[mc/^ 1-11 ABE No. L^KLLa NATIONAL ADVISORY COMMITTIE FOR AERONAUTICS WARTIME REPORT • I ORiGINALLY ISSUED March 19^6 as Advance Eestrlcted Report L^WIIa C0MPAEO:S0N OF WUTO-TlMffiL AKD FLIGHT MEASUeEMEKTS OF STABILITY AND COHTEOL CHARACTERISTICS OF A DOUGLAS A-26 AIRPLAHE By Gerald G. Kayten and William Eoven Langley Memorial Aeronautical Laboratory Langley Field, Ya. AC A 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. T - 99 DOCUMENTS DEPARTMEN:^ Digitized by tine Internet Arcliive in 2011 witln funding from University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation http://www.archive.org/details/comparisonofwindOOIang NAG A ARR l]o, L5Hlla NATIONAI Ai/^^ISCRY GOiailTTEE FOR AERONAUTICS ADVANCE RE3T:iICTED REPORT C0J:PARIS0N op ^VIND-TUNrSL a:^!^ plight MEASUREMENTS OF STABILITY ArU) CONTROL CHARACTERISTICS OP A DOUGLAS k-2'o AIRPLANE 3j Gsrald G, Kayten and vVilllajn Koven SUMMARY Stability and control characteristics determined from tests in the Langley 19-foot pressure tunnel of a 0,2575-3cale model of the Douglas Xa-26 airplane are coiTipared with those measured in flight tests of a Douglas A-26B airplane ^ Agreement regarding static loi^.gitudinal staoillt:/ as Indicated by the elevator-fixed neutral points and by the variation of elevator deflection in both straight and turning flight was found to be good except at speeds approaching the stall. At these lov/ speeds the airplane possessed noticeably improved stability, whicPi \iras . attributed to pronounced stalling at the root of the production y/ing. The pronounced root stalling did not occur on the smooth, well-faired model v;ing . Elevator tab effectiveness determined from model tests agreed v;ell r/ith flight-test tab effectiveness, but control-force variations with speed and acceleration were not in good agreement. Although some discrepancy was introduced by the absence of a seal on the model elevator and by small differences in the determination of elevator deflections, correlation in control-force characteristics tvas also influenced by the effects of fabric distortion at high speeds and by small construction dissimilarities sucPi as differences in trailing-edgo angle. Except for the v/ave- off condition, in v.nich the tunnel results indicated rudder-force reversal at a higher speed than the flight tests, agreement in both rudder-fixed and rudder-free static directional stability v/as good. l.Iodel and airplane indications of stick-fixed and stlck-frse dihedral effect ivere also in good agreement, although some differ- ence in geometric dihedral may have existed because of o NACa ARR No. L5Hlla wing tending in flight. The use of model hin^^e -moment data obtained at zero sideslin ap^oeared to be satisfactory for the dete-rmination of aileron forces in sideslip. Fairly good correlation in aileron effectiveness and control forces was obtained; fabric disbortion .Tiay have been responsible to some extent for hia;h3r' flight values of aileron force at high speeds, ^istimaticn of sideslip developed in an. abrupt aileron roll was fair, but determination of the rudder deflection required to rr.alntain zero sideslip in a ra^ld aileron roll was not entirely satisfactory. INTRODTJCTICN Although the qualitative reliability of v/ind-tunnel stability and control test results is generally accepted, very few opportunities have arisen for determination of the quantitative a^.reenient between liieasured flying qual- ities of an airplane and flying qualities predicted on the basis of model tests. In connection with the development of the Douglas A-26 twin-engine attack bomber, a series of investigations has been conducted at the Langley Laboratory of the National Advisory Committee for ^leronautics , These investigations, the results of vi/hich have not been published, included tests of a 0.2p75"Scale powered model of the XA-26 airplane in the Langley 19-foot pressure tunnel and flight tests of an A-26B airplane. 37/ use of the unpublished wind- tunnel data, calculations have been made predicting the flying qualities of the airplane for correlation with the characteristics .measured in the fllj'ht tests. I'he results of the correlation are --resented herein; the flying qual- ities are not discussed except for the purpose of comparison, ll;0D3L, AIRPLAIjE, AiJD TESTS Photo^,raphs and drawings of ti.\e A-26E airplane and the XA-26 model are sho'.vn as figures 1 and 2, respectively, In table I general dimensions una specifications are shown for the airplane and the model, as -well as for the model scaled up to airplane size. Some discrepancies of neg- ligible importance are noted in this table but it can be seen that, with respect to general dimensions, the XA-26 and the A-263 are essentially the same airplane. As shown NAGA ARR Ko. L^Hlla in figure 1, the inodel during the stability and control tests ivas equipped with a fusela.