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Flight investigation of piloting techniques and crosswind limitations using a research type crosswind landing gear

NASA-TP-1423 · NASA (NTRS) · 1979

Public domain · NASA (NTRS)Technical Reports

Overview

A research-type crosswind landing gear was tested in a flight program which used a light STOL transport in strong crosswind conditions. The research-type crosswind landing gear used enabled the airplane to land to crosswinds up to a magnitude of 25 to 30 knots. Three modes of landing-gear operation…

Publisher
NASA (NTRS)
Document
NASA-TP-1423
Year
1979
Pages
56

Document

NASA Technical Paper 1423

Flight Investigation of

Piloting Techniques and Crosswind

Limitations Using a Research-

Type Crosswind Landing Gear

Bruce D. Fisher, Perry L. Deal, Robert A. Champine, and James M. Patton, Jr.

MAY 1979

NASA Technical Paper 1423

Flight Investigation of

Piloting Techniques and Crosswind

Limitations Using a Research-

Type Crosswind Landing Gear

Bruce D. Fisher, Perry L. Deal, Robert A. Champine, and James M. Patton, Jr.

Larzgley Research Center H a ?npton, Virginia N a t i ~ n a l Aeronautics and Space Administration Scientific and Technical Information OMice A f l i g h t r e s e a r c h program was u n d e r t a k e n by t h e National. A e r o n a u t i c s and Space A d m i n i s t r a t i o n (NASA) t o i n v e s t i g a t e t h e problems a s s o c i a t e d w i t h l a n d i n g a l i g h t STOL t r a n s p o r t i n s t r o n g c r o s s w i n d c o n d i t i o n s w i t h a r e s e a r c h - t y p e , c r o s s w i n d l a n d i n g g e a r . T h i s program was a c o n t i n u a t i o n of an e a r l i e r program where t h e same a i r p l a n e w i t h its c o n v e n t i o n a l , t r i c y c l e l a n d i n g g e a r was used.

With t h e c r o s s w i n d l a n d i n g g e a r used i n t h i s program, c r o s s w i n d l a n d i n g s were made w i t h c r o s s w i n d magnitudes o f 25 t o 30 k n o t s ; whereas w i t h t h e c o n v e n t i o n a l , t r i c y c l e l a n d i n g g e a r used i n t h e e a r l i e r program, t h e c r o s s w i n d l i m i t s were 15 t o 20 k n o t s . Throughout t h i s p a p e r t h e term "crosswind" means d i r e c t c r o s s w i n d component, w i t h a c r o s s w i n d from t h e r i g h t b e i n g a p o s i t i v e v a l u e .

T h r e e l a n d i n g - g e a r modes were s t u d i e d : p r e s e t , a u t o m a t i c , and c a s t o r .

P r e s e t t i n g t h e l a n d i n g g e a r t o a f i x e d c r a b a n g l e p r i o r t o touchdown was found to be an u n d e s i r a b l e method o f o p e r a t i o n b e c a u s e t h e p i l o t s d i d n o t have s u f f i - c i e n t i n f o r m a t i o n t o p r e d e t e r m i n e t h e p r o p e r c r a b a n g l e . The a u t o m a t i c mode w a s l i m i t e d somewhat by t h e i n a d e q u a t e compass-system r e s p o n s e r a t e i n t u r b u - l e n t c o n d i t i o n s . The c a s t o r mode of o p e r a t i o n f o r t h e c r o s s w i n d l a n d i n g g e a r ( p a s s i v e s e l f - a l i g n m e n t ) was p r e f e r r e d by t h e p i l o t s f o r o p e r a t i o n i n s e v e r e c r o s s w i n d s . I n a castor-mode l a n d i n g , t h e p i l o t s would a p p l y t h e main-gear c a s t o r l o c k s a f t e r t h e g e a r s had p a s s i v e l y s e l f - a l i g n e d w i t h t h e d i r e c t i o n o f t r a v e l ; t h e n , t h e y would use nose-wheel s t e e r i n g and some b r a k e s d u r i n g t h e ground r o l l - o u t .

The c o n c l u s i o n s reached i n t h i s s t u d y a r e f o r t h i s p a r t i c u l a r STOL a i r p l a n e w i t h r e s e a r c h - t y p e , c r o s s w i n d l a n d i n g g e a r .

INTRODUCTION I n t h e f l i g h t r e s e a r c h program r e p o r t e d i n r e f e r e n c e 1 , p i l o t i n g t e c h n i q u e s and c r o s s w i n d l i m i t a t i o n s were s t u d i e d f o r a l i g h t STOL a i r p l a n e making c r o s s - wind l a n d i n g s w i t h t h e p r o d u c t i o n , c o n v e n t i o n a l , t r i c y c l e l a n d i n g g e a r . The r e s u l t s o f t h a t program i n d i c a t e d t h a t c o n t r o l d u r i n g ground r o l l - o u t was t h e most c r i t i c a l problem and t h a t aerodynamic c o n t r o l i n f l i g h t r e q u i r e d f o r s l i p o r d e c r a b may l i m i t r o l l - o u t c o n t r o l . These r e s u l t s l e d t o t h e c o n c l u s i o n s t h a t a c r o s s w i n d l a n d i n g g e a r s h o u l d be c o n s i d e r a b l y s a f e r and t h a t t h e c r o s s w i n d l i m i t s c o u l d be s i g n i f i c a n t l y i n c r e a s e d . Throughout t h i s paper t h e term " c r o s s - wind" means d i r e c t c r o s s w i n d component, w i t h a c r o s s w i n d from t h e r i g h t b e i n g a p o s i t i v e v a l u e .

Based on t h e f l i g h t e x p e r i e n c e g a i n e d i n t h e s t u d y of r e f e r e n c e 1 and on model s t u d i e s of s e v e r a l crosswind-landing-gear s y s t e m s r e p o r t e d i n r e f e r e n c e 2 , a r e s e a r c h - t y p e crosswind-landing-gear s y s t e m was d e s i g n e d and i n s t a l l e d on t h e a i r p l a n e , I n a d d i t i o n , w i n g - l i f t s p o i l e r s and r u d d e r - p e d a l s t e e r i n g of t h e nose g e a r were i n c o r p o r a t e d , NASA t h e n conducted a f l i g h t - t e s t program of t h e modi- f i e d a i r p l a n e , The o b j e c t i v e s of t h e program were t o e v a l u a t e and d e m o n s t r a t e t h e e f f e c t i v e n e s s of l i f t s p o i l e r s and v a r i o u s modes of crosswind-landing-gear o p e r a t i o n i n e x t e n d i n g t h e c r o s s w i n d l a n d i n g l i m i t s of t h e a i r p l a n e . P r e l i m i - n a r y r e s u l t s s f t h i s program were r e p o r t e d i n r e f e r e n c e 3 , which c o n t a i n s a summary of NASA l a n d i n g - g e a r r e s e a r c h ; t h e f i n a l r e s u l t s of t h i s program a r e r epor t e d h e r e i n .

SYMBOLS AND ABBREVIATIONS E x c e p t f o r a i r s p e e d and wind s p e e d , which a r e g i v e n i n k n o t s (1 k n o t = 0.51 44 m/sec) , d a t a a r e p r e s e n t e d i n b o t h S I and U.S. Customary u n i t s . The measurements and c a l c u l a t i o n s were made i n U.S. Customary U n i t s .

F a c t o r s r e l a t i n g t h e two s y s t e m s o f u n i t s a r e g i v e n i n r e f e r e n c e 4 .

l a t e r a l a c c e l e r a t i o n measured a t a i r p l a n e c e n t e r of g r a v i t y a~ I t d a t touchdown, p o s i t i v e f o r a c c e l e r a t i o n t o r i g h t , g u n i t s ( l g = 9.806 m/sec2) STOL s h o r t take-off and l a n d i n g VFR v i s u a l f l i g h t r u l e s v~~ l a n d i n g c o n f i g u r a t i o n s t a l l s p e e d , f u l l f l a p , k n o t s V t d i n d i c a t e d a i r s p e e d a t touchdown, k n o t s 6 a n g l e of s i d e s l i p , p o s i t i v e f o r r i g h t s i d e s l i p , deg t o t a l a i l e r o n d e f l e c t i o n , p o s i t i v e f o r l e f t r o l l , deg & a c r a b a n g l e , p o s i t i v e f o r a i r p l a n e n o s e l e f t of runway & c r a b c e n t e r l i n e , deg c r a b a n g l e a t touchdown, p o s i t i v e f o r a i r p l a n e nose l e f t of runway Gcrab,td c e n t e r l i n e , deg main-gear o f f s e t a n g l e , p o s i t i v e f o r g e a r r o t a t e d t o r i g h t o f &m9 a i r p l a n e c e n t e r l i n e , deg main-gear o f f s e t a n g l e a t touchdown, p o s i t i v e f o r g e a r r o t a t e d t o 6rng,td r i g h t of a i r p l a n e c e n t e r l i n e , deg nose-gear o f f s e t a n g l e , p o s i t i v e f o r g e a r r o t a t e d t o r i g h t o f &ng a i r p l a n e c e n t e r l i n e , deg & r rudder d e f l e c t i o n , p o s i t i v e t r a i l i n g edge l e f t , deg (3 t d p i t c h a t t i t u d e a t touchdown, p o s i t i v e f o r nose up, deg cP bank a n g l e , p o s i t i v e f o r r i g h t bank, deg

4 t d r o l l a t t i t u d e a t touchdown, p o s i t i v e f o r r i g h t r o l l , deg

T e s t A i r p l a n e The t e s t a i r p l a n e was a high-wing, t w i n - t u r b o p r o p l i g h t t r a n s p o r t p r e - v i o u s l y d e s c r i b e d i n r e f e r e n c e 9 and s u b s e q u e n t l y m d i f i e d f o r t h i s program.

(11 000 l b ) , w i t h t h e a i r c r a f t The maximm d e s i g n g r o s s w e i g h t was 48 928 N w e i g h t r a n g i n g between 38 253 and 45 370 N (8600 and 10 200 l b ) d u r i n g t h e tests. The a i r p l a n e m o d i f i c a t i o n s added v e r y l i t t l e w e i g h t and d i d n o t s h i f t t h e l o n g i t u d i n a l c e n t e r o f g r a v i t y of t h e a i r p l a n e .

A dimensioned three-view drawing o f t h e a i r p l a n e a s m o d i f i e d f o r t h i s program is g i v e n a s f i g u r e 1 . The m o d i f i c a t i o n s i n c l u d e d r e p l a c i n g t h e f i x e d l a n d i n g g e a r w i t h a r e s e a r c h - t y p e , crosswind l a n d i n g g e a r , i n c o r p o r a t i n g nose- g e a r s t e e r i n g w i t h t h e p i l o t ' s r u d d e r p e d a l s , and adding w i n g - l i f t s p o i l e r s .

The f l a p system, e n g i n e c h a r a c t e r i s t i c s , and b a s i c aerodynamic c o n t r o l s were unchanged from t h o s e d e s c r i b e d i n r e f e r e n c e 1 . The c r osswind-landing-gear and w i n g - l i f t s p o i l e r systems a r e d e s c r i b e d i n t h e n e x t s e c t i o n .

Crosswind-Landing-Gear and Wing-Lift S p o i l e r Systems The o r i g i n a l , s i n g l e main wheels were r e p l a c e d by t h e d u a l wheel u n i t s from a m i l i t a r y h e l i c o p t e r ; e a c h wheel r o t a t e d i n d e p e n d e n t l y o f t h e o t h e r s .

The main-gear l e g s of t h e t r a n s p o r t were i n v e r t e d , t h e r i g h t and l e f t l e g s were i n t e r c h a n g e d , and a new nose wheel and f o r k were i n s t a l l e d . T h i s change l o w e r e d t h e f u s e l a g e r e f e r e n c e l i n e and v e r t i c a l c e n t e r of g r a v i t y a b o u t 1 5 . 2 c m ( 6 i n . ) and reduced t h e t a i l c l e a r a n c e a n g l e from 10.5O t o 8.5O. The c r o s s w i n d l a n d i n g g e a r is shown i n more d e t a i l by t h e drawing i n f i g u r e 2 and by t h e photograph and dimensioned drawing i n f i g u r e 3. The main-gear u n i t s were p h y s i c a l l y i n t e r c o n n e c t e d by m e t a l t i e r o d s ( f i g s . 2 and 3 ) t o i n s u r e t h a t t h e main-gear u n i t s were t r a c k i n g t o g e t h e r and t o f a c i l i t a t e t h e c e n t e r i n g of t h e g e a r . The o r i g i n a l l a n d i n g - g e a r rubber s p r i n g b l o c k s were r e p l a c e d by r i g i d l i n k s shown i n f i g u r e 2 . I n s t e a d of u s i n g t h e r u b b e r s p r i n g b l o c k s , t h e r e s e a r c h - t y p e crosswind l a n d i n g g e a r used a s p r i n g mechanism which is shown i n f i g u r e 3. The d u a l main-gear a x l e was t r a i l e d behind a h o r i z o n t a l p i v o t , and t h e v e r t i c a l motion was c o n t r o l l e d by a l i q u i d s p r i n g ( l i q u i d - f i l l e d s t r u t ) mounted between t h e a x l e and a p o i n t above t h e p i v o t . The r e s e a r c h - t y p e crosswind-landing-gear s y s t e m was d e s i g n e d t o p r o v i d e s e v e r a l modes of o p e r a - t i o n and was n o t o p t i m i z e d f o r w e i g h t , aerodynamics, o r o p e r a t i o n a l s i m p l i c i t y .

T h e r e was no a n t i s k i d s y s t e m f o r t h e s e t e s t s . The main and nose g e a r c o u l d be p i v o t e d +30° f o r c r o s s w i n d l a n d i n g s .

The crosswind-land ing-gear system was d e s i g n e d t o p r o v i d e t h e c a p a b i l i t y o f i n v e s t i g a t i n g t h r e e crosswind-landing-gear c o n c e p t s : p r e s e t , a u t o m a t i c , and c a s t o r . The t h r e e modes of o p e r a t i o n a r e o u t l i n e d i n t a b l e I .

