Free-flight investigation of the deployment of a parawing recovery

Free-flight investigation of the deployment of a parawing recovery

NASA TECHNICAL NOTE
F R E E - F L I G H T I N V E S T I G A T I O N OF T H E
D E P L O Y M E N T OF A P A R A W I N G R E C O V E R Y
DEVICE F O R A R A D I O - C O N T R O L L E D
115-SCALE D Y N A M I C M O D E L S P A C E C R A F T
by C h d r l e s E . L i b b e y
Lungley Reseurck Center
Lungley Station, Hampton, Vu.
N A T I O N A L AERONAUTICS A N D SPACE A D M I N I S T R A T I O N
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WASHINGTON, D. C.
DECEMBER 1963
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TECH LIBRARY KAFB. NM
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TECHNICAL NOTE D-2044
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FREE -FLIGHT INVESTIGATION O F THE DEPLOYMENT
O F A PAMWING RECOVERY DEVICE FOR A RADIO-CONTROLLED
1/5-SCALE DYNAMIC MODEL SPACECRAFT
By C h a r l e s E. Libbey
Langley R e s e a r c h Center
Langley Station, Hampton, Va.
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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
FREE-FLIGHT INVESTIGATION OF THE DEPLOYMENT
OF A PARAWING RECOVERY DEVICE FOR A RADIO-CONTROLLED
1/5-SCALE DYNAMIC MODEL SPACECRAFT
By Charles E. Libbey
A f r e e - f l i g h t i n v e s t i g a t i o n of a radio-controlled model of a manned r e e n t r y
s p a c e c r a f t with a telescoping r i g i d parawing as a recovery system w a s made t o
evaluate t h e deployment process and t h e s t a b i l i t y and c o n t r o l c h a r a c t e r i s t i c s of
t h e configuration. F l i g h t t e s t s showed t h a t t h e parawing could be deployed from
a packaged condition, but t h a t t h e deployment process must be a sequence of caref u l l y c o n t r o l l e d and timed events, and t h a t some p o r t i o n s of t h e deployment should
not occur a t t o o fast a rate. The most s i g n i f i c a n t s i n g l e f a c t o r learned about
t h e deployment process w a s t h a t t h e parawing had t o be slowly r o t a t e d t o a l i f t i n g
condition. T r a n s i t i o n which i s t o o fast from zero l i f t t o m a x i m u m l i f t would
r e s u l t i n a tumbling motion. After t h e parawing w a s deployed, t h e configuration
w a s s t a b l e and c o n t r o l l a b l e .
INTRODUCTION
A f r e e - f l i g h t i n v e s t i g a t i o n o f a radio-controlled model of a manned r e e n t r y
v e h i c l e with a parawing f o r landing has been m a d e as p a r t of an o v e r a l l study
being conducted by t h e NASA Langley Research Center t o determine t h e f e a s i b i l i t y
of s e v e r d a p p l i c a t i o n s of t h e parawing described i n reference 1. References 1
t o 3 present results of wind-tunnel t e s t s and some uncontrolled f l i g h t t e s t s of
parawing g l i d e r s and i l l u s t r a t e t h e uses of t h i s configuration as a h i g h - l i f t
device f o r landing a i r c r a f t and as a recovery system f o r manned space v e h i c l e s .
Reference 4 p r e s e n t s t h e r e s u l t s of f r e e - f l i g h t deployment tests of a f o l d a b l e
r i g i d parawing used as a recovery system f o r a rocket booster. The r e l a t i v e l y
l i g h t w e i g h t and small volume of t h i s type of wing a l s o make it a t t r a c t i v e f o r
recovery and landing a p p l i c a t i o n s of manned r e e n t r y spacecraft.
The present i n v e s t i g a t i o n w a s made with a free-flying dynamic model t o ascert a i n a s a t i s f a c t o r y method f o r t h e deployment of a telescoping r i g i d parawing
from a manned r e e n t r y spacecraft and t o evaluate q u a l i t a t i v e l y t h e s t a b i l i t y and
f l i g h t behavior of t h e combination f o r one system of suspension-line geometry and
one method of control.
The parawing used f o r this i n v e s t i g a t i o n consisted of a f a b r i c m a t e r i a l cut
t o a 45O sweptback modified-delta planform and attached t o t h r e e s t r u c t u r a l
members a l l joined at one end t o form t h e leading edges and t h e root chord, o r
keel, of t h e wing. U s e of pivoted j o i n t s on t h e leading edges at t h e nose of t h e
wing permitted t h e wing t o be r e t r a c t e d i n t o a s m a l l spanwise dimension. U s e of
t e l e s c o p i n g s t r u c t u r a l members f o r t h e leading edges and t h e k e e l permitted t h e
w i n g t o be r e t r a c t e d i n t o a s h o r t chordwise dimension. The s p a c e c r a f t model used
f o r t h i s i n v e s t i g a t i o n w a s a blunted cone suspended below t h e parawing by a system
of f o u r cables e n t e r i n g t h e cone near t h e apex. Radio-control equipment and a
motion-picture camera were mounted w i t h i n t h e model. The c o n t r o l system u t i l i z e d
f o r t h i s i n v e s t i g a t i o n w a s t o s h i f t t h e c e n t e r of g r a v i t y of t h e vehicle f o r e and
aft f o r p i t c h c o n t r o l and s i d e t o s i d e f o r r o l l o r l a t e r a l c o n t r o l by changing
t h e l e n g t h s of t h e various suspension cables. The deployment of t h e parawing w a s
accomplished by using a drogue parachute t o e x t r a c t , open, and s e p a r a t e t h e parawing from t h e model. The drogue a l s o provided s t a b i l i t y t o t h e wing-spacecraft
configuration during t h e deployment process u n t i l a f l y i n g condition w a s reached;
at t h a t t i m e , t h e drogue w a s j e t t i s o n e d .