^e noso vv'hich was so.T.ey.'hat different from that of the airplane. fhe spinners shovm on the model propellers were not used on the airplane, and the airplane oil-cooler ducts cubhoard of the nacelles were removed from the model wing d^iring the stability and control tests with the exception of the aileron tests. Several more significant differences existed between the model and the airplane. During most of the tuanel tests the model rudder and the elevator, vi/hlch vjeve of the plain overhang -balance type, remained unsealed, but the airplane control surfaces were equipped with rubberized canvas seals. The control surfaces, all of which were fabric-covered on the airrjlane, .vere of rigid metal con- struction on the model. The airplane ailerons were equipped wi bh balancing tabs arranged so that 8 of aileron deflec- tion produced ap^^roximately 5° of opposite tab deflection. On the model the balancing tab when connected moved 1° for a 1° aileron deflection. Thin metal strips vvere fastened to the upper and lower of the airrlane elevator causing small ridges dirsctl^^ in front of the tab. These ridges were not represented on the model, but their effect on elevator and tab characteristics is believed to be negligible. The wind-tunnel program included a fairly extensive series of conventional stability and 'control tests. The model aileron bests were made 3.t a .'.eynolds number of approximately 5 •■^ ^ 10°. The remaining model tests were made at a Reynolds number of approximately 3.6 x io° except for the tests at high thrust coefficients, which because of model motor limitations were made at Re^molds numbers reduced to approximately 2.6 x 10° , The portion of the flight tests devoted to stability and control were of the type usually conducted by the LIAGA for the -purpose of determ.lning the flying qualities of an airnlane . The weight of the airplane, which varied from 27,000 to 31,000 pounds in the flight tests^ was assumed for the analysis of the tunnel data to be 2d, 000 pounds corresponding to a wing loading of ^l-S pounds per square foot. The analysis v;a3 based on an altitude of 10,000 feet, which represented an approximate mean of the flight-test altitudes. Analysis of the tunnel data has been m^ade for condi- tions representing airplane rated poviier and ^^-verccnt rated power at the appropriate airplane weight and altitudes l^ IIACA ARR TJo. L3Hlla axid for a gliding flij?iG condition. In represenbatlon of the gliding flight condition, it has been assujrsd that engin-3s-idling and zero-thrust conditions -nay be considered identical. Any discrepancy in results introduced by the difference between these power conditions probably will be 3;nall . In coranuting el3vatcr, aileron, ind rudder control forces frora .model hinge-ir.oment data, ':he corresrionding control linka-es measured on the air'^lane were used. 5q: elevator deflection, dciQ,x\3es df flap deflection, degrees 5^ tab deflection, degrees C|^ hinge -moment coefficient I — ~ Vqhc^^j y. indicated airspeed, miles -oer hour ?Q elevator control force, pounds / "V \ Tq thrust coefficient / VpV^D^y Db 2V v/ing-tip helix angle, radians Cl lift coefficient ( IA±1 I \ ^^ / whe re H hinge moment, foot-pounds b v/ing soan, feet "c root-iiiean-square chord, feet q dyna;nic pressure, nounds nor square foot MAC A ARR Tlo. LpHlla p mass density of air, slugs per cubic foot V airspeed, feet per second T total thrust (two propellers), pounds D propeller diameter, feet p rolling velocity, radians per second S v.'ing area, square feet a angle of attack, degrees a, tail angle of attack, degrees g acceleration of gravity, feet oer second per second RESULTS AND DISCUSSION Longitudinal Stability and Control Curves of elevator angle and elevator control force required for trim in straight flight throughout the speed range are shoi/vn in figure J. Various flap and power combinations are considered at three center-of -gravity locations. For the flaps-retracted conditions, the tunnel control-force curves virere obtained by applying the tab- effectiveness data of figure I], to t]ie tab-neutral curves estii^ated frorr. the tunnel hinge -r.'iornent data. The amount of tab deflection required to adjust the t'unnel curve for tri^ at the flight-test trim speed was determined for each newer condition and center-of -gravity location, and this amount of tab deflection was assumed constant throughout the speed range. Inasmuch as model trim-tab tests were not made with flaps deflected, the trimtrried control-force curves for this condition were obtained by means of a constant adjustment to eacn original curve of C^. against Cy. This constant hinge-moment shift is believed justified because the data of figure i". indicate a negli- gible change in tab ef f ectivenes_s v/itn change in power (flaos retracted) and because analysis of stabillzer- ef f ec Diveness data indicates that the variation in average dynamic-pressure ratio with speed is small for II AC A ARP. No. LSHlla the flaps-deflected condition. The flaps-deflected control-force curves for zero trim tab are included in figure 5* The sideslip required for straight flight at low speeds was considered to have a negligible effect on the longitudinal characteristics of this airplane; hence, the characteristics determined frorf; tunnel data are based on tests at zero sideslip. The variation of tab effectiveness v/it.