I n t h e p r e s e t mode, t h e p i l o t had t o s e t t h e g e a r t o t h e d e s i r e d o f f s e t a n g l e p r i o r t o touchdown by means of a t i l l e r - b a r c o n t r o l i n t h e c o c k p i t , (See f i g . 4 . ) The t i l l e r b a r , which c o n t r o l l e d t h e p i v o t a n g l e o f t h e g e a r , was located on t h e c o n t r o l column behind t h e p i l o t " c o n t r o l wheel, A f t e r t h e main g e a r had been l o c k e d f o l l o w i n g touchdown, t h e t i l l e r bar c o u l d s t e e r o n l y $he nose gear, ( T h i s was t h e purpose of t h e t i l l e r bar i n t h e umodified a i r p l a n e , ) I n t h e automatic mode ( a c t i v e s e l f - a l i g a m e n t ) , the gyrocompass system was used t o g e n e r a t e a n e r r o r s i g n a l p r o w r t i o n a l to t h e a n g l e between a s e l e c t e d runway h e a d i n g and t h e a i r p l a n e heading. T h i s s i g n a l , summed w i t h a main-gear p o s i t i o n f e e d b a c k s i g n a l , was used t o a u t o m a t i c a l l y keep t h e g e a r a l i g n e d w i t h t h e runway c e n t e r l i n e w h i l e i n f l i g h t , I n t h e c a s t o r mode, t h e l a n d i n g - g e a r s y s t e m was f r e e t o a l i g n w i t h t h e d i r e c t i o n of t r a v e l a t touchdown ( p a s s i v e s e l f - a l i g n m e n t ) . However, t o p r e - v e n t t h e a i r p l a n e from v e e r i n g o f f t h e runway, t h e main gear had t o be l o c k e d i n t h e p o s i t i o n e x i s t i n g s h o r t l y a f t e r touchdown and nose-wheel s t e e r i n g t h e n i n i t i a t e d .

I n a l l modes, t h e main g e a r was l o c k e d i n p o s i t i o n by a h y d r a u l i c c a s t o r l o c k on e a c h main-gear u n i t . (See f i g . 3 . ) I n t h e p r e s e t and c a s t o r modes, t h e main g e a r was l o c k e d i n 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 p i l o t ' s con- t r o l wheel. (See f i g . 4 . ) 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 p r i o r t o touchdown by t h e c o n t r o l - w h e e l s w i t c h a l o n e . 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 a c t i v a t e d o n l y when b o t h t h e c o n t r o l - w h e e l s w i t c h was d e p r e s s e d and b o t h main-gear s q u a t s w i t c h e s ( f i g . 3) were a c t i v a t e d . I n t h e a u t o m a t i c mode, t h e g e a r was l o c k e d i n p o s i t i o n a f t e r e i t h e r of t h e two main-gear s q u a t s w i t c h e s were compressed by t h e w e i g h t of t h e a i r p l a n e w i t h o u t r e q u i r i n g t h e p i l o t to p r e s s t h e s w i t c h . The main g e a r had t o be l o c k e d o r r e s t r a i n e d i n o r d e r t o d e v e l o p nose-wheel s t e e r i n g c a p a b i l i t y .

I n any l a n d i n g - g e a r o p e r a t i o n a l mode, a f t e r a s q u a t s w i t c h o n t h e n o s e g e a r had been a c t i v a t e d , t h e p i l o t c o u l d s e l e c t rudder-pedal s t e e r i n g of t h e nose g e a r by d e p r e s s i n g and h o l d i n g 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.

T h i s s w i t c h was a d j a c e n t t o t h e main-gear c a s t o r - l o c k s w i t c h shown i n f i g u r e 4.

The maximum d i f f e r e n t i a l nose-wheel t r a v e l w i t h rudder-pedal s t e e r i n g was from -3O t o 3O a b o u t t h e nose-wheel s e t t i n g a t t i m e of a c t u a t i o n . T h i s f e a t u r e was i n c o r p o r a t e d t o a l l o w t h e p i l o t t o have limited-nose-wheel 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 w i t h o u t 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 to r e a c h t h e t i l l e r b a r .

The p i l o t c o u l d a l s o c e n t e r t h e g e a r i n any mode by p u s h i n g a s i n g l e s w i t c h on t h e crosswind-landing-gear c o n t r o l p a n e l shown i n f i g u r e 4. The g e a r c e n t e r i n g command o v e r r o d e a l l o t h e r i n p u t s o r a c t i o n s . The main g e a r c e n t e r e d through h y d r a u l i c a c t i o n on t h e t i e rod t h r o u g h t h e c e n t e r i n g c y l i n d e r shown i n f i g u r e 2. During c e n t e r i n g , a p s i t i o n s i g n a l was f e d t o t h e nose-gear a c t u a t o r s o t h a t t h e nose g e a r would f o l l o w t h e a n g u l a r p o s i t i o n of t h e main g e a r .

The c o n v e n t i o n a l aerodynamic ( r u d d e r and a i l e r o n ) and low-speed nose-wheel 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 frm t h e o r i g i n a l a i r p l a n e . Main-gear b r a k i n g e f f e c t i v e n e s s was g r e a t l y reduced because h a r d b r a k i n g caused f l a t s p o t s o r blown t i r e s . A p p a r e n t l y , w i t h t h e a i r p l a n e h e e l i n g , one of t h e d u a l wheels d i d n o t c a r r y s u f f i c i e n t l o a d t o overcome b r a k e t o r q u e and s k i d d e d , which c a u s e d a f l a t s p o t on t h a t t i r e , R e v e r s e t h r u s t became t h e p r i n c i p a l b r a k i n g c o n t r o l a l t h o u g h very l i t t l e a c t u a l engine power was d e v e l o p d because of t h e slow e n g i n e r e s p o n s e , (See r e f , 1 , j A crosswind-landing-g@ar p s i t i o n indicator was d e v e l o w d for t h i s pro- gram. Tho location of the indicator i n t h e a i r p l a n e i n s t r u m e n t p a n e l is shown i n figure 4, and a schematic sf the i n d i c a t o r i s shown i n f i g u r e 5, The gyro- The double- c a p a s s card was d r i v e n by a gyro slaved to the c m p a s s h e a d i n g , b a r n e e d l e was s e t by t h e p i l o t t o t h e m a g n e t i c h e a d i n g of t h e l a n d i n g runway.

The a n g u l a r d i f f e r e n c e between t h e a i r p l a n e h e a d i n g and t h e runway m a g n e t i c h e a d i n g (double-bar n e e d l e ) was t h e c r a b a n g l e of t h e a i r p l a n e . The s i n g l e - bar n e e d l e i n d i c a t e d t h e a n g l e of t h e l a n d i n g g e a r 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 . When t h e l a n d i n g g e a r s were p r o p e r l y a l i g n e d w i t h 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 were superimposed. I n t h e example g i v e n i n f i g u r e 5, t h e runway heading and l a n d i n g - g e a r p o s i t i o n are The a i r p l a n e is shown f l y i n g t o a h e a d i n g o f 350°, p u r p o s e l y shown m i s a l i g n e d .

c r a b b e d 15O t o t h e r i g h t of runway c e n t e r l i n e , The l a n d i n g - g e a r system is shown w i t h an o f f s e t of 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 l a n d i n g g e a r s have been r o t a t e d 5O t o o f a r . I n t h e p r e s e t mode, t h e p i l o t used t h e t i l l e r bar t o c o r r e c t t h e e r r o r and b r i n g t h e l a n d i n g g e a r i n t o a l i g n m e n t w i t h t h e runway ( s i n g l e n e e d l e superimposed on t h e d o u b l e n e e d l e ) .

I n t h e a u t o m a t i c mode, n e e d l e misalignment i n d i c a t e d a s y s t e m m a l f u n c t i o n .

Some a i r p l a n e s w i t h p r e s e t c r o s s w i n d l a n d i n g g e a r have been known t o have a c t u a l l y l a n d e d w i t h t h e l a n d i n g gear s e t i n t h e wrong d i r e c t i o n . The u s e of t h i s i n d i c a t o r s h o u l d p r e v e n t such a n o c c u r r e n c e u n l e s s a n u n u s u a l l y s e v e r e wind s h i f t were to occur p r i o r t o touchdown b u t a f t e r t h e l a n d i n g g e a r s were set. The p i l o t c o u l d e a s i l y d e t e r m i n e p r o p e r wheel a l i g n m e n t by a q u i c k g l a n c e w i t h o u t m e n t a l l y p r o c e s s i n g i n f o r m a t i o n t o r e l a t e h e a d i n g and l a n d i n g - g e a r - a l i g n m e n t magnitude and d i r e c t i o n . F u r t h e r d e t a i l s on t h e crosswind-landing- g e a r p o s i t i o n i n d i c a t o r may be found i n r e f e r e n c e 5.

The w i n g - l i f t - s p o i l e r system ( f i g . 1 ) c o n s i s t e d of h y d r a u l i c a l l y a c t u a t e d p a n e l s on t h e upper s u r f a c e of each semispan. The s y s t e m was a u t o m a t i c a l l y l i m i t e d t o deployment a t touchdown by means of main-gear s q u a t s w i t c h e s i n s e r i e s w i t h a n arming s w i t c h and a t h r o t t l e p o s i t i o n s w i t c h . The s q u a t s w i t c h f o r t h e l e f t main g e a r c a n be s e e n i n f i g u r e 3. Each s p o i l e r was 7.7 p e r c e n t of t h e wing c h o r d , w i t h t h e leading-edge p i v o t a t 76 p e r c e n t of t h e wing c h o r d .

The l e n g t h of e a c h l i f t - s p o i l e r s e t was 31.8 p e r c e n t of t h e wing s e m i s p a n , w i t h t h e i n b o a r d end a t 29 p e r c e n t of t h e semispan.

Data A c q u i s i t i o n T h i r t y - t w o p a r a m e t e r s were r e c o r d e d onboard t h e a i r c r a f t by a magnetic- t a p e d a t a system a t 80 s a m p l e s / s e c by a p u l s e code m o d u l a t i o n method. A l l d a t a were c o r r e l a t e d by a t i m e code. An a u t o m a t i c ground-based d a t a s y s t e m was used t o produce t i m e h i s t o r i e s of t h e d e s i r e d d a t a . The p a r a m e t e r s i n c l u d e d a n g l e o f a t t a c k ; a n g l e of s i d e s l i p ; a l t i t u d e ; a i r s p e e d ; c o n t r o l s u r f a c e d e f l e c t i o n s ; p i t c h a n g l e ; r o l l a n g l e ; heading a n g l e ; l i n e a r a c c e l e r a t i o n a b o u t t h e X-, Y-, and Z-axes of t h e a i r p l a n e ; a n g u l a r v e l o c i t y a b o u t t h e X-, Y-, and Z-axes of t h e a i r p l a n e ; t h r o t t l e p o s i t i o n ; e n g i n e t o r q u e f o r e a c h e n g i n e ; e n g i n e s p e e d f o r e a c h e n g i n e ; main-gear a n g l e ; nose-gear a n g l e ; a i r p l a n e c r a b a n g l e ; rudder- p e d a l - s t e e r s w i t e h p s i t i o n ; g e a r - c e n t e r i ng s w i t c h p s i t i o n ; and main-gear- l o c k - s e l e c t e d s w i t c h p o s i t i o n , A i r s p e e d , a n g l e of a t t a c k , and a n g l e of s i d e s l i p were measured w i t h t h e p r o b e d e s c r i b e d i n r e f e r e n c e 1 . The p r o b e , and t h e nose boom upon which t h e probe was mounted, a r e shown i n f i g u r e 1, Nose-gear a n g l e was t a k e n from a p o s i t i o n p o t e n t i o m e t e r on t h e nose-gear s t r u t , and main-gear a n g l e was t a k e n from a p o s i t i o n p o t e n t i o m e t e r on t h e r i g h t main g e a r , A i r p l a n e c r a b a n g l e was taken from t h a t p a r t of t h e compass system which s u p p l i e d c r a b a n g l e t o t h e p i l o t ' s crosswind-landing-gear p o s i t i o n i n d i c a t o r i n t h e c o c k p i t . The touch- down p o s i t i o n , g r o u n d - r o l l d i s t a n c e , maximum l a t e r a l d i s p e r s i o n on r o l l - o u t , and wind-data measurements a r e d e s c r i b e d i n t h e f o l l o w i n g s e c t i o n .

T e s t F a c i l i t y VFR STOL c r o s s w i n d l a n d i n g s were made a t t h e a i r f i e l d shown i n f i g u r e 6.

The f i e l d e l e v a t i o n is 12.5 m (41 f t ) . Landings were made on a l l runways, depending on wind d i r e c t i o n , t o g e t t h e d e s i r e d c r o s s w i n d c o n d i t i o n s . T h i s a i r f i e l d is t h e same a s t h a t used i n t h e program r e p o r t e d i n r e f e r e n c e 1 .

STOL runway m a r k i n g s , a s d e s c r i b e d i n r e f e r e n c e 6 and i l l u s t r a t e d i n f i g u r e 7 , 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 m ( 1 00 f t ) wide and 457 m (1 500 f t ) l o n g . The p a i n t e d l i n e s were 0.305 m (1 f t ) wide, e x c e p t f o r t h e l o n g i t u d i n a l l i n e s i n t h e t a r g e t touchdown z o n e s ; t h e s e were 0.61 m (2 f t ) wide i n o r d e r t o enhance v i s i b i l i t y . The t h r e e runways on which t h e STOL runway markings were p a i n t e d were 1524 t o 2743 m (5000 t o 9000 f t ) l o n g and 46 t o 61 m (150 t o 200 f t ) wide.

The l a n d i n g s were made a t an a p p r o a c h a n g l e of 3O o r 6O. The a n g l e was i n d i c a t e d by t h e v i s u a l g u i d a n c e s y s t e m d e s c r i b e d i n r e f e r e n c e 1 . The v i s u a l g u i d a n c e system was p l a c e d b e s i d e t h e runway, f a r enough ahead of t h e t a r g e t touchdown zone t h a t w i t h t h e combined g l i d e p a t h and a nominal f l a r e , t h e p i l o t c o u l d g u i d e t h e a i r p l a n e t o t h e t a r g e t touchdown p o i n t shown i n f i g u r e 7.

Markers were p l a c e d a l o n g t h e runway edge a t i n t e r v a l s of 30.5 m ( 1 00 f t ) t o a i d t h e o b s e r v e r s i n t h e c o n t r o l tower i n e s t i m a t i n g t h e l o n g i t u d i n a l touch- down p o i n t , t h e s t o p p i n g d i s t a n c e , and t h e p o i n t a t which t h e maximum l a t e r a l d i s p e r s i o n o c c u r r e d .

L a t e r a l touchdown d i s p e r s i o n and maximum l a t e r a l ground r o l l - o u t d i s p e r - s i o n were computed from c a l i b r a t e d v i d e o r e c o r d s of t h e l a n d i n g s . Each l a n d - i n g was r e c o r d e d on a v i d e o t a p e r e c o r d e r whose s i g n a l was t a k e n from a camera l o c a t e d on t h e e x t e n d e d runway c e n t e r l i n e and f a c i n g t h e oncoming a i r c r a f t .

