Handling qualities of a wide-body transport airplane utilizing Pitch Active Control Systems (PACS) for relaxed static stability application

NASA

Technica I

Paper

Handling Qualities of a

Wide-Body Transport Airplane

Utilizing Pitch Active Control

Systems (PACS) for Relaxed

Static Stability Application

William D. Grantham, Lee H. Person, Jr.,

and Philip W. Brown

Langley Research Center

Hampton, Virginia

Lawrence E. Becker and George E. Hunt

Sperry Corporation

Hampton, Virginia

J. J. Rising, W. J. Davis, C. S . Willey, W. A. Weaver,

and R. Cokeley

Lockheed-Calfornia Company

BurbanklPalmdale, Calfornia

NASA

National Aeronautics and Space Administration Scientific and Technical Information Branch 1. Report No.

2. Government Accession No. 3. Recipient's Catalog No.

N A S A TP-2482 5. Report Date December 1985 6. Performing Organization Code 505-34-03-03 7. A u t h o r ( s ) W i l l i a m D. Grantham, L e e H. Person, Jr., 8. Performing Organization Report No.

P h i l i p W. Brown, Lawrence E. Becker, George E. Hunt, L-15928 J. J. R i s i n g , W. J. Davis, C. S. Willey, W. A. Weaver, 10. Work Unit No.

and R. Cokeley 9. Performing Organization Name and Address 11. Contract or Grant No.

NASA Langley Research Center Hampton, VA 23665-5225 13. Type of Report and Period Covered 12. Sponsoring Agency Name and Address Technical Paper N a t i o n a l Aeronautics and Space Administration 14. Sponsoring Agency Code Washington, DC 20546-0001 15. Supplementary Notes

W i l l i a m D. Grantham, Lee k . Person, Jr., and P h i l i p W. Brown: Langley

Research C e n t e r , Hampton, Va.

Lawrence E. Becker and George E. Hunt: Sperry Corporation, Hampton, Va.

J. J. R i s i n g , W. J. Davis, C. S. Willey, W. A. Weaver, and R. Cokeley: Lockheed-California Company, Burbank/Palmdale, C a l i f .

16. Abstract P i l o t e d s i m u l a t i o n s t u d i e s have been conducted t o e v a l u a t e t h e e f f e c t i v e n e s s of two p i t c h a c t i v e c o n t r o l systems (PACS) on t h e f l y i n g q u a l i t i e s of a wide-body t r a n s p o r t a i r p l a n e when o p e r a t e d a t n e g a t i v e s t a t i c margins. These two p i t c h a c t i v e c o n t r o l systems c o n s i s t e d of a simple "near-term" PACS and a more complex "advanced" PACS. E i g h t d i f f e r e n t f l i g h t c o n d i t i o n s , r e p r e s e n t i n g t h e e n t i r e e v a l u a t e d w i t h emphasis on t h e c r u i s e f l i g h t c o n d i t i o n s .

f l i g h t envelope, were These s t u d i e s w e r e made u t i l i z i n g the Langley Visual/Motion Simulator (VMS) whicl has s i x degrees of freedom. T h e , s i m u l a t i o n tests i n d i c a t e d t h a t (1) t h e f l y i n g q u a l i t i e s of the b a s e l i n e a i r c r a f t (PACS o f f ) f o r the c r u i s e and o t h e r high-speec f l i g h t c o n d i t i o n s w e r e unacceptable a t center-of-gravity positions a f t of the n e u t r a l s t a t i c s t a b i l i t y p o i n t ; ( 2 ) w i t h i n the l i n e a r s t a t i c s t a b i l i t y f l i g h t envelope, t h e near-term PACS provided a c c e p t a b l e f l y i n g q u a l i t i e s f o r s t a t i c s t a b i l i t y margins t o -3 p e r c e n t ; and ( 3 ) with t h e advanced PACS o p e r a t i v e , t h e f l y i n g q u a l i t i e s were demonstrated t o be good ( s a t i s f a c t o r y t o very a c c e p t a b l e ) .

f o r s t a t i c s t a b i l i t y margins t o -20 p e r c e n t .

7. Key Words (Suggested by Authors(s)) 18. Distribution Statement T r a n s p o r t a i r p l a n e s F l y i n g q u a l i t i e s A c t i v e c o n t r o l systems Ground-based s i m u l a t i o n F l i g h t tests S u b j e c t Category 08 Negative s t a t i c margin 9. Security Classif.(of this report) 21. No. of Pages 22. Price 20. Security Classif.(of this page) U n c l a s s i f i e d 107 U n c l a s s i f i e d SUMMARY T r a n s p o r t a i r c r a f t f u e l consumption can be s i g n i f i c a n t l y reduced by r e l a x i n g t h e l o n g i t u d i n a l s t a t i c s t a b i l i t y and, consequently, the t r i m drag. However, t h e f l y i n g q u a l i t i e s of an a i r c r a f t with r e l a x e d s t a t i c s t a b i l i t y can be s i g n i f i c a n t l y degraded. The f l y i n g q u a l i t i e s can be r e s t o r e d by u s i n g a h i g h l y reliable p i t c h a c t i v e c o n t r o l system (PACS) t o provide l o n g i t u d i n a l s t a b i l i t y augmentation.

Ground-based s i m u l a t o r s t u d i e s w e r e conducted to e v a l u a t e t h e e f f e c t i v e n e s s of two p i t c h active c o n t r o l systems on t h e f l y i n g q u a l i t i e s of a wide-body t r a n s p o r t a i r p l a n e when operated a t n e g a t i v e s t a t i c margins. These t w o p i t c h a c t i v e c o n t r o l systems c o n s i s t e d of a simple "near-term" PACS and a more complex "advanced" PACS.

F l y i n g q u a l i t i e s w e r e e v a l u a t e d a t e i g h t d i f f e r e n t f l i g h t c o n d i t i o n s , r e p r e s e n t i n g t h e e n t i r e f l i g h t envelope, with emphasis on t h e c r u i s e f l i g h t c o n d i t i o n s .

The p i l o t e d - f l i g h t s i m u l a t i o n tests i n d i c a t e d t h a t ( 1 ) t h e f l y i n g q u a l i t i e s of t h e b a s e l i n e a i r c r a f t (PACS o f f ) f o r t h e c r u i s e and other high-speed f l i g h t condi- t i o n s were u n a c c e p t a b l e a t c e n t e r - o f - g r a v i t y p o s i t i o n s a f t of t h e n e u t r a l p o i n t ( n e u t r a l s t a t i c s t a b i l i t y ) ; ( 2 t h e near-term PACS provided acceptable f l y i n g q u a l i t i e s f o r s t a t i c s t a b i l i t y margins t o -5 p e r c e n t ; and ( 3 ) t h e f l y i n g q u a l i t i e s w i t h the advanced PACS o p e r a t i v e w e r e demonstrated to be good ( s a t i s f a c t o r y t o very a c c e p t a b l e ) f o r s t a t i c s t a b i l i t y margins t o -20 p e r c e n t .

The near-term PACS w a s a l s o f l i g h t t e s t e d on a d e r i v a t i v e L-1011 a i r p l a n e a t n e g a t i v e s t a t i c margins up t o 3 p e r c e n t for a t y p i c a l c r u i s e f l i g h t c o n d i t i o n . I n g e n e r a l , t h e p i l o t s r a t e d t h e f l y i n g q u a l i t i e s t o be better d u r i n g t h e f l i g h t tests t h a n d u r i n g t h e ground-based s i m u l a t i o n tests. However , subsequent s i m u l a t i o n tests i n d i c a t e d t h a t t h e major reason f o r t h e p i l o t - r a t i n g d i f f e r e n c e s w a s t h a t t h e p i l o t s tended t o maneuver t h e a i r p l a n e less a g g r e s s i v e l y d u r i n g t h e f l i g h t tests. Hence, it is extremely i m p o r t a n t t o impress t h e t e s t p i l o t s with t h e n e c e s s i t y of u s i n g t h e same techniques/procedures/tasks f o r s i m u l a t o r tests as f o r f l i g h t tests whenever p o s s i b l e . The r e s u l t s of t h i s s t u d y a l s o i n d i c a t e d t h a t t h e a d d i t i o n of " a r t i f i - c i a l " cues t o s i m u l a t e important cues that are m i s s i n g i n ground-based s i m u l a t o r s may enhance t h e v a l i d i t y of t h e r e s u l t s . S p e c i f i c a l l y , b u f f e t and s t i c k - s h a k e r models were " s u b s t i t u t e d " for continuous a c c e l e r a t i o n cues i n t h e p r e s e n t study, t h e r e b y improving t h e agreement of p i l o t r a t i n g s between t h e s i m u l a t o r tests and t h e f l i g h t tests.

INTRODUCTION J e t - a i r c r a f t f u e l cost has i n c r e a s e d from 12 c e n t s per g a l l o n i n 1972 t o $1 or more i n 1984; t h u s , t h e f u e l p o r t i o n of a i r c r a f t direct o p e r a t i n g cost h a s i n c r e a s e d s u b s t a n t i a l l y . The r e s u l t has been a heavy emphasis on t h e development of n e x t g e n e r a t i o n t r a n s p o r t a i r c r a f t with s i g n i f i c a n t l y improved aerodynamic performance.

Conventional high-speed s u b s o n i c t r a n s p o r t s with i n h e r e n t s t a t i c s t a b i l i t y are designed w i t h l a r g e s t a b i l i z e r s u r f a c e s and a forward center-of - g r a v i t y range, both of which p e n a l i z e performance. A p p l i c a t i o n of t h e concept of r e l a x e d s t a t i c sta- b i l i t y (RSS) p r o v i d e s a t e c h n o l o g i c a l advance which w i l l a l l e v i a t e t h e s e performance p e n a l t i e s . By a p p l y i n g t h e RSS concept and u t i l i z i n g an a c t i v e c o n t r o l s t a b i l i t y augmentation system, an a i r p l a n e can be designed with ( 1 ) reduced aerodynamic t r i m d r a g because of a f a r t h e r a f t c e n t e r - o f - g r a v i t y balance and/or ( 2 ) reduced aerody- namic p a r a s i t e d r a g and lower s t r u c t u r a l weight because of a s m a l l e r h o r i z o n t a l t a i l s u r f a c e . Also, t h e RSS concept w i l l have an even l a r g e r payoff f o r new commercial t r a n s p o r t d e s i g n s having h i g h - a s p e c t - r a t i o wings and a s u p e r c r i t i c a l a i r f o i l t h a t r e s u l t i n s u b s t a n t i a l l y i n c r e a s e d l e v e l s of t r i m d r a g a t "conventional11 s t a t i c margins.

The s t a t e of t h e a r t i n f l i g h t - c o n t r o l - s y s t e m technologies has progressed t o t h e p o i n t where it is b e l i e v e d t h a t t h e RSS concept can be i n c o r p o r a t e d i n t h e n e x t g e n e r a t i o n of commercial t r a n s p o r t s . However, c u r r e n t f l y i n g q u a l i t i e s c r i t e r i a and a i r w o r t h i n e s s requirements may be too r e s t r i c t i v e t o a l l o w f u l l r e a l i z a t i o n of t h e b e n e f i t s of r e l a x e d s t a t i c s t a b i l i t y . Consequently, t h e r e i s a need to develop c r i t e r i a t o i n s u r e s a t i s f a c t o r y handlinq q u a l i t i e s and guarantee s a f e t y of f l i q h t f o r t h e s e advanced t r a n s p o r t designs. Therefore, t h e a p p l i c a t i o n of RSS has been s t u d i e d i n a j o i n t e f f o r t by NASA and t h e Lockheed-California Company t o determine ways of improving t h e energy e f f i c i e n c y i n t r a n s p o r t a i r c r a f t designs. P i l o t e d s i m u l a t o r i n v e s t i g a t i o n s w e r e conducted with t h e six-degree-of-freedom ground-based a math model of a d e r i v a t i v e Lockheed Langley Visual/Motion Simulator (VMS) and L-1011 wide-body j e t t r a n s p o r t . T h i s s t u d y w a s conducted i n two phases: t h e f i r s t phase e v a l u a t e d a simple, near-term, s t a b i l i t y augmentation system s u i t a b l e f o r a p p l i c a t i o n t o a i r c r a f t o p e r a t i n g with " l o w " l e v e l s of n e g a t i v e s t a t i c margin ( u p t o 5 p e r c e n t ) ; and the second phase e v a l u a t e d a more advanced, more complex system designed f o r a p p l i c a t i o n t o f u t u r e t r a n s p o r t concepts r e q u i r i n g o p e r a t i o n a t "high" l e v e l s of n e g a t i v e s t a t i c margin (10 p e r c e n t o r g r e a t e r ) t o achieve optimum perfor- mance. Both systems are d e s c r i b e d i n t h e appendix.

The aforementioned "near-term" PACS w a s also f l i g h t t e s t e d on a d e r i v a t i v e L-1011 a i r p l a n e a t n e g a t i v e s t a t i c margins up t o 3 p e r c e n t f o r a t y p i c a l c r u i s e f l i g h t c o n d i t i o n . The "advanced" PACS has n o t been f l i g h t tested.

The primary o b j e c t i v e of t h e i n v e s t i g a t i o n w a s t o e v a l u a t e t h e e f f e c t i v e n e s s of t h e s e t w o p i t c h a c t i v e c o n t r o l systems i n improving t h e a i r c r a f t h a n d l i n g q u a l i t i e s when operated a t n e g a t i v e s t a t i c margins.

BACKGROUND The NASA A i r c r a f t Energy E f f i c i e n c y (ACEE) program w a s i n i t i a t e d i n 1976. I n 1977, t h e Lockheed-California Company r e c e i v e d a n ACEE program c o n t r a c t f o r t h e development and f l i g h t e v a l u a t i o n of a c t i v e c o n t r o l concepts f o r subsonic t r a n s p o r t a i r c r a f t . The c o n t r a c t r e s u l t e d i n t h e development of an a i l e r o n a c t i v e system (AACS) which provided wing load a l l e v i a t i o n . The AACS allowed a 5.8-percent i n c r e a s e i n wing span f o r t h e L-1011-500 a i r c r a f t ( i n - s e r v i c e d a t e , 1980) t h a t decreased f u e l consumption by approximately 3 p e r c e n t . A l s o , r e s e a r c h s t u d i e s w e r e conducted under t h e contract t o e v a l u a t e t h e b e n e f i t s of a p i t c h active c o n t r o l system PACS. P i l o t e d - f l i g h t s i m u l a t i o n s w e r e conducted, a t Lockheed, on a moving- base s i m u l a t o r w i t h a n L-1011 cab. These s i m u l a t i o n tests showed t h a t w i t h s t a t i c l o n g i t u d i n a l s t a b i l i t y r e l a x e d t o near n e u t r a l , and i n heavy t u r b u l e n c e , a lagged p i t c h - r a t e damper provided f l y i n g q u a l i t i e s t h a t w e r e e q u i v a l e n t t o t h o s e of t h e b a s e l i n e a i r c r a f t with a p o s i t i v e s t a t i c s t a b i l i t y margin of 15 p e r c e n t . Thus, t h e s e r e s u l t s provided a s u f f i c i e n t basis f o r proceeding t o a f l i g h t e v a l u a t i o n of t h e PACS; t h e s e subsequent f l i g h t demonstration tests showed t h a t f o r a nominal c r u i s e f l i g h t c o n d i t i o n , t h e PACS provided good f l y i n g q u a l i t i e s of t h e a i r c r a f t for s t a t i c s t a b i l i t y margins t o +1 p e r c e n t . I n a d d i t i o n , f u r t h e r a n a l y t i c a n a l y s e s of t h i s "simple" PACS i n d i c a t e d t h a t by i n c r e a s i n g t h e PACS feedback-loop g a i n s , s a t i s - f a c t o r y f l y i n g q u a l i t i e s c h a r a c t e r i s t i c s might be p o s s i b l e a t s l i g h t l y n e g a t i v e s t a t i c s t a b i l i t y margins. Consequently, a "near-term" PACS follow-on f l i g h t t e s t program w a s proposed.

The o b j e c t i v e of t h e extended near-term PACS program was to demonstrate by f l i g h t t h a t t h e NTPACS w i t h i n c r e a s e d feedback g a i n s would provide f l y i n g q u a l i t i e s f o r s t a t i c s t a b i l i t y margins t o - 3 p e r c e n t which were e q u i v a l e n t to t h o s e of t h e b a s e l i n e a i r c r a f t w i t h a p o s i t i v e s t a t i c s t a b i l i t y margin of 15 p e r c e n t . The major t a s k s f o r this "extended near-term" PACS program were: e F l y i n g q u a l i t i e s a n a l y s i s e P i l o t e d - f l i g h t s i m u l a t i o n tests e A i r c r a f t p r e p a r a t i o n f o r f l i g h t tests e F l i g h t tests The f l y i n g q u a l i t i e s a n a l y s i s and p i l o t e d - f l i g h t s i m u l a t i o n tests w e r e l i m i t e d t o e v a l u a t i o n of t w o c r u i s e f l i g h t c o n d i t i o n s and one l a n d i n g condition. A i r c r a f t p r e p a r a t i o n included a n a l y s i s r e q u i r e d f o r determining o p e r a t i n g r e s t r i c t i o n s , s a f e t y reviews, and a i r c r a f t m o d i f i c a t i o n s . The f l i g h t tests w e r e l i m i t e d t o e v a l u a t i o n of a series of static s t a b i l i t y margins f o r one c r u i s e f l i g h t c o n d i t i o n .

I n May 1980, when t h e ACEE program w a s r e s t r u c t u r e d to c o n c e n t r a t e on t h e of f u t u r e PACS t e c h n o l o g i e s such as t h e aforementioned "near-term" PACS, development t h e development of an "advanced" PACS w a s also planned. The ADVPACS w a s to provide good f l y i n g q u a l i t i e s t o a n e g a t i v e s t a t i c s t a b i l i t y margin of 1 0 p e r c e n t and f o r high-Mach/high-acceleration f l i g h t c o n d i t i o n s . However, f l i g h t tests of t h e advanced system were t o be l i m i t e d t o f l i g h t a t a n e g a t i v e s t a t i c s t a b i l i t y margin of 3 p e r c e n t because of t h e L-1011 f l i g h t - t e s t a i r c r a f t s t r u c t u r a l and center-of- g r a v i t y management l i m i t a t i o n s .

I n t h e fall of 1981, Lockheed decided t o phase o u t production of t h e L-1011 a i r p l a n e ; consequently, the scope of t h e program w a s reduced. The near-term PACS development w a s t o be continued as p r e v i o u s l y planned ( t h r o u g h f l i g h t t e s t i n g ) , b u t t h e advanced PACS development w a s to be continued o n l y through t h e p i l o t e d s i m u l a - t i o n phase. The advanced PACS program c o n s i s t e d of control l a w development, f l y i n g q u a l i t i e s a n a l y s i s , p i l o t e d - f l i g h t s i m u l a t i o n t e s t i n g on a moving-base s i m u l a t o r , and a r c h i t e c t u r a l development of a PACS t h a t could be used f o r a f u t u r e t e s t program.

This paper d i s c u s s e s the r e s u l t s of t h e f l y i n g - q u a l i t i e s - a n a l y s e s phase of t h e program conducted a t t h e Lockheed-California Company and t h e r e s u l t s of t h e "extended near-term" PACS and t h e "advanced" PACS p i l o t e d - f l i g h t s i m u l a t i o n phases of t h e program conducted a t t h e NASA Langley Research C e n t e r . Also, a brief d i s c u s - s i o n i s p r e s e n t e d wherein t h e f l i g h t s i m u l a t i o n test r e s u l t s with t h e "near-term" PACS o p e r a t i v e are compared w i t h t h e corresponding a i r p l a n e f l i g h t test r e s u l t s .

SYMBOLS Measurements and c a l c u l a t i o n s were made i n U.S. Customary Units, and a l l c a l c u l a t i o n s are based on t h e a i r c r a f t body axes.

A, B t C, D, E c o e f f i c i e n t s of advanced PACS gain-schedule e q u a t i o n pitching-moment c o e f f i c i e n t about a p a r t i c u l a r a i r c r a f t c e n t e r of

cm , c g

g r a v i t y

-

C mean aerodynamic chord column force FC F* m u l t i p l i e r f a c t o r on p i t c h - r a t e damper g a i n a c c e l e r a t i o n due t o g r a v i t y ( l g = 32.17 f t / s e c 2 ) K g a i n combined p i t c h - a t t i t u d e / v e l o c i t y g a i n feedforward g a i n normal-accele r a t i o n g a i n p i t c h - r a t e damper g a i n column f e e l s p r i n g g r a d i e n t , l b f / i n .

c a l c u l a t e d g a i n f o r advanced PACS Mach number d i v e Mach number maximum o p e r a t i o n a l Mach number column mass l o a d factor l i m i t normal a c c e l e r a t i o n s t e a d y - s t a t e normal-acceleration change per u n i t change i n a n g l e of a t t a c k for an i n c r e m e n t a l h o r i z o n t a l - t a i l d e f l e c t i o n a t c o n s t a n t a i r s p e e d , g u n i t s / r a d s t i c k - f r e e n e u t r a l p o i n t NO p i t c h rate Q

-

dynamic p r e s s u r e s Laplace transform o p e r a t o r t i m e , t u r b u l e n c e t a i r s p e e d

v

a i r c r a f t maximum o p e r a t i n g speed s t a l l speed a i r c r a f t weight v e r t i c a l t u r b u l e n c e g u s t value peak v e r t i c a l turbulence g u s t value a n g l e of a t t a c k increment r a t i o of atmospheric p r e s s u r e a t a l t i t u d e t o p r e s s u r e a t sea l e v e l t o t a l column d e f l e c t i o n , i n .

column d e f l e c t i o n due t o Mach t r i m compensation b c , MTC column d e f l e c t i o n due t o p i l o t f o r c e i n p u t 6ClP column d e f l e c t i o n (software o n l y ) due t o p i t c h a c t i v e c o n t r o l Gc,PACS system, i n .

column d e f l e c t i o n due t o c a b l e s t r e t c h , i n .

Gc,str column d e f l e c t i o n due t o p i l o t t r i m beeper i n p u t &c,trim s o f t w a r e s t i c k p o s i t i o n , i n .

