The C-5A active lift distribution control system

THE C-5A ACTIVE LIFT DISTRIBUTION CONTROL SYSTEM William J . Hargrove Lockheed-Georgia Company An Active L i f t Distribution Control System (ALWS) has been developed f o r the C-5A as a meana t o reduce wing fatigue damage due t o maneuver and gust load The Lockheed-Georgia Company proposed a four phase program-8 the de- pources.

velopment and design of a prototype system, flight test evaluation, production pystem fabrication, and airplane fleet i n s t a l l a t i o n of t h i s Subsystem.

This paper describes the AIJ)CS development’and design tasks, ALDCS func- kional configuration, and r e s u l t i n g challenges encountered while accomplishing .the first phase of the program. These Casks are establishing system require- ments and c r i t e r i a and synthesizing a system meohanization t o meet the desired load a l l e v i a t i o n , s t a b i l i t y margins, f l i g h t safety, and f l y i n g q u a l i t i e s per- formance. R e s u l t s of t h e BI;Dcs development and prototype system flight simula- t i o n programs, and control law optimization including system s t a b i l i t y , handling q u a l i t i e s and structural load analyses a r e presented, along with concluding re- marks r e l a t i v e t o the system design integration.

An Active L i f t Distribution Control System (ALDCS) has been developed by Lockheed-Georgia Company under the direction of the USBF C-5 System Project Office t o reduce w i n g fatigue damage due t o incremental maneuver and g u s t load sources .

The ALDCS is an automatic f l i g h t control subsystem which provides redis- t r i b u t i o n of the wing spanwise l i f t through symmetrical deflection of the ailer- ons by inclusion of control inputs t o the e x i s t i n g lateral augmentation sub- system. The net a i l e r o n control effect, as i l l u s t r a t e d i n figure 1, is t o s h i f t the wing spanwise center of pressure inboard, thus reducing the incremental wing root bending momenta. Control input signals from the ALDCS are a l s o provided t o the inboard elevator surfaces through the e x i s t i n g p i t c h augnentation subsyetem f o r reduction of gust induced loads and t o compensate f o r the resulting deg- radation i n airplane handling q u a l i t i e s .

Although the primary objective of the ALDCS is t o reduce wing loads, min- imizing the effects on the basic aircraft S t a b i l i t y and handling qualities and 32 5 t minimizing changes t o e x i s t i n g hardware while u t i l i z i n g e x i s t i n g c o n t r o l s u r - faces were a l s o basic design goals.

SYMBOLS AM) SWSCRIPTS Normal a c c e l e r a t i o n load f a c t o r .

NZ P i t c h rate.

Flap p o s i t i o n .

Bending moment .

Aircraft

-

EQuivalent dynamic pressure.

m c e l e r a t i o n constant (32.2 ft/sec ) Mach number Ve EQuivalent Airspeed Centrhl A i r Data Computer.

CADC c . G O Center of g r a v i t y .

De c i b e 1 db, DB Elevator c a b l e position.

ECP Handling q u a l i t i e s , E . Q .

Hertz.

*Z One thcusand.

K Knots c a l i b r a t e d airspeed.

K C A S Maximum h o r i z o n t a l f l i g h t Mach number.

%

PLDCS Passive L i f t D i s t r i b u t i o n Control System, PSF Pounds p e r square foot.

PSD Power spectrum density.

Root mean square.

32 6 SYMBOLS BND SUBSCBIFTS (CONT'D) VD Maximum dive f l i g h t a i r s p e e d SL Sea level.

VE Maximum h o r i z o n t a l f l i g h t airspeed.

vss Vehicle systems simulator.

L.S. Wing s t a t i o n .

BACKGROUND I n 1969 t h e Lockheed-Georgia Company conducted a program t o e s t a b l i s h t h e f e a s i b i l i t y of reducing t h e maximum C-5 wing upbending loads during a c c e l e r a t e d f l i g h t maneuvers. This e f f o r t c o n s i s t e d of development, f a b r i c a t i o n and f l i g h t test of a prototype subsystem r e f e r r e d t o a s t h e Maneuver LDCS (MLDCS). This subsystem s u c c e s s f u l l y reduced t h e i n n e r wing bending moments f o r p o s i t i v e ac- c e l e r a t i o n s above 1.5g without degrading a i r p l a n e handling q u a l i t i e s . A s i m - p l i f i e d v e r s i o n of t h i s system known a s P a s s i v e L T S (PLDCS) t h a t involves manual a i l e r o n u p r i g through t h e t r i m system w m s d l e c t e d f o r t h e C-5 f l e e t in- corpor9tion.

I n 1972 a survey conducted by t h e C-5 S t r u c t u r a l Independent Review Team (IRT) of t h e p o s s i b l e Lrlethods t o improve t h e C-5 wing fatigue l i f e characteris- t i c s included a recommendation t o consider an a c t i v e c o n t r o l system t o iroprove f a t i g u e l i f e . A decision was made j o i n t l y by t h e USAF C-5 Systems P r o j e c t Office and Lockheed-Georgia Company t o develop and test such a subsystem which was t o be c a l l e d a n Active L i f t D i s t r i b u t i o n Control System. This subsystem was t o be incorporated i n a d d i t i c n t o t h e PLDCS. I n May of 1973 t h e ALDCS pro- gram was i n i t i a t e d f o r t h e development and test of a prototype subsystem with f l i g h t t e s t i n g t o be completed i n J u l y of 1974. The results of t h i s program w i l l a f f e c t n d e c i s i o n t o produce t h e ALDCS f o r C-5 f l e e t r e t r o f i t .

DENELOPMENT MElXODS A flow c h a r t of t h e t a s k s required i n t h e ALDCS development a r e shown i n figure 2. Each t a s k r e q u i r e d d i r e c t involvement of I number of engineering d i s c i p l i n e s t o i n s u r e adequate a s s i m i l a t i o n of design requirements and data and proper maintenance of development results and t h e s t a t u s of t h e subsystem mech- anization. One of t h e paramount challenges was t h e i n t e g r a t i o n of t h e a f f e c t e d design d i s c i p l i n e s i n t o a t o t a l design team since t h e functioning of t h i s ac- tive subsystem had such interwovqn influences on loads, handling q u a l i t i e s , sta- b i l i t y , s t r u c t u r a l dynamics, and e x i s t i n g C-5 f l i g h t c o n t r o l systems. Fortu- n a t e l y , t h e experience of t h e earlier LDCS program provided a n e x c e l l e n t design example.

Requirements and Criteria d e s i g n requirements and c r i t e r i a were P r i o r t o s y n t h e s i z i n g t h e ALDCS, c a r e f u l l y e s t a b l i s h e d a s a d e s i g n b a s e i n t h e areas of s t r u c t u r a l l o a d s , f l i g h t c o n t r o l subsystems, s t a b i l i t y , and h a n d l i n g qualities. These requirements are:

S t r u c t u r a l Loads -

O Continuous t u r b u l e n c e l c a d s a n a l y s i s shall r e s u l t i n RMS bending moments a t t h e wing r o o t (wing s t a t i o n 120) n o t exceeding 7% of t h e free a i r p l a n e values, O The continuous t u r b u l e n c e RMS t o r s i o n a t t h e wing r o o t shall n o t exceed t h e free a i r c r a f t values by more t h a n 5%.

O The ALDCS s h a l l n o t i n c r e a s e d i s c r e t e g u s t loads.