The camera, shown i n f i g u r e 8 , was l o c a t e d 206 m (675 f t ) Erom t h e end of t h e STOL runway ( f i g . 7 ) . A t y p i c a l v i d e o p i c t u r e is shown i n f i g u r e 9 . The v e r - t i c a l g r i d , which was e l e c t r o n i c a l l y superimposed on t h e p i c t u r e , was s c a l e d a t s e v e r a l known p o i n t s a l o n g e a c h STOL runway t o d e t e r m i n e t h e v a r i a t i o n of s c a l e f a c t o r w i t h d i s t a n c e of t h e a i r p l a n e from t h e camera l o c a t i o n . By use of t h i s d i s t a n c e i n f o r m a t i o n and t h e l o n g i t u d i n a l d i s t a n c e s o b t a i n e d from t h e o b s e r v e r s i n t h e c o n t r o l t o w e r , t h e l a t e r a l touchdown d i s p e r s i o n and t h e maximum l a t e r a l ground r o l l - o u t d i s p e r s i o n were d e t e r m i n e d , A s a f u r t h e r means of c o r r e l a t i n g t h e airplane-measured d a t a with t h e video d a t a , Green~qich mean time was a l s o superimposed on the p i c t u r e i n e i t h e r of t h e upper corners, Wind d i r e c t i o n and magnitude were measured a t f i v e e l e v a t i o n s on a wind- sensor tower l o c a t e d a t t h e c e n t r a l l a n d i n g - f i e l d p o s i t i o n shoin i n f i g u r e 6, The sensor e l e v a t i o n s were 3.05, 6.1, 9.1 4, 12.2, and 15.24 m (1 0, 20, 30, 40, and 50 f t j , The d a t a were d i s p l a y e d i n r e a l time on a cathode-ray t u b e i n t h e p r o j e c t c o n t r o l room and recorded on magnetic t a p e i n t h e c o n t r o l tower.

Crosswind Approach and Landing Technique The b a s i c p r i n c i p l e s of a crosswind-landing-gear o p e r a t i o n a r e i l l u s t r a t e d i n f i g u r e 10. During t h e approach, t h e a i r p l a n e was crabbed i n t o t h e wind, s o t h a t its ground t r a c k was along the extended runway c e n t e r l i n e with aerodynamic c o n t r o l s e s s e n t i a l l y n e u t r a l . With a crosswind g e a r , t h e landing gear could be his e l i m i n a t e d t h e a l i g n e d w i t h t h e a i r p l a n e ground t r a c k f o r touchdown.

demanding p i l o t t a s k s and l a r g e c o n t r o l i n p u t s necessary t o decrab or s l i p t h e a i r plane p r i o r t o touchdown.

The s l i p , c r a b , and cross-runway crosswind landing techniques were inves- t i g a t e d and r e p o r t e d i n r e f e r e n c e 1 f o r t h e a i r p l a n e equipped w i t h a conven- t i o n a l , t r i c y c l e landing gear. I n t h e p r e s e n t program, t h e crabbed approach was used throughout, and t h e v a r i a b l e s under i n v e s t i g a t i o n were t h e use of rudder p e d a l s t e e r i n g ; t h e use of w i n g - l i f t s p o i l e r s ; and t h e choice of e i t h e r p r e s e t , automatic, or c a s t o r mode of crosswind landing gear used f o r alignment w i t h t h e runway c e n t e r l i n e ( t a b l e I ) .

T e s t Procedures A t o t a l of 195 crosswind l a n d i n g s were made i n t h i s 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 . Table I1 c o n t a i n 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 grouped according t o crosswind magni- t u d e , approach angle, and crosswind-landing-gear mode of o p e r a t i o n .

T y p i c a l l y , t h e g l i d e s l o p e was i n t e r c e p t e d a t an a l t i t u d e of 183 m (600 f t ) f o r t h e 3O approaches and of 366 m (1 200 f t ) f o r t h e 6O approaches. The a i r - p l a n e was then s t a b i l i z e d on t h e approach p a t h a t an i n d i c a t e d speed of 65 t o 75 knots with f u l l f l a p s . The a i r p l a n e was f l a r e d a t about an a l t i t u d e of 4 . 6 m (1 5 f t ) f o r a touchdown a s c l o s e a s p o s s i b l e t o t h e t a r g e t touchdown p o i n t . The p i l o t ' s t a s k then was t o 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 runway 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.

l a n d i n g s were made on a d r y runway i n d a y l i g h t with VPR c o n d i t i o n s .

A l l A f t e r touchdown, t h e t h r o t t l e s were placed i n t h e r e v e r s e - t h r u s t p o s i t i o n , b u t t h e engine response was t o o slow t o produce a p p r e c i a b l e r e v e r s e t h r u s t d u r i n g t h e ground r o l l - o u t . L i t t l e , i f any, main-gear braking was used. The nose g e a r was s t e e r e d e i t h e r through t h e rudder p e d a l s or t h e s t e e r i n g t i l l e r , T~?ing-lift s p o i l e r s were used a f t e r touchdov~n f o r most of t h e landings.

RESULTS W W D B I SaSS LON Data P r e s e n t a t i o n A s u b s t a n t i a l p r t i o n s f t h e d a t a i n t h i s p p e r is p r e s e n t e d i n t h e form s f histograms, The d a t a given f o r each i n t e r v a l i n e l u d e v a l u e s e q u a l t o t h e Sower l i m i t b u t exclude those e q u a l t o t h e upper l i m i t . The d a t a were s o r t e d i n t o t h e number of samples per i n t e r v a l , o r , f o r c o n t r o l usage, i n t o t h e amount of t i m e during which t h e c o n t r o l d e f l e c t i o n s were w i t h i n an i n t e r v a l . I n most i n s t a n c e s , t h e d a t a f o r each i n t e r v a l were normalized t o produce r e l a t i v e f r e - quency o r r e l a t i v e time e i t h e r by d i v i d i n g by t h e t o t a l number of samples o r d i v i d i n g by t h e t o t a l amount of time, r e s p e c t i v e l y , This is t h e same d a t a p r e s e n t a t i o n scheme used f o r t h e d a t a i n r e f e r e n c e 1 . The a c t u a l t e s t d a t a from t h e 195 l a n d i n g s a r e a l s o given i n t a b l e 111, Although t h e r e is no s i n g l e v a l u e of wind r e a d i n g which completely repre- s e n t s t h e winds d u r i n g an approach and l a n d i n g , i n o r d e r t o have a c o n s i s t e n t r e f e r e n c e a s i n g l e v a l u e was used t o compute t h e crosswind f o r c l a s s i f y i n g t h e d a t a f o r each run. T h i s s i n g l e value was t h a t wind measured on t h e wind-sensor tower a t t h e t i m e o f touchdown a t t h e 6.1 -m ( 2 0 - f t ) e l e v a t i o n (approximate a i r - p l a n e f l a r e h e i g h t ) . The summary of wind c o n d i t i o n s f o r a l l t h e tests is given i n f i g u r e 11 i n histogram form.

Comparison o f Landing-Gear Modes of O p e r a t i o n With t h e crosswind g e a r , t h e p i l o t s s t a t e d , ". . . it is p o s s i b l e t o make crosswind l a n d i n g s 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 be handled w i t h t h e c o n v e n t i o n a l gear." With t h e c o n v e n t i o n a l gear ( r e f . 1 ) t h e crosswind magnitude l i m i t s were 15 t o 20 knots. The l a r g e s t crosswind mag- n i t u d e encountered d u r i n g t h a t program was 22 knots, which caused t h e p i l o t to a b o r t t h e l a n d i n g j u s t p r i o r t o touchdown, It can be seen i n t a b l e I1 t h a t , w i t h t h e crosswind g e a r , 1 1 l a n d i n g s were made w i t h crosswind magnitudes between 20 and 25 k n o t s , and 5 l a n d i n g s were made with crosswind magnitudes between 25 and 30 knots. (The crosswind magnitudes of 26 to 27 knots a r e about one-half t h e s t a l l speed of t h e a i r p l a n e . ) The s e l f - a l i g n i n g f e a t u r e of t h e crosswind l a n d i n g gear ( c a s t o r mode o r automatic mode) was found t o be e s s e n t i a l f o r l a n d i n g s i n s e v e r e crosswinds.

For t h e a i r plane landing-gear 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 o t s found t h e crosswind l a n d i n g gear t o be p ~ r t i c u l a r l y b e n e f i c i a l i n crosswinds above 1 5 knots where t h e c r a b angle approached 20O. As can be 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 l a r g e s t crosswinds were made w i t h t h e c a s t o r mode. Continu- ous time h i s t o r i e s of t h e s i d e s l i p a n g l e , bank a n g l e , t o t a l a i l e r o n d e f l e c t i o n , c r a b a n g l e , main-gear a n g l e , nose-gear a n g l e , and rudder d e f l e c t i o n a r e given i n f i g u r e 1 2 f o r t h r e e t q i c a l crosswind a p r o a c h e s , The wind v e l o c i t y and wind d i r e c t i o n measured on t h e wind-sensor tower a t 1 -sec i n t e r v a l s f o r s e v e r a l seconds near t h e times of touchdom a r e a l s o given f o r each l a n d i n g , Time h i s t o r i e s from a c a s t o r - m d e l m d i n g w i t h a crosswind of 2 7 - 3 knots from t h e l e f t are given i n f i g u r e 1 2 ( c ) , 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 about zero mtiE t h e a i r p l a n e was n e a r l y stopped on the ground; a t that t i m e t h e f o r w a r d s p e d was s o low t h e s i d e s l i p r e c o r d was o f f s c a l e , Bank a n g l e , a i l e r o n d e f l e c t i o n , and r u d d e r d e f l e c t i o n a l s o o s c i l l a t e d about. z e r o , A t touchdown, t h e m a i n and nose gear f r e e l y a l i g n e d with t h e d i r e c t i o n of t r a v e l i n a b o u t I s e e , 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 a n g l e . The main-gear c a s t o r l o c k s were a p p l i e d 2 s e c a f t e r touchdown, and t h e p i l o t used t i l l e r - b a r s t e e r i n g s f t h e nose g e a r , Although t h e p i l o t s gen- e r a l l y p r e f e r r e d r u d d e r - p d a l s t e e r i n g , t h i s time t h e p i l o t f e l t it was neees- s a r y t o u s e t h e t i l l e r bar f o r s t e e r i n g i n o r d e r t o g e t a d d i t i o n a l nose-wheel t r a v e l . ( D i f f e r e n t i a l r u d d e r - p e d a l s t e e r i n g was l i m i t e d from -3O t o 3O,) 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 g e a r 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 - a l i g n i n g f e a t u r e of t h e l a n d i n g g e a r a t touchdown, t h e p i l o t d i d n o t have t o monitor or 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 castor-mode l a n d i n g s , "No p r e c i s i o n is i n v o l v e d . I l i k e them."

The 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 , ' I [ The a u t o m a t i c mode] s h o u l d be e q u a l l y a s good a s 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 comment is r e a s o n a b l e when o n e 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 mode is a c t i v e l y s e l f - a l i g n i n g i n t h a t it r e q u i r e s no p i l o t a d j u s t m e n t . The a u t o m a t i c mode was l i m i t e d somewhat by t h e i n a d e q u a t e compass- s y s t e m r e s p o n s e r a t e i n t u r b u l e n t c o n d i t i o n s . The c a n p a s s l a g l e d t o some m i s - a l i g n m e n t between t h e g e a r and t h e a i r p l a n e heading d u r i n g a few l a n d i n g s .

Time h i s t o r i e s f o r a n automatic-mode l a n d i n g w i t h a r i g h t c r o s s w i n d of 13.6 k n o t s a r e g i v e n i n f i g u r e 12 ( b ) . During t h e a p p r o a c h , t h e main and nose g e a r s t r a c k e d t h e c r a b a n g l e c l o s e l y t h r o u g h some r a t h e r s e v e r e 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 l o c k w i s e ) t o compensate f o r t h e r i g h t c r a b a n g l e . A t touchdown, t h e c a s t o r l o c k s were a p p l i e d a u t o m a t i c a l l y s o t h a t t h e l a n d i n g 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 . I n t h i s l a n d i n g t h e p i l o t used r u d d e r - p e d a l s t e e r i n g of t h e nose g e a r f o r a b o u t 1 3 s e c . Note t h e s m a l l d i f - f e r e n t i a l nose-gear v a r i a t i o n s (from -3O t o 3O) a s s o c i a t e d w i t h t h e l a r g e r u d d e r - p e d a l i n p u t s . The r e c o r d s were t e r m i n a t e d b e f o r e t h e g e a r s were cen- t e r e d . I f t h e touchdown f o r c e s o n t h e w h e e l s a r e a d e q u a t e t o a l i g n t h e g e a r q u i c k l y w i t h o u t p r o d u c i n g an o b j e c t i o n a b l e r e a c t i o n i n t h e a i r p l a n e ( a s is t r u e f o r t h i s a i r p l a n e and l a n d i n g - g e a r c o n f i g u r a t i o n ) , t h e c a s t o r mode would be p r e f e r a b l e to t h e more c a n p l e x and e x p e n s i v e a u t o m a t i c mode.

For 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 s e t t h e c r o s s w i n d l a n d i n g g e a r t o a n a p p r o p r i a t e o f f s e t a n g l e a t some time p r i o r t o touchdown. Time h i s - t o r i e s f o r a preset-mode c r o s s w i n d l a n d i n g w i t h a l e f t c r o s s w i n d of 15.6 k n o t s a r e g i v e n i n f i g u r e 1 2 ( a ) . E a r l y i n t h e a p p r o a c h , t h e p i l o t s e l e c k e d a main- g e a r o f f s e t a n g l e of 12O r i g h t to match t h e a v e r a g e l e f t a i r p l a n e c r a b a n g l e .

D u r i n g t h e a p p r o a c h , t h e p i l o t made s e v e r a l a d j u s t m e n t s , e v e n t u a l l y r e t u r n i n g t h e c r o s s w i n d l a n d i n g g e a r t o 12O, a f t e r which t h e c a s t o r l o c k s were a p p l i e d .

