1、I,.,i. -;1NATIONALADVISORY COMMITTEEFOR AERONAUTICSTECHNICAL NOTENo. 1573.FLIGHT MEASUREMENTS OF THE FLYING QUALITIES OFFIVE LIGHT AIRPLANESBy Paul A. HunterLangley Memorial Aeronautical LaboratoryLangley Field,Va.WashingtonMay 1948.-,/ ,., .-Provided by IHSNot for ResaleNo reproduction or networkin
2、g permitted without license from IHS-,-,-. *.NATIONAL ADVISORY COMMJ3?I%EFOR AERONAUTICSTECHNICKL NOTE NO. 1573FLIGHT MEASUREMENTS OF THE FLYINGFIVIZIJGHT AIRPLANESBy Paul A. HunterSUMMARYResults are presented of an investigationQUALITIES OFmade to determ3.nemeasuremmts of sabflity, controllablliy,e
3、nd stalling charac-teristics of five light airplanes.Comparison of the characteristicsof these airplanes with therequirements for satisfactory flying qualities leads to the followingconclusions:The five airplanes were stable longitudinally in most of theconditions tested. The degree of stabillty var
4、ied considerablyamong the five airplanes, but the up+levator position required tostall with power on was low relative to ths maximum deflection of theelevator.The control surfaces of all the airplaneseffective in producing chenges in attitude endabout their respective sxes.were satisfactorilysngular
5、 velocityWide variations in directional stabillty were encountered amongthethefive airpleneso The adverse yaw was considered objectionable onairplanes which had low directional stability.The dihedral effeetwas positive and generally withfn desirablelimits for all the airplanes tested. The bsnk accom
6、panying sideslipwas favorably large even at low speeds for all airplanes.The pitching moment due to siieslip was generally desirably smallat small angles of sideslip, although at large angles of sideslip anappreciable nosing-down tendencywas measured on several of theairplanes.Stall warnings were co
7、nsidered good for all five airplsnes,although the ensuing instabilitywhich consisted of a rapidlyd increasingconsideredbuffeting,.these lastrolling and yawing oscillation at the comple stall wasobjectionable. The stall warning in general consisted ofIncreased stick force, and rearwxrcistick travel,
8、althoughtwo characteristicswere rather small with power on. TheProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-.ailerons were ineffective in maintaining lateral control In a power-onstall in any of the airplanes. Recovery from the stalled conditionwa
9、s easily made on all airplanes by pushing the elevator controlforwarda71Stalls from turning flight were possible with power on at all speedsIn three of the four airplanes tested but were generally impossible abovea certain airspeedwith power off because sufficientelevator controlwas not available. T
10、he initfal roll+ff in a stall from a sideslippedconditionwas M the direction to cause the trailingwing to drop.The small fixed wing-tip slots on one of the airplane= were foundto have no measurable effect on its flying qualities or stalltngcharacteristiccs.INTRODUCTIONuuring the period beginning Aug
11、ust 31, 1939 and ending July 27,1940, the National Advisory Committee for Aeronautics conducted flyMg-qualities tests on five light airplanes. Data on the individualatrplanes were not prepsred in a form suttable for general releasebecause of the urgency of military work which had begun at that time.