O The i n c r e m e n t a l r o o t bending momentb l o a d p e r g shall n o t exceed 7% of t h e f r e e a i r c r a f t values d u r i n g s t e a d y maneuvers, w i t h i n t h e normal climb, cruise, and d e s c e n t regime of t h e a i r c r a f t .

* The AIDCS shall produce no a i l e r o n i n p u t when t h e a i r c r a f t r e a c h e s t h e d e s i g n p o s i t i v e maneuver l o a d f a c t o r of 2.5.

The system s h a l l n o t be r e q u i r e d t o o p e r a t e i n t h e f l a p s down c o n f i g u r a t i o n s .

O The AIICCS s h a l l o p e r a t e i n t h e r e q u i r e d s p e e d / a l t i t u d e f l i g h t envelope as d e f i n e d i n figure 3 f c r f l a p s up c o n f i g u r a t i o n s .

F l i g h t C o n t r o l Bubsystems -

O Yhe kLDC3 skiall be designed t o fJfail-safelt concepts.

The system shall b e d dual channel a n a l o g deeign.

O Active c p e r a t i o n G f a i l e r o n s and i n b o a d e l e v a t o r s through e x i s t i n g augmentation and primary c o n t r o l a c t u a t o r s are required.

O ALECY w i l l i n t e r f g c e w i t h e x i s t i n g C-5 s e n s o r s t o t h e e x t e n t p o s s i b l e and w i l l b e compatible w i t h e x i s t i n g C-5 a u t o m a t i c f l i g h t con 'ir 01 subs ya tems e No ALDCS mslfunctiGn w i l l affect n o m i l p i t c h and lateral a ugmenta t i o n subs ystem opera ti ons .

The e x i s t i n g C-5 h y d r a u l i c s e r v o a c t u a t o r s f o r t h e a i l e r o n and i n b o a r d e l e v a t c r s w i l l b e used without m o d i f i c a t i o n s .

O The ALDCS w i l l b e required t o operate on a f f f u l l - t i m e basisff within t h e d e s i r e d f l i g h t envelope and design c r i t e r i a boundaries.

S t a b i l i t y -

The incorporation of t h e ALDCS shall not: O Induce adverse s t r u c t u r a l mode coupling.

O Change s i g n i f i c a n t l y t h e e x i s t i n g maneuvering f l i g h t handling q u a l i t i e s .

O Induce s i g n i f i c a n t degradation of e x i s t i n g f l u t t e r margins, O Induce adverse coupling with e x i s t i n g f l i g h t c o n t r o l systems.

O Induce l i m i t c y c l e tendencies.

The following A L N S minimum s t a b i l i t y margin and a t t e n t u i t i o n goals f o r each primary c o n t r o l surface feedback loop were e s t a b l i s h e d t o meet t h e above system s t a b i l i t y requirements. These. g o a l s were considered t o be realistic and a t t c i n a b l e throughout t h e ALDCS f l i g h t envelope.

O 0 Ground Test - 6 db g a i n margin and 45 degree phase margin.

O 0 F l i g h t mcdes through c o n t r o l mode natural frequencies - 6 db g a i n

margin and 45 degree phase margin.

O 0 F l i g h t modes above c o n t r o l mode n a t u r a l frequencies - 6 db

g a i n margin and i n f i n i t e phase margin.

There was a l s o a system a t t e n u a t i o n goal of 60 db/decade e s t a b l i s h e d f o r t h e s e modes.

Handling Q u a l i t i e s -

O There shall be no s i g n i f i c a n t change i n t h e e x i s t i n g C-5 handling q u a l i t i e s .

O The ALDCS s h a l l be disengaged p r i o r t o t h e aircraft s t a l l event.

O C r i t e r i a f o r t h e C-5 handling q u a l i t i e s w i l l be those characteristics e s t a b l i s h e d during previous f l i g h t test programs which concluded t h e C-5A f l y i n g q u a l i t i e s t o be acceptable i n a l l cases.

O Evaluaticn p i l o t comments w i l l be u t i l i z e d t o o b t a i n s a t i s f a c t o r y results.

Design Data Acquisition The t a s k of a c q u i r i n g necessary design data was s i m p l i f i e d by t h e exis- tence of a i r p l a n e math model data, f l i g h t c o n t r o l subsystem mechanizations, and f l i g h t test response c o r r e l a t i o n data from the o r i g i n a l C-5 design programs.

The major void i n design information existed i n t h e characteristics of t h e a i l - eron and e l e v a t o r hydraulic servoactuaters. This void existed due t o t h e C-5 a c t u a t o r s being designed and t e s t e d p r i m a r i l y f o r handling q u a l i t i e s evalua- t i o n s and automatic s t a b i l i z a t i o n of a i r c r a f t low frequency s h o r t period and dutch r o l l modes, whereas t h e A L E S would encompass t h e sensing and active c o n t r o l of higher frequency a e r o e l a s t i c mode dynamics, p o t e n t i a l l y up t o a f a c t o r of I 5 above t h e s h o r t period frequency.

not only included frequency re- These m i s s i n g a c t u a t o r characteristics sponse b u t h y s t e r e s i s , surface rates and t o l e r a n c e bands i n unloaded and load- ed conditions. They were d e s i r e d f o r a c t u a t o r s of various ages up t o a n ex- pected f u l l life. These data were obtained by tests on t h e C-5 Vehicle Systems bimulator of new and worn (over one l i f e span) s e r v o a c t u a t o r s , by tests per- formed by Bertea Corporation ( t h e servoactuator manufacturer), and by frequen- cy response f l i g h t tests on the C-5 aircraft.

A d e f i n i t e "design r i s k " was a s s o c i a t e d with t h e attempt t o u t i l i z e e x i s t i n g C-5 servoactuatore witt;out bandwidth o r a u t h o r i t y l i m i t modifications.

Computer Programs Various computer programs were prepared and c o r r e l a t e d with f l i g h t test data t o provide a n s l y t i c a l techniques f o r development of t h e A L E S mechaniza- t i o n , These programs using hybrid and d i g i t a l computation were:

O S t a b i l i t y - Eigenvalues and Frequency Response

O Dynamic Time H i s t o r y - Loads and Handling Qualities

O Accelerated S t a b i l i t y - S t i c k Force p e r 'gf

O PSD Loads The following a i r p l a n e and c o n t r o l system a n a l y t i c a l models were used f o r t h e above programs.

O Three degrees-of-freedom q u a s i - e l a s t i c l o n g i t u d i n a l a x i s dynamic models.

S i x degrees-of-freedoE q u a s i - e l a s t i c l o n g i t u d i n a l and l a t e r a l - d i r e c t i o n a l axes dynamic models.

O Eighteen mode a e r o e l a s t i c symmetric axis dynamic models, with first 15 f l e x i b l e mcdes and Wagner and Kussner functions and gust p e n e t r a t i o n e f f e c t s , O Two degrees-of-freedom q u a s i - e l a s t i c steady-state maneuver model.

O Eight mode a e r o e l a s t i c symmetric a x i s dynamic model with s i x most s i g n i f i c a n t f l e x i b l e modes.

L O Linear and non-linear f l i g h t c o n t r o l system s e r v o a c t u a t o r models.

