Document
NASA Technical Memorandum 78679
H78-26043
(rasr-ra-7867 3) r.raarer OF srrjr
L A I D I I C - G E A R 8 2 S E A B C B ( U A S A ) 3 4 p 3C A 0 3 / l P A01 CSCL 01C Unclas 3 2337U Sumnary o f NASA Landing Gear Research 0. D. Fisher, R. K. Sleeper, and S. M. Stubbs March 1978 Nar~onal Aeronau!cs ana Space Acjmln~srration B N C ~ D. F i s h e r , Robert K . S l e e p e r . and Sandy N . Stubbs XASA Lagley Research Center Langley Research The lan-fing g e a r r e s e a r c h b e i n g conducted a t Center is suumarized i n t h i s r e p o r t , and r e s e a r c h r e l a t i v e t o tire t r e a d , pcwered-uheel t a x i i n g , a i r cushion l a n d i n g systems, and crosswind l a n d i n p g e a r is d i s c u s s e d i n some d e t a i l .
The purpose of t h i s paper is t o p r e s e n t a b r i e f s u w a r y of t h e a i r p l a n e l a ~ d i n g - g e a r r e s e a r c h underway a t K.GA. The technology a r e a s i n c l u d e : Ground-handling s i m l a t o r T i r e / s u r f a c e f r i c t i o n Antiskid braking s y s t e m c h a r a c t e r i s t i c s Space s h u t t l e nose-gear s h h q T i r e raechanical p r o p e r t i e s Active c o n t r o l landing g e a r T i r e - t r e a d m a t e r i a l s G i r e brush s k i d landing g e a r Powered wheels f o r t a x i i n g A i r cushion l a n d h g systems Crosswind landing g e a r This paper w i i l d e a l n a i n l y w i t h t h e p r o g r a m on t i r e - t r e a d c a t e r i a l s , powered-wheel t a x i i n g , a i r cushion landing s y s t e n s , and crosswind landing-gear research w i t h p a r t i c u l a r emphasis on p r e v i o u s l y unrep3rted r e s u l t s of r e c e n t l y completed f l i g h t tests. L'ork i n t h e remaining a r e a s g i l l only be mentioned b r i e f l y a s f o l l o w s .
An a i r p l a n e ground-handling s i c w l z t o r is being developed t o pro- v i d e a research t o o l f o r i n v e s t i g a t i n g , : n p a r f e c t s a f e t y , d i r e c t i o n a l c o n t r o l and braking problems of a i r p l a n e s on s l i p p e r y runways i n t h e presence of crossuinds. Or.e e x c e l l e n t example of its a p p l i c a t i o n is t o e x p l o r e a i r p l a n e c o n t r o l p r o l l m d u r i n g high-speed t u r n o f f s from main runways o n t o taxiways. The s i m u l a t i o n development vas performed under c o n t r a c t a d is c u r r e n t l y b e i n g adapted t o t h e Langley v i s u a l - ~ o t i o n simulator. ;\ d i s c u s s i o n of sone of t h e s i g n i f i c a n t developments can be found i n e f e r e n c e s 1 and 2.
is i n p r o g r e s s a t An a n t i s k i d b r a k i w system r e s e a r c h t o t h e Laagley a i r c r a f t l a n d i h g l o a d s and t r a c t i o n f a c i l i t y (UT) d e t e r n i n e ways t o improve t h e p e r f o r s a n c e of c u r r e n t a n t i s k i d systems on s l i p p e r y runways and t o o b t a i n d a t a f o r t h e development of more advanced systems. T e s t d a t a from two d i f f e r e n t a n t i s k i d s y s t e n s have been r e p o r t e d i n r e f e r e n c e s 3 and 4 although two a n t i s k i d sy- tems i n t h e program have y e t t o b e t e s t e d .
Space s h u t t l e nose-gear shiauy tests were p e r t o r n e d a t t h e U T p r i o r t o t h e f i r s t l a n d i n g s of t h e s h u t t l e on t h e drv l a k e bed a t . ; A S . \ Dryden F l i g h t Researdl Center. TSese d a t a have not y e t been published, b u t no shimsay problems were encountered e i t h e r i n t h e t r a c k tests o r i n the a c t u a l landings.
Active ccmtrol landing-gear r e s e a r c h is underway i n an a t t e m p t t o a t t e n u a t e landing-gear l o a d s imposed on t h e s t r u c t u r e of l a r g e f l e x i b l e a i r p l a n e s . The g o a l is t o improve t h e s t r u c t u r a l d y n a s i c response d ~ a r a c t e r i s t i c s and t o o b t a i n an e c o n o u i c a l l y a c c e p t a b l e f a t i g u e l i f e of t h e a i r f r a m e s t r u c t u r e . A n a l y t i c a l r e s u l t s f o r l a n d i n g s of a super- s o n i c a i r p l a n e have shown t h a t a s a r e s u l t of a cycle-by-cycle a n a l y s i s of landing impact and r o l l - o u t f o r a p a s s i v e and an a c t i v e g e a r , t h e a c t i v e g e a r was e f f e c t i v e i n s i g n i f i c a n t l y reducing t h e s t r u c t u r a l f a t i g u e danage f o r t h e ground o p e r a t i o n a l phase. m a n i c drop tests a r e c u r r e n t l y underway using a l i g h t a i r p l a n e l a n d i n g g e a r iriodiiiet?
to an a c t i v e r o n t r o l c o n f i g u r a t i m . Xeferencec 5 t o 8 p r e s e n t d i s - cussions of sone of tile a c t i v e c o n t r o l landing-gear r e s e a r c h .
A b r a k e s y s t e s u s i c g w i r e brush s k i t s i n c o n j u n c t i o n w i t h tile wheels of t h e main landing g e a r o f f e r s t h e p o t e n t i a l of s u p e r i o r braking c h a r a c t e r i s t i c s on wet runways when conpared v i t h conventional a i r p l a n e t i r e and brake s y s t e m . X i r e b r u s h s k i d s a r e c u r r e n t l y be in^ i n v e s t i g a t e d t o determine t h e i r f r i c t i o n z n a r a c t e r i s t i c s and wear r a t e s . r e f e r e n c e 9 p r e s e n t s r e s u l t s of s a t e e a r l v work on v a r i o u s p o t e n t i a l = i r e L - a t e r i a l 4 f o r w i r e brush s k i d s .
T i r c / s u r f a c e f r i c t i o n c h a r a c t e r i s t i c s p l a v a very important r o l e in t h e ground-handling behavior of an a i r p l a n e d u r i n g take-off and l a d i n g . :luch e f f o r t i n t h e p a s t has Seen s p e n t on c o d i f y i n g t h e t e x t u r e of t h e rwuay, such as by pavement grooving, and on developiny: n r j t i r e - t r e a d p a t t e r n s i n a t t e m p t s t o delay t h e d e l e t e r i o u s e f f e c t s of t i r e itydroplaninp during wet runwav o p e r a t i o n s . s i x a a r y of run- way s l i p p e r i n e s s r e s e a r c h is g i v e n i n r e f e r e n c e 1 0 , and a r e c e n t r e p o r t on t h e f r i c t i o n c h a r a c t e r i s t i c s of t i r e s w i t h v a r i o u s t r e a l p a t t e r n s and rubber compounds is p r e s e n t e d i n r e f e r e n c e 11.
S e v e r a l e f f o r t s a r e -mderuiy a t Langley Research Center i n t h e g e n e r a l a r e a of tire mechanical p r o p e r t i e s . An a n a l y t i c a l time model is being developed t o a i d i n t h e design of landing-gear systems and t o a s s i s t i n t h e s o l u t i o n of many a i r p l a n e ground o p e r . . t i o n a l problems.
