Document
TECHNICAL MEMORANDUM
X-518
LANDING -GEAR BEHAVIOR DURINlG TOUCHDOWN AND RUNOUT F O R 1 7 LANDINGS O F T H E X - l 5 RESEARCH AIRPLANE: By James M. McKay and Betty J. Scott Flight R e s e a r c h C e n t e r E d w a r d s , Calif.
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON M a r c h 1961
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CONFIDENTIAL NATIONAL AERONAUTICS AND SPACE ADMINISTRATION TECHNICAL, MEMORANDUM X-318 LANDING-GEAR BEHAVIOR DURING TOUCHDOWN P A D RUNOUT FOR 17 LANDINGS OF THE x-15 RESEARCH AIRPLAXP By James M. McKay and Betty J. Scott SUMMARY Data a r e presented f o r t h e pretouchdown condition, t h e impact period, and t h e runout phase of 17 landings made with t h e X-15 airplane.
Vertical v e l o c i t i e s up t o 9.5 f e e t per second and t r u e ground speeds between 145 knots and 238 knots were recorded during t h e landings.
The r e s u l t s of t h e investigation indicate t h a t t h e highest main- gear shock-strut force, drag reaction, airplane upper-mass response, and h o r i z o n t a l - t a i l load occurred during t h e nose-gear touchdown f o r a l l of t h e landings.
The mean value of t h e c o e f f i c i e n t of f r i c t i o n of t h e main-gear skids calculated f o r one landing w a s 0.33. The combined e f f e c t of t h e high skid drag and low rolling f r i c t i o n of t h e nosewheel t i r e s provided more than adequate d i r e c t i o n a l s t a b i l i t y during t h e runout. A s a consequence, pilot-induced inputs resulted i n only small changes t o t h e a i r p l a n e d i r e c t i o n of motion during t h e runout.
No nosewheel shimmy was observed i n any of t h e landings, d e s p i t e t h e absence of a shimmy damper.
INTRODUCTION The approach and landing operation of unpowered rocket airplanes has always required considerable p i l o t concentration, but has usually been accomplished with a r e l a t i v e l y conventional procedure. The X-15 a i r p l a n e i n i t i a t e s a c l a s s of vehicles--manned, boost glide, and maneuverable reentry--that requires a landing-gear system designed t o expend a minimum of a i r p l a n e space and weight, withstand t h e high temperatures r e s u l t i n g from aerodynamic heating, be capable of sustaining high landing speeds, and provide s a t i s f a c t o r y d i r e c t i o n a l * T i t l e , Unc lass i f ied .
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2 CONFIDENTIAL The configuration stability during the runout phase of the landing.
chosen for the X-13 airplane to meet these requirements consists of a skid-type main gear located well to the rear of the airplane center of gravity and a conventional dual-wheel nose gear located well forward of the center of gravity.
In order to investigate the characteristics of such a landing-gear system, the gear and the airplane upper mass of two X-15 airplanes were instrumented by the NASA Flight Research Center, Edwards, Calif., and North American Aviation, Inc., to measure pertinent quantities during the landing.
SYMBOLS center-of-gravity longitudinal acceleration, g units a2 center-of-gravity vertical acceleration, g units an main-gear and nose-gear upper-mass vertical acceleration, 8 , g units airplane drag coefficient, corresponding to full flaps and CD speed brakes and extended landing gear airplane aerodynamic drag, CDqS, lb drag ground reaction, lb shock-strut force, lb horizontal-tail aerodynamic load, lb vertical ground reaction, lb acceleration due to gravity, ft/sec pitching velocity, radians/sec dynamic pressure, lb/sq ft wing area, sq ft time interval between initial main-gear contact and nose-gear contact, sec
v true ground velocity, knots
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CONFIDENTIAL VV v e r t i c a l velocity, f t / s e c a i r p l a n e weight a t landing, l b wL a indicated angle of attack, deg 6h h o r i z o n t a l - t a i l deflection, deg 6, shock-strut displacement, i n .
