Document
EFFECTS OF LATERAL CONTROL
CHARACTERISTICS O N HOVERING
A JET LIFT VTOL AIRCRAFT
by L. Stewurt Rolls, Fred J. Drinkwuter III,
und Robert C. Innis
Ames Reseurcb Center
Moffett Field, CuZ$ . , . .
N A T I O N A L A E R O N A U T I C S A N D SPACE A D M I N I S T R A T I O N W A S H I N G T O N , D. C. M A R C H 1 9 6 5
I
TECH LIBRARY KAFB, NM
I l l l l l l 1 1 1 1 1 lllll lllll lllll l l l l l 1 1 1 l l 1 1 1 1 I l l 1
007974b NASA T N D-2701 EFFECTS O F LATERAL CONTROL CHARACTERISTICS ON HOVERING A J E T LIFT VTOL AIRCRAFT By L. Stewart Rolls, Fred J. Drinkwater 111, and Robert C. Innis Ames Research Center Moffett Field, Calif.
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION For sale by the Office of Technical Services, Deportment of Commerce,
Washington, D.C. 20230 -- Price$1.00
EFFECTS O F IATERAL CONTROL CHARACTERISTICS ON HOVERING A JET LIFT VTOL AIRCRAFT By L . Stewart Rolls, Fred J. Drinkwater 111, and Robert C . Innis Ames Research Center SUMMARY Three l e v e l s of t o t a l c o n t r o l power and three values of m a x i m u m s t i c k A i r f r a m e damping t r a v e l were t e s t e d f o r t h e X-14A VTOL research a i r c r a f t .
w a s a l s o varied. Two N A S A p i l o t s evaluated the relative importance of t h e s e They parameters as maneuvering requirements f o r a hovering VTOL a i r c r a f t .
r a t e d t o t a l c o n t r o l power as having a predominant e f f e c t during v i s u a l hover- ing out-of -ground e f f e c t . Changing t h e c o n t r o l s e n s i t i v i t y ( c o n t r o l power p e r inch of s t i c k t r a v e l ) had only a minor effect over t h e range of s e n s i t i v i t y i n v e s t i g a t e d .
I m O D U C T I O N The response of an a i r c r a f t t o c o n t r o l inputs i s of primary concern t o t h e p i l o t during maneuvering f l i g h t . The amount of c o n t r o l moment required and t h e magnitude of the a i r c r a f t damping, two c h a r a c t e r i s t i c s which influence t h e a i r c r a f t ' s response, have been studied f o r many y e a r s . With t h e advent of t h e v e r t i c a l take-off and landing (VTOL) a i r c r a f t , t h e c o n t r o l requirement s t u d i e s have been extended t o t h i s type of a i r c r a f t . The r e s u l t s of simula- t o r s t u d i e s are presented i n reference 1, v a r i a b l e - s t a b i l i t y h e l i c o p t e r r e s u l t s are presented i n reference 2, and v a r i a b l e - s t a b i l i t y VTOL a i r p l a n e r e s u l t s are presented i n reference 3.
I n t h e s e previous s t u d i e s changes w e r e made i n t h e t o t a l c o n t r o l power a v a i l a b l e , but t h e s t i c k gearing remained constant; thus, t h e s e n s i t i v i t y ( c o n t r o l power p e r inch of s t i c k t r a v e l ) w a s a l s o changed. While it i s r e a l i z e d t h a t both t h e t o t a l c o n t r o l power a v a i l a b l e and t h e c o n t r o l sensi- t i v i t y are s i g n i f i c a n t f a c t o r s a f f e c t i n g t h e p i l o t ' s r a t i n g of a v e h i c l e ' s c o n t r o l l a b i l i t y , very l i t t l e research has been conducted t o resolve t h e i r r e l a t i v e significance. The p r e s e n t research program w a s undertaken t o i n v e s t i g a t e t h e three f a c t o r s a f f e c t i n g l a t e r a l c o n t r o l requirements based on p i l o t opinion ( c o n t r o l power, c o n t r o l s e n s i t i v i t y , and damping) t o determine t h e i r respective importance and perhaps t h e areas of operation where each t e r m supplied t h e more meaningful c r i t e r i a .