I n t h i s development, a computer program is b e i n g f o r m u ~ a t e d t o d e s c r i b e t h e shape and stress of a f r e e , p r e s s u r i z e d e l l i p t i c t ~ r o i d a l s h e l l wnere p r o p e r t i e s of t h e s h e l l may be a n i s o t r o p i c and nonhomogeneous.
I n a r e l a t e d e f f o r t , experimental tests a r e beinp conducted t o determine dynamic c h a r a c t e r i s t i c s of n o n r o t a t i n g tires i n c o n t a c t w i t h a s u r f a c e .
F u r t h e r , tests a r e underway t o o b t a i n t h e mechanical p r o p e r t i e s of two s i z e s of a i r p l a n e tires d u r i n g o p e r a t i o n o v e r a wide range of t e s t parameters, i n c l u d i n g forward speed. Data from t h e s e t e s t s w i l l be incorporated i n t o a t i r e mechanical p r o p e r t y d a t a bank which is b e i n g compiled by The U n i v e r s i t y of Xichigan under a ii.9SA g r a n t .
TIRE-TREAD KATERIt\LS WSEARCii T i r e wear is of major economic concern t o c o m e r c i a 1 and m i l i t a r y a v i a t i o n s i n c e t i r e replacement accounts f o r approximately h a l f of t h e o v e r a l l landing-gear maintenance c o s t of present-day j e t a i r p l a n e s .
For example, it is e s t i m a t e d t h a t f o r the vorldwide f l e e t of Bseing 7 2 7 a i r p l a n e s , t h e c o s t of t i r e replacement approaches $20 ni l l i o n annually.
The Chemical Research P r o j e c t s O f f i c e a t t h e .hes Resear ' Center r e c e n t l y i n s t i t u t e d a program t o develop new t r e a d m a t e r i a l s i n an attempt t o improve t h e o v e r a l l l i f e t i m e and t h e c u t and blowout r e s i s t a n c e of a i r p l a n e tires. Langley Research Center was requested t o p a r t i c i p a t e i n t h e program by e v a l u a t i n g t h e wear c h a r a c t e r i s t i c s and tile f r i c t i o n behavior of tires r e t r e a d e d with t h e newly developed rubber compounds.
I n t h e i n i t i a l e f f o r t , a number of s i z e 49 x 1 7 a i r p l a n e tires were r e t r e a d e d w i t h one of t h e experimental m a t e r i a l s which, f o r s m a l l specimen l a b o r a t o r y tests, e x h i b i t e d improved h y s t e r e s i s and f a t i g u e l i f e . For comparison purposes, a d d i t i o n a l t i r e s of t h i s s i z e were r e t r e a d e d i n t h e same mold but with a s t a n d a r d s t a t e - o f - t h e - a r t n z t e r i s l . To a c q u i r e f r i c t i o n d a t a , a t i r e from each s t o c k w a s i n s t a l l e d on a t e s t c a r r i a g e a t t h e a i r c r a f t landing l o a d s and t r a c t i o n f a c i l i t y shown i n f i g u r e 1 and w a s exposed t o high-speed b r a k i n g t e s t s on dry and wet c o n c r e t e s u r f a c e s . Wear d a t a were obtained by e n l i s t i n g t h e s e r v i c e s of t h e Federal Aviation Administration, which flew a Boeing 7 2 7 a i r p l a n e equipped with s e t s of t i r e s made from Sotli t h e experimental and s t a n d a r d s t o c k s .
The i n i t i a l t e s t s were encouraging i n t h a t t r a c k tests showed t h e l e v e l of d e v e l ~ p e d f r i c t i o n d i d n o t d e t e r i o r a t e f o r t h e experimental s t o c k , and t h e wear performance , , u r i n g . f l i g h t tests proved t o be e q u i v a l e n t t o t h e s t a n d a r d s t o c k . S i n c e t h e f o r m u l a t i o n of t h e s t o c k t h a t was t e s t e d was only an i n i t i a l a t t e m p t and was n o t considered t h e optimum blend of i n g r e d i e n t s , i t is l i k e l y t h a t a blend could be p e r f e c t e d t h a t would c o n s i d e r a b l y improve t r e a d l o n g e v i t y . Such an o p t i m i z a t i o n , however, would b e s t b e accomplished by tile t i r e i n d u s t r y .
I n c o n t i n u a t i o n of t h e t r e a d m a t e r i a l test program, t h e new ground test v e h i c l e shown i n f i g u r e 2 was developed t o o b t a i n f o r d e t a i l e d s t u d y simultaneous neasureclents of t i r e f r i c t i o n and v e a r p r o p e r t i e s under c l o s e l y c o n t r o l l e d b r a k i n g and c o r n e r i n g c o n d i t i o n s . The f i r s t group of tires t o b e t e s t e d w i t h t h e new v e h i c l e were e i g h t y 22 x 5.5 a i r p l a n e tire c a r c a s s e s o b t a i n e d from t h e U . S . Navy. Twenty of t h e s e t i r e s were r e t r e a d e d w i t h a s t a t e - o f - t h e - a r t polyblend, twenty v i t h n a t u r a l rubber, and twenty each w i t h two d i f f e r e n t experimental con- pounds.
F r i c t i o n and wear t e s t s v e r e conducted d u r i n g t h e p a s t y e a r i n which t h e s e tires were exposed t o a v a r i e t y of b r a k i n g and c o r n e r i n g o p e r a t i o n s on s e v e r a l t y p i c a l runway s u r f a c e s , w i t h a s q l e of t h e preJiminary r e s u l t s presented i n f i g u r e 3. The f i g u r e shows t h a t d u r i n g t h e slow speed t e s t s a t v a r i o u s amounts of s l i p ( b r a k i n g ) , a l l compounds develop approximately t h e same f r i c t i o n c h a r a c t e r i s t i c s .
The wear r a t e ( r u b b e r removed p e r u n i t d i s t a n c e ) f o r t h e two e x p e r i m e n t a l t r e a d s , however, does appear t o be s l i g h t l y g r e a t e r t h a n t h a t of t h e s t a t e - o f - t h e - a r t polyblend b u t much l e s s than f o r n a t u r a l rubber. 2,s mentioned e a r l i e r , an optimized b l e n d of t h e i n g r e d i e n t s i n one o r both of t h e s e e x p e r i n e n t a l t r e a d s could conceivably improve t h e i r wear performance.
I n a d d i t i o n t o t h e s e t e s t s , more f l i g h t programs a r e b e i n g con- ducted t o o b t a i n wear d a t a on t h e s e t r e a d m a t e r i a l s under k l i g h t o p e r a t i o n a l c o n d i t i o n s by using t h e R-727 a i r p l a n e . A c o ~ w r c i a l a i r l i n e is c u r r e n t i y f l y i n g K : th s e t s of t i r e s w!lich i n c l u d e 50 e x ~ e r i m e n t s 1 aaC 53 s ~ a n d a r a t r e a d s t o determine comparative wear c h a r a c t e r i s t i c s under r e a l i s t i c commercial f l e e t use. :io v e a r d a t a a r e y e t a v a i l a b l e from t h i s program.