CI c o e f f i c i e n t of f r i c t i o n Subscripts: m main gear n nose gear AIRPLANE The X-15 a i r p l a n e ( f i g s . 1 and 2) is a rocket-powered research a i r c r a f t designed t o a t t a i n speeds up t o 6,600 f e e t per second or a l t i t u d e s up t o 250,000 f e e t . The l i f t - d r a g r a t i o i n t h e landing configuration i s about 3.3. The a i r p l a n e ' s control system incorporates an all-movable and d i f f e r e n t i a l l y operated horizontal t a i l f o r p i t c h and roll motion and a v e r t i c a l t a i l consisting of a fixed portion and an all-movable portion f o r yaw control. The all-movable section of t h e lower v e r t i c a l t a i l is j e t t i s o n e d j u s t p r i o r t o touchdown t o a l l o w f o r ground clearance.
The airplane was designed by North American Aviation, Inc., through t h e cooperative e f f o r t of t h e U.S. A i r Force, t h e U.S. N a v y , and t h e National Aeronautics and Space Administration. Physical c h a r a c t e r i s t i c s of t h e a i r p l a n e a r e given i n t a b l e I.
W I N G - G E A R SYSTEM The landing-gear system of t h e X-15 c o n s i s t s of a nonsteerable, full-castering dual-wheel nose gear located 23.3 f e e t forward of t h e a i r p l a n e center of gravity (landing condition) and a skid-type main gear located under t h e t a i l 15.8 f e e t rearward of t h e center of gravity.
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L CONFIDENTIAL Main Gear The main-gear l e g s a r e Inconel X struts attached t o t h e fuselage by trunnion f i t t i n g s ( f i g s . 3(a) and 3 ( b ) ) and through bell-crank arms The two t o high-pressure shock struts i n s t a l l e d inside t h e fuselage.
6-inch-wide, 3-foot-long skids, fabricated from 4130 s t e e l , a r e universally mounted t o the struts t o allow f o r pitching and r o l l i n g motion, but a r e restrained f o r p a r a l l e l alinement. The drag braces a r e attached t o t h e fuselage by semiuniversal f i t t i n g s and, similarly, connect with t h e skids ahead of t h e strut-attachment pin. Bungee-type springs connect t h e leading edge of t h e skid t o t h e main-landing-gear l e g t o insure nose-up a t t i t u d e of t h e skids p r i o r t o touchdown.
I n t h e r e t r a c t e d position t h e landing-gear l e g s a r e folded forward against t h e outside of t h e fuselage, and t h e skids a r e stored with t h e i r r e a r portion overlapping t h e landing-gear leg. After release, t h e gear i s extended down and rearward by g r a v i t y and a i r l o a d s .
Since t h e engine and i t s accessories l i m i t t h e s i z e of t h e landing- gear components mounted i n t h e fuselage, t h e shock-strut w a s designed with a minimum of stroke. The shock s t r u t i s of t h e oleopneumatic type with a pressure-relief valve and a metering pin acting i n p a r a l l e l t o c r e a t e t h e hydraulic load. During t h e main-gear phase of t h e landing, t h e hydraulic load i s created by t h e metering pin. When t h e t o t a l stroke i s one-half complete, t h e metering p i n closes off t h e o r i f i c e and t h e hydraulic load i s provided by t h e r e l i e f valve f o r t h e remainder of t h e stroke. With t h e r e l i e f valve open, t h e shock-strut force i s a function of piston position; t h e t o t a l reaction i s t h e sum of t h e hydraulic and a i r s p r i n g force. The r e l i e f valve provides f o r an e s s e n t i a l l y constant pressure drop and allows f o r a f r e e flow f o r fast extension during rebound.
The s t r u t - a i r s p r i n g c h a r a c t e r i s t i c i s a function of t h e a i r pressure and t h e quantity of o i l pumped i n t o t h e strut i n i t s f u l l y extended position. With t h e strut f u l l y compressed, t h e a i r pressure i s s u f f i c i e n t t o r e s t o r e t h e strut t o i t s normal s t a t i c height. The s t r u t - i n f l a t i o n pressures a r e given i n t a b l e I1 f o r each f l i g h t of t h e airplane.