A n a l y s i s and Synthesis Tasks The a n a l y s i s and s y n t h e s i s t a s k s involved t h e development of a n ALDCS mechanization t o meet t h e load a l l e v i a t i o n requirements and t h e determination on s t a b i l i t y , handling q u a l i t i e s and e x i s t i n g f l i g h t c o n t r o l of its effects subsystem performance. Feedback c o n t r o l laws were synthesized t o a t t a i n these requirements while minimiraing system coupling effects with undesirable struct- u r a l modes and r i g i d body dynamics.

Development of a r e a l i s t i c mechanization that could p o t e n t i a l l y be u t i l - i z e d as a guide f o r production design required indepth s t u d i e s t o e s t a b l i s h t h e system's t o t a l f l i g h t envelope f u n c t i o n a l c h a r a c t e r i s t i c s , s e n s o r t o l e r a n c e and response s p e c i f i c a t i o n s , and p r o t o t n e parameter a d j u s t c a p a b i l i t i e s . Also involved were t h e analyses t o determine e f f e c t s of subsystem failures, component t o l e r a n c e build-up, and s e r v o a c t u a t o r response c h a r a c t e r i s t i c s .

Other major a n a l y t i c a l s t u d i e s were accomplished t o determine t h e impact of t h e A L E 8 on handling q u a l i t i e s i n t h e following a r e a s : O Dynamic S t a b i l i t y O Maneuverability ( A t t i t u d e Control) O Accelerated S t a b i l i t y (St-ick Force p e r ' g f ) O R o l l Control Performance O Development of a n ALDCS Handling Q u a l i t i e s Command Nodel The i n t e r a c t i o n coupling e f f e c t s of t h e f l e x i b l e bending and r i g i d body response with t h e f l i g h t c o n t r o l system was thoroughly analyzed. This insured proper c o n t r o l law compensation f o r those f l i g h t conditions during which struct- u r a l modes and handling q u a l i t i e s tend t o degrade each other.

F l i g h t Simulaticn Tasks Tasks accomplished on t h e C-5 Developmental Handling Q u a l i t i e s Cockpit Simulator provided p i l o t e v a l u a t i e n s of t h e AI;DCS e f f e c t on t h e C-5 handling characteristics. The i n f l i g h t t a s k s performed by t h e e v a l u a t i n g p i l o t con- s i s t e d of t h e following: O Symmetric 'g' pull-ups O S t a b i l i z e d batik t u r n s and r o l l - o u t s Landing approach and f l a r e O Constant 'gf r o l l i n g pull-out maneuvers O Take-of f r o t a t i o n s O A t t i t u d e t r a c k i n g maneuvers during turbulence O A i r t r a f f i c c o n t r o l maneuvering (speed, a l t i t u d e and heading changes) The C-5 Developmental Handling Q u a l i t i e s Cockpit Simula t o r is real-time digital computatjon and a termi- six degrees-of-freedom s i m l a t i o n with a n a l l n a l m e a t e r r a i n medel visual system.

Vehicle Systerc Simulator (VSS) Tasks Simulation a f f o r d e d t h e c a p a b i l i t y t o v e r i f y t h e prototype design and system s a f e t y a s p e c t s i n f u n c t i o n a l operation checkout and f l i g h t c o n t r o l sub- system haraware i n t e g r a t i o n , This technique a l s o provided f i n a l p i l o t evalua- t i o n s u t i l i z i n g t h e prototype subsystem. P i l o t t a s k s were similar t o those ueed on t h e C-5 Developmental Handling Qualities Cockpit Simulation discussed previous 1 y .

The VSS incorporates a c t u a l C-5 mechanical and hydraulic f l i g h t c o n t r o l systems , moving s u r f a c e s and i n t e r f a c i n g automatic f l i g h t c o n t r o l subsystems.

The accomplishment of t h e a n a l y s i s , s y n t h e s i s , simulation and design tasks t o meet a restrictive schedule was paramount. F l i g h t test evaluations of t h e ALDCS were t o begin w i t h i n eleven months from c o n t r a c t u a l go-ahead, prototype Figure 4 illustrates t h e c r i t i c a l i t y of t h e design program schedule. With go-ahead occurrinq on 7 M y 1973, t h e subsystem design met t h e 90 percent func- t i o n a l r e l e a s e date of 21 Septeaber 1973. The final mechanization was r e l e a s e d on t h e scheduled aate of 7 November 1973 and t h e first prototype subsystem was I n f l i g h t made a v a i l a b l e f o r f l i g h t simulation e v a l u a t i o n on 7 January 1974.

system evaluations began on 15 Wirch 1974, approximately t e n months a f t e r go- ahead.

SYSTEN M E C M I Z A T I O N The ALDCS has been mechanized t o meet t h e demanding requirements placed on it and t o i n t e r f a c e with e x i s t i n g C-5 sensors, augmentation and servo- a c t u a t i o n s ubs ys tems Figure 5 provides a s i m p l i f i e d i n t e r f a c e diagram i n d i c a t i n g t h e integrti- t i o n of t h e AQCS computer w i t h t h e e x i s t i n g C-5 f l i g h t c o n t r o l subsystems.

The dual channel redundancy design ALDCS computer provides signals t o both t h e l a t e r a l augmentation series s e r v o t o c o n t r o l t h e a i l e r o n a c t u a t o r s sy~imetrical- l y and t h e p i t c h augmentation series servo t o a c t u a t e t h e inboard e l e v a t o r con- t r o l surfaces, Aileron a c t u a t o r s a l s o r e c e i v e commands from t h e pi.iots, auto- p i l o t , and passive LDCS. The p i l o t s and a u t o p i l o t command inboard a s w e l l as outboard e l e v a t o r s , Figure 6 shows t h e C-5 a i r p l a n e l o c a t i o n s of t h e ALDCS sensors and i n t e r f a c i n g computers and a f f e c t e d c o n t r o l s u r f a c e s , The wing mounted accelerometers a r e t h e only a d d i t i o n a l C-5 sensors required f o r ALDCS i n t e g r a t i o n .

The ALDCS mechanization c o n s i s t s of a n a r r a y of s e n s o r s , g a i n s , and f i l - Figure 7 is a block diagram of t h e AIJ3cS s i m p l i f i e d mechanization t o be ters.

used a s a roadmap during t h e i n s u i n g discussion of t h e i n d i v i d u a l components and system development changes. The a i l e r o n and e l e v a t o r channels w i l l be dis- cussed s e p a r a t e l y .

Aileron Channel .

The a i l e r o n c o n t r o l channel commands t h e r i g h t and l e f t a i l e r o n s symmet- r i c a l l y t o accomplish t h e maneuver load r e l i e f function, The feedback sensors u t i l i z e d f o r t h e a i l e r o n channel a r e provided by two v e r t i c a l accelerometer (W.S. .i186) and t h e l o c a t i o n s p e r wing, one l o c a t e d on t h e forward main beam (W.S. 1152) b o t h a t a n o u t e r wing location. The signals o t h e r on t h e r e a r beam frcm t h e s e accelerometers a r e averaged and compensated by smoothing f i l t e r s t h a t a t t e n u a t e s e n s o r noise and a i d i n t h e e l i m i n a t i o n of higher frequency wing v i b r a t i o n modes beyond t h e ALDCS c o n t r o l bandwidth.

