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LANDING LOADS INVESTIGATION LABORATORY DROP TESTS

September 1962

"Contract NOa(s) 59-6226-c

'" v • M • 2' £63

REPORT NO. ES 4o64I _v;__ A

Qaalified requesters may obtain copiesof this report direct from ASTIA.

Copy No. 6

DOUGLAS AIRCRAFT DIVISION * LONG BEACH, CALIFORNIA

BestAvaillable.

COPY

REPORT NO. 13 40641

LANDING LOADS INVESTIGAT ION LABORATORY DROP TESTS

CONTRACT NO. NOa(s) 59-62260 DATES SEPTEMBER, 1962MODEL A4D-2

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PREPARED BY: P. C. AllenH. D. MoriwetherL. B. Mosby

APPROVED BY: ,,J T.-' -m N. Stone, ChiierAeroutruetural Mechanios Seotion

DOUGLAS AIRCRAFT COMPANY, INC.

LONG BEACH, CALIFORNIA

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"I" si PREPARED GY, F.C.A.llen DOUGLAS AIRCRAFT COMPANY. INC. PAGE. t_ _

CHECKED BY, L.B. Mosby 9/Ot//62 LONG BEACH DIVISION MODEL: A4D-2

TITLE: LANDING LOADS IWASTIGATION LABOPATOPY DROP TESTS ,R* T,;.S 4061I

FOPEWORD

The work described In this report was accomplishedby Douglas Aircraft Company, Aircraft Division,Long Beach, California, for the Bureau of NavalWeapons, Wasntr.tr, D. C., under Contract NOa(s)50- 6 22 6 c. It represents one phase of a comprehensiveprogram for the examination of loads experienced byNaval Aircraft during landings and the determnationof the accuracy with which these loads may be dupli-cated by drop tests and anslysis.

The project was performed under the general directionof Mr. C. T. Newby of the Bureau of Naval Weaponswith Mr. D. C. Lindquist acting as cognizant technicalproject head. It was c-"T'hrted by Douglas AircraftCompany with Mr. F. C. Allen providing the technicaldirection and Mr. L. B. Mosby acting as Chief TechnicalTnvestigator.

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s.Sal PREPARED B: F. C. Al len DOUGLAS AIRCRAFT COMPANY, INC. PAGEs,____DATl

CHECKED OY, L, B. Mosby LONG lEACH DIVISION MODELs A4D-2

TITLE: LANDING LOADM ItSTIGA'r1ON LABORATORY DROP TESTS BEPorTHO. ES- 4- 064

TABI' OF CONTENTS

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TTLI, LANDING lOADS INVESTIGATION LABORATORY DROP TESTS aiupeT . ES 406•

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SUI¶ARY

This report describes and presents the results ofcertain airplane drop tests which are part cf anextensive program to compare the landing loadsexperienced by an A4D-2 airplane during flight testsand drop tests with those computed by analyticalmethods. Other phases of the program are reported inReferences (1), (2) and (3).

The instrumentation used in these tests was nearlyidentical to that used in the flight test program andwas sufficient to determine the loads applied to theairplane at the ground, the position of the strut,the internal pressures in the gear and significant struc-tural accelerations.

The results are presented in the form of curves ofmeasured parameter versus time. Vertical and hoxfizontalloads on the gear at the ground were computed from thestrut instrumentation and are compared with data fromthe reaction platforms.

Discussion on the significance of the data is reservedfor the Summary Report on this project (Reference (3)),however, two recommendations pertaining to the needfor further work arise from this drop test program.The first is that a study of the dynamic characteristicsof the reaction platforms be made in order that confi-dence in the strut instrumentation can be improved, andsecond, that a sliding coefficient of friction test bemade of the tire on the reaction platform surface for thepurpose of substantiating the high coefficients of frictionregistered by the left hand strut.

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TTLEUAflIO I S* ATION LAN""" M•r Z= RE FORpT yNOUIA2A

IA- Axial load in the strut at the axle, pounds.Positive up.

IW - Normal load in the strut at the axle, pounds.Positive aft.

FAA - Inertia for•e on the lower mass in the strut axialdirection, pounds. Positive down. l

=- Acceleration of the lower owe in g's times Itswe bt•.(The lower mass weight, which includes the whoolp t41eaxle and instrumentation, is 120 pounds.)

PAN - Inertia force on the lower mass in a fore-aft directionnormal to the strut# pounds. Positive forward.

PHO - Force on the gear at the ground parallel to the ground,pounds.

FYG 0 Force on the gear at the ground normal to the ground,pounds.

I I Intercept constant. (except as noted)

K - Calibration constant. (except as noted)

L - Total wing lift,, pounds.

IUA w Average coefficient of frietions of the tire an thelanding surface.

XUA 1 , Instantaneous coefficient or friction.

P The value of an parameter. Subsoript denotes theosaillograph ohannel from which the parameter was taken.

t Time , secoends.

T Tmne from instant of release to istant of sroundoontaot, sCeonds.

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3113x (Cent ime )Vv a Airplane vertolal velocity (sinking speed), at contact,*

feet per second.

W a Airplane weight, pounds.

5 Displacement of any oseilleo;prph trao frmits zero positien, inches.

81 - Displascmmet f any osoillegraph traoo tfrethe ref•rnneo lino, insheos

A - Displacement of any oseillograph trace fromzero during the emaibratmion im,, Imbs.

he - Distance betwen the zero pesitien of an•y t"eand tM refere o line, Inohes.,

Ai - Displasement of any .soillograph traco 1iethe reference line,, inches.

# = Angle of the fuselage reference line with respeet* to the horizontal - d egrees, Positive airplano

nos" up.

FHOG FA-

FVG

Positive 0ear Faore* Positive Strut (Axle) Poseso

@o.illegrsph Traoe Tominoleo,

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P• PARED @Yt F.C.Al*•n DOUGLAS AIRCRAFT COMPANY, INC. PACEIC L..--.

CHLeCICED&Y, i•,B..L L2Ab/±/62 LONG WEACH DIVISION MODEL:. -AD-2

TITLinG LD INVEST2OAT EON LABORATORY MUOP TISTS m *EPOITWO._4Q

INTRODUCTION

The landing loads Investigation, of which this reportforms a part, provides for an experimental flight testprogram and an airplane drop test program with consistentinstrumentation in conjunction with an analytical dy-namic loads program. The purpose of the investigationis to determine the differences, if any, in the loadsexperienced in actual landings and the loads experiencedIn drop tests, and to determine the accuracy with whichthe landing loads can be duplicated by advanced analyticalmethods. This report describes the airplane drop testsand presents the results of the drop test phase of theInvestigation.

An additional objective of the program was to comparethe loads resulting from actual landings with the loadsmeasured on the moving drop test rig at the landingloads test facility of the National Aeronautics andSpace Administration (NASA) at Langley Field, Virginia.

"The airplane used was the Douglas A4D-2, generalcharacteristics of which are shown in Figure 1. TheNASA tests used a left hand A4D-2 gear which, togetherwith similar instrumentation, was later used on theairplane durfng its flight tests and drop tests. Inthe flight and drop tests, a right hand gear with nearlyIdentical Instrumentation was also used.

The cQmplete investigation is contained in three reportsin addition to the present volume. A detailed descrip-tion of the instrumentation and the calibration techniquesis presented in Reference (1). A description of theflight tests and the results thereof are given inReference (2) and the analytical investigation includingthe comparisons described above is presented inReference (3). The NASA test results are containedin Reference (4).