FLCG'ET-TEST TECHNIQUE, TEST FACILITY, AND EQUIPMENT
The f l i g h t - t e s t technique consisted of launching an unpowered radioc o n t r o l l e d model from a h e l i c o p t e r and c o n t r o l l i n g i t s f l i g h t from t h e ground.
Evaluation of t h e f l i g h t behavior w a s based on t h e model p i l o t s ' observations and
t h e q u a l i t a t i v e information w a s obtained from motion-picture records.
The f l i g h t t e s t s were performed a t an open f i e l d approximately 1 m i l e wide
and 3 miles long. Two ground s t a t i o n s were used f o r c o n t r o l l i n g t h e model; one
f o r t h e p i l o t who operated t h e p i t c h controls, and one f o r t h e p i l o t who operated
t h e r o l l c o n t r o l s . Each ground s t a t i o n w a s provided with a radio-control u n i t ,
communications equipment, and a motorized t r a c k i n g system equipped with binoculars
t o assist t h e p i l o t s and t r a c k e r s i n viewing t h e f l i g h t of t h e model and with a
t e l e p h o t o motion-picture camera. (See f i g . 1.) A h e l i c o p t e r equipped with a
s p e c i a l launching r i g w a s used t o c a r r y t h e model t o an a l t i t u d e of approximately
3,000 f e e t and then r e l e a s e it. The launching r i g w a s mounted on t h e s i d e of t h e
h e l i c o p t e r near t h e door ( s e e f i g . 2 ( a ) ) and w a s r a i s e d and lowered by a hydraulic
h o i s t . When t h e model w a s ready t o be released, t h e r i g w a s lowered s o t h a t t h e
model w a s below t h e h e l i c o p t e r (see f i g . 2 ( b ) ) . Magnetic t a p e recorders were used
t o record c o n t r o l s i g n a l s and a l l voice communications between t h e h e l i c o p t e r ,
coordinator, and model p i l o t s i n order t o assist i n a n a l y s i s of t e s t r e s u l t s .
MODEL
Parawing
A drawing of t h e parawing used i n t h e t e s t i s presented i n f i g u r e 3 . The
f l a t planform of t h e wing f a b r i c w a s a 45' sweepback modified d e l t a ; t h e f a b r i c
w a s attached t o a r i g i d framework which provided 50' of sweepback i n f l i g h t .
This configuration w a s s e l e c t e d because most of t h e s t a t i c wind-tunnel d a t a and
dynamic f l i g h t - t e s t d a t a a v a i l a b l e a t t h e t i m e t h e model w a s designed had been
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obtained with t h i s configuration. The s i z e of t h e parawing was determined by
s e v e r a l considerations. F i r s t , a f u l l - s c a l e wing loading between 10 and 15 pounds
per square f o o t w a s desired. Second, it was desired t o have only t h r e e t e l e scoping sections f o r each of t h e s t r u c t u r a l members from t h e standpoint of simp l i c i t y . A n d t h i r d , t h e length of t h e parawing i n i t s packaged condition w a s not
t o exceed t h e length of t h e s i d e of t h e spacecraft. Because of these considerations, a f u l l - s c a l e parawing 30 f e e t long with a w i n g area of 636 square f e e t was
assumed. Based on a recovery weight of 9,000 pounds, t h e wing loading w a s
14.1 pounds per square f o o t . For t h e l / 5 - s c a l e model, t h e root chord w a s 6 feet
long as shown i n f i g u r e 3. The weight of t h e wing w a s 6.75 pounds.
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The wing w a s constructed from acrylic-coated 1.2-ounce-per-square-yard nylon
r i p s t o p f a b r i c over an aluminum-alloy-tubing framework. The f a b r i c material w a s
e s s e n t i a l l y nonporous and very f l e x i b l e as well as being very l i g h t . It was cut
t o t h e 4.5' sweepback modified d e l t a planform and had wide casings sewn a t t h e
leading edges and root chord t o accept t h e s t r u c t u r a l members. The t r a i l i n g edges
of t h e casings were attached t o f r e e - f l o a t i n g f a b r i c attachment r i n g s ( s e e d e t a i l
i n f i g . 3 ) on t h e leading edges and k e e l . The apex of t h e f a b r i c w a s attached t o
t h e apex of t h e a,luminum tube framework.
