Document
NASA-TM-4703 NASA Technical Memorandum 4 7 03 [ _ q [ 00 £) [o ]C_ I
The NASA Landing Gear Test Air pl ane
John F . Cart er and Chri stoph er J . N agy
F OR REFERENCE
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LANGLEY RESEARCH CENIE R June 1 9 9 5 LIBRARY NASA NASA Technical Library i 3 1176 01423 7045
T he N A S A La n ding Gear Test A irplane
John F . Carter NASA Dryden Flight Research Center Edwards , CA Christopher J . Nagy PRC Inc .
Edwards , CA
Technical Me m orandum 470 3 June 1995
ABSTRAC T A tire and landing gear test facility has been developed and incorporated into a Convair 990 aircraft.
The system can simulate tire vertical load profiles to 250,000 lb, sideslip angles to 15 degrees, and wheel braking on actual runways. Onboard computers control the preprogrammed test profiles through a feed- back loop and also record three axis loads, tire slip angle, and tire condition. The aircraft to date has pro- vided tire force and wear data for the Shuttle Orbiter tire on three different runways and at east and west coast landing sites.
This report discusses the role of this facility in complementing existing ground tire and landing gear test facilities, and how this facility can simultaneously simulate the vertical load, tire slip, velocity, and surface for an entire aircraft landing. A description is given of the aircraft as well as the test system. An example of a typical test sequence is presented. Data collection and reduction from this facility are dis- cussed, as well as accuracies of calculated parameters. Validation of the facility through ground and flight test is presented.
Tests to date have shown that this facility can operate at remote sites and gather complete data sets of load, slip, and velocity on actual runway surfaces. The ground and flight tests have led to a successful validation of this test facility.
NO M E N C L AT U RE deg degrees DFRC Dryde n Flight Research Center, Edwards, California Hz Hertz KGS knots ground speed KIAS knots indicated airspeed KSC John F. K ennedy Space Center, Florida LSRA Landing Systems Research Aircraft n mi nautical miles psi pounds per square inch STS Space Transportation System I NTRODU C T IO N Tire and landi n g gear de v elopment and testing for aircraft are usual l y d one by ground test faci l ities due to the expense and hazards associated with testing on aircraft.
Tire dynamometer and sled tire track are the two facilities used mainly for dynamic tire testing. Exist- ing facilities have limitations in simulating the landing surface, time varying vertical loads, and tire slip angles.
Tire dynamometer facilities roll aircraft tires against a metal drum at any combination of velocity, vertical load, and slip angle. These facilities have the advantage of long run times, very good load and speed control, and good control of the slip angle of the tire. However, dynamometers have disadvantages for dynamic tire testing, such as 1) the dynamometer rotary drum surface does not accurately simulate a runway surface, 2) the curvature of the contact area of the drum causes incorrect radial tire deflection during the test, and 3) heat build up of the drum causes the temperature of the test tire to be abnormally high.
Because of these problems, dynamometer data are used primarily to measure the strength and endurance of tire carcass material, not the tire surface forces or wear. Appendix A shows a tire dynamometer at Wright Patterson Air Force Base in Dayton, Ohio. An example of data obtained from this type of dyna- mometer is given in reference 1.
Tire sled-type facilities mount the tire on a carriage and move the carriage down a straight path. 2 A test surface can be constructed which simulates an aircraft runway, but the process can be time consum- ing and may not accurately represent the surface. Existing facilities also have problems due to their limit- ed run times, limited capability for time varying vertical load, speed, and tire slip angle control. Because of limited track length, simulations of complete aircraft landings typically are completed in segments, with a single landing test requiring as many as five test runs. In addition to the inconvenience of multiple runs, cooling of the test tire between runs can cause inaccurate results.
The unique design of the Space Shuttle Orbiter landing gear with its highly loaded tires, hazards asso- ciated with tire failure, as well as limited opportunities for landing test data from the vehicle resulted in a strong reliance on tire test facilities. Because of high landing speeds, high vertical loads, long roll out dis- tances, and unusually rough runway surfaces, existing tire test facilities have had difficulties in accurately simulating the tire wear and forces of an entire shuttle landing.
The Landing Systems Research Aircraft (LSRA) is a unique addition to complement existing aircraft dynamic tire testing facilities. Its capabilities are compatible with the Space Shuttle Orbiter requirements.
The design goal of the LSRA is to conduct dynamic tire testing on an actual surface while simulating ver- tical loading, tire slip angle, and speed of an entire aircraft landing simultaneously. Computer control of a tire test fixture allows for precise control of vertical load and slip angle of the test tire. The computer con- trol software also provides a speed advisory to the pilot. These capabilities make it possible for the LSRA to recreate a realistic combination of run distance, runway surface, vertical load, tire slip angle, and ground velocity for aircraft landings.