The i n i t i a l landings (one with t h e X-15 number 1 a i r p l a n e and t h r e e with t h e X-17 number 2) indicated t h a t additional energy-absorbing a b i l i t y w a s required f o r t h e main-gear system f o r landing weights up t o 14,500 pounds. To meet t h i s requirement, t h e m a x i m u m shock-strut stroke w a s increased from 2.38 inches t o 3.38 inches. The remainder of t h e f l i g h t s were made with t h e redesigned shock strut. The increase i n
maximum stroke made it necessary t o add 4 inches t o each main-gear l e g
for ground clearance of t h e unjettisonable portion of t h e lower v e r t i c a l f i n with t h e shock struts f u l l y compressed.
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CONFIDENTIAL Nose Gear The nose gear ( f i g . 4) i s of conventional design, nonsteerable, with full 360" c a s t e r i n g i n t h e deflected condition. D u a l corotating wheels are u t i l i z e d f o r prevention of shimmy and a l s o f o r l o w c a s t e r i n g r e s i s t a n c e t o provide s a t i s f a c t o r y d i r e c t i o n a l s t a b i l i t y during t h e runout. I n order t o insure proper wheel alinement p r i o r t o touchdown, t h e nose gear is r e s t r a i n e d i n t h e f u l l y extended p c s i t i o n .
The shock strut was designed with a t o t a l t r a v e l of 18 inches and a nominal design s t r u t - i n f l a t i o n pressure of 184 p s i i n t h e f u l l y extended position. 18 inches x 4.4 inches i n The VII-type nose-gear t i r e s a r e s i z e with a r a t i n g of 8 ply. The t i r e s a r e i n f l a t e d t o a pressure of 185 p s i and have a r o l l i n g radius of 8 inches a t t h i s pressure.
I n order t o r e t r a c t t h e nose gear i n a minimum of space during f l i g h t , t h e shock strut is compressed and i s held i n t h i s p o s i t i o n by a lock arrangement that i s automatically released when t h e gear extends ( f i g . 4 ) . Aerodynamic heating of t h e pneumatic t i r e s and oleopneumatic shock s t r u t i s kept t o a minimum by i n s u l a t i o n of t h e storage compart- ment .
The initial landings of t h e a i r p l a n e indicated a rebounding of t h e nosewheels on t h e lakebed following t h e spin-up period. A s an i l l u s t r a t i o n of t h e nose-gear rebound, t h e d i s c o n t i n u i t y of t h e nosewheel t r a c k i s shown i n figure 5. Examination of t h e system showed t h a t v i o l e n t m i x i n g of t h e air and f l u i d occurred, which r e s u l t e d i n foaming of t h e f l u i d . I n s u f f i c i e n t time elapsed between landing-gear extension and touchdown t o allow t h i s foam t o d i s s i p a t e .
Consequently, t h e r e was a decreased hydraulic r e s i s t a n c e at t h e beginning of t h e stroke, which resulted i n lower energy-absorbing a b i l i t y of t h e strut. The fcaming was l a r g e l y eliminated by adjusting t h e strut a i r s p r i n g i n the s t o r e d p o s i t i o n t o just enough pressure t o elongate t h e s t r u t during extension, and by increasing t h i s pressure a f t e r extension t o i t s normal value of 184 p s i . The strut was pressurized by using an external nitrogen b o t t l e mounted i n t h e nose-gear compartment and actuated during release. I n order t o check t h e operation of t h i s system, t h e nose-gear strut pressures were measured immediately after each landing.
INSTRUMENTATION The q u a n t i t i e s measured during t h e approach, touchdown, and runout phases of t h e landings are given i n t h e following tabulation: .