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EQUIPMENT

Details of' the airplane Instrumentation used in thisprogram are provided in Reference (1). A summary isprovided In Table I for the reader's convenience.

Landin& gear vertical and drag loads were measured by0 the landing gear instrumentation and by reaction platforms

the configuration of which is shown in Figure 2. VariationsIn friction coefficient were obtained by varying the sizeof grooves in the surface of' the platform. An average co-efficient of friction of approximately 0.h4 was sought bythis procedure.

T.he airplane used in the drop tests was not the sameas that used in flight test although the mass distributionand rigidities were Identical In all important respects.Thus, all acc~lerometera In the body of the drop testarticle were mounted at the same location and with bracketsthat were Identical to the flight test artiale. Thelanding ffears were those used in flight test and therecording apparatus was the aame.

In these flight tests, the recording apparatus was containedin a reworked 300 gallon external fuel tank mounted onthe centerline of' the airplane. This store was returnedto the laboratory alter flight testing for use in the droptest program. In the first 62 drops this store wasmounted on the airplane in the same manner as in flighttest. After Drop 62, the instrumented store was removedfrom the airplane and placed on the ground. Data wastransmitted from the airplane to the store by a cable.This change reduced the maintenance required on the record-ing apparatus and eliminated some of the high frequencypulses on the oscillograph traces. A dummy store of equiv-alent Mass and Inertia was mounted on the airplane to re-lace the instrumentation package.

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THE TEST SET-UP

Figlire 3 shows the airplane In its pre-drop positionand provides a picture of tne test set-up. Theapparatus and test procedures are, perhaps, typicalof those used In the industry with the possible ex-ceptions dicussed below.

Because of the special !nstrumentation located on themain landing gear- axles, the wneEl s.pin-up deviceshown In Figures 4 nnd 5 was designed. Angular velocitywas Imparted to the airplane wheels by bringing thetires In contact with two additional tires mounted ona Jack shaft which was driven by two air motors. TheJack shaft and its mounting was assembled on a carriagewhlch was moved clear of the airplane Immediately be-fore it was dropped.

Wing lift was simulpted by two -36 Inch diarmeter pneumaticdampers (lift 1pots) shown In Figure 6. These wereattached to the ilrjl~ine at wing Statlons r2.0 (right"and left) as shown in F'gure 7. The attachment mech-anism was such that the load was applied shortly beforethe wheel contacted the ground. P.n essentially con-stant load was maintained tnroAvhout the stroke. Sincetno, method of load apFlication was one of the knownsignificant differences between drop tests and flighttests, the attacnmetl, i.nks of the dampers to the air-plane were instrumented with strain vauges In order thatthe wing lift time-nistory could be determined. Asindicated In Figure 7, additional lift da.mpers wereprovided to catch the airplane In the event of a struc-tural failure. These lift pots applied no load to theairplane under normal circumstances.

Sinking speed was measured during the tests by -i TFODIInstrument set-u: as shown In Figure 8. SinkIng speedcould not be obtained directly from the drop heightwithout correcting for the forces introduced by the liftpots prior to wheel contact, hence TODI was ,sed as araFId means of obtaining this parameter during test.

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fl E . TRODI

Top beam out 1/8 inch above platform.

Sink speed measured 2 1/8 inch above platform.

E( "Figure 8. TRODI Installation

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"PREPARROsY, F.C.Allme DOUGLAS AIRCRAFT COMPANY, INC. PAC% 1

CHECKED W, L.1.0sby 9/f2/62 LONG IACH DIVISION MOoEL, _A#D*.2TITL LI, dLINO LOADS InVETIGATION ZANOUT'oRY DROP TESTS REPORT NOJ 0 4

PROCEDURE

Prom a preliminary examination of the flight test data,several landings were chosen for duplication In droptests. Numerous drops were made for the purpose ofchecking the instrumentation and to provide accurateduplication of the landings. A log of all drops iscontained in Appendix A.

Table II provides a list of the Initial conditions ofall drops for which detailed data are pr'esented hereinand the initial conditions of those flight landingswhich will be compared with drop tests in the SummaryReport (Reference 3). Not all drop tests were dupli-cated by landings because of the fact that after thedrop tests were conducted, the data from some flightlandings were found to be unacceptable.

The following paragraphs describe the methods of mea-suring the initial conditions and the estimatedaccuracy of the readings.

A. Weight and Weight Distribution.

Weight and C.G. position were determined by means"of Cox and Stevens Electronic Weighing Unitsplaced under the jacking points of the airplane.The accuracy of the weighing units is *0.l'9and their location was known within 0.2 inch.The maximum possible error on airplane weightis, therefore, t13.5 lb. and on 0.0.position O.4 inch.

The moment of inertia of the airplane In pitchwas determined by measuring the frequency ofoscillation of the airplane when supported inthe manner shown in Figure 10. The measurementwas made for one distribution only, analyticalcorrectifns being made for other gross weights.Overall accuracy of t2% is estimated for themoment of inertia.

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MOMENT OF INERTIA

2r + M/• b•20 + c2 )

1 Ka 2 Wc M(b 2 + c 2 )4, -r .2

K - 6400 lbs/ft.

a - (132.6/12) ft.

W - 12770 lbs. a Mg

- (17.3/12) ft.

b - (28.1/12) ft.

f - 0.88 cps

I - 19328.2/f 2 - 2998.8 - 21960 slug ft 2

Xcg = 0

LiYog - 232.5

Zag - -16.0

Figur. 10. Neasuarnt of Moment of Inertia

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B. Fuselage Reference Line Angle (*)

The fuselage reference angle was measured priorto drop by a bubble protractor level. The pitch-roll gyro in the airplane (Item 20 Page 4 ) wasset on this value, and the airplane attitude atthe time of contact was determined from theoscillograph trace of this instrument. Theangle listed In Table II is the angle at timeof contact.

The protractor was placed on the #irplane at thegun-eight level points which were manufacturedparallel to the fuselage reference line withintO.1 degree at the time the fuselage was in itstooling Jig. Structural deflections caused bydifferences In method of support created a cer-tain amount of change in the relative positionof the level points and the fuselage referenceline and, consequently, introduced an error inthe value of s. Investigations of such de-flections made for the purpose of calculating

( gun-sight errors lead to the conclusion that theerror in this case is of the order of 0.1 degree.The combined error introduced by the protractorand gyro Is also estimated at 0.1 degree, hence,the overall accuracy ot the value of * is es-timated to be within V0.2 degree.

Vsriation In pitch attitude was obtained bymoving the hoist point fore and aft. OscillaLtions of the aircraft caused by wheel spin-upand airplane rotation after release caused lackof precise duplication of the landing attitude,however, analytical considerations indicated thataccuracy greater than ±1.0 degree was unnecessary.

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PRtPAUUDsy: P.C.Allen DOUGLAS AIRCRAFT COMPANY, INC. PAGE:

cm.cxaogy, L.1,1einby 9/W/62 LONG BEACH DIVISION MODEL. A49-2

TITLE, LAINM• O LOADINTIOATION LABORATORY DROP TJllS REPORT HOJI__O61

C. Wing Lift

Wing lift was determined from the instrumentedlinks attaching the lift dampers to the airplane.Since fluctuations of the lift occurred duringthe stroke, the average values shown in Table IIwere computed from the oscillograph records.Lack of precise agreement between flight testand drop test values was caused by the fact thatthe average lift was approximated during droptests and computed more accuratley later. Theaccuracy of the lift, as measured, was within* 2A.