The leading edges and t h e k e e l were constructed of t h r e e telescoping sections
each. Each section had a long s t r a i g h t c y l i n d r i c a l portion with a s h o r t f l a r e d
o r tapered portion at t h e ends ( s e e d e t a i l i n f i g . 3 ) . Thus they were able t o
form a self-jamming union with t h e adjoining s e c t i o n when i n t h e f u l l y extended
position. This type of construction eliminated t h e need f o r any bearings o r close
tolerance f i t s i n t h e telescoping s e c t i o n s except f o r t h e s h o r t f l a r e d portions
at t h e ends. Therefore, t h e telescoping s e c t i o n s could be made with a very loose
f i t and consequently had low f r i c t i o n between s l i d i n g members, thus requiring a
m i n i m u m f o r c e t o extend and lock them. When i n t h e f u l l y extended and locked
position, t h e telescoping s e c t i o n had no s i d e o r end play.
The two leading edges and t h e k e e l were joined t o a common f l a t p l a t e a t t h e
forward end, and t h e two leading edges were hinged on t h i s p l a t e s o t h a t they
could be folded back along t h e keel. Two spreader b a r s were used (one between
each leading edge and t h e k e e l ) t o maintain t h e leading edges a t 50' sweepback
angle regardless of t h e various loads imposed on t h e s t r u c t u r e during maneuvering
f l i g h t . The spreader b a r s were hinged i n t h e middle and at t h e points where they
joined t h e leading edges and k e e l t o allow t h e leading edges t o be r e t r a c t e d . A
tension device ( i n t h i s p a r t i c u l a r case, shock cord) w a s attached t o each spreader
bar at i t s center hinge j o i n t and t o t h e f l a t p l a t e a t t h e nose of t h e wing. This
tension device w a s used t o f o r c e t h e spreader bars t o unfold and thus t o f o r c e t h e
leading edges t o extend t o t h e i r 50' sweepback, o r normal open, position. The
spreader b a r s were self-locking i n t h e i r unfolded condition and were located as
f a r back from t h e nose of t h e parawing as was p o s s i b l e with t h e following cons i d e r a t i o n : While t h e spreader b a r s were i n t h e i r folded condition, they w e r e
not t o extend p a s t t h e ends of t h e leading edges and t h e keel while t h e leading
edges and t h e k e e l were i n t h e i r telescoped condition ( i n order not t o increase
t h e o v e r a l l length of t h e parawing package). This arrangement required a m i n i "
tension f o r c e ( c o n s i s t e n t with a short package l e n g t h ) t o unfold t h e spreader
bars.
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Spacecraft
A drawing of t h e s p a c e c r a f t model i s presented i n figure 4. It i s a symm e t r i c a l blunted cone w i t h a maximum diameter of 31 inches. The weight of t h e
s p a c e c r a f t model, including t h e w e i g h t of a l l t h e equipment mounted i n it w a s
78.25 pounds. The equipment was i n s t a l l e d i n t h e model i n t h e most convenient
manner and i n such a l o c a t i o n that t h e c e n t e r of g r a v i t y of t h e spacecraft w a s
l o c a t e d on t h e axis of symmetry and 5.8’3 inches above t h e plane of maximum diameter, as shown i n figure 4, b u t no attempt w a s made t o ballast t h e model f o r any
p a r t i c u l a r moments of i n e r t i a .
Suspension System
The s p a c e c r a f t w a s suspended below t h e parawing by a system of f o u r nylon
cables of 3/16-inch diameter. Two of t h e cables were attached t o t h e k e e l of t h e
parawing; t h e l o c a t i o n of t h e attachments on t h e k e e l w a s influenced by t h e f o l lowing considerations: F i r s t , t h e attachment p o i n t s had t o be f a r enough a p a r t
t o prevent e i t h e r of t h e cables from becoming s l a c k during g l i d i n g o r maneuvering
f l i g h t ; second, they had t o be c l o s e enough t o g e t h e r s o as not t o require l a r g e
changes i n cable l e n g t h s t o provide adequate p i t c h control; and t h i r d , they had
t o be l o c a t e d s o t h a t t h e y d i d not r e q u i r e excessive f o r c e s f o r p i t c h control.
The l e n g t h of t h e forward and rearward suspension l i n e s , with t h e c o n t r o l s n e u t r a l
w a s 68 and 60.5 inches, r e s p e c t i v e l y . The o t h e r two cables were attached one t o
each leading edge and w e r e used f o r roll control. They w e r e so l o c a t e d t h a t t h e y
w e r e unaffected when p i t c h c o n t r o l w a s applied.
These l i n e s were
67-5 inches long.
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Controls
The f l i g h t c o n t r o l system, t o g e t h e r with c e r t a i n elements of t h e deployment
c o n t r o l system and an emergency recovery system w e r e housed i n t h e s p a c e c r a f t .
The f l i g h t c o n t r o l system consisted of e l e c t r i c motor a c t u a t o r s which provided
f l i c k e r , o r bang-bang, c o n t r o l i n which t h e p i t c h and r o l l c o n t r o l s were moved
r a p i d l y t o predetermined p o s i t i o n s i n e i t h e r d i r e c t i o n from t h e n e u t r a l p o s i t i o n
i n response t o c o n t r o l s i g n a l s and t h e n back t o n e u t r a l with t h e c e s s a t i o n of t h e
s i g n a l . An electric-motor-driven winch was used as p a r t of t h e deployment system
t o c o n t r o l t h e r a t e a t which t h e parawing separated from t h e s p a c e c r a f t . This
winch extended a l i n e at an approximately constant rate f o r as long as i t s r a d i o
s i g n a l w a s being given and remained f i x e d when t h e s i g n a l w a s stopped. A 12-foot
emergency parachute w a s i n s t a l l e d i n t h e model t o f a c i l i t a t e a s a f e landing and
minimize damage i f t h e parawing d i d not deploy properly. A pyrotechnic device
w a s used t o a c t u a t e t h e parachute and w a s c o n t r o l l e d by r a d i o from t h e ground.
