Document
I
By Perry L. Deal and J u l i a n L. Jenkins, Jr.
NASA Langley Research Center
Langley Station, Hampton, Va.
Presented a t t h e 24th A n n u a l National Forum
of t h e American Helicopter Society
~-
GPO PRICE s
CSFTl PRICE(S) $
Hard copy (HC) 3, Bd
a
Microfiche (MF) / 6 J
ff 653 July65 Washington, D.C.
I%Y 8-10, 1968
~
--
(THRU)
I
(CATEGORY)
FLIGHT INVESTIGATION OF THE WING-ROTOR LD+ -S&NG CHARACTERISTICS
O F A HINGEMSS R O T O R CoMpouND' HELICO.WER Perry L. Deal and J u l i a n L. Jenkins, Jr.
Aerospace Technologists NASA Langley Research Center Langley S t a t i o n , Hampton, Va.
summary n a i r c r a f t load f a c t o r
The r e s u l t s of an NASA f l i g h t - t e s t program rpm r o t o r r o t a t i o n a l speed expressed as a u t i l i z i n g t h e AmTy/Lockheed hingeless r o t o r com- percent of designed operating speed pound a i r c r a f t t o determine t h e l i f t - s h a r i n g (355 revlmin) c h a r a c t e r i s t i c s of t h e wing and r o t o r i n both l e v e l and maneuvering f l i g h t are presented. The
v t r u e airspeed, knots
d a t a show that t h e r e i s an inherent reduction i n r o t o r l i f t as l e v e l f l i g h t airspeed is increased.
a boom indicated angle of attack, deg This reduction i n r o t o r l i f e provides a margin between t h e t r i m lift i n level f l i g h t and t h e incremental change from l e v e l f l i g h t t r i m A maximum l i f t i n g c a p a b i l i t y of t h e r o t o r which m y value be u t i l i z e d i n maneuvers. I n addition, t h e meas- ured reduction i n r o t o r - l i f t s e n s i t i v i t y i n accel- blade root c o l l e c t i v e p i t c h angle, deg
eo
e r a t e d f l i g h t which occurs with increasing speed helps t o a l l e v i a t e t h e r o t o r s t a l l problems.
Description of Test A i r c r a f t Although t h e load-sharing t r e n d s c o n t r i b u t e favor- ably t o t h e p i l o t i n g t a s k i n t h e compound mode, The t e s t a i r c r a f t , shown i n f i g u r e 1, i s t h e t h e r o t o r overspeed tendencies could r e q u i r e con- Army/Lockheed XH-51A compound h e l i c o p t e r which s t a n t a t t e n t i o n during maneuvering f l i g h t .
The air- incorporates a hingeless r o t o r system.
c r a f t i s described i n d e t a i l i n reference 1. The Introduction basic physi.cal 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 a r e presented i n t h e following t a b l e : I n recent years, s e v e r a l h e l i c o p t e r s have been nodified t o incorporate various degrees of PHYSICAL CKARACTERISTICS OF TEST AIRCRAFT
compounding ( i. e . , auxiliary propulsion and/or
wings) i n order t o v e r i f y t h e expected improve-
. . . . . . 5,160 l b
Nominal take-off weight . . .
ments i n high-speed performance and t o explore
. . . . . . 695 1b
Fuel capacity . . . . . . . .
t h e problems a s s o c i a t e d with high-speed rotary- . . . . . .
Rotor diameter . . . . . . .
35 ft winged a i r c r a f t . These i n t e r i m compound aircraf't
S o l i d i t y . . . . . . . . . . . . . . . . 0.0810
were modified and t e s t e d under c o n t r a c t s by t h e . . . . . .
Normal r o t o r operating speed
355 rw
U . S . Army. A s one phase of t h e Amy c o n t r a c t ,
. . . . . . 16.03 f t
Wing span . . . . . . . . . .
2 weeks were a l l o t t e d t o NASA Langley Research
. . . . . . 7 0 f t 2
Wing a r e a . . . . . . . . . .
Center f o r a f l i g h t - t e s t program u t i l i z i n g t h e
Primary powerplant . . . . . . . . . . Turboshaft
Amy/Lockheed hingeless r o t o r compound h e l i c o p t e r .