T h i s r e p o r t p r e s e n t s t h e r e s u l t s of a f l i g h t i n v e s t i g a t i o n conducted with t h e X-14A VTOL research vehicle i n which a range of both l a t e r a l - c o n t r o l power and s e n s i t i v i t y w e r e studied. The lateral axis w a s chosen f o r t h i s study because previous studies (refs. 1, 2, and 3) i n d i c a t e d t h a t c o n t r o l about t h i s a x i s w a s t h e more c r i t i c a l from t h e standpoint of p i l o t opinion.
Two NASA t e s t p i l o t s p a r t i c i p a t e d i n t h e program t o determine t h e p i l o t opinion boundaries based upon systematic v a r i a t i o n s of c o n t r o l power, s e n s i - t i v i t y , and airframe damping.
DESCRIPTION O F AIRPLANE The r e s u l t s presented i n t h i s r e p o r t w e r e obtained from a f l i g h t i n v e s t i - gation using t h e X-14A v a r i a b l e - s t a b i l i t y and c o n t r o l VTOL t e s t vehicle. The X-14A ( f i g . 1) i s a fixed-wing, jet-propelled, vectored thrust a i r c r a f t . The exhaust from t h e j e t engines passes through cascade-type d i v e r t e r s which allow t h e p i l o t t o s e l e c t v e r t i c a l o r horizontal t h r u s t . During hover and low speed f l i g h t , control of t h e a i r p l a n e a t t i t u d e w a s maintained by t h e use of r e a c t i o n jets at t h e wing t i p s and t a i l with air f o r these controls being b l e d from t h e compressor of t h e t u r b o j e t engines. A d e t a i l e d d e s c r i p t i o n of t h e X-14A and i t s v a r i a b l e - s t a b i l i t y and c o n t r o l system i s presented i n reference 3. During t h e s e t e s t s t h e operational weight of t h e t e s t vehicle w a s 3,700 pounds with a thrust-to-weight r a t i o a v a i l a b l e of 1.1 t o 1.2.
I n t h e present i n v e s t i g a t i o n t h e gearing i n t h e l a t e r a l c o n t r o l system w a s modified t o permit, through a ground adjustment, t h e s e l e c t i o n of l a t e r a l s t i c k t r a v e l of k4.5, 23.5, or 53.0 inches. These values were considered t o be i n t h e range of p r a c t i c a l i n t e r e s t f o r j e t l i f t VTOL a i r c r a f t . The i n s t a l - l a t i o n of t h e mechanical system, which afforded t h i s a b i l i t y t o vary t h e s t i c k gearing, required a change i n t h e o r i g i n a l s t i c k t r a v e l ; thus, it w a s impos- s i b l e t o conduct t e s t s with t h e k5 inches of s t i c k t r a v e l used i n reference 3.
To a l l e v i a t e any change i n t h e f r i c t i o n and breakout f o r c e c h a r a c t e r i s t i c s which normally would accompany t h e s e changes i n s t i c k t r a v e l , a hydraulic boost cylinder w a s i n s t a l l e d i n t h e l a t e r a l c o n t r o l system. The c h a r a c t e r i s - t i c s of t h i s hydraulic system were such t h a t a f o r c e of about 1/3 t o 1/2 pound w a s required a t t h e s t i c k g r i p and no f o r c e gradient e x i s t e d . The con- t r o l moment and damping functions of t h e v a r i a b l e c o n t r o l system remained unchanged f r o m t h a t used i n reference 3.