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Parawing Packaging
The packaged parawing w a s a r b i t r a r i l y attached t o t h e outside of t h e spacec r a f t f o r reasons of mechanical simplicity. On t h e premise t h a t t h e f u l l - s c a l e
parawing would be contained within t h e vehicle, t h e suspension l i n e s were m a d e
long enough so t h a t they would permit t h e e x t r a c t i o n of t h e e n t i r e length of t h e
parawing through a hatch a t t h e apex of t h e spacecraft. Such a suspension system
would allow t h e s i d e s of t h e spacecraft t o be a continuous u n i t with no doors o r
blow-amy panels along i t s length.
The parawing w a s contained i n a deployment b,ag t o f a c i l i t a t e packing and
handling problems and a l s o t o p r o t e c t t h e w i n g f a b r i c and suspension cables from
t h e airstream during t h e e a r l y stages of t h e deployment process. The bag w a s J u s t
long enough t o completely encase t h e parawing with t h e s t r u c t u r a l members f u l l y
collapsed.
Drogue Parachute
A drogue parachute was used t o control t h e deployment sequence since it w a s
easy t o i n s t a l l , had excellent r e l i a b i l i t y , required l i t t l e volume, and produced
r e l a t i v e l y l a r g e f o r c e s f o r long periods of time. The drogue w a s made t o perform
many functions. F i r s t , it pulled t h e deployment bag o f f t h e parawing and extended
t h e leading edges and t h e k e e l t o t h e i r full length from t h e i r telescoped condition; second, it pulled a p i n which a c t i v a t e d t h e tension devices attached t o t h e
spreader bars forcing them t o unfold and lock with t h e parawing a t i t s 50' sweepback condition; and t h i r d , it separated t h e wing from t h e spacecraft and caused
it t o r o t a t e up i n t o i t s f l y i n g a t t i t u d e . The drogue a l s o added s t a b i l i t y t o t h e
configuration during t h e deployment process.
TESTS
F l i g h t t e s t s of t h e model were made by launching it from a h e l i c o p t e r a t an
airspeed of near zero knots a t an a l t i t u d e of approximately 3,000 f e e t . The
deployment t e s t s of t h e wing were started a t approximately 2,500 f e e t and were
usually completed by approximately 1,500 f e e t . A t t h e average deployment a l t i t u d e
of 2,000 f e e t ( a i r density of 0.002242 slug/cu f t ) and t h e assumed l/5 scale, t h e
model dynamically simulated a f u l l - s c a l e r e e n t r y v e h i c l e with a gross weight of
9,000 pounds a t an approximate a l t i t u d e of 7,500 f e e t . For t h e s e t e s t conditions,
t h e t o t a l f l y i n g weight of t h e spacecraft p l u s t h e parawing w a s 83 pounds. The
t e s t s were made with t h e e f f e c t i v e center of g r a v i t y of t h e parawing-spacecraft
combination located 65 percent of t h e k e e l length back from t h e apex of t h e wing
and 81 percent of t h e k e e l length below t h e keel. Reference 5 i n d i c a t e s t h a t
t h i s configuration has s t a t i c l o n g i t u d i n a l s t a b i l i t y with t h i s center-of-gravity
location.
The t e s t s consisted of a s e r i e s of f l i g h t s t o determine a deployment sequence
f o r s a t i s f a c t o r y t r a n s i t i o n between a spacecraft i n i t s reentxy configuration with
a rigid-parawing recovery system stowed onboard and t h e trimmed g l i d i n g - f l i g h t
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configuration with t h e spacecraft suspended below t h e parawing. I n order t o
i s o l a t e t h e deployment problems and be able t o correct them one a t a time, a
systematic s e r i e s of t e s t s w a s conducted beginning with f r e e - f l i g h t t e s t s of t h e
parawing-spacecraft configuration being released from t h e h e l i c o p t e r i n t h e
trimmed g l i d i n g condition, and progressing i n a reverse sequence one phase a t a
time u n t i l f i n a l l y t h e spacecraft was released from t h e h e l i c o p t e r with t h e parawing completely collapsed, stowed on board, and deployed during f r e e v e r t i c a l
descent. No complete deployment t e s t s t a r t i n g with t h e parawing packed i n t h e
deployment bag on t h e s i d e of t h e spacecraft and ending with t h e spacecraft and
parawing i n g l i d i n g f l i g h t w a s conducted during a s i n g l e f l i g h t .
A q u a l i t a t i v e evaluation of t h e s t a b i l i t y of t h e configuration with i t s
p a r t i c u l a r suspension-line geometry and t h e effectiveness of s h i f t i n g t h e c e n t e r
of g r a v i t y as a means of c o n t r o l was a l s o made as t h e model glided t o t h e ground
following some of t h e deployment t e s t s .