A w t i l i a i y powerplant . . . . . . . . . . Turbojet
This paper p r e s e n t s some of the results Thr p i l o t ' s c o n t r o l s a r e b a s i c helicopter-type obtained during t h e NASA t e s t s . I n p a r t i c u l a r , control::, and t h e r e a r e no movable aerodynamic con- t h e l i f t - s h a r i n g c h a r a c t e r i s t i c s between t h e wing t r o l surfaces incorporated. The a i r c r a f t i s and r o t o r i n both l e v e l f l i g h t and maneuvers are equippe3 with t h e standard XH-51A 'control gyro.
presented and discussed. I n a d d i t i o n , d a t a a r e The a u x i l i a r y power system, of course, r e q u i r e s an presented t o i l l u s t r a t e t h e r o t o r speed c o n t r o l a d d i t i o n a l c o n t r o l which i s incorporated i n t o t h e 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 maneuvers and t w i s t g r i p of t h e c o l l e c t i v e p i t c h handle. Because autorotat,ions. The r e s u l t s presented h e r e i n a r e of t h i s modification, t h e primary power c o n t r o l i s r e l a t e d t o t h e f l y i n g q u a l i t i e s of t h i s compound i n s t a l l e d as a t h r o t t l e on a quadrant mounted t o h e l i c o p t e r , and t h e advantages and disadvantages t h e lef't of t h e c o l l e c t i v e p i t c h l e v e r .
of some of t h e t r e n d s e s t a b l i s h e d a r e pointed out Results and Discussion Symb 01s The d a t a presented h e r e i n represent a sampling l o n g i t u d i n a l c y c l i c p i t c h angle, deg B1 of t h e d a t a accumulated during t h e N A S A f l i g h t - t e s t program. Included a r e t h e l e v e l f l i g h t l i f t GW a i r c r a f t gross weight, l b sharinz between t h e wing and rotor, t h e dynamic o r maneuver l i f t sharing, and a l s o d a t a i n d i c a t i n g t h e
LR r o t o r lift, l b
r o t o r r p m c o n t r o l c h a r a c t e r i s t i c s during maneu- vering f l i g h t .
Presented at t h e 24th Annual National Forum of t h e American Helicopter Society, May 1968.
L-6004 at t h e higher airspeeds. I n order t o e s t a b l i s h The majority of t h e test results a r e pre- more c l e a r l y t h e t r e n d i l l u s t r a t e d , t h e slopes of sented f o r a nominal c o l l e c t i v e p i t c h s e t t i n g of approximately 4'. This value i s t h e recommended
t h e r o t o r loading w i t h load f a c t o r ("y) were
minimum p i t c h s e t t i n g f o r t h e compound mode of f l i g h t f o r t h e a i r c r a f t .
determined and a r e p l o t t e d as a function of air- speed i n f i g u r e 5 . The curve i l l u s t r a t e s t h e Level F l i g h t L i f t Sharing e f f e c t i v e decrease i n r o t o r - l i f t s e n s i t i v i t y with increasing airspeed. For example, i n a maneuver The v a r i a t i o n of t h e rotor-lift-gross-weight t h e r o t o r provides approximately 75 percent of t h e r a t i o with airspeed f o r two c o l l e c t i v e p i t c h incremental lift a t 120 knots, but only 44 percent s e t t i n g s i s presented i n f i g u r e 2. For t h e 4 ' of t h e incremental lift a t 210 knots. The reduc- c o l l e c t i v e p i t c h s e t t i n g , t h e r o t o r lift i s equiv- t i o n with speed i s very b e n e f i c i a l s i n c e less lift a l e n t t o 57 percent of t h e gross weight at demands a r e made on t h e r o t o r during maneuvers as 110 knots and decreases almost l i n e a r l y with it penetrates t h e more unfavorable environment at increasing airspeed. Extrapolation i n d i c a t e s higher speeds.
that t h e r o t o r would be completely unloaded at approximately 240 knots. Increasing c o l l e c t i v e The decreasing r o t o r - l i f t s e n s i t i v i t y with p i t c h , of course, increases t h e r e l a t i v e r o t o r airspeed i s i n c o n t r a s t t o t h e t r e n d s e s t a b l i s h e d loading; however, t h e maximum airspeed at t h e f o r other experimental compounds where t h e r o t o r higher c o l l e c t i v e p i t c h i s r e s t r i c t e d by an e a r l y provides a progressively l a r g e r share of t h e l i f t onset of v i b r a t i o n a l problems. The 4' s e t t i n g increment as i s indicated by t h e upper curve i n provides t h e maximum range of airspeed wherein f i g u r e 5. It i s t h i s high r o t o r - l i f t s e n s i t i v i t y t h e a i r c r a f t could be flown without need for which has required c o n t r o l modifications t o a c o l l e c t i v e p i t c h change. In addition t o d e s e n s i t i z e t h e r o t o r during accelerated f l i g h t .