TESTS This i n v e s t i g a t i o n w a s conducted during v i s u a l hovering, out-of-ground e f f e c t , and i n generally calm wind conditions. The p i l o t opinion of t h e l a t e r a l c o n t r o l system w a s derived by performing r a p i d r o l l maneuvers t o i n i t i a t e or stap sideward v e l o c i t y and by noting t h e a i r c r a f t response t o rapid c o n t r o l r e v e r s a l s as well as an evaluation of t h e a b i l i t y t o hover pre- c i s e l y over a spot. To f u r n i s h a systematic v a r i a t i o n of control s e n s i t i v i t y , c o n t r o l power, and damping, a t o t a l of nine combinations of c o n t r o l power and were r a t e d by t h e p i l o t s for each of t h e t h r e e s t i c k t r a v e l s , unless damping t h e p i l o t f e l t a combination would give t h e vehicle a n unacceptable c h a r a c t e r i s t i c (> 6 . 5 ) . These conditions covered, t o t h e a b i l i t y of t h e X-14A, a high-, medium-, and low-control power f o r each of a high, medium, and low damping.
During t h e s e t e s t s with varying lateral c o n t r o l powers, t h e l o n g i t u d i n a l and d i r e c t i o n a l c o n t r o l c h a r a c t e r i s t i c s were kept constant and a t a s a t i s f a c - t o r y l e v e l (see r e f . 3 ) . The r e s u l t s presented here are based upon t h e fligkrt performance of two N A S A research p i l o t s who have considerable experience i n both h e l i c o p t e r s and VTOL a i r c r a f t .
RESULTS AND DISCUSSION I n t h e evaluation of hovering and low-speed c o n t r o l requirements f o r a VTOL a i r c r a f t , two types of operation can be considered. These include (1) gross maneuvering where r e l a t i v e l y l a r g e c o n t r o l i n p u t s are used t o provide r a p i d changes i n a i r c r a f t p o s i t i o n and ( 2 ) steady or p r e c i s i o n f l i g h t where accuracy of a i r c r a f t p o s i t i o n i s important. It can be expected t h a t maneu- vering type f l i g h t w i l l determine the t o t a l c o n t r o l power (maximum moment) required; however, t h e a s s o c i a t e d s t i c k t r a v e l ( s e n s i t i v i t y ) m u s t be s u i t a b l e f o r a l l types of operation, including p r e c i s i o n f l y i n g . These p o i n t s are dis- cussed i n t h e following s e c t i o n s of t h e r e p o r t .
Maneuvering F l i g h t The numerical p i l o t r a t i n g system shown i n t a b l e I, and described i n reference 4, w a s used by t h e p i l o t s i n r a t i n g t h e various c h a r a c t e r i s t i c s .
Each p i l o t r a t e d three d i f f e r e n t amounts of c o n t r o l power a t three l e v e l s of damping f o r each of t h e t h r e e s t i c k t r a v e l ranges. The r e s u l t s are presented i n t a b l e I1 and are a l s o summarized on f i g u r e 2. The s m a l l c i r c u l a r symbol shows the c o n t r o l power and damping conditions being evaluated and t h e numbers within t h e l a r g e r symbols are t h e r a t i n g s t h e p i l o t s assigned t o that condi- t i o n f o r each s t i c k t r a v e l . The p i l o t r a t i n g boundaries of 3-1/2 and 6-1/2, as derived i n t h e t e s t s of reference 3, are included on t h i s f i g u r e f o r refeY- ence. Examination of t h e p i l o t s ' r a t i n g s shows t h a t over t h e range t e s t e d changes i n s t i c k gearing had only a s m a l l a f f e c t on t h e p i l o t ' s opinion of a given l e v e l of c o n t r o l power and damping. These p i l o t r a t i n g d a t a i n d i c a t e f a i r agreement between t h e two p i l o t s . The l a r g e r discrepancies occurred' i n t h e values l i s t e d f o r the lowest rate damping conditions t e s t e d . This i s probably because t h e p i l o t who assigned t h e lower numbers w a s extremely familiar with t h e v e h i c l e ' s c h a r a c t e r i s t i c s and appreciated t h e increased responsiveness a t t h e s e low damping values. The other p i l o t being less familiar with t h e vehicle r a t e d t h e c o n t r o l power and damping values more i n l i n e with t h e r e s u l t s of reference 3.