POIJERED 'JHEELS FOR A 1 K P L X K TAXI I I t G Another a r e a of r e s e a r c h is a powered-wheel concept f o r movements of a i r p l a n e s around congested a i r t e r m i n a l s . Energy c o n s e r v a t i o n and e c o l o g i c a l c o n s i d e r a t i o n s have caused t h e t r a n s p o r t a t i o n i n d u s t r y t o review systems and o p e r a t i o n a l procedures i n an e f f o r t t o achieve The a i r - s a v i n g s i n energy and r e d u c t i o n s i n n o i s e and a i r p o l l u t i o n .
c r a f t i n d u s t r y i n p a r t i c u l a r h a s conducted s t u d i e s t o achieve g r e a t e r A number of s t u d i e s have o p e r a t i o n a l e f f i c i e n c y i n terms of energy.
c e n t e r e d around a l t e r n a t i v e s t o t h e use of t h e j e L engines as a m e a s of p r o v i d i n g t h e power f o r t a x i i n g a i r p l a n e s . A s p e c i f i c a l t e r n a t i v e using a secondary p w e r s o u r c e i n v o l v e s i n d i v i d u a l l y powered wheels i n t h e main l a n d i n g g e a r ; t h u s , dependence on a ground-based power s o u r c e such a s a tar t r a c t o r would b e e l i m i n a t e d .
The main o b j e c t i v e of t h e powered-wheel program undertaken a t Langley was t h e d e s i g n , manufacture, and t e s t of a s u i t a b l e , f u l l - s c a l e , i i y d r a u l i c a l l y powered motor t h a t would b e compatible w i t h t h e outboard wheels of a l a r g e t r a n s p o r t a i r p l a n e and capable of providing s u i t a b l e taxi performance. C o m p a t i b i l i t y i n c l u d e d no i n t e r f e r e n c e w i t h b r a k i n g o t h e r than removal of t h r e e - f i f t h s of t h e b r a k e s t a c k i n t h e outboard wheels and e s s e n t i a l l y no change i n t h e ground check-out o r removal and replacement f o r t i r e s , a n t i s k i d systems, and brakes.
C u r r e n t l y under NASA c o n t r a c t , The Uendix Corporation has a p p l i e d t h e i r DYNAVECTOR concept t o t h e motor a c t u a t o r , g e a r box, and c l u t c h ~ e c h a n i s m shown i n f i g u r e 4 t h a t can be mounted i n t h e outboard wheels of t h e B-737-100 landing g e a r , one of which is shown i n f i g u r e 5.
Hvdraulic p r e s s u r e from an a u x i l i a r y pcwer u n i t would be used t o power t h e motor, and it is a n t i c i p a t e d t h a t t a x i speeds up t o 2 4 kmlhr (15 m i l e s l h r ) can be obtained on runway grades up t o 4 p e r c e n t , w i t h an a d d i t i o n a l c a p a b i l i t v of r e v e r s e o p e r a t i o n f o r Lacking away from t e r m i n a l a r e a parking. C u r r e n t l y , t h i s u n i t i s undergoing s t a t i c s t a l l torque tests and no-load high-speed t e s t s . I f c u r r e n t p r o b l e e s can be s o l v e d , dynanometer t e s t s may be attempted t o s t u d y t h e u n i t ' s c h a r a c t e r i s t i c s under s e v e r a l t y p i c a l s i m u l a t e d a i r p l a n e t a x i and landing-to-take-off c y c l e s .
Ground loads t r a n s n i t t e d through conventional landing g e a r play a n a j o r r o l e i n t h e design of t h e a i r f r a m e s i n c e t h o s e loads a r e coa- c e n t r a t e d a t d i s c r e t e p o i n t s G n t h e a i r p l a n e s t r u c t u r e . S i m i l a r l y , pavenent design (runway, taxiway, ramps, e t c . ) is based u p m l o a d i n g s i n t h e t i r e f o o t p r i n t . I;ith t h e c u r r e n t t r e n d of l a r g e r and h e a v i e r a i r p l a n e s , e f f o r t s t o maintain a c c e p t a b l e l o a d i n g s both i n t h e a i r f r a m e and on t h e ground have r e s u l t e d i n a n l u l t i p l i c j t y of g e a r s .
The expense i n volume and weight f o r such systems, which s e r v e no use- f u l purpose once t h e a i r p l a n e i s a i r b o r n e , i s high. Furthermore, t h e concentrated wheel loads a r e beginning t o exceed t h e b e a r i n g s t r e n g t h of t h e runway. One approach t o t h e s e problems t b a t is c u r r e n t l y under consideration is t o replace the conventional gear with an a i r cushion landing system (ACLS). In addition t o reduced runway loads, t h e a i r a t t r a c t i v e amphibious cushion may o f f e r improved crosswind performance, c a p a b i l i t i e s , and simple r e t r a c t i o n and storage mechanisms, a l l a t a p o t e n t i a l system weight saving. I n view of these f e a t u r e s , con- s i d e r a b l e a t t e n t i o n has been given t o e s t a b l i s h i n g the f e a s i b i l i t y of such a landing system, p a r t i c u l a r l y in terms of its landing impact behavior and its ground-handling performance.
Figure 6 s h w s s e v e r a l photographs of air cushion t e s t i n g a t NASA Langley Resear& Center. In f i g u r e 6 ( a ) , a s c a l e model ACLS representing a 1/4-scale C-8 transport is shown which was t e s t e d a t the d r c r a f t landing loads and t r a c t i o n f a c i l i t y f o r b e h a v i ~ r a t landing impact, v u l n e r a b i l i t y t o obstacles, and ground s t a b ~ . l i t y a t forward speeds up t o s c a l e landing speeds. The nodels were con- s t r a i n e d only l a t e r a l l y and longitudinally, and model motion:; and f o r a v a r i e t y accelerations, as well as ACLS t n m k pressures and f l w s of t e s t conditions, were measured. Also shovn i n the f i g u r e is the model as it approaches a d i t c h obstacle. Similar i :sts were made using a 0. +scale model of a Navy f i g h t e r airplane ( r e f . 12).
Testa of a concept t o provide a l l - t e r r a i n launch and recovery of (RPV) w i n g an ACLS were conducted a t high Remotely P i l o t e d Vehicles forward speeds on a t e s t carriage a t the a i r c r a f t landicg loads and t r a c t i o n f a c i l i t y as shown i n f i g u r e 6(b). The concept featured separate launch and recovery trunks, the l a t t e r being ground stowed within a zippered cover while the launch trunk was attached over t h i s assembly d i r e c t l y t o the fuselage with Velcro s t r i p s and was jettisoned a f t e r take-of f . The purpose of the t e s t s was t o observe any f l u t t e r of the i n f l a t e d launch trunk, t o i n i t i a t e and monitor the j e t t i s o n of t h a t trunk, and t o observe the i n f l a t i o n of the ground- stowed recovery trunk, a l l a t speeds of 100 knots. These t e s t s have resulted i n a redesigned retention-release system f o r the launch trcmk.
Figure 6(c) is 3 photograph of a free-body t e s t vehicle designed t o investigate the ground s t a b i l i t y and ground-handling problems of a number of ACLS concepts t o a l a r g e r s c a l e than i s presently possible with the e x i s t i n g t e s t carriages. The vehicle is t r a i l e r transportable so that t e s t s may be carried out on a wide v a r i e t y of p o t e n t i a l landing surf aces such as swamps, beaches, and plowed f i e l d s . This vehicle has been o u t f i t t e d , and t e s t i n g i s imminent. Other experimental ACLS t e s t s a r e reported i n references 1 3 and 14.
A n a n a l y t i c a l model of an ACLS h a s been developed f o r NASA by Foster-Miller A s s o c i a t e s , Inc. under c o n t r a c t . (See r e f . 15 .) The model i n c l u d e s a s y s t e m a t i c and r a t i o n a l a n a l y s i s of each of t h e f o u r primary subsystems a f f e c t i n g ACLS behavior: t h e air supply fan, t h e a i r f e e d i n g o r d u c t i n g system, t h e t r u n k , and t h e cushion.