6co1 e l e v a t o r s u r f a c e d e f l e c t i o n , deg f l a p d e f l e c t i o n , deg 6f h o r i z o n t a l - t a i l d e f l e c t i o n , deg modified h o r i z o n t a l - t a i l feedback s i g n a l f o r secondary g a i n schedul- i n g ( f u n c t i o n of a, I$, and M ) commanded s t a b i l i z e r d e f l e c t i o n , deg 6 H, com damping r a t i o 6 p i t c h a t t i t u d e , deg f i l t e r e d p i t c h - a t t i t u d e feedback s i g n a l 0i ? numerator t i m e c o n s t a n t of lag-lead t r a n s f e r f u n c t i o n T denominator t i m e c o n s t a n t of lag-lead t r a n s f e r f u n c t i o n f o r c e s e n s o r f i l t e r t i m e c o n s t a n t p i t c h damper l a g bank a n g l e , deg frequency damped frequency undamped n a t u r a l frequency S u b s c r i p t s : c g c e n t e r of g r a v i t y FRL f u s e l a g e r e f e r e n c e l i n e Ph phugoid mode short-period mode SP t r i m m e d f l i g h t t r i m Abbreviations: AACS a i l e r o n a c t i v e c o n t r o l system accel a c c e l e r a t i o n ADVPACS advanced p i t c h a c t i v e c o n t r o l system a n g l e an9 cog. c e n t e r of g r a v i t y c o l column fwd forward ILS instrument landing system KEAS knots of e q u i v a l e n t a i r s p e e d max maximum min minimum M T C Mach t r i m compensator NTPACS near-term p i t c h a c t i v e c o n t r o l system PACS p i t c h a c t i v e c o n t r o l system POS p o s i t i o n PR p i l o t r a t i n g RSS r e l a x e d s t a t i c s t a b i l i t y SAS s t a b i l i t y augmentation system stab s t a b i l i z e r vert v e r t i c a l VMS Visual/Motion Simulator DESCRIPTION OF SIMULATED AIRPLANE The Lockheed L-1011 i s a c u r r e n t - g e n e r a t i o n , subsonic, commercial t r a n s p o r t a i r c r a f t ( f i g . 1 ) . The a i r c r a f t is powered by t h r e e Rolls-Royce RB 211-22B high- b y p a s s - r a t i o t u r b o f a n e n g i n e s , and the s t a b i l i z e r , which h a s a geared elevator, is t h e primary l o n g i t u d i n a l c o n t r o l . A i r c r a f t geometry and weiqht d a t a are given i n table I. A unique v e r s i o n of t h e L-1011 a i r c r a f t w a s used throughout t h e PACS/RSS program a n a l y s e s , d e s i g n , s i m u l a t i o n , and f l i g h t tests. F e a t u r e s of t h i s a i r c r a f t , a basic Lockheed L-1011-1 w i t h an extended-span wing and a n a i l e r o n a c t i v e c o n t r o l system (AACS), are i n d i c a t e d i n f i g u r e 2. These f e a t u r e s w e r e i n s t a l l e d prior t o the s u b j e c t RSS s t u d i e s f o r improved aerodynamic e f f i c i e n c y and maneuver load r e l i e f .

RSS s t u d i e s a downrigged elevator, a center-of-gravity management system, For t h e and the near-term PACS w e r e added (see f i g . 2 ) .

The s i m u l a t e d L-1011 u s e s elevator, s t a b i l i z e r , and a c t i v e outboard a i l e r o n s for l o n g i t u d i n a l c o n t r o l , inboard and outboard a i l e r o n s and spoilers f o r l a t e r a l c o n t r o l , and r u d d e r f o r d i r e c t i o n a l c o n t r o l ( f i g . 3 ) .

Aircraft l o n g i t u d i n a l c o n t r o l i s achieved by t h e b a s i c l o n g i t u d i n a l c o n t r o l system and t h e active c o n t r o l s t a b i l i t y augmentation system ( S A S ) t h a t determine s t a b i l i z e r , elevator, and a c t i v e a i l e r o n d e f l e c t i o n s . The b a s i c - l o n g i t u d i n a l - control-system modeling i n c l u d e s s e r v o a c t u a t o r , cable stretch, and c o n t r o l sur- face p o s i t i o n and rate l i m i t i n g . The l o n g i t u d i n a l active c o n t r o l SAS i n c l u d e s the "near-term" or t h e "advanced" p i t c h a c t i v e c o n t r o l system (PACS) and the a i l e r o n a c t i v e c o n t r o l system (AACS). I n a d d i t i o n t o column p o s i t i o n commanded by t h e p i l o t , b o t h PACS u t i l i z e p i t c h - a n g u l a r - r a t e feedback and column-force feedforward t o compute a c o n t r i b u t i o n t o "software" column p o s i t i o n . (The advanced PACS a l s o u s e s a d d i t i o n a l feedbacks, such as normal a c c e l e r a t i o n , p i t c h a n g l e , e t c , ) The AACS also u s e s a n g u l a r and a n g u l a r - r a t e feedbacks t o determine a symmetric ( b o t h outboard same d i r e c t i o n ) outboard a i l e r o n p o s i t i o n . The a i l e r o n s e q u a l l y d e f l e c t e d i n t h e Mach t r i m compensator (MTC)--while a c t u a l l y a t y p e of S A S - - i s i n c l u d e d as a basic c o n t r o l s i n c e it is u s u a l l y a c t i v e and is, t h e r e f o r e , an i n t e g r a l part of column d e f l e c t i o n . The "normal" high-speed M T C w a s designed t o a l l e v i a t e t h e nose-down ( tuck under) maneuver t h a t t r a n s p o r t s e x p e r i e n c e as Mach number approaches 0.8.

T h i s i s due t o t h e rearward s h i f t of t h e a i r c r a f t c e n t e r of p r s s s u r e a s Mach number i n c r e a s e s . The low-speed M T C w a s s p e c i f i c a l l y designed for column p o s i t i o n c o n t r i - b u t i o n s when Mach number i s less t h a n 0.295, flaps-down c o n f i g u r a t i o n . ( T h i s l o w - speed M T C w a s designed e s p e c i a l l y for the s u b j e c t RSS s i m u l a t i o n program and i s n o t used on c o n v e n t i o n a l L-1011 a i r c r a f t . ) The low-speed M T C has a n e g l i b l e e f f e c t a t h i g h e r Mach numbers. B o t h M T C c o n t r i b u t i o n s add d i r e c t l y t o t h e p h y s i c a l column p o s i t i o n . A d e t a i l e d d e s c r i p t i o n of t h e basic l o n g i t u d i n a l c o n t r o l system of t h i s d e r i v a t i v e L-1011 a i r p l a n e i s p r e s e n t e d i n t h e appendix.

A i r c r a f t l a t e r a l c o n t r o l is achieved by the b a s i c l a t e r a l c o n t r o l system, which determines a i l e r o n and spoiler d e f l e c t i o n s and i n c l u d e s s e r v o a c t u a t o r and p o s i t i o n 1imiter.modeling. Only t h e f o u r outboard spoiler p a n e l s (per wing) are modeled f o r l a t e r a l c o n t r o l .

Aircraft d i r e c t i o n a l c o n t r o l is achieved by t h e d i r e c t i o n a l c o n t r o l system, which determines manual and SAS c o n t r i b u t i o n s t o t h e rudder p o s i t i o n . The direc- t i o n a l S A S c o n s i s t s of a yaw damper t h a t i n c l u d e s a i l e r o n i n p u t , s e r v o a c t u a t o r , and rate and p o s i t i o n l i m i t e r modeling f o r improved t u r n c o o r d i n a t i o n .

Although t h e s u b j e c t s i m u l a t i o n s t u d y u t i l i z e d six-degree-of-freedom e q u a t i o n s of motion ( w i t h n o n l i n e a r aerodynamic and t h r u s t i n p u t d a t a ) , t h e lateral- d i r e c t i o n a l f l i g h t c h a r a c t e r i s t i c s are n o t addressed i n t h i s paper s i n c e t h i s w a s a " l o n g i t u d i n a l " handling q u a l i t i e s study.

DESCRIPTION OF SIMULATION EQUIPMENT The s i m u l a t i o n s t u d y w a s made w i t h t h e general-purpose c o c k p i t of t h e Langley Visual/Motion Simulator ( V M S ) , a qround-based motion s i m u l a t o r w i t h s i x degrees of freedom. For t h i s s t u d y , it had a t r a n s p o r t - t y p e cockpit equipped w i t h c o n v e n t i o n a l f l i g h t and e n g i n e - t h r u s t c o n t r o l s and a f l i g h t - i n s t r u m e n t d i s p l a y r e p r e s e n t a t i v e of t h e c o n t r o l s and p a n e l found i n c u r r e n t t r a n s p o r t a i r p l a n e s . (See f i g . 4 . ) I n s t r u - ments t h a t i n d i c a t e a n g l e of a t t a c k , angle of sideslip, f l a p a n g l e , h o r i z o n t a l s t a b i l i z e r a n g l e , and column force w e r e also provided.

The c o n t r o l f o r c e s on t h e wheel, column, and rudder p e d a l s w e r e provided by a h y d r a u l i c system coupled with an analog computer. The system i n c o r p o r a t e d v a r i a b l e - f e e l c h a r a c t e r i s t i c s of s t i f f n e s s , damping, Coulomb f r i c t i o n , breakout forces, d e t e n t s , and i n e r t i a . The l o n g i t u d i n a l c o n t r o l loading system of t h e VMS is d e s c r i b e d i n the appendix.

The a i r p o r t - s c e n e d i s p l a y used f o r approach and l a n d i n g w a s an 'out-the-window" v i r t u a l image system of t h e beam-splitter, r e f l e c t i v e - m i r r o r type. (See f i g . 5.) A runway "model" w a s programmed t h a t had a width of 200 f t , a t o t a l l e n g t h of 1 1 500 f t , roughness c h a r a c t e r i s t i c s , and a slope from t h e c e n t e r of t h e edge repre- s e n t i n g a runway crown. Only a d r y runway w a s considered i n t h i s study.

The average t o t a l motion d e l a y of the VMS, i n c l u d i n g computational throughput, i s less than 70 msec and is q u i t e compatible w i t h t h e rest of t h e system, i n c l u d i n g v i s u a l d e l a y s . The washout system used t o p r e s e n t t h e motion-cue commands t o t h e base i n nonstandard. It w a s conceived and developed a t the NASA Langley motion Research Center (ref. 1 ) . The b a s i s of the washout is t h e continuous a d a p t i v e change of parameters t o ( 1 ) minimize a cost f u n c t i o n a l through continuous s t e e p e s t d e s c e n t method and ( 2 ) produce t h e motion c u e s i n t r a n s l a t i o n a l a c c e l e r a t i o n s and rates w i t h i n the motion envelope of the s y n e r g i s t i c base.

r o t a t i o n a l The o n l y a u r a l cues provided w e r e engine n o i s e s and landing-gear e x t e n s i o n and r e t r a c t i o n n o i s e s .

TESTS AND PROCEDURES T h i s s t u d y e v a l u a t e d t h e handling q u a l i t i e s by a n a l y s i s of recorded aircraft- motion t i m e h i s t o r i e s , c a l c u l a t i o n of v a r i o u s f l y i n g q u a l i t i e s parameters, and p i l o t comments on the f l y i n g q u a l i t i e s of t h e s i m u l a t e d L-1011 t r a n s p o r t aircraft and t h e e f f e c t s of v a r i o u s s t a b i l i t y and c o n t r o l augmentation systems on t h e s e characteristics.

The e i g h t f l i g h t c o n d i t i o n s i n d i c a t e d i n table I1 and f i g u r e 6 were simulated d u r i n g t h e p r e s e n t s t u d i e s . These f l i g h t c o n d i t i o n s r e p r e s e n t t h e e n t i r e f l i g h t envelope of the L-1011 a i r c r a f t - - f r o m t a k e o f f , t o cruise, t o landing. When e v a l u a t - i n g t h e e f f e c t s of t h e NTPACS, t h e t h r e e f l i g h t c o n d i t i o n s d e s i g n a t e d c o n d i t i o n s 10, 1 1 , and 1 8 w e r e flown; b u t , when e v a l u a t i n g t h e ADVPACS, a l l f l i g h t c o n d i t i o n s were flown e x c e p t c o n d i t i o n 1 1 . Five r e s e a r c h test p i l o t s p a r t i c i p a t e d i n t h e f l i g h t s i m u l a t i o n program, a l t h o u g h a l l p i l o t s d i d n o t e v a l u a t e e i t h e r PACS c o n c e p t a t a l l of its d e s i g n a t e d f l i g h t c o n d i t i o n s .

Evaluation Tasks During C r u i s e Wind-up turns.- Wind-up t u r n s were performed t o e v a l u a t e maneuvering force and a t i n c r e a s i n g load f a c t o r s .

s t a b i l i t y c h a r a c t e r i s t i c s by s t a b i l i z i n g S - p a t t e r n turns.- The a i r c r a f t w a s banked t o a 4-min t u r n a t t i t u d e and flown through a 90° heading change while descending 500 f t . Then, t h e bank a n g l e w a s r e v e r s e d , and t h e a i r c r a f t w a s t u r n e d back and r o l l e d o u t on the i n i t i a l heading while climbing 500 f t .

Trimmabi1ity.- The workload t o i n i t i a l l y t r i m t h e a i r c r a f t and t o r e c a p t u r e t r i m from a d i s t u r b e d c o n d i t i o n w a s used as a n o t h e r measure of performance. The t r i m r e c a p t u r e w a s e v a l u a t e d by advancing power t o u p s e t t h e a i r c r a f t a l t i t u d e and f l y i n g back t o t h e i n i t i a l a l t i t u d e w i t h o u t retrimming.

A i r l i n e o p e r a t i o n a l turns.- Banked t u r n s of 20° and 30° w e r e performed while m a i n t a i n i n g c o n s t a n t speed and u s i n g column force t o c o n t r o l a t t i t u d e and a l t i t u d e .

Turn e n t r y and e x i t c h a r a c t e r i s t i c s w e r e also e v a l u a t e d .

I P i t c h - a t t i t u d e change.- A t t i t u d e s t a b i l i t y w a s e v a l u a t e d by changing and hold- i n g a new p i t c h a t t i t u d e with column force i n p u t s .

Power e f f e c t s . - Power w a s advanced and r e t a r d e d t o r e s t a b i l i z e t h e a i r c r a f t on a new p i t c h a t t i t u d e w h i l e m a i n t a i n i n g speed by a p p l y i n g column c o n t r o l force.

I

Emergency descent.- Power w a s p u l l e d back t o i d l e , and the nose of the a i r c r a f t w a s pushed over t o start t h e a i r c r a f t d e s c e n t . The a i r c r a f t w a s manuevered i n t o a banked t u r n , a f t e r start of d e s c e n t , t o i n c r e a s e drag.

I

I Short-period dynamic s t a b i l i t y . - The s h o r t - p e r i o d c h a r a c t e r i s t i c s w e r e evalu- a t e d by u s i n g q u i c k forward and a f t c o n t r o l column i n p u t s and r e l e a s i n g t h e column t o u p s e t t h e aircraft from l g f l i g h t . P i t c h a t t i t u d e and load factor were observed while the a i r c r a f t r e t u r n e d t o lg t r i m .

Phugoid dynamic s t a b i l i t y . - The a i r c r a f t w a s d i s p l a c e d s l i g h t l y from t r i m , and t h e phugoid damping and period w e r e e v a l u a t e d by observing e x c u r s i o n s i n rate of climb and p i t c h a t t i t u d e .

S t a t i c s t a b i l i t y . - L o n g i t u d i n a l s t a t i c s t a b i l i t y , sometimes ref e r r e d to a s speed s t a b i l i t y , w a s e v a l u a t e d by determining t h e v a r i a t i o n of column f o r c e w i t h d e v i a t i o n from t r i m speed.

Evaluation Tasks a t Maximum Operating Speed Tasks performed a t maximum o p e r a t i o n a l speeds included wind-up t u r n s , opera- t i o n a l t u r n s , and trimmability. D e s c r i p t i o n s of t h e s e t a s k s are t h e same as those d e s c r i b e d f o r t h e cruise f l i g h t c o n d i t i o n s .

Evaluation Tasks During Landing Wind-up turns.- Wind-up t u r n s w e r e conducted to e v a l u a t e maneuvering f o r c e c h a r a c t e r i s t i c s by s t a b i l i z i n g a t load factors up t o 1.29.

ILS approach.- The approach t a s k w a s i n i t i a l i z e d 8 m i l e s from t h e airport, a t an a l t i t u d e of 2000 f t , and with a 1000-ft l a t e r a l o f f s e t from t h e l o c a l i z e r beam. The t a s k involved f l y i n g t h e airplane t o t h e l o c a l i z e r , c a p t u r i n g t h e g l i d e s l o p e , and t r a c k i n g t h e l o c a l i z e r and g l i d e slope down t o an a l t i t u d e of 50 f t . A few f l a r e s and touchdowns were performed, b u t t h e p i l o t s commented t h a t t h i s p a r t of t h e t a s k added nothing t o the e v a l u a t i o n i n t h i s p a r t i c u l a r study. Most approaches w e r e made u t i l i z i n g "raw-data" d i s p l a y s ; however, a f e w approaches w e r e flown u s i n g t h e avail- a b l e f l i g h t d i r e c t o r .

E v a l u a t i o n Tasks While Holding A i r l i n e o p e r a t i o n a l t u r n s (30° banked t u r n s ) were flown while m a i n t a i n i n g speed and u s i n g column f o r c e t o c o n t r o l a t t i t u d e and a l t i t u d e .

E v a l u a t i o n Tasks a t Takeoff The t a k e o f f c o n d i t i o n was i n i t i a l i z e d with t h e a i r c r a f t climbing i n t h e second- segment c o n f i g u r a t i o n . C o n t r o l l a b i l i t y w a s e v a l u a t e d d u r i n g 30' banked t u r n s through 30° heading changes.

RESULTS AND DISCUSSION The r e s u l t s of t h i s s t u d y are d i s c u s s e d i n terms of t h e p r e v i o u s l y s t a t e d o b j e c t i v e s . The t w o p i t c h a c t i v e c o n t r o l systems (PACS) e v a l u a t e d are d i s c u s s e d s e p a r a t e l y - - f i r s t , t h e more simple (near-term) PACS and, second, t h e e f f e c t s of t h e more complex (advanced) PACS on t h e a i r c r a f t h a n d l i n g q u a l i t i e s . F i n a l l y , with t h e near-term PACS o p e r a t i v e i n each test, a b r i e f d i s c u s s i o n is p r e s e n t e d wherein t h e f l i g h t s i m u l a t i o n t e s t r e s u l t s are compared with t h e a i r p l a n e f l i g h t test r e s u l t s .

Since t h i s w a s a " l o n g i t u d i n a l " handling q u a l i t i e s s t u d y , t h e l a t e r a l - d i r e c t i o n a l are n o t addressed i n t h i s paper. The f l i g h t c h a r a c t e r i s t i c s of t h e a i r c r a f t l a t e r a l - d i r e c t i o n a l c h a r a c t e r i s t i c s simulated were judged by t h e p i l o t s t o be " w e l l - enough-behaved" t h a t t h e y would n o t i n f l u e n c e t h e p i l o t s ' a b i l i t y t o a d e q u a t e l y e v a l u a t e t h e l o n g i t u d i n a l c h a r a c t e r i s t i c s .

Table I11 p r e s e n t s t h e Cooper-Harper p i l o t r a t i n g system used f o r t h e handling q u a l i t i e s e v a l u a t i o n s . Unless s p e c i f i c a l l y noted otherwise, t h e r e s u l t s are d i s - cussed i n r e l a t i o n t o t h e c r u i s e f l i g h t c o n d i t i o n s d e s i g n a t e d f l i g h t c o n d i t i o n 10 i n f i g u r e 6 and t a b l e 11.

Near-Term PACS A block diagram of t h e near-term PACS is p r e s e n t e d i n f i g u r e 7. This augmenta- t i o n system c o n s i s t s of ( 1 ) a p i t c h damper loop with p i t c h rate f e d back i n t o t h e series s e r v o t o enhance t h e a i r c r a f t short-period c h a r a c t e r i s t i c s and ( 2 ) a feed- forward loop with column p o s i t i o n (column minus t r i m ) f e d back t o enhance t h e a i r c r a f t maneuver s t a b i l i t y . The nonlinear g a i n s and t i m e l a g schedules of t h i s system are i n d i c a t e d i n f i g u r e 8. This PACS ( f i g . 7 ) i s described i n more d e t a i l i n t h e appendix of t h i s paper and i n r e f e r e n c e 2.

The t h r e e f l i g h t c o n d i t i o n s evaluated d u r i n g t h e near-term PACS s i m u l a t i o n program w e r e t h o s e d e s i g n a t e d as 10, 1 1 , and 18. (See table I1 and f i g . 6 . ) The f l y i n g q u a l i t i e s f o r f l i g h t c o n d i t i o n 10, a nominal c r u i s e c o n d i t i o n , w e r e evaluated more e x t e n s i v e l y than t h e o t h e r two f l i g h t conditions. The s i m u l a t i o n tests were performed with s t a t i c s t a b i l i t y margins from +15 p e r c e n t t o -5 percent. (The previous near-term PACS s t u d y by Lockheed covered a range of center-of-gravi t y posi- t i o n s from 0.25E t o 0.39Ef r e p r e s e n t i n g s t a t i c s t a b i l i t y margins from +15 p e r c e n t t o +1 p e r c e n t , r e s p e c t i v e l y , f o r t h e c r u i s e f l i g h t c o n d i t i o n . ) The a n a l y s e s and p i l o t e v a l u a t i o n s included speed s t a b i l i t y , maneuver s t a b i l i t y , dynamic s t a b i l i t y , and turbulence response. The r e s u l t s are compared with t h e f l y i n g q u a l i t i e s r e q u i r e m e n t s / c r i t e r i a of r e f e r e n c e 3 (FAR P a r t 25) and r e f e r e n c e 4 (MIL-F-8785C) t o PACS c a p a b i l i t i e s .

determine t h e adequacy of t h e near-term Speed s t a b i l i t y . - The s t a b i l i t y a n a l y s i s determined t h e column f o r c e Fc r e q u i r e d t o maintain t h e a i r c r a f t a t a speed o t h e r than t r i m speed. Reference 3 d e f i n e s s a t i s f a c t o r y column f o r c e c h a r a c t e r i s t i c s as follows: 1 . A p u l l f o r c e s h a l l be required t o maintain speed below t r i m speed, and a push f o r c e s h a l l be r e q u i r e d t o maintain speed above t r i m speed.