D u r i n g t h e f l a r e , a sudden change i n h e a d i n g due to wind s h e a r o c c u r r e d , and t h e a i r p l a n e t o u c h e d down w i t h a 5.5O c r a b a n g l e which gave a 6.5O m i s a l i g n m e n t w i t h d i r e c t i o n of t r a v e l . F o l l o w i n g touchdown, t h e c r a b a n g l e s t a r t e d i n c r e a s - i n g a g a i n ; t h e r e f o r e , d u r i n g t h e ground r o l l - o u t , t h e p i l o t used r u d d e r - p d a l s t e e r i n g to e m p n s a t e w i t h t h e f u l l 3O nose-wheel t r a v e l a v a i l a b l e i n t h a t d i r e c t i o n t h r o u g h t h e r u d d e r - p d a l system. T h i s approach i l l u s t r a t e s t h e prub- bem s f c s o r d i n a t i n g crab a n g l e and g e a r o f f s e t a n g l e , e s p e c i a l l y i n u n s t e a d y c o n d i t i o n s when t h e c r a b a n g l e i s c o n t i n u a l l y changing. T h i s problm i s par- 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 , One of t h e p i l o t s s a i d , " I n t h e f l a r e , t h e p i l o t c a n ' t be l o o k i n g 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 he f i n d s i t d i f f i c u l t t o judge i f t h e a i r p l a n e crab a n g l e is t h e same (i. e . , same i n magnitude, b u t o p p s s i t e i n d i r e c t i o n ) a s t h e gear a n g l e * " The l a r g e c r o s s w i n d s e n c o u n t e r e d i n t h i s progrann were always a c c m p a n i e d 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 u n s t e a d y c o n d i - t i o n s can be s e e n i n t h e wind r e c o r d s i n f i g u r e 1 2 and a r e a l s o r e f l e c t e d i n t h e t i m e h i s t o r i e s of a i l e r o n d e f l e c t i o n , rudder d e f l e c t i o n , and c r a b a n g l e f o r a l l t h r e e a p p r o a c h e s . I t is d o u b t f u l i f t h e p i l o t s would have a t t e m p t e d a p r e s e t - mode c r o s s w i n d l a n d i n g i n t h e u n s t e a d y c o n d i t i o n s e x p e r i e n c e d d u r i n g t h e c a s t o r - mode approach ( f i g . 1 2 ( c ) ) and t h e autanatic-mode approach ( f i g . 1 2 ( b ) ) . The c a s t o r and a u t o m a t i c modes r e l i e v e d t h e p i l o t s of c o n t i n u a l l y a d j u s t i n g and m o n i t o r i n g t h e l a n d i n g - g e a r p o s i t i o n .

They found t h e p r e s e t mode t o be v e r y u n d e s i r a b l e i n u n s t e a d y c o n d i t i o n s s i n c e f r e q u e n t a d j u s t m e n t s were r e q u i r e d d u r i n g t h e l a n d i n g approach and f l a r e .

When t h e c r o s s w i n d magnitudes were g r e a t e r t h a n 1 5 t o 20 k n o t s , t h e p i l o t s would n o t a t t e m p t l a n d i n g s w i t h t h e l a n d i n g g e a r p r e s e t p r i o r t o touchdown. I n f a c t , t h e y s t a t e d t h a t , he 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."

Landing Data E f f e c t of w i n g - l i f t s p o i l e r s . - A f t e r o n l y a few l a n d i n g s had been made, it was o b v i o u s t h a t t h e w i n g - l i f t s p o i l e r s were r e l a t i v e l y i n e f f e c t i v e i n d e s t r o y - i n g wing l i f t and i n c r e a s i n g t h e wheel l o a d s . The s p o i l e r s were l o c a t e d i n t h e a r e a of t h e wing covered by t h e p r o p e l l e r s l i p s t r e a m . (See f i g . 1 . ) When t h e p r o p e l l e r s went t o f l a t p i t c h w i t h t h e a p p l i c a t i o n of r e v e r s e t h r u s t , t h e l i f t on t h a t p a r t of t h e wing a f f e c t e d by t h e s p o i l e r s was a l r e a d y d e s t r o y e d , w i t h o n l y a s m a l l i n c r e m e n t c o n t r i b u t e d by t h e s p o i l e r s . However, t h e p i l o t s con- t i n u e d t o use t h e w i n g - l i f t s p o i l e r s f o r most l a n d i n g s , b u t no a t t e m p t was made t o q u a n t i f y t h e i r e f f e c t i v e n e s s .

P i t c h a t t i t u d e a t touchdown.- I n f i g u r e 13, t h e touchdown p i t c h - a t t i t u d e d a t a , combined f o r a l l v a r i a b l e s , a r e shown a s a h i s t o g r a m f o r r e l a t i v e f r e - quency of o c c u r r e n c e . For c a n p a r i s o n , t h e c a n b i n e d p i t c h - a t t i t u d e d a t a f o r t h e c o n v e n t i o n a l , t r i c y c l e l a n d i n g g e a r from r e f e r e n c e 1 a r e a l s o i n c l u d e d . The mean v a l u e of p i t c h a t t i t u d e f o r t h e l a n d i n g s w i t h t h e c r o s s w i n d l a n d i n g g e a r ( l o ) is 2.8O less t h a n t h e mean v a l u e f o r t h e p r e v i o u s t e s t s . I n t h e unmodi- t h e touchdown p i t c h a t t i t u d e ranged from -4O t o 12O, b u t i n t h e f i e d a i r p l a n e , c u r r e n t tests, t h e touchdown p i t c h a t t i t u d e ranged from -6O t o 8O.

The h i g h e r c r o s s w i n d s e n c o u n t e r e d i n t h i s program were accompanied by h i g h t u r b u l e n c e l e v e l s . I n o r d e r t o compensate, t h e p i l o t s sometimes u s e d h i g h e r s t a l l - s p e e d m a r g i n s i n t h e approach. These h i g h e r s p e e d s would t e n d t o p r o d u c e t h e lower touchdown p i t c h a t t i t u d e s found w i t h t h e c r o s s w i n d l a n d i n g g e a r .

One p i l o t a l s o f e l t t h a t t h e lower p i t c h a t t i t u d e s were p a r t i a l l y c a u s e d by t h e need t o r o t a t e down o n t o t h e nose wheel soon a f t e r touchdown i n o r d e r t o u s e nose-wheel s t e e r i n g , Q b v i o u s l y , s h a l l o w e r touchdown p i t c h a t t i t u d e s would a l l c d f a s t e r nose-down r o t a t i o n s o n t o t h e nose wheel. A r e d u c t i o n i n maximum tail-down a n g l e w i t h t h e c r o s s w i n d l a n d i n g g e a r (8.5O compared w i t h 10.5°) may have had some i n f l u e n c e on t h e touchdown p i t c h a t t i t u d e chosen by t h e p i l o t s , A i r s p e e d a t touchdown .- W d e c r e a s e i n p i t c h a t t i t u d e would be e x p e c t e d t o produce a c o r r e s p o n d i n g i n c r e a s e i n touchdown s p e e d . I n f i g u r e 1 4 it can be s e e n t h a t t h i s was n o t t r u e . The r a t i o s of a i r s p e e d a t touchdown t o t h e s t a l l s p e e d have been combined from a l l t h e l a n 8 i n g s w i t h t h e c r o s s w i n d l a n d i n g g e a r and a r e p r e s e n t e d as a h i s t o g r a m showing r e l a t i v e f r e q u e n c y of o c c u r r e n c e .

The combined d a t a from r e f e r e n c e 1 a r e a l s o i n c l u d e d . The d i s t r i b u t i o n of touchdown s p e e d r a t i o s is n e a r l y t h e same a s t h a t of t h e p r e v i o u s t e s t s w i t h t h e c o n v e n t i o n a l , t r i c y c l e l a n d i n g g e a r . N e a r l y 90 p e r c e n t of t h e l a n d i n g s w i t h t h e c r o s s w i n d l a n d i n g g e a r were made a t o r above t h e s t a l l speed (Vtd/VSO = 1 . O ) , w i t h t h e mean v a l u e o f 1 .07 a s compared w i t h a v a l u e o f 1.08 f o r t h e p r e v i o u s tests.

R o l l a t t i t u d e a t touchdown.- The d a t a f o r r o l l a t t i t u d e a t touchdown, combined f o r a l l c r o s s w i n d s , p i l o t s , modes of crosswind-landing-gear o p e r a t i o n , and b o t h approach a n g l e s , a r e p r e s e n t e d i n f i g u r e 1 5 a s a h i s t o g r a m of r e l a t i v e f r e q u e n c y o f o c c u r r e n c e . The r o l l - a t t i t u d e d a t a f o r c r a b - t e c h n i q u e l a n d i n g s w i t h t h e c o n v e n t i o n a l , t r i c y c l e l a n d i n g g e a r from r e f e r e n c e 1 a r e a l s o shown.

The r o l l a t t i t u d e h a s been m u l t i p l i e d by t h e s i g n of t h e c r o s s w i n d , s o t h a t l a n d i n g w i t h t h e wing down i n t o t h e wind is a p o s i t i v e v a l u e , and a l a n d i n g w i t h t h e wing up i n t o t h e wind is a n e g a t i v e v a l u e . The r o l l a t t i t u d e s a t touchdown w i t h t h e c r o s s w i n d l a n d i n g g e a r a r e q u i t e s i m i l a r t o t h e r o l l a t t i - t u d e s w i t h t h e c o n v e n t i o n a l , t r i c y c l e l a n d i n g g e a r f o r t h e c r a b - t e c h n i q u e land- i n g s . I n b o t h programs t h e mean r o l l a t t i t u d e was 1.8O, w i t h a b o u t 35 p e r c e n t o f t h e l a n d i n g s made w i t h t h e wings l e v e l . I n r e f e r e n c e 7 t h e cross-runway t e c h n i q u e r e s u l t e d i n a l a r g e number of w i n g s - l e v e l l a n d i n g s b e c a u s e t h e a i r - p l a n e was headed c l o s e r to t h e r e l a t i v e wind. The r e s u l t s s h o u l d have been s i m i l a r f o r t h e p r e s e n t tests. However, a l a r g e i n c r e a s e i n t h e number o f w i n g s - l e v e l l a n d i n g s was n o t e x p e r i e n c e d w i t h t h e c r o s s w i n d l a n d i n g g e a r b e c a u s e of t h e t u r b u l e n t and s h i f t i n g wind c o n d i t i o n s and h i g h c r o s s w i n d s ; t h e s e c o n d i t i o n s sometimes r e q u i r e d t h e p i l o t s t o p u t a wing down i n t o t h e wind t o keep t h e a i r p l a n e from d r i f t i n g a c r o s s t h e runway d u r i n g t h e f l a r e .

Main-gear a n g l e and a i r p l a n e c r a b a n g l e a t touchdown.- The p u r p o s e of t h e crosswind-landing-gear s y s t e m was t o p e r m i t t h e p i l o t t o l a n d t h e a i r p l a n e i n a c r a b b e d a t t i t u d e w i t h t h e l a n d i n g g e a r a l i g n e d w i t h t h e runway c e n t e r l i n e .

The p o t e n t i a l f o r t h e l a r g e s t m i s a l i g n m e n t s between c r a b a n g l e and main-gear a n g l e e x i s t e d f o r t h e p r e s e t mode, s i n c e t h e p i l o t had t o set t h e l a n d i n g g e a r w h i l e still a t some a l t i t u d e p r i o r t o touchdown and m e n t a l l y compensate f o r wind s h e a r and g u s t s . A comparison of main-gear a n g l e and a i r p l a n e c r a b a n g l e a t touchdown f o r t h e preset-mode l a n d i n g s is g i v e n i n f i g u r e 16. The d a t a have been combined f o r a l l p i l o t s , a l l c r o s s w i n d s , and b o t h approach a n g l e s . I n e v e r y preset-mode l a n d i n g , t h e main-gear a n g l e was l a r g e r t h a n t h e a i r p l a n e c r a b a n g l e a t touchdown, w i t h d i f f e r e n c e s r a n g i n g from 0.5O t o 5.5O. The a n g l e s d i f f e r e d b e c a u s e t h e c r a b a n g l e u s u a l l y d e c r e a s e d s l i g h t l y i n t h e f l a r e due t o wind s h e a r , whereas t h e main-gear a n g l e was set and locked e a r l i e r i n t h e approach i n d i f f e r e n t wind c o n d i t i o n s . Even f o r t h e p r e s e t mode, however, t h e l a n d i n g - g e a r m i s a l i g n m e n t was s m a l l . I n f a c t , t h e r e were no l a r g e r v a l u e s of misalignment f o r any of t h e t h r e e modes of crosswind-landing-gear o p e r a t i o n because t h e p i l o t s c h o s e n o t t o use t h e p r e s e t mode when t h e crosswind was l a r g e and v a r i a b l e . Under t h e s e c o n d i t i o n s , t h e p i l o t s c o u l d n o t e s t i m a t e t h e amount of c r a b ( o r main-gear a n g l e ) t h a t would be needed a t touchdown, The same l i m i t a t i o n s a l s o were e x e r c i s e d by t h e p i l o t s r e g a r d i n g t h e a u t o m a t i c mode, b e c a u s e t h e s y s t e m performance L i m i t a t i o n s ( s t i c k i n g and l a g ) l e d t o e x c e s s i v e v a l u e s o f misalignment a t touchdown.

The c a s t o r mode, however, a l l o w e d t h e p i l o t s t o o p e r a t e i n h i g h c r o s s w i n d s and t u r b u l e n c e , s i n c e t h e l a n d i n g g e a r s a l i g n e d t h e m s e l v e s a t touchdown t h r o u g h ground f o r c e s w i t h no p i l o t i n p u t and no dependence on t h e a i r p l a n e compass system, t h a t is, a p a s s i v e s e l f - a l i g n m e n t system. The b r e a k o u t f o r c e s on t h e main and nose g e a r s were l o w enough t h a t t h e p i l o t s f e l t v e r y l i t t l e e f f e c t o f t h e a l i g n m e n t f o r c e s i n t h e castor-mode l a n d i n g s . The c a s t o r mode was p r e - f e r r e d by a l l t h r e e p i l o t s f o r its s i m p l i c i t y and v e r s a t i l i t y .

The a i r p l a n e c r a b a n g l e a t touchdown is p r e s e n t e d i n f i g u r e 1 7 a s a h i s t o - gram showing r e l a t i v e f r e q u e n c y of o c c u r r e n c e . (The d a t a have been combined f o r a l l p i l o t s , a l l c r o s s w i n d s , a l l modes of crosswind-landing-gear o p e r a t i o n , and b o t h a p p r o a c h a n g l e s . ) The mean c r a b a n g l e was 9.53O, w i t h some v a l u e s a s h i g h a s 35O. The l a n d i n g s w i t h h i g h c r a b a n g l e s ( h i g h c r o s s w i n d s ) were made w i t h t h e c a s t o r mode; a l l l a n d i n g s w i t h c r o s s w i n d magnitudes above 20 k n o t s were i n t h e c a s t o r mode. (See t a b l e II .)