12、The present paper gives a summary ofdata that has been compiled forthe purpose of making available the findings of the IVACAin regard tothe stability and control characteristicsof this type of aircraft.The investigation comprised measurements of stability, controlla-bility, end stalling characterist
13、ics. The results are based on dataobtained from photographic records of continuouslyrecording instru-ments supplementedby ptlots observations.TESTSDescription of AirplanesDescriptive characteristicsof the five light airplanes are givenin table I. Photographs of the five light airplanes are shown asf
14、igure 1 and three-tiewdrawings are shown in figure 2. All fiveairplaneswere tw-place or three-place cabin land nrmoplanes and,except for airplane 2, all had fixed I.andSnggears. Airplane 4was the only one that had wing flaps and/or slots. The control+mrfacegaps were unsealed, except in the case of t
15、he rudder snd elevator ofairplane 2. The longitudinal trimming device consistedofan elevatortrim tab for airplanes 1, 2, and k; an adjustable stabilizer forairplane 3; and an independent airfoil munted below the horizontaltail for airplane 5.b.Provided by IHSNot for ResaleNo reproduction or networki
16、ng permitted without license from IHS-,-,-NACATN No. 1573The gross weights and center-of-gravitypositions for which thevarious airplanes were tested are as follows:Airplane Gross weight(lb)1 11002 1503975? 13855 1060. Cente=f-gratity position(percent M.A.C.) 26.922.()25.129.024.4.The center-of-gravi
17、typositions given In this table ere thoseapproximately at the middle of the allowable center-ofavi.ty rangeand are those at which mst of the testswere conducted. Other center-of-gravity positions were tested in connectionwith the effect ofcenter of gravity and stalls. Som3 shift in center+f-gravity
18、positionoccurred with fuel consumption.*InstrumentationContinuous photographic records of control movemsnts and theresultlng motions and accelerations of each airplane were obtainedby an Installation of NACA recording instruments, The deflections ofthe three controls were registered by a three-compo
19、nentcontrol-position recorder; the angular velocities in roll, yaw, and pitch,by three tu-ters; end the linear accelerations along the threeaxes of the airplane, by a three-componentaccelerometer. Theserecords, together with those from a pressure recorder which masuredairspeed and altitude change, w
20、ere synchronizedby mans of a timer.In addition to the recording instruments, an indicating yaw vaneto assist the pilot in making specific maneuvers and a spring scaleto measure the elevator control forces were used. The yaw vane,together with a calibrated sectorit could be read by the pilot., was nm
21、nted above the cabin whereThe airspeed recorder was connected to a swiveling pitot-stattchead set a distance of 1 wing chord ahead of the leading edge of thewing at about the middle of the semlspan. Both the airspeed recorderand the airspeed indicator,werecalibrated by meens of a trailingairspeed he
22、ad for airplanes 1 and 2, and the corrections derived for.airplane 1 were assumed to apply to airplanes 3, k, and 5 because oftheir similar configurations. The swiveling pitotistatic head may beseen on the right wing in figures l(a), l(c), and l(e) end on the left.wing in figures l(b) and l(d).Provi
23、ded by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-4 NACATN No. 1773In additfon to the instrumentationpreviously described,airplane 2 was equipped with an Indicating accelerometer end asideslfgle recorder. Alrplene k carried a sideslip-anglerecorderand a rec
24、ording inclinometeras well as the standd. instrumentation.The sideslip-snglerecorder vsnes may be seen mounted ahead of theright wing in figures l(b) end l(d).Elevator angles e presented with reference to the thrust axisexcept for the case of airplane 4, for which the stabilizer is usedas a referenc
25、e. If elevator engles had been given with respect tothe thrust axis for this airplsme, all values of elevator angle wouldhave been shifted uprard 3. The control-positionrecorderswerelocated in the cockpit, and cable stretch may therefore have causedsome error in control positions.RESULTS AND DISCUSS
26、IONThis investigation covered longitudinal and maneuvering stablity,landing characteristics,lateral stability and control, stalling andspinning characteristics,and the effect of slots on flying qualities.Further discussion of the effects of the asured stability sndcontrol par-ters on the flying qual
27、ities end a set of quantitativerequirements for satisfactoryflying qiuil.itieswill be found inreference 1.Longitudinal Stability and Control CharacteristicsStatic longitudinal stability.-The static longitudinal stabilitycharacteristicsof the five light airplanes for the power-n cruisingcondition at
28、a center+f-gravity position in the middle of theallowable rsnge are shown in figure 3. The trim devices were set atneutral for four of the five airplanes. No data on airplsne 2 withtab neutral were available; therefore data with the airplane trinmdfull nose heaw (tab 3 up) were used. It is not belie
29、ved that thistab deflection would cause much variation in elevator angle and stickforce from those with neutral tab position. This conditionwas chosenbecause it Is the one in which the mst flying time is spent an isthe one for which the most comparabledata were available. Thevariation of elevator an
30、gle with airspeed, shown in the lower pert offigure 3, fs an indication of the so-called stick-fixed static longi-tudinal stability end provides an indication of the stabillty in terms of the pilotts feel of stick position. Positive stick-fixed stabilityinsures that the airplane will tend to return
