hJktA L^lZi ^ NATIONAL ADVISORV COMMITTEE FOR AERONAUTICS WARTIME REPORT ORIGINALLY ISSUED J;me 19U4 as Memorandum Report AEROCniAMIC TESTS OF AU AH-M-65-AZOH 1000-PODHD RADIO -COHTROLIED BOMB IN THE LMAL I6-FOOT HIGH-SPEED TUMEL By E. 0. Pearson, Jr. Langloy Memorial Aeronautical Laboratory Langley Field, Va. NACA WASHINGTON NACA WARTIME REPORTS are reprints of papers originally issued to provide rapid distribution of advance research results to an authorized group requiring them for the war effort. They were pre- viously held under a security status but are now unclassified. Some of these reports were not tech- nically edited. All have been reproduced without change in order to expedite general distribution. I L - 131 DOCUMENTS DEPARTMENT i_ Digitized by tlie Internet Archive in 2011 witli funding from University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation http://www.archive.org/details/aerodynamiccharaOOIang -Ill f3^ u NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS Ma?^ORAND:J"[ REPORT for the Army Air Forces, Materiel Command AERODYNAMIC TESTS OF AN AN-M-65-AZON 1000-POUND RADIO-CONTROLLED BOMB IN THE LMAL I6-FOCT HIGH-SPEED TUNNEL 33'- E. 0. Pearson, Jr. STO.MARY Tests were T.ade in the U.IAL l6-foot high-speed tionnel to determine the aerod^mainic characteristics of a 1000-pound AN-Iv'i-65-AZON radio-controlled bomb at Mach nwiibers ranging from 0.2 to 0,6, Over the Mach number range covered in the tests the hinge-moment coefficients, yawing-moment coefficients, and lateral-force coefficients exhibited no important changes with increasing speed. The drag coefficients increased gradually with Increasing Mach number but no sudden increases v/ere observed. The effect on the bomb aerod3mai:iJ c characteristics of antenna struts mounted on the bomb tail was found to be small. The rudder and aileron operating mechanisms wore found to be capable of supr)l:'ring several times the required torques for maximum control deflections at a Mach number of 0.6 at sea level. The operating mecha- nism is also adequate for maximum control deflections at a Mach number of 1.0 provided that no appreciable increases in hinge-moment coefficient occur between M = 0,6 and M = 1.0. Hov;ever, because of uncertainty as to the value of the hinge-moment coefficient at or near M = 1,0, the desirability of providing m.ore powerful control mechanisms was indicated. INTRODUCTION Tests have been conducted in the LL'AL l6-foct high-speed tunnel to determine the aerodynamic characteristics of a 1000-pound _'\i\[-M-65-AZON radio- controlled bomb, Measure.mentG of rudder hinge moment, yav;lng inoment, lateral force, end drag were made at a number of tunnel speeds up to a Mach number of about 0.6 v\rhich corresponds to a speed of 67O feet per second at sea level. Aerodjniamlc tests of a two-thirds scale model of a similar bomb were conducted previously at the Daniel Guggenheim Airship Institute at Akron, Ohio. These tests, however, were made at low airspeeds and, there- fore, uncertain extrapolations of the data to the higli- speed operating conditions were necessary in the design of the control mechanism and in performance computations. In drop tests of the bombs it was found that, vvhile some of the experimental bombs performed satisfactorily, a large percentage of the production version failed to respond properly to the control. The present investiga- tion was undertaken principally to determine if the lack of control of the production bombs was due to adverse compressibility effects. It was also desired to obtain high-speed test data upon which to base per- formance calculations and the design of the control mechanism. The investigation was undertaken at the request of the Army Air Forces, Materiel Oommand. 