The LSRA is the result of a cooperative effort of the Dryden Flight Research Center (DFRC), Lyndon B. Johnson Space Center (JSC), John F. Kennedy Space Center (KSC), Langley Research Center (LaRC), Ames Research Center (ARC), and many industry and military organizations. Flight test has been conducted on runways at Edwards Air Force Base and KSC.
This paper describes the systems and capabilities of the LSRA vehicle. In addition, this paper discuss- es ground calibration and flight tests used to validate the LSRA as a test facility.
AIRCRA F T DESCRIPTI O N Th e NASA Convai r 990 ( SN 10- 2 9 , tail No . 8 1 0 ) i s a h ig h - spe ed , medium r ange , lo w - sw e p t- w ing j e t tran s port ( fig . 1). T h i s aircra f t i s equipped w it h f ou r w ing-pylon mounted G ene r al Ele c t r ic ® CJ80 5 - 2 3 a f t f an tu rb o j et engine s and a f ully r et r acta b le t r i c ycle landing gear ( t h e main gea r can no longe r b e re - t r act e d wit h t h e LS R A modifi c ation ). T h e air c raf t i s controlled b y dual wh eel and c olumn s located in t h e coc kp it . The c ontrol s u rf ace s ar e mov ed u s ing a com b ination o f m ec h anically d r iven fl ig h t ta bs an d h y- drauli c s . Th e b a s ic cont r ol s yst e m is augmented w it h a ya w damper wh ic h d r iv es t h e r udd e r .
Th e LS R A under w ent signific an t structuralmodifi c ation to provide s p ac e f or t h e test ge ar and als o to r e a c t t h e t es t gear load s into t h e aircra f t. No r mal ai rcraft structur al facto rs of sa fe ty wer e maintained fo r all t h e original str u ct ural de s ign condition s plu s t h e additional loading c ondition s f or landing gear testing as defined in t h i s r eport .
Th e p r imary com p onent s o f t he landing g e a r test s yst e m added to t he LS R A ar e s h o w n in fi gu r e s 2 an d 3 . Figure 2 id e ntifi e s th e test pallet sy s tem el e ment s wit h in th e aircraft . T h e h yd r aulic po w er of t h e ge ar t e st pallet i s provided b y ac c umulator s wh ic h u s e compres s ed nitrogen ga s . On b oard h ydraulic pump s ar e us e d to pr e ss urize t h e a cc umulators. T h e t e st p allet sy s t e m i s controlled b y a test conducto r c onsol e w h i ch cont ai ns har d ware s w it ch ing c apa b ility an d syst e m monitoring capa b ility . Included in t h e system i s a comput e r wh i ch controls t h e motion of t h e test ge ar p alle t . I n addition to t he vertical load, t he t e st p al let s ystem can apply b raking to t h e te s t tire. Aircraft p e rf orm anc e s pe c ifi c ations bef o r e and after t he LS R A modification are presented in ta b le 1.
F igur e 3 s h o ws t h e pall e t w h i ch i s t h e interface point be t we en t he test fixture and t he landing gea r t es t s y s tem. T h e p allet is atta ch ed to t h e air c ra f t t h roug h a p ai r of p a ral lelogram swing lin ks wh ic h rest rai n t h e t es t ge ar in pitc h, roll , and ya w. T h e top of t h e test p al let is attac h ed to t w o h ydrauli c a c tuators wh i ch provide t he ve rt i c al reaction load. T h e vertic al load s ar e r e a c t e d into t h e ai rframe t hr oug h a t ru ss syst e m lo c ated inside t h e c a b in.
® T h eCJ805- 2 3 engineis aregistered trademark ofGeneral E lectric, Lynn,MA .
T able 1. Aircraft o perati o nal limi t s bef o re an d after L SRA modificat io ns.
Original LSRA CV99 0 Aircraft Max. taxi weight, lb 255, 000 250, 000 Max. take o ff weight, lb 245,0 00 245,00 0 Max. landing we i ght, lb 2 0 2, 0 0 0 225, 0 00 Max. lan d ing speed, kgs 195 23 0 Max. range, n mi 30 0 0 600 Max. ceiling, ft 41,000 13,0 00 Max. vel o city, KIAS 520 25 0 Empty weight, lb 115,000 177,0 00 NOTE: d ata taken fr o m o perati o ns manuals o f the CV99 0 / LSRA.
