car, rudders and stabil- 
 izing surfaces. 
 
 Non-Rigid — A dirigible whose form is maintained by the pressure of the 
 contained gas assisted by the car suspension system. 
 Rigid — A dirigible whose form is maintained by a rigid structure con- 
 tained within the envelope. 
 
 Semi-Rigid — -A dirigible whose form is maintained by means of a rigid 
 keel and by gas pressure. 
 
 DIVING RUDDER— (See ELEVATOR.) 
 
 DOPE — A preparation, the base of which is cellulose acetate or cellulose 
 nitrate, used for treating the cloth surfaces of airplane members or the fabric 
 of balloon gas bags. It increases the strength of the fabric, produces taut- 
 ness, and acts as a filler to make the fabric impervious to air and moisture. 
 DRAG — The component parallel to the relative wind of the total force on an 
 aircraft due to the air through which it moves. 
 
 That part of the drag due to the wings is called "Wing Resistance" 
 (formerly called "Drift") ; that due to the rest of the airplane is called "Para- 
 site Resistance" (formerly called head resistance). 
 
 The total resistance to motion through the air of an aircraft, that is. the 
 sum of the drift and parasite resistance. Total Resistance. 
 DRIFT — The component of the resultant wind pressure on an aerofoil or 
 wing surface parallel to the air stream attacking the surface. 
 
 Also used as synonymous with lee-way. 
 (See DRAG.) 
 DRIFT INDICATOR — An instrument for the measurement of the angular 
 deviation of an aircraft from a set course, due to cross winds. 
 
 Also called Drift Meter. 
 DRIFT WIRES— Wires which take the drift load and transfer it through 
 various members to the body of the airplane.
 
 112 APPLIED AERONAUTICS 
 
 DRIP CLOTH — A curtain around the equator of a balloc^n wliich prevents 
 
 rain from dripping into the basket. 
 
 DROOP— 
 
 (a) An aileron is said to have droop when it is so adjusted that its trailing 
 edge is below the trailing edge of the main plane. 
 
 (b) When a wing is warped to give wash-out or wash-in. its trailing 
 edge will, relative to the leading edge, be displaced progressively from 
 one end to the other. A downward displacement is called droop. 
 
 ELEVATOR — A hinged surface, usually in the form of a horizontal rudder, 
 mounted at the tail of an aircraft for controlling the longitudinal attitude of 
 the aircraft, i. e., its rotation abovit the lateral axis. 
 EMPANNAGE — A term applied to the tail group of parts of an airplane. 
 
 (See TAIL.) 
 ENGINE SILL, BEARERS, SUPPORTS— The members forming the en- 
 gine bed. 
 
 ENTERING EDGE — The foremost part or forward edge of an aerofoil or 
 propeller blade. 
 
 ENVELOPE — The portion of the balloon or dirigible which contains the gas. 
 EQUATOR — The largest horizontal circle of a spherical balloon. 
 FAIRING — A wood or metal form attached to the rear of struts, braces or 
 wires to give them a streamline shape. 
 FAIR LEAD— A guide for a cable. 
 
 FIN — A small fixed aerofoil attached to part of an aircraft to promote stabil- 
 ity; for example, tail fin, skid fin, etc. Fins may be either horizontal or ver- 
 tical and are often adjustable. 
 
 (See STABILIZER.) 
 FIRE DASH — A metal screen dividing the engine section of an airplane body 
 from the cockpit section. 
 
 FLIGHT PATH — The path of the center of gravity of an aircraft with ref- 
 erence to the earth. 
 
 FLOAT — That portion of the landing gear of an aircraft which provides 
 buoyancy when it is resting on the surface of the water. 
 FLYING BOAT— (See AIRPLANE.) 
 
 FLYING POSITION — The position of a machine, assumed when flying 
 horizontally in still air. When on the ground the machine is placed in a fly- 
 ing position by leveling both longitudinally and laterally. The two longerons, 
 engine sills or other perpendicular parts designated by the maker are taken 
 as reference points from which to level. 
 FOOT BAR— (See RUDDER BAR.) 
 FUSELAGE— (See BODY.) 
 
 FUSELAGE COVER — A cover placed on a fuselage to preserve a streamline 
 shape. 
 