-i speed has been calculated from flaps-retracted v/ind-tunnel tests made at elevator-tab settings of 5° and -3° with Bg - ^ and is sho'im. in figure 1;. compared with the flight-test curve. Elevator deflections and control forces in steady turning flight are shown in figures 5 to 7 f'o^r' various center-of -gravity locations. The calculated results are based on tunnel tests at the tlirust coefficient approxi- mately corresponding to the approp-riate flight-test conditions . Althougii sortie small differences exist in tne absolute elevator angles, the slopes of the curves in figures 5> 5> and 7 show good agreement between tunnel and flight results for both straight arid turning flight, except at speeds close to the stall. At these lov/ speeds, the flight data show pronounced increases in the ainount of up-elevator movement required for speed reduction in straight flight. These marked increases are not apparent in the tunnel data. This discrepancy in results is believed due largely to the fact that the production airplane exliibited a decidedly miore definite stall at the wing root than did the smiooth, polished model. Although direct comparison of identical configurations is not possible, the difference in stalling characteristics at the wing root is indicated by the dia- grams of tunnel and flight-test tuft studies shown in figures 8 and 9« The more -oronounced root stalling on the airplane v/ould, in all orob ability, be accompanied by a reduction in dovmwash and rate of dovm-.vash at the Hori- zontal tail as well as a decrease in wing pitching moment, resulting in an ii;:nrcveMent in stability and requiring greater up-elevator deflections for trim. At higher air- speeds the agreemei;;t between flight and tunnel results Is reasonably consistent with tlie experimental accuracy of both. MAC A ARR Ho. L^Hlla The tunnel and flight curves of slevator-f ixed neu- tral point plotted against airspeed in figure ]. for the flaps-neutral conditions agree to within approximately 2 percent of the mean aerod^/^iamic chord except at low speeds with idling power. This difference is practically within the bounds of the experiineatt.1 accuracy with which the fligiit and the wind-tunnel neutral ooints are deter- mined. The discrepancy increases with reduced airspeed as the airplane demonstrates co(r;paratively greater stability. Because of the difficulty in obtaining consistent neutral- point results, particularly at very high airspeeds, neutral points were not determined for these speeds. The curves of fij;ure 5 serve as a measure of the stability in the high-speed range and are, in fact, believed ?nore reliable for comparison througho\;t the speed range than the neutral- point curves. Although the curves for the flaps-deflected conditions are included for coT.ipleteness, direct comparison should not be made inasmuch as the flap settings used in flight and ti.umel tests were not identical. Examination of the straight-flight control-force curves of figui'e 5 reveals comparatively poor agreement between tunnel and flight results. The force measurements shov/n in the tab-effectiveness curves of figure k, hov/ever, are in excellent agreement. Both flight and tunnel control- force measurements are believed to be accurate to within aiDproximately ±3 pounds . Although some discrepancy in the elevator control-force curves of figure 3 would be exnected because of the absence of a seal on the model elevator, analj'-sis based on brief check tests in which the model elevator v^as sealed indicated that differences of the magnitude shovi^n in figure 3 cannot be attributed to effects of the elevator seal. In an effort to determine the cause of the disagreement, the effects of the discrep- ancies in elevator deflection were investigated. Hypo- thetical control forces were computed, from tunnel hinge- moment data by using the values of elevator deflection determined from flight rather than those determined from tunnel data. For these computations, the wind-tunnel tab- effectiveness data Mere used, but the tab deflection was that employed in the flight tests. The curves obtained in this manner are shown in figure 11 compared with the flight- test data. In general, agreement in figure 11 appears considerably improved; for several flight con- diticns, in fact, agreement is excellent up to speeds above 200 m.ilss per hour, beyond which the flight-test curves becci'rie noticeably more stable. This difference may be explained to some extent by the observations of I: AC A ARR No. L5Hlla elevator-fabric distortion and internal ■■oressures made during the flight tests. The Internal ressures vvere found to be only slightly hirher than free-stream static pressure, causing; fabric distortion of the type illus- trated in figure 12. As deinonstrated In reference 1, elevator-fabric distortion of this tyoe rr^a^' be e::pected to produce increases in the variation of force with airs-oeed at high speeds. Inas-ucn as the flaps-retracted flight-test tri;n speeds of figure 5 ai''e all in this high-speed range, the trim-tab deflections^ required to trim tne control forces conv.