minimizing t h e p i l o t workload, t h e t r e n d of Reference 2, f o r example, presents some results decreasing r o t o r l i f t a s airspeed increases i s of e f f o r t s t o c o n t r o l t h e maneuver l i f t sharing a l s o advantageous from another standpoint. A s by c o l l e c t i v e feedback. It was indicated t h a t t h e r o t o r p e n e t r a t e s a more unfavorable environ- c y c l i c c o n t r o l feedback would a l s o provide a means ment a t t h e higher speeds, it gradually unloads f o r c o n t r o l l i n g t h e r e l a t i v e loading between t h e without p i l o t a c t i o n and t h u s tends t o eliminate wing and r o t o r .
problems associated with r o t o r stall.
An a n a l y s i s of t h e data obtained during t h e There a r e r e s t r i c t i o n s a t both ends of t h e tests i n d i c a t e s that t h e r e i s considerable c y c l i c airspeed range. F i r s t , as i l l u s t r a t e d i n f i g - p i t c h feedback occurring during maneuvers which u r e 2, t h e r o t o r would be completely unloaded at i s apparently produced by t h e mechanical c o n t r o l about 240 knots and would probably produce nega- gyro. Further, it appears that t h e feedback r a t i o t i v e lift above t h i s airspeed, with obvious per- increases as airspeed increases. For example, formance p e n a l t i e s . Secondly, with t h e low f i g u r e 6 i l l u s t r a t e s t h e v a r i a t i o n of t h e longi- c o l l e c t i v e p i t c h s e t t i n g , t h e a i r c r a f t a t t i t u d e t u d i n a l c y c l i c p i t c h increment (mi) with load increases r a p i d l y as t h e airspeed i s reduced f a c t o r f o r s e v e r a l airspeeds. The increment AB1 toward 100 knots. For example, t h e v a r i a t i o n of i s t h e d i f f e r e n c e between t h e l e v e l f l i g h t trim t h e l e v e l f l i g h t fuselage angle of a t t a c k with l o n g i t u d i n a l c y c l i c p i t c h and t h e maneuvering airspeed i s presented i n f i g u r e 3 , These d a t a s t e a d y - s t a t e value. It i s a c t u a l l y a combination a r e f o r t h e same c o l l e c t i v e p i t c h s e t t i n g s as of t h e p i l o t input and t h e c o n t r o l gyro feedback.
shown i n f i g u r e 2. The lower c o l l e c t i v e p i t c h It should be noted t h a t i n a l l cases an a f t s t i c k r e q u i r e s an excessive nose-high a t t i t u d e i n order displacement w a s required t o maintain a given load t o achieve t h e required lift on both t h e w i n g and f a c t o r ; however, t h e steady-state l o n g i t u d i n a l r o t o r . Thus, f l i g h t a t airspeeds near 100 knots c y c l i c p i t c h was documented t o be i n t h e opposite r e q u i r e s a higher c o l l e c t i v e p i t c h s e t t i n g i n d i r e c t i o n a t t h e higher speeds. I n o t h e r words, order t o maintain a more comfortable a i r c r a f t t h e feedback i s l a r g e enough a t high speeds t o a t t i t u d e .
wash out t h e p i l o t ' s a f t c y c l i c input ( i . e . , a negative B1 increment) and a c t u a l l y produce a L i f t Sharing i n Maneuvers p o s i t i v e c y c l i c p i t c h increment. Thus, as speed increases, t h e e f f e c t i v e r o t o r angle-of-attack O f p a r t i c u l a r importance with regard t o change i n maneuvers becomes progressively smaller.
f l i g h t i n t h e compound mode is t h e r e l a t i v e load This c h a r a c t e r i s t i c , i n t u r n , reduces t h e r o t o r - sharing between t h e wing and r o t o r during maneu- lift s e n s i t i v i t y i n maneuvers as speed is increased vers. Windup t u r n s were executed i n order t o ( s e e f i g . 5 ) .