L a t e r a l a c c e l e r a t i o n a t touchdown.- The l a t e r a l a c c e l e r a t i o n s h o u l d be z e r o i f t h e crosswind-landing-gear s y s t e m is a l i g n e d w i t h t h e runway c e n t e r l i n e , and i f t h e r e is no d r i f t o r bank a n g l e . T h e r e f o r e , l a t e r a l a c c e l e r a t i o n a t touchdown c a n be used a s a measure of any o r a l l of t h e f o l l o w i n g c o n d i t i o n s : g e a r m i s a l i g n m e n t , bank a n g l e , and a i r c r a f t d r i f t a t touchdown. F i g u r e 18 p r e - s e n t s t h e magnitude o f l a t e r a l a c c e l e r a t i o n a s a f u n c t i o n of mode of l a n d i n g - g e a r o p e r a t i o n i n terms of h i s t o g r a m s of r e l a t i v e f r e q u e n c y of o c c u r r e n c e f o r a l l p i l o t s and c r o s s w i n d s and b o t h approach a n g l e s . The mean l a t e r a l a c c e l e r a - t i o n s f o r a l l t h r e e modes were n e a r l y e q u a l ; t h e h i g h e s t m a g n i t u d e s o c c u r r e d d u r i n g t h e castor-mode l a n d i n g s . The l a t e r a l a c c e l e r a t i o n s f o r t h e a u t o m a t i c - and preset-mode l a n d i n g s were n o t h i g h e r b e c a u s e t h e p i l o t s l i m i t e d t h e u s e of t h e s e modes t o lower c r o s s w i n d s where t h e p r o b a b i l i t i e s of m i s a l i g n m e n t and d r i f t were r e l a t i v e l y s m a l l . The c a s t o r mode, however, was used i n a l l c r o s s - wind c o n d i t i o n s . Even i n t h e s e v e r e wind c o n d i t i o n s e x p e r i e n c e d w i t h t h e c a s - t o r mode, o n l y t h r e e r u n s ( 2 . 5 p e r c e n t ) had l a t e r a l a c c e l e r a t i o n s above 0.69, and i n e a c h o f t h e s e t h e c r o s s w i n d magnitude exceeded 15 k n o t s .

Although t h e d a t a do n o t r e f l e c t it, t h e p i l o t s s a i d t h e l a t e r a l a c c e l e r a - t i o n s f e l t lower i n t h e castor-mode l a n d i n g s , which made t h e s e l a n d i n g s f e e l more c o m f o r t a b l e . The l a t e r a l a c c e l e r a t i o n s a l s o d i d n o t c a u s e any u n u s u a l wear on t h e t i r e s , even i n t h e c a s t o r mode where t h e g e a r s were r e q u i r e d t o s n a p around from a i r p l a n e c e n t e r l i n e i n a v e r y s h o r t time. The o n l y e x c e s s i v e t i r e wear was produced by h a r d main-gear b r a k i n g .

Touchdown d i s p e r s i o n . - The l o n g i t u d i n a l and l a t e r a l touchdown d i s p e r s i o n d a t a a r e shown i n f i g u r e s 1 9 and 2 0 , r e s p e c t i v e l y , The d a t a were grouped t o g e t h e r b e c a u s e t h e r e were no a p p r e c i a b l e d i f f e r e n c e s between p i l o t s , modes o f o p e r a t i o n , or approach a n g l e s . Too few r u n s were made t o e s t a b l i s h d e f i n i t e t r e n d s with c r o s s w i n d magnitude, The s p r e a d i n l o n g i t u d i n a l t o u c h d o m d i s p e r - s i o n is very s i m i l a r t o t h e s p r e a d i n the d i s p r s i o n d a t a for t h e c r a b and s l i p l a n d i n g s w i t h t h e c o n v e n t i o n a l g e a r ( r e f . 4 ) . With t h e c r o s s w i n d l a n d i n g g e a r , t h e p i l o t s n e v e r l a n d e d s h o r t e r t h a n t h e STOE s t r i p , and t h e y landed beyond t h e t a r g e t touchdown zone o n l y 2 3 - 8 p e r c e n t of t h e time, Hwever, t h e mean v a l u e f o r l a n d i n g s w i t h t h e c r o s s w i n d l a n d i n g gear, 3 3 . 3 rn (109.4 f t ) beyond the t a r g e t touchdown p o i n t , was a b o u t t w i c e t h e mean v a l u e f o r t h e c r a b and sP i p l a n d i n g s r e p o r t e d i n r e f e r e n c e 9 f o r t h e c o n v e n t i o n a l l a n d i n g g e a r . The p i l o t s a t t r i b u t e t h i s d i f f e r e n c e t o t h e a i r p l a n e o p r a t i n g i n h i g h e r c r o s s w i n d s , and h i g h e r a t t e n d a n t t u r b u l e n c e , i n t h e crosswind-landing-gear t e s t s . The more s e v e r e wind c o n d i t i o n s f o r c e d t h e p i l o t s t o use l a r g e r s t a l l - s p e e d m a r g i n s d u r i n g t h e approach; t h e s e s t a l l - s p e e d m a r g i n s c a u s e d a t e n d e n c y f o r t h e a i r - p l a n e t o f l o a t beyond t h e t a r g e t touchdown p o i n t . I n t h e tests r e p o r t e d i n r e f e r e n c e 1 , t h e runway markings c o n s i s t e d of p a i n t e d s q u a r e s 30.5 m (1 00 f t ) o n a s i d e . The d i f f e r e n c e between t h e p r e v i o u s runway markings and t h e STOL- s t r i p markings used i n t h e s e tests a l s o may have had some e f f e c t .

The l a t e r a l touchdown d i s p e r s i o n d a t a a r e g i v e n i n h i s t o g r a m form i n f i g - u r e 20; t h e d a t a have been c a n b i n e d f o r b o t h a p p r o a c h a n g l e s , a l l c r o s s w i n d s , a l l p i l o t s , and a l l modes of crosswind-landing-gear o p e r a t i o n . For comparison, t h e combined d a t a f o r .the c r ab-technique l a n d i n g s w i t h t h e c o n v e n t i o n a l , t r i c y - c l e l a n d i n g g e a r (from r e f . 1 ) a r e a l s o shown. The d a t a from t h e two l a n d i n g - g e a r s y s t e m s a r e q u i t e s i m i l a r . When u s i n g t h e c r a b t e c h n i q u e w i t h t h e conven- t i o n a l g e a r , t h e mean l a t e r a l o f f s e t was 0.1 m (0.33 f t ) upwind of runway c e n t e r l i n e ( a p o s i t i v e v a l u e ) , whereas w i t h t h e c r o s s w i n d l a n d i n g g e a r , t h e mean l a t - e r a l o f f s e t was 0.3 m (0.9 f t ) downwind of t h e c e n t e r l i n e ( a n e g a t i v e v a l u e ) .

The m a j o r i t y of l a n d i n g s were made w i t h i n 21.5 m ( + 5 f t ) of t h e c e n t e r l i n e - 8 3 p e r c e n t of t h e l a n d i n g s w i t h t h e c o n v e n t i o n a l l a n d i n g g e a r and 60 p e r c e n t w i t h t h e c r o s s w i n d l a n d i n g g e a r . On t h e o t h e r hand, t h e e x t r e m e v a l u e s were less w i t h t h e c r o s s w i n d l a n d i n g g e a r ( f 7 . 6 m (525 f t ) compared w i t h 11 0.7 m ( + 3 5 f t ) ) . T h i s f a c t is s i g n i f i c a n t s i n c e t h e l a n d i n g s w i t h t h e c r o s s w i n d l a n d i n g g e a r were made i n h i g h e r c r o s s w i n d s and g r e a t e r t u r b u l e n c e t h a n t h o s e w i t h t h e c o n v e n t i o n a l , t r i c y c l e l a n d i n g g e a r . The c r o s s w i n d l a n d i n g g e a r per- m i t t e d t h e p i l o t s t o c r a b t h e a i r p l a n e i n t o t h e wind, w i t h no d e c r a b o r s l i p maneuver r e q u i r e d f o r touchdown; t h e r e f o r e , l a n d i n g s were p o s s i b l e i n h i g h e r c r o s s w i n d s w i t h l e s s d r i f t a c r o s s t h e runway t h a n w i t h t h e unmodified a i r p l a n e .

Maximum l a t e r a l d i s p e r s i o n d u r i n g ground r o l l - o u t . - The maximum l a t e r a l d i s p e r s i o n from t h e runway c e n t e r l i n e d u r i n g t h e ground r o l l - o u t was measured a s w e l l a s t h e l a t e r a l touchdown d i s p e r s i o n . The maximum l a t e r a l d i s p e r s i o n d u r i n g ground r o l l - o u t is d e f i n e d as t h e maximum l a t e r a l o f f s e t of t h e a i r p l a n e c e n t e r of g r a v i t y £ r a n t h e runway c e n t e r l i n e d u r i n g t h e time between touchdown and when t h e a i r p l a n e comes t o a s t o p . I f t h e maximum o f f s e t o c c u r r e d a t touch- down, t h a t v a l u e of o f f s e t was used a s t h e maximum l a t e r a l d i s p e r s i o n f o r t h a t l a n d i n g . The maximum l a t e r a l d i s p e r s i o n d a t a a r e p r e s e n t e d i n f i g u r e 21 f o r e a c h crosswind-landing-gear mode of o p e r a t i o n . The d a t a i n f i g u r e 21 have been combined f o r a l l t h r e e p i l o t s , a l l c r o s s w i n d s , and b o t h approach a n g l e s . For aPP modes of crosswind-landing-gear o p e r a t i o n , t h e maximum l a t e r a l d i s p e r s i o n exceeded t h e s i m u l a t e d STOL-strip e d g e s (upwind f o r t h e a u t o m a t i c and c a s t o r modes and downwind f o r t h e p r e s e t mode). I t is n o t known how much t h e s e r e s u l t s a r e i n f l u e n c e d by t h e s i m u l a t i o n of t h e SiZdL-strip e d g e s by l i n e s p a i n t e d e n wider paved runways (i.e., no p e n a l t y f o r c r o s s i n g t h e e d g e ) .

I n none of t h e l a n d i n g s d i d t h e d i s p e r s i o n exceed t h e paved runway l i m i t s .

However, t h e d a t a i n d i c a t e t h a t a runway w i d t h of 1 1 5 . 2 4 m (?ti0 f t ) is too nar- row f o r h i g h crosswind l a n d i n g s w i t h t h e e x i s t i n g crosswind-land ing-gear system; a more r e p r e s e n t a t i v e minimum runway w i d t h would be k 3 0 . 5 m ( ? I 0 0 f t) , t h e max- imum paved runway w i d t h used i n t h e s e t e s t s , T h i s c o n c l u s i o n is i n agreement w i t h t h e r e s u l t s of r e f e r e n c e 1.

R e l a t i v e l y few preset-mode l a n d i n g s were a t t e m p t e d , and t h o s e were l i m i t e d t o t h e lower c r o s s w i n d s i n r e l a t i v e l y smooth a i r . I n c o n t r a s t , t h e castor-mode l a n d i n g s were made i n t h e most e x t r e m e c r o s s w i n d s and t u r b u l e n c e w i t h d i s p e r - s i o n performance t h a t was e s s e n t i a l l y t h e same a s w i t h t h e p r e s e t mode. The automatic-mode l a n d i n g s would be e x p e c t e d t o produce r o l l - o u t d a t a s i m i l a r t o t h e d a t a f o r castor-mode l a n d i n g s . However, t h e l i m i t a t i o n s of t h e a i r p l a n e compass s y s t e m degraded l a t e r a l r o l l - o u t performance , e s p e c i a l l y when t h e r e were s h a r p g u s t s j u s t p r i o r t o touchdown. The compass s y s t e m responded t o o s l o w l y i n h i g h l y t u r b u l e n t c o n d i t i o n s t o a l i g n t h e l a n d i n g g e a r s c o m p l e t e l y ; t h i s l e d t o some misalignment a t touchdown and h i g h e r l a t e r a l d i s p e r s i o n s dur- i n g ground r o l l - o u t .

G r o u n d - r o l l d i s t a n c e . - G r o u n d - r o l l d i s t a n c e is t h e l o n g i t u d i n a l runway d i s t a n c e from t h e p o i n t o f touchdown t o t h e p o i n t where t h e a i r p l a n e s t o p s .

G r o u n d - r o l l d i s t a n c e is p r e s e n t e d f o r e a c h crosswind-landing-gear mode o f o p e r a t i o n i n f i g u r e 22. The d a t a have been combined f o r a l l t h r e e p i l o t s , a l l c r o s s w i n d s , and b o t h approach a n g l e s . T h e r e was no c o n s i s t e n t a t t e m p t t o s t o p t h e a i r p l a n e i n t h e s h o r t e s t d i s t a n c e p o s s i b l e ; however, t h e p i l o t s d i d a t t e m p t t o s t o p t h e a i r p l a n e w i t h i n t h e p a i n t e d o u t l i n e s of t h e STOL s t r i p s .

The p i l o t s c o u l d n o t s t o p t h e m o d i f i e d a i r p l a n e w i t h t h e c r o s s w i n d l a n d i n g g e a r i n a s s h o r t a d i s t a n c e a s t h e y c o u l d t h e unmodified a i r p l a n e w i t h t h e conven- t i o n a l , t r i c y c l e l a n d i n g g e a r . The mean g r o u n d - r o l l d i s t a n c e ranged from 140 m (458 f t ) t o 147 m (481 f t ) w i t h t h e unmodified a i r p l a n e ( r e f . 1 ) and from 280 m (91 9 f t ) t o 301 m (987 f t ) w i t h t h e m o d i f i e d a i r p l a n e . The ground r o l l - o u t s were l o n g e r b e c a u s e t h e p i l o t s c o u l d n o t u t i l i z e t h e f u l l b r a k i n g c a p a b i l i t y of t h e m o d i f i e d a i r p l a n e system. The p i l o t s r a r e l y used t h e b r a k e s b e c a u s e of t h e tendency t o f l a t t e n one o r more of t h e main-gear t i r e s . One p i l o t , however, had c o n s i s t e n t l y s m a l l e r r o l l d i s t a n c e s because he was a b l e t o a p p l y b r a k e s l i g h t l y near t h e end of t h e ground r o l l - o u t w i t h o u t a f f e c t i n g t h e t i r e s . I n a d d i t i o n t o t h e t i r e problem, a n o t h e r p i l o t used t h e b r a k e s l e s s t h a n t h e o t h e r two p i l o t s because he f e l t t h a t h a r d b r a k i n g l e d t o u n a c c e p t a b l e p a s s e n g e r r i d e q u a l i t y .

One p i l o t s a i d t h a t even i f t h e a i r p l a n e had a more e f f e c t i v e b r a k i n g s y s - tem, it c o u l d n o t have been used w i t h t h e l a r g e r c r o s s w i n d s and c r a b a n g l e s .