2. Column force s h a l l vary monotonically w i t h speed.

3. The average column-force g r a d i e n t s h a l l be a t least -1 l b f / 6 KEAS through- o u t t h e speed range.

Speed s t a b i l i t y c h a r a c t e r i s t i c s f o r f l i g h t c o n d i t i o n 10 are p r e s e n t e d i n f i g - u r e 9. For a i r s p e e d s of approximately f50 k n o t s from t r i m , t h e r e f e r e n c e 3 design criteria f o r speed s t a b i l i t y are s a t i s f i e d f o r c e n t e r - o f - g r a v i t y p o s i t i o n s of 0.25c and 0.45E. Since p i t c h rate is n o t generated when t h e a i r c r a f t is s t a b i l i z e d a t t h e v a r i o u s speeds, t h e PACS o f f and PACS on "with p i t c h damper only" have t h e same column f o r c e c h a r a c t e r i s t i c s . Column f o r c e s w e r e reduced s i g n i f i c a n t l y f o r t h e PACS pitch damper and feedforward modes were o p e r a t i v e .

c o n f i g u r a t i o n wherein t h e Column f o r c e s f o r t h e PACS with p i t c h damper and feedforward washout would be the same as with the PACS o f f , except f o r l i g h t e r c o n t r o l column f o r c e r e q u i r e d t o i n i t i a t e t h e speed change.

Manuever s t a b i l i t y . - Manuever a n a l y s i s determined t h e column f o r c e s r e q u i r e d t o maintain the a i r c r a f t i n s t e a d y wind-up t u r n s .

Maneuver column force c r i t e r i a of r e f e r e n c e 4 r e q u i r e a s t e a d i l y i n c r e a s i n g push f o r c e t o m a i n t a i n l o a d factors less t h a n 1 and a s t e a d i l y i n c r e a s i n g p u l l f o r c e t o m a i n t a i n load factors g r e a t e r t h a n 1 . The upper and lower column force maneuver g r a d i e n t c r i t e r i a f o r c r u i s e are

0 Upper boundary = 120/(nL - 1 1, l b f /g u n i t s

0 L o w e r boundary = 35/(nL - 1 1 , l b f / g u n i t s

(The load f a c t o r l i m i t nL f o r t h e commercial L-1011 a i r c r a f t i s 2.5q.l The c a l c u l a t e d maneuver s t a b i l i t y c h a r a c t e r i s t i c s of f l i g h t c o n d i t i o n 10 are shown i n f i g u r e s 10, 11, and 12 f o r 25 p e r c e n t , 39 p e r c e n t , and 45 percent c e n t e r - o f - g r a v i t y p o s i t i o n s , r e s p e c t i v e l y . P a r t ( a ) i n each of t h e s e f i g u r e s p r e s e n t s t h e maneuver c h a r a c t e r i s t i c s f o r t h e PACS o f f and f o r t h e PACS on with p i t c h damper only; p a r t ( b ) i n each f i g u r e p r e s e n t s t h e maneuver c h a r a c t e r i s t i c s for t h e PACS on with p i t c h damper and feedforward. (The p i l o t s confirmed t h e s e " c a l c u l a t e d " maneu- v e r s t a b i l i t y c h a r a c t e r i s t i c s on t h e simulator.) The PACS-on c o n f i g u r a t i o n w i t h p i t c h damper and feedforward washout is n o t shown i n t h e f i q u r e s because it i s dependent upon t h e rate a t which t h e maneuver w a s accomplished. However, t h e column forces f o r t h i s c o n f i g u r a t i o n l i e between those of t h e o t h e r t w o PACS-on configura- t i o n s . A l s o , t h e c o n f i g u r a t i o n i s e q u i v a l e n t t o t h e PACS with o n l y p i t c h - r a t e damper f o r s u s t a i n e d maneuvers and i s l i k e t h e PACS w i t h b o t h p i t c h damper and feed forward f o r rapid maneuvers.

The p i t c h - r a t e damper i n c r e a s e s f o r c e g r a d i e n t s , and t h e feedforward reduces t h e g r a d i e n t f o r each c e n t e r - o f - g r a v i t y position shown i n f i g u r e s 10, 1 1 , and 12.

A l s o , t h e " i n i t i a l " force g r a d i e n t s ( g r a d i e n t s for load f a c t o r s up t o approximately are shown t o l i e w i t h i n t h e p r e s c r i b e d l i m i t s 1.69) f o r t h e PACS-on c o n f i g u r a t i o n s of r e f e r e n c e 4. A t a l o a d f a c t o r of 1.69, t h e column f o r c e g r a d i e n t s begin t o reduce--they " f l a t t e n " f o r t h e 0.25E c e n t e r - o f - g r a v i t y p o s i t i o n and "reverse" f o r t h e 0.39E and 0.45E center-of-gravi t y p o s i t i o n s . These reduced g r a d i e n t s r e p r e s e n t t h e of t h e r e g i o n where t h e aerodynamic d a t a v a r y l i n e a r l y w i t h a n g l e of a t t a c k .

end S i n c e t h e o b j e c t i v e of t h e near-term PACS extended f l i g h t test program w a s t o evalu- ate t h e PACS a t l i n e a r s t a b i l i t y c o n d i t i o n s , t h e l o a d f a c t o r l i m i t of t h e f l i g h t t e s t a i r c r a f t w a s determined t o be approximately 1.69.

The maneuver s t a b i l i t y a n a l y s i s f o r f l i g h t c o n d i t i o n 1 1 showed t h a t €or l o a d f a c t o r s less t h a n approximately 2.29 the f o r c e g r a d i e n t s w i t h PACS on were w i t h i n t h e l i m i t s p r e s c r i b e d by r e f e r e n c e 4.

The a n a l y s i s showed t h a t t h e column force g r a d i e n t s f o r f l i g h t c o n d i t i o n 18 ( l a n d i n g ) , w i t h the PACS on or o f f , i n c r e a s e d as t h e c e n t e r - o f - g r a v i t y p o s i t i o n w a s moved a f t . A l s o , a t t h e a f t c e n t e r - o f - g r a v i t y p o s i t i o n s , t h e column f o r c e g r a d i e n t s exceeded t h e maximum l i m i t s p r e s c r i b e d by r e f e r e n c e 4. The g r a d i e n t increase a t t h e w a s caused by t h e primary c o n t r o l system g e a r i n g and a f t c e n t e r - o f - g r a v i t y p o s i t i o n s a s s o c i a t e d f e e l system which were n o t designed f o r f l i g h t with t h e c e n t e r of g r a v i t y a t t h e a f t p o s i t i o n s .

Dynamic s t a b i l i t y . - The dynamic s t a b i l i t y a n a l y s e s were performed t o evaluate l o n g i t u d i n a l mode c h a r a c t e r i s t i c s of t h e PACS c o n f i g u r e d a i r c r a f t . The a i r c r a f t w a s considered t o be r i g i d . The aileron a c t i v e c o n t r o l system (AACS) and t h e Mach t r i m compensator ( M X ) w e r e considered t o be o p e r a t i n g . The dynamic s t a b i l i t y c h a r a c t e r - istics w e r e determined by o b t a i n i n g roots of t h e a i r c r a f t and control system l i n e a r - i z e d e q u a t i o n s .

The s h o r t - p e r i o d and phugoid frequency and damping c h a r a c t e r i s t i c s f o r f l i g h t c o n d i t i o n 10 a r e p r e s e n t e d i n f i g u r e 13. The b a s e l i n e a i r c r a f t (K* = 0 ) with a 0.25E c e n t e r - o f - g r a v i t y p o s i t i o n has a short-period damping r a t i o C n e a r 0.7 and a frequency w n of 1.25 r a d / s e c , both meeting t h e Level 1 f l y i n g q u a l i t i e s criteria of r e f e r e n c e 4 ( f i g . 1 3 ( a ) ) . The damping r a t i o of the phugoid mode f o r t h e b a s e l i n e a i r c r a f t was 0.076, which a l s o meets t h e requirement of r e f e r e n c e 4. (Ref. 4 r e q u i r e s t h a t SpH be a t l e a s t 0.04. (See f i g . 1 3 ( b ) . ) With t h e PACS on and t h e a i r c r a f t center of g r a v i t y l o c a t e d a t 0.43c, it can he s e e n from f i g u r e 1 3 ( b ) t h a t 1.8Kq i s r e q u i r e d b e f o r e t h e phugoid mode i s s t a b i l i z e d .

Also, n o t e from f i g u r e 1 3 ( a ) t h a t t h e s h o r t - p e r i o d mode of t h i s c o n f i g u r a t i o n (PACS

on, c.g. = 0.43E, 1.8%) has csp of 0.512 and wn of 2.543, v a l u e s which s t i l l

s a t i s f y t h e requirements of r e f e r e n c e 4. Therefore, p r i o r t o t h e p i l o t e d s i m u l a t i o n tests, it was expected t h a t t h e p i l o t s would p r e f e r t h e 1.8Kq PACS.

The near-term PACS was considered t o have f o u r c o n f i g u r a t i o n s f o r purposes of a n a l y s e s and s i m u l a t i o n test e v a l u a t i o n s . They were 0 PACS o f f ( b a s e l i n e a i r c r a f t ) 0 P i t c h damper only 0 P i t c h damper w i t h feedforward 0 P i t c h damper with feedforward washout I n a d d i t i o n t o t h e i n f o r m a t i o n provided i n f i g u r e 13, which i n d i c a t e s t h e e f f e c t of v a r i o u s l e v e l s of Kq on t h e e i g e n v a l u e s as t h e c e n t e r - o f - g r a v i t y p o s i t i o n is v a r i e d , f i g u r e 1 4 p r e s e n t s time h i s t o r i e s of t h e p i t c h - a t t i t u d e response f o l l o w i n g a p u l s e of t h e column for v a r i o u s l e v e l s of for a c e n t e r - o f - g r a v i t y p o s i t i o n of 0.45E and Kq with no feedforward. Even t h e " b a s i c " p i t c h - r a t e feedback g a i n (F* = 1.0) makes t h e a i r c r a f t appear t o have a s t a b l e response w i t h i n t h e i n d i c a t e d t i m e frame. (The p i t c h a t t i t u d e is beginning t o r e t u r n toward i t s t r i m value.) It may a l s o be seen from f i g u r e 15 t h a t t h e feedforward p o r t i o n of the PACS (KFF) t e n d s t o quicken the p i t c h response t o a column f o r c e i n p u t . Therefore, t h e f u l l - t i m e feedforward may be expected t o be p r e f e r r e d by t h e p i l o t s .

Simulated test results.- The p i l o t e d - f l i g h t sirnulation test r e s u l t s are p r e s e n t e d i n terms of Cooper-Harper r a t i n g s ( t a b l e 111) f o r two c r u i s e f l i g h t condi- t i o n s ( c o n d i t i o n s 10 and 1 1 ) and t h e landing f l i g h t c o n d i t i o n ( c o n d i t i o n 1 8 ) . (See table 11.) The r a t i n g s are f o r calm-air atmospheric c o n d i t i o n s e x c e p t f o r p o i n t s on t h e f i g u r e s marked w i t h t h e letter "t" t h a t r e p r e s e n t f l i g h t i n moderate t u r b u l e n c e .

The t h r e e f l i g h t c o n d i t i o n s a r e d i s c u s s e d s e p a r a t e l y , with t h e PACS o n and o f f , f o r t h e c e n t e r - o f - g r a v i t y range from 0.2515 t o 0.45I3. The b a s e l i n e a i r c r a f t was config- ured w i t h t h e a i l e r o n a c t i v e c o n t r o l system (AACS) o p e r a t i n g and t h e PACS o f f ; t h a t is, t h e AACS w a s always o p e r a t i v e u n l e s s s p e c i f i c a l l y i n d i c a t e d otherwise. It should be noted t h a t t h e AACS may have a s i g n i f i c a n t impact on t h e s t a b i l i t y margin of t h e a i r c r a f t . As i n d i c a t e d i n f i g u r e 16 f o r a t y p i c a l c r u i s e f l i g h t c o n d i t i o n , when t h e AACS is o f f , t h e n e u t r a l p o i n t would be a t a c e n t e r - o f - g r a v i t y p o s i t i o n of approximately 0.4513; b u t when t h e AACS is on, t h e e f f e c t i v e n e u t r a l p o i n t could be a t a c e n t e r - o f - g r a v i t y p o s i t i o n of approximately 0.40E. For example, when t h e AACS i s o p e r a t i n g d u r i n g a " p o s i t i v e g" maneuver , t h e a i l e r o n s move symmetrically "upward" t o p r o v i d e wing-load a l l e v i a t i o n and cause a nose-up p i t c h i n g moment--this r e s u l t s i n a forward s h i f t of t h e n e u t r a l p o i n t t o a c e n t e r - o f - g r a v i t y p o s i t i o n of approximately 0.40c. Thus, a p o s i t i v e increment i n s t a b i l i t y margin may be r e a l i z e d by disengaging t h e AACS.

F l i g h t c o n d i t i o n 10: P i l o t r a t i n g s f o r t h e a i r c r a f t a t c r u i s e c o n d i t i o n 10 with t h e PACS o f f a r e p r e s e n t e d i n f i g u r e 17 f o r t h e AACS on and o f f . The t h r e e p i l o t s who evaluated t h i s f l i g h t c o n d i t i o n r a t e d t h e handling q u a l i t i e s of t h e a i r c r a f t as being s a t i s f a c t o r y whether t h e AACS w a s on o r o f f , when t h e center of g r a v i t y w a s a t 0.25C. Based upon t h e d a t a shown i n f i g u r e 17 ( f o r example, see p i l o t 1 1 , t h e base- l i n e a i r c r a f t (AACS on) boundaries f o r satisfactory/unsatisfactory (Level l/Leval 2 ) and unsatisfactory/unacceptable (Level 2/Level 3 ) handling q u a l i t i e s r a t i n g s were approximately 0.37c' and 0.42E, r e s p e c t i v e l y . ( T h i s c e n t e r - o f - g r a v i t y range repre- s e n t s a static margin range from approximately +3 p e r c e n t t o -2 p e r c e n t . ) Also n o t e t h a t t h e p i l o t r a t i n g s d e t e r i o r a t e d very r a p i d l y f o r c e n t e r - o f - g r a v i t y posi- t i o n s a f t of t h e n e u t r a l p o i n t (c.g. PI 0.04F, with t h e AACS o n ) . I n f i g u r e 17, t h e AACS o f f c o n f i g u r a t i o n received a c c e p t a b l e p i l o t r a t i n g s f o r a l l c e n t e r - o f - g r a v i t y p o s i t i o n s evaluated (c.g. = 0.25E t o 0.45E.), an i n d i c a t i o n t h a t t h e A A C S had a d e s t a b i l i z i n g e f f e c t on t h e l o n g i t u d i n a l c h a r a c t e r i s t i c s . This d e s t a b i l i z i n g e f f e c t of t h e AACS i s f u r t h e r i l l u s t r a t e d i n f i g u r e 1 8 , which compares t h e i n c r e m e n t a l (from t r i m ) p i t c h a t t i t u d e response experienced, due t o a p u l s e of t h e column, f o r AACS on and o f € f o r a n a i r c r a f t with c.g. = 0.41E. It i s shown t h a t t h e p i t c h a t t i t u d e t e n d s t o r e t u r n t o t r i m soon a f t e r t h e column is r e l e a s e d (t = 2.0 sec) when t h e AACS i s o f f ; b u t , a t least f o r t h e t i m e frame presented and t h e c e n t e r of g r a v i t y i n d i c a t e d (c.g. = 0.41z), the a i r c r a f t does n o t tend t o r e t u r n t o i t s t r i m c o n d i t i o n when t h e AACS i s o p e r a t i v e . ( I t should be noted t h a t t h e n e u t r a l p o i n t i s a t c.g. = 0.4OE w i t h t h e A A C S o p e r a t i v e f o r t h e cruise f l i g h t c o n d i t i o n . ) For comparison, f i g u r e 19 shows t h e e f f e c t s of t h e AACS when t h e a i r c r a f t i s q u i t e s t a b l e (c.g. = 0.25E) and i n d i c a t e s t h a t a f t e r a d i s t u r b a n c e t h e a i r c r a f t r e t u r n s t o t r i m q u i t e r e a d i l y even when the AACS is o p e r a t i v e .

Engagement of t h e PACS improved t h e p i l o t r a t i n g s s i g n i f i c a n t l y ; compare f i g u r e s 17 and 20. I n f i g u r e 20, t h e PACS c o n f i g u r a t i o n s t e s t e d f o r each center-of- g r a v i t y p o s i t i o n and a t v a r i o u s p i t c h - r a t e feedback g a i n s are r a t e d by f o u r of t h e p i l o t s . The r a t i n g a t 0.25e r e p r e s e n t s the b a s e l i n e a i r c r a f t (PACS o f f , AACS o n ) .

The PACS c o n f i g u r a t i o n s p r e f e r r e d by t h e p i l o t s are shown f o r each s p e c i f i c c e n t e r - o f - g r a v i t y p o s i t i o n .

The t h r e e p i l o t s who f l e w t h e complete c e n t e r - o f - g r a v i t y range f o r f l i g h t c o n d i t i o n 10 r a t e d t h e handling q u a l i t i e s of the PACS-on a i r c r a f t t h e same as o r b e t t e r than t h e b a s e l i n e a i r c r a f t (PACS o f f ; AACS on; c.g. = 0.25E) a t center-of- g r a v i t y p o s i t i o n s as f a r a f t a s 0.41E. P i l o t 1 and p i l o t 3 r a t e d t h e PACS-on air- c r a f t s l i g h t l y worse than t h e b a s e l i n e aircraft a t c e n t e r - o f - g r a v i t y p o s i t i o n s a f t of 0.41E; however, t h e i r r a t i n g s remained i n t h e s a t i s f a c t o r y region. P i l o t 2 found t h e a i r c r a f t more degraded with center-of-gravity p o s i t i o n s a f t of 0.41C and r a t e d t h e a i r c r a f t " a c c e p t a b l e , b u t u n s a t i s f a c t o r y . " P i l o t 2 a l s o provided r a t i n g s wherein he excluded t h e phugoid c h a r a c t e r i s t i c s ; and although t h e s e r a t i n g s are n o t i n d i c a t e d i n f i g u r e 20, h i s r a t i n g s became " s a t i s f a c t o r y " with t h e c e n t e r of g r a v i t y a t 0.43E. P i l o t 4 o n l y e v a l u a t e d t h e PACS c o n f i g u r a t i o n with 2Kq, f u l l - t i m e feed- forward, and c.g. = 0.43c' a t f l i g h t c o n d i t i o n 10; h e a l s o found the PACS-on air- c r a f t handling q u a l i t i e s t o be " u n s a t i s f a c t o r y , b u t a c c e p t a b l e . " A t c.g. = 0.39E, t h e p i l o t opinions f o r t h e p r e f e r r e d PACS c o n f i g u r a t i o n w e r e d i v i d e d between t h e p i t c h damper p l u s feedforward and t h e p i t c h damper with feedforward washout. A t c e n t e r - o f - g r a v i t y p o s i t i o n s a f t of 0.39E, t h e p i l o t s p r e f e r r e d t h e PACS configura- t i o n with p i t c h damper p l u s feedforward. The t r e n d i n t h e d e s i r e d value of p i t c h - rate feedback g a i n w a s t o increase F* from 1.6 t o 2.0 as t h e center of g r a v i t y w a s moved from 0.395 t o 0.455.

The r a t i n g s by p i l o t 1 i n moderate t u r b u l e n c e i n d i c a t e d t h e h a n d l i n g q u a l i t i e s t o be u n s a t i s f a c t o r y b u t a c c e p t a b l e . (See f i g . 20.) The p r e f e r r e d PACS configura- t i o n s were t h e same i n t u r b u l e n c e as i n calm a i r - - n e i t h e r an i n c r e a s e d p i t c h - r a t e damping g a i n n o r a d i f f e r e n t PACS o p e r a t i n g c o n f i g u r a t i o n improved t h e p i l o t r a t i n g .

The p i t c h - r a t e damping g a i n s of 1 .OKq, 1 .3Kq, and 1.6% appeared t o be acceptable f o r t h e planned f l i g h t test program, which would be l i m i t e d t o a maximum a f t center of g r a v i t y of 0.43E and f l i g h t c o n d i t i o n 10.

F l i g h t c o n d i t i o n 11: F i g u r e 21 i n d i c a t e s t h a t t h e p i l o t r a t i n g s f o r t h e PACS- o f f a i r c r a f t a t f l i g h t c o n d i t i o n 11 w e r e similar t o t h o s e of f l i g h t c o n d i t i o n 10.

(See f i g . 6 and table I1 f o r d i f f e r e n c e s i n t h e two f l i g h t c o n d i t i o n s . ) The AACS- o f f p i l o t r a t i n g s a t a f t c e n t e r - o f - g r a v i t y p o s i t i o n s w e r e better t h a n t h e AACS-on r a t i n g s ; t h e AACS-on r a t i n g t r e n d changed from s a t i s f a c t o r y t o unacceptable as t h e center of g r a v i t y w a s moved from 0.25E t o 0.43E. The d a t a p r e s e n t e d i n f i g u r e 21 i n d i c a t e t h a t t h e b a s e l i n e a i r c r a f t (PACS o f f ; AACS o n ) boundaries for p i l o t r a t i n g s of satisfactory/unsatisfactory and unsatisfactory/unacceptable would be a t c e n t e r - o f - g r a v i t y p o s i t i o n s of 0.37E and 0.43C, r e s p e c t i v e l y .

The PACS-on p i l o t r a t i n g s f o r f l i g h t c o n d i t i o n 11 ( f i g . 2 2 ) i n d i c a t e d similar r e s u l t s as those f o r f l i g h t c o n d i t i o n 1 0 ( f i g . 2 0 ) . I n calm a i r , t h e r a t i n g s of a l l p i l o t s showed s a t i s f a c t o r y f l y i n g q u a l i t i e s a t t h e 0.39c and 0.41c c e n t e r - o f - g r a v i t y p o s i t i o n s . Whereas t h e r a t i n g s of p i l o t s 2 and 4 i n d i c a t e d u n s a t i s f a c t o r y f l y i n q q u a l i t i e s a t c.9. = 0.43~3, t h e r a t i n g s of p i l o t s 1 and 3 showed s a t i s f a c t o r y f l y i n g q u a l i t i e s t o a c e n t e r - o f - g r a v i t y p o s i t i o n of 0.45E, f o r t h e p r e f e r r e d PACS configu- r a t i o n ( p i t c h damper plus feedforward). The d e s i r e d t r e n d i n p i t c h - r a t e feedback g a i n w a s t h e same for f l i g h t c o n d i t i o n 1 1 as for f l i g h t c o n d i t i o n 10; t h a t is, F* v a r i e d between 1.6 and 2.0 as t h e c e n t e r of g r a v i t y w a s moved from 0.39E t o 0.45c.