 GAP — The shortest distance between the planes of the chords of the upper 
 and lower wings of a biplane. 
 GAS BAG— (See ENVELOPE.) 
 GLIDE — To fly without power and under the influence of gravity alone.
 
 NOMENCLATURE FOR AERONAUTICS 113 
 
 GLIDER— A form of aircraft similar to an airplane but without any power 
 plant. 
 
 When utilized in variable winds it makes use of the soaring principles 
 of flight and is sometimes called a soaring- machine. 
 GLIDING ANGLE— (See ANGLE.) 
 
 GORE — ( )ne of the segments of fabric comprising the envelope of a balloon. 
 GROUND CLOTH — Canvas placed on the ground to protect a balloon. 
 GUIDE ROPE — A long trailing rope attached to a spherical balloon or diri- 
 gible to serve as a brake and as a variable ballast. 
 
 GUY — A rope, chain, wire or rod attached to an (.>bject to guide or steady- 
 it, such as guys to wing, tail or landing gear. 
 HANGAR — An airplane shed. 
 
 HEAD RESISTANCE— (See PARASITE RESISTANCE.) 
 HELICOPTER — A form of aircraft whose supi)ort in the air is derived from 
 the vertical thrust of propellers. 
 
 HORN-CONTROL ARM— An arm at right angles to a control surface to 
 which a control cable is attached, for example, aileron horn, rudder horn, 
 elevator horn, etc. More commonly called a Mast. 
 HULL— (See BODY.) 
 
 INCLINOMETER — An instrument for measuring the angle made by the 
 axis of an aircraft with the horizontal. 
 
 Indicator-Banking — An inclinometer indicating lateral inclination or 
 bank. 
 INSPECTION WINDOW — A small transparent window in the envelope 
 of a balloon or in the wing of an airplane to allow inspection of the interior, 
 or of aileron controls when the latter are mounted inside an aerofoil section. 
 INSTABILITY — An inherent condition of a body, which, if the body is dis- 
 tributed, causes it to move toward a position away from its first position, 
 instead of returning to a condition of equilibrium. 
 
 KEEL PLANE AREA — The total effective area of an aircraft which acts to 
 prevent skidding or side slipping. 
 
 KITE — A form of aircraft without other propelling means than the tow-line 
 pull, whose support is derived from the force of the wind moving past its 
 surfaces. 
 
 LANDING GEAR — The understructure of an aircraft designed to carry the 
 load when resting on, or running on, the surface of the land or water. 
 LEADING EDGE— (See ENTERING EDGE.) 
 
 LEEWAY — The angle of deviation from a set course over the earth, due to 
 cross currents of wind. Also called Drift. 
 
 LIFT — The component of the force due to the air pressure of an aerofoil re- 
 solved perpendicular to the flight path in a vertical plane. 
 LIFT-DRIFT RATIO— The proportion of lift to drift is known as the lift- 
 drift ratio. It expresses the efficiency of the aerofoil. 
 LIFT BRACING— (See STAY.) 
 LOAD— 
 
 Dead — The structure, power plant and essential accessories of an air- 
 craft.
 
 114 APPLIED AERONAUTICS 
 
 Full — The maximum weight which an aircraft can support in flight; 
 
 the gross weight. 
 
 Useful— "J he excess of the full load over the dead weight of the aircraft 
 
 itself, i. e., over the weight of its structure, power plant and essential 
 
 accessories. (These last must be specified.) 
 
 (See Capacity.) 
 LOADING — The weight carried by an aerofoil, usually expressed in pounds 
 per square foot of superficial area. 
 
 LOBES — Bags at the stern of an elongated balloon designed to give it direc- 
 tional stability. 
 
 LONGERON — The principal fore-and-aft structural members of the fuselage 
 or nacelle of an air])lane. 
 
 (See LONGITUDINAL.) 
 LONGITUDINAL — A fore-and-aft member of the framing of an airplane 
 body, or of the float in a seaplane, usually continuous across a number of 
 points of support. 
 
 LONGITUDINAL DIHEDRAL— (See DIHEDRAL.) 
 MAST— (See HORN.) 
 MONOCOQUE— (See BODY.) 
 
 MONOPLANE — A form of airplane whose main supporting surface is a single 
 wing extending equally on each side of the body. 
 