The d a t a of t a b l e I1 have been p l o t t e d as a f u n c t i o n of lateral c o n t r o l s e n s i t i v i t y on f i g u r e 3. On t h i s f i g u r e , a l s o , t h e numbers within t h e sym- b o l s i n d i c a t e t h e p i l o t ' s r a t i n g for t h a t p a r t i c u l a r set of conditions.
Since both t h e q u a n t i t i e s which govern sensitivity, that is, t o t a l c o n t r o l power and s t i c k t r a v e l , were changed, it w a s p o s s i b l e f o r t h e p i l o t t o rate t h e same s e n s i t i v i t y with two d i f f e r e n t t o t a l c o n t r o l powers. The p i l o t ' s d e s i r e f o r c o n t r o l power r a t h e r t h a n s e n s i t i v i t y i s i l l u s t r a t e d by t h e l a c k of uniform v a r i a t i o n of p i l o t ' s opinion as s e n s i t i v i t y w a s changed. It w i l l be seen t h a t i n t h e areas of nearly t h e same s e n s i t i v i t y with d i f f e r e n t con- t r o l powers t h e p i l o t r a t e d t h e higher c o n t r o l power superior (lower p i l o t r a t i n g nmiber) . To o b t a i n t h e higher s e n s i t i v i t i e s with low c o n t r o l powers it w a s necessary t o use small amounts of s t i c k t r a v e l ; thus, t h e p i l o t contin- ually h i t t h e s t o p s during maneuvering f l i g h t . The f a c t t h a t t h e s t i c k h i t stops during t h i s c o n t r o l a c t i v i t y quickly informed t h e p i l o t t h a t he had t h e used m a x i m u m a v a i l a b l e c o n t r o l and he tended t o downgrade t h i s condition.
Further comparison of t h e p i l o t ' s r a t i n g of c o n t r o l power o r s e n s i t i v i t y i s shown i n figure 4. These d a t a are f r o m t a b l e I1 f o r a damping of 1.75 p e r see. This f i g u r e shows t h a t at a given l e v e l of c o n t r o l power, v a r i a t i o n s i n s e n s i t i v i t y have l i t t l e a f f e c t on t h e p i l o t ' s r a t i n g . However, t h e p i l o t ' s r a t i n g s showed considerable change when t h e s e n s i t i v i t y w a s constant and t h e c o n t r o l power v a r i e d . A l s o shown on t h i s f i g u r e are t h e r a t i n g s f o r p i l o t B y obtained from a s i m i l a r study conducted i n a v a r i a b l e - s t a b i l i t y and c o n t r o l helicopter.' The c h a r a c t e r i s t i c s of t h i s h e l i c o p t e r and i t s "model" v a r i a b l e - s t a b i l i t y system are discussed i n reference 5 . The p i l o t ' s d e s i r e f o r increased c o n t r o l power r a t h e r t h a n increased s e n s i t i v i t y i s a l s o shown by t h e h e l i c o p t e r results. The r e l a t i v e l e v e l s of c o n t r o l power f o r s a t i s f a c t o r y r a t i n g (PR = 3 . 5 ) f o r t h e h e l i c o p t e r i s considerably less than t h a t f o r t h e X-14A. The reason f o r t h i s i s unknown. Possible reasons f o r t h i s discrepancy may b e a leading lateral a c c e l e r a t i o n from t h e rapid-responsive rotor-plane r o t a t i o n , o r due t o t h e model technique used t o compute t h e variable- s t a b i l i t y inputs c a n c e l l i n g a l l gust and extraneous i n p u t s .