Evaluation of t h e f l i g h t c h a r a c t e r i s t i c s w a s based on q u a l i t a t i v e observat i o n s of t h e control by t h e observers and on t h e q u a n t i t a t i v e measurements
obtained from motion-picture records. The motion p i c t u r e s were taken from t h e
ground and from t h e h e l i c o p t e r .
RESULTS AND DISCUSSION
A motion-p2cture f i l m supplement covering f l i g h t t e s t s of t h e model has been
prepared and i s a v a i l a b l e on loan. A request card form and a d e s c r i p t i o n of t h e
f i l m w i l l be found at t h e back of t h i s paper on t h e page with t h e a b s t r a c t cards.
Deployment Sequence
Not a l l deployment attempts were successful, but much u s e f u l d a t a were
obtained from t h e unsuccessful attempts which pointed t h e way t o t h e f i n a l satisf a c t o r y deployment sequence.
The complete successful deployment sequence as f i n a l l y derived i s shown s t e p
by s t e p i n t h e s t a t i c displays i n f i g u r e 5. Figure 5(a) shows t h e model with t h e
parawing packaged i n a deployment bag on t h e s i d e of t h e Spacecraft. A drogue
parachute i s attached t o t h e spacecraft with a three-point b r i d l e , and a separate
l i n e is attached t o t h e end of t h e deployment bag. The bottom of t h e deployment
bag i s secured t o t h e spacecraft with break cords. Figure 5 ( b ) shows t h e model
with t h e drogue released from t h e spacecraft and t h e deployment bag pulled off
t h e parawing. The drogue l i n e is now attached t o t h e ends of t h e telescoping
tubes. The parawing i s s t i l l i n i t s packaged condition. Figure 5 ( c ) represents
t h e model j u s t after t h e drogue has pulled t h e telescoping tubes t o t h e i r f u l l y
extended p o s i t i o n s and j u s t p r i o r t o unfolding t h e parawing. Figure 5 ( d ) shows
t h e parawing unfolded but with t h e nose s t i l l attached t o t h e spacecraft. The
drogue parachute i s now attached t o t h e parawing by a three-point b r i d l e , one
point at t h e apex and one point on each of t h e leading edges at t h e l o c a t i o n of
t h e r o l l - c o n t r o l l i n e s . Figure 5 ( e ) shows t h e p o s i t i o n of t h e parawing j u s t a f t e r
6
t h e nose i s r e l e a s e d from t h e spacecraft. The drogue parachute i s providing a
f o r c e t o p u l l t h e parawing away from t h e s p a c e c r a f t and at t h e same t i m e i s
causing t h e parawing t o pitchup so as t o s t a r t producing l i f t . Figure 5 ( f ) repres e n t s t h e parawing p o s i t i o n approximately halfway through t h e t r a n s i t i o n phase.
Note t h a t t h e drogue chute i s s t i l l attached t o t h e parawing. Figure 5 ( g ) i l l u s t r a t e s t h e paratring and spacecraft i n t h e g l i d i n g condition. The drogue parachute
i s r e l e a s e d soon a f t e r t h i s condition has been reached. O f course, i n f i g u r e s 5 ( e )
t o 5 ( g ) t h e sail i s not f i l l e d , s i n c e t h e photographs were taken with t h e model
hanging up i n s t i l l a i r .
A s pointed out previously, no complete deployment w a s c a r r i e d o u t i n one
f l i g h t . Each phase of t h e deployment w a s f l i g h t t e s t e d i n sequence with suffic i e n t overlap of t h e deployment phases from one f l i g h t t o t h e next t o i n s u r e t h a t
t h e operation of one phase does not i n t e r f e r e with t h e successful operation of
t h e succeeding,phases. m e deployment s t e p s as i l l u s t r a t e d i n f i g u r e s 5(a) t o
5 ( d ) were conducted during one f l i g h t . Then t h e s t e p s i l l u s t r a t e d i n f i g u r e s 5 ( c )
t o 5 ( g ) were conducted i n another f l i g h t except t h a t t h e drogue parachute w a s not
released. And, f i n a l l y , t h e s t e p s as i l l u s t r a t e d i n f i g u r e s 5 ( d ) t o 5 ( g ) w e r e
conducted i n one f l i g h t and included t h e r e l e a s e of t h e drogue parachute. It
should be remembered, however, t h a t t h e t e s t s were a c t u a l l y conducted i n a reverse
sequence.
Glide Tests
The model w a s t e s t e d i n a g l i d i n g condition before any deployment attempts
were made i n order t o o b t a i n a t r i m condition near t h e maximum l i f t - d r a g r a t i o
and a l s o t o determine t h e c o n t r o l t r a v e l s necessary f o r maneuvering.
A s pointed out previously, a center-of-gravity l o c a t i o n of 65 percent of t h e
k e e l l e n g t h back from t h e apex and 81 percent of t h e k e e l length below t h e k e e l
f o r t h e spacecraft-parawing combination w a s a r r i v e d a t as being t h e l o c a t i o n which
would be used during t h e deployment t e s t s . With t h i s center-of-gravity location,
t h e model appeared t o have a smooth and r e l a t i v e l y f l a t g l i d e path. The model w a s
l o n g i t u d i n a l l y and l a t e r a l l y s t a b l e and d i d not appear t o have any r o l l i n g ,
pitching, or yawing o s c i l l a t i o n s , and no f l u t t e r w a s observed i n t h e wing f a b r i c .