 (See AIRPLANE.) 
 MOORING BAND — The 1:)and of tape over the top of a balloon to which are 
 attached the mooring ropes. 
 NACELLE— (See BODY.) 
 
 NET — A rigging made of ropes and twine on spherical balloons, which sup- 
 ports the entire load carried. 
 
 NOSE DIVE — A dangerously steep descent, head on. 
 
 NOSE PLATE — A plate at the nose or front end of the fuselage in which 
 the longerons terminate. 
 
 NOSE SPIN — A nose dive in which the airplane rotates about its own axis 
 due to the reaction from the propeller. It usually results from failure to shut 
 off the engine in time when going into a nose dive, and is likely to cause 
 complete loss of control. 
 
 ORNITHOPTER — A form of aircraft deriving its support and propelling 
 force from flapping wings. 
 
 OUT-RIGGER — -Members, independent of the body, extending forward or 
 
 to the rear and supporting control or stabilizing surfaces. 
 
 OVERHANG — The distance the wings project out beyond the outer struts. 
 
 PAN CAKE, TO — To descend as a parachute after a machine has lost for- 
 ward velocity. To strike the ground violently without much forward "motion. 
 PANEL — A portion of a framed structure between adjacent posts or struts. 
 Applied to the fuselage it is the area bounded by two struts and the longerons. 
 An entire wing is often spoken of as a panel. Thus the upper lifting surface 
 of a biplane is usually of three parts designated as the right upper panel, left 
 upper panel and the center panel.
 
 NOMENCLATURE FOR AERONAUTICS 115 
 
 PARACHUTE — An a|)])aralus made like an nnihrclla used to retard the 
 ilescent of a fallini;' Ixxlw 
 
 PARASITE RESISTANCE— 'Ihe total resistance to motion through the air 
 
 of all parts of an aircraft not a j)art of the main lifting- surface. 
 
 PATCH SYSTEM — A system of construction in which patches or adhesive 
 
 tlaps are use<l in place of the suspension band in a balloon. 
 
 PERMEABILITY — The measure of the loss of gas by diffusion through the 
 
 intact l)alloon fabric. 
 
 PHILLIPS ENTRY — A reverse curve on the lower surface of an aerofoil, 
 
 towards the entering L'd^t:, designed to more evenly divide the air. 
 
 PITCH-OF A PROPELLER— (See PROPELLER.) 
 
 PITCH-OF A SCREW — The distance a screw advances in its nut in one 
 
 rex'olution. 
 
 PITCH, TO — To ])lunge in a fore-and-aft directittn. 
 
 PITOT TUBE — A tube with an end open sciuare to the fluid stream, used as a 
 
 detector of an impact pressure. It is usually associated with a concentric 
 
 tube surrounding it, having perforations normal to the axis for indicating 
 
 static pressure ; or there is such a tube placed near it and parallel to it, with a 
 
 closed conical end and having perforations in its side. The velocity of the 
 
 fluid can be determined from the difference between the impact pressure and 
 
 the static pressure, as read by a suitable gauge. This instrument is often 
 
 used to determine the velocity of an aircraft through the air. 
 
 PLANE OF SYMMETRY— A vertical plane through the longitudinal axis 
 
 of an airi)lane. It divides the airplane into two symmetrical portions. 
 
 PONTOON- (See FLOAT.) 
 
 PROPELLER OR AIR SCREW— A body so shaped that its rotation about 
 
 an axis produces a thrust in the direction of its axis. 
 
 Disc-Area of Propeller — The total area of a circle swept by the propeller 
 tips. 
 
 Pitch Of — The distance a propeller will advance in one revolution, sup- 
 posing the air to be solid. 
 
 Race — The stream of air driven aft by the pro{)eller and with a velocity 
 relative to the airi)lane greater than tliat of the surrounding body of 
 still air. (Frequently called slip-stream.) 
 
 Slip Of — The difference between the distance a propeller actually ad- 
 vances and the distance it would advance while making the same number 
 of revolutions in a solid medium. Usually expressed as a percentage 
 of the total distance. 
 
 Torque Of — The turning moment of the propeller. The effect of pro- 
 peller torque is an equal reaction tending to rotate the \vhole airplane 
 in the opposite direction to that of the propeller. 
 PUSHER— (See AIRPLANE.) 
 