A l l p e r t i n e n t p r e s s u r e s and flows are r e p r e s e n t e d as is t h e t r u n k shape, t h e r e s u l t i n g cushion a r e a , and p r e s s u r e f o r b o t h s t a t i c and dynamic o p e r a t i o n . The f o r c e s t h u s g e n e r a t e d on t h e body a r e summed t o g e t h e r w i t h e x t e r n a l f o r c e s due t o aerodynamic and ground f r i c t i o n , and t h e r e s u l t i n g a i r p l a n e motions i n heave, p i t c h , and r o l l a r e com- puted. The program is c o n s t r u c t e d i n modular form and has been w r i t t e n w i t h s u f f i c i e n t g e n e r a l i t y such t h a t a wide v a r i e t y of p r a c t i c a l ACLS designs may b e i n v e s t i g a t e d .
Figure 7 p r e s e n t s a comparison of a p u r e l y a n a l y t i c a l dynamic a n a l y s i s w i t h an experiment u s i n g t h e small ACIS model shown i n f i g u r e 6(d). P o r t r a y e d a r e t r u n k p r e s s u r e and v e r t i c a l motion r e s u l t i n g The from a drop w i t h t h e model r e s t r a i n e d t o pure heave motion only.
agreement between a n a l y s i s and experiment is thought t o be q u i t e good, w i t h n o d e l behavior and o v e r a l l p r e s s u r e and motion b e i n g q u i t e accu- r a t e l y p r e d i c t e d by t h e a n a l y s i s . Following impact, t h e f i r s t few c y c l e s i n trunk p r e s s u r e a r e q u i t e l a r g e owing t o r e p e t i t i v e s t a l l i n g of t h e fan. H y s t e r e s i s l o s s e s d u r i n g t h e s t a l l e v e n t u s l l y d i s s i p a t e enough of t h e drop energy s o t h a t f a n s t a l l no l o n g e r occurs and s y s t e E reduced t o a low and m a r g i n a l l y s t a b l e value.
damping is I n a d d i t i o n t o t h i s work, a e l l Aerospace Textron under c o n t r a c t with NASA is s t u d y i n g seven d i f f e r e n t c a t e g o r i e s of f u t u r e a i r p l a n e s t o d e t e r n i n e t h e most a t t r a c t i v e a p p l i c a t i o n s of a i r cushion l a n d i n g could be expected u s i n g systems and t o q u a n t i f y t h e b e n e f i t s which such a l a n d i n g system. Another o b j e c t i v e of t h e s t u d y is t o i d e n t i f y t h e t e c h n i c a l b a r r i e r s t h a t y e t remain t o a p p l i c a t i o n s of ACLS t o t h e v a r i o u s c a t e g o r i e s of a i r p l a n e s .
CRQSSWIXD LAIJDING GEAR The landing and take-off o p e r a t i o n s of an a i r p l a n e i n t h e presence of a crosswind r e q u i r e s p e c i a l p i l o t i n g techniques which can impose s i g n i f i c a n t a d d i t i o n a l demands on t h e p i l o t . For i n s t a n c e , one l a n d i n g technique used by p i l o t s r e q u i r e s t h a t an a i r p l a n e approach t h e runway i n a s i d e - s l i p p i n g a t t i t u d e such t h a t immediately b e f o r e touchdown t h e a i r p l a n e must be r o l l e d t o l e v e l t h e wings p r i o r t o touchdown.
Another method u t i l i z e s a crabbed approach. Immediately be£ o r e touchdown, t h e a i r p l a n e must b e decrabbed t o a l i n e t h e g e a r s w i t h t h e runway r.enter- l i n e . S p e c i a l a t t e n t i o n must be given i n t h e former technique t o
c l e a r a c e f o r low-winged a i r p l a n e s , and b o t h techniques r e q u i r e
c o n s i d e r a b l e p i l o t s k i l l and f a m i l i a r i t y w i t h t h e a i r p l a n e f l i g h t A croasvind landing-gear system could response c h a r a c t e r i s t i c s .
permit an a i r p l a n e t o approach t h e runway i n a manner s i m i l a r t o t h a t of t h e crabbed l a n d i n g technique and y e t could e l i m i n a t e t h e need f o r t h e c r i t i c a l decrabbing menuevtr b e f o r e touchdown.
Landing-gear concepts intended t o p e n n i t an a i r p l a n e t o touch dowa in t h e crabbed a t t i t u d e have been designed, a few u n i t s have been i n s t a l l e d on c e r t a i n a i r p l a n e s , and one type of crosswind l a n d i n g g e a r h a s been i n c o r p o r a t e d on two l a r g e types of m i l i t a r y a i r p l a n e s .
I n an e f f o r t t o i n v e s t i g a t e v a r i o u s landing-gear systems, t h e Langley Research Center engaged i n a crosswind landing-gear program which included small-scale landing-gear model s t u d i e s , development of ground- run e q u a t i o n s of motion t o d e s c r i b e t h e r o l l - o u t motion of an a i r p l a n e s u b j e c t e d t o l a t e r a l f o r c e s , and t h e i n s t a l l a t i o n of a r e s e a r c h landing-gear system on an a i r p l a n e capable o f b e i n g adapted t o d i f f e r e n t , crosswind landing-gear modes of o p e r a t i o n .
Model S t u d i e s Four d i f f e r e n t crosswind landing-gear concepts f o r which t h e main g e a r s were f r e e t o p i v o t , t o be s t e e r e d , o r t o be otherwise c o n s t r a i n e d , were e v a l u a t e d i n small-scale model t e s t s i n r e f e r e n c e 16. For t h e s e tests t h e model, which w a s equipped w i t h pneumatic tires, w a s launched o n t o t h e l a t e r a l l y s l o p e d runway shown i n f i g u r e 6 , where t h e l a t e r a l l y s l o p e d runway simulated a crosswind.
Following launch t h e model w a s f r e e , and subsequent t o s o l e n o i d engagement, each g e a r could be i n d i v f d u a l l y s t e e r e d by remote c o n t r o l .
S u b j e c t t o t h e l i m i t a t i o n s of t h e tests, t h e model o p e r a t o r p r e f e r r e d t h a t t h e main g e a r s be a l i n e d w i t h t h e d i r e c t i o n of motion p r i o r t o touch- down and t h a t nose-gear s t e e r i n g be provided.
Ground-Run Equations of ?lotion
To supplenent crosswind landing-gear s t u d i e s , p l a n a r e q u a t i o n s
of motion were derived t o d e s c r i b e t h t ground-.run t r a j e c t o r y of an a i r p l a n e . Tlie e q u a t i o n s were programed t o compute t h e p o s i t i o n and heading of an a i r p l a n e subjected t o d i s t u r b i n g f o r c e s and t o t h e s t e e r i n g a c t i o n of t i r e s . The d i s t u r b l n g f o r c e s included aerodynanic f o r c e s and g r a v i t y f o r c e s due t o runway tilt.
The l a t t e r f o r c e s were included t o permit c o r r e l a t i o n with t h e nodel s t u d i e s .
Furtherno r e , s i n c e f o r some crosswind landing-gear s y s t e x t h e g e a r s may be momen- t a r i l y without s t e e r i n g c o n t r o l , equations t o i ? s c r i b e f r e e l y s w i v e l i n g
f'f /d
PBmmII'IG PACE BI,.4NU NOT F(Lh(gD
I n t h e c a s t o r and p r e s e t modes, t h e main g e a r could be locked i n (See p o s i t i o n by p r e s s i n g a s w i t c h on t h e ~ i l o t ' s c o n t r o l wheel.