P i t c h c o n t r o l w a s achieved by moving t h e c e n t e r of g r a v i t y k6 percent of t h e k e e l
l e n g t h from t h e n e u t r a l p o s i t i o n a t a rate of approximately 10 percent p e r second.
Although t h i s rate produced l a r g e p i t c h i n g v e l o c i t i e s , it w a s not fast enough t o
make c o n t r o l of t h e model d i f f i c u l t . The 6-percent t r a v e l t o e i t h e r s i d e of neut r a l w a s s u f f i c i e n t t o maneuver t h e model from a s t e e p dive t o beyond stall. R o l l
c o n t r o l w a s achieved by r o l l i n g t h e wing +30 about t h e axis of t h e k e e l which corresponded t o a l a t e r a l s h i f t i n t h e c e n t e r of g r a v i t y of k5 percent of k e e l length.
A c o n t r o l r a t e of approximately 10 percent p e r second produced s a t i s f a c t o r y
l a t e r a l control.
Separation of Parawing From Spacecraft and Rotation t o Flying A t t i t u d e
The f i r s t phase of t h e deployment sequence t o be i n v e s t i g a t e d a f t e r t h e
g l i d i n g f l i g h t s w a s t h e separation of t h e parawing from t h e spacecraft and r o t a t i o n of t h e wing up t o i t s f l y i n g a t t i t u d e . For t h i s phase of t h e tests, t h e
parawing w a s attached t o t h e s p a c e c r a f t with t h e s t r u c t u r a l m e m b e r s f u l l y extended
and t h e spreader b a r s opened and locked, holding t h e leading edges a t t h e 50°
sweepback condition. The nose of t h e parawing w a s a t t a c h e d t o t h e spacecraft by
a s l i d i n g b o l t which could be r e l e a s e d by an e l e c t r i c motor a c t u a t o r responding
t o a radio signal from the ground. Even though t h e parawing separated from t h e
spacecraft, it would not p i t c h up i n t o a f l y i n g a t t i t u d e so as t o start producing
l i f t . The s p a c e c r a f t and parawing f e l l i n t h i s condition u n t i l t h e f l i g h t had t o
be terminated with an emergency recovery parachute.
To solve t h i s problem, a l i n e from a drogue parachute w a s attached a t t h e
nose of t h e parawing t o produce a p i t c h i n g moment. The e f f e c t i v e n e s s of t h i s
arrangement w a s i n v e s t i g a t e d i n t h e Langley 20-foot free-spinning t u n n e l ( r e f . 6).
The t e s t s showed t h a t t h i s arrangement i n i t s e l f w a s not a complete s o l u t i o n s i n c e
on some occasions, t h e parawing would not p i t c h up b u t r a t h e r would yaw t o one
s i d e o r t h e o t h e r and t h u s f a i l t o develop l i f t . Therefore, two a d d i t i o n a l l i n e s
from t h e drogue parachute were added t o t h e parawing; one l i n e w a s attached t o
each of t h e leading edges s o t h a t t h e t e n s i o n i n t h e l i n e from t h e drogue parachute prevented t h e parawing from yawing but l e f t it f r e e t o p i t c h up.
(See
f i g s . > ( e ) and 5 ( f ) . ) The t h r e e l i n e s from t h e drogue were run through e y e l e t s on
t h e parawing t o a common p o i n t on t h e k e e l t o f a c i l i t a t e release of t h e drogue at
t h e end of t h e deployment sequence. For purposes of mechanical s i m p l i c i t y t h e
drogue w a s automatically j e t t i s o n e d as soon as t h e parawing w a s i n i t s normal
f l y i n g condition.