Steady Hovering It had been expected t h a t increased s e n s i t i v i t y , g r e a t e r t h a n t h a t nor- mally used i n t h e X-lkA, would be h e l p f u l during a steady hovering t a s k i n t h a t t h e magnitude of s t i c k motion and t h e r e f o r e t h e p i l o t ' s work load required t o remain over a spot would be reduced. To i n v e s t i g a t e t h i s , t h e p i l o t s were asked t o evaluate t h e various s t i c k t r a v e l and c o n t r o l power c h a r a c t e r i s t i c s used i n t h i s study, i n l i g h t of t h e i r a b i l i t y t o maintain t h e vehicle hovering over a s p o t . The p i l o t s f e l t t h a t t h e increased s e n s i t i v i t y w a s b e n e f i c i a l during steady hovering, b u t t h e X - 1 4 A Y which i s not self- disturbing during hover, could be successfully hovered over a spot using a small f r a c t i o n of t h e c o n t r o l power required f o r maneuvers. The increased s e n s i t i v i t y would be more b e n e f i c i a l i n a hovering vehicle with self- d i s t u r b i n g tendencies where t h e p i l o t ' s work load would be decreased as a r e s u l t of having t o supply smaller movements of t h e s t i c k t o c o n t r o l t h e u p s e t t i n g moments.
_ _ - ._ more d e t a i l e d accounting of the study i n t h e v a r i a b l e - s t a b i l i t y h e l i - copter a t Langley Research Center w i l l b e published by John F. Garren and James R. Kelley.
I
CONCLUDING REMARKS F l i g h t t e s t s of a hovering VTOL a i r c r a f t with varying amounts of c o n t r o l power and s t i c k t r a v e l indicated t h a t t h e p i l o t s ' opinions of t h e maneuvering requirement were predominantly influenced by t o t a l c o n t r o l power available and t h a t changing t h e s t i c k t r a v e l over t h e range t e s t e d had only a minor e f f e c t . During steady hovering, t h e increased s e n s i t i v i t y reduced t h e p i l o t ' s work load, thus, it would be more favorable.
Ames Research Center National Aeronautics and Space Administration Moffett Field, C a l i f . , Nov. 30, 1964 REFERENCES 1. Faye, Alan E., Jr.: Attitude Control Requirements for Hovering Determined Through t h e Use of a P i l o t e d F l i g h t Simulator. NASA TN D-792, 1961.
2. Salmirs, Seymour, and Tapscott, Robert J.: The E f f e c t s of Various Combi- nations of Damping and Control Power on Helicopter Handling Q u a l i t i e s During Both Instrument and Visual F l i g h t . N A S A TN D-58, 1959.
3. Rolls, L. Stewart, and Drinkwater, Fred J., 111: A Flight Determination of t h e Attitude Control Power and Damping Requirements for a Visual Hovering Task i n t h e Variable S t a b i l i t y and Control X-14A Research Ve- h i c l e . N A S A TN D-1328, 1962.
4. Cooper, George E . : Understanding and I n t e r p r e t i n g P i l o t Opinion. Aero.
Eng. Rev., v o l . 16, no. 3, Mar. 1957, pp. 47-51, 56.
5 . Garren, John F., Jr., and Kelly, James R . : Description of an Analog Com- p u t e r Approach t o V/STOL Simulation Fhrploying a Variable S t a b i l i t y Helicopter. N A S A TN D-1970, 1964.
TABLE I.- PILOT OPINION M T I N G SCHEDUI8 Primary Can be Adjective Numeric a1 mission De s c r i p t ion landed r a t i n g r a t i n g c omp 1 i shed ac I 1 I Yes 1 1 Yes Excellent, includes optimum Yes Yes I Good, pleasant t o f l y I Satisfactory, but with some mildly I t unpleasant c h a r a c t e r i s t i c s Y e s
I Yes
4 Acceptable, but with unpleasant
c h a r a c t e r i s t i c s Yes Yes fiergency Unsatisfactory 5 Unacceptable f o r normal operation Doubt f U Ye s operation 6 Acceptable f o r emergency condition
only1 Doubtful 1 Yes 'I
I
1 Unacceptable even f o r emergency
Doubtful, I
condition1 No
Unacceptable - dangerous No N o ~
Unacceptable - uncontrollable No NO '
I $1 J .