3YLIECL3 AND DEFINITIONS V free -stream velocity, feet per second a speed of sound in air, feet -ner second M Mach number (V/a) p mass density of air, slugs per cubic foot q d3niariiic pressure, pounds per square foot ipv^) Mtj hinge moh.enfc acting on one rudder, inch-pounds Positive hinge moments tend to change the ruddei' angle in a positive direction. (See sketch in figure 1 illustrating the sign conventions . ) n distance from rudder hinge axis to trailing edge of rudder, i^. .8l inches area of one rudder, 0.232 square foot hinge -moment coe f f i ci ent ( 'ViT-i/qSd ) N yawing-mcment, round -feet r-csitive yawing moments tend to change the angle of sideslip in a positive direction. (See fig. 1. ) P area of rnaximvim cross section of bomb, I.91S square feet I over-all length of borab, ^,ol^ feet C^ yawing-raoment coefficient (N/qPl) Y lateral force, pounds Cy lateral-force coefficient (Y/'qF) D d^ag, pounds Gq drag coefficient (D/qF) v}/ angle of sideslio, degrees Per positive angles the boiub nose is to the right of the line of flight. 5r- rudder angle v;'th respect to the neutral position, degress For Dositive an^sles the trailing edge is to the left'. The dimensions given above, together with other di'Tiensions which .night nrove useful, are Ghcj\rn in fig- ure 2 . DESCRIPTION OF BOMB ^WO APPARATUS The AN-M-65-AZON bomb consists of a standard fv!-D5 bomb case to -.vhich is fitted a special tail unit equipped with novable control surfaces and housing a control mechanism capable of being operated remotely k by radio. The bc'Ti'b cen be controlled onl:'- in the left and right or azimuth direction, hence, the designation AZON an abbreviation of "azlimith only." A gyroscopic control mechanism operates the horizontal control sur- faces differentially as ailerons to prevent the bomb from rolling in flight. For these tests part of bhe control apparatus was removed from the tail and strain-gage equipment for measuring rudder hinge moments vi/as Installed. Since the ailerons and rudders were identical, hingo-mom.ent data apnly eqtially to both. For this reason no provision was made 'f'or measuring aileron hinge moments directly and the ailerons were locked in tho neutral position throughout the tests. In order to facilitate Installation and testing the bomb was m.ounted in the tunnel In a position 9^° in roll from its normal flight position so that rudders The bom:b vi^as supported on the tunnel center line by means of a single vertical strut 8 inches in chord and of NACA section 16-OO9. The strut was shielded by a fairing of tiie same section to within about 10 inches of the bomb case. In addition, four 0.030-inch wires were attached to the bomb to provide lateral siipport. The wires and support strut were mounted on the balance frame and were included in the force measurements. A photograph of the bomb installed in the tunnel is shown in figure 5 . The angle of sideslip of the bom.b was variable from -20'^ to 2.0^^ throt^gh fixed increments by moans of an internal indexing mechanism while the rudder angle was continucusl.^'- variable from, -20^ to 20*^ by means of a slotted plate arrangement. As received, the bomb tall was fitted with four struts wh:ch, in addition to serving as braces for the tail surfaces, also served as the radio antenna. The strirbs may be seen in figure 3. TEST PROGSDuRE The test procedure consisted, of measuring rudder hinge moinent, yawing mcment, lateral force, and drag at a numoer of speeds up to a Llach nuiuher of approxi- mately 0.6 for each combination of rudder angle and angle of sideslip. In datcrmining the bomb charac- teristics only the negative range of sideslip angles (0° to -20") was investigated in order to keep the bomb tail outside the wake of the support strut and its fairing. The angular range of Qo to 20° was employed in determining the support-strut tares. The range of rudder angles tested v/as from -15° to 20°. Most of the test r-uns were made with the antenna tail struts installed but a few runs were made with the struts removed for purposes of comparison. This information on the effect of the antenna struts was specifically requested by the Army. The resiilts tliroughout the report are given for the struts-installed configuration unless otherwise specifically noted. During the tests deflectionii of the bomb in the direction of the air flow v/ere measured and corrections to the yawing moment applied to accoijuat for the change in position. In addition, a calibration was later made to determine the angular deflections of bomb and rudders vinder the influ.