T h i s s w i t c h a c t i v a t e d a h y d r a u l i c c a s t o r lock on each main f i g . 1 .
g e a r u n i t . I n t h e c a s t o r mode, t h e c a s t o r l o c k s would a c t i v a t e when t h e switch was depressed and t h e main g e a r weight s w i t c h e s were I n t h e p r e s e t mode, t h e c a s t o r l o c k s were a c t u a t e d i n t.he actuated.
I n t h e a i r i n o r d e r t o l o c k t h e g e a r i n p o s i t i o n p r i o r t o touchdown.
automatic mode, t h e g e a r was locked i n p o s i t i o n af ter e i t h e r of t h e two main g e a r weight s w i t c h e s was compressed without t h e p i l o t h a v i ~ g It should be noted t h a t t h e main g e a r must be t o p r e s s t h e switch.
locked o r r e s t r a i n e d i n o r d e r t o develop nose-wheel s t e e r i n g c a p a b i l i t y .
I n any mode, a f t e r a weight switch on t h e nose g e a r had been a c t i v a t e d , t h e p i l o t could s e l e c t rudder p e d a l s t e e r i n g of t h e nose g e a r by depressing and holding a thumb s w i t c h on t h e p i l o t ' s c o n t r o l wheel.
This switch was a d j a c e n t t o t h e main g e a r c a s t o r lock s w i t c h , as shown i n f i g u r e 13. The nose-wheel t r a v e l w i t h rudder pedal s t e e r i n g was This f e a t u r e was i n c o r p o r a t e d t o allow t h e p i l o t t o have l i m i t e d + 3 O .
-
a u t h o r i t y nose-xhesl s t e e r i n g f o r t h e high-speed p a r t of t h e ground r o l l without having t o r e l e a s e t h e c o n t r o l wheel o r t h r o t t l e t o reach t h e tiller bar.
The p i l o t could a l s o c e n t e r t h e gear i n any mode by pushing a The s i n g l e switch on t h e crosswind c o n t r o l p a n e l shown i n f i g u r e 13.
The con- gear c e n t e r i n g command overrode a l l o t h e r i n p u t s o r a c t i o n s .
v e n t i o n a l aerodvjnamic (rudder and a i l e r o n ) and law-speed nose-wheel Main g e a r s t e e r i n g c o n t r o l s were r e t a i n e d from t h e o r i g i n a l a i q l a n e .
braking e f f e c t i v e n e s s w a s g r e a t l y reduced because hard b r a k i n g caused Apparently, w i t h t h e a i r p l a n e h e e l i n g , one f l a t s p o t s o r blown t i r e s .
of t h e d u a l wheels would n o t c a r r y s u f f i c i e n t load t o overcome brake torque and would b e ground f l a t . Reverse t h r u s t became t h e p r i n c i p a l developed due braking c o n t r o l although very l i t t l e a c t u a l t h r u s t was t o t h e slow engine response.
A crosswind landing-gear p o s i t i o n i n d i c a t o r was developed f o r t h i s program. The l o c a t i o n of t h e i n d i c a t o r i n t h e a i r p l a n e instrument panel is shown i n f i g u r e 13, and a schematic of t h e i n d i c a t o r is shown i n f i g u r e 14. The gyro compass card was d r i v e n by a gyro s l a v e d t o t h e compass heading. The double-bar n e e d l e pointed t o t h e landing runway magnetic heading, which was i n p u t t o t h e system w i t h t h e runw;ly heading s e l e c t o r knob ( p a r t of t h e h o r i z o n t a l s i t u a t i o n i n d i c a t o r on t h e test a i r p l a n e ) . The angular d i f f e r e n c e between t h e c e n t e r l i n e of t h e f i x e d and t h e runway neading (double-bar needle) was t h e crab a i r p l a n e symbol angle of t h e a i r p l a n e . The single-bar needle i n d i c a t e d t h e angle of t h e gear w i t h r e s p e c t t o t h e a i r p l a n e c e n t e r l i n e . [ h e n t h e g e a r were properly a l i n e d with t h e runway c e n t e r l i n e , t h e s i n g l e - b a r and double-bar n e e d l e s superimposed. I n t h e example given i n f i g u r e 1 4 , t h e runway The air- heading and g e a r p o s i t i o n a r e purposely shown misalined.
plane is stiown f l y i n g t o a heading of 350°, crabbed 15O t o t h e r i g h t of runway c e n t e r l i t r e . The g e a r a r e shown o f f s e t 20' t o t h e l e f t of a i r p l a n e c e n t e r l i n e , which means t h a t t h e g e a r have been r o t a t e d 5' Ip t h e p r e s e t mode, t h e p i l o t would use t h e t i l l e r b a r i n t o o f a r .
t h e c o c k p i t t o b r i n g t h e g e a r i n t o alinement w i t h t h e runway. I n t h e automatic mode, t h e misalinement would i n d i c a t e a system malfunction.
It is understood t h a t some a i r p l a n e s w i t h crosswind l a n d i n g g e a r have a c t u a l l y landed w i t h t h e landing e e a r s e t i n t h e wrong d i r e c t i o n .
The use of t h i s i n d i c a t o r should p r e v e n t such an occurrence. The p i l o t can determine proper wheel alinement from a quick scan w i t h o u t mentally having t o p r o c e s s i n f o r m a t i o n t o r e l a t e heading and landing-gear D e t a i l s on t h e crosswind landing- d e f l e c t i o n magnf t u d e and d i r e c t i o n .
gear p o s i t i o n i n d i c a t o r may b e found i n r e f e r e n c e 19.
R e s u l t s . - A m a t r i x of t h e t e s t c o n d i t i o n s f o r t h i s i n v e s t i g a t i o n is given i n t a b l e 11. A t o t a l of 195 crosswind landings were made i n t h e program by t h r e e t e s t p i l o t s who used t h e t h r e e modes of crosswind landing-gear o p e r a t i o n . The crosswinds given i n t h i s paper a r e t h e d i r e c t crosswind components computed from t h e wind magnitude and d i r e c t i o n recorded a t t h e time of touchdown by a wind s e n s o r a t t h e 6.1-m (20-ft) e l e v a t i o n of a m e t e o r o l o g i c a l tower l o c a t e d n e a r the t e s t runways. A l l landings were made i n V i s u a l F l i g h t Rules (VFR) c o n d l t i a n s t o s dry runway s u r f a c e . The p i l o t ' s t a s k was t o l a n d , r o l l o u t , and s t o p t h e a i r p l a n e w i t h i n t h e STOL runwav markings t h a t were p a i n t e d on t h e e x i s t i n g runways. The STOL runways were 30.5 n (100 f t ) wide and 457 m (1500 f t ) long. The markings f o r t h e s e run- ways a r e g i s e n i n r e f e r e n c e 20. The t h r e e runways on v h i c h they were painted were 1524 t o 2 7 4 3 m (5000 t o 9000 f t ) long and 46 t o 6 1 m (150 t o 200 f t ) wide. i h e landings were made u s i n g a 3 O o r 6 O approach a n g l e , which was i n d i c a t e d by t h e v i s u a l guidance system described i n r e f e r e n c e 18. A11 l a n d i n g s were made u s i n g f u l l f l d p d e f l e c t i o n and t h e w i n g - l i f t s p o i l e r s were used aftc?r touchdowi, f o r n o s t of t h e t e s t s .