D. Sink Speed

Sink speed was measured during the tests by aTRODI instrument set-up as shown in Figure 8.Sinking speed was subsequently obtained forDrops 68, 70, 82, 84 and 93 by the followingapplication of the classic equations of motionin which consideration was given to the effectof wing lift applied prior to the instant ofground contact:

V a-g L t - dt

where E is the time from the instant of releaseto the instant of ground contact, L is the liftapplied to the airplane through the lift potsand W is the gross weight of the airplane. Acomparison of the TRODI readings with Vv obtainedfrom solution of the above equation is of in-terest in the evaluation of the accuracy of thesinking speed measurement.

The variation of wing lift with time, as obtainedfrom the oscillograph records, for the periodbefore ground contact is shown in Figure 11.Integratign of these curves provides the in-formation'for the second term of the right handmember of the above equation. The followingtable provides a comparison of sinking speedsobtained by the two methods.

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Drop No. g Ld t (Computed) (TRODI)

8. •46o 14.8 .90 13.9 13.8

70 .41 9 13.5 1. 3 •4 12.2 12.0

68 .504 16.2 1.15 15.0 14.8

93 .551 17.7 .95 16.7 16.8

82 .540 17.4 1.20 16.2 15.8

TODT readings agree with the calculated within*0.2 fps with the exception of Drop 82. A notationon the log (Appendix A) for drops made on the sameday as Drop 82 to the effect that the TPODI sensi-tivity was set too low leads to the conclusion thatthe computed value is more correct. In addition,the only experimental parameter in the computed valuehaving a significant effect on the results If T.A conservative estimate of the maximum error in f ist.004 sec. which produces 1.13 fps error in sinkingspeed. In view of these factors, the computedsink speeds are used in preference to the TRODIreadings for the drop tests which are to be comparedwith flight landings in subsequent Investigations.

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E. Horizontal Speed (Wheel Rotational Velocity)

The rotational velocity of the wheels of thedrop test airplane and of the flight test air.;plane was measured by a magnetic pickup mountedon the brake assembly which was activated bysteel studs fastened to the wheel at 10 degreeintervals. As each' stud passed the sensor, anelectrical current was generated which was re-corded on the oscillograph.

The relationship between wheel maximum rotationalvelocity and airplane forward velocity on theflight landings was a variable which dependedupon the tire deflection at the time of spin-up. The procedure used in the drop tests was tomatch as closely as possible the maximum wheelRPM obtained In the flight landings. Since therelationship between RPM and airplane velocityis indefinite, no airplane speed is listed forthe drop tests in Table II.

In drop tests the wheels were spun by the devicedescribed on Page 7 . After spin-up It was nec-essary for the spin-up apparatus to be moved andfor the airplane to stop oscillating, during whichtime the wheel rotational velocity varied. Itwas necessary, therefore, to make allowance forthis variation and, again, exact duplication ofthe flight condition was not possible.

The accuracy of the rotational speed measurementat these speeds was very good being limited onlyby the accuracy of the recording apparatus andthe time signal. Without a detailed analysis Itcan be stated that the accuracy Is well withint 1 RPM. Accuracy of this device reduced as thespeed reduced, hence, it was not possible toobtain a satisfactory reading as the rotationalvelocity approached zero or to determine accu-rately the time at which rotation stopped.

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REDUCTION OF DATA

Figure 12 is a reproduction of the osaillograph recordsobtained during a typical drop test. In acOordanoce withstandard practice each record was preceded by a ali-bration run in which zero'sa and the respons, or ceahchannel to known voltages were obtained. Channel 22on eaoh sacillegraph monitored the voltage of the powersupply since this was not precisely constant throughoutthe run.

The osoillograph data, in terms of trace defloetion froma reference line was read by a Benson-lArbner "Oscar 3"reader which provided punched cards for input to an 1I=program for reduction of the data. The data were readat .001 sec. intervals.

The reduction equations were not identical for allchannels. The channels and the equations wed by themachine are identified in Table II1 and in the followingparagraphs

When Fla 1 and Flag -0; b (" -

A .i - Ao. •

When Flag 1• 0 and Flag 3• =0; 1 .Ao) (3)

When lag 1 o0 Flag• 3 - 1 i1 o)

Flags 2 and 4 control the equations$tq be used inconverting O/A trparaemter value, "r.

When Flag 2 =0,

P K+ (5)

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PREPARED IBy P.C .Allen Ai 2

cHEcic , L.B.1oeb• 911/62 LONG ,ACH DIVSION "oo.L AMD-2

TITLE: , I LMDS INANIGATION LABMATRY DU)P T=3S REPoRTno MJSO64

When 7laM 2 a 1, is minus, and the alternate constant

is used i

P ( (6)

When 1156 4 - 1, an intercept constant Is added. Then,

Table III provides the calibration constants, K, and thefla• information pertaining to each channel. The inter-O, 1, applies to pressures only and is equal to the strut

initial absolute pressure with strut extended (14.7 + 25.0 -39.7 psi).

Additional operations were required on certain parametersto present information in a preferred tam. Thus, theaxle strain gauge readings, channels 10 and 14, wereconverted to strut axial and normal force, after whichstrut axial and nermal fore* combined with the axle aecelera-tions wre converted to loads at the ground. Also, theInstantaneous, coefficient of friction fas computed as wellas the averzae coefficient. The equations applicable tothese operations are as followsi

A. Axle readings to strut load*

L.H. Gear (oee 1)

nA - (43,5T4-l42.1P6 )PI 0 + (-223.8-66.7T6)?13 (8)

11 . (983.3-99.1P6)P10 + (4575.0-5.0P 6 ) 1 3 (9)

R.H. 0ear (Ose 2)

1PA - (56,995+"37.2P6)P10 + (1200-101.116)Pl, (10)

IV a (4800-l45.3P6)1lo + (8,455.8 + 3o.876)113 (11)

ift T equations are derived in reference (1).

rOgi Lost. C. IA

PREPDyS. S,, Pnp.o .F.C.Allen DOUGLAS AIRCRAFT COMPANY, INC. PAGE: gkD-

cuuCKDo sy, L.*,Mzrg.zZ/62 LONG IEACH DIVISION MODELi A_ __

TITLE. LANDING LOADS I IGATION LABORATORY DROP TESTS REPORTHOM 4064i

B. Strut leads to ground leads

m - ('A + PAA) c08(4-6) - liN + PAN) SlI(4-6) (12)

M- (7w + PAlN) oos(d-6) + (PA + PAM) SIN(,-6) (13)

C. Ceetfieient of friction

HUA 1L 7 (14)

Averag 1U a TimAverge RUA . •[L(NUAIl + MUAi)] (15)

The reduced data were printed nmmerialy and plottedmeohanieally.

4.