e s t a b l i s h t h e r o t o r - l i f t v a r i a t i o n with load fac- t o r f o r s e v e r a l airspeeds. Sample r e s u l t s a r e While t h e t r e n d of decreasing r o t o r - l i f t presented i n f i g u r e 4 t o i l l u s t r a t e t h e t r e n d s s e n s i t i v i t y with increasing airspeed i s advan- e s t a b l i s h e d f o r t h e t e s t a i r c r a f t . The d a t a pre- tageous with regard t o avoidance of r o t o r s t a l l sented were taken a t a c o l l e c t i v e s e t t i n g of problems, it should be emphasized that t h e sensi- approximately 4 ' . The v a r i a t i o n i n r o t o r lift t i v i t y change i s obtained a t t h e expense of a with airspeed a t 1.Og merely r e f l e c t s t h e l e v e l reduced nosedown l o n g i t u d i n a l c y c l i c c o n t r o l f l i g h t lift v a r i a t i o n indicated previously. The c a p a b i l i t y . Although not encountered during t h e d a t a i n d i c a t e that t h e r o t o r i s providing a program, t h e r e a r e combinations of airspeed and smaller increment of lift f o r a given load f a c t o r load f a c t o r that would u t i l i z e t h e maximum a v a i l a b l e nosedown c y c l i c p i t c h . Once t h i s con- A t higher speeds, t h e maneuver envelope expands as indicated by t h e a u t o r o t a t i v e boundary d i t i o n i s reached, t h e a i r c r a f t would be unstable with f u r t h e r increase i n angle of a t t a c k . f o r 1 . 7 0 knots i n f i g u r e 7. It i s possible t o achieve a load f a c t o r of 1.6g at 170 knots without Rotor Speed Control exceeding 1.00-percent rpm. If t h e airspeed decays during a maneuver while maintaining a constant Rotor speed c o n t r o l is important i n terms of load f a c t o r , t h e r o t o r speed would i n c r e a s e t o both t h e a u t o r o t a t i o n a l and maneuvering r o t o r achieve a new equilibrium condition.
overspeed c h a r a c t e r i s t i c s . Since both of t h e s e c h a r a c t e r i s t i c s are a function of t h e load f a c t o r The range of airspeeds and load f a c t o r s pre- required t o a u t o r o t a t e t h e r o t o r , c r i t e r i a which sented a r e i n regions where a high percentage of define t h e s e load f a c t o r s a r e adequate f o r estab- operation i s likely t o occur, and t h i s could l i s h i n g t h e maneuver overspeed r e s t r i c t i o n s as represent maneuvering r e s t r i c t i o n s of a cornpound w e l l as t h e a u t o r o t a t i o n a l requirements. Tests helicopter. The overspeed tendencies would were accomplished t o e s t a b l i s h t h e r o t o r rpm r e q u i r e t h e p i l o t t o monitor r o t o r rprn t o prevent v a r i a t i o n with load f a c t o r f o r t h e a i r c r a f t with r o t o r overspeed during maneuvering f l i g h t unless a fixed c o l l e c t i v e p i t c h of 4'. Sample r e s u l t s provisions are made t o absorb t h e excess energy.
are presented i n f i g u r e 7.
Concluding R e m a r k s The boundary l i n e s i n d i c a t e t h e combinations The f l i g h t - t e s t r e s u l t s presented and d i s - of rpm and load f a c t o r that w i l l cause t h e r o t o r cussed herein have indicated s e v e r a l t r e n d s which t o a u t o r o t a t e f o r two d i f f e r e n t speeds, and t h e dashed l i n e s represent t h e d e s i r e d operating rpm are of i n t e r e s t concerning both t h e performance and f l y i n g q u a l i t i e s of a compound helicopter.
range. The a r e a t o t h e l e f t of each boundary and between t h e dashed l i n e s represents t h e envelope S p e c i f i c a l l y , t h e reduction i n r o t o r lift as l e v e l f l i g h t airspeed i s increased i s d e s i r a b l e since no wherein shaft power must be supplied t o d r i v e t h e r o t o r . p i l o t a c t i o n i s required, and t h e reduced trim l i f t tends t o provide a margin between t h e trim l i f t From t h e standpoint of maintaining r o t o r r p m and t h e l i f t i n g c a p a b i l i t y of t h e r o t o r which may i n t h e event of primary engine f a i l u r e , t h e be u t i l i z e d i n maneuvers.