SYSTEM CAPABILITIES Many landing g ea r te st fix t u r e s can b e attached t o the LSRA te st palle t . C u rr en t ly two a tt achmen ts have b een de s igned. O ne i s a modified s hu tt le main landin g g e ar s t r ut wi t h dual t i r e s , the o t he r i s a s ingle ti r e fixtu r e t hat contain s a r ota r y ac t uato r w h i ch c an b e t u r ned fo r de s i r ed s lip angle. Table 2 p r e s en ts th e maximum load and s tee r ing capabili t y of t he L SRA fo r the s e two fix t u r e s .
Figu r e 4 s how s a model of t h e s ingle t i r e fix t u r e. T h e fixtu r e f r ame i s at t ached t o th e t e st palle t . Thi s f r ame hou s e s t he ro t a r y actuato r which t urn s the te s t t ire axle a ss em b ly. Ti r e br akin g i s applied t h r ou gh t he b r a k in g a ss embly. Thi s te s t fixtu r e wa s u s ed exclu s i v ely fo r all t he t e s ting de s cribed in thi s r epo r t.
A t e st compute r con tr ol s t he te s t ti r e v e rt ical load and slip angle u s ing feedbac k loop s , and s end s a di s c r e t e s ignal to ac t i v ate the wheel b r a k e. Table 3 s how s th e capabili t ie s of the con tr ol s y st em. D u r ing a te s t, the compute r al s o di s play s to th e pilo t th e diffe r ence b e t ween t h e cu rr en t mea s u r ed g r ound s peed and the de s i r ed s peed p r ofile fo r t h e te s t. The t e st t i r e ve rt ical load feedback i s p r o v ided directly f r om ve rt ical T able 2. Structural l o ad capabilities o f the L SRA.
Main gear Variable yaw fixture dual tire single tire Vertical load, lb 250 , 000 , -50,000 150,000, - 25,000 Drag load at tire contact point , lb + 100 , 000 + 50 , 000 Side load at tire contact point, lb + 40,000 + 40,000 + 800 , 000 Brake torque, in-lb N / A - 250,000 Steering torque , in-lb N / A 380,000 Table 3 . Performance of the LSRA test system with the single rotational tire fixture.
Load control system max rate, unloaded -- - t-5 ir d sec Load control system max rate, max load 7 ir d sec Steering control system max rate 35 deg / sec Maximum steering angle + 20 deg Load control system bandwidth 2 Hz Steering control system bandwidth 3 Hz Maximum error from commanded profile, load + 3000 lb Maximum error from commanded profile, slip .25 deg Typical error from commanded profile, speed + 10 kts load cell measurements while the slip angle is computed, as seen in figure 5, from a combination of an angular displacement sensor on the steering fixture and two optical ground velocity sensors which pro- vide aircraft slip angle across the runway.
SAFETY SYSTE M S The test pallet system includes a fail - safe fe a ture which retr a cts the test pallet to its stowed position.
Pallet retraction can be caused by fault detection in hardware or software. The gear control system fault detection software performs comparisons between redundant input signals, compares input signals to minimum and maximum output values, and compares steering and extension values to simulated predic- tions. Hardware fault switches detect over extension, ground contact, and over rotation of the test pallet.
If the test pallet cannot be retracted due to a mechanical failure, the hydraulic actuators can be separated from the test pallet by explosive bolts. The tire retraction and the actuator separation can be performed manually by either the test conductor or the pilot.
In addition t o the test pallet retr a ction system, there are t wo fi re suppression systems associated with the test pallet system. A water deluge system was installed which can spray water directly on the CV990 main landing gear tires, brakes, and the test tire. A halon fire suppression system was placed in the cargo bay near the hydraulic pumps to extinguish any fires in that area.
TES T O PERA T I O NS Flight planning a n d data analysis are performed with the aid of a six-degree-of-freedom simulation resident on a desktop workstation. This simulation was programmed using the FORTRAN® computer language and executes at 100 Hz, with a 400-Hz execution for landing gear dynamics. Aerodynamic data used in the simulation were obtained from wind tunnel models, and then refined using data obtained dur- ing early NASA flight test of the CV990. The workstation is interfaced with a gear control computer which is a duplicate of the aircraft gear control computer. This configuration allows for production and hardware-in-the-loop simulation testing of new time history profiles, as well as verification and valida- tion of flight software revisions. The workstation and duplicate aircraft gear control computer configura- tion were designed to be portable so that simulation, analysis, verification, and validation functions would be retained at remote testing sites.
The time history profiles of load, slip, and speed are produced using output from this simulation, and then converted to a binary format which is loaded onto a data diskette. After testing the profiles on this disk using the hardware-in-the-loop configuration, this data diskette is then used to load the profiles onto the aircraft gear control computer. A new time history profile can be developed in approximately one hour. A new gear control software version can be qualified for flight in approximately three hours.