PREPARED BY: F.C .A11@n DOUGLAS AIRCRAFT COMPANY. INC. P AGE: 26

CHECKED BY; L*B.Muoby 9MT/62 LONG BEACH DIVISION MO0DEL:A-QTITLEi LANDiNa WADs In~lkrIGATION 1ABORATORY DROP TESTS 111111T .0. 40641

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PREPARED BY: F.C.A11@n- _ DOUGLAS AIRCRAFT COMPANY, INC. PAGE: 27

CHECKED BY: L.B.Mosby 91iý/62 LONG 1EACH DIVISION MOD EL: A4D-2

TITLE: IANDING WADS IAfSTICATION LABORTORY DROP-TESTS- mEPOwo.& 404

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.21 PREPARED BmY F.C.AJ..L f DOUGLAS AIRCRAFT COMPANY, INC. PAGE:

C"IECEID iYt •L]•.lB.m 9TY~2/62 LONW MACH DIVISION O&DELt AMD-2

TITLE LAJED I JAA XKf28TZ@ATM LASjAM RP TSITS REPORT 0110.4 ,,641

TABIZ K. OSCILLOORAPH TRACE IDWITIPICATION AND CALIBRATION CCOSANTS.

OSCILLUGRAPH NUMmER I

L4ANNLL NU. 111IL CUNST' (K+) CONS1. (K-) FLAG1 2 3 4

4. L. H. STRU AIk PRESSURk, P.S.|. 3942.OOOU 0. 0. 0. 1. I .6. L.H.S.RuI PU IIIUN, INCHES 16.0040 0. 1. 0. k. 0.1. L.H.STKUl VkLULIIYV F.P.S. 21.7300 0. 1. 0. 1. 0.0. Letf.VLRFILAL PLAIFORM, Lob. 48450.0000 0. 1- 0. 1. 0.9. Lt. SI9uf MkItKIM G PRkSSUkE, P.S.I. 4406.0O00 0. 1. 0. 1. 1.

10. L.HAXLL STAIN LAbL I# VERTICAL U.v4? 0. 0. 0. 1. 0.I . LH. AALL VL rICAL ALCLLtRATIONt. S S1.2390 0. o0 0. 1. 0.il. L.H. OA6 bRACE, LBO. S6910.0000 56711.0000 0. 1. 1. 0.13. L.H.AALL UkAG ALLkLItArIo#, G S S2.3*IO 0. 0. 0. 1. 0.14. L.H:.ALL SIkAIN *AGk 3. URA6 1.0101 0. 0. 0. 1. 0.II. L.H.DNAu PLAtF0kM, LBS. 11644.0000 0. I 0. 1. 0.19. L.I1.RLBUUNU, LHAMnEK PRLESURE 5640.0000 0. t. 0. 1. I.al. L.H.AALE LArILAL ALLELERAFIUN. 6 S 49. Vb1O 0. 0. 0. 1. 0.22.' VOLIAuL MUNIT•R 1.0000 0. 1. 0. 0. 0.23. NIJSL UAR brkur PUsjIILJN INCHES 16.0060 0. 1. 0. |. 0.24. NOU "AR UPPLR MASS VEKI.ALL., G S -11.4640 0. 0. 0. |. 0.20. STRUT 110t bLNUIN6 SITAIN 6AGE 0.9980 0. 0. 0. 1. 0.27. C.0.NUXNAL ACLLLtHAIIUN Is 1. S 0.6117 0. 0. 0. 1. 0.28. FRL PAILH ATTITUDE, ULORLL5 3.S950 0. 0. 0. 0. 0.2v. L.•.LUNvIIuuINAL ACCELtkAlIUN. G S 0.!488 0. 0. 0. 1. 0.30. AlL RULL ATIIIIUUt, UtGRtS 11.095o 0. 0. 0. 0. 0.31. L.0.NUXMAL ACLkLtkAI ION 10, G S 1.8645 0. 0. 0. 1. 0.33. L.H.OEAR UPPER MASS VtRI.AC,., G S I1.5j2O 0. 0. 0. 1. 0.34. L.H.GtAK UPPER( MASS LON6.ACL.o G S 11.6390 0. 0. 0. 1. 0.

OSCILLOGRAPH NUMBER 2

4. R.H.STRUT AIR PRFSSURE, P.S.I. 3850.0000 0. 0. 0. 1. I.6. R.H.STRUT POSITION, INCHES 16.0000 0. I. 0. |. O.7. R.H.STRuT VELOCITY, F.P.S. 21.3400 0. 1. 0. I. 0.8. R.H.VCMTICAL PLATFORM, LBS. 47650.0000 0. 1. 0. 1. 0.9. R.N.STRuT METERING PRESS4RE, P.S.I. 5290.0000 0. I. 0. I. 1.

10. R.H.AXLE STRAIN GAGE . VERTICAL 1.00160 0. 0. 0. 1. 0.II. R.H.AXLE VERTICAL ACCELERATION, G S 53.6280 0. 0. 0. 1. 0.12. R.t1.ORAG PLATFORM. LBS. 11411.7999 0. I. 0. I. 0.13. R.h.AXLE STRAIN GAGE 5 DRAG 1.0000 0. 0. 0. I. 0.14. R.H.AXLE DRAG ACCELERATION* G S 67.2030 0. 0. 0. I. 0.15. R.-. ORAL BRACE, LBS. 5?626.0000 57639.0000 0. I. I. 0.16. L.". DRAG BRACE, LBS. 57243.0000 56775.0000 0. I. I. 0.22. VOI tAr MONITOR 1.0000 0. 1. 0. 0. 0.23. L.H.WING LIFT, LBS. 5044.0000 0. 0. 0. I. 0.21s. R.H.WINC LIFT, LBS. 5123.0000 0. 0. 0. I. 0.26. R.H.WING TIP ACCELEROMETER, G S 38.0670 0. 0. 0. 1. 0.27. L.H.WING TIP ACCLLEKOMETER, G S 37.4600 0. 0. 0. %. 0.28. FRL PITCH ATTITUDE, OEGREES 5.5340 0. 0. 0. 0. 0.29. R.H.GEAR UPPER MASS VERT.ACC., G S 19.11.30 0. 0. 0. 1. 0.il. R.H.GEAR UPPER MASS LONG.ACC.. G S 12.0950 0. 0. 0. I. 0.33. R.H.AXLE STRAIN GAGE 3 SIDE 1.0033 0. 0. 0. I. 0.35. R.H.AXLE LATERAL ACCELERATION# G $ -39.1`000 0. o. 0. I. 0.

CIIIE I IIII II1 •1

PREPARED BY: R__' Al len DOUGLAS AIRCRAFT COMPANY, INC. PAGE: 29DATE

CHECKED BY, L.B. Mcsoy Q-/12/62 LONG BEACH DIVISION MODELA4D-2DATE

TITL.E IANDING LOADS INVESTIGATION LABORATORY DROP TESTS PORT NO. ES 4064

RESULTS

The results o_' the drop teaTs are presented on pages 58to 6l in the form of curves showing the variation ofparameter versus time. Wherever right and left handreadings are available, the cruve.; are drawn so as topresent a comparison of' left and right parameters. Theaccuracy of the data _13 estimated in Reference (1).A summary of these estim3tes is Included herein asTable IV :'or conveniene. The response characteristicsof each channel are described in Table V. Since therecords were -esd at .DO! zecond intervals and in mostcases pl,)ttea aL .0ý)2 seccnd intervals, the accuracy ofthe plotted results wltn respect to frequency respensewill be limltccu In some instan;ces by the number of pointsper cycle.

The comments wnIch follow art! made In the oraer thatdata appears on Pages z) tc 4.