>uted froin tunnel data are different fron: tne tab angles used in flight, and the control forces origirially coruputed from tunnel data (by using the pj.iount of tab aeflection required for zero force at the high-speed flight trim point) could not be exoected to agree well v/ith the flight control forces. The lack of agreerrient in the original results was further aggravated .:y the elevator-def lecti^tn differ- ences at low speeds, caused by the root stalling effects. In addition to tne effects of slevator'-def lection differences, fabric distortion, and elevator gap, agree- ment in the control-force results is believed to be influenced by small but significant construction discrep- ancies as, for exa-mole, differences in surface condition and in trailing-sdge angle. At a representative section the trailing-edge ans^le measured on the model elevator was lc?.7 , v.'hereas the corres'oondinf: angle measured on the airolnne was 11°. i:one of these effects ^'ould be expected to influence a;~'Prociabl7 the agreement in tab- effectiveness results. As seen in figures 6 and 7j the flight tests shov/ considerably greater variations of control force with acceleration, an-i the values of I'orco per g show con- siderably s-reater variation with center-of -gravity location, although the elevator-free mataeuver point F —2. = is anoroxlmately the s Siue . Because the absence g of an elevator seal .vas believed to be more significant in accelerated fligVit tnan in straight flight, control forces vi/ere estimated for both tne sealed aiid the unsealed elevators by ass-umlng constant p itching-moment ai:a hinge- ino'C'hnt slooes and using the sealed-elevator hinge -luOinent data obtained in the previously mentioned cnecK tests. NAG A A?.l I:0. L5Hlla 9 The respective values of dCh/-5e snd bCh/bo-t used in these comoutations -.vere -O.OO57 ^^^ -0.0013 for the ■ unsealed elevator and -O.GO5O and -O.OO32 for the sealed elevator. The resultinr? curves of force oer g against center-of -gravity location are shov/n in figure I5. The curve for the unsealed elevator is rractically identical with that -oreviously determined for the unsealed elevator (fig. 7) by the ir.etliod of reference 2. For tiie sef'led elevator the values of force per g are still very much lower than the flight-test values, although the variation of ?e/s with cen ber-of -gravitr'- location is rr.ore nearly oarallel to that determined in flight. The cormarison of control forces in accelerated flight has been made at a fairly high speed. Reference 1 indicates that fabric distortion of the type experienced in the A-2dB flight tests may be expected to produce increases in the variation of force with acceleration in the normal center -of -gravity range and in the variFtion of force per g witli center-of-gravity location. This comparison as well as that for straight flight would also be influenced by any differences in c ontr o 1- s ur f ac e c on 3 tr uc t i on . Agree:nent in the curves of elevator-free neutral ■ooint against airsoeed (fig. 10(c) )is rather poor esid becomes ivorse as the soeed increases. The flight-test elevator-free neutral ooint mioves raoidly rear'ward with increasinr-: speed, and at high speeds the airplane aooears more stable with elevator free thaxj with elevator fixed. It is believed that this large rearward shift in the elevator-free neutral point with increasing air- speed may be a result of the fabric distortion. In general, the present correlation Indicates that successful orediction of elevator control-force charac- teristics from v;ind-tunnel data can be m.ade only if extreir.e care is used in representing closely the air- plane in its construction forn'i - particularly with regard to the control s'orfaces. Agreeii^ent with flight nieasurements might also be im.proved considerably if effects such as fabric distortion could be taKen into account. A more beneficial solution, liowever, v;ould be to minimize these effects in the construction of the airolane. 10 NAG A A3R V.o. L^HH^- Lateral Stability and Control Steady sideslip ch ar acteristics . - Criprscteristics of the airplane in steady sideslips," Vi'hich are used as f li!a;ht-test measures of directional stability, directional control, dihedral effect, 3±de-force ciiar ecterlstics , and pitching rioment due to sideslip, are shown in figure- ll|_. AlthouP'h corrolete hinge -nionent data for the inodel ailerons and elevator were not obtained in sideslip, aileron forces in sideslip were estimated fron the tunnel data by taking into account the change in effective angle of attack due to sideslip but assuming no direct change in aileron hinge-moment characteristics with sideslip. For both idling ai:'d rated-power flight with flaps retracted, figure la shows e;:cell3nt agreement in the variation of contml settings, angle of bank, and rudder force with sideslip, although come difference exists in absolute values. Some of the difference in absolute values may be due to the fact that model tare tests were not miade in sideslip. It is especially interesting to note the close agreem^ent in the variation of aileron angle with sideslip, which serves as a flight-test indication of dihedral effect. It was found in the flight tests that the airplane vnng in normal flight aooeared to bend u"!Dward noticeably/ with respect to its position at rest. Despite the wing bending, however, the am.ount of effective dihedral determined from flight tests was also found to be no greater than tnat which would ordinarily be exoected for an airplane of this type with l\.