^nce of the uerodjmamic loads. Strut tare ^orces were measured v/ith the aid of an image strut mounted as shov/n in figure I4., Wire tare forces were determined simply by making measurements with the wires rem.oved. Yawing moment, lateral force, and drag data have been corrected both for tares and for the angular deflections of bomb and rudders under aerodj'/namic loads. Corrections for the deflections have not been applied to the hinge -m.oment data. As presented the hinge -moment coefficient is aboi.it 9 percent too low at the greatest negative bomb and rudder angle and at the highest tunnel speed, which is the extreme case. RESULTS AND DISCUSSION Curves of jraYi^ing-moment coefficient, lateral-force coefficient, and drag coefficient versus Mach number are presented in figures 5 through l3. It should be pointed out that the ^^ = -0.5^ and Cp ~ 0° curves shown in figures 5i 11, and 17 aro helieved to be slightly in error due to friction in the Dalanco sjsten durjng that particu- lar test run. This is in.dicated by the scatter of the test points ■nartloularly at uhe lower speeds. Derived curves of yaving r.Oinent, lateral force, and drag coefficients versus sideslip angle are given in fig- ures IQ, 20, and 21. Figure 22 sho\/s the lateral force and drag coefficients at tri:in as, a function of the rudder angle. The ei'fect of center-of-gravity location on the stability and trim angles of the bomb is shown in fig- ure 25. Einga-moinent data are presented in figures ?1\. through 5.1. F'igure 52 is a photograph of a rudder after structural fail^ire has occurred. Ya"/irg norent .- Yawing-moment coefficient data are presentad in figures 5 through 10. Turing the tests yav/ing moments were measured about a point 22.58 inches from the bomb nose. In the data nresented in the report the moments were transferred to a point 2b. 60 inches from the nose of the bomb, which was the center-of- gravity location of sand-filled bombs used in the drop tests, mentioned earlier in the report. The figures sliow that the variation of the yawing- moment coefficient with Mach laumber is sm.all for all the rudder angles and angles of sideslip over the range of speeds cox'ered in this investigation. Figures 9 ^^c' 10 show the i-ariation of yav/ing-mom.ent coefficient with Mach mxnber with the antenna struts removed. From a comparison of these figures Vifith figures 5 and 7 it will be seen that the struts have -oractically no effect on the yawlng-mioment coefficient. Later a l force .- Curves of lateral-force coefficient versus Mach nuriiter for the various rudder angles and angles of sidoslio are presented in figures 11 through 16, In general, the coefficient increases negatively with increasing Mach nixnber. The change :s slight, however. Figures 15 and I6 show the variation of lateral-force coefficient with Mach niuaber with the antenna struts removed. As in the case of the yawing-moment coefficients the effect of the struts on the lateral-force coefficient is small. Drag .- The variation of drag coefficient with Mach number is shown in figure I7 for various angles of side- slip and rudder angles. No sudden increases in the drag coefficient occurred in the speed range of the tests. Curves for a few of the sice slip and rudder angles have not been plotted in figure I7 to avoid excessive con- gestion and overlapping. Gurvos of the drag coefficient versus Maoh number with the anbenna tail struts removed are ujiven in figure I8. A coTioai':! son of this figure with figure 17 shows that for a sideslip angle of -0.5° and a rudder angle of 0° removal of the struts results In a decrease xn the drag coefficient of O.OO9 or about 5 per- cent of the minimUiTi drag. BOTib characters 3 1 i C3__as_a ^ft xn.c bi or of sidosli p angle" .- Curves of yawTng-monient coefriciexit, lateral- forct! coefficient, and drag coefficient versus the angle of sideslip are presented in figures I9, 20, and 21, respectively. These curves are cross plots of the faired yawing -moment, Isteral-force, and drag coefficient curves prsv?. ously presented. Since the variation cf the coeffi- cients v;ith Maoh nuinber was not appreciable except for the drag coefficient only the curves for a Maoh number cf 0.6 are shown. It will be noted from figure I9 that the bomb stability decreases slightly as the angle of sideslip approaches zero. At the Icirger negative side- slip angles and positive rudder angles there is also some decrease in stability with increasing angle of sideslip. Trim conditions.