The S t a b i l i t y and Load Control Gain and F i l t e r i n g p o r t i o n of t h e a i l e r o n channel provides t h e necessary compensation t o adequately phme t h e feedback accelerometer signals f o r c o n t r o l of t h e i n n e r wing bending moments and t o at- t a i n t h e design g o a l s t a b i l i t y margins, A p i l o t ' s feedforward comnand, acquired from t h e e x i s t i n g C-5 e l e v a t o r c a b l e p o s i t i o n (ECP) transducer, is summed with t h e compensated a c c e l e r a t i o n c o n t r o l s i g n a l t o provide a b r u p t maneuver load c o n t r o l . sig- The feedforward nal is f i l t e r e d f o r proper abrupt load a l l e v i a t i o n a i l e r o n command phase, These c o n t r o l signals a r e then gain scheduled by a i r c r a f t dynamic pres- sure from t h e C e n t r a l A i r Data Computer (CADC) t o provide proper s t a b i l i t y and load relief schedules and t o minimize handling q u a l i t i e s degradations through- o u t t h e a i r c m f t speed envelope. Cut-off f i l t e r s are provided t o preclude ad- verse coupling with higher frequency uncontrolled modes, The ALDCS a i l e r o n command s i g n a l is c o n t r o l l e d by boundary c o n t r o l l o g i c which contains t h e c i r - c u i t r y t o disengage t h e signal when exceeding f l i g h t boundaries where t h e ALDCS is not required. These o p e r a t i o n a l boundary c o s d i t i o n s a r e when t h e f l a p s a r e lowered, t h e S t a l l i m i t e r subsystem is a c t i v a t e d , t h e a i r p l a n e exceeds maximum h o r i z o n t a l airspeed/Mach (350 KCBS / I 1 = 0.825), and! when t h e a i r p l a n e load 1.9 g * s . These l o g i c c o n t r o l s i g n a l s a r e obtained from e x i s t i n g f a c t o r exceeds aircraft subsystems d t h t h e exception of load f a c t o r . This s i g n a l is derived from ALDCS wing and fuselage accelerometers t o c l o s e l y r e p r e s e n t aircraft C.G.

a c c e l e r a t i o n . The system i s a u t o m a t i c a l l y re-engaged as t h e a i r c r a f t re-enters t h e ALDCS o p e r a t i The a i l e r o n command s i g n a l is then l i m i t e d 1 envelope.

and i n t e r f a c e d with t h e l a t e r a l SAS a i l e r o n series servoactuators.

Elevator Channel The e l e v a t o r channel c c n t a i n s t h r e e s e n s o r s , two active feedback param- eters and one feedforward command. Airplane p i t c h r a t e , a s provided by t h e p i t c h SAS r a t e g y r o , is u t i l i z e d t o augment t h e a i r p l a n e s h o r t period damping and thereby a l l e v i a t e t h e e x c i t a t i o n of s h o r t period induced gust loads and t o r e s t o r e t h e handling q u a l i t i e s degraded by the a i l e r o n p i t c h i n g moment e f f e c t s .

An e x i s t i n g C-5 a u t o p i l o t subsystem v e r t i c a l accelerometer mounted i n t h e forward fuselage provides a d d i t i o n a l gust load c o n t r o l and compensates t h e air- plane p i t c h response c h a r a c t e r i s t i c s .

A feedforward s i g n a l , p i l o t ' s eleviitor i n p u t ccmmnd, is r e q u i r e d t o re- store t h e a i r p l a n e maneuverability and a c c e l e r a t e d s t a b i l i t y ( s t i c k f o r c e p e r 'g') c h a r a c t e r i s t i c s t'hat a r e s i g n i f i c a n t l y degraded by t h e load c o n t r o l sig- nhls. 'This s i q n e i is scheduled a s a f u n c t i o n of a i r p l a n e dynaniic p r e s s u r e tlnd oompensated by ti comand model f i l t e r t o provide the proper system handling q u a l i t i e s throughout t h e o p e r a t i o n a l envelope.

These three s i g n a l s , p i t c h rate, normal a c c e l e r a t i o n and p i l o t e l e v a t o r command i n p u t a r e summed and a g a i n scheduled with dynamic pressure and passed through system cut-off f i l t e r s f o r s t a b i l i t y and g u s t load c o n t r o l phasing.

The e l e v a t o r signal is provided t o a boundary c o n t r o l l o g i c network that disengages t h e signal under t h e 9itL.e conditions as t h e a i l e r o n channel.

This c i r c u i t includes a fade-out f i l t e r t o minimize a c c e l e r a t i o n t r a n s i e n t s r e s u l t i n g from a b r u p t s u r f a c e disengagement. The command signal is then l i m i t - ed and i n t e r f a c e d with t h e p i t c h augmentation subsystem.

Sys tem Changes The f u n c t i o n a l development of t h e AUCS provided t h e u s u a l subsystem c h n g e s which caused agonizing p e r t u r b a t i o n s i n t h e design of t h e prototype subsystem hardware. These modifications of t h e mechanization f a l l i n t o t h e f o l l o v i n g major areas: O Wing accelerometer l o c a t i o n O Operational f l i g h t envelope

O Subsystem s t a b i l i t y - f i l t e r compensation

Wing Accelerometer Location -

Trade s t u d i e s were accomplished t o determine t h e number and l o c a t i o n s of The C-5 w i n g l o c a t i o n s acceptable t o s e n s o r t h e wing mounted accelerometers, i n s t a l l a t i o n are e s s e n t i a l l y l i m i t e d t o t h e f r o n t and rear beams due t o f u e l tank locations. Original s t u d i e s of t h e wing accelerometer l o c a t i o n i n d i c a t e d t h e need f o r two sensors p e r wing, one on the mid-wing a f t main beam and one i n t h e o u t e r wing t o be mounted on t h e f r o n t main beam. These s e n s o r s were t o pro- v i d e "high gain" feedback c o n t r o l of t h e f i r s t and second wing f l e x i b l e bending modes. Additional s t u d i e s proved t h e "high gain" system design t o be impracti- c a l and t h a t t h e second wing mode d i d not c o n t r i b u t e s i g n i f i c a n t l y t o g u s t loads, t h u s t h e mid-wing s e n s o r l o c a t i o n s were eliminated, This removal and r e l o c a t i o n of t h e o u t e r wing f r o n t beam accelerometer t o t h e r e a r beam, caused a favorable i n f l u e n c e on subsystem s t a b i l i t y and allowed t h e maneuver and gust load c o n t r o l functions t o be simply combined with reduced gains i n t h e a i l e r o n channel .

L a t e r a second accelerometer was placed i n . i t s present l o c a t i o n on t h e f r o n t beam t o mjninize a 48 r a d i a n p e r second o u t e r wing coupling mode t h a t , i n t u r n , increased t h e s t a b i l i t y margins and eliminated a n o r i g i n a l need f o r com- p l e x notch filtering. Figure 8 i n d i c a t e s t h e effect of single and blended mul- t i p l e accelerometer l o c a t i o n s on t h e ALDCS a i l e r o n closed loop frequency re- sponse. The r e a r bean sensor p e r n i t s a n amplitude g a i n peak of 7 db a t 48 rad- i a n s p e r second, The a d d i t i o n of t h e f r o n t beam accelerometer adequately blended with t h e r e a r accelerometer t o simulate t h e c r i t i c a l 48 radians p e r sec- ond node l o c a t i o n , reduces t h i s peak t o approximately one db. An e x t e r n a l wing accelerometer i n s t a l l a t i o n was considered; however, t h e a d d i t i o n a l c o s t and a s s o c i a t e d design r i s k s eliminated t h i s desiga.