c r i t e r i a represent t h e load f a c t o r necessary t o prevent a n underspeed condition, assuming no I n addition, a reduction i n r o t o r l i f t sensi- o t h e r c o r r e c t i v e a c t i o n . For example, a t t i v i t y i n accelerated f l i g h t which occurs with 120 knots t h e r o t o r will maintain 100-percent increasing speed a l s o helps t o a l l e v i a t e t h e r o t o r stall problem as it p e n e t r a t e s a more unfavorable rpm with a load f a c t o r of approximately l.25g.
environment at high speeds. It should be noted, A t 170 knots t h e load f a c t o r required t o maintain however, t h a t t h e reduced lift s e n s i t i v i t y occurs 100-percent rpm has increased t o 1.6g.
at t h e expense of reduced forward l o n g i t u d i n a l I n terms of r o t o r overspeed, t h e same d a t a c o n t r o l c a p a b i l i t y .
m y be i n t e r p r e t e d as t h e maneuver r e s t r i c t i o n s f o r t h e a i r c r a f t i n powered f l i g h t . I f a t a While t h e s e load-sharing trencls c o n t r i b u t e constant airspeed t h e load f a c t o r i s increased favorably t o t h e p i l o t i n g t a s k i n t h e compound beyond that required t o a u t o r o t a t e the r o t o r , t h e mode, t h e r o t o r overspeed tendencies would r e q u i r e rpm w i l l increase from t h e i n i t i a l s e t t i n g . p i l o t a t t e n t i o n during maneuvering f l i g h t .
Figure 8 i l l u s t r a t e s t h e rpm v a r i a t i o n with load f a c t o r f o r two d i f f e r e n t i n i t i a l r o t o r speeds a t References 120 knots. I n both cases t h e r o t o r rprn remains f a i r l y constant as load f a c t o r i s i n i t i a l l y 1. Wyrick, Donald R., Extension ,of t h e High-speed increased. However, i f t h e load f a c t o r i s F l i g h t Envelope of t h e XH-5lA Compound H e l i - copter, U S A A W B S Technical Report 65-71.
increased beyond t h a t required t o a u t o r o t a t e t h e r o t o r , t h e r o t o r r p m increases along t h e boundary 2. Blackburn, W. E . , Methods f o r Improving F l y i n g as indicated. For t h e case shown, a steady load f a c t o r of 1.45g would r e s u l t i n a f i n a l r o t o r r p m Qualities of Compound A i r c r a f t , J o u r n a l of t h e of l l 0 percent, regardless of t h e i n i t i a l rpm. American Helicopter Society, Vol. 13, No. 1, Jtrnuary 1968.
.2 'r
Figure 1.- Test a i r c r a f t .
. l 0 100 L L L L u u 120 140 160 180 200 220 240
A I RSPEED, KNOTS
Figure 2.- Rotor l i f t variation i n l e v e l f l i g h t .
I I
01 i I I I
100 120 140 160 180 200 220 240
AIRSPEED, KNOTS
Figure 3 . - Angle-of-attack variation i n l e v e l f l i g h t .
1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
LOAD FACTOR, n
Figure 4.- Rotor l i f t variation i n maneuvering f l i g h t .
z 2
TREND FOR COMPOUNDS
P
WITHOUT FEEDBACK n
W v,
- r V = 210
= 1
\
H I NGELES S ROTOR
COMPOUND
l n
W V = 170
u - 0 d m
V = 140J
-1 a =I w V I
z
I I I I I I I I - 2 -
1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
LOAD FACTOR, n
" Figure 6.- Longitudinal cyclic pitch increment variation with load factor.
100 120 1 4 0 160 180 200 220 240
AIRSPEED, KNOTS
Figure 5.- Effect of airspeed on rotor loading in maneuvers.
lG8
f
* 102
E' INITIAL. rpm = 100 %
L1 L
e 100
I
E
ct 98
I
' I
I
I I I I I I I
I I
I I I I I I I
1.0 1.1 1.2 1.3
1.4 1.5 1.6 1.7 1.8
1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
LOAD FACTOR, n
Figure 8.- Variation of r o t o r rpm with load factor.
Figure 7.- Power off variation of rotor r p m with v = l . 2 0 knots.
load factor.
NASA-Langley, 1968