Figure 6 shows a t ypical l anding test seque n ce. The CV990 a ircraft makes a final approach. After touchdown and derotation, the pilot calls for test initiation and uses spoilers, thrust reversers, and brakes to follow the pilot speed advisory. The test gear is extended and controlled to match the preprogrammed test profiles of vertical load, slip angle, and braking on the test tire. Upon completion of the test, the test gear is automatically retracted. If a problem occurs during the test, either the computer or the hardware fault detection system will command a retraction of the test gear. If a retraction does not occur, the test ®FORTRANis a registeredtr a demarkof Information ProcessingTechniquesCorp . ,P a loAlto,CA.
conductor or pilot can unload the test fixture by exploding the bolts connecting the test gear assembly to the hydraulic actuators, thus relieving the vertical load to the test gear assembly.
The LSR A has performed approximately 100 test operations at Edwards AFB and KSC. During these operations, all flight test profile preparation, data reduction, and analysis were performed at the test site.
DATA REDUCTION The LSRA can collect onboard data or telemetered data. The data rates for the parameters range from 25 to 200 Hz. The test pallet has been instrumented with load cells in three axes. Appendix B presents the equations for calculations and corrections for vertical, side, and drag loads. Accuracies of the measured loads for the Shuttle Orbiter tire tests are + 3000 lb vertical load, + 500 lb side load, and + 300 lb drag load.
In addition to the onboard and telemetered data, the LSRA has video cameras which can provide five different views of the tire fixture. These cameras allow for real-time monitoring of tests, as well as post flight analysis using video tape which is synchronized with the other data. High-speed film of tests is also available.
TEST VALIDATION / FLIGHT TEST RESULTS Calibration of the LSRA load cells was performed at DFRC. This was done by attaching static test equipment to the test pallet and loading it to known values of vertical, side, and drag loads. This calibra- tion effort provided information to validate the LSRA gear control software calibrations, provided infor- mation on elastic deformation of the test fixture, and verified post flight data measurements.
The LSRA has performed two validation landing simulations; one was performed at the Edwards AFB concrete runway, the other at KSC. The purpose of these tests was to validate the LSR A as a tire testing facility by simulating an actual Space Shuttle Orbiter landing and comparing the test tire wear from the LSRA to the tire wear of the Space Shuttle Orbiter. While both tests were successful, only the KSC test will be discussed in detail to illustrate the process. The Space Shuttle Orbiter landing chosen for the comparison was the STS 51-D landing. On this landing, the Space Shuttle Orbiter landed on Runway 33 with approximately 8 knots of crosswind from the right-hand side of the vehicle. The weight of the Space Shuttle Orbiter was approximately 200,000 lb. Inertial platform data as well as strain gage data recorded from this landing were used to derive the load, slip, and speed profiles for the left inboard main gear tire of the Space Shuttle Orbiter. The local tilt angle of this tire during the Orbiter landing was simulated by raising the right-hand strut of the LSRA until the test tire tilt angle was approx- imately -1.6 deg (left wing down).
The LSRA performed the profile shown in figure 7 on Runway 33. A load "spike" was placed at the beginning of the load time history profile to create the initial load of 70,000 lb to simulate initial tire touchdown. After the initial load, the average load control for the time history stayed within +3000 lb of the target value. The slip controller held the slip angle to within approximately .40 deg until the speed fell below 50 knots, at which point the resolution of the optical sensors caused some steering oscillations. The steering system exhibited an oscillation of approximately .2 deg at 2 Hz. Subsequent slip controller im- provements have eliminated these two anomalies. Figure 8 shows a time history of the achieved slip an- gle plotted against the commanded slip angle after the improvements were made. The steering system currently holds the slip angle to within .25 deg o f c o mmanded slip angle throughout the speed range. The roll out of this test was estimated to be 10,300 ft, and the roll out of the Space Shuttle Orbiter test was 10,000 ft. The outside air temperatures were approximately the same between the LSRA test and STS 51-D landing. Figure 9 compares the LSRA test tire with the STS 51-D Space Shuttle Orbiter tire.
For both tires, three cords were exposed on the left-most rib, and most of the other ribs were worn off.
This near identical tire wear was a significant factor in the validation of the LSRA as an Space Shuttle Orbiter tire test bed.