Turbulence e v a l u a t i o n s by p i l o t s 1 and 3 showed t h a t t h e f l y i n g q u a l i t i e s i n moderate t u r b u l e n c e w e r e degraded, r e l a t i v e t o t h e f l y i n g q u a l i t i e s i n calm a i r .

(See f i g . 22.) However, t h e i r r a t i n g s remained e s s e n t i a l l y c o n s t a n t over t h e c e n t e r - o f - g r a v i t y range, with p i l o t 1 r a t i n g t h e a i r c r a f t " u n s a t i s f a c t o r y b u t acceptable" and p i l o t 3 r a t i n g the a i r c r a f t "marginally s a t i s f a c t o r y " (PR = 3.5).

Randomly i n s e r t e d PACS f a i l u r e s throughout t h e t e s t e v a l u a t i o n s of f l i g h t c o n d i t i o n 11 a t c.g. = 0.43C i n d i c a t e d t h a t p a s s i v e f a i l u r e s were benign. The pilots c o u l d e a s i l y d e t e c t when a f a i l u r e occurred and w e r e a b l e to d i s e n g a g e t h e AACS t o produce a positive increment i n s t a b i l i t y margin. These p a s s i v e PACS f a i l - u r e s t h e r e f o r e caused no appreciable handling and/or s a f e t y problems with t h e a i r c r a f t i n t h e c r u i s e f l i g h t c o n d i t i o n . (The term " p a s s i v e f a i l u r e " as used h e r e means t h a t the PACS w a s simply disengaged, t h e r e b y c a u s i n g t h e i n c r e m e n t a l def lec- t i o n of t h e h o r i z o n t a l t a i l "due t o t h e PACS" t o become zero.)

Maximum-PACS-servo-authority hardover f a i l u r e s p r e s e n t e d some d i f f i c u l t y i n c o n t r o l l i n g the a i r c r a f t . The best recovery procedure w a s ( 1 ) t o q u i c k l y d e a c t i v a t e t h e PACS, ( 2 ) t o r e t u r n t h e a i r c r a f t t o l g f l i g h t , and ( 3 ) t o disengage t h e AACS.

This procedure w a s adopted as the f l i g h t test procedure--should such a f a i l u r e occur.

F l i g h t c o n d i t i o n 18: P i l o t r a t i n g s of t h e b a s e l i n e a i r c r a f t (PACS o f f ; AACS on) for t h e approach and landing t a s k ( f l i g h t c o n d i t i o n 1 8 ) are p r e s e n t e d i n f i g u r e 23. Three of t h e f o u r p i l o t s who f l e w t h e approach and l a n d i n g t a s k r a t e d t h e b a s e l i n e - a i r c r a f t handling q u a l i t i e s as s a t i s f a c t o r y (Level 1 ) over t h e c e n t e r - o f - g r a v i t y range t o 0.41 E ; b u t t h e r a t i n g s d e t e r i o r a t e d t o u n s a t i s f a c t o r y (Level 2 ) a t a c e n t e r - o f - g r a v i t y p o s i t i o n of 0.43c.

Engagement of t h e PACS ( f i g . 24) o n l y s l i g h t l y improved t h e a i r c r a f t f l y i n g q u a l i t i e s f o r f l i g h t c o n d i t i o n 18. T h i s w a s n o t s u r p r i s i n g , however, s i n c e t h e n e u t r a l p o i n t of t h e l a n d i n g c o n f i g u r a t i o n i s approximately 0.48E, compared with 0.40E f o r the c r u i s e c o n f i g u r a t i o n ; it had been determined d u r i n g t h e c r u i s e simula- t i o n tests t h a t t h e b e n e f i t s of t h e PACS were most obvious f o r center-of-gravity p o s i t i o n s a f t of t h e a i r c r a f t ' s n e u t r a l p o i n t . The column-minus-trim feedforward g a i n ( K F F ) of t h e PACS w a s i n c r e a s e d f o r some of these tests, as i n d i c a t e d i n f i g u r e 24, b u t d i d not improve t h e handling q u a l i t i e s . The d e s i r e d p i t c h - r a t e feed- back g a i n i n c r e a s e d from 1 .3Kq t o 1 .6Kq as t h e c e n t e r of g r a v i t y w a s moved from 0.39E t o 0.43E.

I t may b e seen from f i g u r e 24 t h a t t h e p i l o t r a t i n g s were only s l i g h t l y worse when i n moderate turbulence f o r f l i g h t c o n d i t i o n 18.

Summary of near-term PACS s i m u l a t i o n r e s u l t s . - The b a s e l i n e a i r c r a f t (PACS o f f ; AACS on) had unacceptable f l y i n g q u a l i t i e s f o r c r u i s e f l i g h t c o n d i t i o n s 10 and 1 1 a t center-of-gravity p o s i t i o n s a f t of approximately 0.42E. The a i r c r a f t f l y i n g q u a l i - t i e s w e r e s i g n i f i c a n t l y better, however, with t h e AACS o f f . Therefore, i n case of a PACS f a i l u r e d u r i n g t h e f l i g h t t e s t program, t h e AACS could be disengaged t o enhance t h e a i r c r a f t f l y i n g q u a l i t i e s . The f l y i n g q u a l i t i e s of t h e b a s e l i n e a i r c r a f t f o r were a c c e p t a b l e throughout t h e center-of-gravi t y test t h e l a n d i n g f l i g h t c o n d i t i o n range.

Engagement of the near-term PACS s i g n i f i c a n t l y improved the f l y i n g q u a l i t i e s f o r cruise f l i g h t c o n d i t i o n s 1 0 and 1 1 , b u t o n l y s l i g h t l y improved t h e f l y i n g q u a l i - t i e s f o r t h e landing f l i g h t c o n d i t i o n . With t h e PACS o p e r a t i v e , t h e f l y i n g q u a l i - t i e s were, i n g e n e r a l , considered t o be good over t h e c e n t e r - o f - g r a v i t y range tested and were c l o s e t o meeting t h e design g o a l s , which r e q u i r e d t h e PACS configured a i r c r a f t f l y i n g q u a l i t i e s f o r t h e e n t i r e c e n t e r - o f - g r a v i t y range t o be e q u i v a l e n t t o or b e t t e r than those of t h e b a s e l i n e a i r c r a f t w i t h a 0.25E c e n t e r - o f - g r a v i t y p o s i t i o n .

The p r e f e r r e d PACS o p e r a t i n g c o n f i g u r a t i o n w a s determined t o be t h e p i t c h - r a t e damper p l u s feed-forward c o n f i g u r a t i o n . The d e s i r e d t r e n d of p i t c h - r a t e feedback

g a i n w a s from 1 . O % a t c.g. = 0.39E t o between 1.6% and 2.0% a t

c.g. = 0.45E.

However, t h e m a j o r i t y of p i l o t r a t i n g s i n d i c a t e d t h a t a g a i n of 1.6Kq w a s adequate a t a c e n t e r - o f - g r a v i t y p o s i t i o n of 0.43E.

Advanced PACS s a t i s f a c t o r y The p r e v i o u s l y d i s c u s s e d near-term PACS w a s desgined t o provide s t a t i c s t a b i l i t y margins ( u p t o 3 p e r c e n t ) .

f l y i n g q u a l i t i e s a t s l i g h t l y n e g a t i v e However, t h e d e s i g n o b j e c t i v e of t h e advanced PACS program w a s t o develop a PACS which would provide f l y i n g q u a l i t i e s , a t n e g a t i v e s t a t i c s t a b i l i t y margins as h i g h as 10 p e r c e n t , t h a t were a t l e a s t e q u i v a l e n t t o t h o s e of t h e b a s e l i n e a i r c r a f t (PACS AACS on) w i t h a c e n t e r - o f - g r a v i t y p o s i t i o n of 0.25E. (The 0.25E center-of- o f f ; g r a v i t y p o s i t i o n r e p r e s e n t s the e x i s t i n g L-1 01 1 c o n f i g u r a t i o n which i s considered t o have s a t i s f a c t o r y f l y i n g q u a l i t i e s . ) Also, t h e advanced PACS w a s t o compensate f o r high-Mach/high-g i n s t a b i l i t i e s t h a t degrade t h e f l y i n g q u a l i t i e s d u r i n g "upset" r e c o v e r i e s and maneuvers.

A block diagram of t h e advanced PACS i s p r e s e n t e d i n f i g u r e 25, and t h e PACS are i n d i c a t e d i n t a b l e I V .

gain-schedule e q u a t i o n and e q u a t i o n c o e f f i c i e n t s This augmentation system i n p u t s i g n a l s c o n s i s t of f o u r types--feedforward, feed- back, primary g a i n scheduling, and secondary g a i n scheduling. (See t a b l e V.) This advanced PACS ( f i g . 25) i s d e s c r i b e d i n more d e t a i l i n t h e appendix of t h i s paper and i n r e f e r e n c e 5.

s i m u l a t i o n program The f l i g h t c o n d i t i o n s evaluated d u r i n g t h e advanced PACS c o n s i s t e d of a l l c o n d i t i o n s i n d i c a t e d i n t a b l e I1 and f i g u r e 6, with t h e exception of f l i g h t c o n d i t i o n 1 1 . ( F l i g h t c o n d i t i o n 1 1 w a s only evaluated d u r i n g t h e near- term PACS s i m u l a t i o n study.) The s i m u l a t i o n tests w e r e performed with s t a t i c s t a b i l i t y margins from +15 p e r c e n t t o -20 p e r c e n t , r e p r e s e n t i n g center-of-gravity p o s i t i o n s f o r t h e c r u i s e f l i g h t c o n d i t i o n s from 0.25E t o 0.60E. ( I t should be noted t h a t t h i s advanced PACS w a s "optimized" f o r f l i g h t with a n e g a t i v e s t a t i c margin of 10 p e r c e n t (c.g. = O.O5E), b u t t h e p i l o t e d s i m u l a t i o n tests were extended t o a n e g a t i v e static margin of 20 p e r c e n t (c.g. = 0.60E).) The a n a l y s e s and p i l o t e v a l u a t i o n s included speed s t a b i l i t y , maneuver s t a b i l i t y , dynamic s t a b i l i t y , and t u r b u l e n c e response. The r e s u l t s are compared w i t h t h e f l y i n g q u a l i t i e s r e q u i r e - ments and criteria of r e f e r e n c e s 3 and 4 t o determine t h e adequacy of t h e advanced PACS c a p a b i l i t i e s . The a n a l y s i s of the advanced PACS c o n c e n t r a t e d on h i g h - a l t i t u d e c r u i s e f l i g h t ( c o n d i t i o n 7 ) because of t h e a i r c r a f t aerodynamic c h a r a c t e r i s t i c s a t t h i s f l i g h t c o n d i t i o n . (For f l i g h t c o n d i t i o n 7, t h e a n g l e of attack r e q u i r e d f o r t r i m is w i t h i n , or very n e a r , t h e region of i n h e r e n t pitch-up.)

A s s t a t e d p r e v i o u s l y , t h e advanced PACS configured a i r c r a f t w a s designed t o have t h e c a p a b i l i t y of o p e r a t i n g over t h e f u l l f l i g h t envelope with n e g a t i v e s t a t i c s t a b i l i t y margins up t o 10 p e r c e n t and t o have f l y i n g q u a l i t i e s e q u i v a l e n t t o o r b e t t e r than t h o s e of t h e b a s e l i n e a i r c r a f t with t h e center-of-gravity a t 0.25E.

Other design o b j e c t i v e s of t h i s advanced PACS were as follows: 1. The short-period and phugoid modes frequency and damping characteristics should f a l l w i t h i n t h e shaded s-plane areas i n d i c a t e d i n f i g u r e 26.

2. The column f o r c e g r a d i e n t s should f a l l w i t h i n t h e column-force load-factor boundaries i n d i c a t e d i n f i g u r e 27 and should have n e a r l y c o n s t a n t s l o p e .

Speed s t a b i l i t y . - The speed s t a b i l i t y c h a r a c t e r i s t i c s f o r t h e h o l d i n g and c r u i s e c o n d i t i o n s ( f l i g h t c o n d i t i o n 17 and 7, r e s p e c t i v e l y ) w i t h t h e advanced PACS o p e r a t i v e are p r e s e n t e d i n f i g u r e 28. Column f o r c e g r a d i e n t s f o r t h e h o l d i n g f l i g h t c o n d i t i o n comply w i t h t h e design criteria of r e f e r e n c e 3 i n a l l r e s p e c t s , whereas t h e column force f o r t h e c r u i s e f l i g h t c o n d i t i o n does n o t vary monotonically with a i r s p e e d as i s d e s i r e d . However, t h e speed s t a b i l i t y c h a r a c t e r i s t i c s f o r a l l f l i g h t c o n d i t i o n s e v a l u a t e d with t h e advanced PACS w e r e considered t o be s u f f i c i e n t t o continue t h e a n a l y s e s with piloted-f l i g h t s i m u l a t i o n tests.

Maneuver s t a b i l i t y . - The maneuver s t a b i l i t y a n a l y s i s determined t h e column S a t i s f a c t o r y f o r c e s r e q u i r e d to maintain t h e a i r p l a n e i n s t e a d y wind-up t u r n s .

maneuver s t a b i l i t y column f o r c e s , as r e q u i r e d by r e f e r e n c e 4, are a s t e a d i l y i n c r e a s i n g p u l l t o maintain p o s i t i v e load f a c t o r s and a s t e a d i l y i n c r e a s i n g push t o maintain n e g a t i v e load f a c t o r s . I n a d d i t i o n , t h e upper and lower column f o r c e maneuver criteria boundaries f o r aircraft with wheel c o n t r o l l e r s are

upper boundary = 1 20/(nL - 1 1 , l b f / g Units

0 Lower boundary = 35/(nL - 1 1 , l b f / g u n i t s

(The load f a c t o r l i m i t nL f o r t h e commercial L-1011 a i r c r a f t i s 2.59.)

The maneuver s t a b i l i t y c h a r a c t e r i s t i c s of t h e b a s e l i n e a i r c r a f t i n t h e t a k e o f f c o n f i g u r a t i o n ( f i g . 29) i n d i c a t e t h a t t h e column f o r c e s were s t a b l e throughout t h e c e n t e r - o f - g r a v i t y range from 0.25E t o 0.50E. However, when compared t o t h e r e f e r - ence 4 g u i d e l i n e s , t h e g r a d i e n t s w e r e very s t e e p f o r t h e more a f t c e n t e r - o f - g r a v i t y p o s i t i o n s . The n a t u r e of these column f o r c e s can be a t t r i b u t e d t o t h e low-speed aerodynamics and t h e " b a s i c " c o n t r o l system of t h e L-1011 a i r c r a f t . Figure 30 pre- s e n t s the maneuver s t a b i l i t y c h a r a c t e r i s t i c s of t h e a i r c r a f t i n t h e takeoff config- u r a t i o n with t h e advanced PACS o p e r a t i v e . These data i n d i c a t e t h a t t h e advanced PACS reduces t h e spread of t h e column f o r c e g r a d i e n t s f o r t h e c e n t e r - o f - g r a v i t y range from 0.25E t o 0.50~5 and t h a t t h e g r a d i e n t s a r e w i t h i n the boundaries of r e f e r e n c e 4.

The maneuver s t a b i l i t y c h a r a c t e r i s t i c s of the b a s e l i n e a i r c r a f t i n t h e c r u i s e c o n f i g u r a t i o n ( f i g . 31 ) i n d i c a t e u n s a t i s f a c t o r y column f o r c e c h a r a c t e r i s t i c s f o r t h e complete c e n t e r - o f - g r a v i t y range. These u n s a t i s f a c t o r y f o r c e c h a r a c t e r i s t i c s can be a t t r i b u t e d t o t h e n o n l i n e a r high-speed pitching-moment c h a r a c t e r i s t i c s and t o t h e AACS. The maneuver s t a b i l i t y c h a r a c t e r i s t i c s of t h e a i r c r a f t i n t h e c r u i s e configu- r a t i o n with t h e advanced PACS o p e r a t i v e a r e p r e s e n t e d i n f i g u r e 32; t h e s e d a t a i n d i c a t e t h a t t h e advanced PACS completely removes t h e " d i p " i n t h e column f o r c e g r a d i e n t s p r e s e n t e d i n f i g u r e 31 f o r t h e PACS-off c o n f i g u r a t i o n . This was accom- p l i s h e d p r i m a r i l y by t h e pitch-up c o n t r o l l e r which is scheduled w i t h Mach number and a n g l e of a t t a c k . (See t a b l e V.) The manuever s t a b i l i t y c h a r a c t e r i s t i c s p r e s e n t e d i n f i g u r e 32 i n d i c a t e t h a t t h e column f o r c e c h a r a c t e r i s t i c s a r e s a t i s f a c t o r y € o r a l l c e n t e r - o f - g r a v i t y p o s i t i o n s , e x c e p t a t high load f a c t o r s . Note t h a t t h e " i n i t i a l " ( l o a d f a c t o r s up t o approximately 1 . 4 9 ) force g r a d i e n t s are e s s e n t i a l l y the s a m e for t h e e n t i r e c e n t e r - o f - g r a v i t y range.

Dynamic s t a b i l i t y . - The dynamic s t a b i l i t y c h a r a c t e r i s t i c s were o b t a i n e d by c a l c u l a t i n g t h e e i g e n v a l u e s of t h e small-disturbance e q u a t i o n s of motion, and t h e f l y i n g q u a l i t i e s s p e c i f i c a t i o n s of r e f e r e n c e 4 were used as g u i d e l i n e s t o e v a l u a t e t h e a c c e p t a b i l i t y of t h e s e c h a r a c t e r i s t i c s . Figure 33 p r e s e n t s t h e s-plane eigen- v a l u e s ( c r u i s e c o n d i t i o n 7 ) f o r t h e b a s e l i n e a i r c r a f t s h o r t - p e r i o d and phugoid modes. A s can be seen, t h e s h o r t - p e r i o d c h a r a c t e r i s t i c s do n o t meet t h e r e q u i r e - m e n t s of r e f e r e n c e 4 when t h e c e n t e r of g r a v i t y i s a f t of 0.25E. These d a t a a l s o i n d i c a t e t h a t t h e phugoid c h a r a c t e r i s t i c s become u n s t a b l e a s t h e c e n t e r of g r a v i t y is moved a f t and v i o l a t e t h e requirement f o r a minimum damping r a t i o of 0.04.

Figure 34 i n d i c a t e s t h a t t h e dynamic s t a b i l i t y c h a r a c t e r i s t i c s of t h e a i r c r a f t i n cruise c o n d i t i o n 7, with t h e advanced PACS o p e r a t i v e , comply with t h e s p e c i f i c a - t i o n s of r e f e r e n c e 4. I n f a c t , with t h e advanced PACS o p e r a t i v e , t h e dynamic sta- b i l i t y c h a r a c t e r i s t i c s of a l l f l i g h t c o n d i t i o n s s a t i s f i e d t h e r e f e r e n c e 4 r e q u i r e - ments e x c e p t f o r the holding f l i g h t c o n d i t i o n ( c o n d i t i o n 1 7 1 , which had a mild phugoid i n s t a b i l i t y with t h e c e n t e r of g r a v i t y a t 0.25c'. ( T h i s f l i g h t c o n d i t i o n had an u n s t a b l e phugoid w i t h a time-to-double amplitude of 700 sec.)

S a t i s f a c t o r y f l y i n g q u a l i t i e s a r e d e f i n e d i n terms of s t a b l e responses t o e x t e r n a l d i s t u r b a n c e s and p i l o t c o n t r o l i n p u t s . A f t e r e x p e r i e n c i n g a d i s c r e t e v e r t i c a l g u s t , t h e a i r c r a f t should q u i c k l y r e t u r n t o its t r i m e q u i l i b r i u m c o n d i t i o n and any o s c i l l a t i o n s should be w e l l damped. Also, t h e a i r p l a n e should respond p r e d i c t a b l y t o a column f o r c e s t e p i n p u t , and t h e c o n t r o l s should g i v e t h e p i l o t t h e c a p a b i l i t y of changing t h e p i t c h a t t i t u d e p r e c i s e l y .

Figure 35 p r e s e n t s t h e d i s c r e t e v e r t i c a l g u s t model used i n t h e a n a l y s i s of c r u i s e c o n d i t i o n 7; t h i s model was p a t t e r n e d a f t e r t h e g u s t model p r e s e n t e d i n r e f e r e n c e 4. A g u s t amplitude of 54 f t / s e c i s c o n s i d e r e d a s e v e r e d i s t u r b a n c e of heavy thunderstorm magnitude.

Figure 36 compares t h e responses t o a -54 f t / s e c v e r t i c a l g u s t ( u p d r a f t ) of t h e b a s e l i n e a i r c r a f t (PACS o f f ) and t h e advanced PACS a i r c r a f t i n f l i g h t c o n d i t i o n 7.

These t i m e h i s t o r i e s i n d i c a t e t h a t f o r t h i s s e v e r e d i s t u r b a n c e , t h e b a s e l i n e air- c r a f t with t h e c e n t e r of g r a v i t y a t 0.25E w i l l r e t u r n t o i t s i n i t i a l t r i m condition.

However, f o r center-of-gravity p o s i t i o n s a f t of 0 . 2 5 s , t h e a i r c r a f t d i v e r g e s from i t s t r i m c o n d i t i o n and seeks a new equilibrium a t high angle of a t t a c k . The d i s t u r - bance i s s t r o n g enough t o d r i v e t h e a i r c r a f t i n t o t h e high-angle-of-attack, heavy- b u f f e t r e g i o n where t h e a i r c r a f t i s q u i t e s t a b l e . (See f i g . 37 f o r t h e p i t c h i n g - moment c h a r a c t e r i s t i c s . ) The response of t h e advanced PACS configured a i r c r a f t t o t h e s e v e r e v e r t i c a l g u s t had well-behaved, s t a b l e response c h a r a c t e r i s t i c s and were determined t o be e s s e n t i a l l y t h e same f o r a l l center-of-gravity p o s i t i o n s from 0.25E t o 0.50E. (See f i g . 3 6 . ) Figure 38 p r e s e n t s t h e a i r c r a f t response t o v a r i o u s column f o r c e s t e p i n p u t s f o r t h e h i g h - a l t i t u d e c r u i s e f l i g h t c o n d i t i o n ( c o n d i t i o n 7 ) w i t h t h e c e n t e r of g r a v i t y a t 0.50s. These d a t a i n d i c a t e t h a t t h e b a s e l i n e a i r c r a f t d i v e r g e s q u i c k l y from i t s t r i m c o n d i t i o n f o r any c o n s t a n t f o r c e i n p u t u n t i l it reaches a region of i n c r e a s e d s t a b i l i t y a t high angle of a t t a c k . However, t h e responses of t h e PACS configured a i r c r a f t t o column f o r c e s t e p i n p u t s i n d i c a t e t h a t t h e advanced PACS works t o reduce e x e s s i v e excursions i n angle of a t t a c k and load f a c t o r .