Operational F l i g h t Envelope -

To i n s u r e proper f u n c t i o n i n g of t h e ALES throughout t h e required f l i g h t envelope, g a i n scheduling and subsystem disengagement are necessary. The orig- i n a l subsystem mechanization r e q u i r e d complex nonlinear scheduling i n t e r f a c e s with t h e c e n t r a l a i r data computer. A s t h e development progressed t h e s e sched- ules were s i m p l i f i e d t o l i n e a r functions. Also a n o r i g i n a l ALDCS requirement f o r f l a p s down operation was d e l e t e d , thereby e l i m i m t i n g t h e need f o r f l a p g a i n schedules and automatic landing i n t e r f a c e s . These functions were replaced by a f l a p s down boundary l o g i c c o n t r o l disengagement signal. Another change n e c e s s i t a t e d by f l i g h t envelope requirements was t h e development of a f a d e r t o smoothly disengage t h e subsystem when t h e a i r p l a n e exceeds t h e boundary condi- t i o n of noma1 a c c e l e r a t i o n , s t a l l approach, and speed/Mach. Acceptable hand- l i n g q u a l i t i e s were a t t a i n e d a t t h e s e boundary conditions with a simple t m c k and fade-out c i r c u i t i n t h e e l e v a t o r channel.

Subsystem S t a b i l i t y - F i l t e r Compensation -

The problem of subsystem s t a b i l i t y followed t h e mechanization development throughout t h e program i n both t h e a i l e r o n and e l e v a t o r channels. P e r t u r b a t i o n s i n t h e mechanization occurred c o n t i n u a l l y with t h e a l t e r i n g of f i l t e r compensa- t i o n . Major modifications were t h e e l i m i n a t i o n of o r i g i n a l design notch f i l t e r - i n g and t h e a d d i t i o n s of simple f i r s t order s t a b i l i t y f i l t e r s t o improve a 2.4 Hertz s t a b i l i t y margin i n t h e a i l e r o n channel and t h e i n c l u s i o n of a low,pass s t a b i l i t y and f u s e l a g e l o a d c o n t r o l phasing f i l t e r i n t h e e l e v a t o r channel.

S'UBSYSTm PERFORMANCE The kLDCS a s mechanized has provided t h e load a l l e v i a t i o n requirements without s i g n i f i c a n t l y i n t e r f e r i n g with a i r p l a n e s t a b i l i t y , handling q u a l i t i e s , a u t o p i l o t performance o r f l i g h t s a f e t y . The performance, a s discussed i n t h e follo-xing paragraphs, has been obtained u t i l i z i n g e x i s t i n g C-5 a i l e r o n and in- board e l e v a t o r c o n t r o l s u r f a c e s , without modification t o t h e primary servo- a c t u a t o r s .

Ijlaneuver and G u s t Loads The r e s u l t i n g ALDCS maneuver and gust loads performance data a r e summariz- ed i n f i g u r e s 9 through 12. These perfomance results i n d i c a t e that t h e incre- mental load r e l i e f meets t h e design c r i t e r i o n of a t t a i n i n g 30 percent bending moment reduction a t t h e wing r o o t , while not exceeding five percent t o r s i o n a l i n c r e a s e during continuous turbulence f l i g h t .

The s t e a d y maneuver incremental wing r o o t load p e r ( g c r a t i o s of ALDCS on t o t h e b a s i c a i r c r a f t are presented i n figure 9, This summary covers a t y p i c a l cruise payload c o n f i g u r a t i o n of 160,000 pounds and 94,250 pounds of With ALDCS o p e r a t i v e , t h e s e fuel f o r a v a r i a t i o n of Mach number and a l t i t u d e .

The b a s i c de- results i n d i c a t e i n n e r wing load reductions of 32 t o 52 percent.

s i g n g o a l r a t i o of 0.70 was achieved for a l l c o n f i g u r a t i o n s within t h e normal C-5 operationcll speed, a l t i t u d e and payload f l i g h t envelopes.

A t y p i c a l wing r o o t bending moment g u s t frequency response and PSD output spectrum a r e shown f o r t h e a i r p l a n e with and without AZ;DCS i n figure 10. The ALDCS gust output spectrum is s i g n i f i c a n t l y reduced from that of t h e free a i r - plane, The t r a n s f e r f u n c t i o n shows that t h e first v e r t i c a l wing bending mode amplitude a t O e 9 Hx is reduced t o approximately one-half with AmCS operative.

ALDCS c o n t r o l bandwidth encompasses p r i m a r i l y t h e s h o r t period and first w i n g bending a i r p l a n e modes through t h e frequency of approximately one Hz.

Wing r o o t RT4.S bending and t o r s i o n a l moment r a t i o s o f ALDCS on t o ALDCS o f f , f o r a v a r i a t i o n of a l t i t u d e and Mach n m b e r s , Eire giver- i n f i g u r e s 11 and 32. The ALES reduces t h e WIS wing r o o t bending moments by 30 t o 50 percent of t h e free a i r p l a n e without i n c r e a s i n g t h e t o r s i o n a l moment by more m a n t h e de- s i g n g o a l of 5 percent f o r any case. The t o r s i o n a l moment i s less than that of t h e b a s i c a i r p l a n e f o r t h e m a j o r i t y of f l i g h t cases investigated.

Loads criteria f o r discrete g u s t were only s p e c i f i e d t o the e x t e n t that t h e ALDCS shall not i n c r e a s e t h e basic a i r p l a n e discrete gust loads. Seven f l i g h t c a s e s , similar t o those presented i n figure 9, were analyzed f o r t h e "1-cosine" d i s c r e t e g u s t model. The wing r o o t bending inoclent peaks, with ALDCS on, were reduced t o values ranging from 78 t o 52 percent sf t h e free a i r - plane f o r t h e c r i t i c a l gust frequency wavelengths.

Although no criteria were e s t a b l i s h e d f o r abrupt maneuver load c o n t r o l , analyses were conducted t o e v a l u a t e t h e e f f e c t of ALDCS on abrupt maneuver load c o n t r o l characteristics. These analyses, conducted f o r seven s e l e c t e d f l i g h t conditions, revealed that t h e load reduction was from one t o seventeen percent depen6ing upon t h e p a r t i c u l a r f l i g h t case response c h a r a c t e r i s t i c s . I n a n ef- f o r t t o improve t h i s performance, a f e e d f o m a r d p i t c h c o n t r o l command signal Results of a n a l y s i s w i t h the a i l e r o n was provided t o t h e a i l e r o n channel.

feedforward s i g n a l f o r a selected number of c r u i s e f l i g h t conditions i n d i c a t e d t h a t t h e wing r o o t bending moments could be reduced by 30 percent of t h e basic a i r p l a n e . This feedforward signal mechanization was then incorporated i n t h e A L E S prototype system f o r f l i g h t test evaluation.

Fuselage loads performance was monitored during t h e continuous turbulence a n a l y s i s t o e v a l u a t e t h e effects of ALDCS. Results i n d i c a t e d t h a t t h e a f t fuselage bending moments were being increased up t o 15% over the f r e e a i r p l a n e .

4 low-pass f i l t e r was added t o t h e e l e v a t o r channel that increased s t a b i l i t y margins and decreased t h e a f t body fuselage bending moments below those of t h e b a s i c a i q l a n e f o r a l l cases.