A t l a r g e c r a b a n g l e s , b r a k i n g f o r c e s t e n d t o t i p t h e a i r p l a n e f o r w a r d a b o u t t h e h o r i z o n t a l a x i s between t h e nose g e a r and t h e l e a d i n g main g e a r . For s u f f i c i e n t l y l a r g e c r a b a n g l e s and f o r c e s , t h e t i p p i n g moments c o u l d o v e r t u r n t h e a i r p l a n e . Even w i t h t h e s m a l l e r c r a b a n g l e s and f o r c e s , t h e t i p p i n g motion was q u i t e u n p l e a s a n t and would sometimes l e a d t h e p i l o t s t o back o f f on b r a k i n g .

Thus, t h e t i p p i n g problem c o u l d r e d u c e t h e u t i l i t y o f i n c r e a s e d main-gear brak- i n g a u t h o r i t y and l e a d t o a tendency f o r l o n g e r ground r o l l - o u t s f o r h i g h e r c r o s s w i n d s .

No combined touchdown and ground r o l l - o u t exceeded t h e l o n g i t u d i n a l bound- a r i e s of t h e s i m u l a t e d STBL s t r i p s , al.though a number of ground r o l l - o u t s ended n e a r t h e end l i n e , I n an emergency, t h e a i r p l a n e c o u l d have been s t o p p e d in a d i s t a n c e w e l l s h o r t of t h e end l i n e , b u t t h i s would have l e d t o v e r y heavy t i r e w e a r .

C o n t r o l Use C o n t r o l o f a i l e r o n and r u d d e r d e f l e c t i o n and c o n t r o l o f c r a b a n g l e f o r t h e f i v e l a n d i n g s w i t h c r o s s w i n d magnitudes o f 25 t o 30 k n o t s were computed w i t h t h e t e c h n i q u e o f r e f e r e n c e 1 . A s i n d i c a t e d i n t a b l e 11, t h e f i v e l a n d i n g s a n a l y z e d u s e d t h e c a s t o r mode. Two of t h e l a n d i n g s were made w i t h l e f t c r o s s - w i n d s ; t h r e e l a n d i n g s were made w i t h r i g h t c r o s s w i n d s . The r e s u l - t s o f t h e a n a l y s i s f o r t h e a p p r o a c h , f l a r e , and ground r o l l - o u t of t h e f i v e l a n d i n g s a r e g i v e n i n f i g u r e 23, which p r e s e n t s a i l e r o n and r u d d e r d e f l e c t i o n and c r a b a n g l e a s h i s t o g r a m s o f t h e r e l a t i v e t i m e t h e v a l u e s were w i t h i n p a r t i c u l a r i n t e r v a l s .

During t h e approach p h a s e of t h e l a n d i n g s ( f i g . 23 ( a ) ) , t h e a i l e r o n and r u d d e r d e f l e c t i o n s were c l u s t e r e d a b o u t t h e n e u t r a l datum, a s would b e e x p e c t e d , s i n c e t h e n o s e o f t h e a i r p l a n e was n e a r l y a l i g n e d w i t h t h e r e l a t i v e wind i n a c r a b b e d approach. With t h e r i g h t c r o s s w i n d s , t h e rudder was w i t h i n 2O or a g a i n s t t h e l e f t s t o p o n l y 0.3 p e r c e n t o f t h e time. There was a d e q u a t e c o n t r o l f o r t h e approach phase of c r o s s w i n d l a n d i n g s w i t h c r o s s w i n d m a g n i t u d e s of 25 to 30 k n o t s .

I f f i g u r e 2 3 ( a ) is compared w i t h f i g u r e 2 3 ( b ) , it can be s e e n t h a t l a r g e r c o n t r o l d e f l e c t i o n s were r e q u i r e d i n t h e f l a r e p h a s e t h a n i n t h e a p p r o a c h p h a s e . The p i l o t s i n c r e a s e d t h e i r e f f o r t s f o r p r e c i s i o n o f f l i g h t - p a t h c o n t r o l i n t h e f l a r e . The a i l e r o n s were used t o keep t h e upwind wing from l i f t i n g and to c o u n t e r a c t any tendency f o r t h e a i r p l a n e to d r i f t a c r o s s t h e runway. The r u d d e r was used i n c o o r d i n a t i o n w i t h t h e a i l e r o n s t o o f f s e t yaw and s i d e f o r c e s on t h e a i r p l a n e . The u s e of a i l e r o n and r u d d e r is q u i t e s i m i l a r t o t h a t f o r t h e f l a r e s from c r a b b e d a p p r o a c h e s w i t h c r o s s w i n d magnitudes of 15 t o 20 k n o t s f o r t h e c o n v e n t i o n a l , t r i c y c l e l a n d i n g g e a r ( r e f . 1 ) . The p r i n c i p a l d i f f e r e n c e is t h a t t h e r u d d e r h i t b o t h c o n t r o l s t o p s a t t h e c r o s s w i n d l i m i t s o f 1 5 t o 20 k n o t s w i t h t h e c o n v e n t i o n a l , t r i c y c l e l a n d i n g g e a r ; b u t w i t h t h e c r o s s w i n d l a n d i n g g e a r , t h e r u d d e r h i t o n l y t h e l e f t c o n t r o l s t o p i n c r o s s w i n d s 10 k n o t s g r e a t e r ( 2 5 t o 30 k n o t s ) .

During t h e ground r o l l - o u t ( f i g . 2 3 ( c ) ) , l a r g e a i l e r o n c o n t r o l i n p u t s were r e q u i r e d f o r much less time w i t h t h e c r o s s w i n d l a n d i n g g e a r t h a n w i t h t h e con- v e n t i o n a l , t r i c y c l e l a n d i n g g e a r . The rudder d a t a a r e n o t comparable s i n c e some of t h e r u d d e r u s a g e was r e l a t e d t o ground c o n t r o l of nose-wheel s t e e r i n g r a t h e r t h a n t o aerodynamic c o n t r o l ( f o r example, f i g . 12 ( a ) ) .

The c o n t r o l of a i l e r o n and r u d d e r shown i n f i g u r e 23 was q u i t e s i m i l a r to t h e c o n t r o l f o r t h e c r a b l a n d i n g s w i t h t h e c o n v e n t i o n a l , t r i c y c l e l a n d i n g g e a r a t c r o s s w i n d s 90 k n o t s l e s s , The c r o s s w i n d l a n d i n g gear a l l o w e d t h e a i r p l a n e t o l a n d i n a c r a b b e d a t t i t u d e s o t h a t t h e aerodynamic l i m i t s were n o t r e a c h e d u n t i l 25 t o 30 k n o t s , t h e crosswind m a g n i t u d e s a t which t h e c r o s s w i n d l a n d i n g g e a r r o t a t e d to its f u l l p h y s i c a l l i m i t s . The p i l o t s b e l i e v e d t h a t it m i g h t be p o s s i b l e t o e x t e n d t h e c r o s s w i n d l i m i t s to h i g h e r v a l u e s by i n e o r p r a t i n g t h e changes o u t l i n e d i n t h e n e x t s e c t i o n , S u g g e s t i o n s f o r F u r t h e r I n c r e a s i n g t h e Crosswind Landing L i m i t s W E 1 t h r e e p i l o t s b e l i e v e d t h a t improved c r o s s w i n d l a n d i n g p e r f o r m a n c e , i n t e r m s of minimizing l a t e r a l d i s p e r s i o n s and ground r o l l - o u t d i s t a n c e and i n c r e a s i n g t h e c r o s s w i n d l a n d i n g l i m i t s , c o u l d be a c h i e v e d i f f u r t h e r improve- ments were made t o t h e e x p e r i m e n t a l crosswind-landing-gear system. Improved r u d d e r - p e d a l s t e e r i n g c a p a b i l i t y t o t h e nose g e a r would p e r m i t t h e p i l o t s t o s t e e r t h e a i r p l a n e more p r e c i s e l y i n s t r o n g c r o s s w i n d c o n d i t i o n s . I n t h e p r e s - e n t crosswind-landing-gear conf i g u r a t i o n , r udder-pedal s t e e r i n g of t h e n o s e g e a r was o n l y e f f e c t i v e from -3O t o 3O a b o u t t h e s e t t i n g a t t i m e o f a c t u a t i o n .

The p i l o t s found t h a t t h i s d e g r e e o f nose-wheel t r a v e l was i n a d e q u a t e , s o t h a t t h e y were f o r c e d t o use asymmetric main-gear b r a k i n g o r t i l l e r - b a r s t e e r i n g o f t h e nose g e a r . The p i l o t s f e l t t h a t t h e r u d d e r - p e d a l s t e e r i n g c a p a b i l i t y s h o u l d be a t l e a s t doubled t o 6O i n e i t h e r d i r e c t i o n w i t h no l a g i n s t e e r i n g r e s p o n s e .

An e q u a l l y i m p o r t a n t m o d i f i c a t i o n recommended by t h e p i l o t s was t o modify t h e main-gear b r a k i n g and t i r e s y s t e m t o i n c r e a s e t h e b r a k i n g s y s t e m c a p a b i l i t y t o a t l e a s t t h a t of t h e unmodified, p r o d u c t i o n a i r p l a n e . An improved b r a k i n g s y s t e m would p e r m i t improved d i r e c t i o n a l c o n t r o l and s h o r t e r ground r o l l , a l t h o u g h a t l a r g e c r a b a n g l e s t h e u s a b l e b r a k e c a p a b i l i t y may be l i m i t e d by an a i r p l a n e t i p - o v e r tendency.

W i n g - l i f t s p o i l e r s were i n s t a l l e d t o augment t h e crosswind-landing-gear s y s t e m by d e s t r o y i n g wing l i f t and i n c r e a s i n g t h e wheel l o a d s . T h i s s p o i l e r i n s t a l l a t i o n , however , was found t o be r e l a t i v e l y i n e f f e c t i v e b e c a u s e of t h e s p o i l e r l o c a t i o n on t h e wing. The p i l o t s s u g g e s t e d t h a t f o r an o p e r a t i o n a l c r o s s w i n d - l a n d i n g - g e a r system, t h e s p o i l e r s s h o u l d be l o c a t e d f u r t h e r o u t b o a r d on t h e wings, c l e a r of t h e p r o p e l l e r s l i p s t r e a m . I n a d d i t i o n , t h e y t h o u g h t t h a t a f a s t e r f l a p r e t r a c t i o n c y c l e would be b e n e f i c i a l d u r i n g t h e ground r o l l - o u t t o f u r t h e r r e d u c e wing l i f t . The p i l o t s a l s o t h o u g h t t h a t improved e n g i n e r e s p o n s e would a s s i s t i n terms o f r e v e r s i n g t h r u s t and improving s t e e r i n g (asymmetric t h r u s t ) .

O v e r a l l , t h e p i l o t s f e e l t h a t g r e a t l y improved s a f e t y , c o m f o r t , and e x t e n d e d crosswind l a n d i n g l i m i t s can be r e a l i z e d by u s e of an o p e r a t i o n a l castor-mode crosswind-landing-gear system i n c o r p o r a t i n g c a s t o r l o c k s and r u d d e r - p e d a l s t e e r i n g . S i d e f o r c e s c o u l d be reduced a t touchdown t o p r o d u c e a smooth l a n d i n g f o r t h e p a s s e n g e r s . The o p e r a t i o n of a c r o s s w i n d l a n d i n g g e a r on s l i p p e r y runways needs f u r t h e r s t u d y , a n a l y s i s , and t e s t i n g . The a p p l i c a - t i o n of a n t i s k i d b r a k i n g s y s t e m s a l s o needs f u r t h e r s t u d y b e c a u s e o f t h e v a r i a - t i o n s i n v e r t i c a l l o a d on t h e l a n d i n g g e a r i n s t r o n g c r o s s w i n d c o n d i t i o n s .

NASA has u n d e r t a k e n a f l i g h t r e s e a r c h program t o i n v e s t i g a t e t h e problems a s s o c i a t e d w i t h l a n d i n g a light, STOL t r a n s p r t i n crosswind c o n d i t i o n s by using a r e s e a r c h - t s e crosswind Sanding gear. The c a n e l u s i o n s reached i n t h i s s t u d y a r e f o r t h i s p a r t i c u l a r type s f a i r p l a n e and r e s e a r c h - t p e crosswind- landing-gear system, This s t u d y i n d i c a t e d t h e f o l l m ~ i n g results: I . The crosswind landing gear p e r m i t t e d t h e p i l o t s t o c r a b t h e a i r p l a n e i n t o t h e wind, with no deerab o r s l i p maneuver r e q u i r e d For touchdown; t h e r e - f o r e , l a n d i n g s were p o s s i b l e i n higher crosswinds w i t h l e s s d r i f t across t h e runway than were p o s s i b l e with t h e unmodified a i r p l a n e with t h e crosswind land- i n g gear. Crosswind l a n d i n g s were made w i t h crosswind magnitudes of 25 to 30 knots, whereas t h e crosswind magnitude l i m i t s with t h e conventional, t r i c y - c l e landing gear were 1 5 t o 20 knots.

2. For t h e l i g h t t r a n s p o r t used i n t h i s i n v e s t i g a t i o n , t h e s e l f - a l i g n i n g f e a t u r e of t h e crosswind l a n d i n g gear ( e i t h e r automatic or c a s t o r mode) was found t o be e s s e n t i a l f o r landing i n s e v e r e crosswinds.

3. If, a s with t h e a i r p l a n e and landing-gear c o n f i g u r a t i o n t e s t e d , t h e touchdown f o r c e s on t h e . w h e e l s a r e adequate t o a l i g n t h e gear q u i c k l y without producing an o b j e c t i o n a b l e r e a c t i o n i n t h e a i r p l a n e , t h e c a s t o r mode is p r e f - e r a b l e t o t h e more complex and expensive automatic-mode landing gear.

4. Because of t h e d i f f i c u l t y i n c o o r d i n a t i n g c r a b angle and gear p r e s e t a n g l e , t h e p i l o t s would n o t a t t e m p t preset-mode l a n d i n g s when t h e crosswind magnitudes were g r e a t e r t h a n 1 5 t o 20 knots.

5. The d a t a i n d i c a t e t h a t a runway width of 215.24 m (250 f t ) is too narrow f o r high crosswind l a n d i n g s w i t h t h e e x i s t i n g crosswind-landing-gear system; a more r e p r e s e n t a t i v e minimum runway width would be 130.5 m (+lo0 f t ) , t h e maximum paved runway width used i n t h e s e t e s t s .

Langley Research Center N a t i o n a l Aeronautics and Space Administration Hampton, Va 23665 March 30, 1 979 1 , F i s h e r , Bruce D.; Champine, R o b e r t A , ; D e a l , P e r r y L , ; P a t t o n , James M,, J r . ; and H a l l , A l b e r t W . : A P 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 L i m i t a t i o n s During V i s u a l STOL-Type Landing O p e r a t i o n s .