 PYLON — A post, mast or pillar serving as a marker of a flying course. Also 
 used infrequently to designate the control masts such as the aileron mast, 
 rudder mast, elevator mast, etc.
 
 116 APPLIED AERONAUTICS 
 
 RAKE — The angular deviation of the outer end of a wing from a line at right 
 angles to the entering edge. 
 
 RELATIVE WIND — The motion of the air with reference to a moving body. 
 Its direction and velocity, therefore, are found by adding two vectors, one 
 being the velocity of the air with reference to the earth, the other being equal 
 and opposite to the velocity of the body with reference to the earth. 
 
 RETREAT— (See SWEEP BACK.) 
 
 RIB — A member used to give strength and shape to an aerofoil in a fore- 
 and-aft direction. 
 
 Web — A light rib, the central part of which is cut out in order to 
 lighten it. 
 
 Compression — A rib heavier than the w^eb type and so constructed as to 
 resist the compression due to the wire bracing of the airplane. 
 Secondary Nose— Small ribs extending from the front sj^ar to the nose 
 strip (entering edge). Placed between the main ribs to give support 
 to the fabric near the entering edge. Sometimes called Stub Ribs. 
 RIGGING — The art of truing up an airplane and keeping it in flying con- 
 dition. 
 
 RIP CORD — The rope running from the rip panel of a balloon to the basket, 
 the pulling of which causes immediate deflation. 
 
 RIP PANEL — -A strip in the upper part of a ballooii which is torn off when 
 immediate deflation is desired. 
 
 RUDDER — A hinged or pivoted surface, usually more or less flat or stream- 
 lined, used for the purpose of controlling the attitude of an aircraft about its 
 vertical axis, i. e., for controlling its lateral movement. 
 
 RUDDER BAR — A bar pivoted at the center, to the ends of which the rud- 
 der control cables are attached. The pilot operates the rudder by moving the 
 rudder bar with his feet. 
 
 RUDDER POST — The post to which the rudder is hinged, generally forming 
 the rear vertical member of the vertical stabilizer. 
 
 SEA PLANE — An airplane fitted with pontoons or floats suitable for alight- 
 ing on or rising from the water. 
 (See AIRPLANE.) 
 
 SERPENT — A short heavy guide rope used with balloons. 
 SERVING — A binding of wire, cord or other material. Usually used in con- 
 nection with joints in wood, and cable splices. 
 
 SIDE SLIPPING — Sliding sideways and downward toward the center of a 
 turn, due to an excessive amount of bank. It is the opposite of skidding. 
 SIDE WALK — A reinforced portion of the wings near the fuselage serving 
 as a support in climbing about the air])lane. Otherwise known as running 
 board. 
 
 SKIDDING — Sliding sideways away from the center of a turn, due to an in- 
 sufficient amount of bank. It is the opposite of side slipping.
 
 NOMENCLATURE FOR AERONAUTICS 117 
 
 SKIDS-LANDING GEAR — Long wooden or nKtal runners designed to pre- 
 vent nosing of a land machine when landing, or to prevent dropping into 
 holes or ditches in rough ground. Generally designed to function in case the 
 wheels should collapse or fail to act. 
 
 Tail — A skid supporting the tail of a fuselage while on the ground. 
 Wing — A light skid placed under the lower wing to i)revent possible 
 damage on landing. 
 SKIN FRICTION — Friction between the air and a surface over which it is 
 passing 
 
 SLIP STREAM— (See PROPELLER RACE.) 
 SOARING MACHINE— (See GLIDER.) 
 SPAN-WING — .Span is the dimension of a surface across the air stream. 
 
 Wing Span or Spread of a machine is length overall from tip to tip 
 of wings. 
 SPARS-WING — Long pieces of wood or other material forming the main 
 supporting members of the wing, and to which the ribs are attached. 
 SPREAD— (See SPAN.) 
 
 STABILITY — The cjuality of an aircraft in flight wdiich causes it to return 
 to a condition of equilibrium after meeting a disturbance. 
 
 Directional — That property of an airplane by virtue of which it tends to 
 hold a straight course. That is, if a machine tends constantly to veer off 
 its course necessitating exercise of the controls by the pilot to keep it on 
 its course, it is said to lack directional stability. 
 