S t a b i l i t y The concern t h a t t h e ALNS possess adequate s t a b i l i k y g a i n and phase margins caused considerable design optimization a t t e n t i o n .

This require- ment was accomplished a s i n d i c a t e d i n figures 13 and 14. These g a i n and phase margins r e p r e s e n t a series of reserve f u e l loading cases that i n h e r e n t l y pos- sess t h e minimum a i l e r o n loop s t a b i l i t y . The e l e v a t o r loop s t a b i l i t y is mini- mum with a high fuselage cargo loading, b u t i n no cases were t h e phase margins less than 64 degrees o r t h e g a i n margins less than 10 db.

The g a i n margins f o r both a i l e r o n and inboard e l e v a t o r channels a r e w e l l above t h e minimum requirement of 6 db f o r a l l cases.

The only f l i g h t case found t o have t h e minimum phase margin of 45 degrees was that of a high a l t i t u d e , reserve f u e l and maximum ALDCS o p e r a t i o n a l Mach number of 0,825. A s f u e l weight is added t o t h i s configuration, t h e a i l e r o n g a i n and phase margins a r e increased.

A f u e l c a p a c i t y of approximately 30 percent f o r t h i s case has a g a i n margin of 16.5 db and a phase margin of 62 de- grees .

Ninimum a i l e r o n g a i n and phase margins f o r a l l configurations occur a t frequencies between 33 t o 53 r a d i a n s p e r second and between 6 and 17 r a d i a n s p e r second, respectively. The minimum e l e v a t o r g a i n margins f o r a l l configurations occur a t frequencies between 6 and 8.6 r a d i a n s p e r second with t h e phase margin frequencies ranging from 0.6 t o 3.41 r a d i a n s p e r second.

Handling Qualities 1 ! b a s i c ALDCS design goal was that t h e r e would be no s i g n i f i c a n t degrada- t i o n of t h e e x i s t i n g C-5 handling q u a l i t i e s . Extensive a n a l y s i s and pilot-in- the-loop f l i g h t simulation evaluations were accomplished t o i n s u r e that t h e ALDCS was compatible with t h e C-5 f l y i n g characteristics.

The handling q u a l i t y a r e a s of most concern that could be a l t e r e d o r sig- n i f i c a n t l y degraded by t h e SLUCS were: O Maneuver response O Accelerated s t a b i l i t y - s t i c k f o r c e p e r ?g' O Short period s t a b i l i t y O Phugoid s t a b i l i t y O Roll performance Development of a n ALDCS e l e v a t o r channel p i l o t command model f i l t e r was e s s e n t i a l t o r e t a i n t h e C-5 maneuver response and s t i c k f o r c e p e r ?g* character- ALDCS s h o r t period and phugoid s t a b i l i t y effects were compensated by i s t i c s .

appropriate system g a i n and f i l t e r parameter optimization. The r o l l performance e f f e c t was g r e a t l y reduced by using t h e minimum a i l e r o n channel g a i n schedule re- quired f o r maneuver load control.

The time h i s t o r i e s shown i n figure 15 present t h e effects of ALDCS on a i r - plane normal C.G. a c c e l e r a t i o n and p i t c h rate responses f o r a t y p i c a l pull-up maneuver. The i n p u t f o r c i n g f u n c t i o n f o r t h i s maneuver is a constant c o n t r o l f o r c e rate and hold a f t e r 3 seconds. This figure shows that t h e time t o o b t a i n steady-state maneuver values a r e p r a c t i c a l l y t h e same with ALDCS off o r on. The only d i f f e r e n c e w i t h ALDCS on is that of a s l i g h t undershoot i n peak p i t c h rate and a s l i g h t rise time improvement t o a c q u i r e t h e s t e a d y s t a t e response. Simu- l a t o r p i l o t ev8luations of t h e s e type maneuvers i n d i c a t e d no degradation i n a i r - plane handling q u a l i t y performance.

The l o n g i t u d i n a l axis accelerated maneuvering s t a b i l i t y , a s shown i n fig- The ALDCS s t i c k f o r c e p e r ure 16, was not s i g n i f i c a n t l y impaired by t h e ALDCS.

lg' values a r e well within t h e demonstrated boundaries of previously e x t r a c t e d f l i g h t test d a t a w i t h o u t ALNS. The s t e a d y - s t a t e e l e v a t o r command model g a i n w a s optimized t o provide i d e n t i c a l s t i c k f o r c e p e r 'gf characteristics f o r mid C.G. f l i g h t c o n f i g u r a t i o n s w i t h ALDCS on o r o f f . P i t c h column f o r c e r e q u i r e d t o hold a g i v e n a c c e l e r a t i o n f o r forward and a f t C.G. w i t h ALDCS on are s l i g h t - r e s p e c t i v e l y from t h e b a s i c a i r p l a n e . The s i m u l h t - l y decreased and i n c r e a s e d , o r p i l o t s were unable t c d i s t i n g L i s h t h e s e ALDCS characteristics from t h o s e of t h e b a s i c a i r p l a n e .

No s h o r t p e r i o d and phugoid s t a b i l i t y damping d e g r a d a t i o n 'was n o t i c e d d u r i ng t h e devefopzent f l i g h t s i m u l a t i o n program and a n a l y t i c a l results, as p r e s e n t e d i n figures 17 and 18, confirm t h e p i l o t e v a l u a t i o n s .

b a s i c C-5 s h o r t p e r i o d dalnping r e q u i r e m m t f e r t h e cruise c o n f i that it s h l l dan:p t o one-tenth arrplitude w i t h i n one c y c l e . This requirement has been exceeded by the b a s i c a i r p l a n e and is s l i g h t l y g o r e damped w i t h AZDCS opera t ive b The phugoid mode, a s shown i n figure 18 e x h i b i t s s u f f i c i e n t s t a b i l i t y , a l t h o u g h t h e frequency is s l i g h t l y reduced from that o b t a i n e d from previous The o r i g i n a l C-5 phugoid s t a b i l i t y re- f l i g h t test d a t a c o r r e l a t i o c s t u d i e s .

quirement was t h s t i f t h e periGd is less t h a n 15 seconds, t h e n t h i s mode shall be a t least n e u t r a l l y s t a b l e . Data shown i n figure 18 does not i n d i c a t e any f r e q u e n c i e s w i t h p e r i o d s less t h a n a p p r c x i n a t e l y 65 seconds w i t h ALDCS on.

There was a concern e a r l y i n t h e development program, that t h e ALDCS wculd reduce t h e C-5 r o l l p e r f o m a n c e . This concern a r o s e p r i m a r i l y due t o symmetrical c o n t r o l of a i l e r o n s w i t h high a c c e l e r a t i o n g a i n s t h a t may cause a c t u a t o r s a t u r a t i o n . T h e o r e t i c a l l y , t h e r e i s a s l i g h t decrease i n a v a i l a b l e r o l l power due t o a i l e r o n s a t u r a t i o n ; however, f l i g h t s i a u l a t i o n e v a l u a t i o n s d e t e r n i n e d t h a t t h e p i l o t s c c u l d n o t d e t e c t t h i s degradation. For maximuro r o l l rate maneuvers, t h e s i m u l a t i o n p i l o t s wc.uld mask BT;DcS e f f e c t s b y commanding a i l e r o n s f o r a s l i g h t a d d i t i o n a l amount of time t o perform t h e same maneuver.