The LSRA effort has provided significant data to the Space Shuttle program. Tests on the Edwards Air Force Base dry lakebed runways were used to redefine the tire drag model used in Space Shuttle Or- biter simulations and flight planning. A 20-knot crosswind capability was demonstrated for Space Shuttle Orbiter landings on the Edwards Air Force Base concrete runway, and LSRA testing helped define the ef- fects of ply steer and wheel tilt on the Space Shuttle Orbiter tire force model. The most significant contri- bution of the LSRA to the Space Shuttle Orbiter program is the tire wear data that contributed to defining the need for the KSC shuttle landing facility runway resurfacing.
CONCLUDING REMA RK S The L anding Systems Research Aircraft (LSRA) provides a unique test bed for landing gear testing which can reproduce vertical load, speed, slip angle, and actual runway surface.
Validation of the LSRA concept was achieved by recreating tire wear from actual Space Shuttle Or- biter landings based on profiles from Space Shuttle Orbiter data. Static load calibration tests have verified the flight measurements of the LSRA. Flight testing has shown the LSRA to be an efficient test facility at remote sites.
The LSRA has had a significant impact on the Space Shuttle Orbiter program. Tire force and wear data from the LSRA were instrumental in upgrading tire force and wear models used by the Space Shuttle Orbiter program. LSRA data helped to define the resurfacing requirements for the smoothing of the KSC runway su rf ace.
The testing on the L SRA i s complementary to the existing national dynamometer an d test track facil- ities. By comparing and cross checking tire force and wear data under actual landing conditions, this fa- cility can validate results from other tire testing facilities.
Flight test of the system showed that the vertical load time history profile can be tracked within + 3000 lb, and the tire slip profile can be tracked within + .25 deg. This performance was considered ac- ceptable for this application.
Features such as a generic test pa l let th a t can have many d i f ferent test fixtures att a ched to it, and the ability to change commanded time history profiles of the load, slip, and speed have ensured that the LSRA is a useful tool as a generic test bed.
REFERENCES 1 . Beall , Leman G ., Dyna mometer Evaluati on of Continu ous Ta pe Wound Type III Aircra ft tir es , Tec h - nical Repo r t AFFDL- TR -69- 1 0 2, Dec . 1 969 .
2. Davi s, Pa m ela A ., S an dy M . S t u bbs, and Jo h n A . T anner , Aircra ft Landi ng Dyna mics Facili ty , A Uni qu e Fac ili ty Wi th New Ca pa bili ti es . SAE Tec h Paper Se r. 85 1 938 , Oct . 1 98 5.
BIBLIOGRAPHY Beall, Leman G . : Dyna mometer Evalua tion of Con tinu ous Ta pe Wound Type III Aircra ft tir es, Tec h nical R epo rt AFFDL- TR -69- 1 0 2, Dec . 1 969 .
Davi s , Pamela A ., San d y M . Stu bbs , an d Jo h n A . T anner , Aircra ft La nd ing Dynam ics Fac ili ty , A Uni que Fac il ity With New Ca pa bilities , SAE Tec h Paper Se t . 8 5 1938 , Oct . 1 985 .
Daug h erty , R o b er t F. , S and y M . Stu bbs , and Ma rth a P . R o b in s on, Corn er in g Charac ter is tics of th e Ma in - Gear Tir e of th e Spac e Shut tle Or biter , NASA TP- 2 790 , 1 988 .
Leland , T raf f ord J . W. , Th omas J . Yage r, and Ups h ur T . Joyner , E ffects of Pa ve m e n t tex tur e o n Wet - Run - wa y Bra king Perfor manc e, NASA TN D-43 2 3 , 1 968 .
Tanne r, Jo h n A ., Sandy M. Stu bbs, and Jo h n L . McCarty , Sta tic and Ya wed - R oll ing Mechan ical Pr oper - ties of two ty pes VI II A ircra ft Tir es, NASA TP- 1 863 , 1 98 1 .
V ogler , W ilia m A ., and Jo h n A . Tanner , Corn ering Charac ter is tics of th e Nos e - Gear Tir e of th e Spac e Sh uttl e Orbiter , NASA TP- 1 9 1 7, 1 98 1.
Figure 1. Convair 990 with test fixture.
_ ,-Test conductor conso l e _ Linear act u a tors / T Nitrogen _ , , , J / !
---=- o
Hydraulic pumps Nitrogenbottles Hydraulic accumulators 950187 Fi g ure 2 . Primary comp on ents for the L SRA t e st fix t ur e sy s tem.
Hydraulic actuator = alload reaction truss Test Sw i ng links 9 5 01 88 Figure 3. Mechanical test system of the CV990 LSRA.
Figure 4. Single tire fixture.