Outdoor free-flight tests revealed t h a t i f t h e parawing were allowed t o
p i t c h up quickly, and i f it w e r e unrestrained except by t h e suspension l i n e s ,
extremely high loads were imposed on t h e suspension system. Also t h e parawing
made an almost instantaneous t r a n s i t i o n from Oo angle of a t t a c k t o 90' angle of
a t t a c k . A t 90' angle of a t t a c k , t h e r e w a s a l a r g e nose-down p i t c h i n g moment s i n c e
t h e t r i m angle of a t t a c k f o r t h e parawing-spacecraft combination w a s approximately 2 5 O . The parawing would p i t c h down so r a p d i l y t h a t it would not s t o p at
i t s t r i m angle of a t t a c k b u t would continue p i t c h i n g so as t o e n t e r a tumbling
condition. When t h e parawing- spacecraft combination became inverted, t h e spacec r a f t f e l l onto t h e w i n g . Because of t h e geometry of t h e spacecraft, it would
u s u a l l y roll o f f t h e wing; however, t h e model d i d not achieve t h e d e s i r e d t r i m
g l i d i n g f l i g h t from t h i s condition. Sometimes t h e l i n e s became entangled and
sometimes t h e wing s t a b i l i z e d i n a v e r t i c a l dive a t a condition of zero angle of
a t t a c k and zero l i f t . Keeping t h e drogue attached t o t h e parawing f o r a longer
t i m e a l l e v i a t e d t h e tumbling problem but d i d not reduce t h e high loads imposed on
t h e system by a n e a r l y instantaneous t r a n s i t i o n from low drag a t 0' angle of
a t t a c k t o high drag a t an angle of a t t a c k of goo. Therefore, a snubber l i n e was
attached between t h e nose of t h e parawing and t h e s p a c e c r a f t . This l i n e l i m i t e d
t o approximately 20' t h e i n i t i a l p i t c h travel of t h e wing when it w a s separated
from t h e s p a c e c r a f t . From t h i s p o s i t i o n t h e snubber l i n e w a s extended by a motoroperated winch u n t i l it f i n a l l y became s l a c k and all t h e load was being c a r r i e d
by t h e suspension l i n e s . A t t h i s t i m e t h e drogue parachute w a s automatically
j e t t i s o n e d . The extension of t h e snubber l i n e on t h e model required approximately 6 seconds. No attempt w a s made t o determine t h e fastest r a t e a t which t h e
snubber could be extended without causing a tumbling motion, but it i s believed
t h a t rates f a s t e r t h a n t h o s e used are p o s s i b l e . Extending t h e snubber l i n e slowly
allowed t h e parawing-spacecraft configuration t o m a k e a smooth t r a n s i t i o n from a
v e r t i c a l descent with zero l i f t t o a g l i d i n g descent with t h e donfiguration
trimmed a t approximately i t s b e s t l i f t - d r a g r a t i o .
Opening t h e Wing
The next s t e p backward i n t h e deployment process w a s t o r e t r a c t t h e leading
edges u n t i l they w e r e p a r a l l e l t o t h e keel. A t t h i s stage, a deployment bag w a s
used t o p r o t e c t t h e parawing f a b r i c and suspension l i n e s from t h e a i r s t r e a m
before t h e deployment process w a s begun. It a l s o f a c i l i t a t e d the packing and
handling of t h e wing. The forward end of t h e deployment bag w a s attached t o t h e
nose of t h e parawing by a lightweight cord t o prevent t h e bag from blowing off
prematurely. This cord w a s broken e a s i l y and t h e bag w a s quickly p u l l e d o f f t h e
parawing when t h e load from t h e drogue parachute w a s applied t o t h e back end of
t h e deployment bag. This w a s accomplished when t h e b r i d l e l i n e s between t h e
drogue and t h e spacecraft were released, automatically t r a n s f e r r i n g t h e load of
t h e drogue t o t h e bag. A f t e r t h e bag w a s p u l l e d c l e a r of t h e parawing, t h e l o a d
from t h e drogue w a s t r a n s f e r r e d t o t h e t h r e e - l i n e b r i d l e used t o p i t c h t h e wing
up t o i t s g l i d i n g a t t i t u d e . Several t e s t s were conducted i n t h e Langley 20-foot
free-spinning tunnel t o i n v e s t i g a t e t h e operation of t h e system. From t h e s e spint u n n e l t e s t s , t h e amount of t e n s i o n required t o spread t h e leading edges t o t h e i r
50' sweepback condition w a s determined, and a system of packing t h e wing f a b r i c
and t h e suspension l i n e s w a s devised which prevented entanglements and d i d not
hinder deployment. S t e e l a i r c r a f t cables were t e s t e d a s suspension l i n e s , but
proved t o be t o o s t i f f f o r e f f i c i e n t packing. Therefore, nylon cables were used
on t h e f i n a l configuration. Once t h e technique had been worked out i n t h e tunnel,
outdoor f r e e - f l i g h t t e s t s were conducted t o confirm t h e t u n n e l r e s u l t s .
The l a s t phase t o be checked i n t h e deployment sequence w a s t h a t of unpackaging t h e wing and extending t h e telescoped members. This phase w a s a l s o checked
i n t h e Langley 20-foot free-spinning t u n n e l p r i o r t o t h e out'door f r e e - f l i g h t t e s t .
For t h i s phase of t h e t e s t s , t h e drogue parachute had t o extend and lock t h e
telescoping members. This w a s accomplished by securing t h e l i n e from t h e drogue
parachute first t o t h e end of t h e keel, t h e n t o t h e end of one of t h e leading
edges, and f i n a l l y t o t h e end of t h e o t h e r leading edge. The drogue l i n e had
enough s l a c k between t h e ends of t h e t e l e s c o p i n g members so t h a t t h e k e e l could
be f u l l y extended and locked without p u l l i n g on t h e f i r s t leading edge, and t h e n
t h e f i r s t leading edge could be extended without p u l l i n g on t h e second leading
edge. A f t e r t h e k e e l w a s extended, a r e e f i n g l i n e c u t t e r w a s used t o s e p a r a t e t h e
drogue l i n e from t h e end of t h e k e e l and t h u s allow t h e l o a d t o be t r a n s f e r r e d t o
t h e end of one of t h e leading edges causing it t o be extended next. I n a similar
manner, t h e f i n a l leading edge w a s extended and t h e drogue l i n e w a s r e l e a s e d from
it s o as t o t r a n s f e r t h e load of drogue t o t h e b r i d l e on t h e wing. This sequence
w a s used t o o b t a i n t h e f u l l f o r c e of t h e drogue parachute on each of t h e t e l e scoping members. Tests showed t h a t i f all t h e telescoping members were extended
at one t i m e , all t h e f l a r e j o i n t s would not j a m c o n s i s t e n t l y . There would be a
random f a i l u r e with no p a r t i c u l a r j o i n t being more s u s c e p t i b l e t o f a i l u r e than
any o t h e r . A s an added s a f e t y f e a t u r e , s m a l l spring-loaded p i n s w e r e made t o
drop i n t o p o s i t i o n t o prevent t h e t e l e s c o p i n g tubes from r e t r a c t i n g once t h e y
w e r e extended. Sometimes when all t h e tubes w e r e extended simultaneously, one of
t h e s e c t i o n s would f a i l t o t r a v e l f a r enough t o allow t h e spring-loading p i n t o
9
drop i n t o t h e lock p o s i t i o n .