NASA TN D-8284, 9976.

2 . S t u b b s , Sandy M . ; Byrdsong, Thomas A . ; and S l e e p e r , R o b e r t K . : An Experi- m e n t a l S i m u l a t i o n Study of Four Crosswind Landing-Gear C o n c e p t s . NASA 'IN D-7864, 1975.

3. F i s h e r , Bruce D . ; S l e e p e r , R o b e r t K . ; and S t u b b s , Sandy M . : Summary of NASA Landing Gear R e s e a r c h . NASA TM-78679, 1978.

4. S t a n d a r d f o r M e t r i c p r a c t i c e . E 380-76, American Soc. ~ e s t i n g & M a t e r . , 1976.

5. Champine, R o b e r t A. : Crosswind Landing-Gear P o s i t i o n I n d i c a t o r . NASA Tech B r i e f LAR-11941, 1976.

6 . S p a n g l e r , Roman M. , J r .: S i m u l a t e d Ground-Leve 1 STOL Runway/Air c r a f t E v a l u a t i o n . FAA-RD-73-110, S e p t . 1973.

TABm 1,- m B E S OF m B I N G - . G E A R B P E M T I B W FOR mOSSWIND RESEARCH n a l s from a i r p l a n e ( 2 ) Nose-wheel s t e e r i n g a t h i g h s p e e d t h r o u g h

P a s s i v e - by ground r u d d e r p e d a l s

f o r c e s dur i ng touchdown ( 3 ) W i n g - l i f t s p o i l e r s ( 4 ) R e t u r n g e a r to c e n t e r

TABLE I1 .- MATRIX OF TEST mNDITIONS REC0EU)ED FOR 195 LANDINGS

TABLE 111.- TEST DATA F R O M 1 9 5 LANDINGS Ground- Wind L o n g i t u d i n a l L a t e r a l Maximum component touchdown touchdown l a t e r a l r o l l Crosswind- Crosswind, Approach d i s p e r s i o n d i s p e r s i o n d i s t a n c e B t d , p a r a l l e l t o d i s p e r s i o n k n o t s Run 1 anding-gear P i l o t a n g l e , S p o i l e r s runway, ( c ) ( d ) ( e ) deg mode deg k n o t s m f t m f t m f t (b) m f t - -- ~ - -4.0 22.9 75 0 0 -4.1 -13.3 221 .O 725 '-3 1 Automatic -3.7 45.7 150 1.1 3.5 -13.9 -45.5 259.1 850 -2.5 2 Automatic 3.6 30.5 100 0 0 -2.0 -6.5 213.4 700 -2.5 3 Automatic .9 38.1 125 0 0 -5.0 -16.3 205.7 675 -2 4 Automatic 5.3 -3.0 -10 -1.1 -3.5 -4.6 -15.2 271.3 890 -2.5 5 Automatic 4.1 38.1 125 -1.0 -3.3 -3.1 -10.2 266.7 875 -3 Automatic 5.9 30.5 100 -2.0 -6.6 -9.1 -30 335.3 1100 -1.5 7 Automatic 7.7 27.4 90 -1.0 -3.3 -4.3 -14 277.4 9 1 0 , - 2 8 Automatic 5.0 15.2 50 -.5 -1.7 -2.9 -9.6 320.0 10501-3 9 Automatic 3.7 48.8 160 0 0 -1.9 -6.4 286.5 9401-1.5 1 0 Automatic 1.0 3.4 -3.7 -12.3 228.6 7501 1.5 .8 15.2 50 11 Automatic 33.5 110 0 0 -4.9 -16 301.8 9901-2.5 -. 2 1 2 Automatic 13 C a s t o r 14 C a s t o r 15 C a s t o r 1 6 C a s t o r 17 C a s t o r 18 C a s t o r 1 9 C a s t o r 2 0 C a s t o r 21 P r e s e t 22 P r e s e t 23 P r e s e t 24 P r e s e t 25 P r e s e t 2 6 P r e s e t 27 , P r e s e t 2 9 6.1 -2.6 97.5 320 1-2.1 -7 -5.4 -17.9 298.7 980 Automatic B - 3 UP 13.9 -1 - 8 30.5 100 ' - 1 . 0 -3.3 -3.8 -12.5 396.2 1300 Automatic B Down -3

1 3 0

18.1 6.2 45.7 150 1.0 -3.2 -4.9 -16 289.6 950 - 3 B Down 31 Automatic 3 2 13.5 5.6 70.1 230 l--.9 - 3 1.0 3.2 265.2 870 Automatic - 3 B Down 3 3 14.8 6.9 1.7 5.5 -6.8 -22.4 259.1 850 Automatic - 3 B Down 34 13.6 5.4 .9 2.9 - 7 . 7 - 2 5 . 2 2 8 9 . 6 950 Automatic -3 B UP 35 -12.4 5.1 .9 3.1 2 . 6 8 . 7 2 9 8 . 7 980 Automatic -3 B UP 36 -1 1 2.1 1.0 3.3 2.4 7.8 300.2 985 Automatic -3 B U P 37 10.9 1.1 30.5 100 .9 3.1 2.5 8.2 198.1 650 Automatic -3 B Down 38 11 - 1 .2 45.7 150 .9 2.9 3.3 11.0 253.0 830 Automatic -3 B Down a c r o s s w i n d is p o s i t i v e f o r crosswind f r a n r i g h t .

h i n d component p a r a l l e l t o runway i s p o s i t i v e f o r headwind.

C L o n g i t u d i n a l touchdown d i s p e r s i o n is p o s i t i v e f o r l a n d i n g l o n g of touchdown p o i n t .

d ~ a t e r a l touchdown d i s p e r s i o n is p o s i t i v e f o r l a n d i n g t o p i l o t ' s r i g h t of runway c e n t e r l i n e .

eMaximum l a t e r a l d i s p e r s i o n is p o s i t i v e f o r l a n d i n g t o p i l o t ' s r i g h t of runway c e n t e r l i n e .

-- m w m > -, m m m m m m m m m m m m . . . . . . . . .

, m - - .-.. ~ e m ~ ~ ~ ~ ~ ~ m r w m ~ m ~ ~ w ~ ~ r : m ~ m m m m m m ~ I - - I I I I I I I I I I ? - , - - - _ _ - I

- - ?

q q q q y q 7 q q q ~ q y y y ~ ~ ~ w ~ m ~ ~ ~ y r w ~ ~ ~ ~ r e ~ - e w w . . . . . . . . . . . . . . . .

Z ~ Z % P C Z G ~ S Z Z F Z F ; E G 2 2 E Z X ; ; C : % S ; ; g 2 G 6 2 % % % G U N N N m N - N N N N N N m N N m N N N N N N N N N N N N N N N N N N N N N N N 3 4 C w . a , * U U C 5 >,8 fig & - C 3 3 g U C ' u W U C 0 B u " d 0 C U m u .rl C w u m O l o ' : , m - C u - t n 0 0 . d 4 U ; F.2; 3 . . I o a v ' u u m C 0 2 2 F " .rl m 4 u v C .,0,0 S a " u r i C C W O m m 3 S U d .,, .d .A 0 4 u u w U .4 .* 0 tn lo o w EPp, W m tn 'rl .A m .A .rl m u

.5 , , C P.2

E Z Z t n a 10 c m . - 0 s U 4 4 g g . 2 U 3 .2 ' Z g 0 v u . 4 u 4 rl a , C ?Lm m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m I l l I I I I I I I I I I I I l l I I I I I I I l l l l l l l l l l l l l l l l sig.22 .A m v a ,?

u " C

.- 2: gz

8:uZz

m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m a d u a, . r l e m 3 u ,P23,.

. - E 3 r i s E U 2 , " , g % FZ.2 " ' r l S Z 2 2 d u v a, TABLE 111.- Continued Ground- Wind L o n g i t u d i n a l L a t e r a l Maximum Crosswind- r o l l l a t e r a l Approach Crosswind, component touchdown touchdown l a n d i n g - g e a r d i s t a n c e d i s p e r s i o n P i l o t a n g l e , S p o i l e r s k n o t s p a r a l l e l t o d i s p e r s i o n d i s p e r s i o n e t d r Vtd/VSO @tdr 6m t d t mode deg %;g runway, d e g ( c ) (d ( e ) deg .

k n o t s m m it m f t m f t (b) f t (a) Automatic C -3 -8 6 0 0 2.1 7 2.1 7 365.8 0 1200 1.07 0.5 4.5 UP Automatic C -3 -9.3 3.8 76.2 250 1.8 6 1.8 6 289.6 9 5 0 - 3 . 5 1.08 1.5 5.5 UP Automatic C -3 UD -7.1 3.5 121.9 400 1.6 5.4 1.6 5.4 243.8 -3.5 800 1.13 .5 6 Automatic C -3 -6.9 8 30.5 100 1.0 3.3 1.0 3 . 3 2 1 3 . 4 700 0 1.06 -1 6 Automatic C -3 -9.2 7.3 0 0 0 0 -1.8 -6 274.3 900 1.1 1.11 -1 6.33 UP Automatic C -3 -8.4 9.7 15.2 50 0 0 -.9 -2.9 137.2 450 -2.5 1.13 1 7.3 UP Automatic C -3 -11.6 0 0 -1.6 -5.4 121.9 400 -1.5 1.13 1.3 6.5 6.7 30.5 100 UP Automatic C -3 -1 1 0 0 1.1 1.1 3.5 152.4 500 -1 1.07 -.8 7 8.7 3.5 UP C a s t o r C -3 11.3 - 3 -15.2 -50 -1.1 -3.6 2.2 7.3 350.5 1150 2 1.11 UP ----- ---- C a s t o r C -3 13.1 1.2 -6.1 -20 -1.1 -3.6 -2.6 -8.4 1.8 1.02 UP C a s t o r C - 3 14.4 -4.2 15.2 50 -1.0 -3.4 -2.5 - 8 . 3 3 8 8 . 6 1275 -.5 1.08 UP ----- ---- C a s t o r C -3 9.2 .3 -18.3 -60 -2.2 -7.3 -4.3 -14.0 2.7 1.08 UP C a s t o r -3 14 0 C -14.4 5.1 0 0 4.3 14.0 4.3 365.8 1200 1.09 UP -20.1 -66 C a s t o r C -3 -16.8 2.5 15.2 50 4.1 13.4 259.1 850 1.4 1.03 UP C a s t o r -3 -15.2 14.6 4.3 1 4 381.0 1250 o 1.07 C -15.7 4.8 -50 4.4 u p ----- ---- ---- ----- ----- ----- ----- ---- C a s t o r C -3 -8 - 9 0 1.14 5.5 UP C a s t o r - 3 - 3 . 5 - 1 1 . 4 3 0 1 . 8 9 9 0 - 6 1.16 C -15.7 6.2 64.0 210 .8 2.7 UP C a s t o r C -3 -10 9.3 61.0 200 .8 2.7 2.8 9 . 3 3 0 4 . 8 1 0 0 0 - 2 . 5 1.12 UP C a s t o r C -3 -17.7 7.5 6.1 20 1.6 5.1 1.6 5.1 359.7 1180 -.9 1.12 UP C a s t o r C -3 -1 1 6.0 -7.6 -25 1.1 3.6 1.1 3.6 373.4 1225 -1.0 1.05 UP C a s t o r C -3 -7.9 6.9 -15.2 -50 1.7 5.6 1.7 5.6 381.0 1250 -1.0 1 - 1 0 UP C a s t o r C -3 -14.7 -4 -7.6 -25 1.1 3.6 -4.0 -13.1 373.4 1225 -.3 1.06 Up C a s t o r C -3 15.6 2 -15.2 -50 2.3 7.4 8.0 26.4 381.0 1250 .3 1.09 UP C a s t o r C -3 18.9 6.1 15.2 50 2.0 6.5 -2.6 - 8 . 4 3 5 0 . 5 1 1 5 0 0 1.12 UP C a s t o r C -3 25.5 9 30.5 100 1.9 6.1 - 5 . 1 - 1 6 . 8 3 3 5 . 3 1 1 0 0 0 1.08 UP C a s t o r C -3 17.7 6.3 45.7 150 1.8 5.8 2.8 9 . 3 3 2 0 . 0 1 0 5 0 - 2 . 5 1.18 UP C a s t o r C -3 18.9 2.9 22.9 75 1.9 6.3 1.9 6 . 3 3 4 2 . 9 1 1 2 5 - 1 1.23 UP C a s t o r C -3 18.5 1.6 22.9 75 1.9 6.3 6.6 21.7 342.9 1125 -1.5 1.13 UP C a s t o r C -3 19.3 8.6 15.2 50 2.0 6.5 3.7 12 3 5 0 . 5 1 1 5 0 - 1 1.14 UP C a s t o r C 1.9 6.1 1.9 1100 -3 1.23 -3 19.9 5.6 30.5 100 6.1 335.3 U P C a s t o r C 1.09 -3 23.6 4.3 30.5 100 1.9 6.1 5.7 18.6 335.3 1100 -.5 UP C a s t o r C -3 22.4 3.4 6.1 20 1.0 3.4 3.6 11.9 359.7 1180 1.3 1.14 U P C a s t o r C 2.1 1.14 -3 23.6 5 0 0 7 7.8 25.5 365.8 1200 -.5 UP C a s t o r C 2.4 -3 17.1 3.9 61.0 200 1.6 5.4 7 . 8 3 0 4 . 8 1 0 0 0 - 4 1.09 UP C a s t o r C -3 17.1 7 0 0 1.1 3.5 3.6 11.9 365.8 1200 -.5 1.05 UP C a s t o r C -3 18.8 7.2 30.5 100 1.9 6.1 1.9 6.1 335.3 1 1 0 0 - 2 1.14 UP C a s t o r C -3 22.5 8.5 45.7 1.8 5.8 4.5 14.8 320.0 1050 -2 1.23 UP C a s t o r C -3 22.1 61.0 200 3.3 10.8 -7.8 -25.5 304.8 1000 -4.3 1.20 6.6 UP C a s t o r C -3 17.6 6.6 30.5 100 2.8 9.2 3.5 11.6 335.3 1100 -4 1.16 UP C a s t o r C -3 20.2 5.9 76.2 250 1.6 5.7 - 8 . 5 - 2 8 289.6 9 5 0 - 6 1.31 UP acrosswind is p o s i t i v e f o r c r o s s w i n d i s a n r i g h t .

h i n d component p a r a l l e l t o runway is p o s i t i v e f o r headwind.