CV990 centerline V ground (optical speed sensor) Drift Tire X velocity / / Slip
an gs
angl e Steering__ / _v " (optical speed _ _ Yveloci ty sensor) Note: All angles shown in positive direction.
Slip angle = steering angle - dri ft angle 950190 Figure 5. Parameters used to determine the test tire slip angle.
Approach-flaps up Derotation Deploy spoilers test gear extension _0 Computer-controlled / _ Target profile Test complete retract test gear Time Safe systems 950191 Figure 6. Typical landing sequence for an LSRA.
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_ 5 4 ..................................................... _............................. _ ............................ _ ............................ :............................ ": ............................. i Slip 2 ....... _ ........ . T ................. i .......... i , : ' ,. , . , . ,, I , . = :i P i , _ ' i angle, deg 0 '" ' "__ + - : -2 1 300 ................................................................................... _ ............................ : ............................ " ........................... " ............................
200 .............. . ............................ _ ............................. _ ............................ _ ............................. _....................................................... i Speed, ,- i i ! i !
i = i i i kgs ......._ ................ i ............................ !............................. i................... i............................ _ ........................... _ ............................ i 100 _ i 0 10 20 30 40 50 60 70 Time, sec 950192 Figure 7. LSRA / STS 51-D vali d ation test.
1 2 1 ................................................................................................ " .................................. • .................................. - ..................................
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angle, deg - 3 ................................................................................................................
i :i ' i
I 0 10 20 30 40 50 60 Time , sec 950193 Figure 8. Slip control after control system improvements.
1 3 LSRA tire Orbiter tire 950194 Figure 9. Comparison between Orbiter STS 51 - D tire and LSRA tire from validation test.
APP E NDIX A Th i s appendix s h o ws a typical large aircraf t t i r e dynamomete r at t h e DoD Landing gea r test facili t y wh ic h i s managed b y t h e Flig h t Dynamics La b orato r y at Wr ig h t - Patterson AFB , O h io . Some ti r e tes t ing on t h e S p ace S h uttle Or b iter P r ogram h a s b een done h ere .
350 mph / 120 inch Tire Test Dynamometer Test Machine 350 mph / 120 inch Tire Test Dynamometer Applications This computer controlled "state-of-the-art" machine is intended for high-speed takeoffs and landings or long distance taxi roll testing of aircraft tires. Critical speed / standing wave tests are also possible. An automated handling system for the large carriage removes hot tires to cooling stations and inserts cool ones ready for testing. Thus, inactive dynamometer time is kept to a minimum. Controlled constant side load is possible on the large carriage through variable yaw.
Machine specifications.
Large carriage: Tire size 18 to 57 in. diameter Radial load 150,000 lb, maximum (programmable) Sink rate 3-1 / 2 ft / s, maximum (programmable) Camber + 20° (programmable) Yaw + 20° (programmable) Small carriage: Tire size 14 to 57 in. diameter Radial load 84,000 lb, maximum (programmable) Camber + 15°, manually preset Yaw + 15°, manually preset Flywheel: Diameter 120 in. (168 rev / mile) Width 24 in.
Speed range 0 to 350 mph (programmable) Accel. / Decel. rate 24 ft / s, maximum (programmable)
Data Collection
Sampling can be done by various computers and information stored o n a magnetic disc. Data is trans- ferrable to magnetic tape in customer' s format. Resolution is one percent or better, of full-scale readings.
Accessories
Flywheel flat plates and video monitoring. Provision to mount either "lab" or aircraft wheels and heating (ambient to 300 °F) and cooling (ambient to -65 ° F) chambers for thermal preconditioning of the tire.
A._ _ ¢ _p _ Figure A - 1. Large carri a ge, DoD Land i ng Gear Test F a c i lity.
APPENDIX B These equations were taken from the flight 77 flight report on the CV990 program. They give a typi- cal example of the data reduction used for the CV990 data. These equations correct and convert the mea- sured loads to the test tire axes.
LSRA P arameters and P l ot Descriptions Note: All data have been thinned to 50 samples per second.
AIR1P Test tire internal air pressure in psia. This measurement is transmitted from the ro- tating test tire to the aircraft by an FM transmitter. Occasionally, the receiver would not lock on the transmission frequency and the receiver would pick up a lo- cal FM radio station. For this reason, the internal pressure (and temperature) are not always accurate. These occasions are identified in the text under "Anomalies - Data System".
AIR1T Test tire internal air temperature in degrees F. See discussion of accuracy for AIR1P.
DIST An optical measurement of the distance between the test tire axle and the ground in inches. A bias of 19.5 in. needs to be applied to the measurement.
GCANGLE.S Commanded tire slip angle in degrees.
GCSPEED.S Commanded aircraft speed in knots.