The p i l o t s have s t a t e d t h a t with t h e crosswind g e a r ". . . . i t is
p o s s i b l e t o make crosswind Iai:dit,gs i n crosswind c o n d i t i o n s t h a t a r e f a r more s e v e r e than could b e handled with t h e conventional gear. " With t h e conventional g e a r ( r e f . 1 8 ) , t h e crosswind l i n i t s were 15 t o 20 knots. The l a r g e s t crosswind encountered d u r i n g t h a t program was 22 k n o t s , which caused t h e p i l o t t o a b o r t t h e landing j u s t p r i o r t o touchdown. I t can b e seen i n t a b l e 11 t h a t , with t h e crosswind g e a r , 11 lnndings were made with crosswinds betwt-en 20 and 25 k n o t s , and 5 hndir:gs were made w l t h crotswinds between 25 and 3 ' k n o t s . I n t h r e e tests, t h e main g e a r r o t a t e d t o t h e r i g h t c o n t r o l l i m i t s a t 30'.
The c r o s s w i n d s of 26 t o 27 k n o t s are a b o u t m e - h a l f t h e s t a l l speed of the a i r p l a n e .
The s e l f - a l i n i n g feciture of t h e crosswind l a n d i n g g e a r ( c a s t o r mode o r a u t o m a t i c mode) w a s found t o be e s s e n t i a l f o r l s n d i n g s i n !?iph crosswinds. For tbc* a i r p l a n e g e a r con£ i g u r a t i o n t e s t e d , t h e p r e f e r r e d mode of crosswind landing-gear o p e r a t i o n s was t h e c a s t o r mode. The p i l c i s found t h e crosswind l a n d i n g g e a r t o be p a r t i c u ! a r l > b e n e f i c i a l i n c r o s s w i n d s above 15 k n o t s where tile c r a b angle approaclied 20'. As can b e s e e n i n t a b l e 11, t h e l a n d i n g s w i t h t h e i a r g e s t cross- winds were made u s i n g t h e c a s t o r mode. 2 . s c h e m a t i c of a t y p i c a l i a r p r crosswind l a n d i n g , u s i n g a c t u a l v a l u e s measured d u r i n g one t e s t , i s g i v e n i n f i g u r e 15. The a i r p l a n e was crabbed 23.5' t o :!)e r i g h t of runway c e n t e r l i n e a t touchdown t o compensate f o r t h e r i g h t crosswind of 26 knots. The touchdown s p e e d of 58 k n o t s was j u s t o v e r t w i c e t h e crosswind magnitude. Time h i s t o r i e s from a c a s t o r mode l a n d i n g w i t h even g r e a t e r c r o s s w i n d (23.7 k n o t s from t h e l e f t ) a r e g i v e n i n f i g u r e 1 6 ( a ) . During t h e approach and l a n d i n g , t h e s i d e s l i p o s c i l l a t e d a h o u t z e r o , u n t i l t h e a i r p l a n e was n e a r l y s t o p p e d on t h e ground, a t which time t h e forward s p e e d was s o low t h e s i d e s l i p r e c rd was o f f s c a l e . Bank, a i l e r o n , and r u d d e r a l s o o s c i l l a t e d a b o u t zero.
A t touchdown, t h e main and nose g e a r f r e e l y a l i n e d w i t h ttie d i r e c t i o n of t r a v e l , s w i v e l i n g t o t h e r i g h t ( c l o c k w i s e ) t o o f f s e t t h e l e f t c r a b angle. The main g e a r c a s t o r l o c k s were a p p l i e d 2 scC a t t c r t o ~ ~ c l i d o w ~ , and tlie p i l o t used t i l l e r b a r s t e e r i n g of t h e n o s e g e a r . X l t h o u g l ~ tile p i l o t s p r e f e r r e d r u d d e r ped,.l s t e e r i n g , t h e p i l o t f e l t i t was n e c e s s a r y t h i s time t o u s e t h e t i l l e r b a r f o r s t e e r i n g i n o r d e r t o g e t d d d i t i o n a l n o s e wheel t r a v e l . (Rudder p e d a l s t e e r i n g was l i m i t e d t o + 3 ' . ) A t t h e end of t h e ground r o l l , t h e " c e n t e r " s w i t c h was used t o b r i n g a l l gedr back t o t h e a i r p l a n e c e n t e r l i n e . Because of t h e s e l f - d i n i n g f e a t u r e of t h e gear a t touchdown, t h e p i l o t d i d n o t have t o nionitor o r o p e r a t e t h e g e a r d u r i n g t h e approach. A s one p i l o t s a i d of c a s t o r node l a n d - i n g s , "No p r e c i s i o n is involved. I l i k e them."
Tlie p i l o t s ' second p r e f e r e n c e was f o r t h e a u t o m a t i c mode, s a y i n g t h e a u t o m a t i c mode "should b e e q u a l l y es good as t h e c a s t o r mode i f we had a h i g h e r r e s p o n s e r a t e i n t h e g e a r . " T h i s c o m e n t i s r e a s o n a b l e when one c o n s i d e r s t h a t t h e a u t o m a t i c node is a c t i v e l y s e l f - a l i n i n g i n s o f a r a s r e q u i r i n g n o p i l o t a d j u s t m e n t . Time h i s t o r i e s t o r an 'lute- olatic mode l a n d i n g w i t h a r i g h t crosswind of 13.6 knots ar:! g i v e n i n f i g u r e 1 6 ( b ) . During t h e approach, tile main ar?d r 2 s e gea;. t r a c k e d tile c r a b dngle c l a s e l y through - ,me r a t h e r sc-?ere h e a d i n g c h a n g e s , w i t h t h e g e a r o f f s e t t o t h e l e f t , c o u n t e r c ~ o c k w i s e ) t o cornpenscite f o r tlic r i g h t c r a b a n g l e . t l t touchdown, t h e c a s t o r l o c k s were , ~ u t o r r . , i t i c ~ l l y a p p l i e d , and tlie n o s e g e a r s t o p p e d t r a c k i n g c r a b a n g l e t o mahc i t a v a i l a b l e f o r s t e e r i n g . I n t h i s landing, t h e p i l o t used rudder pedal The records were terminated s t e e r i n g of t h e n t e e g e a r f o r about 1 3 s e c .
b e f o r e t h e g e a r were centered. I f , as i n t h e p r e s e n t c a s e , t h e touch- d m f o r c e s on t h e wheels a r e adequate t o a l i n e t h e g e a r without pro- t h e c a s t o r mode ducing an o b j e c t i o n a b l e r e a c t i o n ia t h e a i r p l a n e , would be p r e f e r a b l e t o t h e more complex and expensive automatic mode.
PC, t h e p r e s e t mode, t h e p i l o t is r e q u i r e d t o choose and set t h e crosew,nd landing gear tt an a p p r o p r i a t e o f f s e t a n g l e f o r touchdown.
Time h i s t o r i e s f o r a 15.6 knot crossu::id l a n d i n g i n t h e p r e s e t mode E a r l y i n r h e approach, t h e p i l o t s e l e c t e d are given i n f i g u r e 16(c).
an o f f s e t angle of 12' r i g h t , t o match t h e average l e f t a i r p l a u e crab During t h e approach, t h e p i l o t made s e v e r a l ad) us tments , e v e n t u a l l y anple.
r e t u r n i n g t h e crosswind landing g e a r t o 12', a f t e r which t h e c a s t o r locks were applied. D ~ r i n g t h e f l a r e , t h e r e was a sudden change i n heading due t o wind s h e a r and t h e a i r p l a n e landed w i t h a crab angle of only The 5.5' l e f t , g i v i n g a 6.5' misalinement with d i r e c t i o n of ravel.
p i l o t used rudder pedal s t e e r i n g t o compensste d u r i n g t h e ground r o l l o u t , w i t h t h e f u l l 3' of nose-wheel t r a v e l a v a i l a b l e through t h e rudder pedal s y s tern. This approach i l l w t r a t e s t h e prcblem of c o o r d i n a t i n g crab angle and g e a r o f f s e t a c p l e , e s p e c i a l l y i n unsteady ~ o n d i t i o n s , i n which t h e crab angle is c o n t i n u a l l y changing. This problem is p a r t i c u l a r l y s e v e r e i n t h e f l a r e . Quoting one of t h e q i l o t s , "In t h e f l a r e , t h e p i l o t c a n ' t b e looking a t t h e c o c k p i t i n s t r u m e n t s , s o tle f i n d s i t J i f f i c u l t t o jxdge i f t h e a i r p l a n e crab angle is tlie same ( i . e . , same i n magnitude, b u t o p p o s i t e i n d i r e c t i o n ) as t h e gear angle."