 Dynamical — The ciuality of an aircraft in flight which causes it to return 
 to a condition of ecjuilibrium after its attitude has been changed by meet- 
 ing some disturbance, e. g., a gust. This return to equilibrium is due to 
 two factors ; first, the inherent righting moments of the structure ; second, 
 the damping of the oscillations by the tail, etc. 
 
 Inherent — Stability of an aircraft due to the disposition and arrangement 
 of its fixed parts, i. e., that property which causes it to return to its nor- 
 mal attitude of flight without the use of the controls. 
 
 Lateral — The property of an airplane by virtue of which the lateral axis 
 tends to return to a horizontal position after meeting a disturbance. 
 Longitudinal — An airplane is longitudinally stable wdien it tends to fly 
 on an even keel without pitching or plunging. 
 
 Statical — In wind tunnel experiments it is found that there is a definite 
 angle of attack such that for a greater angle or a less one the righting 
 moments are in such a sense as to tend to make the attitude return to 
 this angle. This holds true for a certain range of angles on each side of 
 this definite angle ; and the machine is said to possess "statical stability" 
 through this range. 
 STABILIZER — Balancing planes of an aircraft to promote stability. 
 
 Horizontal — A horizontal fixed plane in the empannage designed to give 
 
 stability about the lateral axis. 
 
 Vertical — A vertical fixed plane in the enii)annage to promote stability 
 
 about the vertical axis. 
 
 Mechanical — Any mechanical device designed to secure stability in flight.
 
 118 APPLIED AERONAUTICS 
 
 STABILIZING FINS — Vertical surfaces mounted longitudinally between 
 planes, to increase the keel plane area. 
 
 STAGGER — The amount of advan.cc of the entering edge of a superposed 
 aerofoil of an airplane, over that of a lower, expressed as a percentage of the 
 gap. It is considered positive when the upper aerofoil is forward. 
 STALLING — A term describing the condition of an airplane which, from any 
 cause has lost the relative speed necessary for steerageway and control. 
 STATION — The points at which struts join the longerons in a fuselage, are 
 termed stations and are numbered according to some arbitrary system. Some 
 makers begin with No. 1 at the nose plate and number toward the rear. Other 
 makers begin with at the tail post and number toward the front. 
 STATOSCOPE — An instrument to detect the existence of a small rate of 
 ascent or descent, principally used in ballooning. 
 
 STAY— A wire, rope, or the like used as a tie piece to hold parts together, or 
 to contribute stiffness ; for example, the stays of the wing and body trussing. 
 STREAMLINE-FLOW — A term used to describe the condition of continu- 
 ous flow of a fluid, as distinguished from eddying flow, where discontinuity 
 takes place. 
 
 STREAMLINE-SHAPE — A shape intended to avoid eddying or discon- 
 tinuity and to preserve streamline-flow, thus keeping resistance to progress 
 at a minimum. 
 
 STRINGERS — A term applied to the slender wooden members running lat- 
 erally through the wing ribs for the purpose of stiffening them. 
 STRUT — A compression member of a truss frame, for instance, the vertical 
 members of the wing truss of a biplane. 
 
 STRUT-INTERPLANE— A strut holding apart two aerofoils. 
 SUPPORTING SURFACE— Any surface of an airplane on which the air 
 produces a lift reaction. 
 
 SUSPENSION BAND— The band around a balloon to which are attached 
 the basket and the main bridle suspensions. 
 
 SUSPENSION BAR— The bar used for the concentration of basket suspen- 
 sion ropes in captive balloons. 
 
 SWEEP-BACK — The horizontal angle between the lateral (athwartship) 
 axis of an airplane and the entering edge of the main planes. 
 TACHOMETER — An instrument for indicating the number of revolutions 
 per minute of the engine or propeller. 
 
 TAIL CUPS — The steadying device attached at the rear of certain types of 
 elongated captive balloons. 
 
 TAIL-NEUTRAL — A tail, the horizontal stabilizer of which is so set that it 
 gives neither an upward lift nor a downward thrust when the machine is in 
 normal flight. 
 
 Positive — A tail in which the horizontal stabilizer is so set as to give an 
 upward lift and thus assist in carrying the weight of the airplane when 
 it is in normal flight. 
 