T A B U 11.- PILOT RATING LATERAL SEPJSITIVITY Control power radians/se c2 2 1.4 0.8 Pilot Damp ing f Sensitivity radians/sec2/in.
l / s e c
I I
0.73 0.31 0.40 0.51 ' 0.18
0.23 0.29 0.45 0.59 A-28473-8 Figure 1.- Photograph of test a i r c r a f t i n hovering f l i g h t S t i c k P i l o t A 8 A B A B travel b o u n d a r y
6.5 f 3.5 . b o u n d a r y
( R e f . 3 ) I ’ ’ /
+//
I I I I I 0 I 2 3 M a x i m u m l n t o r n l r n n t r n l nower. r a d i a n s / s e c 2 Figure 2.- Summary of t h e p i l o t s ’ r a t i n g of t h e l a t e r a l c o n t r o l c h a r a c t e r i s t i c s .
-4 Control power
0 0.8 r a d i a n s / s e c
0 1.4 radians/sec
0 2.0 r a d i a n s / s e c
P i l o t A B -3
Q
u a , v) \ - a .
CT c .- a E A -u - 2 B a , t
E !
-
a , 4- -I - I A B
B
I 1 1 1 I I I I I
.2 .4 . 6 . 8 I .o
L a t e r a l control sensitivity, radians/sec2/ in.
Figure 3.- P i l o t s ' rating of t h e lateral c o n t r o l s e n s i t i v i t y .
0 X - 1 4 A a i r p l a n e
0 V a r i a b l e s t a b i l i t y helicopter
2.4 2.0 N 1.6 cn \ U J c .- U I . 2 ” L a Q.
-
+- .8 c
El
0 U .4 1 I I 1 1 I 1 1 1 .
0 .2 .4 S e n s i t i v i t y , r a d i a n s /sec2/in.
Figure 4.- Comparison of p i l o t s ’ r a t i n g s for c o n t r o l power and s e n s i t i v i t y ; X-14A and v a r i a b l e s t a b i l i t y h e l i c o p t e r , p i l o t B.
NASA-Langley, 1965 A- 1050 “The aeronautical and space activities of the United States shall be conducted so as to contribute . . . to the expansion of human RnowI- edge of phenomena in the atmosphere and space. The Administration shall provide for the widest practicable atid appropriate dissemination of information concerning its activities and the resrrlts thereof .” -NATIONAL AERONAUTICS A N D SPACE ACT OF 1958
NASA SCIENTIFIC A N D TECHNICAL PUBLICATIONS
TECHNICAL REPORTS: Scientific and technical information considered important, complete, and a lasting contribution to existing knowledge.
TECHNICAL NOTES: Information less broad in scope but nevertheless of importance as a contribution to existing knowledge.
TECHNICAL MEMORANDUMS: Information receiving limited distri- bution because of preliminary data, security classification, or other reasons.
CONTRACTOR REPORTS: Technical information generated in con- nection with a NASA contract or grant and released under NASA auspices.
TECHNICAL TRANSLATIONS: Information published in a foreign language considered to merit NASA distribution in English.
TECHNICAL REPRINTS: Information derived from NASA activities and initially published in the form of journal articles.
SPECIAL PUBLICATIONS: Information derived from or of value to NASA activities but not necessarily reporting the results -of individual NASA-programmed scientific efforts. Publications include conference proceedings, monographs, data compilations, handbooks, sourcebooks, and special bibliographies.
Details on the availability o f these publications may be obtained from: SCIENTIFIC AND TECHNICAL INFORMATION DIVISION
N AT I 0 N A L A E R 0 N A U T I CS A N D S PA C E A D M I N I ST R AT I 0 N
Washington, D.C. 20546