The f o l l o w i n g h a n d l i n g q u a l i t i e s p i l o t opinions were a t t a i n e d d u r i n g t h e ALDCS development a n d p r o t o t y p e Vehicle System S i m u l a t i o n Program.

O Ease of trimming t o new speed - no degradation.

O Phugoid and s h o r t p e r i o d damping - no d e p a d a t i o n .

O Roll power - no n o t i c e a b l e degradation.

O Stick f o r c e p e r 'gt characteristics - no degradation.

O ALDCS fails t o s w i t c h o f f - no d e g r a d a t i o n w i t h f l a p extension.

A t o t a l of s i x p i l o t s , i n c l u d i n g two from t h e A i r Force, flew t h e develop- ment s i m u l a t o r w i t h ALDCS on and o f f .

The effect of ALDCS on t h e C-5 h a n d l i n g qualities can be summarized by t h e fact that t h e s i m u l a t i o n p i l o t s were unable t o d e t e c t whether t h e ALDCS was on o r o f f d u r i n g e v a l u a t i o n s w i t h i n t h e normal f l i g h t envelope.

Autopilot Compatibility The ALDCS i s designed t o be engaged during a u t o p i l o t operation, thus con- s i d e r a b l e design a t t e n t i o n was d i r e c t e d t o subsystem compatibility. This de- velopment was concentrated on a u t o p i l o t i n t e r f a c e s t a b i l i t y , response perform- ance and f l i g h t , s a f e t y . It was found necessary t h a t t h e ALDCS e l e v a t o r channel c o n t r o l signals of p i t c h rate and p i l o t ' s feedforward command be disengaged during a u t o p i l o t operation. Elimination of t h e s e c o n t r o l s i g n a l s during auto- p i l o t operation improved t h e s t a b i l i t y margins and minimized c o n t r o l wheel s t e e r i n g s e n s i t i v i t y , and a i r p l a n e a c c e l e r a t i o n response due t o a n a u t o p i l o t hardover f a i l u r e .

R e s u l t s i n d i c a t e no apparent degradation i n e i t h e r s t a b i l i t y o r response of the a u t o p i l o t a t t i t u d e , a l t i t u d e hold o r c o n t r o l wheel s t e e r i n g modes. The effect of ALDCS on a u t o p i l o t a l t i t u d e hold and r o l l performance was i n s i g n i f i - c a n t with t h e a i r p l a n e achieving l i m i t bank a n g l e w i t h minimum a l t i t u d e l o s s .

P i t c h a u t o p i l o t hardover f a i l u r e s , with ALES engaged, y i e l d a normal a c c e l e r - a t i o n response s l i g h t l y below t h a t of t h e b a s i c a i r p l a n e and a u t o p i l o t .

F l i g h t S a f e t y To i n s u r e t h a t ALDCS f a u l t s would not a f f e c t t h e C-5 f l i g h t s a f e t y , f a i l u r e effects a n a l y s i s and prototype vehicle system simulation evaluatiorw were accomplished. These f a i l u r e s involved l o s s of ALDCS sensor s i g n a l s , l o s s of AI;DCS, hardovers of sensors and channel loop commends, g a i n schedule f a i l - ures, and various s t a b i l i t y augmentation subsystem (SAS) f a i l u r e s that could be effected by t h e ALDCS, The a n a l y s i s and s i m u l a t o r t e s t i n g i n d i c a t e s that t h e ALDCS adequately meets t h e s a f e t y requirements and c r i t e r i a . There i s s u f f i c i e n t subsysten s t a b i l i t y should any one sensor o r channel i n t h e ALDCS be l o s t . Neither of t h e v a r i o u s SAS f a i l u r e s were worse than those of t h e e x i s t i n g system; however, some f a i l u r e d e t e c t i o n and a i r p l a n e t r a n s i e n t improvement was e x h i b i t e d with A L E S operative.

R e s u l t s of t h e s e s t u d i e s i n d i c a t e d that t h e r e were no s i n g l e ALDCS o r automatic f l i g h t c o n t r o l i n t e r f a c e failures that caused p i l o t concern, Bde- quate f a u l t d e t e c t i o n and annunciation of t h e s e failures was apparent t o t h e p i l o t . The ALDCS has met t h e basic s a f e t y c r i t e r i a and is acceptable f o r prototype development f l i g h t t e s t i n g .

Ride Control No r e a l attempt was made during t h e ALES development program t o improve levels t h e C-5 r i d e c o n t r o l characteristics.

The p i l o t ' s s t a t i o n a c c e l e r a t i o n were monitored thrcughout t h e continuous turbulence a n a l y s i s however, t o in- sure t h a t t h e r i d e q u a l i t y was not a d v e r s e l y affected by t h e ALDCS, R e s u l t s of t h e s e a n a l y s e s r e v e a l e d t h a t t h e p i l o t ' s a c c e l e r a t i o n levels were reduced by 7 t o 35 p e r c e n t throughout t h e C-5 ALDCS f l i g h t envelope, CONCLUDING RENARKS g p r o t o t y p e maneuver and g u s t l o a d a l l e v i a t i o n c o n t r o l system has been s u c c e s s f u l l y developed, f a b r i c a t e d and s i m u l a t o r t e s t e d meeting demanding schedules a n d f u n c t i o n a l requirements. It is f e l t that a major a i r p l a n e ac- tive c o n t r c l subsystem i n t e g r a t i o n accomplishment has been a c h i e v e d by i n t e - g r a t i n g t h e ALDCS i n t o t h e t o t a l C-5 Vehicle System w h i l e m a i n t a i n i n g compat- i b i l i . t y w i t h e x i s t i n g a i r p l a n e s t a b i l i t y , h a n d l i n g qualities, and f l i g h t con- t r o l subsystems. Tiihile no s p e c i f i c requirements were e s t a b l i s h e d , it is note- worthy t h a t t h e ALDCS has f a v o r a b l y i n f l u e n c e d the p i l o t s t a t i o n a c c e l e r a t i o n s ( r i d e c o n t r o l ) , a b r u p t maneuver l o a d c o n t r o l , a f t fuselage g u s t l o a d s , and some f a i l u r e d e t e c t i o n levels of i n t e r f a c i n g a u t o m a t i c f l i g h t c o n t r c l subsystems.

Now B S t h e Active L i f t D i s t r i b u t i o n C o n t r o l Subsystem e n t e r s development f l i g h t test e v a l u a t i o n s t h e development e n g i n e e r s and t h e d e s i g n personnel frcm t h e s f f e c t e d d i s c i p l i n e s c o n f i d e n t l y f e e l t h a t t h e subsystem w i l l c o n t i n u e t o meet its d e s i g n o b j e c t i v e s , These d e s i g n e n g i n e e r s have i n t e g r a t e d t h e i r e x p e r i e n c e , development t e c h n i q u e s , and computer programs t o meet a v e r y re- s t r i c t i v e schedule. The success of t h i s development program c a n l a r g e l y b e a t t r i b u t e d t c t h e f a c t t h a t t h e p r o t o t y p e systems were p r i m a r i l y designed and f a b r i c a t e d w i t h i n t h e structure of one company.