GCVLOAD.S Commanded vertical load in lb.
PITCH Aircraft pitch a ngle i n degrees as me a sured by the Inerti al Na v ig a t i on Sys t em.
Nose up is positive.
PYRO2 Test tire tread temperature in degrees F measured by a pyrometer pointed at the center of the tire about 150 degrees aft of the contact patch.
TBRKP Test tire brake pressure in psig.
TGBAN K .M Aircraft roll angle in degrees (positive right wing down) as determined from dif- ferent i al main gear strut extensions: TGBANK.M = arctan[(left mg ext. - right mg ext.) / 239] TQGROS_VERT Uncorrected vertical load in lb determined from summing the left and right vertical load cells.
TGNETDRAG.M Corrected test tire drag in lb. Positive force is aft. Corrections are made for trans- forming the body axis measurements into the test tire axis. The transformation equation is: TGNETDRAG.M = DRAGFORCE / cos(PITCH) + (VERTFORCE * sin(PITCH) * cos(PSI)) - (VERTFORCE * sin(PSI) * sin(BANK)) + (VERTFORCE * sin(FORKANGLE) * cos(PSI)) 1) DRAGFORCE = TG_GROS_DRAG- DRAGBIAS 2) VERTFORCE = 1.02 * (TG_GROS_VERT- VERTBIAS) 3) SIDEFORCE = TG_GROS_SIDE- SIDEBIAS 4) PSI is the tire steering (not slip) angle 5) THETA.M was substituted for PITCH when the INS angle measurement failed 6) FORKANGLE = -(0.15 + 4.7e-05 * DRAGFORCE) 7) BANK = TGBANK.M + 2.7e--05 * SIDEFORCE 8) DRAGBIAS, VERTBIAS, and SIDEBIAS are biases applied to the load cells as determined from zero force conditions TGNETSIDE.M Corrected test tire side force in lb. Positive force is left. Corrections are made for transforming the body axis measurements into the test tire axis. The transformation equation is: TGNETSIDE.M = [SIDEFORCE - (VERTFORCE * sin(BANK)) - (DRAGFORCE * sin(PSI)] / cos(PSI) + (VERTFORCE * sin(PITCH) * sin(PSI) 1) DRAGFORCE = TG_GROS_DRAG - DRAGBIAS 2) VERTFORCE = 1.02 * (TG_GROS_VERT - VERTBIAS) 3) SIDEFORCE = TG_GROS_SIDE - SIDEBIAS 4) PSI is the tire steering (not slip) angle 5) THETA.M was substituted for PITCH when the INS angle measurement failed 6) BANK = TGBANK.M + 2.7e-05 * SIDEFORCE 7) DR A GBIAS, VERTBIAS, and SIDEBIAS are biases applied to the load cells as determined from zero force conditions TGNETVERT.M Corrected test tire vertical force in lb. Positive force is up. Corrections are made for transforming the body axis measurements into the test tire axis. The transfor- mation equation is: TGNETVERT.M = VERTFORCE * cos(PITCH) * cos(BANK) - (DRAGFORCE * sin(PITCH) * cos(BANK)) + (SIDEFORCE * sin(BANK) * cos(PITCH)) , 1) DRAGFORCE = TG_GROS_DRAG - DRAGBIAS 2) VERTFORCE = 1.02 * (TG_GROS_VERT - VERTBIAS) 3) SIDEFORCE = TQGROS_SIDE - SIDEBIAS 4) PSI is the tire steering (not slip) angle 5) THETA.M was substituted for PITCH when the INS angle measurement failed 6) BANK = TGBANK.M + 2.7e-05 * SIDEFORCE 7) DRAGBI A S, VERTBIAS, and SIDEBIAS are biases applied to the load cells as determined from zero force conditions TGSPEED.M Aircraft ground speed in knots as measured by the Inertial Navigation System.
TLGRPM Test wheel RPM in revolutions per minute. The measurement is made by counting magnetic pulses as the wheel turns. Because of the electronics used in counting the pulses, there is some delay as the wheel begins to turn.
THETA.M Aircraft pitch angle in degrees as computed fr o m the aircraft landing gear strut po- sitions. The equation is: THETA.M = arctan[(NG strut - ((LMG strut + RMG strut) / 2) - 18.5) / 686.3] TLGAY Test landing gear pallet lateral acceleration in G's. The measurement is shown pri- marily to determine if the test gear is in a quasi-static condition. Test gear side forces under high lateral accelerations must be modified by an inertial correction.
The magnitude of this correction is unknown but could be as high at + 4000 lb.