1. ý'.G. Acelerations

The ncr.ial a.'celiraticn (lI g's) trace is themost signli'icanr anu useful. Both the normalacceler'onetc•' (ig) and the lungitudinal accel-eromet,!r had maximum ranges of approximately

i.jg ai.d higher accelerations were notrecuocded. The 1g nurmal a,celerometer was useddurin,; flight tests to measure wing lift.

2. Nose and Main Gear Strut 1 osition

Tnls is thc reading from the slide-wire in-strumentation. Left and right gear positionsare consistenL. These data are compared to thestrut position determined from integrating thestrut velocity under Item 14 and comment on theaccuracy of this measurement is included therein.

3. Main Gear Side Bending Gauge

No calibration was obtained for this portion ofthe instrumentation in terms of the basic groundloads, henc.e these data are not useful exceptas a qualitative indication of the variationof bending stress in the gear at the point ofattachment of the gauges.

"PREPARIEDBY: F.C.Allen DOUGLAS AIRCRAFT COMPANY, INC. PACE: 30CHECKED BY L.B.Nosb1 LONG BEACH OIVISION MODEL. A- AD-2

TTLE: LANDIWO-M AMD NZTGTO ABR''R BLhT REPORT WO]M 9406

4. Main Gear Drag Gauge

This Is the gauge on the axle responding primarilyto fore and aft force at the ground. The read-ings presented here were used in conjunctionwith the vertical strain gauge reading to givethe ground loads presented on Pages 69 to ý4.Differences In magnitude of the trace dis-placement between right and left gears is com-pensated for by different calibration constants(see Table III). The first .08 second of thisrecord Is of greatest importance in this in-vestigation since it includes the spin-up andspring back phenomena of interest to designers.

5. Pitch and Roll Attitude

The attitude readings were derived from thepitch-roll gyro. Pitch attitude at time zeroprovides the Initial condition for Table II andthe subsequent values were used as 0 In the ex-pressions for FVG and FHG in Equations (12)and (13) to determine the ground loads plottedon Pages r() to E, . The roll attitude readingssubstantiate the fact that the drops wereessentially symmetrical. Maximum readings of1/2 degree were registered.

6. Main G-ar Vertical Gauge

This gauge, mounted on the axle, respondedprimarily to vertical load and the reading wasused in conjunction with the main gear draggauge to obtain the ground loads plotted onPages 6b, to •:4 . The ground loads are one of themost Important parameters in this investigation.Their accuracy and reliability are discussedin detail on Pages '-' to to

;ns• Lfi2Z ' tAAIC FT1 f

• PREPAREDBY: F.C.Allen DOUGLAS AIRCRAFT COMPANY, INC. 31PR'ARESYPAGE:

CHECKED mY, - L.B.Noeb7 9nt/62 LONG BEACH DIVISION MODEL: AD-2

TITLE: A.DING LOAD8 1 ,iNkIGATION LABORATtlY DROP TW'T__ REPORT NOZ8_9fQ.j

7. Wing Tip Acceleration

The consistency between right and left accelera-tions creates confidence in these readings.Certain differences can be expected, especiallyin the Initial accelerations because of theslight time differential in the application ofthe wing lift loads (Figure 11).

8. Nose Gear Vertical Acceleration

With the exception of Drops 82 and 93, the nosegear vertical accelerations are those inducedby main gear loads. In Drops 82 and 93 thenose gear toiuried down before tne main gear loadhistory was complete and additional accelerationswere produced by the nose gear load.

9. Fight and Left Upper Mass Accelerptions

Certain of these records show inconsistenciesbetween right and left gear both In the magni-tude and phasing. Where such is the case, ItIs recommended that the results be used withcaution, since no reason has been establishedfor this lack of symmetry.

10. Right and Left Lower Mass Accelerations

The vertical and drag acceleration data areused in the determ~nation of the ground loadsand consequently are of primary interest.Detailed examination and extensive usage ofthese data has established a high confidencein their accuracy. The side accelerations havenot been used as extensively, but because ofthe similarity of sensing and recording units,the reliability of these curves is also con-sidered to be good.

01 ?S S 1A

" PREPARED BY:, 1'.C. Allen DOUGLAS AIRCRAFT COMPANY, INC. PAGE, : 2

cHECKE BY, L.B. Mc•sby 9Ai,2/62 LONG lEACH OIYSION M.oL-,.._A -_=2ý____DAle

TITLE, T.ANDTNO LOADS INVESTIGATION LABORATORY DROF TESTS REPORT Mo. ES 40641

11. Wing Lift

These curves shcw the extent to which a 2onstantlift w•z maintained durirn the stroke. Variationsof + 10% fron the mean are noted with the larrervarfatýc-.n c'curring generally in the first partotf thoc str-kc. Inasmuch as the 21ft dampers mayhave individual characteristics and are notapplied exactly simultaneously, -,onsistency ofphase relatton3hip between right and left lii'tcurves Is not expected. Also, during the dropthe wing will be vibratinE because of the Impulseintroduced at the instanjt of release, and the liftdamper will connect at difference times In thewing': deilectl,_n cycle. Hence, precise consistencybetween drops cannot be txpected. The averagevalues cf' 11't determIned from these data were usedfor comp•arlson with the ;'light test landing lift(Table TT). It is believed that these recordspresent an :,curate descrIption of the loadsapylled to tne airplane by the lift dampers, andthe data can be used with confidence.

12. Drag f1race Axial Load

Goud consistency between rl.ht and left draZbraces is noted for all recordA except Drop 70.The bLf.':erenoes noted In the Drop 70 record areconsistent with a similar departure from sym-metry bctdoen right and left axle drag accelera-tion (item 1C) and meterinc chamber pressure(Item 15). These phenomena may be associatedwith roll of the airplane since Drop 70 has thelargest Initial angle of roll.

FOWL L02, ' A

"PREPARED Y: F.C.Allen DOUGLAS AIRCRAFT COMPANY, INC. PAGE

CHECKED eyý L.B.Mosby 9A'2/62 LONG BEACH DIVISION MODEL: _ AD-2UAlk

"TITLE: LANDING LOADS INVESTIGATION LABORATORY DROP TEBTA REPORT NOES-"J4.I4

13. Pressure Readings

Good consistency is noted between right andleft gear readings both as to magnitude andphasing again with the exception of Drop 70.Because of the fact that non-symmetry of dataIn Drop 70 !s registered on several channels,it Is considered a real phenomenon, and thereliability of the records is strengthenedrather than reduced by the noted differencesbetween right and left readings.

The rebound chamber pressure was measured onlyon the left gear and orly in drop tests. ThisInstrumentation was added as a result of theanalytical study which showed that the reboundchamber pre:3s,,,re had a prcnounced effect on the gearoperation during the compression stroke.

14. Strut Velocity

As Indicated In Table I, strut velocity wasmeasured by a Sanborn velocity generator. Theaccuracy of this Instrument has been estimatedat * 4f (Table VI). The resulting data appearsconsistent within itself and in comparison to theopposite side. A comparison was made for three"cases ofthetntegrated velocity and the stroke(Item 2 above) with the results shown inFigure 13. The agreement between slide-wirereading and integrated velocity reading issubstantially less tnan the accuracy of eachInstrument since at certain times a differenceof stroke of 1 1/2 inches is noted. In aneffort to establish which of the readings Ismore reliable, a comparison was made with theanalytical, or computed, stroke (see Figure 14).Slightly better correlation Is noted for theintegrated stroke. It is of interest to notethat both the theory and the Integrated strokeare high with respect to the slide wire readingin the middle time range.