31、to a given sngle ofattack or airspeed following a disturbance. The five light airplanestested were statically stable, longitudinally,with stick fixed endpower on, as shown by the negative slope of the curve of elevatorposftion against airspeed, although the degree of stability variedProvided by IHSN
32、ot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACATN 0. 1573 5considerably among the five airplanes. The curves also show that, for.each airplane, the ulevator position required to stall with poweron was low relative to the maximum deflection of the elevator.Desir
33、able stall-warning characteristicswould be represented by morerearward stick positions an larger stick forces at the stall.The stick-free static longitudinal stability characteristics inthe power-n cruising condition are shown by the curves of elevatorstick force plotted against airspeed in ths uppe
34、r part of figure 3.The variation of elevator stick force with airspeed is an importsntcriterion of the pilotts control “feel.” The curves show that allfive airplanes were statically stable, longitudinally,with stick freeend power on and that the forces were small compared to the pilottsphysical capa
35、bilities.The friction in the control system is a factor that should alsobe included in any discussion of control forces. The force gradientexperienced by the pilot with change in airspeed is highly influencedby the amount of friction that must be overco. Friction in theeystem also reduce6 the abilit
36、y of the airplane to return to its trim.position when the stick is displaced end then released. Friction willprevent a pilot from obtaining a consistent “feel” for a given attitudein a given configuration and w1ll make trlmtningthe airplane mre. difficult. The tendency of the airplane to return to i
37、ts trim airspeedwhen the stick is displaced and then released will be lsrge if theslope of the force curve is lsrge but will always be reduced if thefriction is large. The friction in the elevator system of each ofthe airplanes tested was as follows:Airplane1 1Friction(lb)1 +2 13 44 Not determined5
38、5The control friction of airplanes 1, 3, and 5 was reported by the pilotsto be excessive; on the other hand, that of airplane 2 was considered.unusually, but favorably, low.The effect of power on the static loitudinal stability is shown.in figure 4 for airplanes 2 and 4. The stick-fixed static longi
39、tudinalstability of both airplanes was increased with power off, as shown byProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA TN NO. 1773the steeper slope of the curve of elevator angle against airspeed.TMs effect was the ssme for all five airplan
40、es tested. The Increasedpull forces required to trim at a given airspeed with power off maybe seen from the curves of figure 4 for both airplanes although theforce changes are greater for airplane 4. Had the airplanes beentrimmed at the sam airspeed for the power-off condition as for thepower-on con
41、dition,the slopes of the power-off curves would have beenincreased and would indicate an increase In stick-free staticlongitudinal stability.The effect of retracting the lending gear on static longitudinalstability is shown in figure for airplane 2. No appreciable changein stabilitywas obtained, sti
42、ck-fixed or stick-fne, but the up-elevator angles and pull forces required to trim at various airspeedswere reduced throughout the speed range by retracting the laning gear.This reduction of the angles aud forces would be expected because ofthe nosing-down tendency resulting from the combination of
43、the dragof the extended landing gear and the forward end downward movementof the center of gravity relative to the thrust axis.The effect of flaps on the static longitudinal stability ofairplane 4 is shown in figure 6. Deflecting the flaps caused adecrease in stability,both stick-fixed and stick-fre
44、e, and alsoreduced the uplevator angles and pull forces required to trim atvarious airspeeds throughout the speed range. These effects wereprobably caused by a change in downwash over the horizontal tailsnd/or a change In dynamic pressure at the tail with flaps down.Notice the slight stick-free inst
45、ability and stick-fixedneutralstabilitywhich occurs in the power-on flaps-down condition at speedsabove 60 miles per hour. This conditionwas the only one in whichnegative stabilitywas found to exist for any of the airplanes tested.The effect of center-of-gravityposition on static longitudinalstabili
46、ty is shown in figure 7. A forward shift in center=ofravityposition resulted in en $ncrease fn stability,both stick-fixed andstick-free. The stick-force curves shown were obtatned with a constanttrin+tab setting, and as a result the trim speed was increased by theforward movement of the center of gr
47、avity. Figure shows thatapproximately a constant Increment of force was required to maintaintrim at any speed when the center+f-gra.vityposition was changed.If the alrpbne had been trimmed at the same airspeed :n each case, ,the slope of the curves for the ?mre forward center-of-gravitypositionswoul
48、d have been increasedand those for the more rearwardcenter+f-gmvity posftions would have been decreased; thus thechanges of stabilitywith centef-gravity position would have beenmore obvious.The effect.of the trimming+evice setting on the variation ofthe force with speed for three of the alrplsnes te
49、sted is shown infigure 8. The adustable stabilizer on airplane 3 and the elevator.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACATN No. 1573 7.trim tab on airplane h were satisfactory for trimming the airplanesunder all conditions. Although the curve for the tab nose-heavycondition of airpl