*5'^ of geometric dihedral. Analysis of the elastic i^roperties of the model wing under load indicates that the riiodel wmg bending ',vas negligible. On the basis of the agreem.ent betv/een r.odel and airplane results, it a./pears that the observed airplane wing bending m.ay have had very little effect in increasing the dihedral effect beyond the norm.al am.ount for Ii-.5° of geometric dihedral. Further inform.ation regarding the elastic properties of the airplane wing and the effects of these oroperties would have been desirable but was not available. Gom"narison of the flight and tivnnel aileron-force curves &:roears to indicate that little error was introduced in determination of the latter by the assumotion that aileron hinge -mi omient characteristics remained unaffected by sideslip. The sideslip charac- teristics with flaps deflected do not agree as closely NACA ARR Ko. L^Hlla 11 as do the f laps-retrac tod characteristics, particularly in the case of the fiileron-defiection and rudder- Corce - vari?ticns. The flight-test rudder forces shov; a tendency tov.'ard reversal in figure ll|(c) but do not actually reverse as in the case of the model forces. At an airs-peed slightly lower thar; that for '.vhich the data are presented, hov/ever, rudder-force reversal did appear in the flight tests in this wave-off condition. Dihedral effect with flares deflected and rated power at low speed appears somewhat lower in the tunnel rneasure;;;ents than in the fliglit data. The flap deflection nowever, was S^ greater on the model than on the air- plane. In figure I5 , rudder hinge -morient characteristics estin.ated from flight-test rudder kicks are coripared with rudder hinge-moment characteristics measured in the tunnel tests with flaps retracted. Although the model rudder hinge -moiiient and force results are for an unsealed rudder and are also subject to effects of small surface and traillng-edge irregularities ss in the case of the elevator results, agreement in this respect is good. As previously shovm in figure ll|, the rudder forces in steady sideslip are in good agreement for this flap condition. In regard to rudder hinge moments, tae tunnel results, which showed no positive values of the pararaeter 6 Cii/^ c for the rudder, indicated that no rudder snaking Vifould occur in flight. This indication was confirm.ed in the flight tests. Aileron characteristics .- No tunnel tests were made to investigate aileron characteristics for the J:3 tab linkage vvith v;hich the airplane was tested. If, however, linear tab effectiveness is assumed, these characteristics for the f laPS-retracted condition can be estimated from the results of tunnel tests of the plain ailerons and the ailei'ons with a 1:1 balancing-tab ratio. Estimates of control force and helix angle made in this manner are compared with flight raeasure;rients in figure lb for indicated airspeeds of I35 ^^^^ 385 miles per hour. As recommended in reference 2, helix angles were pb _ O.BGj 2V " Ci-. estimated as ^^— = , where C7 is the total aileron f rolling-ir.om^ent coefficient and a value of 0.57 w&s used as the dam.plng -moment coefficient C^ . Although 12 NAG A AHR llo. LSElla the erigles of attack selected for these estimates correspond to rated-power flight at the appropriate sr)eeds, the raode 1 aileron data v^ero obtained in p Dwer- off static tests. Inasmuch as the tunnel measurexiients wei'e made for right rolls onl^' , the tunnel estimates are exactly' symmietricai for right and left rolls, v/hereas the flight results are not. Agreer:.ent in the curves of ]ielix angle is excellent in the range w'lere comparison was possii^la. Thez'^e is, however, some indication that tlie tunnel estimates, based on the arbitrary 0.3 factor, might be slightly optima.stic for his-h deflections at hi^h speea. At tna low airspeed, agreement in the force curves is good except at the highest aileron deflections, where the control forces for given aileron deflections are slightly higher in the flight records than in the tunnel eotimates. At the high soeed, the control force required in flight for a total aileron deflection of I'l^^ is approximately L(.0 pouiids (or ^ci nercent) greater then the force indicatea by the estimated curve. The greater dis- crepancies in the control forces at the high speed are believed largely due to the ei'fects of aileron fabric distortion. As in the case of tne elevator, the aileron fabric was found in the flight tests to undergo considerable distortion at this high speed. The distortion was in a direction to produce higher control forces . If the assumiption of linear tab effectiveness is not entirely valid, actual wind-tunnel tests witli a 3:8 tab linkage would indicate the control forces somewhat lower than those estimated herein for the 5:6 linkage at the Viigher deflections. Sideslip due to aileron d eflection .