The dynamic s t a b i l i t y c h a r a c t e r i s t i c s , as w e l l as t h e speed and maneuver PACS a i r c r a f t w e r e determined u s i n g both s t a b i l i t y c h a r a c t e r i s t i c s , of t h e advanced l i n e a r and n o n l i n e a r aerodynamic and c o n t r o l system c h a r a c t e r i s t i c s i n v a r i o u s a n a l y t i c t o o l s . A s a r e s u l t , t h e dynamic s t a b i l i t y c h a r a c t e r i s t i c s w e r e considered t o be s u f f i c i e n t t o warrant f u r t h e r s t u d i e s i n v o l v i n g p i l o t e d - f l i g h t simulation.

Simulated test r e s u l t s .- The p i l o t e d - f l i g h t s i m u l a t i o n tests were performed t o i d e n t i f y any p i l o t / c o n t r o l i n t e r f a c e problems and e v a l u a t e t h e f l y i n g q u a l i t i e s of t h e advanced PACS. The s p e c i f i c f l i g h t c o n d i t i o n s s e l e c t e d f o r t h e s e s i m u l a t i o n tests are i n d i c a t e d i n table I1 and f i g u r e 6 . The r e s u l t s of t h e tests, d i s c u s s e d for each f l i g h t c o n d i t i o n i n t h e subsequent paragraphs, i n d i c a t e d t h a t t h e advanced PACS f u l f i l l e d t h e f u n c t i o n s f o r which it w a s designed. The p i l o t r a t i n g s i n d i c a t e d t h a t t h e f l y i n g q u a l i t i e s of t h e advanced PACS configured a i r c r a f t with c.g. = 0.5Oc’ were as good as t h e b a s e l i n e a i r c r a f t with c.g. = 0.25E. A l s o , t h e b e n e f i t s of t h e PACS w e r e the most impressive a t high-speed c o n d i t i o n s where t h e h a n d l i n g q u a l i t i e s of the b a s e l i n e aircraft q u i c k l y degraded t o unacceptable levels ( p i l o t r a t i n g s g r e a t e r than 6.5) f o r center-of-gravity p o s i t i o n s a f t of approximately 0.42E. The d a t a f o r t h e PACS configured a i r c r a f t i n d i c a t e d s a t i s f a c t o r y handling q u a l i t i e s ( p i l o t r a t i n g s e q u a l t o o r less than 3 . 5 ) f o r a center-of-gravity p o s i t i o n of 0.50E.

I n a d d i t i o n , very l i t t l e degradation occurred when t h e c e n t e r of g r a v i t y w a s moved from 0 . 5 0 s t o 0.60c‘.

F l i g h t c o n d i t i o n 10 (nominal c r u i s e ) : F l i g h t c o n d i t i o n 10 i s an average cruise c o n d i t i o n f o r commercial a i r l i n e S e r v i c e (W/6 = 1 . 4 x l o 6 l b f ) . For t h e L-1011 a i r - plane, t h e v a l u e of 1 . 4 x 1 O6 l b f f o r t h e parameter W/s, and Mach number of 0 . 8 3 , r e p r e s e n t s a l i f t - c o e f f i c i e n t value of 0 . 4 . Since a c o n s t a n t l i f t - c o e f f i c i e n t value i s r e q u i r e d t o p r o p e r l y e v a l u a t e c o n t r o l c h a r a c t e r i s t i c s , each test f o r f l i g h t c o n d i t i o n 10 w a s i n i t i a t e d a t t h e same value of W/6 and Mach number. The maneuver s t a b i l i t y about t r i m is e s s e n t i a l l y l i n e a r a t t h i s f l i g h t c o n d i t i o n , b u t a region of reduced maneuver s t a b i l i t y can be reached a t high load f a c t o r s . (The a i r c r a f t remains i n t h e r e g i o n where t h e aerodynamic d a t a are n e a r l y l i n e a r f u n c t i o n s of a f o r small maneuvers about t h i s f l i g h t c o n d i t i o n , b u t high-load-factor maneuvers can r e s u l t i n t h e p e n e t r a t i o n i n t o t h e region where pitch-up occurs.)

Five p i l o t s e v a l u a t e d t h e f l y i n g q u a l i t i e s of t h e simulated L-1011 a i r c r a f t a t f l i g h t c o n d i t i o n 10; however, a l l c e n t e r - o f - g r a v i t y p o s i t i o n s (which covered t h e range from 0.25E t o 0.60E) w e r e n o t e v a l u a t e d by a l l p i l o t s . P i l o t r a t i n g s f o r t h e c e n t e r - o f - g r a v i t y p o s i t i o n s t e s t e d by each p i l o t i n calm a i r and i n moderate turbu- l e n c e are p r e s e n t e d i n f i g u r e s 39 and 40, r e s p e c t i v e l y . The b a s e l i n e - a i r c r a f t p i l o t r a t i n g s f o r t h e calm-air and t u r b u l e n c e c o n d i t i o n s i n d i c a t e unacceptable f l y i n g q u a l i t i e s f o r c e n t e r - o f - g r a v i t y p o s i t i o n s a f t of approximately 0.40E. The wide scatter i n the p i l o t r a t i n g s f o r c.g. = 0.39.E i s due t o t h e s e n s i t i v i t y of t h e v a r i o u s p i l o t s i n judging t h e o n s e t of unacceptable f l y i n g q u a l i t i e s . Engagement of t h e advanced PACS i n calm a i r produced s a t i s f a c t o r y f l y i n g q u a l i t i e s f o r center-of- as f a r a f t as approximately 0.55F and very a c c e p t a b l e (PR < 4 ) f l y - g r a v i t y p o s i t i o n s i n g q u a l i t i e s f o r c.g. = 0.60C. The f l y i n g q u a l i t i e s i n moderate t u r b u l e n c e w e r e n o t as good as i n calm a i r b u t were considered by t h e p i l o t s t o be very acceptable f o r c e n t e r - o f - g r a v i t y p o s i t i o n s t o 0.555 and a c c e p t a b l e a t 0.603. (See f i g . 4 0 , ) Typical p i l o t comments r e g a r d i n g s p e c i f i c f l y i n g q u a l i t i e s c h a r a c t e r i s t i c s f o r f l i g h t c o n d i t i o n 10 a t center-of-gravity p o s i t i o n s from 0.25E t o 0.60E ( r e p r e s e n t i n g s t a t i c margins from +15 p e r c e n t t o -20 p e r c e n t ) are p r e s e n t e d i n t a b l e V I .

F l i g h t c o n d i t i o n 15 (maximum-range c r u i s e ) : The s t a b i l i t y c h a r a c t e r i s t i c s of t h e simulated L-1011 a i r c r a f t a t this c o n d i t i o n w e r e e s s e n t i a l l y t h e same as a t t h e i n t e r m e d i a t e W / 6 ( f l i g h t c o n d i t i o n I O ) , e x c e p t t h a t the i n h e r e n t pitch-up r e g i o n i s encountered a t a l o w e r load f a c t o r . F l i g h t c o n d i t i o n 15 w a s flown by only one p i l o t , and h i s e v a l u a t i o n s of t h e f l y i n g q u a l i t i e s of t h e a i r c r a f t as t h e c e n t e r of g r a v i t y w a s varied f r o m 0.25E t o 0.602., w i t h and without t h e advanced PACS engaged, i n calm a i r and i n moderate t u r b u l e n c e are p r e s e n t e d i n f i g u r e s 41 and 4 2 . These d a t a i n d i c a t e t h a t t h e b a s e l i n e a i r c r a f t f l y i n g q u a l i t i e s degrade r a p i d l y f o r c e n t e r - o f - g r a v i t y p o s i t i o n s a f t of 0.40E. Engagement of t h e advanced PACS i n calm a i r provided p i l o t r a t i n g s t h a t w e r e near t h e satisfactory/unsatisfactory boundary l f o r t h e e n t i r e c e n t e r - o f - g r a v i t y range t e s t e d ( f i g . 41 1. I n t u r b u l e n c e with t h e PACS o p e r a t i v e , t h e p i l o t r a t i n g s w e r e about the same over t h e center-of-gravity range b u t were n o t as good as f o r t h e calm-air c o n d i t i o n s ( f i g . 4 2 ) .

F l i g h t c o n d i t i o n 7 ( h i g h W / 6 c r u i s e ) : F l i g h t c o n d i t i o n 7 i s t h e h i g h e s t W/S a t which t h e simulated a i r c r a f t can o p e r a t e w i t h a 1.3g maneuver c a p a b i l i t y t o b u f f e t onset. (The 1.3g c r i t e r i o n i s a t y p i c a l t r a n s p o r t a i r c r a f t o p e r a t i n g r e s t r i c t i o n . ) F l i g h t c o n d i t i o n 7 i s n e a r a r e g i o n where t h e aerodynamic d a t a are n o n l i n e a r f u n c t i o n s of a which i s due t o wing aerodynamic flow s e p a r a t i o n . The n o n l i n e a r r e g i o n begins approximately 0.lg from t r i m and i s w e l l i n t o t h e u n s t a b l e r e g i o n of b u f f e t o n s e t , which i s 0.3g.

Three p i l o t s e v a l u a t e d t h e f l y i n g q u a l i t i e s a t f l i g h t c o n d i t i o n 7, and t h e i r r a t i n g s i n calm a i r and i n moderate t u r b u l e n c e are p r e s e n t e d i n f i g u r e s 43 and 4 4 , r e s p e c t i v e l y . This f l i g h t c o n d i t i o n w a s t h e least s t a b l e of t h e t h r e e c r u i s e condi- t i o n s evaluated because of t h e c l o s e n e s s of t h e r e g i o n of flow s e p a r a t i o n . This "reduced" s t a b i l i t y is r e f l e c t e d by t h e r a p i d d e g r a d a t i o n of t h e b a s e l i n e - a i r c r a f t f l y i n g q u a l i t i e s . Engagement of t h e advanced PACS i n calm a i r provided s a t i s f a c t o r y f l y i n g q u a l i t i e s t o an a f t center-of-gravity p o s i t i o n of 0.50F ( f i g . 43). A comparison of t h e p i l o t r a t i n g s i n d i c a t e d i n f i g u r e s 43 and 44 shows t h a t , with e x c e p t i o n of p i l o t 4, the r a t i n g s i n moderate t u r b u l e n c e are h i g h e r (degraded) than calm air. The r a t i n g s of p i l o t 4 w e r e s a t i s f a c t o r y i n both calm a i r and moderate i n t u r b u l e n c e t o t h e 0.50E center-of-gravity p o s i t i o n .

P e r t i n e n t parameters w e r e recorded on strip c h a r t s d u r i n g t h e p i l o t e v a l u a t i o n

I

tests. Three s t r i p c h a r t segments have been s e l e c t e d t o i l l u s t r a t e d i f f e r e n c e s i n p i l o t opinion between the b a s e l i n e a i r c r a f t and t h e advanced PACS a i r c r a f t f o r f l i g h t c o n d i t i o n 7. F i g u r e s 45, 46, and 47 compare t h e f l i g h t c h a r a c t e r i s t i c s a t center-of-gravity p o s i t i o n s of 0.39E, 0.435, and 0.50E, r e s p e c t i v e l y .

The 0.39s center-of-gravity c o n d i t i o n ( f i g . 4 5 ) w a s flown i n moderate turbu- l e n c e f o r only shallow banked t u r n s . I n each i n s t a n c e t h e a i r p l a n e w a s first evalu- a t e d with t h e PACS disengaged; t h e n t h e PACS w a s engaged, and t h e e v a l u a t i o n w a s repeated. The p i l o t workload, i n d i c a t e d by t h e c o n t r o l - f o r c e trace, w a s high; and t h e excursions i n t h e normal a c c e l e r a t i o n a t t h e a i r c r a f t c e n t e r of g r a v i t y were approaching 0.59 w i t h t h e PACS disengaged. W i t h t h e PACS engaged, t h e normal- a c c e l e r a t i o n e x c u r s i o n s and the c o n t r o l column i n p u t f o r c e s w e r e s i g n i f i c a n t l y reduced.

Figure 46 p r e s e n t s t h e t i m e h i s t o r i e s obtained d u r i n g t h e e v a l u a t i o n of t h e f l y i n g q u a l i t i e s a t f l i g h t c o n d i t i o n 7 with c.g. = 0.4313 i n calm air. with t h e PACS disengaged, t h e workload w a s similar t o that when t h e c e n t e r of g r a v i t y w a s a t 0.39E and t h e a i r c r a f t w a s flown i n moderate turbulence. (Again, only shallow banked t u r n s w e r e attempted.) With t h e PACS engaged, t h e p i l o t workload w a s d r a m a t i c a l l y reduced, and t h e p i l o t comfortably r o l l e d i n t o a 30° banked t u r n .

Figure 47 p r e s e n t s t h e e v a l u a t i o n t i m e h i s t o r i e s i n calm a i r with c.g. = 0.50E.

With the PACS disengaged, t h e a i r c r a f t w a s d i f f i c u l t t o c o n t r o l , and l a r g e , r a p i d , c y c l i c , c o n t r o l column i n p u t s w e r e r e q u i r e d t o f l y l e v e l . w i t h t h e PACS engaged, however, t h e a i r p l a n e could be comfortably r o l l e d i n t o a 30° banked t u r n .

F l i g h t c o n d i t i o n 16 ( h i g h speed): F l i g h t c o n d i t i o n 16 i s near t h e knee of t h e s i m u l a t e d - a i r c r a f t maximum o p e r a t i o n a l speed boundary ( f i g . 6). Because of t h e high dynamic p r e s s u r e , t h e load f a c t o r to b u f f e t o n s e t is beyond t h e load f a c t o r l i m i t (2.59) of t h e L-1011 a i r c r a f t , and maneuvers about t r i m remain i n t h e region where t h e aerodynamic d a t a are l i n e a r with angle of a t t a c k .

The handling q u a l i t i e s of t h e a i r c r a f t a t f l i g h t c o n d i t i o n 16 w a s e v a l u a t e d by t h r e e p i l o t s i n calm a i r and by one p i l o t i n turbulence. The p i l o t r a t i n g s r e s u l t i n g from these e v a l u a t i o n s are p r e s e n t e d i n f i g u r e s 48 and 49. The PACS-on r a t i n g s i n d i - c a t e d s a t i s f a c t o r y f l y i n g q u a l i t i e s f o r t h e e n t i r e center-of-gravity range when i n calm-air c o n d i t i o n s ( f i g . 4 8 ) and near s a t i s f a c t o r y f l y i n g q u a l i t i e s when i n t u r b u l e n t - a i r c o n d i t i o n s ( f i g . 4 9 ) .

F l i g h t c o n d i t i o n 17 is a t y p i c a l interme&ate- F l i g h t c o n d i t i o n 17 ( h o l d i n g ) : speed, flaps-up, holding p a t t e r n c o n d i t i o n which is o f t e n encountered when approach- i n g airports w i t h heavy t r a f f i c . Maneuvers about t h i s low-dynamic-pressure f l i g h t c o n d i t i o n remain i n t h e r e g i o n of l i n e a r aerodynamic c h a r a c t e r i s t i c s .

Only one p i l o t evaluated the handling q u a l i t i e s a t f l i g h t c o n d i t i o n 17, and t h e r a t i n g s i n calm a i r and moderate t u r b u l e n c e a t t h i s f l i g h t c o n d i t i o n are p r e s e n t e d i n f i g u r e s 50 and 51, r e s p e c t i v e l y . The b a s e l i n e a i r c r a f t had reasonably good f l y i n g q u a l i t i e s ( s a t i s f a c t o r y t o acceptable p i l o t r a t i n g s ) i n calm a i r t o a center-of- g r a v i t y p o s i t i o n of 0.50E; b u t t h e f l y i n g q u a l i t i e s became unacceptable a t a c e n t e r of g r a v i t y of approximately 0.55I3. Engagement of t h e PACS r e s u l t e d i n s a t i s f a c t o r y f l y i n g q u a l i t i e s over t h e e n t i r e center-of-gravity range i n calm-air c o n d i t i o n s ( f i g . 50). When flown i n moderate t u r b u l e n c e and with t h e PACS engaged, t h e simu- l a t e d a i r p l a n e had u n s a t i s f a c t o r y ( b u t acceptable) f l y i n g q u a l i t i e s f o r f l i g h t condi- t i o n 17--with the p i l o t r a t i n g s being between 4 and 5 over t h e e n t i r e center-of- g r a v i t y range ( f i g . 51 1 .

F l i g h t c o n d i t i o n 18 ( l a n d i n g ) : F l i g h t c o n d i t i o n 18 r e p r e s e n t s a t y p i c a l land- i n g c o n f i g u r a t i o n a t normal approach speeds and i s c h a r a c t e r i z e d by l i n e a r aero- dynamic c h a r a c t e r i s t i c s . The handling c h a r a c t e r i s t i c s a t f l i g h t c o n d i t i o n 18 w e r e evaluated by t h r e e p i l o t s i n calm a i r and i n moderate turbulence f o r t h e center-of- l i m i t e d g r a v i t y range from 0.25E t o 0.50E. The a f t center-of-gravity p o s i t i o n w a s t o 0.50E by t h e nose-down a u t h o r i t y of t h e t r i m system f o r t h i s landing f l i g h t condition. The p i l o t r a t i n g s are p r e s e n t e d i n f i g u r e s 52 and 53.

The b a s e l i n e - a i r c r a f t f l y i n g q u a l i t i e s i n calm a i r ( f i g . 52) were r a t e d as being s a t i s f a c t o r y f o r center-of-gravity p o s i t i o n s forward of approximately 0.39E and acceptable, b u t u n s a t i s f a c t o r y ( P R G 4.51, f o r center-of-gravity p o s i t i o n s a f t of 0.39c'. Engagement of t h e advanced PACS showed only s l i g h t improvements i n t h e f l y i n g q u a l i t i e s . The p i l o t r a t i n g s f o r t h e b a s e l i n e a i r c r a f t , when flown i n moderate turbulence, w e r e s c a t t e r e d throughout t h e u n s a t i s f a c t o r y , b u t a c c e p t a b l e , r a t i n g band ( f i g . 5 3 ) . Engagement of t h e advanced PACS reduced t h e scatter of t h e and i n d i c a t e d some improvement i n t h e f l y i n g qualities--although t h e y p i l o t r a t i n g s remained less t h a n s a t i s f a c t o r y . (Note t h a t t h e f l y i n g q u a l i t i e s of t h e PACS-off c o n f i g u r a t i o n were evaluated as being a c c e p t a b l e f o r t h e center-of-gravity range tested--due t o the rearward s h i f t of t h e n e u t r a l p o i n t f o r t h e flaps-down configura- t i o n s , t h a t is, No 0.48E.)

F l i g h t c o n d i t i o n 19 ( t a k e o f f ) : F l i g h t c o n d i t i o n 19 r e p r e s e n t s t h e t a k e o f f c o n f i g u r a t i o n for the second-segment climb speed (1.2Vs) and i s i n a r e g i o n of e s s e n t i a l l y l i n e a r aerodynamic c h a r a c t e r i s t i c s . Evaluations w e r e m a d e by one p i l o t a t t h i s f l i g h t c o n d i t i o n , f o r calm a i r and moderate t u r b u l e n c e , over a center-of- g r a v i t y range from 0.25E t o 0.50C. (See f i g s . 54 and 55.)

For t h e calm-air c o n d i t i o n s , t h e b a s e l i n e a i r c r a f t had s a t i s f a c t o r y t o accept- able f l y i n g q u a l i t i e s o v e r t h e c e n t e r - o f - g r a v i t y range t e s t e d , and t h e engagement of t h e advanced PACS i n d i c a t e d an improvement i n t h e s e f l y i n g q u a l i t i e s , p a r t i c u l a r l y a t t h e more a f t center-of-gravity p o s i t i o n s ( f i g . 54). F l i g h t i n turbulence degraded t h e f l y i n g q u a l i t i e s and r e s u l t e d i n t h e b a s e l i n e a i r c r a f t being r a t e d between 4 and 5 ( f i g . 5 5 ) . Engagement of t h e PACS enhanced t h e f l y i n g q u a l i t i e s o n l y s l i g h t l y .

Summary of advanced PACS s i m u l a t i o n r e s u l t s . - Figure 56 p r e s e n t s t h e spread i n t h e p i l o t r a t i n g s of t h e b a s e l i n e and t h e PACS configured a i r c r a f t f o r t h e c r u i s e and high-speed f l i g h t c o n d i t i o n s ( 7 , 10, 15, and 1 6 ) . These p i l o t - r a t i n g "spreads" i n c l u d e both calm-air and t u r b u l e n t - a i r f l i g h t c o n d i t i o n s . These d a t a i n d i c a t e t h a t t h e f l y i n g q u a l i t i e s of t h e b a s e l i n e simulated a i r c r a f t i n t h e s e f o u r f l i g h t condi- t i o n s became unacceptable ( p i l o t r a t i n g g r e a t e r than 6.5) f o r center-of-gravity p o s i t i o n s a f t of approximately 0.40E. Figure 56 a l s o i n d i c a t e s t h a t t h e advanced PACS improved t h e f l y i n g q u a l i t i e s of t h e a i r c r a f t s i g n i f i c a n t l y f o r t h e center-of- g r a v i t y p o s i t i o n s a f t of approximately 0.35E i n t h a t t h e p i l o t r a t i n g s v a r i e d between 2 and 4 ( v e r y s a t i s f a c t o r y t o q u i t e a c c e p t a b l e ) . The h o l d i n g f l i g h t condi- t i o n 17 w a s n o t included i n f i g u r e 56, b u t t h e p i l o t - r a t i n g t r e n d w a s similar.

The advanced PACS d i d n o t provide a s i g n i f i c a n t b e n e f i t f o r t h e landing and takeoff f l i g h t c o n d i t i o n s ( 1 8 and 1 9 ) although some improvement i n t h e f l y i n g q u a l i - ties i n t u r b u l e n t f l i g h t w a s experienced.