There is Insufficient evidence to establishwhich of the two measured values Is more correct,however, the comparisons presented here castsome doubt on the accuracy of the slide wire.Further work needs to be done to clarify thispoint.

"REPAREO BY P.C.Allen DOUGLAS AIRCRAFT COMPANY, IINC. PACE 34

CHECKED BY Lk.B.Moby 9/1M/62 LONG BEACH DIVISION MoDor. A4D-2,ITtE LANDING LOADS I'NSTIQATION LABORATORY DROP TESTS_ REPOP IWOES 4o.64i

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1 11,2 PEPARED BY.?. C. Allen DOUGLAS AIRCRAFT COMPANY, INC. PAGE: 34___

cmEcxtED By. L.B.ftsby 9/V/62 LONG MEACH DIVISION MODEL; -- D-2T .ITLE: .1lDNO WADS INN'iTIOATION LABORATORY DROP TESTS- REPORT NO.93 406*1

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CHECKED ST. L.*B.Hosby 97T/62 LONGS BACH DIVISION MODE L: AD-2TITLE: LANDINO LOADS IN~fk~IGATION LADORAORY DRO0P TU'TS RE PORT WOES 40~6l1

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CHECKED BY: DA LONG BEACH DIVISION MODEL:- A#D-2

TITLE. ADINGLO IAM1OATION LAORATOYROP NTIM WEPORT NO. 3 061

ESTIIhTED OVERALL RECORDED PARAMETER ACCURACY

PARMETER ACCURACY..

R.H. Gear Vertical Load 3R.H. Gear Drag Load 3L.H. Gear Vertical Load 3L.H. Gear Dreg Load 3L.H. Gear Lower Mess Vertical Acceleration 2L.H. Gear Lower Mess Drag Acceleration 2L.H. Gear Lower Mass Lateral Acceleration 2R.H. Gear Lower Mass Vertical Acceleration 2R.H. Gear Lower Mass Drag Acceleration 2R.H. Gear Lower Mess Lateral Acceleration 2R.H. Gear Upper Meass Vertical Acceleration 2R.H. Gear Upper Mess Longitudinal Acceleration 2L.H. Gear Upper Mass Vertical Acceleration 2L.H. Gear Upper Mass Longitudinal Acceleration 2R.H. Gear Strut Position 3L.H. Gear Strut Position 3R.H. Gear Strut Velocity 4L.H. Gear Strut Velocity 4R.H. Gear Metering Chamber Pressure 3L.H. Gear Metering Chamber Pressure 3L.H. Geer Shock Strut Rebound Chamber Pressure 2R.H. Gear Strut Air Pressure 3L.H. Gear Strut Air Pressure 3R.H. Gear Drag Brace Load 2L.H. Gear Drag Brace Load 2Nose Gear Strut Position 3Nose Gear Upper Mass Vertical Acceleration 2C.G. Normal Acceleration (Low Range) 2C.G. Normal Acceleration (High Range) 2C.G. Longitudinal Acceleration 2Aircraft Pitch Attitude 3Aircraft Roll Attitude 3R.H. Wing Tip Vertical Acceleration 2L.H. Wing Tip Vertical Acceleration 2R.H. Gear Reaction Platform Vertical Load 2R.H. Gear Reaction Platform Drag Load 8L.H. Gear Reaction Platform Vertical Load 2L.H. Gear Reaction Platform Drag Load 8Nose Gear Reaction Platform Vertical Load 2R.H. Wing Lift Link Load 2L.H. Wing Lift Link Load 2Timing Clock 0.1

PREPARED BY: S. Iydesant DOUGLAS AIRCRAFT COMPANY, INC. PAGE _ -_37_-_ - -CHECKED BY; LONG BEACH DIVISION MODEL: __•4D--

TITLE._IAUAn- AD INV-PUI•GATION LAB0RATORY 110111 T .S - REPaORT NO. I8 40641

FREOUENCY RESPONSE CHARACTERISTICS OF RECORDED PARAMETERS

FLAT RESPONSE-CPSPAUb EE__R.H. Gear Vertical Load 115 135R.H. Gear Drag Load 55 95R.H. Gear Side Bending Moment 90 180L.H. Gear Vertical Load 65 195L.H. Gear Drag Load 50 100L.H. Gear Side Bending Moment 65 190L.H. Gear Lower Mass Vertical Acceleration 60 180L.H. Gear Lower Mass Drag Acceleration 135 150L.H. Gear Lower Mass Lateral Acceleration 155 175R.H. Gear Lower Mess Vertical Acceleration 110 130R.H. Gear Lower Mass Drag Acceleration 45 75R.H. Gear Lower Moss Lateral Acceleration 40 60R.H. Gear Upper Mass Vertical Acceleration 50 85R.H. Gear Upper Moss Longitudinal Acceleration 105 130L.H. Gear tipper Mass Vertical Acceleration 50 85L.H. Gear Upper Mass Longitudinal Acceleration 60 90R.H. Gear Strut Position 65 110L.H. Gawr Strut Position 55 90R.H. Gear Strut Velocity 45 70L.H. Gear Strut Velocity 50 90R.H. Gear Metering Chamber Pressure 70 180L.H. Gear Motering Chamber Pressure 60 185L.H. Gear Strut Rebound Chamber Pressure 55 185R.H. Gear Strut Air Pressure 15 40L.+4. Gear Strut Air Pressure 15 40R.H. Gear Drag Brace Load 60 100L.H. Gear Drag Brace Load 50 80Nose Gear Strut Position 80 135Nose Gear Upper Mass Vertical Acceleration 120 145C.G. Normal Acceleration (Low Range) 25 40C.G. Normal Acceleration (High Range) 40 55C.G. Longitudinal Acceleration 20 35Aircraft Pitch Attitude 30 35Aircraft Roll Attitude 20 35R.H. Wing Tip Vertical Acceleration 65 160L.H. Wing Tip Vertical Acceleration 50 80R.H. Wing Lift Link Load 55 170L.H. Wing Lift Link Load 125 145

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DATE- August D6 'IVISION m409.

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CIK9BY FC.AIAl*RCR FT _______MOEL__,_D _

DATE! August l MSO MbL ______

_____Trnc DROP TESTS O LAýrJTNC al,0ADS INVhSTTGPTTON RsOR -OE4 0 6 41

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D'iOP TESTS FOFH LANDING LOADS INVEnTIGATION 4 E-064

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CHECKED mrs I9 Mouby LONG REACH DIVISION MODEL: A4D-?

TITLE, L 'NDINA; LoADS I•h'EFTTGATION LABORATORY DROP. TEý';1 REPORT NO.ES- 4 0641

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TITLE, L&NDTNG LWAn INVFSTIGATION LABORATORY DROP TESTS EPORT. -q-0641!

GROUND LOADS

Vertical and horizontal loads at the ground obtained fromthe strut instrumentation and the equations on Page 24are presented on Pages 69 to 84. A comparison is madewith the loads registered on the reaction platfirm.

In discussing the probable accuracy and reliability ofthese data, it is desireable to review briefly theprocedure used in the calibration of the axle straingauges which supp'ly the primary input for the "strut"ground loads data. A complete discussion of the calibrationprocedure is contained in Reference 1.