- Figure 22. shov/s the lateral -force and drag coefficients obta^'ning jxt triir. for various rudder deflections. It will be seen that i'or tl-;e maxi- mum rudder deflection of 20° and at a Maoh number of 0.6 the bomb trims in an attitude ^or which the lateral-force coefficient is -0.Ii.22 and the. drag coefficient is O.56O. Reference to figure l*^) shov/s that the corresponding angle of sideslip for trim js -10.5°, Bomb maneuverability .- The following table is pre- sented to illustrate roughly the magnitude of the lateral deviations possible rrtien the bomb is dropoed from dif- ferent altitudes. It is assumed that the bomibing air- plane is fl^d-ng at a constant indicated airspeed of 175 ^'iiiles per hour and that the maximum Dorab rudder deflection of 20° is maintained over the entire flight path. The left-hand column givds the height above sea level v/hich is also considered to be ground level and the right-hand column gives the approximate value of the maximum lateral deviation possible when the bomb is released at the corresponding altitude. 8 Altitude of releaso (ft) 5,000 10,000 IS, 000 20,000 25,000 Apppoxiinate snaximu.-a lateral deviation (ft) 6 00 i6oo 2800 lj.200 5300 location. - E f f e c t of cb anges in the ce nter- of -gravity gure ~?3 sViOViTs the effect unon trim angle and stability of a change in the center-of-gravity location 2 Inches hackiivard or forv/ard from, the 23.6-inch point. A more rearv;ard location of the center of gravity results in a reduction in stability and an increase in the angle of sideslip for trijn with a consequent increase in the lateral-force coefficient. A location forward of the 23.6-inch point results, of course, in the opposite effect. 7/ith the data presented yawing-moment coefficients may be transferred from the 2o. 6-inch point to any new point by the relation ^n ~ (cy cos *)f d + C- sm i^ *) d where the new no The value o''^ roar of is the distance fron the 28,6-inch point to int measured along the bomb longitudinal axis. : is rositive if the new point Is to the .6-inch noint and negative if to the front. H i nge m oine n t » - Rudder hinge-moment data are presented in figures 24 TFrough 31. Figures 2li through 27 shov; the variation of rudder hinge-moraent coefficient with Mach nijinber for various rudder aagles and angles of sideslip. It may be seen that for the smaller angles of sideslip and rudder angles bhero is little variation oj moment coefficient v.'ith Mach nvimber. ^Qjop nrOnOU^^ -^.c*-^ r^r^7-> -t-Vi/.:! "l t-i^n^c^-\-* Q^->ri[»l in any case the hinge- The change becomes for the larger angles but is not important over the range of speeds covei'ed in the tests. It is clear that any loss of control of the oomb at Mach numbers of 0.6 and belov/ cannot be attributed to radical changes in hinge moments due to compressibility effects. Figure 28 shows the variation of hlnge-mom.ent coefficient with rudder angle for varioixs angles of sideslip and PTach ntUTi'bers. Fi'2;ure3 29 a^^i 30 show the variation of hinge -moment cosfricient with Mach n-umber with the antenna struts removed. Figure Jl 3hows the variation of hinge- moment coefficient vd th rudder angle for the same con- figuration. A comparison of these figures with fig- ures 2l|., 26, and 2^ shows that the struts have no aDPreciable effect on the rudder hinge-mom.ent coefficient. ■'o ■ From tests in the LMAL Instnuiient Research Division on tho rudder and aileron operating mechanisms it has been determ.ined that the maximum torque available for holding the rudde'^s in a given position is 200 inch- pounds. For a rudder deflection of 20° and the corre- sponding angle of sideslip for trim of -10.5^ the total hinge moment acting on both rudders at a Mach number of 0.6 at sea level is 52 inch-pounds. If it is assumed that no change in the hinge-moir.ent coefficient occurs between M = 0.6 and M = 1.0, the torque required at a Mach munber of 1.0 is 1l|.5 Inch-po-unds . Such an assump- tion is somewhat doubtful, however, and if appreciable increases in the hinge -mcm.ent coefficieiit do occur, then at or near a Mach number of 1.0 at sea level the torque may be insufficient to maintain the maximum rudder deflection of 20°. For the maximum, aileron deflection of ±6° and an angle of sideslip of -0.'