eliminated t h i s s i t u a t i o n .
E x t r a c t i o n of t h e telescoping tubes one a t a t i m e
CONCLUDING REMARKS
I n general, t h e f l i g h t t e s t s showed t h a t t h e radio-controlled model of t h e
parawing-spacecraft configuration w a s s t a b l e and could be c o n t r o l l e d by s h i f t i n g
t h e c e n t e r of g r a v i t y . The deployment system which w a s developed i s a satisf a c t o r y method f o r use with a t e l e s c o p i n g r i g i d parawing. The deployment process
of t h e parawing, however, must be a sequence of c a r e f u l l y c o n t r o l l e d and timed
events, and some p o r t i o n s of t h e deployment should not occur t o o quickly. The
most s i g n i f i c a n t single f a c t o r learned about t h e deployment process w a s t h a t t h e
parawing had t o be slowly r o t a t e d t o a l i f t i n g condition s i n c e t o o f a s t a t r a n s i t i o n from zero l i f t t o m a x i m u m l i f t would result i n a tumbling motion.
Langley Research Center,
National Aeronautics and Space Administration,
Langley Station, Haznpton, Va., September 3, 1963.
REFERENCES
1. Rogallo, Francis M., Lowery, John G., Croom, Delwin R., and Taylor, Robert T.:
Preliminary I n v e s t i g a t i o n of a P a r a g l i d e r . NASA TN D-443, 1960.
F l e x i b l e Reentry Gliders.
2. Rogallo, F. M., and Lowery, J. G.:
No. 175C, SOC. of Automotive Eng., Apr. 1960.
Preprint
3. Naeseth, Roger L.:
for A i r c r a f t .
An Exploratory Study of a Parawing as a H i g h - L i f t Device
NASA TN D-629, 1960.
4. Burk, Sanger M.,
Jr.: Free-Flight I n v e s t i g a t i o n of t h e Deployment, Dynamic
S t a b i l i t y , and Control C h a r a c t e r i s t i c s of a 1/12-Scale Dygamic RadioControlled Model of a Large Booster and Parawing. NASA TN D-1932, 1963.
5. Hewes, Donald E.:
Parawings.
Free-Flight I n v e s t i g a t i o n of Radio-Controlled Models With
NASA TN D-927, 1961.
6. Zimmerman, C. H.: Preliminary T e s t s i n t h e N.A.C.A.
NACA Rep. 557, 1936.
Free-Spinning Wind Tunnel.
10
I
L-61-4144
Figure 1.-Photograph of ground s t a t i o n s showing t h e roll-yaw p i l o t and p i t c h p i l o t i n position.
( a ) Model r a i s e d .
L-61-273
( b ) Model lowered.
Figure 2.- Photograph of model on launch r i g i n r a i s e d and lowered p o s i t i o n s .
L-61-274
Free floating fabric
";.
\\
Typical flared joint detail
IL"
, \
Figure
3.- Two-view drawing
of telescoping parawing.
1-
..cG2J-J- )pre:
end fitting detail
I
I
Suspension-line
attachment points
ti
I
!
I
tI /
T
5.850"
Figure
14
4.- Two-view
drawing of model spacecraft.
100"
( a ) Spacecraft with parawing stowed onboard.
Figure 5 .
-
Deployment sequence.
L-63-4752
L-63-4753
(b) Drogue parachute r e l e a s e d from spacecraft and deployment bag p u l l e d off parawing.
Figure
16
5 . - Continued.
( e ) Telescoping tubes extended by means of t h e drogue parachute.
Figure 5 .
-
Continued.
L-63-4754
(a)
Leading edges spread t o 50° sweepback p o s i t i o n .
Figure
5.- Continued.
L-63-4755
L-65-4756
( e ) Apex of parawing released from s p a c e c r a f t , drogue s t a r t i n g t o r o t a t e parawing t o l i f t i n g condition.
Figure 5 .
- Continued.
L-63-4757
( f ) Parawing approximately halfway through t h e t r a n s i t i o n from zero l i f t t o g l i d i n g f l i g h t condition.
Figure
5.- Continued.
I
( g ) Parawing-spacecraft configuration i n f i n a l g l i d i n g f l i g h t condition.
L-63-4758
Figure 5.- Concluded.
NASA-Langley, 1963
L-3640
21