Comparison of Simulator and F l i g h t Test R e s u l t s A near-term PACS w a s developed by t h e Lockheed-California Company i n 1979 and w a s i n s t a l l e d on a Lockheed L-1011 f l i g h t test a i r c r a f t ( r e f . 2 ) . F l i g h t demonstra- t i o n tests, w i t h i n t h e r e g i o n of e s s e n t i a l l y l i n e a r aerodynamic c h a r a c t e r i s t i c s , showed t h a t t h e PACS provided good f l y i n g q u a l i t i e s of t h e a i r c r a f t f o r s t a t i c sta- b i l i t y margins t o +1 p e r c e n t . The o b j e c t i v e of the p r e s e n t near-term PACS program w a s t o demonstrate, by f l i g h t tests, t h a t t h i s PACS w i t h i n c r e a s e d feedback g a i n s would provide f l y i n g q u a l i t i e s , f o r s t a t i c s t a b i l i t y margins t o - 3 p e r c e n t , which were e q u i v a l e n t t o those of t h e b a s e l i n e a i r c r a f t with a +15-percent s t a t i c s tabi li t y margin.

A s s t a t e d p r e v i o u s l y , t h e f l y i n g q u a l i t i e s a n a l y s e s and p i l o t e d - f l i g h t simula- t i o n tests f o r t h e near-term PACS configured a i r c r a f t w e r e l i m i t e d t o e v a l u a t i o n of t w o c r u i s e c o n d i t i o n s ( f l i g h t c o n d i t i o n s 10 and 1 1 ) and one l a n d i n g c o n d i t i o n ( f l i g h t c o n d i t i o n 18). The f l i g h t tests, however, w e r e l i m i t e d t o t h e e v a l u a t i o n of a series of s t a t i c s t a b i l i t y margins f o r one f l i g h t c o n d i t i o n ( c r u i s e c o n d i t i o n 1 0 ) .

Therefore, t h e subsequent d i s c u s s i o n of t h e comparison of t h e ground-based simula- t i o n and t h e f l i g h t test r e s u l t s p e r t a i n t o t h e e f f e c t s of t h e AACS and t h e near- t e r m PACS on t h e a i r c r a f t f l y i n g q u a l i t i e s f o r f l i g h t c o n d i t i o n 10.

Two major d i f f e r e n c e s w e r e i d e n t i f i e d between t h e ground-based s i m u l a t o r and f l i g h t test r e s u l t s . F i r s t , t h e b a s e l i n e f l i g h t test a i r c r a f t w a s rated by t h e p i l o t s as having b e t t e r f l y i n g q u a l i t i e s than those demonstrated d u r i n g t h e simula- t i o n tests; and second, h i g h e r p i t c h - r a t e damping feedback g a i n s w e r e d e s i r e d d u r i n g f l i g h t tests than d u r i n g s i m u l a t i o n tests.

The better f l y i n g q u a l i t i e s of t h e b a s e l i n e f l i g h t test a i r p l a n e a t t h e a f t center-of-gravity p o s i t i o n s are i n d i c a t e d by comparing t h e two c h a r t s p r e s e n t e d i n f i g u r e 5 7 ( a ) . The t w o c h a r t s p r e s e n t e d i n f i g u r e 5 7 ( b ) i n d i c a t e d t h a t t h e r e w a s no d i f f e r e n c e i n t h e f l y i n g q u a l i t i e s w i t h t h e AACS o f f . The e x p l a n a t i o n f o r t h e d i f f e r e n c e i n t h e p i l o t r a t i n g s with t h e AACS engaged w a s t h a t i n t h e f l i g h t tests t h e a i r c r a f t w a s g e n t l y maneuvered around t r i m and i n shallow banked t u r n s ; whereas d u r i n g t h e s i m u l a t i o n t h e a i r c r a f t w a s maneuvered more a g g r e s s i v e l y . Subsequent s i m u l a t o r tests ( u t i l i z i n g p i l o t i n g techniques similar t o t h e f l i g h t tests) v e r i f i e d t h i s hypothesis. (See f i g . 58.)

A comparison of t h e s i m u l a t o r and f l i g h t test r e s u l t s a l s o i n d i c a t e d t h a t higher p i tch-rate damping feedback g a i n s w e r e d e s i r e d d u r i n g f l i g h t tests ( f i g . 59).

F u r t h e r i n v e s t i g a t i o n i n d i c a t e d a p o s s i b l e reason f o r t h i s d i f f e r e n c e w a s due t o t h e lack of realistic load factor (9) cues i n t h e motion-base simulator. I n t h e test aircraft t h e g-cues were much more a p p a r e n t t o t h e p i l o t s , and s i n c e i n c r e a s i n g t h e p i t c h - r a t e damping g a i n s tended t o reduce t h e g - o s c i l l a t i o n s , they p r e f e r r e d t h e h i g h e r damping gains. The aforementioned a d d i t i o n a l s i m u l a t i o n tests also included i n c o r p o r a t i o n of high-speed b u f f e t and stick-shaker models which were used i n conjunction w i t h t h e a v a i l a b l e motion cues. The s i m u l a t i o n w a s t h u s more realistic, and t h e d i f f e r e n c e s i n t h e p r e f e r r e d p i t c h - r a t e damping g a i n s between t h e s i m u l a t i o n and f l i g h t tests w e r e c o n s i d e r a b l y reduced (see f i g . 60).

CONCLUDING REMARKS A six-degree-of-freedom, ground-based simulator s t u d y h a s been conducted t o e v a l u a t e t h e e f f e c t i v e n e s s of t w o p i t c h a c t i v e c o n t r o l systems (PACS) i n improving a wide-body t r a n s p o r t a i r p l a n e when operated a t negative t h e handling q u a l i t i e s of The f l i g h t c h a r a c t e r i s t i c s w e r e evaluated a t e i g h t d i f f e r e n t f l i g h t s t a t i c margins.

c o n d i t i o n s r e p r e s e n t i n g t h e e n t i r e f l i g h t envelope, with emphasis on t h e c r u i s e f l i g h t conditions. The two p i t c h a c t i v e c o n t r o l systems evaluated c o n s i s t e d of a simple "near-term" PACS and a more complex "advanced" PACS. (The near-term PACS w a s a l s o f l i g h t t e s t e d , and t h o s e f l i g h t test r e s u l t s are compared with t h e ground-based s i m u l a t o r r e s u l t s . ) Five r e s e a r c h test p i l o t s p a r t i c i p a t e d i n t h e f l i g h t s i m u l a t i o n program although a l l p i l o t s d i d n o t e v a l u a t e e i t h e r PACS concept a t a l l f l i g h t con- d i t i o n s . This paper summarizes t h e r e s u l t s of t h e s t u d y which support t h e following major conclusions.

Near-Term PACS

I

The b a s e l i n e a i r c r a f t ( p i t c h a c t i v e c o n t r o l system (PACS) o f f ; a i l e r o n a c t i v e c o n t r o l system (AACS) on) had unacceptable f l y i n g q u a l i t i e s f o r t h e c r u i s e f l i g h t c o n d i t i o n s evaluated a t center-of-gravity p o s i t i o n s a f t of t h e n e u t r a l p o i n t (neu- t r a l s t a t i c s t a b i l i t y ) . However, t h e f l y i n g q u a l i t i e s w e r e s i g n i f i c a n t l y b e t t e r with t h e AACS o f f because t h e AACS has a d e s t a b i l i z i n g e f f e c t f o r maneuvering f l i g h t . The b a s e l i n e - a i r c r a f t f l y i n g q u a l i t i e s for t h e landing f l i g h t c o n d i t i o n w e r e a c c e p t a b l e throughout t h e center-of-gravity test range.

I Engagement of t h e near-term PACS improved the f l y i n g q u a l i t i e s for t h e c r u i s e f l i g h t c o n d i t i o n s s i g n i f i c a n t l y b u t only s l i g h t l y improved t h e a l r e a d y a c c e p t a b l e f l y i n g q u a l i t i e s f o r t h e landing f l i g h t condition. W i t h t h e PACS o p e r a t i v e , t h e i n g e n e r a l , considered t o be good over t h e center-of-gravity f l y i n g q u a l i t i e s w e r e , test range and w e r e close t o meeting t h e design goals.

A PACS o p e r a t i n g c o n f i g u r a t i o n w i t h p i t c h damper p l u s feed forward w a s pre- f e r r e d t o a c o n f i g u r a t i o n w i t h p i t c h damper only, o r t o a c o n f i g u r a t i o n of p i t c h damper w i t h feedforward washout. It w a s determined d u r i n g t h e a n a l y s i s p o r t i o n of t h e s t u d y t h a t t h e PACS must have p i t c h - r a t e g a i n s , column-minus-trim (feedforward) g a i n s , and t i m e l a g g a i n s t h a t are f u n c t i o n s of t h e a i r c r a f t c a l i b r a t e d a i r s p e e d .

The column-minus-trim g a i n s and t i m e l a g are independent of t h e s t a t i c s t a b i l i t y margin; however, t h e d e s i r e d p i t c h - r a t e feedback g a i n requirements w e r e determined t o double i n v a l u e as t h e s t a t i c s t a b i l i t y margin w a s changed from n e u t r a l t o -5 percent.

Advanced PACS The p i l o t e d - f l i g h t s i m u l a t i o n r e s u l t s i n d i c a t e d t h a t t h e a d d i t i o n of t h e advanced PACS t o the L-1011 l o n g i t u d i n a l c o n t r o l system provided f l y i n g q u a l i t i e s .

t o a 20-percent negative s t a t i c s t a b i l i t y margin which were similar t o t h e best b a s e l i n e - a i r c r a f t f l y i n g q u a l i t i e s ( 1 5-percent p o s i t i v e s t a t i c margin) f o r t h e c r u i s e f l i g h t conditions. The PACS s e n s o r i n p u t s r e q u i r e d f o r f l i g h t i n t h e l i n e a r sta- b i l i t y region were normal a c c e l e r a t i o n , p i t c h rate, and p i t c h a t t i t u d e ; while addi- t i o n a l sensor i n p u t s of a n g l e of a t t a c k , bank angle, and Mach number were r e q u i r e d f o r nonlinear s t a b i l i t y f l i g h t c o n d i t i o n s .

The advanced PACS d i d n o t provide a s i g n i f i c a n t b e n e f i t f o r t h e t a k e o f f and landing f l i g h t c o n d i t i o n s although some improvement i n t h e f l y i n g q u a l i t i e s f o r t u r - b u l e n t f l i g h t w a s experienced.

Comparison of Simulator and F l i g h t T e s t R e s u l t s Two major d i f f e r e n c e s were i d e n t i f i e d between t h e ground-based s i m u l a t o r and f l i g h t test r e s u l t s as follows: ( 1 ) t h e b a s e l i n e f l i g h t test a i r c r a f t (PACS o f f ; AACS on) w a s r a t e d by t h e p i l o t s as having better f l y i n g q u a l i t i e s than those demon- s t r a t e d d u r i n g t h e s i m u l a t i o n tests; and ( 2 ) with t h e PACS and AACS engaged, h i g h e r p i t c h - r a t e damping feedback g a i n s w e r e d e s i r e d d u r i n g t h e f l i g h t tests than d u r i n g t h e simulation. There w e r e e s s e n t i a l l y no d i f f e r e n c e s , between t h e f l i g h t test and s i m u l a t o r r e s u l t s , i n t h e p i l o t opinion of t h e f l y i n g q u a l i t i e s of t h e a i r c r a f t when both t h e PACS and AACS w e r e i n o p e r a t i v e . (The aircraft w a s o n l y flown a t p o s i t i v e static margins when t h e AACS w a s i n o p e r a t i v e . ) AACS engaged The e x p l a n a t i o n f o r t h e d i f f e r e n c e i n t h e p i l o t r a t i n g s w i t h t h e w a s t h a t i n t h e f l i g h t tests t h e a i r c r a f t w a s g e n t l y maneuvered around t r i m and i n shallow banked t u r n s , whereas d u r i n g t h e s i m u l a t i o n t h e a i r c r a f t w a s maneuvered more a g g r e s s i v e l y . A l s o , i n d i c a t i o n s w e r e t h a t t h e p r e f e r e n c e f o r h i g h e r p i t c h - r a t e damping during t h e f l i g h t tests w a s due t o t h e l a c k of r e a l i s t i c load f a c t o r cues i n t h e motion-base s i m u l a t o r .

The r e s u l t s of t h e p r e s e n t s t u d y i n d i c a t e ( 1 ) t h e extreme importance of impress- i n g upon t h e test p i l o t s t h e n e c e s s i t y t o use t h e same techniques/procedures/tasks f o r s i m u l a t o r tests as f o r f l i g h t tests and ( 2 ) that t h e s u b s t i t u t i o n of p i l o t i n g cues may be used i n ground-based s i m u l a t o r s to enhance the v a l i d i t y of t h e simula- t i o n r e s u l t s . For example, b u f f e t and s t i c k - s h a k e r models were used i n t h e p r e s e n t s i m u l a t i o n study, i n conjunction w i t h t h e a v a i l a b l e motion cues, to compensate f o r t h e l a c k of continuous a c c e l e r a t i o n cues. That is, a better agreement of p i l o t r a t i n g s between t h e f l i g h t tests and t h e s i m u l a t o r tests was achieved.

NASA Langley Research Center Hampton, VA 23665-5225 August 5, 1985 APPENDIX DESCRIPTION O F AUGMENTATION SYSTEMS D e t a i l e d d e s c r i p t i o n s of t h e l o n g i t u d i n a l c o n t r o l systems evaluated d u r i n g t h e s u b j e c t handling q u a l i t i e s s i m u l a t i o n s t u d i e s are given i n r e f e r e n c e s 2 , 5, and 6.

However, f o r convenience, a b r i e f d e s c r i p t i o n of these v a r i o u s c o n t r o l systems i s presented i n t h e following s e c t i o n s .

Basic C o n t r o l System The b a s i c l o n g i t u d i n a l c o n t r o l system i s comprised of both a high-speed and a low-speed Mach t r i m compensator, a c o n t r o l l o a d i n g system ( f e e l s p r i n g s y s t e m ) , and a nonlinear c o l u m n / s t a b i l i z e r gearing. (See f i g . 61.)

Both Mach t r i m compensator models compute an incremental column d e f l e c t i o n t h a t a u t o m a t i c a l l y changes t h e p h y s i c a l p o s i t i o n of t h e column i n t h e cockpit. ( A d i s t i n c t i o n i s made between " p h y s i c a l " and "software" column p o s i t i o n s s i n c e t h e s t a b i l i t y and c o n t r o l augmentation system i n p u t s do n o t change t h e p h y s i c a l column p o s i t i o n ; whereas they do c o n t r i b u t e t o a f i c t i t i o u s "software" column p o s i t i o n t h a t determines control s u r f a c e d e f l e c t i o n . ) The high-speed MTC u t i l i z e s a first-order l a g w i t h a 10-sec t i m e c o n s t a n t t o r e p r e s e n t the Mach s e n s o r . The column d e f l e c t i o n data are a look-up f u n c t i o n of t h e f i l t e r e d Mach number. The low-speed MTC u t i l i z e s a f i r s t - o r d e r lag with a 20-sec t i m e c o n s t a n t t o r e p r e s e n t a s t a b i l i z e r f i l t e r s i g n a l t h a t is used w i t h t h e Mach s e n s o r s i g n a l and f l a p s e t t i n g to compute the column o f f s e t gain. (The column t r i m s e r v o o f f s e t g a i n i s a scheduled f u n c t i o n of f l a p s e t t i n g and t h e Mach s e n s o r s i g n a l . ) A s i n d i c a t e d i n f i g u r e 61, i f t h e PACS i s o f f o r i f t h e system s w i t c h i s o f f , t h e compensation due t o t h e low-speed M T C w i l l be zero. When t h e low-speed MTC is o p e r a t i v e , t h e high- and low-speed MTC s i g n a l s are summed and s e n t through a f i r s t - o r d e r l a g t h a t models t h e s t i c k s e r v o a c t u a t o r .

This s i g n a l i s i n t u r n added t o t h e t r i m b u t t o n i n t e g r a t o r o u t p u t as shown i n f i g u r e 61. It should be noted t h a t t h e low-speed M T C w a s designed s p e c i f i c a l l y f o r t h e s u b j e c t RSS s i m u l a t i o n program and is n o t used on c o n v e n t i o n a l i n - s e r v i c e L-1011 a i r c r a f t .

The f e e l s p r i n g system i s composed of t h e c o n t r o l l o a d i n g system with s t i c k g r a d i e n t feedback and summed i n t e g r a t o r and M T C i n p u t s . (See f i g . 61.) The control-loading-system block diagram i s p r e s e n t e d i n f i g u r e 62. The system i s implemented on t h e Langley VMS by means of a McFadden a n a l o g computer. Force break- s t a t i c f r i c t i o n , v i s c o u s f r i c t i o n , and v e l o c i t y and p o s i t i o n l i m i t s are set by o u t , potentiometers. The s t a t i c and viscous f r i c t i o n a l f o r c e s , s t i c k f o r c e , bob weight, hinge moment, e x t e r n a l aerodynamic f o r c e , and computed s p r i n g g r a d i e n t ( m u l t i p l i e d by t o t a l s t i c k displacement) are summed and d i v i d e d by column mass t o determine s t i c k a c c e l e r a t i o n . (See f i g . 62.)

The c o l u m n / s t a b i l i z e r g e a r i n g determines 6 , , and 6, based upon s o f t w a r e s t i c k p o s i t i o n (6c01), as shown i n f i g u r e 61. The s t i c k p o s i t i o n i n t e g r a t o r and MTC d e f l e c t i o n sum (6c,MTc ) is added t o the PACS o u t p u t ( 6c,pAcs 1 , cable s t r e t c h ) , and hardware b i a s e d s t i c k p o s i t i o n (6 + 1.2) t o determine s o f t w a r e ('c,str C,P s t i c k p o s i t i o n (6c01). The t r i m b u t t o n moves t h e s t a b i l i z e r and the s t i c k a t t h e same t i m e , thus compounding t h e t r i m b u t t o n a c t i o n . That is, the commanded s t a b i l i z e r d e f l e c t i o n ( 6H,com ) is determined from a look-up f u n c t i o n of n o n l i n e a r g e a r i n g ratios (termed J-curve d a t a , f i g . 6 3 ) . This g e a r i n g is a l s o dependent upon t h e s t a b i l i z e r p o s i t i o n commanded from the t r i m button, as can be seen from t h e d i f f e r e n t curves generated with t h e s t a b i l i z e r trimmed a t v a r i o u s d e f l e c t i o n s . The s t a b i l i z e r s e r v o a c t u a t o r is modeled by a f i r s t - o r d e r l a g , with a t i m e c o n s t a n t of 0.17 sec. (See f i g . 61.) The e l e v a t o r d e f l e c t i o n is a look-up f u n c t i o n dependent upon s t a b i l i z e r p o s i t i o n . (See f i g . 64.)

Near-Term PACS A near-term PACS w a s developed by t h e Lockheed-California Company i n 1979 and e v a l u a t e d , by Lockheed, on t h e i r Rye Canyon Simulator F a c i l i t y . Subsequent f l i g h t demonstration tests showed t h a t t h e PACS provided good f l y i n g q u a l i t i e s of t h e a i r c r a f t f o r relaxed statis margins t o +1 p e r c e n t , v e r i f y i n g t h e s i m u l a t i o n r e s u l t s .

Further a n a l y s i s of those f l i g h t test r e s u l t s , and a d d i t i o n a l a n a l y t i c s t u d i e s , i n d i c a t e d t h a t by i n c r e a s i n g t h e PACS feedback loop g a i n s , s a t i s f a c t o r y f l y i n g q u a l i t y c h a r a c t e r i s t i c s may be p o s s i b l e a t negative s t a t i c margins. Therefore, t h e earlier Lockheed near-term PACS s t u d y w a s extended, a t t h e Langley Research Center, t o e v a l u a t e the augmentation system ( w i t h modified system g a i n s ) a t n e u t r a l t o s l i g h t l y s t a t i c a l l y u n s t a b l e f l i g h t c o n d i t i o n s .

The b a s i c PACS a n a l y t i c a l block diagram, with t h e s i g n i f i c a n t c o n t r o l system dynamics r e p r e s e n t e d by Laplace domain t r a n s f e r f u n c t i o n s , i s p r e s e n t e d i n f i g u r e 7.

The diagram shows t w o loops: a feedback lagged p i t c h damper loop, a feedforward lagged column-minus-trim loop. P r o v i s i o n s are a l s o made i n t h e feedforward loop f o r t h e column-minus-trim s i g n a l washout d u r i n g maneuvers. The PACS i s considered t o have f o u r c o n f i g u r a t i o n s f o r purposes of a n a l y s e s and test e v a l u a t i o n s ; they are 0 PACS off ( b a s e l i n e a i r c r a f t ) 0 P i t c h damper only 0 P i t c h damper with feedforward 0 P i t c h damper with feedforward washout The pitch-rate g a i n Kq, t i m e l a g tlag, and feedforward g a i n KFF w e r e scheduled as a f u n c t i o n of c a l i b r a t e d a i r s p e e d , as shown i n f i g u r e 8. The schedul- i n g w a s necessary t o a s s u r e t h a t t h e f l y i n g q u a l i t i e s of t h e PACS configured a i r p l a n e , f o r a l l f l i g h t c o n d i t i o n s , w e r e e q u i v a l e n t t o t h e b a s e l i n e - a i r c r a f t f l y i n g q u a l i t i e s with a 0.25c'center of g r a v i t y . Increased p i t c h - r a t e g a i n s (1.3 < F* G 2.01, scheduled as a f u n c t i o n of airspeed, were r e q u i r e d t o provide improved f l y i n g q u a l i t i e s f o r center-of-gravity p o s i t i o n s between 0.39c' and 0.456.

Advanced PACS The advanced PACS block diagram is shown i n f i g u r e 25, and t h i s system i s d i v i d e d i n t o t h r e e p a r t s f o r d i s c u s s i o n as follows: 0 Control column and a c t u a t o r system--control column, column t r i m , series servos, J-curve, and s t a b i l i z e r t r i m .

0 Feedback loops--pitch rate, normal a c c e l e r a t i o n , and p i t c h a t t i t u d e .

0 Feed-forward loop--column f o r c e .

Control column and a c t u a t o r system.- C o n t r o l column displacement, column t r i m , and r e s u l t i n g s t a b i l i z e r d e f l e c t i o n a r e d i s c u s s e d i n t h e basic-longitudinal-control- system s e c t i o n .

t r i m c o n s i s t s of t h e p a r a l l e l t r i m (which r e l i e v e s t h e f o r c e on t h e The column c o n t r o l column) and t h e series t r i m (which p l a c e s t h e c o n t r o l column a t t h e d e s i r e d l o c a t i o n ) . The parallel t r i m and series t r i m are set simultaneously by an e l e c t r i - c a l "beeper" t r i m switch l o c a t e d on t h e c o n t r o l column.