The l a r g e crosswinds encountered i n t h i s program were always accompanied by c o n s i d e r a b l e t u r b u l e n c e , g u s t i n e s s , and wind s h e a r . These unsteady conditions a r e r e f l e c t e d i n tile a i l e r o n , rudder, and crab a n g l e tirne h i s t o r i e s f o r a l l t h r e e approaches i n f i g u r e 16. For t h e unsteady conditions experienced d u r i n g t h e c a s t o r mode approach ( f i g . 1 6 ( a ) ) and t h e automatic mode a p ~ r o a c h ( f i g . 1 0 ( b ) ) , i t is d o u b t f u l i f t h e p i l o t s would have attempted a p r e s e t mode crosswind l a n d i ~ , . The c a s t o r and automatic modes r e l i e v e d t h e p i l o t s of ,lavinr t o c o n t i n u a l l y a d j u s t and n o n i t o r t h e g e a r p o s i t i o n . T h e p i l o t s f o u n i t h e p r e s e t node t o be very u n d e s i r a b l e : n unsteady conditions. 'n f a c t , they s t a t e d t h a t t h e p r e s e t mode was t h e "most u n d e s i r a b l e of t h e t h r e e modes. " The maximum l a t e r a l d i s p e r s i o n during ground r o l l out was 18.3 m (60 f t ) , and t h e maximur, a i r p l a n e r o l l d i s t a n c e was l e s s than 457.2 tn (1500 f t ) s l t h ~ u g h very l i t t l e main gear braking was used. Thz p i l o t s b e l i e v e t h a t much s m a l l e r l s t e r a l d i s p e r s i o n s and s h o r t e r r o l l d i s t n - 1 ~ ~ 1 s would have been p o s s i b l e i f t h e a i r p l a n e had improved ciain gear brakin:. , i n c r e a s e d nose-gear s t e e r i n g t r a v e l through t h e rudder p e d a l s , more e f f e c t i v e wing-lif t s p o i l e r s , and f a s t e r engine spool-up time f 01- improved braking a n d s t e e r i n g (asymmetric t l i r u s t ) .
n e p i l o t s f e e l t h a t g r e a t l y i q r o v e d s a f e t y and e d o r t can b e realized by devvloping .n operaticmal c a s t o r lwde c r o s s w i d lmxling- gear system incorporating c a s t o r lo& and rudder pedal s t e e r i n g - Si& forces w u l d bc reduced a t touchdam t o produce a smooth landing f o r the passeagerso The operation of a crosswind landing gear oa slippery nmways needs f u r t h e r study, a a a l y s i s , imdfor t e s t i n g .
The landing-gear research being conducted at M A Langley W e a r c h Center is s i z e d a d research relative t o t i r e t r e a d developeents, povered-uheel taxiing, air cushion landinp svst-. a d c r o s s w i d The s t a t u s of these landing gear is discussed in saee d e t a i l , four p r o g r a are as follaus:
Tire-tread wear - ?he preliminary ground t e s t s are coaplete and
f l i g h t tests t o determine wear c h a r a c t e r i s t i c s i n f l e e t use a r e imde w a y
Powered wheels - the prototype is under development
Air cushion landing gesr - analysis and experiaental tests
a r e underway
Crosswicd landing gear - model and f l i g h t tests a r e now c a p l e t e
and equations of motion describing the ground-run t r a j e c t o r y have been derived f o r a w d e l t e s t The preliminary r e s u l t s of the crosswind landing-gear f l i g h t t e s t s indicated: Landings can be made with crosswinds up t o 27 knots with a 1.
crosswind landing gear; the previous cr-ssxind l i m i t s with t l ~ e ccnventional t r i c y c l e landing gear were 15 t o 20 knot: .
I 2. For the l i g h t transport airplane t e s t e d , tile s e l f - a l i n i n g feature of the crosswind landing gear was forild t o be e s s e n t i a l f o r landing i n severe crosswinds.
? . The c a s t o r mode (passive self-alineoeni; uas preferred by the p i l o t s ; p r e s e t t i n g the landing gear p r i o r t o i\;uci*- down was the l e a s t desirable of the three modes of operation t h a t were investigated.
S t d s , S d y 1 1 . ; aul Tamer, John A. : S t a t u s of Recent A i r c r a f t Braking md Cornering Ilseuch. A i r c r a f t S l f e t y a d Operating Ptoblcrs, NASA SP-416, 1976, pp. 257-269.
McDmaell N r c r a f t Co.: Expmsioa of F l i g h t Simulator C a p d i l i t y f o r Study and S o l u t i a r of A i r c r a f t Directional Control Problers
on Rtmrays. Phase 11 - F i n a l Report. -A CR-145046, 1976-
Behavior of Aircraft Antf- Stubbs, S d y H . ; m d Zamer, Jdm A. :
skid Ir.king Systems an Dry and Y e t W a y Surfaces - A Velod*-y-
Rate-Coatrolled, Pncsun-Bi.r-XodtsLated System. U S A 0-83;2, 1976.
T m t , J o b A. ; etd Stubbs, Sandy H . : Behavior of A i r c r a f t Anti-
skid B r w S y s t m on D r y rad W e t b a y Surfaces - A S l i p -
Ratio-Controlled System Y i t h Gromd Speed Refereace F r a UnbraLed :bse Wheel. NASA R3 D-8455, 1977, BcPder, E . K . ; Berktugl, E , F.; and Bieber, 3 . : A F e a s i b i l i t y Study of Active Landing Gear. mL-TR-70-126. 6.S. Air Force, J u l y 1971. (Available from DDC as AD 887 451L).
Wignot, Jack t . ; Durup, Paul C. ; and Camm, Xax A. : Design FO~IEG- latiar and Analysis of an Active Landinp Gear. Volume I.
Analysis, AFFDL-TR-71-80, Vol. I, U.S. Air Force, Aug. 1971.
(Available f tom 3DC as AD 887 127L.)
!%Sehee, John R.; and Carden, H w y 0 . : A Nathematical Sodel of an Active Coatrol Landing Cear f o r Load Control During Impact and 1 - t :USA Til D-8080, 1976.
Barrois, U . : Use of Ceneral Fatigue Data i n the ' I n t e r p r e t a t i m of F u l l - h a l e Fatigue Tests. AO-9G-228, Oct. 1977, pp. 62-66.
Dreher, Robert C.: Studies of F r i c t i o n and Urar C h a r a c t e r i s t i c s of Various Wires f o r liire-brush Skids. X A S A TN 0-8517, 1977.
Horne, 'Jalter B.: S t a t u s of R w a y Slipperiness Research. A i r - c r a f t Safety and Operating P.-oblenu, :USA SP-416, 1976, pp.
191-245.