 Negative — One in which the horizontal stabilizer is so set as to give a 
 downward thrust on the tail when the machine is in normal flight.
 
 NOMENCLATURE FOR AERONAUTICS 119 
 
 TAIL POST— The vertical strut at the rear end of the fuselage. 
 
 TAIL SKID — A skid su])|)()rtiiii;- the tail of a fuselas^e wliile on the ground. 
 
 TAIL SLIDE — A steep descent, tail downward. I'sually caused by stalling 
 on an attenij)t to climb too steeply. 
 
 THIMBLE — An elongated metal eye s])lice(l in the end of a ro[)e or cable. 
 
 TRACTOR— (See AIRPLANE.) 
 
 TRAILING EDGE — The rearmost ])ortion of an aerofoil. 
 
 TRIPLANE — A form of airplane whose main supporting surface is divided 
 
 into three jjarts, superimposed. 
 
 TRUSS — The framing by wiiicli the wing loads are transmitted to the body; 
 comprises struts, stays and spars. 
 
 UNDERCARRIAGE— (See LANDING GEAR.) 
 
 VETTING — The process of sighting by eye along edges of spars, planes, etc., 
 
 to ascertain their alignment. An experienced man can detect and remedy 
 
 many faults in alignment by this method. 
 
 VOL-PIQUE'— (See NOSE DIVE.) 
 
 VOLPLANE— To glide. 
 
 WARP — To change the form of the wing by twisting it, usually by changing 
 
 the inclination of the rear spar relative to the front spar. 
 
 WASHIN — A progressive increase in the angle of incidence from the fusel- 
 age toward the wing tip. 
 
 WASHOUT — A i^rogressive decrease in the angle of incidence from the 
 fuselage toward the wing tip. 
 
 WEIGHT-GROSS— (See LOAD, FULL.) 
 
 WINGS — The main supporting surfaces of an airplane. Also called Aerofoils. 
 WING FLAPS— (See AILERON.) 
 WING LOADING— (See LOADING.) 
 
 WING MAST — The mast structure projecting above the wing, to which the 
 toj:) load wires are attached. 
 
 WING RIB — A fore-and-aft member of the wing structure used to support 
 the covering and to give the wing section its form. (See RIB.) 
 WING SPAR OR WING BEAM— A transverse member of the wing struc- 
 ture. (See SPARS-WING.) 
 
 WIRES— 
 
 Drift — Wires that take the drift load and transfer it through various 
 members to the body of the airplane. 
 
 Flying — The wires that transfer to the fuselage, the forces due to the 
 lift on the wings when an airplane is in flight. They prevent the wings 
 from collapsing upwards during flight. 
 
 Landing — The wires that transfer to the fuselage, the forces due to the 
 weight of the wings when an airjilane is landing or resting on the ground. 
 Stagger — The cross brace wires between the interplane struts in a fore- 
 and-aft direction.
 
 120 APPLIED AERONAUTICS 
 
 YAW — To yaw is to swing off the course and turn about the vertical axis 
 owing to side gusts of wind or lack of directional stability. 
 
 Angle Of — The temi)orary angular deviation of the fore-and-aft axis 
 
 from the course. 
 
 Physical and Mechanical Terms 
 
 ACCELERATION— The rate of increase of velocity. 
 
 CENTER OF GRAVITY— The center of gravity of a body is that point 
 
 about which, if suspended, all the parts will be in ecpiilibrium, that is, there 
 
 will be no tendency to rotation. 
 
 CENTRIFUGAL FORCE— That force which urges a body, moving in a 
 
 curved path, outward from the center of rotation. 
 
 COMPONENT — A force which when combined with one or more like forces 
 
 produces the effect of a single force. The single force is regarded as the 
 
 RESULTANT of the component forces. 
 
 DENSITY — Mass per unit of volume; for instance, pounds per cubic foot. 
 
 EFFICIENCY-(Of a machine.) — The ratio of output to input of power, usu- 
 ally expressed as percentage. 
 
 ELASTIC LIMIT — The greatest stress per unit area which will not produce 
 
 a permanent deformation of the material under str'ess. 
 