The i n p u t t o t h e s e r i e s s e r v o s i s an electrical s i g n a l from t h e summed feed- forward and feedback loops. The t r a n s f e r f u n c t i o n i n each s e r v o block r e p r e s e n t s t h e s e r v o l a g c h a r a c t e r i s t i c s . The o u t p u t of t h e series s e r v o s a r e position-summed so t h a t t h e c o n t r o l a u t h o r i t y of each s e r v o i s 1.5O a t t h e c r u i s e t r i m s e t t i n g of - l o . ( T h i s p r o v i d e s a maximum position-summed o u t p u t of 3 O a t t h e c r u i s e t r i m set- t i n g . ) The series s e r v o s were position-summed so t h a t f a i l u r e of one s e r v o would n o t provide a s t a b i l i z e r hardover--which would r e s u l t i n loads g r e a t e r than t h e a i r c r a f t l i m i t loads.

Feedback loops.- The q and nz feedback s i g n a l s are used for c o n t r o l of t h e s h o r t - p e r i o d mode. These s i g n a l s a r e f i l t e r e d through t h e f i r s t - o r d e r , low-pass f i l t e r s i n d i c a t e d i n f i g u r e 25, where t h e f i l t e r t i m e c o n s t a n t s are both e q u a l t o 0.03 sec. The f i l t e r e d s i g n a l s a r e s u b j e c t t o g a i n s of and K,,, and t h e g a i n

K

scheduling parameters 9 and 6hT a r e provided t o set t h e d e s i r e d g a i n values.

A normalizing c o n s t a n t i s used i n each feedback loop so t h a t t h e g a i n (from t h e g a i n s c h e d u l e s ) through t h e J-curve f o r ~ H T of - l o o i s e q u a l t o 1 .O.

The p i t c h - a t t i t u d e ( 8 ) feedback s i g n a l is used t o c o n r o l t h e phugoid mode.

This s i g n a l is processed through a p i t c h synchronizer, a l a g - l e a d c i r c u i t , and a g a i n a m p l i f i e r . The p i t c h synchronizer s u p p r e s s e s t h e a t t i t u d e hold d u r i n g maneu- v e r s and sets a new a t t i t u d e r e f e r e n c e a t t h e s y n c h r o n i z e r o u t p u t when a c o n t r o l i s a p p l i e d . (See f i g . 65.) The lag-lead c i r c u i t e l i m i n a t e s t h e need column f o r c e f o r a v e l o c i t y g a i n s e n s o r t h a t would be r e q u i r e d f o r phugoid-mode c o n t r o l .

Feedforward loop.- The feedforward loop is used to provide t h e d e s i r e d c o n t r o l column feed-forward g r a d i e n t s . The f e e l s p r i n g ( p a r t of t h e b a s i c c o n t r o l system) c o n v e r t s t h e column displacement t o pounds, and t h e f o r c e c o n v e r t s Fc t o an e l e c t r i c v o l t a g e . A flaps-up/flaps-down b i a s s i g n a l switches t h e t i m e c o n s t a n t of t h e feedforward, low-pass f i l t e r , which is r e l a t e d t o t h e r e f e r e n c e b a s e l i n e a i r c r a f t s h o r t - p e r i o d mode. This provides t h e frequency v a r i a n t p a r t of t h e feed- forward t r a n s f e r f u n c t i o n , and t h e feedforward s i g n a l is then passed through t h e g a i n a m p l i f i e r ( K F F ) and summed with t h e feedback s i g n a l s to provide t h e series s e r v o i n p u t s i g n a l .

The feedback and feedforward gain values are changed by augmenting the gain- scheduling 6HT v a l u e by a r e q u i r e d increment t o provide ~ H T v a l u e . (See

*

f i g u r e 66.) The modified value (6HT) changes t h e feedback g a i n s t o provide t h e i n c r e a s e d c o n t r o l command f o r t h e h o r i z o n t a l s t a b i l i z e r and changes t h e feedforward g a i n s t o provide t h e " d e s i r e d " column-force g r a d i e n t s . I f t h e feedforward g a i n s were n o t provided, t h e column-force g r a d i e n t s would be i n c o r r e c t and s e v e r e column- f o r c e r e v e r s a l s might be experienced.

Active Ailerons Control System (AACS) A d e t a i l e d d e s c r i p t i o n of t h e A A C S i s given i n r e f e r e n c e 6; t h e r e f o r e , only a f u n c t i o n a l d e s c r i p t i o n i s p r e s e n t e d i n t h i s paper.

Reductions i n wing design loads are achieved by a u t o m a t i c a l l y moving t h e out- board a i l e r o n s symmetrically i n response t o a c c e l e r a t i o n s sensed a t t h e wing t i p s and i n t h e fuselage. I n a positive-g maneuver ( p u l l u p o r banked t u r n ) o r long-turn u p d r a f t , t h e a i l e r o n s d e f l e c t upward (downward f o r negative maneuvers and down- d r a f t s ) , t h u s moving t h e wing c e n t e r of p r e s s u r e inboard and reducing t h e wing bend- i n g stresses. This a c t i v e c o n t r o l s a p p l i c a t i o n is d e s i g n a t e d "maneuver load c o n t r o l . " A l s o , when i n t h e presence of atmospheric turbulence, motion i n t h e first wing bending m o d e ( i n t h e frequency range of 1 t o 2 h e r t z ) is sensed by accelerome- ters a t t h e wing tips. The a i l e r o n s are moved symmetrically so t h a t t h e r e s u l t i n g a i r p r e s s u r e s oppose t h e wing-tip v e l o c i t i e s and t h u s f u r t h e r reduce t h e stresses produced by t h e turbulence. This f u n c t i o n is designated "elastic mode suppression."

I n a d d i t i o n t o moving t h e a i l e r o n s symmetrically, t h e system moves t h e h o r i - z o n t a l s t a b i l i z e r a u t o m a t i c a l l y to compensate f o r t h e a i r p l a n e p i t c h i n g moment produced when t h e a i r p l a n e encounters a g u s t . This f u n c t i o n is designated " g u s t a l l e v i a t i o n . I' REFERENCES 1 . Martin, D. J., Jr.: A D i g i t a l Program f o r Motion Washout on Langley's Six- Degree-of-Freedom Motion Simulator. NASA CR-145219. 1977.

2. Guinn, Wiley A.: Development and F l i g h t Evaluation of an Augmented S t a b i l i t y Active C o n t r o l s Concept. NASA CR-165951, 1982.

3 . Airworthiness Standards: T r a n s p o r t Category Airplanes. F A R P t . 25, FAA, June 4. M i l i t a r y S p e c i f i c a t i o n - Flying Q u a l i t i e s of P i l o t e d Airplanes. MIL-F-8785C, Nov. 5, 1980. (Supersedes MIL-F-8785B1 Aug. 7, 1969.)

5. Guinn, Wiley A.; Rising, J e r r y J.; and Davis, W a l t J.: Development of a n Advanced P i t c h Active Control System f o r a Wide Body Jet A i r c r a f t . N A S A CR-172277, 1984 6 . Johnston, J. F.; e t al.: Accelerated Development and F l i g h t Evaluation of Active

Controls Concepts f o r Subsonic T r a n s p o r t A i r c r a f t - Volume I: Load

Alleviation/Extended Span Development and F l i g h t T e s t s . N A S A CR-159097, 1979.

I 30 TABLE I.- AIRCRAFT GEOMETRY AND WEIGHT Wing:

Reference area, f t 2 . . . . . . . . . . . . 3456

Reference mean aerodynamic chord, f t 2 . . . 24.46

Span, f t . . . . . . . . . . . . . . . . 164.33

Aspect r a t i o . . . . . . . . . . . . . . . 7.817

Leading-edge sweep, deg . . . . . . . . . . 35

H o r i z o n t a l tail:

A r e a , f t 2 . . . . . . . . . . . . . . . . . 1282

. . . . . . . . . . . . . . . . . 71.58

Span, f t

Aspect r a t i o . . . . . . . . . . . . . . . 4.0

Leading-edge sweep, deg . . . . . . . . . . 35

vertical tail:

Area, f t 2 . . . . . . . . . . . . . . . . . 550

Span, f t . . . . . . . . . . . . . . . . . 29.67

Aspect r a t i o . . . . . . . . . . . . . . . 1.6

Leading-edge sweep, deg . . . . . . . . . . 35

Weight:

Maximum ramp, l b f . . . . . . . . . . . . 424 000

Maximum t a k e o f f , l b f . . . . . . . . . . 422 000

Maximum l a n d i n g , l b f . . . . . . . . . . 358 000

Zero f u e l , l b f . . . . . . . . . . . . . 312 460

O p e r a t i n g empty, l b f . . . . . . . . . . 261 000

TABLE 11.- PILOTED-FLIGHT SIMULATION TEST CONDITIONS :enter of g r a v i t y , Weight, F l i g h t h l t i t u d e , Airspeed, p e r c e n t E Mode l b f f t KEAS :ondi t i o n ( a ) C r u i s e 25 t o 60 7 400 000 37 000 254 (W/6 = 1.9 x 10 6 1 M = 0.83) C r u i s e 360 000 25 t o 60 33 000 200 ( W / 6 = 1.4 x 10 6 ) M = 0.83) C r u i s e 360 000 25 to 60 26 000 325 ( W / 6 = M = 0.83) C r u i s e 360 000 25 t o 60 36 000 260 ( W / 6 = M = 0.83) 350 000 25 t o 60 25 000 357 %o/Vmo ( W / 6 = 0.9 x 10 ) Holding 335 000 25 t o 60 10 000 250 Landing 330 000 25 to 60 2 000 135 1 8 ( 6 f = 330) *3vs) ( 1 19 Takeoff 380 000 25 to 60 2 000 137 ( 6 f = 26O) ( 1 *2Vs) aNear-term PACS c e n t e r - o f - g r a v i t y range from 25 to 45.

- 3 U m m m 0 - c d W U U I 1 4 n u I c c m l r . a l m m u alu 6 6 C a l m u a 0 a l b a l a d 3 0 % m o alu C d O U E 0, . o a u r o r l u aal V P . 3 c 7 0 W U h E D r 4 d V P d u u .

W d V a l 0 a s c w a al .rl w M o w al r a l d V d d W U 4 d a v c v m a * m d L o w m r 0 w . C W d 0 6 0 W d alv W u 4 7 u P m a l a 0 - E u 6 v a l e @ s b C d m M m 0 d Q w v V U O C d b d c a l u w W a c 4 C d d m a l W 6 m S O r O B C -4s h W h a C O E 3 u m 0 W a 0 o l d v u .3 r d c u .r( a l a l 0 L O 6 o L o c m 4 u u w a . U m h d 4 a l u d a m o r m m m d W 4 r l o V V 0 5 6 s U M .3 c m d a c C U al s u m o u e o m r c c P C d . 3 e W r l U W . 3 . 3 u a l a l r l V C.U J b E W V 6 r t P %4 0 4 W W U O W V al alD u v a a l v c c 3 c ’-23 m u a l v w r c + o m a 0 4 a u m a m 0 b . 3 al Q C 6 rl rl E b E a b a s v r u m o u W W E 0 h E 3 u 0 0 C d O V ‘-2U d u U E ” U u . 3 m m W 4 W m P E - H PI W cl a

!

c H E H W H U V 5 1 2 a a l b r o r l w P N m l 1 1 1 1 0 0 0 0 0 r r 7 7 - w x x x x x - Q E d c o - m m c o E \ N P - P N

* 2

m l n m m w r 0 0 U ) m v) - w N m P I I I I I I I z 0 0 0 0 0 0 0 w 7 c c c c 7 7 H m X X X x x x x co

z

w E 0 m 0 0 P c o - o . 3 c o E

. N

0 I- N m m c o w r m P 0 0 . 3 c o m 0 m r- e m N . 3 I W . . .

. . . 0

w r m r r w P z I I I I I

E

. .

P I l l 0 0 0

d

c r - c w n P X X X P r4P I n P N P O U X * a m N

8 rg

r O N m w I C ? : * 0 z

+

- s - m 0, I P P u x R 4 w W u r n I a I I 0 0

8 0 0

r r c r

+ 9

w x x x x d N m 0 0 0 N . 3 0 0 0

!3 % 9

N . 3 d m P w N r E m . 3

X +

P P r a m . .

. .

zz

c o w

'8 N N

I I I

+

E

r m - m

- * N N

I I I I I I I I

3 4

0 0 0 0 0 0 0 0 r c r r r c r c v) II u x x x x x x x x

6 gx

w r o o w U m o o - N N c o P P m w r m a N N N w o w P m W N m u ' 1 p : ? ? F : ?

W G Y f i P r l - r I I I I I I m r N N r N I I I I I I 0 0 0 0 0 0 c - c r c r

!

m m w x x x

z m x x x

.- N w o m m q m o w o w

N r 4 m

N C O N G i w m m w r O m w m I r o m o w . . .

I ? . .

m c I 7 7 w m I I I I TABLE V.- ADVANCED PACS CONTROLLER INPUT SIGNAL S i g n a l

Type I us e

I

i Column f o r c e Feedforward Column-force g r a d i e n t

I

N o r m a l a c c e l e r a t i o n Short-period mode P i t c h rate Feedback P i t c h a t t i t u d e Primary g a i n Compensation f o r Dynamic p r e s s u r e scheduling f l i g h t - c o n d i t i o n Modified h o r i z o n t a l - t a i l changes d e f l e c t i o n Compensation f o r p i t c h - Angle of a t t a c k Secondary g a i n Bank angle up and AACS outboard s c h e d u l i n g aileron o p e r a t i o n Mach number TABLE VI.- TYPICAL PILOT COMMENTS FOR CRUISE FLIGHT CONDITION 10 I N CALM A I R c.9. I PACS off Advanced PACS on % E 0 Trimmability w a s good. 0 PACS improved a t t i t u d e c o n t r o l , b u t f o r c e s t o 0 A l t i t u d e hold w a s 220 f t i n 20° maneuver around t r i m were banked t u r n s . heavier.

0 Column f o r c e s w e r e o b j e c t i v e l y 0 S t a b i l i t y about t r i m w a s good and column f o r c e s were acceptable. high during l a r g e maneuvers.

0 High column f o r c e s during l a r g e 0 Short-period mode w a s more maneuvers made c o n t r o l d i f f i c u l t . h e a v i l y damped.

0 Short-period mode w a s w e l l damped.

0 p i t c h a t t i t u d e response w a s c r i s p and t h e r e was no bobble around t h e new a t t i t u d e ~~~ ~ ~ 0 Trimmabi li t y w a s degraded. 0 A l t i t u d e hold w a s +30 f t i n 20° banked t u r n s .

0 A l t i t u d e hold w a s 240 f t i n 20° banked t u r n s .

0 Force l i g h t e n i n g w a s apparent a t 0 Forces were h i g h e r , b u t the air- about 1 .8g. plane w a s much easier t o c o n t r o l 34.5 s i n c e it appeared more stable.

0 Short-period mode damping w a s good.

0 Phugoid mode w a s d i v e r g e n t .

0 Airplane appeared l o o s e r , and p r e c i s e c o n t r o l w a s more d i f f i c u l t .

TABLE V I .- Continued

-

z . g . , PACS off

Advanced PACS on - 1

% E T r i m m a b i l i t y w a s d i f f i c u l t .

Trimmability w a s s i g n i f i c a n t l y improved.

A l t i t u d e hold w a s 2 5 0 ft i n 20° banked t u r n s . i n g c h a r a c t e r i s t i c s were improved.

S i g n i f i c a n t f o r c e l i g h t e n i n g w a s observed a t high load f a c t o r s .

Forces were t o o l i g h t .

Short-period mode w a s reasonably damped.

Phugoid mode w a s r a p i d l y d i v e r g e n t .

P i t c h a t t i t A d e o s c i l l a t i o n s were B A t t i t u d e c o n t r o l was improved.

observed.

Considerable p i l o t a t t e n t i o n w a s r e q u i r e d .

C o n t r o l l a b i l i t y w a s marginal.

Trimmability w a s very d i f f i c u l t . B Trimmability w a s e x c e l l e n t .

A l t i t u d e hold w a s f150 f t i n 20° B Forces and c o n t r o l l a b i l i t y i n banked t u r n s . t u r n s and high-g maneuvers were good.

f0.5g o s c i l l a t i o n s occurred d u r i n g 20° banked t u r n s .

Large maneuvers were no longer considered p o s s i b l e .

~~ Airplane w a s no longer considered B Same comments as PACS on a t 43% E , .

f l y a b l e Not f l y a b l e B A l t i t u d e c o n t r o l w a s s l i g h t l y l o o s e r than a t 50% c'.

TABLE VI.- Concluded Advanced PACS on PACS off A l t i t u d e c o n t r o l n o t i c e a b l y D Not f l y a b l e l o o s e r .

0 Nose wandering occurred during S-turns .

A w a r e of reduced f o r c e s a t about 1 . 8 ~ ~ .

0 Control s e n s i t i v i t y was i n c r e a s e d because of reduced s t a b i l i t y and l i g h t e r forces.

37 I

I-!-

I L-83-11,999 ( a ) Flight t e s t airplane.

(b) Modifications made for current program are shown i n blocks.

Figure 2.- Photograph and features of simulated a i r c r a f t .

L U c, m u L ru S t u > .r aJ >, n c c K w LL c . . ) u

I

L-7 5-7 5 70 ( a ) Langley Visual/Motion Simulator.

L-78-7794 ( b ) Instrument panel.

Figure 4.- Langley Visual/Motion Simulator and i n s t r u m e n t p a n e l d i s p l a y .

L-7 9-5 999 ( a ) Approach scene.

L- 79-6000 ( b ) Landing scene.

Figure 5.- View of a i r p o r t scene as seen by pilot.

K ; = 0 Pi: O

-0.90 F1 i g h t = 0.95 A l t i t u d e , ft

i oo 150 200 250 300 350 400 450

E q u i v a l e n t airspeed, k n o t s Figure 6. - F l i g h t s i m u l a t i o n test c o n d i t i o n s .

u al

<

m It E .F L c,

Lo* I

U

F*

S ~ ~ n

> L a J ln cc S .I- n I U Y

-

.20

I I I I I I

160 200 240 280 320 360 C a l i b r a t e d a i r s p e e d , k n o t s ( a ) Pitch damper gain.

V a J ln n (3, r u

-

P 160 200 240 280 320 360 Cal i b r a t e d a i r s p e e d , k n o t s (b) P i t c h damper l a g .

O a J >r- h % 1.

l n v 1.

cccc o o 1.

. .

s s .

*r *F Cal i b r a t e d airspeed, k n o t s ( c ) Feedf orward gain.

Figure 8.- Gain and t i m e lag schedules of near-term PACS.

-

c.g., % c P u l l 0.25

----

0.45

8o r

PACS o f f , o r PACS on d w i t h p i t c h damper o n l y 40 PACS on

---

\ w i t h p i t c h T r i m I b f damper and FC , f e e d f o r w a r d FAR P a r t 25 c r i t e r i o n , -1 l b f / 6 KEAS '\-

t L J

-40 Push 180 200 220 240 260 280 300 E q u i v a l e n t a i r s p e e d , k n o t s Figure 9 . - Speed s t a b i l i t y c h a r a c t e r i s t i c s for f l i g h t c o n d i t i o n 1 0.

P u l l

80 - Feel system

FC , -1.0

' 1 I 1 I 1 1

-40' p u s h 1 . 0 1.2 1 . 4 1 . 6 11.8 2.0 2.2 2.4 Load f a c t o r , g units ( a ) PACS on with p i t c h damper only.

F 1 . 6 1 . 3

L) 1 . o

- 4 O L I I I I I I I J P u s h 1 . 0 1 . 2 1 . 4 1 . 6 1 . 8 2.0 2.2 2 . 4 Load f a c t o r , g units ( b ) PACS on with p i t c h damper and feed forward.

Figure 10.- C a l c u l a t e d maneuver s t a b i l i t y c h a r a c t e r i s t i c s f o r f l i g h t c o n d i t i o n 10 and c.g. = 0.2515.

Pull FC P u s h 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4

I

Load factor, g units ( a ) PACS on with pitch damper only.

( b ) PACS on with pitch damper and feedforward.

Figure 1 1 . - Calculated maneuver s t a b i l i t y characteristics for f l i g h t condition 10 and c . g . = 0 . 3 9 c ' .

a = Y O

n = 18.69

I a Pull

- Feel system

/

s a t u r a t i o n a t 65 Fc, l b f \ 1 i 3 ’ / I I

1 .o A . i I

I I I I I I ;-- 1 I

-40 Push1.0 1 . 2 1 . 4 1 . 6 1 . 8 2.0 2.2 2.4 Load f a c t o r , g units ( a ) PACS on with p i t c h damper only.

Pull Fc, l b f 1 1 I 1 I I I 1 -40 Push1.0 1.2 1 . 4 1 . 6 1 . 8 2.0 2.2 2.4 Load f a c t o r , g units ( b ) PACS on w i t h p i t c h damper and feedforward.

Figure 12.- Calculated maneuver s t a b i l i t y c h a r a c t e r i s t i c s f o r f l i g h t c o n d i t i o n 10 and c.g. = 0.45E.

1.. 0 MIL- ~ - 8 7 8 5 ~ 3.5 3.0 5 = 2.5 2.0 ud, l/sec 1.5

n 41

A 43

A 45 1 .o 0.5

-3.0 -2.5 -2.0 -1.5 -1 .o -0.5 0

C W , , Usee

( a ) Short-period mode.

Figure 13 .- E f f e c t of p i t c h - r a t e feedback g a i n and c e n t e r - o f -

g r a v i t y p o s i t i o n on l o n g i t u d i n a l dynamic s t a b i l i t y c h a r a c t e r i s t i c s of near-term PACS f o r f l i g h t c o n d i t i o n 10.

I

F* = 0 o k ’ F * = 1.8 A .

F* = 2 c . g . y % E I I u d y l / s e c

0 25

F* = 1.0 0 D 43 - . l o F* = 2.0 I I I

- .05

- . l o -.05 0 .05 .10

5w, Y 1 I sec

(b) Phugoid mode.

Figure 13.- Concluded.

I !-I II I, N

* k/ I I

II c LL I J I- t

I I

I I I I I I

I

I I I I I I I I I I I I I I

I

I I I

I

I I I I 1 I m 0 m 0 m 0 0 0 N N F ?