Yager, Thomas J. ; and !:cCarty, Jahn L . : F r i c t i o ~ t C t ~ a r a c t e r i s t f c s of Three 30 x 11.5-14.5, Type VIII, A i r c r a f t Tires Yith Various Tread Groove P a t t e r n s and Rubber Compounds. SASA TP-1080, 1977.
Leland, T r a f f o r d J . U.; and Thompson, U i l l i a m C.: Landing-Impact S t u d i e s of a 0.3-Scale We1 Mr Cushion Landing System f o r z Navy F i g h t e r X r p l a n e . ?USA RJ 0-7875, 1975.
Thorpson. W l l l l a m C.: Landing Performance of an Air-Cushion Landing System I n s t a l l e d on a l/lO-Scale Dynamic Xodel of t h e C-8 Buffalo Airplane. M A TH D-7295, 1973.
Thompson, EJilliam C.; Bogi:ani, Ash& 5 . ; and Leland, T r a f f o r d J.k'.: E x p e r i s e n t a l and h a l y t i c a l Rynamic Flcw C h a r a c t e r i s t i c s of an A x i a l - F l w Fan From m fir r3us;?fon Landing System ?lodel. XASX RJ D-8413, 1977.
Boghani , A. 3 . ; Captain, L . N. ; and VL w l e y , D. N. : tieave-Pi tch-
R o l l Analysis and T e s t i n g of A i r Cushion L a d i n g Systems. XASA CK-2917, 1978.
Stubbs , Sandy X. ; Bvrdsong, Thomas A. ; a r c i S l e e p e r , Robert E . : An Experimental Simulation Studv of Four Crosswind L a d i n g - Gear Concepts. SASA TN I)-7864, 1975.
S l e e p e r , Robert K . ; and Smith. Eunice G.: X Transformation Xethod for Deriving From a Photograph, P o s i t i o n and Heading of a Vehicle i n 3 Plane. SXSX TX P-8201, 1976.
F i s h e r , Bruce D. ; Champine, Robert A . ; Deal, Perry L.; P a t t o n , James ?I., Jr.; and H a l l , A l b e r t W.: A F l i g h t I n v e s t i g a t i o n of P i l o t i n g Techniques and Crosswind !.imitations During Visual STOL-Type Landing Operat icms. ::SA TS D-8264, 1976.
Champine, Robert A.: Crosswind Landing-Gear P o s i t i o n I n d i c a t o r .
NASA Tech Brief LhR-? 1941, 1976.
Spangler, Roman Y., -Jr.: Simulated Ground-Level STOL Runway/ a i r c r a f t Evaluation. FrU-RD-73-110, Federal Aviation Xdministra- t i o n , Sept. 1973.
TABLE 11. - MATRIX OF T E S T CONDITIONS RECORDED FOR 195 LANDINGS
# Crosswind Approach Number of landing8 for each 5-knot angle, mode crosswind interval deg 0 t o 5 5 Lo 10 10 t o 15 20 to 2 5 15 t o 20 25 to 30 Castor 4 11
- 3 2 0 5 37 4 5
Automat1 c 0 17 20 0 0 5 Preset 11 0 0 11 4 1 0 C a n t or 3 0 0 0 Automatic 0 1 0 0 0 Preset -6 0 0 0 0 0 0 I.
* LONGITUDINAL DISTANCE, 5 ---MEASURED
1 .o
-COMPi,TED 7 1 4
LATERAL
I ' \ 4
D I S T A N C E LONGITLOINAL 6r 'f S,MULAltD
k , m 0 - RIGHT DISTANCE. 5 : .f 2 R O S S I V I N D
Y. m 1 I I ,
t -
- .5
4 1 4J
- 1 0 -
0 .5 1.0 1.5 2.0 2.5 T I M . sec DISTANCE. x, m Figure 9 . - Computed ground r o l l trajectory of landing-gear model.
RUNWAY
I -
CROSSWIND I
I HEAD\i'lND
E'igurr 10. - Schcmat i c of typic.11 crosswind l a n d i n g w i t h c r o s s w i n d :car.
26 knots CROSSW~ND
58 kWs A l K ~ P E E D
Figure 15.- A 26-knot crosswind landing with crosswind gear.
RIGHT
2 0
S I M S L I P, deg 0 ?&\*%k/p-.i,+w, -20' 1.
-a! LEFT OFF- SCALE
20 RIGHT
'l &-F+---- BANK, deg 0-:4-.--.- ,
-20 LEFT
25 LEFT
. .
A I LE RON, deg 0 v ; T -$, r ' ~ & ~ ' ~ ~ - - .
I . b
-b RIGHT
40 LEFT
. I
. .
C R A 8 , deg 2 0 ' L
3 0 RIGHT
M A 1 N GEA9, deg
0 -
\TI LLER-BAR
60 RIGHT
STEERING
NOSE GEAR, deg 30.
.,li \ . . ~. ,
10 . LEFT
.
1 4
RUDDER, d q ~ + i ? + i . Y % - ry-L. L?4t. ,a,A--
, ' & '\3
-10. ,
-20 RIGHT 1 2 3
n I
0 1'0 20 30 40 50 60 10 80
NOTES: (1) TOUCHDOWN
T I M E , sec
(2) CASTOR LOCKS O N
(3) GEAR "CENiER"
REQUESTED
Fijiurc 1 6 . - t:rosswind ligndin); t i m e t l i s t o r i c . ~ .
r7-
30 RIGHT
ij/ Y F F - S C A L E
4 ,
SIDESLIP, deg O ~ ~ ~ , ' a . : i . l ; v ; i $ q \'PC$@
-20 LEFT
1 0 RIGHT
BANK, deg OL..,. ,u,idbh.b---..- -~.j>~~x?~-
-lo kn
25 LEFT . :
A I LERON, deg
0 , j.* m3~,+i*,,L*i-. r q i r nt!+)P4Y'C --. . . - -
i
-25 RIGHT
-
. \ > . . -.\\, l.- -- w-., L-
CRAB, deg
- RIGHT
L -.
c--- - - - -
,- .-----
M A I N GEAR, deg
- 3 0 -LEFT
NOSEGEAR,deg . - . - - . . - - z - \--. _ _ -- - -
-30 - L E ~
10 LEFT
-
R U D DE R, deg 0 -*4k-.-~,-k- e~rb~*\4Ll~7/, iL rj-
I: 1
R l GHT
-15
1 ~ . . . v v , 2 3 v - l - 4
0 1 0 2 0 3 0 4 0 % 6 0 7 0 8 0 9 0 1 0 0
NOTES: 1 - AUTOMATI C MODE ON TIME, sec
2 - TOUCHDOWN
3 - BEGIN RUDDER PEDAL STEER
4 - END RUDDER PEDAL STEER
( b ) Autdn,at i c mcde 1andir.g.
Figure 16. - Continued.
20 R I G H T
0 -: --. ,.. 4,- C _ . & - - ' , -w::,
S I DESLI P, deg
.i
-20
$1
-40 LEFT SCALE
20 R I G H T
BANK, deg 0 - - . - - $ \ - . % - - - - -
-20 LEFT
25 LEFT
-25 R I G H T
20 LEFT
CRAB, deg -
\ -
3 0 R I G H T
GEAR ADJUSTMENT
M A 1 N GEAR, deg
/'-
\GEAR ADJUSTMENT
RIGHT -STEERING INPUT
NOSE GEAR, deg
10 LEFT
. . a 1
, +.. ..... .*,3!:
RUDDER, deg 0
' .
8 , a \ ; **
- 10
-20 RIGHT
NOTES: 1- CASTOR LOCKS O N v l v 2 r 3 r S 5 1
2- TOUCHDOWN 0 10 20 30 40 50 60 70 80 90 100 110