- Curves of sides li'p angle and rolling velocity against tim.e in an abrupt rudder-fixed aileron roll out of a 30° banked turn are shov;n in figure 17 . In addition to the simpli- fied sidesli^; estim.ate of reference 2, the ;notions have been calculated by the operational method of reference 5 and also by the tabular-integration method of reference I4., in Vifhich slope variations in the curves of rolling- mom.ent , y awing -mom.en t , and side-force coefficients against angle of sidesliD are taken into consideration. This method of tabular integration has been sho\.vn in reference 4 to be m.ore reliable for general use tiian methods requiring the assumotion of constant slopes. L^Hlla -y ?or the subject air^ilaiie, which exhibited essentinll-; constant slooes, 'che tixree methods of coinoutatior: based on wind- tunnel results aoaear to tive very 5 im liar- results v;itj.i respect to .T.a.ciinurr. sidesli'o an'"le, all or v.'hich are aoproxinatel^" li-° higher tha:.'; the flip-ht-test value. Among t.ie factors possibly conbributinp; to the lack 01! Nerfect agreei.iert is the cifferenoe betvveen the instantaneous control deflection assu/aed for the ccaou- tetlons arid t.lae actual control .;:cverr.3nt in the flight test. Another factor influencing tne results may be the chP:np.e in normal acceleration experienced by the aii^'plane in its roll out of the turn. Although no flight record of nornal acceleration was obtaiiied for the test in question, similar f li.rrht-test results indicate ti'iat a considerable variption r.ay heve occurred during the ir.aneuver. Analysis indicates tnat the change in norraal acceleration and, consequently, lift coefficient nay introduce conditions considerably different from these considered in tne theoretical calcul^:tions . A si.Tole static estir.ate of tlie air.ount of rudder deflection required to maintain zero sideslip in en aileron roll v/es made as su^rgested in reference 2; that Is, it v^as f'ESUified that the desired rudder deflection would be tnat required to counteract the coinbination of aileron adverse yawing moiTient and ;■/ awing r.ior-ent due to rolling. The estimsted value obtained hj this tr.ethod was approximate iy 8'-' for flaps-retracted flight ¥;fith level- fll-'^ht power at an indicated alrs'oesd of i1l5 ir.iles oer hour. Altnough no flight-test dar.a were recorded for full-aileron rolls at 'chis fli.-^ht condition in wiich zero sldeslio was maintained by iiioans of varying rudder- def Iscrions , flight-test records for constant rudder settings indicate fnat the rudder deflection estimated fro;:: turjiel results would be noticeably lo-.;er than that required in flight. For several rolls with ;oartly deflected aileron£, however, essentiall:/ zero sideslip was maintained, and the estir.iated rudder deflections were found to be in fair agreei-nent y\/ith the maxlirii,UTi deflections required in flight. COuCLjDirG RS^^ARKS Stability and control characteristics determined froir; Langley 19-f oot-nressure-turinel tests of a ll|. FACA nRR No. L5Hlla 0.2375-scale powered model of the Douglas XA-25 airplane hav^ been compared vvith results of flight testa of a Douglas A-26B airplane. The significant results of the conparison xTiay be suirm:arized as follovvs: 1, Good correlation was obtained regarding elevator- fixed neutral points and the variation of elevator deflection in both straight and tiii'ning flight except at speeds approaching the stall. At these lovif speeds the airplane shovved a distinct Lmproveiiient in stability'" not indicated by the model tests. The difference was attributed to the fact that the pronounced stalling at the root of the ^'roduction airplane Yjing did not take place on the s?nootr. , '.vell-f aired nodel v/ing, 2. The variatioiis of elevator control force with airspeed and acceleratio:^ -vvcre not in good agreei.ient. Although some discrepancy vvas inti'oduoed by the absence of a seal on the model elevator and by small differences in absolute valur.s of ele\.ator do-flection, the coi*re- lation in control-force cibaracteristics v/as also influexiced by the effects of fabric distortion at high speeds and by small construction dissimilarities such as differences in trail Ing-ecige angle. 5. Elevator tab effectiveness as determined from tunnel data was in good agreement with flight-test tab effectiveness, !].• Agreement in both rud.der-f ixed and rudder-free static directional stability was good except in the wave-off condition, in which the model tests indicated rudder-force reversal at a higher speed than the flight U Cr O Lr O • 5. Mode] and airplane indications of stick- fixed and stick-free dihedral effect vvere in good agreement, although some slight difference in geometric dihedral may have exlstsd because of wing bending in flight. The use of model hinge-moment data obtained at zero sideslip appeared to be satisfactory fo:- the determination of aileron forces in sideslip, 6, Fairly good correlation in aileron effectiveness and control forces was obtained. Fabric distortion was •ArA A.n? No. L5Klla believed res'jonsible to some extent for higrier flirht values of sileron force at nigh speeds. 