^^ the torqiie required for one aileron at a I.Iach number of 0.6 at sea level is 11 inch- pounds. Assuming as before that no change in the hinge- moment coefficient occurs betv;een M = 0.6 and M = 1.0 the torque roqiiired at I.' = 1.0 is 30 inch-pounds. The maximum aileron torque available at the 6*^ deflection was determined to be l\.0 inch-pounds, although the assuroption of no change in the hinge-mom.ent coefficient between M = 0.6 and V =1.0 is more reasonable for the case of the small aileron deflection than for the larger rudder deflection, the margin of torque available over torque required at the higher speeds is not large in anj case . It would thus appear desirable from the foregoing considerations to employ both aile^'on and rudder ODeratlng mechanism.s m.ore conservative v/ith regard to torque available. Rudder failure .- During a routine Inspection of the bomb upon coinple tlon of a test run It was found that failure of one of the rudders had occurred along the 10 spot-welded skin joint at the hinge axis. Up to the time the fail^ire v/as discovared 33 test runs, each of about [j.5 T^iinu'^^es dM.ration, had been cornp?et9d. The failure appeared to be due to fatigue. Figure 52 is a photograph of tha broken rudder. ;oi:glusion^ Aorod^'namic tests cf a 1000-pound AZON bomb at Mach nuiiibers ranging f"oir 0.2 to 0,6 have indicated the following conclusions: 1. There we:^e no urpreciable compressibility effects on the rudder hinge-moment coefficients, the yawing- moraent coefr'icients , or on the lateral-force coefficients < The drag coefficients increased gi'adually but no sudden increases occurred. 2, Reiiioval of the antenna struts from the tail had only a slight effect on the aerodynamic characteristics. 5. The torques supplied by the rudder and aileron operating mechanisms were foijjnd to be several times the torques required at a Mach mimber of 0.6 at sea level for iaaximuin conti'ol doflecbions. If no appreciable increases In the liinge-moment coefficient occur between M = 0,6 and M = 1.0, the available torque will be adequate at a Mach mjutf'^er of 1.0, Becai^se of some uncertainty regarding the hinge -morr.ent coefficient at a = 1,0, however, it would appear desirable to employ nidder and aileron operating mechanisms having greater available torque. Langlev Memorial Aeronr-utical Laboratory National AdTdsorv Co.-nmittee for Aeronaiatics Langlev Field, Va., Jiune l6, 19-1^ Ernest 0. Pearson, Jr. Aeronautical Engineer Approved; John Stack Chief of Compressibility Research Division E3 FI'lTTRE LEGETOS Figure 1.- Sketch showing sign conventions for angles, forces and moments. Figure 2.- Sketch showing dimensions cf AN-M-65-AZON hoTib, Figure 5.- AN-?'-65-AZCN lOOC-poimd bomb Installed in the 16-foot high-speed tiinnel. Figure 4..- Setup employed for determining support-strut tares. Figure 5«- Variation of yawing-moment coefficient v;1 th Mach niunber i'or several rudder angles J/ ~ -.5°' Figure 5.- Variation of yawing-racment coefficient v;lth Mach number for several rudder angles ^ = -10.5^. Figure ?•- Variation of yawing-moment coefficient vi/ith Mach nui'flber for several rudder angles ^ = -15.5^^. Figur-e 3.- Variation of yav/ing-raoment coefficient with I'ach number ''or several rudder angles \|/ - -20.5^. Figure 9«- Variation of :^'-awing-mo;nent coefficient with Mech niimber for several rudder angles \|; = .5*^; antenna struts removed. Figure 10.- Variation of yawing-m^oment coefficient with ■lach number for several rudder angles ■]; = -15.5^; antenna struts removed. Figure 11.- Variation of latere.l-force coefficient v/ith Mach number for several rudder angles '\f - -.5°. Figure 12.- Variation of lateral-force coefficient v;ith Mach number for several rudder angles \l/ = -10.5°. Figure 13.- Variation of lateral-force coefficient with Mach number for several rudder angles 'I' = -15.5°. Figure 1I4..- Variation of lateral-force coefficient '-vith Mach number for sevex'al rudder angles 'e ax/s /fu.dc/er ■/? \ NATIONAL ADVISORY COMMintL FOR AERONAUTICS /if^ure l.-S/refc/? s/iomng s/g/? converTf/io/ys for a/ygf/es. forces. ar?c/ /7?o/7?enf6. ^ *^ ^ oo ^ CO <^ =r OS 1 C3 Sc _J o ^ <;i