 ELONGATION — When any material fails by tension it usually stretches 
 
 and takes a permanent set before it breaks. The ratio of this permanent 
 
 elongation to the original length, expressed as a percentage, is a measure of 
 
 the elongation. 
 
 ENERGY — The capacity of a body for doing work. Heat is a form of energy. 
 
 Any chemical reaction that generates heat or electricity liberates energy. 
 
 Bodies may possess energy by virtue of having work done upon them. 
 
 EQUILIBRIUM — When two or more forces act upon a body in such a way 
 
 that no- motion results, there is said to be equilibrium. 
 
 FACTOR OF SAFETY— The ratio of the load required to cause failure in 
 
 a structural member to the usual working load the member is designed to 
 
 carry. Thus if a member be designed to carry a load of 500 lbs. and it would 
 
 require a load of 2000 lbs. to cause failure, the factor of safety would be four. 
 
 FOOT-POUND — The foot-pound is a unit of work. It is equal to a force of one 
 
 pound acting through a distance of one foot. This is a foot-pound of energy. 
 
 INERTIA — That property of a body by virtue of which it resists au}^ attempt 
 
 to start it if at rest, to stop it if in motion, or in any way to change either 
 
 the direction or velocity of motion, is called Inertia. 
 
 MASS— The mass of a body is a measure of the quantity of material in it. 
 
 MOMENT — Moment is the product of ^a force times its lever arm. It is 
 
 usually expressed in Inch-Pounds. 
 
 MOMENTUM — Momentum is the product of .the mass and velocity of a 
 
 moving body. It is a measure of the quantity of motion. 
 
 POWER — Power is the time rate of doing work. 
 
 Horsepower — The horsepower is a unit of work. One horsepower rep- 
 resents the performance of work at the rate of 33,000 foot-pounds per 
 minute, or 550 foot-pounds per second.
 
 NOMENCLATURE FOR AERONAUTICS 121 
 
 RESULTANT OF A FORCE— 'I'lie resultant of two or more forces is that 
 single force which will ])r()(luce the same effect upon a body as is produced 
 hv the joint action (if the component forces. 
 
 STRESS — The internal condition of a body under the actiijn of opposing- 
 forces. The unit of measure is usually |)Ounds per square inch. 
 
 Compression — When forces are a])i)lied to a Ixxly in such a way as to 
 
 tend to crush it, there results a compressive stress in the body. 
 
 Tension — When forces are ap])lied to a body in such a way as to tend to 
 
 se])arate or j)ull it apart, the l)ody is said to be in tensi(jn or a tensile 
 
 stress has been j^rodnced within it. 
 
 Shear — W'hen external forces are a])i)lic(l in such a way as to cause a 
 
 tendency for particles of a body to sli]) or slide ])ast each other, there 
 
 results a shearing' stress in the l)ody. 
 STRAIN — Strain is the deformation jiroduced in a body by the a])i)lication 
 of external forces. 
 
 TORQUE — When forces are so disposed as to cause (jr tend to cause rotation, 
 there is produced a turning' moment which is also called torque. It is usually 
 measured in inch-pounds. Thus if a force of 10 pounds be applied tangen- 
 tiall}' to the rim of a wheel of 10-incli radixis. the torcjue or turning moment 
 will be 100 inch-pounds. 
 
 ULTIMATE STRENGTH— The load per s(juare inch required to produce 
 fracture. 
 
 VELOCITY — In uniform motion, the distance passed over in a unit of time, 
 as one second. This may also be obtained by di\-iding the length of an\' por- 
 tion of the path by the time taken to describe that portion, no matter how 
 small or great. 
 
 In N'ariable motion, where velocity varies from point to point, its \'alue 
 at any point is expressed as the quotient of an infinitely small distance, con- 
 taining the given point by the inhniteh- small portion of time in which this 
 distance is described. 
 
 WORK —The product of a force by the distance descrilK'd in the direction 
 of the torce by the point of application. If the force moves forward it is 
 called a working force, and is said to do the work expressed by this product; 
 if backward, it is called a resistance, and is then said to have the work done 
 U])on it, in overcoming" the resistance through the distance nientioned (it 
 might also be said to have done negative work). 
 
 In a uniform translation, the working forces do an amount of work which 
 is entirely a])plie(l to overcoming the resistances.
 
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