7- EstiniPtioi: of sideslip developed in an abrupt axleron roll v/as fair, but determination of the i.iaxl;?.u.u rudder deflection required to naintain zero sidesli-p in an abru-rit roll was not entirely satisfactory. On the basis of these findings, it apoears that Q.-r^e^Xient between stability sjr;d coritrol character'iatics esti!T;ated from wind-tunnel recults and those raeasured in flight cpjinot be co/i^iietely satisfactory "ai-^.less certain factors now usually neglected in wind-tunnel tssting can be taken into consideration. These factors involve small differences between the i.iodel ai'id the air'jlane and include differences in elastic properties, surface finish, and construction accuracy. These factors should be considered, if po::sible, in future investi- gations . Langley liemorial Aeronautical Laboratory National Advisory COiTXuittee for Aeronautics Lane-ley Field, Va. KACA ARR No. L^Hlln 1. 'lathews, Charles W. : Aii Ai^.alytical Investigation of the Effects of Elsvr^tcr-Pabrio Distortion on the Lonp^itudinal Stability and Control of an Airolane. FACA ACR No. LuEjO, l^Uh- 2. Kayten, Gerald G. : Analysis of vKind-Tui;nel stability and Control Tests in Terms of Flying Qualities of Full-Scale Airplanes. NAG A ARR Ko. ZJ22., l^ky ' J. oTones, Robert T.: A Siir.plified Application of the ?,';ethoc' of Operators to the Calculation of Disturbed I'/otions of an Airolane. KAOA Reo. ilo. ^oO, IS?*-'* I4.. "Yolo'vvicz, Chest3r I-.: prediction of 'loticnc of an Alrnlene Resulting from Abrupt i-ov3;r:ent of Lateral or Directional Controls. IJACA ARR Ro. L5E02, 19^l5. NACA ARR No. L5Hlla 17 Id m I I ir> trv rH-— rH — ' nj o nj o o 1 • 1 • i-H X^ J^^ a rO[-^Lr«0 ^ II sj3 II ONO o ir\ LTs CO O (Q OOrHO-rtCTN U-NrHXIrHXl CTs Rj::™ OJvOO ooj ooj o t~i nacm r\j <-! 1 -d^r^ ita? lpvlt^ LTN Cy rH i-t K\rH KA [^f\J rH rH r^ < m sO • vO * rH 3 Qc (J) <0 y (0 c<-t o o ir\ u~N ■a rH ^-^ rH '^ -o o njo cv] o ® E 1 • 1 • tn — rH >-* <-H rnryKNCOiTNO rH -o rH ja rH roryco CO O C0--O OCO ^o lTnOJOO CO a lr^(^i rH O-d-CTN ITNOJ CM ON oj a\K\ so D u rH m O OCO ONO rH f\JrHJ-i/vaO iT^LT. Lr\ FJS"' (\J sO o o f\J o f>J o rH ^f^(\J ry « t -d'^- ^ *-~o • ir^ OJ rH rH K\rH KN r-oj r^ rH o tr\ TA ^o o ■H cnr- *^ li < ii S^SJ* r-4 • 2 :z: £° 1 IT. ir\ rH '— rH -^ < ojo nj o X 1 • 1 • • -p ■p o* P C P 0«H — > «H «-i rH n *J (m .h <;-, 4J rH • *J © c +J • cr o*© bO »H © n -^ cr +3 01 0) © © 01 C C W tH •H 0*rH &0 01 a .Q C -"-H > © r^ .a © •H rH - bOP © XJ (D © *i rH bO -C « ©«H " C V. n O CO •D C c « a 4^ wo rH ,H 3 E ■HO) -P -p --f *H llO -U rH T) O C a s: cft^ O AJ TJ bO op. ■P rH rH C O © C HJ -H . m to *3 dl 4) t^ O -H i-f 4-J n •H +> j2 o ti T3 ^ M t, -.-O O fn +J rH O © TJ 3 ^ Vt " • c * • T) n to EC 3 Pd * • • c C rH 0) ^ cr © o • j^ © a O t 4J - C C O -rH •HO © W3 -^ oj t, P E W.P •H- — n «-t t +J © 4J -P 3 T3 TJ r-t TJ'0©©«J3©C T3 ^0 ■p 4^ ffl O O -O O O o c C « -D •H 3 TII,©arH© © rHk (8t4.p©U .. 3 a a > ^ 4_i +J W * • « 9 03 -H •H C 01 rH rH © +J (u; 3 e]0 a - O'-W ^ (0 O O OrH o © L p 1 ■PCOrHt, to©© u OTQ-» *E^EhOCC« <-H rH n X3 X) © JD ® ID t, -rt -H p.^ ••'—■-' o a © t^ 4-j o -H c 4J * »TJ -o a c E a u-\ Cca*H©>S gpoj o3©ox:©rH-^n ^ t^ -< +> U -P * *o ® r. a-o T3 'O o o a caeca O © a rH rH © E j:: © © fflC«EO©^TH(D ^ ^ r-t m a a T! s bt/ ^i «H «) © "O -H ^ bO< CO £■ U H C/1 M M O < < ^ o < tn CD NatjC-rHrHaCn-H •Hcn A- fc < O z (O o t-t cc O b] h-t td Eh e- < E- S t-t NACA ARR No. L5Hlla Fig. la 0) c U CQ cd 03 c o3 f-1 Q- S^ •H ce CM I < CO cd cH bD o o o CO • 3 -^ (D O e ♦J C t3 O C CD ■p cr 0) a; tj bD NACA ARR No. L5Hlla Fig. lb >, ■H E -H Ci. (D .— i a o CO 1 1 t- to C\3 NACA ARR No. L5Hlla Fig. 2a P 3 "C3 I I I On I Fig. 2b NACA ARR No. L5Hlla 5 0) Oi s .. O Q) ^1 ^s 1 ^ i| 5 -^ 1 5: S c c2 S I o o S I NACA ARR No. L5Hlla Fig. 3a $ $) Q> ^ 55 O ^< O VO ^J u1^ M i^' ^ ^vS [^ I. I I \ I '^ < T '^ u Qi 1 3 n n n n n n ( -J D o > o ^ ^ Qi ^ c:^ UMO(J P < t < \ < 1 ( ) ( 1 <' ( r 1 A ( c o\ i n 1 n 0/ r ' — r 1 c 1"^ '^ — ' 58 l< < "^ Z UJ 2 1^ I- <- SI 3> y c < > <^ c 1 1 < 1 .^1 t3 o ^ ^ ^ S I //^d Q/'y9JJOI jOJ^UOD JOJO/I<9/J q?n^ \ I I Fig. 3b NACA ARR No. L5Hlla ( ) ( c r ( n^ ' V ^ ^ Q) ^ ^ <;:) i □ "TJ [] []' D -EH ■3- O □ O 0> 00 O) •< K <\i <>) ^j ^J vr\— •) ( 1 G O ( \ r >n Ci s 7 H [ ] D [ ] D,' D,' Di o\ n°. n qU ° ; ^ % ^ Q) Qi ^ //^d ^ 1 - 1- o 5 < '^ Z UJ o ^ ^ §^ §1 ^:^ , c > 1 ^ < > J ^1 < 1 I _fj_ ^0 ' y H ^ ^ I Q/ 'y 'sDJOj foj^uoj jojo/ia/j U^n^ I 5 NACA ARR No. L5Hlla Fig. 3c - bap '^g 'a/ duo jojo/ia/j o ^ S) C>-Q C5 -o -G -Q Q o9 o si V> O □ O ^ o ^^ o S 1 r i / o o :v> -^ ^ ^ p ^ z ^- ll Jo X- ^ ^ ^ <;:) § Lisn^ ^a qi y dDJoj fOJ^uoD jo/d/is/j Fig. 3d NACA ARR No. L5Hlla ^ o u: I □ O o r c ) j'\ / c A -■ D o ll ' A H — 13 / — ffl- k o< 7 r V <>> o n I % N \ [ ' (n [ 1 ^ O ^ ^ O >- p a 3 O z !2o > S5 §- Z ui 9 " I- t < ; ^ § '^ \ ^ H f- / "0 ^'"^^ qi '^ '3JJ0J lOJ^uoJ Jojoyi9/J ^^'^^ I I NACA ARR No. L5Hlla Fig. 4 100 I40 /SO 220 260 300 3-^ Indicated o/rspeed^Vc^mph Figure 4. -Variafion of elevator trim -fab effectiveness w/th airspeed. Fig. 5 NACA ARR No. L5Hlla >- ~+- c >$ (J 1* _.g ' Z uj t- t- -< 5 Z X o ^ \ \ \ I 1 1 1 \ 1 \ 4_ \ 1 1 1 1 1 \\ ^ll U Ull ^ 1 ^ s> t- ' J c , ^ M § M ^ ^1 ^ ' 1 1 ^ ^ 1 O r\J 1 OCi ' ^ c^ \\ "^ I ^ ■ 1 .