It is planned, i f s u c c e s s f u l i n T l i g h t t e s t , t h a t t h e fiLECS b e produced and r e t r o f i t t e d t o The C-5 fleet. This A L E S developnetit program, even thr/ugh i t i s n c t a t r u e p r e l i m i n a r y design a p p l i c a t i o n of a c t i v e c o n t r o l t e c h m l o g y , hes provided a n understanding of t h e problems f a c i n g t h e d e s i g n e r and t h e ex- p e r i m s e and d e s i g n t e c h n i q u e s needed t o a p p l y active cGntrols t o a i r c r a f t of t h e f u t u r e .

t t

I I

CENTER-0 F-PRESSURE WING SEMISPAN Figure 1.- E f f e c t of a i l e r o n c o n t r o l on C-5 wing l i f t d i s t r i b u t i o n .

MODELS ALDCS MECHANIZATION 0 STABILITY DESIGN REQUIREMENTS SIMULATOR - FINAL EVALUATION A N D FAILURE EFFECTS TESTING Figure 2,- C-5 BI;DCS development program flow diagram.

Figure 3.- C-5 ALDCS speed altitude envelope.

PROTOTYPE DESIGN AND FABRICATION FLIGHT SIMULATION FLEET UPDATE Figure 4.- C-5 aLDCS development program schedule milestones .

, PILOT AND OUTBOARD

I AUTOPILOT l~-~l ELEVATOR I

COMMAI ID ACTUATORS

i'"lo PITCH

SAS - ELEVATOR SAS SERIES ACTUATORS SENSORS COMPUTER SERVO

----------- ----._-----

COMPUTER INTERFACE b ---------_.------------ I

m o SENSORS

AND PLDCS COMMANDS Figure 5.- ALDCS f l i g h t control system interface diagram.

MAJCR AIRCRAFT INTERFACE SUB SYSTEMS & I A ALDCS COMPUTER B CADC COMPUTER C PITCH SAS COMPUTER

'

D YAWLATERAL sAS COMPUTER LEVATOR E STALLIMITER :ABLE P 'OSITION (ECP) F AUTOPILOT

c

W I N G ROOT ( W . S . 120) ACCELEROMETER S AILERON 1186) Figure 6.- C-5 ALDCS major airplane components interface.

PITCH FILTER

G A I N . AILERON

--. .- -3NTROL I I SCHEDULE CUT-OFF -y 1 G A I N A N D FILTERS

ACCELERATION L

(AILERON CHANNEL) * SCHEDULED GAINS - DYNAMIC PRESSURE ACCELERATION LEFT WING REAR BEAM Figure 7.- C-5 ALDCS simplified functional block diagram, REAR-BEAM ACCELERATION m FRONT AND REAR BEAM n BLENDED ACCELERATION I z o Q 2 -5 v) -10 -15 3 IO 30 FREQUENCY - RADIANS P E R SECOND Figure 8,- C-5 ALDCS aileron closed-loop frequency response.

CARGO WEIGHT 160,OOO L0 Wx/G (ALDCS) ALTITUDE MACH

(FEET) 1 WX/G (NO ALDCS)

SEA LEVEL 0 . 3 0 0.55 SEA LEVEL 0 . 4 0 0.48 SEA LEVEL 0.50 0.52 12,000 0.40 0.64 12,000 0.50 0.58 12,000 0.60 0.55 1 I 26,000 0.60 0.67 0.66 26,000 0.70 0.65 26,000 0.75 40,000 0.72 0.68 40,000 0.77 0.63 40,000 0.82 0.61 s

FIGURE 9. - C-5 ALDCS WING ROOT BENI)IBG MOMENT

RATIOS - STEADY MILNEWER

o FUEL WT = 94,250 LB o CARGO WT = 160,000 LB

-

FREE AIRCRAFT o MACH=0.400 - - - ALDCS o ALT = 1500 FT I I 1 a X m A i - I z - I - u z U Dz w U m Z Q Dz c I I I 1 2 3 FREQUENCY - Hz FREQUENCY - Hz

Figure 10.- C-5 AI;DCS wing r o o t bending moment -

1 f p s RMS vertical g u s t , FUEL ’AEIGHT 94,250 LB CARGO WEIGHT 160,000 LB I I I I ALTITUDE SEA LEVEL

- - - 1,500 FEET

- - - 15,000 FEET

- - - - - - - 40,000 FEET I I I I c 0 0.2 0.4 0.6 0.8 0 MACH NUMBER,

Y i g u r e 11. - C-5 BLDCS wing r o o t g u s t RMS

bending moment r a t i o .

FUEL WEIGHT 94,250 LB CARGO WEIGHT 160,000 LB

---

Y U

I2

I

c

I- L Q 0.8 cr Q 3 ALTITUDE SEA LEVEL

- _ _ 1,500 FEET

- - - 15,000 FEET

_ _ _ _ - - 40,000 FEET

I I I I I 0 0.2 0.4 0.6 0.8 1 .o 30 I I I I * RESERVE FUEL LOADING 0 ELEVATOR CLIMB STALL a AILERON - 4oK 20-

. . I I

~ G A I N < MARGIN - dB MH -2% - - I I , I . O b 100 200 300 400 DYNAMIC PRESSURE, - PSF Figure 13.- C-5 aLDCS s t a b i l i t y g a i n margins.

0 RESERVE FUEL LOADING 0 ELEVATOR 0 MINIMUM PHASE MARGINS A AILERON PHASE MARGIN - DEG .

80 - -- 40 - .~ O O 100 200 300 400 500 DYNAMIC PRESSURE, ;I - PSF F i g u r e 14.- C-5 BLDCS s t a b i l i t y phase margins.

0 240 KCAS

* M I D C G - ALDCS OFF

0 ELEVATOR RAMP/HOLD INPUT 0 ALDCS ON I I I I i I I I I i -0 2 4 6 8 10 TIME (SECONDS) h U Lu

x

w 2 w

t 5

w n W w I-

a

e 1 I U != 0 2 4 6 8 10 TIME (SECONDS) Figure 15.- C-5 M S C S symmetricr pull-up t i m e history.

CRUISE SUMMARY I I I I I I

- ALDCS OFF, FLIGHT TEST BOUNDARIES

0 FWD CG, ALDCS ON, ANALYTICAL 0 AFT CG, ALDCS ON, ANALYTICAL \FWD cc-

s

m A c n 60 oi w Q w Y c v,

u

AFT CG I . I I I I I 2 0.3- 0.4 0.5 0.6 0.7 0.8 ( MACH NUMBER Figure 16.- C-5 ALDCS maneuvering longitudinal axis stability - Stick force per g .

CRUISE SUMMARY 0.4 I I I

z

J a .

z

Q

- 0.2-

‘2-

- FLIGHT TEST, ALDCS OFF

0 ANALYTICAL, ALDCS ON 0 c l A Lu

dd > - o

u o 0.2 0.4 0.6 0.8 1.0 DAMPING R A T I O Figure 17.- C-5 pII;DCS short period s t a b i l i t y .

CRUISE SUMMARY 0.16 I I 1 I

I

-

MINIMUM FLIGHT TEST, ALDCS 0 ANALYTICAL, ALDCS O N n

6 0.12

E

s

Z 4.

- n Q 0.08 az I 2 ; Z w 0 0.04 W E L L 1 I I f 1 0 0.04 0.08 0.12 0.16 0.20 DAMPING RATIO Figure 1 8 . - C-5 U C S phugoid s t a b i l i t y .