This procedure consisted of comparing the verticalground load from strut data computed by Equation 12,with the vertijal readings of the reaction platform.The comparison was made at .002 second intervals andthe strain gauge constants were chosen such that theaverage error was minimum. Since the reaction platformdrag measurement was not considered to be reliable,

4 comparisons were made for the drag direction in perfectlyvertical drops without spin-up, in which the drag load

Puwas known to be zero.

Thus, good agreement between the average vertical plat-fc;rm load and the average vertical strut load could beexpected by the nature of the calibration. At anyInstant of' time, however, differences might be expected,such differences being introduced primarily by relativeaccuracy of the dynamic- responses of the strut instru-mentation and the platform.

It is noted tl~t In the first .03 seconds the peak verti-cal load from the reaction platform always exceeds thepeak verticýal load measured by the strut. This phenomenonis attributeo to the response characteristic of theplatform. Although a complete investigation of the dynamiccharacteristics of the platform has not been made, ithas been determined (Reference 5) that the fundamentalfrequency in the vertical direction is 22 cycles per secondwhich is close to the frequency of the first load peak.The high reaction platform load at this point is, therefore,believed to be dynamic overshoot. In view of this fact,the load variation shown by the strut in this region isconsidered more reliable.£

b,)

FOmi Lots. S. I AOLS,.) PREPAROSY: F. C. Allen DOUGLAS AIRCRAFT COMPANY, INC. PAGE: 64

DATh

CHICKED BY1 L. B. N. LONG $LACH DIVISION MODELt A4D-2TTLEt LANDING LOADS IMSTIOATION LAORATOR DROP TUSTS REFoRTNO. ES-40641

Substantial diffoie on are noted between the strutdrag lead and the reactien platform drag load. Fteadingsof the reaction platform in the drag direction have beenviewed with skeptiolem for some time inasiuuh as theeis a high coefficlint of friction between the plate andthe rollers under high load which inhibits an aseurateresponse to hfh frequencies. This leek of high frequeneyresponse is evident both in the initial peak drag leadsand in the subsequent eseillations where Atke reaetienplatform appears to be a reugh average between the peaksof the load obtained by the strut instrumentation. Onthe other hand, the eoetfisients of friction cemputedfrem the left hand gear strut leads are hhr than anyknom previous ebszevation, and in view of the ditfrenmoesbetween the left and right hand coefficients, sme skepti-aim regarding the acuracy of the left gear drag leadreadizns Is warantod. The following paragraphs disownsthis point in detail.

Table VI sumarizes the coefficients of friction data.

VOWN L62%.S. tAS.,1 PREPARED BY, F. C, *Allen DOUGLAS AIRCRAFT COMPANY, INC. PAGE 65

cHecKED SY, L. B. X. LONG IEACH DIVISION 0 MOCEL, A4-2TITLE. LANDING LAON INVESTIOATION LABORATORY DR9; TESTS .REPORT NO.3-406 41

Table vi

COWXPICIENTS OF FRICTION AND SPIN-UP TINE

Drop Source Coefficient of Friction Spin-Up Time**No. Left Gear Right Oear Seoonds

Average Mazimum* Average Maxinm*m Left Right

84 Strut .73 1.28 .48 .76 .044 .050

Platforo .52 .64 .30 .42 .0o4 .048

70 Strut .65 1.19 .55 .68 .047 .059

Platform .63 .63 .46 .60 .046 .05868 strut .66 1.0* .53 .75 .o01 .050

Platform .46 .59 .44 .61 .040 .04793 Strut. .80 1.33 .54 .70 .036 .040

Platform .47 .58 .46 .70 .036 .040

82 Strut .76 1.14 .65 .72 .042 .048

Platform .50 .64 .5 .78 .041 .048

75 Strut .72 1.10 .52 .66 .035 .042

Platform .48 .63 .51 .63 .035 .04378 Strut .72 1.36 .44 .68 .047 .054

Platform .48 .66 .50 .91 .043 .05388 Strut .87 1.55 .62 1.03 .0o8 .057

Platform .47 .62 .*5 .61 .0o45 .053

* Points prior to t .01 are ignored.

* To be preOise, in drop tests this is "spin-down" time.

MOW LeaS. S. I'%PRE 5, PARIED my' P. C. Allen DOUGLAS AIRCRAFT COMPANY, INC. 66

CHICKDIJ• , e M oTtPAGE 6CHECKEDV L. B 1 LONG B.ACH DIVISIN MODEL,_ A4D-2

YTuLE, LANDING LOADS IMSTIOATION LABORATORY DROP TESTS ... 301'I'

The data We further summarized in the following tablein whioh the peculisar nature of the left gear data isapparent:

Coef'ficient of F'riction Avg.Spin-Up

Average 11aximun Average Average Timeo-oe

Left gear - Strut 1.25 .7-4 .3

Platform .63 .50 .41

Right gear - Strut i •75 .54 .50

Platfemr .66 .46 .49

This table shows that the strut instrumentatien (bothright and left) gives higher drag loads than theplatform. It also shows that the left gear spit-up

nie is on the averose substantially less than theright, homes higher drag loads would be expeooted forthe left gear.

To further explore the aoouraoy of the drag data, thevheel RPM was eomputed froe the equation

RM W 0 [(R- C) - FM * dt

Where IZ , the polar umoent of inertia of the retating

massi,

R , Tire radius

C 0 Tire deflection

IHO - Drag fore* at the ground

The integration was carried out from time of sontaotto the time that F11 reduees to zero. The followingresult•s were obtained s

4

Fo040 L211. S- IA

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TITLE: LANDING LOADSI•STIGATION LABORATORY DROP TESTS R1PONT NO.ES-- 4 064 1

Table VII

Comparison of Caloulated and Measured Wheel Angular Velocity

Drop Source Wheel Rotational VelocityNo. Left Gear Right eaar

RM Dev.Frm RPM Dev.Frommesa. % .mess. %

84 Diract Measurement 1811 1794

Calculated - Strut Data 2112.8 +16 1671 - 7.1

Zalculaaed - Platform Data 1734.6 -4.3 928 -48.4

70 Direct Measurement 2097 2089

Calculated - Strut Data 2082 - .1 2037 - 2.8

Calculated - Platform Data 2035 - .3 1937 - 7.9


Calculated - Strut Data 2138 +11 2137 +11

Calculated - Platform Data 1670 -15 1810 - 5.7

93 Direoc measurement 1936 1912Calculated - Strut Data 2352 +21 2016 + 5.1

Calculated - Platform Data 1628 -19 1781 - 7.1


Calculated - Strut Data 2542 +22 2257 +10

Calculated - Platform Data 1794 -b15 1921 - 6.3

Average Deviation from Measured INI

loft Right

Strut +14.4 + 3.0

Platform -10.1 - 6.8 •

,s Neglets Damop 84

FO06NL6Z2 S IA

PREPARED BY, F. C. Allen DOUGLAS AIRCRAFT COMPANY, INC. PAGE, 68CHECKED ,.S. L. B. X. 0"" LONG iACH DIVISION MODEL,: AD-2TITLE: LANDING LOADS I MSTIOATION LABORATORY DROP TESTS REPORT Mo. ES-4064I1

The caleulations associated with the foregoing tableare inherently of low accuracy because of the possiblevariation in polar moment of inertia of the wheel andtire. 3he value used in these ealculations, 11.26slug-in , was obtained from manufacturer's data and isconsidered accurate within -15%. In addition to varia-tions eaused by dimensional tolerances and wear of thetire, 1p will vary with rotational velocity and with age,these latter variations tending to increase the momentof inertia by approximately 10%. If the left hand gearmoment of inertia were lO higher than the right, Table VIIwould show reasonable eorrelation for the left hand gear(I.e., the deviations shown would be reduced by 10%).Definite conelusions regarding the aceuracy of the dragdata cannot, therefore, be drawn from the spin-upcalculatiens.