\ -^ -K 1 c> \ VJ\ 1 vjn 1 " U VO ^ 00 ^^ o o c/p UMOQ bap ' ^ ^dibuD /0J4. uoD J04 da a/j c o I U i 0) On C O -C I C3 % I 1 o C3 S I 5 o I I =,8 O II NACA ARR No. L5Hlla Fig. 6 qi 'dDJoj /oj^uoD jQicyidfd u/dduixij >- K « 2 !2 o > > 1^ s 2ti o s" I 1 s 6 C3 i 1^ '• s ^ ^ ^ $ Q "N §^^ Q) o ^ § > ^ ^ ■§ - O ^ ^ >^ § O V ::k: § ^ ^ ^ ^~" o o ^ ^ Fig. 7 NACA ARR No. L5Hlla S ft 8 6 Tunnel Flight • A =;c:^ 2 / 1 / / A, > 1, n 1 ^ \ II \ / / / / ^R 1 1 / / ii k5^ > ^ ^ y s ^ 00 O 8 § O o o o ^ 00 Q) 8 o ■b O'V'N ■/<^^^-^<5c/ 'j-U/od /Djj.ndf\j c: Q) [ NACA ARR No. L5Hlla Fig. 10c C\) ■K 1 1 ^^ Z uj 8 1 \ \ 1 1 ^Ix / \ \ \ -\x / \ \ \ \ / ^ /\ f / / \ > J \ A J \ o 7 f i 1 h ^ 1 > ^ \\ ?^ 1; :3 J ^ ^ 00 ^ ^M 'OV'hl y^^^^^c/ '^u/od /oj^Pd/y o ^ ^M O) -Q ^ O ^ i^ ^ ^ ::> •N Q) :is Q i ^ § Q ^ o 5 •«> vo ^ V^ Oi k ^^ -K O 5 ~6 0) o ^ ^1 ^ '■^ ^ u C o C^ ^ 1 1 Fig. 11a NACA ARR No. L5Hlla :5 o I 40 40 40 40 40 40 ■ ■■ o - N G ^^ ^>^ ^ ^^ o n ^d /\ O < \ >^ >J ^' i^ — O o 6 NATIONAL ADVISORY COMMITTEE FOB AERONAUTICS 1 1 1 1 /OO 140 ISO 220 260 In d I CO ted air^p q Qd, i^ , mph (a) Flaps refracted} rated power. 300 FiqurQ 1 1 -Variation of elevator control torce w/tti indicated airspeed. Model elevator and tab det lec- tions Identical witti flight-test settings. NACA ARR No. L5Hlla Fig. lib c^ k^ ^ I 40 O 40 40 40 40 40 o — c \ L O o r\ (^ rf ^ (J (dec/) (percent MAC^ Tunnel ri/ghf 2.0 up 31.9 O 1.2 up 27.8 □ 0.3 down 22.9 O □ n c ■-€}-- - — - --ET u n - — ^ ^ n u < > \ o— ^ o — 7!^:— \} < A COM ATIONAL ADV HITTEE FOR AER ISORY ONAUTI CS 3CD 100 140 ISO 220 260 Indicoted a/rspeed, V^^ mph (b) Flaps retracted ', 7J-percent rated power Figure IL- Continued. Fig. lie NACA ARR No. L5Hlla :3 S 40 O 40 40 40 40 O 40 o — Cu h A O--^ ^ — TV— ^ 4- i. _i KJ o (deg) (percent MAC) Tunnel F/iahf 2.3 up 32.0 1.7 up 21.4 o □ 1.2 up 23.0 O □ e D b 3 □ ( — 1 "-^ 1 — 1 LiJ- — u — 6 > '^ "v C> o ^ /^ k ^ \y \. 6 NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS /OO /40 /80 220 260 300 Indicated airspeed, V^-, mph (c) Flop^ refracted'^ ^ ^ O - FlgurQ 11. -ConcludGd. NACA ARR No. L5Hlla Fig. 12 VJ = 360 mph Vi^STO mph--' eg. crt Z6 percenf MAC. Approximate - poinl of fabric oiiochmenf Vi^SOOmph \fi = 3Z0 mph- Q^at Z6 percent MAC- No-load fabric iens/on, 2.7 /b y^^ 210 mph ■Sect/on under no load Section in flight Vl^ZZO mph Vi^nO mph Elevator section dH:! in. from center line of airplane NATIONAL ADVISORY COMMITTEE FOP AERONAUTICS Hgure I Zr Elevator -fabric distortion at various indicated airspeeds. Pougtas A-26B air/o/ane with cGnfer of qrav/tt/ of J2 percenf MAC excepf wfiere r/oted. Fig. 13 NACA ARR No. L5Hlla Q Q) o o si. o CD I/) u > (- a 3 O 2 <£> o > « ex -" P < "^ Z uj 2 K t- t- o o ^ .yac/ (7/ OS Y o ^ NACA ARR No. LbHlla Fig. 14a X ^ /O Con fro/ f7/^1s (^ -C 0: ^ '-v 'n O C^ 1 ^ O^ D Q -K -^ "^i :> 0^ -Su r> c t \ Q) ^ 1 ^ 4C cc or |o ( ) k i< O ^ 1 V ^ -^ rs X 40 ^ 20 10 o 10 20 10 10 o \ c -o- o" •X -ti ^^_£: z ^ II o OH ^v ~o -X- \ 3 NACA ARR No. L5Hlla Confrol Fliqhf Tunnel O Rudder O Ele i/atot □ Aileron {total) ^ ^ p 1 ^ A 200 100 n •^ ^J H K^ r n n _B ^ ^ 'i ^ 100 -d P^ 3 on/-» NATIONAL ADVISORY COMMITTEE FOR AERONIUTICS Tunnel A Flight ^^ 20 JO JO 20 Left Sides/ip anql6,deg R/ghf {^ Flaps retracted; Tc'^O; V^^ 133 miles per hour. Figure 14 -Continued. NACA ARR No, L5Hlla Fig. 14c % g- 1> ^. cf Q o <: jv Q Q. ■--. -K O V Contr hwn Le 20 \ 10 \ r \ c ] o < ^. ^ . •y a LJ Q\ 10 a txJ ^ y > Control Flight Tunnel O Rudder O Ele\/afor Q Aileron ifofal) ^ < "^ 10 10 --JMT- Tunnel A Flight » "0 til i3\ ■K "k «: g (il 1^ ^ o □ C ^ s c^ 00 o O 3 00 Q o o o o V ^ P° 1 1 ^ ^ .A X / ^ J n^ AiD / y //' p / ./ y ' ■^^^-"^ ^ o o o R ^ 5 >■ I- of 2 O z > ^ O^ Z -J ^ !; - zi C3 9- g -c 5 c § 8 o ^ 4.UdlDIJ.J.aOD 4.UdUJOUJ-dbUIUl ui douoq'^ ^ < >^» ■c ^( 1^ !s ^- K < ?' ^ -k C h .^ K) s u: CD O k ^ Q <: b^ s O ^, ^ ^ 1 1^ u; oi, O \ ^ ^ ^ o s^ ^ Q) It g :^ -■^ +^ k D ^ O ^ Q ^ o V) ^ c: n :^ Cij 1 C> ^ § F" T>i S ic: NACA ARR No. L5Hlla Fig. 16 ^ Cc o CD C I •Q Q- Q? C D I 04 o -.04 -08 Tunnel Fl/g/it 135 o 3S>3 a ^_^ ^"l' -JiZ. —J^— ------ ■'^Y' " — 40 30 ZO 10 O 10 20 30 40 Left Change in total aileron angle, deg Rigtit Figure 16. - Variation of aileron wheel force and helix angle pb/ZV with change in total aileron angle in rolls with rudder fixed, flaps retracted, and rated power. NATIONAL ADVISORY COMMITTEE FOB AERONAUTICS Fig. 17 NACA ARR No. L5Hlla is s c I .6 .6 4 .3 2 .1 -- Z — . - __ — -- — — — .^ ^^^'~^^ ^ ■^ \ / / -^ ::_^ -^ //I 1 "^ ^ ^_ ^ / 1 I / 1 / ' / / /' Reference 4} Calculated from Reference 3 ) wind-tunnel date Reference z\ flight 20 Qj 16 (b § § a ^ 4 O 1 __. . ^ / ,.^ ^ - ^^ v^ /' ^ \ / ,''/ y _^^ -- - " / /^ / ^ / / .{, / ^ y //, ^ i^ g^ ^-^ ^ O .4 .(5 12 1.6 ZO 2.4 2.8 3.2 3.6 40 Time, sec NATIONAL ADVISORY COMMITTEE FOd AERONAUTICS Figure 17.- Rolling velocity and sideslip during aileron roll out of 30° banked Turn. 6f = 0°; Vc^l45m//es per hour at /q,ooo- foot altitude-, level riight power. UNIVERSITY OF FLORIDA - — - ■■-Jill 111 mil iiiiiiiii 3 1262 08104 970 1 UNIVERSITY OF FLORIDA DOCUMENTS DEPARTMENT 1 20 MARSTON SCIENCE UBRARY -P.O. BOX 117011 GAINESVILLE. FL 32611-7011 USA