REP O RT DOCUMENTATION PAGE F or m Approved
OMB No.070 4- 0 188 Pub]icreportingburd enforthisco l lectionofinformationisesti m ate d toav e ragel h_urp e rresp_nse ' inc_u d _ n gtheti m ef_rrevi e w_nginst r ucti_ns_searc h ing e xist _n gdat a s_urces ' g ath e ri n g a nd ma inta i n in gt h edata neede d,an d co mpletin gan d r e v iewi ngt he c oll ectio n ofi n f o r m a t i on. S en dco mme nts re gardingt hi sbu rde n esti ma t e or a nyot h e r as p ecto f t h is c__ I e _t i _n__n f _n_nat i _n_inc_ud i ngsuggesti _ nsf_r redu cin gt hisi _ urd e n_IoWashingt_nH e adqu a rte r sS e rvices _Di re c t_ ra te f _dn f ormati_n _ perations a nd R e to o _ ts_12 15` ` 1_ _ er s_n Davis Highway,Suite 1204, Arlington, VA 2220 2 -4302, and toth e Offic e o f Manage m ent andBudg e t , Pa p erworkReductionProject(0704 - 0188), W a shington,DC 2 0 5 0 3 .
1. AGENCY USE ONLY(Leav e blank) 2 . REPORT DATE 3. REPORT TYPE AND DATES COVERED June 1995 TechnicalMem o randum 4.TITLE AN D SUBTITLE 5.FU N DING NUMBERS The NASA Landing Gear TestAirplane 6.AUTHOR(S) WU 551 - 15 - 01 J o hn F. Carter and Christopher J. Nagy 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(E S ) 8. PERFORMING ORGANIZATION REPORT NUMBER NASA Dryden Flight Research Center P.O.Box273 H-2045 Edwards, California 93523-0273 9 . SPONSORING / MONOTORING AGEN C Y NAME(S) AND AD D RESS(E S ) 10. S PONSORING / MONITORING AGENCY REPORT NUMBER Nati o nal A er o nautics and Spa c e A dministrati o n NASA TM-4703 Washington, DC 20546-0001 11. SUPPLEMENTARY NOTES J o hn Carter : N ASA Dryden Flight Research Center, Edwards, CA 93523 - 0273.
ChristopherNagy:PRC Inc.,Edwards,CA 93523-0273.
12a. DISTR IB UTION / A VAILABILITY STATEMENT 12b . DISTRIB UT ION CODE Unclassified--Unlimited Subject Categ o ry 33 13. AB S TRAC T (M a ximum 2 0 0 w ord s ) A tire and landing gear test facility has been devel o ped and in co rp o rated int o a C o nvair 990 aircraft . The system c an simulate tire vertical load profiles to 250,000 lb, sideslip angles to 15 degrees, and wheel br a king on actual runways. Onboard computers control the preprogrammed test profiles through a feedback loop and also record three axis loads, tire slip angle, and tire condition. The aircraft to date has provided tire force and wear data f o r the Shuttle Orbiter tire on three different runways and at East and West coast landing sites.
This report discusses the role of this facility in complementing existing ground tire and landing gear test facilities, and how this facility can simultaneously simulate the ver t ical load, tire slip, velocity, and surface for an entire aircraft landing. A description is given of the aircraft as well as the test system. An example of a typical test sequence is presented. Data colle c tion and reduction from this facility are discussed, as well as accuracies of calculated parameters. Validation of the facility through ground and flight test is pre s e n ted.
Tests to date have shown that this facility can operate at remote sites and gather complete data sets of load, slip, and velocity on actual runway surfaces. The ground and flight tests have led to a su c cessful validation of this test facility.
14. SUBJECT TERMS 15 . NUMBER OF PAGES Landing gear, Air c raft tire, CV990, Space Shuttle O rbiter TestFacility, La n ding 19 Systems Research Aircraft 1 6 . P RI CE CODE A03 17. SECURITY C LA SSIF I CAT I ON 18. SECURITY C LA SSIF I CAT I ON 19. SECURITY C LA SSIFICATION 20. LIMITATION O F ABSTRACT OF REPORT OF TH I S PAGE OF ABSTRA CT U nclassified Unclassified Unclassified Unlimited N S N 7540-01 - 28 0 - 5 5 00 Available fr o m the NASA Center for Ae ro Space Information, 800 Elkridge Landing Road, S tan d ard Form2 98 (R e v . 2 -89 ) Linthicum Heights, MD 21090; (301)621-0390 Presc r i bed byANS I Std . Z39-18 298 - 102 National Aeronautics and SPECIAL FOURTH-CUSS RATE POSTAGE AND FEES PAID Space Administration
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