The high coeffioient of friction for the left gear stillremains to intriae an element of doubt on othe accuracyof the left gear drag data. Before the possibility ofdrag coefficients in excess of 1.0 is abandoned, it isreomeended that a low speed sliding coefficient offriction test be conducted using the actual platformsurface. Reference (6), Page 23, shows a rough corre-lation between sliding coefficient of friction and valuesobtained from dynamic tests. Should the sliding coeffi-cisnt of friction for the platform be substantially higherthan that shown in Reference (6), there would be cause tobelieve that dynamic coefficients in excess of 1.0 couldbe reached in drop test.

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CHECKED MYLI Be me N LONG BEACH DIVISION MODEL.- A:D-

TITLEM LANDINO LOADS INVAITIGATION LABORATORY DROP TESTS REPORT O... __-_0_

SUNlARY 01 N]IWSTS AND COrWSIONS

The signLficanoe of these dreop test data and comparisonswith flight landings, theory and NASA data are consideredin the sunmary report Reference (3)). The present reportis more concerned with the presentation of data and anevaluation of the overall accuracy of the instrumentatienunder test conditions.

The estimated accuracy of the individual instrumentssupplied by Reference (1) and avmarised in Table IVis foor the most part substantiated by a study of theresulting data and by subsequent usage in the comparisonscarried out in Referenlo (3). Area" of conoern have beennoted and discussed In previous sections and eonsist prin-cipally of the followings

1. Sinking Speed

Accurate measurement of the sinking speed, Vo,has proved difficult even under laboratory a Q I-tions. An noted on Page 19, the determinationof sinking speed by the elapsed time method is themost accurate and is limited by the determinationof the precise mements of release and contact.Instrument accuracy is sufficient to determine timeto .001 seconds or leos, but since the airplane inflexible, aocelerations created by operation of thereleae mechanism and by contact with the groundare not felt simultaneously by all parts of theairplane. Hesse, 1, can be ascertained only tot.004 seconds which introduces a possible error

* of +.13 feet per second. This, in turn, createsa possible error of 2% in the kinetic energy of anominal 13 fps drop.

The difficulties described above will probably beencountered with any existing eMhod of measurementand considerable effort would be required to improveaocuraoy. It is believed, however, that the accuracyobtained in sufficient for the purposes of thisproject.

room LS25- S LA

13 S PREPARED BY: F. C. Allen DOUGLAS AIRCRAFT COMPANY, INC. PAGE: 86DATL

CHECKED BY: L. B. K. LONG lEACH DIVISION MODEL: A4D-2DATE

TITLE, LANDING LOADS INVESTIGATION LABORATORY DROP TSTS- REPORT NO.ES-'6•4

2. Strut Position

Strut position was obtained from two sources,namely, the slide-wire device and by integra-tion of the velocity generator reading.Differences up to 1.5 inches have been noted indata from these two instruments. Since theslide wire is the more direct measurement andis less complicated, its readings would noremallybe considered the more reliable. However, thedata frz' the velocity generator agrees betterwith thfery and, hence, some doubt is east onthe slide-wire reading. This discrepancy canonly be resolved by additional testing or cali-bration. Such work should consist of (a) simul-tAneous readings of the two instruments while thestrut is being moved rapidly through a known dis-placement and (b) with the strut fixed, simultarmuoreadings during the application of a high load.The first test would determine the effects ofvelocity on instrument accuracy, and the second,the effects of structural deformations.

3. Ground Loads

The comparison of vertical ground loads providedon Pages 69 to 84 indicates general agreementbetween strut instrumentation and reaction plat-form. One exception is on the first peak wherethe reaction platform Is consistently higher.This has been attributed to dynamic overshootof the reaction platform.

Agreement between drag loads obtained from strutinstrumentation and the reaction platform isgenerally poor. This lack of agreement wasexpected since lack of accuracy of the reactionplatform in the drag direction under dynamicconditions has been previously noted in ether work.The right hand gear drag loads from strut instru-mentation appear to be generally consistent andreasonable. The left hand gear drag loads fromstrut instrumentation appears to be hgh" by afactor of 10 to 20% although definite proof ofthis fact is not available.

FOW L925. S. I1A

(, 52) PREPAREDBYi P. C. Allen DOUGLAS AIRCRAFT COMPANY, INC. PAGE: 87

CHECKED Sy, L. B. M. DTt LONG lEACH DIVISION MODEL_ AD-2

TITLE, LANDING LOADS IMSTIGATION LABORATORY DROP TESTS REPORT 0.o.ES-0641

Conclusions

1. The drop test data presented herein can generallybe used with confidence within the limits ofaccuraoy specified in Table IV with the followingexceptions:

a. Sinking speed, Vv, accuracy is within .+0.13feet per second.

b. Strut position given by the slide wire is Inquestion since results obtained therefromdiffer from the velocity generator data by asmuch as 1.5 inches.

c. Vertical ground loads and right hand gear dragloads are considered to be accurate withint5%. Left hand gear drag loads appear to behigh and should be used with discretion.

2. Additional calibration of the slide wire andvelocity generator is recommended in order toresolve the discrepancy noted above. A dynamiccalibration of the reaction platfor• is alsorecommended in order to provide better data onfuture tests. A test is recommended for deter-mining the sliding coefficient of friction of thetire on the platform surface.

I I I 0

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CHECKED Y: Z- LONG B DIVISION AOO,.A..-iTLEL•MID•A WADS i-MIGAT!ON I LUEUO'ORY DKOP TES& REPORT NO. 0641

REFERENCES

1. Harris, I. E. and Meriwether, H. D. : Landing LoadsInvestigation Instrumentation. Douglas Aircraft Co.Report ES 40636, September 1962.

2. Harris, I. E. and Tydeman, S. F.: Flight TestMeasurement of Landing Loads on the AD-2 Airplane.Douglas Aircraft Co. Report DEV 3616, Oetober 1962.

3. Mosby, L. B.: An Investigation of the Landing LoadsExperienced by the A4D-2 Airplane During Flight Testsand Drop Tests and a Comparison with Theory.Douglas Airoraft Co. Report LB-31038, October 1962.

4. Horme, Walter B.i Experimental Investigation ofSpin-Up Friction Coefficients on Concrete and .Non-Skid Carrier Deck Surfaces. NASA TN D-214, April 1960.

5. Cook, P. E.s Analysis of Model A3D Series LandingGear and Flexible Airplane Structure During LandingImpact. Douglas Aircraft Co. Report ES 26886,November 1957.

6. Batte*rsen, Sidney A.1 Investigation of the MaxImmSpin-Up Coeffielonts of Friction Obtained During Testsof a Landing Gear Having a Static Load Rating of20,000 Pounds. NASA Memo 12-20-58L.

I

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DATE

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TITLe LANDING LOADS INVESTIGATION LABORATORY DROP TESTS REPORT o.ES-4064l

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