C ~ o n g i t u d i n a l touchdown d i s p e r s i o n is p o s i t i v e f o r l a n d i n g l o n g of touchdown p o i n t .

d ~ a t e r a l touchdown d i s p e r s i o n is p o s i t i v e f o r l a n d i n g t o p i l o t ' s r i g h t of runway c e n t e r l i n e .

e~aximum l a t e r a l d i s p e r s i o n is p o s i t i v e f o r l a n d i n g t o p i l o t ' s r i g h t of runway c e n t e r l i n e .

TABLE: I11 .- Concluded

~ o n g i t u i n a a t e 1 x i I ~;:",;d- 1 I I I 1

Crosswind- I ( W r o a c h I l C r o s s w i n d , co?;dent touchdown touchdown l a t e r a l l a n d i n g - g e a r P i l o t a n g l e S p o i l e r s k n o t s d i s t a n c e I e t d . Ivtd&~l@ t d r 16q,td8 / b c r a b , t d

mode 1 I deg / I d e g d e g e g deg

I

k n o t s ( a ) (b) m f t m f t m f t m C a s t o r C -3 UP 24 7.2 30.5 100 2.8 9.2 8 . 5 27.9 335.3 C a s t o r C - 3 UP 19.7 6.7 61 . O 200 1.6 5.4 1.6 5.4 304.8 C a s t o r C -3 UP 17.6 6.9 0 0 2.1 7 2.1 7 365.8 C a s t o r C -3 UP 26 3.6 0 0 2.1 7 ---------- 365.8 ---- ---- ----- ----- ----- ----- C a s t o r C -3 UP 18.1 5.5 ----- C a s t o r C - 3 UP -3.5 6.9 0 0 2.1 7 2.1 7 304.8

E l ; I ; ; I ,:;I ti;!

1075 1.0 1.01 1 . 5 -8.8 c ~ o n g i t u d i n a l touchdown d i s p e r s i o n is p o s i t i v e f o r l a n d i n g l o n g of touchdown p o i n t .

' ~ a t e r a l touchdown d i s p e r s i o n is p o s i t i v e f o r l a n d i n g t o p i l o t ' s r i g h t of runway c e n t e r l i n e .

eMaximum l a t e r a l d i s p e r s i o n is p o s i t i v e f o r l a n d i n g t o p i l o t ' s r i g h t of runway c e n t e r l i n e .

Probe (angle of attack, angle of

' sideslip, airspeedl

Diameter = 2.59 F i g u r e 1 .- Three-view drawing o f t e s t a i r p l a n e w i t h m o d i f i c a t i o n s f o r crosswind- l a n d i n g - g e a r program. A l l d i m e n s i o n s a r e i n m e t e r s ( f e e t ) .

Original leg reversed from right to left side and turned upside down Tire size, 0.44 x 0.1 Center of gravity, 3.26 (10.69) L-f . - aft of nose gear Estimated center-of-gravity height = 1.67 (5.48) Twin contact tire size, 0.184 x 0.152 (0.6 x 0.5) F i g u r e 2.- D e t a i l e d views of c r o s s w i n d l a n d i n g g e a r .

A l l d i m e n s i o n s a r e i n m e t e r s ( f e e t ) .

F i g u r e 3 . - L e f t main-gear u n i t , a [I) [I) [I) n [I) a) a cd Cl C l a ) a cd 4-I X

g : (d e r . 4

M lt-4 CI !-I

CI -

0 - $4 h C3 id' 0

E 2

1 a) d [I) n a) h 4 cd e 3 a) .d 1 6 4 Cl 0 5 a a) [I) a) 0 G a Figure 6 .- Test s i t e .

Tailwind Headwind Wind component p a r a l l e l t o runway, k n o t s Crosswind magnitude, k n o t s

Figure 1 1 .- Summary of wind conditions f o r a l l t e s t s . Data based on readings

from wind sensor a t 6.1 m ( 2 0 f t ) on wind-sensor tower.

Begin rudder-pedal steer End rudder pedal steer ~ o u c h d o x m I Gear center 20/- Castor locks onl; \/requested I ! !

I I Gear adjustment i I b$- 6 , g , deg I 1 L I I , 0 I Time, set (a) preset-mode landing with l e f t crosswind of 15.6 k n o t s - F i g u r e 12.- Crosswind landing time h i s t o r i e s .

Begin rudder-pedal S t e e r rudder-pedal s t e e r O f f - s c a l e I I I I I I I I I I I 1 0 1 I

Y , deg 0 ~ v ~ ~ v v ~ v A v ~ - /

I I I -10 1 I I I I I I I I I I I I I I I ! I --t------ I I I 6ng , deg

-

I I I I I I I I I I I I I I I I I I I 1 1 1 I I I I I t 1 I I L I 0 10 20 30 40 50 60 70 80 90 100 Time, s e c (b) Automatic-mode l a n d i n g w i t h r i g h t c r o s s w i n d of 1 3 . 6 k n o t s .

F i g u r e 1 2 .- C o n t i n u e d .

Touchdown (b) Concluded.

F i g u r e 12 ,- C o n t i n u e d .

/--Castor l o c k s on T i m e , sec (c) Castor-rode landing with left crosswind of 27.3 knots.

F i g u r e 1 2 , - C o n t i n u e d , Touchdown (c) Concluded.

F i g u r e 12.- C o n c l u d e d , - Crosswind landing gear 190 runs Plean. lo - - -- Conventional, t r i c y c l e l a n d i n g g e a r (from r e f . 1 ) - 415 runs Elean, 3.8' r - - - - I - - - - - - - - - A I I f L - - -

I I

- I I I New maximum tail-down ..-- - - I I - a n g l e , 8.5' k - - - l I Old maximum tail-down I T a n g l e , 10.5' - - - - - - rL-,

-A -4 -2 0 2 4 6 8 10 1 2

Data combined F i g u r e 13.- P i t c h a t t i t u d e a t touchdown.

f o r a l l p i l o t s , c r o s s w i n d s , modes of crosswind- l a n d i n g - g e a r o p e r a t i o n , and b o t h a p p r o a c h a n g l e s .

-Crosswind l a n d i n g g e a r 190 runs Elean, 1.07 --- Conventional, t r i c y c l e l e a d i n g g e a r (from r e f . 1 ) 417 r u n s Elean, 1.08

. r

Touchdown speed r a t i o , V t d / V S O F i g u r e 1 4 . - Touchdown s p e e d r a t i o s , Data combined for a l l c r o s s w i n d s , p i l o t s , modes of crosswind-landing-qgar opera- t i o n and b o t h approach a n g l e s , Crosswind l a n d i n g gear 190 r u n s Mean, 1.8O

- - -- C o n v e n t i o n a 1 , t r i c y c l e landing g e a r (from ref. 1 )

Crab technique 162 r u n s Mean, 1.8' Wing up i n t o wind Wing down i n t o wind $td X s i g n (crosswind), deg Data combined f o r a l l c r o s s w i n d s , F i g u r e 15.- R o l l a t t i t u d e a t touchdown.

p i l o t s , modes of c r o s s w i n d - l a n d i n g - g e a r o p e r a t i o n , and b o t h a p p r o a c h a n g l e s .

F i g u r e 16.- Comparison of main-gear a n g l e and c r a b a n g l e a t touchdown f o r preset-mode l a n d i n g s . Data combined f o r a l l c r o s s - winds, p i l o t s , and b o t h approach a n g l e s .

160 runs Mean, 9.53' F i g u r e 97.- Crab a n g l e magnitude a t t o u c h d o m , Data esmbined for a l l crosswinds, p i l o t s , modes sf crosswind-landing-gea~ operation, and b t h approach angles, Automatic mode 42 runs Mean, 0.186 Castor mode 122 runs Mean, 0.22 Preset mode 25 runs Mean, 0.23 Figure 18.- Lateral acceleration magnitude a t Wuchdown as a function of c r ossurind-landing-gear modes of o p e r a t i o n Data combined for a i l crosswinds pilots and both approach angles.

Direction of flight Beginning of STOL-runway ,' / Target touchdown point End of target touchdown zone Distance from target point, f t Long Short Mean, 33.3 m (109.4 ft) 193 runs Short Long Distance from target point, m Data combined f o r a l l F i g u r e 19.- L o n g i t u d i n a l touchdown d i s p e r s i o n .

c r o s s w i n d s , p i l o t s , modes of crosswind-landing-gear o p e r a t i o n , and b o t h a p p r o a c h a n g l e s .

Distance x sign (crosswind) , f t

Crab technique ( r e f . 1 ) 1 4 9 runs Mean, 0 . 1 m (0.33 f t ) Extremes, 2 10.7 m ( k 35 f t ) Downwind Upwind Crosswind landing gear 184 runs Mean, -0.3 m (-0.9 f t ) Extremes, k 7 . 6 rn (+ 25 f t ) Distance X s i g n (crosswind), m Figure 20.- L a t e r a l touchdown dispersion. Data combined f o r a l l crosswinds, p i l o t s , crosswind-landing-gear modes of operation, and both approach angles. Crab-technique data a r e from reference 1 .

Distance x sign (crosswind), f t STOL strip edge Automatic mode 42 r u n s Mean, 0 . 0 7 m ( 0 . 2 4 f t )

- C a s t o r mode

115 r u n s Mean, 0 . 2 6 m ( 0 . 8 f t )

-

-

P r e s e t mode 26 r u n s Mean, - 2 . 8 m ( - 9 . 2 3 ft) D i s t a n c e x s i g n ( c r o s s w i n d ) , m

Downwind 4) Upwind

F i g u r e 21 .- Maximum l a t e r a l d i s p e r s i o n from runway c e n t e r l i n e d u r i n g ground r o l l - o u t , Data combined f o r a l l c r o s s w i n d s , p i l o t s , and b o t h a p p r o a c h a n g l e s , Distance, f t 400 600 800 LO00 1200 1400 I I I I I I Automatic mode 43 runs Mean, 280 m (919 ft) Castor mode 122 runs Mean, 285 m (937 ft) I I Preset mode 25 runs (987 ft) Mean, 301 m Distance, m F i g u r e 2 2 .- Ground-roll d i s t a n c e . Data combined f o r a l l c r o s s w i n d s , p i l o t s , and b o t h a m r o a c h a n g l e s .

[7 R i g h t c r o s s w i n d s

L e f t l i m i t

R

-50 -40 -30 -20 -10 0 1 0 20 30 40 50 A i l e r o n d e f l e c t i o n , tia , deg

ls

a

L e f t 6, l i m i t R i g h t 6, l i m i t 1 . 0 . 8 m U . 6 + .r( U 2 .4 m d .2 -20 -16 -12 -8 -4 0 4 8 1 2 1 6 20 Rudder d e f l e c t i o n , tir , deg Crab a n g l e , , deg ( a ) Approach p h a s e .

F i g u r e 23.- A i l e r o n d e f l e c t i o n , r u d d e r d e f l e c t i o n , and c r a b a n g l e h i s t o g r a m s from c a s t o r - m d e l a n d i n g s w i t h c r o s s w i n d s from 25 to 30 k n o t s ,

0 L e f t c r o s s \ r i n d s

0 R i g h t c r o s s w i n d s

L e f t 6 l i m i t R i g h t tir l i m i t Rudder d e f l e c t i o n , 6r , deg Crab a n g l e , , deg (b) Flare phase.

F i g u r e 23.- C o n t i n u e d .

rn L e f t crosswinds rn L e f t crosswinds

Right crosswinds L e f t l i m i t -40 -30 -20 -10 0 1 0 20 30 40 50 A i l e r o n d e f l e c t i o n , 6, , deg

a Right 6 r l i m i t 8 L e f t A r l i m i t

-20 -16 -12 -8 -4 0 4 8 12 16 20 Rudder d e f l e c t i o n , 6r , deg -50 -40 -30 -20 -10 0 1 0 20 30 40 50 Crab a n g l e , G c r a b , deg ( c ) R o i l - o u t phase.

F i g u r e 2 3 , - C o n c l u d e d , 3. Recipient's Catalog No. 2. Government Accession No.

1. Report No.

NASA TP-1423 5. Report Date 4. Title and Subtitle May 1979 FLIGHT INVESTIGATION OF PILOTING TECHNIQUES AND 6. Performing Organization Code CROSSWIND LIMITATIONS USING A RESEARCH-TYPE CROSSWIND LANDING GEAR 8. Performing Organization Report No.

7. Author(s) L-12682 Bruce D. F i s h e r , P e r r y L. D e a l , Robert A. Champine, 10. Work Unit No.

and James M. Patton. Jr.

505-08-33-1 2 9. Performing Organization Name and Address N A S A Langley Research Center 11. Contract or Grant No.

Hampton, Va 23665 13. Type of Report and Period Covered Technical Paper 12. Sponsoring Agency Name and Address N a t i o n a l Aeronautics and Space Administration 14. Sponsoring Agency Code Washington, DC 20546 15. Supplementary Notes 16. Abstract A research-type crosswind landing gear was t e s t e d by NASA i n a f l i g h t program which This study was a con- used a l i g h t STOL t r a n s p o r t i n s t r o n g crosswind c o n d i t i o n s .

t i n u a t i o n of an earlier program which used t h e same a i r p l a n e with conventional, The research-type crosswind landing gear used i n t h e pres- t r i c y c l e landing gear.

e n t program enabled t h e a i r p l a n e t o land i n crosswinds up to a magnitude of 25 t o 30 knots. I n t h e previous program, landings were accomplished i n crosswind magni- Three modes of landing-gear o p e r a t i o n were inves- tudes o n l y up t o 15 t o 20 knots.

t i g a t e d : p r e s e t , automatic, and c a s t o r ( p a s s i v e self-alignment). Actual test d a t a and histograms a r e given f o r t h e 195 VFR crosswind l a n d i n g s made f o r t h i s program.

17. Key Words (Suggested by Author(s)) 18. Distribution Statement

U n c l a s s i f i e d - Unlimited

A i r c r a f t o p e r a t i o n s Crosswinds Crosswind l a n d i n g gear Subject Category 02 22. price* 21. No. of Pages 19. Security Claoif. (of this report) 20. Security Classif. (of this page) $5.25 U n c l a s s i f i e d 52 , U n c l a s s i f i e d A * For sale by the Nat~onal Technical Information Service, Springfield, Virginla 22161

NASA-Langley . 1979

THIRD-CLASS BULK RATE Postage and Fees Paid National Aeronautics and National Aeronautics and Space Administration Space Administration NASA-451 Washington, D.C.

USMAIL 20546 Official Business Penalty for Private Use, $300 POSTMASTER: If Undeliverable (Section 158 Postal Manual) Do Not Return

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Document details

Doc number
NASA-TP-1423
Publisher
NASA (NTRS)
Year
1979
Pages
56
File size
3.7 MB
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