N m rc aJ h c n m C D V a L L / I I * I O ' : I 0, c, aJ ' % / I -0 z aJ I r I v) I

s I

- 0 ' L I U ' a J I

\I 2 1

I I I I W o a l u 4 J L l u o a l W W w e W E I I d 0 0 C m N r- 0 0 0 0 m u 0 r- N rc n m r- a , -0 n n V LI a

lu

AACS o f f c, S 0) V L P a J 15

AACS on

n =3 c, i o c, v, -5

- 10

25 30 35 40 45

Center o f g r a v i t y , percent C

I I I I I

25 30 35 40 45

Center o f g r a v i t y , percent C

Figure 16.- E f f e c t of a i l e r o n a c t i v e c o n t r o l system (AACS) and c e n t e r - o f - g r a v i t y p o s i t i o n on s t a t i c s t a b i l i t y f o r a t y p i c a l c r u i s e f l i g h t c o n d i t i o n .

P i l o t 1 P i l o t 2 9 r Unacceptable Unacceptable Unacceptable

0 0

:E 7

cn cn I c c *I- *I- 0 c, 0 c, ru L

-

Un s a t i s f ac t o r y

5 1 Unsatisfactory

A

- A

- S a t i s f a c t o r y

X S a t i s f a c t o r y 2 c

1 Illlllr 1 Illlllr

20 25 30 35 40 45 50 20 25 30 35 40 45 50 Center of g r a v i t y , percent E Center of g r a v i t y , percent E P i l o t 3 Unacceptabl e 0 AACS on Unsatisfactory

A

A AACS o f f

Sat i s f a c t o ry

20 25 30 35 4 0 45 50 Center of g r a v i t y , percent Figure 17.- I n d i c a t i o n of t h e e f f e c t s of AACS and c e n t e r - o f - g r a v i t y p o s i t i o n on p i l o t r a t i n g f o r f l i g h t c o n d i t i o n 10 with PACS o f f .

rc rc v, V Q ' Q

I

i

Ln 0 Ln 0 ~ In 0 0 0 N N c N u - c n - n a J

-

-0 n n u a L L a

I

W aJ v) n aJ E -I- I -

I I

I I 1 I I I I 1 I I m m d cr) N ? 0 d cr) N ? 0 0 0 07 07 N 1 4 - aJ aJ n -0 -0 a a n UJ UJ W a a LL v1

5%

PI Q, 4J Q, a Y J L e o

I? O L U

d .rl PI

!

1 1 1 1 o o c ' , . .

I - - -

0 0 0

I 9 - 8 - Unacceptabl e 0 AACS on 7 -

A AACS off

6 - 0

5 - Unsatisfactory 4 -

A A

3 -

* Sat i sfactory

2 -

I I I I I 1

1 - P i l o t 3 P i l o t 4 Unacceptable 0

Unacceptabl e

n

7 t

v 6 -

5 - Unsatisfactory 0 Unsatisfactory A

4 -

A

3 - 0

* S a t i s f a c t o r y

S a t i s f a c t o r y 2 -

I I I I I I

1 ; 2 0 25 30 35 40 45 50 Center of gravity, percent E Figure 21.- I n d i c a t i o n of t h e e f f e c t s of AACS and center-of-gravity p o s i t i o n on p i l o t r a t i n g f o r f l i g h t c o n d i t i o n 11 with PACS o f f .

w c (3 h 1 1 1 1 t T u r b u l e n t atmosphere 0 AACS on P i l o t 1 P i l o t 2 Unacceptable Unacceptable 0, E

-I- 6 :E

C) icr L

- U n s a t i s f a c t o r y

U n s a t l s f a c t o r y A t Ot

-

g L

0 0 -

W 0 0

- 0 0

S a t i s f a c t o r y 0 Sat i s f a c t o r y o

20 25 30 35 40 4 5 50 20 25 30 35 40 45 50 Center of g r a v i t y , p e r c e n t c' Center o f g r a v i t y , p e r c e n t E P i l o t 4

9 -

8 - Unacceptable Unacceptabl e

7 -

tn S

.?

6 - c, m U n s a t i s f a c t o r y U n s a t i s f a c t o r y 5 - c,

- .I-- 4 -

, t - 0 I v U

= 3 -

S a t i s f a c t o r y 0 S a t i s f a c t o r y 2 -

1 1 1 1 1 1 1 1

1 Illrrll

I -

20 25 30 35 40 45 50

20 25 30 35 40 45 50 Center o f g r a v i t y , p e r c e n t E Center o f g r a v i t y , p e r c e n t Figure 23.- I n d i c a t i o n of the e f f e c t s of c e n t e r - o f - g r a v i t y p o s i t i o n on p i l o t r a t i n g f o r f l i g h t c o n d i t i o n 18 with PACS o f f and AACS on.

I 0 2 n I L

! I

1 - 1 N

c r - w m r o n m r - w n w n ~ 9MlV11 U3dUVH 113d003 9wllVU U3dUVH U3d003 I

o o o O D

I

f -

li n i m u m s h o r t - p e r i o d a t 0.25F, f r e q u e n c y w0 = w S P open- 1oop condi ti on

kdo s i n '

f

(a) Short-period mode.

r- 0.1

I- 0.5

0.16 Minimum p h u g o i d p e r i o d = 40 sec ~ (b) Phugoid mode.

Figure 26.- .Dynamic s t a b i l i t y design objectives of advanced PACS.

1 4 6 8 10 20 40 60 80 100 n g units/rad a’ ( a ) MIL-F-8785C wheel control l i m i t s with nL = 2 . 5 .

Figure 27.- Pitch maneuvering force gradient l i m i t s .

Upper 1 irni t , Upper 1 irni t ,

n < 4.17

1 imit,

n ‘ s

a Fc, l b f 1 5

.o 1.2 1 . 4 1.6 1.8 2 . 0

Load f a c t o r , g units ( b ) Wheel c o n t r o l f o r c e g r a d i e n t design o b j e c t i v e s of advanced PACS.

MIL-F-8785C; Level 1 .

Figure 27.- Concluded.

P u l l

hc*g*y %

b f 0 FcY 1 L I - 40 P u s h I I I 1 1 160 200 240 280 320 360 Equ i v a l e n t a i r s p e e d knots ( a ) F l i g h t c o n d i t i o n 17 ( h o l d i n g mode).

P u l l

- -

I

F c y l b f o I FAR PART 2 5 CRITERIA

/

- 1 l b f / 6 KEAS - 40 - 8 0 P u s h I I 1 1 I I 180 200 220 240 260 280 300 k n o t s Equ i v a l en t a i r s peed ( b ) F l i g h t c o n d i t i o n 7 ( c r u i s e mode).

Figure 28.- Typical speed s t a b i l i t y column f o r c e c h a r a c t e r i s t i c s f o r simulated L-1 01 1 w i t h advanced PACS o p e r a t i v e .

n = 3.31

Pull a Feel f o r c e s a t u r a t i o n

\

c.g., % c'

1 .o

1.4 1.6

1.2

Load f a c t o r , g units Figure 29.- I n d i c a t i o n of maneuver s t a b i l i t y c h a r a c t e r i s t i c s of b a s e l i n e L-1011 a i r c r a f t (PACS o f f ; AACS on) i n takeoff c o n f i g u r a t i o n . I n d i c a t e d boundaries are from r e f e r e n c e 4.

I P u l l

1 .o 1.2 1.4 1.6

Load f a c t o r , g u n i t s Figure 30.- Maneuver s t a b i l i t y c h a r a c t e r i s t i c s of advanced PACS configured a i r c r a f t i n t a k e o f f f l i g h t condition. I n d i c a t e d boundaries are from r e f e r e n c e 4 .

= 13.57 na Pull F c , l b f -20 -40

- 60

P u s h I I I I I I I

1 .o 1 . 2 1 . 4 1 . 6 1.8 2.0 2.2

Load f a c t o r , g u n i t s Figure 31 .- I n d i c a t i o n of maneuver s t a b i l i t y c h a r a c t e r i s t i c s of b a s e l i n e L-1011 a i r c r a f t (PACS o f f ; AACS on) i n c r u i s e c o n f i g u r a t i o n ( f l i g h t c o n d i t i o n 7 1 .

n = 13.57

a Pull F c , l b f

0 L

1 I I I I 1

1 .o 1.2 1.4 1.6

1.8 2.0

Load f a c t o r , g units

Figure 32 .- Maneuver s t a b i l i t y c h a r a c t e r i s t i c s of advanced PACS

I n d i c a t e d configured a i r c r a f t f o r c r u i s e f l i g h t c o n d i t i o n 7 .

boundaries are from r e f e r e n c e 4.

=a-

, 3 9 c . Q . , YJ

II

- 4 3

34.5

.50 A - t , -.l 0 . 1 .2 \ EXPANDED SCALE OF PHUGI 3 M O D E MlL.F.8785C CRITERIA \":.

- 1.6

- 1.2 WdY -1

C.Q., \ % E

- 0.8 - 0.4 50 43 V - V I L 1

/ \ - / \

-2.0 - 1 . 6 - 1 . 2 .8 Figure 33.- Dynamic s t a b i l i t y c h a r a c t e r i s t i c s of b a s e l i n e a i r c r a f t (PACS off; AACS on) f o r cruise f l i g h t c o n d i t i o n 7.

7 2

-1.6 - 1 . 2 - .8 - .4 0 .4 .8

(a) Short-period mode.

Figure 34.- Dynamic s t a b i l i t y c h a r a c t e r i s t i c s of c r u i s e f l i g h t c o n d i t i o n 7 with advanced PACS o p e r a t i v e .

- 0.2

5 = 0.041; MIL- F-8785C c r i t e r i a -1

c.g. = 0.25C t o 0.60C

cod, sec

- 0.1

I I - 1 5wn Y sec ( b ) Phugoid mode.

Figure 34.- Concluded.

-1000 0 1000 2000 3000 4000 5000 6000 Horizontal distance, ft Figure 3 5 . - D i s c r e t e g u s t model used i n a n a l y s i s of f l i g h t Condition 7 .

c.g., % c

6 - 4 - \ I I I I I I I 0 4 8 12 16 20 24 6 - b - 2 - 0 -

-

- 2

I \L

- 4 -

- 4 A

0 4 8 1 2 16 20 2 4

3 2.0 -

2.0 1

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-

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'I 0 I

I 1 1 1 1 1 0 4 a 12 16 20 24 0 4 8 1 2 16 20 2 4 Time, sec Time, sec ( a ) B a s e l i n e a i r c r a f t (PACS o f f ; ( b ) Advanced PACS a i r c r a f t .

AACS o n ) .

Figure 36.- Comparison of a i r c r a f t response, with and w i t h o u t PACS engaged, t o a s e v e r e v e r t i c a l g u s t f o r f l i g h t c o n d i t i o n 7 w i t h W = -54 f t / s e c .

9 I peak I .2 .1 cm 9 cg

/

% E . ¶ -.l 39 34 . 5 -.2 10 1 2 Figure 3 7 . - I n d i c a t i o n of aircraft s t a t i c pitching-moment c h a r a c t e r i s t i c s for f l i g h t c o n d i t i o n 7.

-

Fc, l b f

' l r

- 8 - 6 - 4 -

0 0 ' 1

I 1 1 I 1 1 I I I 1 I 1 1 1 0 4 8 12 16 20 24 0 4 8 12 16 20 24 - l t

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/

-

la - 1;5

-

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Oa5 t

Oo5 0 1

O L 1 1 I 1 1 1 1 b J e 1 2 16 20 2 4 0 4 0 4 0 1 2 16 20 24

Time, sec

Time, sec

( a ) Baseline a i r c r a f t (PACS off; (b) Advanced PACS a i r c r a f t .

AACS on).

Figure 30.- Comparison of a i r c r a f t response, w i t h and without PACS engaged, t o various levels of control column step inputs for f l i g h t condition 7 with c.g. = 0.5Oc'.

- 0 PILOT 1

A PILOT 2 0 PILOT 3

0 PILOT 4

v

V PILOT 5

- Solid symbols

denote PACS o f f

A

U N A C C E PT AB LE Pilot rating UNSATISFACTORY

v v v

- A A

2 A A

-

SATISFACTORY 20 30 40 50 60 Center o f gravity, percent Figure 39.- I n d i c a t i o n of e f f e c t of center-of-gravity p o s i t i o n on p i l o t opinion with and without t h e advanced PACS engaged f o r c r u i s e f l i g h t c o n d i t i o n 1 0 i n calm a i r .

h PILOT 2

-

0 PILOT 3

0 PILOT 4

9 - V PILOT 5

Solid symbols e

8 - denote PACS o f f A

7 - v UNA C C E PTAB L E

------------------------

6 - P i 1 o t r a t i n g

5 - e A

e v 0

UNSATISFACTORY

4 : - 3---- 8-8_g__,--8--

3 - U O A

A

2 - 1- 20 30 40 50 60 Center o f g r a v i t y , percent c' Figure 40.- I n d i c a t i o n of e f f e c t of center-of-gravity p o s i t i o n on p i l o t opinion with and without t h e advanced PACS engaged f o r c r u i s e f l i g h t c o n d i t i o n 10 i n moderate turbulence.

I

v

V PACS O F F (BASELINE AIRCRAFT ~7 PACS ON

v

Pilot rating

SAT I S F ACT 0 R Y

I I I I I

20 30 40 50 60

Center o f gravity, percent

Figure 41.- I n d i c a t i o n of effect of c e n t e r - o f - g r a v i t y p o s i t i o n on p i l o t o p i n i o n w i t h and without the advanced PACS engaged f o r c r u i s e f l i g h t c o n d i t i o n 1 5 i n calm air.

10 - v

PACS OFF (BASELINE A I R C R A F T )

v PACS ON

9 - 8 -

v

7 - UNA C C E PT AB LE

-----------,-- --

6 -

Pilot rating

5 - U NS AT IS FACT 0 R Y

v

V V V

4 -

v v v v V

V

- - - - - - - o - - - - - - - - - - - o o - - c 3 - 2 -

1 L

SATISFACTORY 20 30 40 50 60

Center o f gravity, percent E

Figure 42.- I n d i c a t i o n of effect of c e n t e r - o f - g r a v i t y p o s i t i o n on p i l o t o p i n i o n w i t h and w i t h o u t t h e advanced PACS engaged €or c r u i s e f l i g h t c o n d i t i o n 15 i n moderate t u r b u l e n c e .

I

- 0 PILOT 1

0 PILOT 4

V PILOT 5

Sol id wmbol s

denote PACS o f f

-

*

v

Pilot rating 0

5 e

UNSATISFACTORY

- 0 0 0 0

-

SATISFACTORY

1 I I I I

20 30 40 50 60 Center o f gravity, percent S Figure 43.- I n d i c a t i o n of e f f e c t of c e n t e r - o f - g r a v i t y p o s i t i o n on p i l o t opinion with and without t h e advanced PACS engaged f o r c r u i s e f l i g h t c o n d i t i o n 7 i n calm air.

v

- 0 PILOT 1

0 PILOT 4

V PILOT 5

t

Solid symbols

denote PACS o f f

-

v

v

P i 1 o t rating

- 0 0 0 0

-

SATISFACTORY

I I I 1 I

20 30 40 50 60

Center o f g r a v i t y , p e r c e n t S

Figure 44.- I n d i c a t i o n of e f f e c t of c e n t e r - o f - g r a v i t y p o s i t i o n on p i l o t opinion w i t h and without t h e advanced PACS engaged f o r c r u i s e f l i g h t c o n d i t i o n 7 i n moderate turbulence.

ADVANCED PACS O F F PACS ON

l 6 r

ANG. O F ATTACK Idegl

25 r

PITCH ANGLE ldegl O r = = - - 25

5 r

PITCH RATE ldeglsecl 2 5 C o t . FORCE 0 IIbl - 2 5 c.g. VERT. ACCEL , (g) BANK ANGLE (degl - 5 0 L COLUMN POS.

linl - 5 5 - STAB. POS.

(degl - 1 0 I TIME Figure 45.- Comparison of damping response c h a r a c t e r i s - tics of c r u i s e f l i g h t c o n d i t i o n 7 i n moderate turbulence, with and without advanced PACS engaged, a t c . g . = 0.393.

ADVANCED PACS ON PACS OFF

l 6 r

ANG. O F ATTACK

‘1

Ideg) - 4 PITCH ANGLE (deg)

-25 -

PITCH RATE ideglsecl COL. FORCE (Ib) - 25 C.g. VERT. ACCEL , hll

A

BANK ANGLE Ideg)

- 1 0 I

T I M E Figure 46.- Comparison of damping response c h a r a c t e r i s t i c s of c r u i s e f l i g h t c o n d i t i o n 7 i n calm a i r , with and without advanced PACS engaged, a t c . g . = 0.43E.

ADVANCED PACS ON PACS O F F

l 6 r

ANG. OF ATTACK A Idegl - 4 L 25 r PITCH ANGLE ldegl PITCH RATE ldegisecl 2 5 COL. FORCE Ilbl

- 2 5 'u Y r l ' r Ill\ I ' I

2 r c.g. VERT. ACCEL 1 kl1 0- BANK ANGLE Idegl - 5 0 1 COLUMN POS. 0 lid - 5 STAB. POS. ' 0 , Idegl - 1 0 '

TIME

Figure 47.- Comparison of damping response c h a r a c t e r i s t i c s of c r u i s e f l i g h t c o n d i t i o n 7 i n calm a i r , with and without advanced PACS engaged, a t c.g. = 0 . 5 0 c ' .

h PILOT 2

-

A

V PILOT 5

Sol i d symbols 9 - denote PACS off 8 -

v

7 - UNA C CEPTAB LE

----------.I-- -------

6 - A

e

P i 1 o t r a t i n g 5 -

e

4 - UNSATISFACTORY

v

-b-b- i5 - - 7- -b -3

---8---

V

S TISFACTOR’

1 1 I 1 I

20 30 40 50 60

Center o f g r a v i t y , percent C

Figure 48.- I n d i c a t i o n of e f f e c t of c e n t e r - o f - g r a v i t y p o s i t i o n on p i l o t opinion with and without advanced PACS engaged f o r high-speed f l i g h t c o n d i t i o n 16 i n calm a i r .

0 PACS OFF (BASELINE A I R C R A F T ) 0 PACS ON

-

-

U N ACCEPTAB LE UNSATISFACTORY SAT IS FACTO R Y 20 30 40 50 60

Center o f gravity, percent E

Figure 49.- I n d i c a t i o n of e f f e c t of c e n t e r - o f - g r a v i t y p o s i t i o n on p i l o t opinion with and without advanced PACS engaged f o r high-speed f l i g h t c o n d i t i o n 16 i n moderate turbulence.

-

9 - 'I PACS OFF (BASELINE AIRCRAFT)

v PACS ON

8 - 'I 7 - U N AC CE PTAB LE

L I I I L I I I I I I - - -- - - I. --. - - -

v--

6 -

Pilot r a t i n g

5 -

v

4 - UNSATISFACTORY ---.----.-- -0-

-7---- -- ---

3 -

v v v v

V

2 - 1 - SATISFACTORY

1 1 I I J

20 30 40 50 60

Center o f gravity, percent E

Figure 50.- I n d i c a t i o n of e f f e c t of c e n t e r - o f - g r a v i t y p o s i t i o n on p i l o t opinion with and without advanced PACS engaged f o r h o l d i n g f l i g h t c o n d i t i o n 17 i n calm a i r .

v

PACS OFF (BASELINE AIRCRAFT)

v PACS ON

I I I I I

20 30 40 50 60

Center o f gravity, percent

Figure 51.- I n d i c a t i o n of e f f e c t of center-of-gravity p o s i t i o n on p i l o t opinion with and without advanced PACS engaged f o r holding f l i g h t c o n d i t i o n 17 i n moderate turbulence.

0 PILOT 1

- A PILOT 2

V PILOT 5

- Solid symbols

denote PACS o f f c

A

-

SATIS FACTO RY

I I I I 1

20 30 40 50 60 Center o f g r a v i t y , percent c' Figure 52.- I n d i c a t i o n of e f f e c t of center-of-gravity p o s i t i o n on p i l o t opinion with and without advanced PACS engaged for landing f l i g h t c o n d i t i o n 18 i n calm a i r .

0 PILOT 1

- A PILOT 2

1 0

V PILOT 5

- Solid symbols

denote PACS o f f

Pilot rating

SATISFACTORY

I I I I 1

20 30 40 50 60

Center o f gravity, percent E

Figure 53.- I n d i c a t i o n of e f f e c t of center-of-gravity p o s i t i o n on p i l o t opinion with and without advanced PACS engaged f o r landing f l i g h t c o n d i t i o n 18 i n moderate turbulence.

PACS O F F (BASELINE AIRCRAFT)

V PACS ON

P i l o t r a t i n g UNSATISFACTORY

v

SATISFACTORY

1 I I 1 I

20 30 40 50 60 Center o f g r a v i t y , p e r c e n t E Figure 54.- I n d i c a t i o n of e f f e c t of center-of-gravity p o s i t i o n on p i l o t opinion w i t h and without advanced PACS engaged f o r takeoff f l i g h t c o n d i t i o n 19 i n calm a i r .

PACS OFF (BASELINE AIRCRAFT)

v PACS ON

P i l o t r a t i n g UNSATISFACTORY

v

v v

v V

SATISFACTORY

I I I 1 1

20 30 40 50 60

Center o f g r a v i t y , p e r c e n t t

Figure 55.- I n d i c a t i o n of e f f e c t of c e n t e r - o f - g r a v i t y p o s i t i o n on p i l o t opinion with and without advanced PACS engaged f o r t a k e o f f f l i g h t c o n d i t i o n 19 i n moderate t u r b u l e n c e .

Base1 ine Unacceptable l a i r c r a J P i l o t r a t i n g S a t i s f a c t o r y I I I I 1 20 30 40 50 60

Center o f gravity, percent c'

Figure 56.- Summary of e f f e c t of c e n t e r - o f - g r a v i t y p o s i t i o n on p i l o t opinion, w i t h and without advanced PACS, f o r t h e c r u i s e and high- speed f l i g h t c o n d i t i o n s evaluated. Both calm a i r and t u r b u l e n t c o n d i t i o n s are included.

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25 39 40 41 42 43 Center o f gravity, percent c‘ Figure 58.- Comparison of p i l o t r a t i n g s between s i m u l a t o r and f l i g h t test a i r p l a n e f o r b a s e l i n e a i r p l a n e (PACS o f f , AACS o n ) . P i l o t i n g proce- d u r e s a r e same f o r both tests.

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Figure 63.- I n d i c a t i o n of n o n l i n e a r s t a b i l i z e r / c o l u m n g e a r i n g ( J - c u r v e ) .

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