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6 CONFIDENTIAL Nose gear Airplane Main gear ~ Center-of-gravity Shock-strut f o r c e Vertical ground v e r t i c a l acceleration r eac ti on1 Airspeed Drag ground reaction' Drag ground r e a c t ion1 Shoek - s t r u t d e f l e c t ion Shock-strut d e f l e c t i o n Angle o f a t t a c k Pitching v e l o c i t y Upper-mass v e r t i c a l Upper-mass v e r t i c a l a c c e l e r a t i o n acceleration Rolling v e l o c i t y S i d e s l i p angle Flap angle Hor i z o n t a l - t a i l load Horizontal-tail angle Airspeed was measured w i t h an N A S A P i t o t - s t a t i c tube mounted on Free-floating vanes, a l s o mounted on t h e nose t h e end of t h e nose boom.
boom, were used t o measure angles of a t t a c k and s i d e s l i p .
Akeley phototheodolite cameras, mnning a t 19 frames per second, tracked t h e a i r p l a n e from a height of approximately 80 f e e t above t h e runway through touchdown and f i n a l landing runout. From t h i s photo- graphic coverage, such i n f o m a t i o n as landing coordinates, a i r p l a n e a l t i t u d e , flight-path velocity, and v e r t i c a l v e l o c i t y at landing w a s obtained.
The l o c a t i o n of some of t h e main-landing-gear instrumentation i s shown i n f i g u r e 3(a). S t r a i n gages were mounted on t h e upper and lower surfaces of each of t h e bell-crank arms and were arranged t o measure t h e axial f o r c e applied t o t h e shock-strut cylinder, The s t r a i n gages mounted on each main-gear drag brace were arranged t o measure tension loads i n t h e drag brace r e s u l t i n g from t h e drag force a c t i n g on t h e skids. S t r a i n gages mounted on both the l e f t and r i g h t spindles of t h e all-movable h o r i z o n t a l t a i l were located i n a v e r t i c a l plane t o measure t h e bending moment, torque, and shear r e s u l t i n g from t h e load normal t o t h e t a i l . S t r a i n gages were mounted on t h e nose-gear trunnion and down-lock mechanism t o measure the v e r t i c a l loads and drag loads a t t h e nose-gear axle.
The a i r p l a n e center-of-gravity a c c e l e r a t i o n was measured by means of a vane-type, magnetically damped three-component accelerometer with a n a t u r a l frequency of 32 cycles per second. Linear strain-gage accelerometers were located a t the a i r p l a n e c e n t e r of gravity, d i r e c t l y above each main gear, and a t t h e nose gear t o measure v e r t i c a l accelerations. The n a t u r a l frequency of t h e strain-gage accelerometers was g r e a t e r than 125 cycles per second. The record- galvanometers had a natural frequency of about 100 cycles per second.
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CONFIDlWTIAL 7 Shock-strut displacement f o r t h e l e f t and r i g h t main gear and t h e nose gear was measured by s t r u t - p o s i t i o n t r a n s m i t t e r s . The t r a n s m i t t e r s consisted of a circular-type potentiometer connected between the upper and lower sections of each shock s t r u t by lightweight l e v e r s t o conform A t y p i c a l w i t h the s c i s s o r s p r i n c i p l e during strut displacement.
i n s t a l l a t i o n is shown i n f i g u r e 4 f o r t h e nose gear.
All strain-gage, accelerometer, and shock-strut-displac ement outputs were recorded on photographically recording oscillographs and were synchronized by a common timer.
CALIBRATION AND DATA REDUCTION The a c c e l e r a t i o n a t the a i r p l a n e center of g r a v i t y presented as data p r i o r t o touchdown w a s measured by t h e three-component acceler- ometer. The a c c e l e r a t i o n s a t t h e center of gravity, as well as a t t h e nose-gear and main-gear upper mass, during the landing impact and runout were measured by t h e l i n e a r strain-gage accelerometers.
For each main gear, t h e bell-crank-arm s t r a i n gages were c a l i b r a t e d t o give t h e axial load on t h e shock-strut cylinder. The s t r a i n gages on t h e l e f t and r i g h t main-gear drag braces were c a l i b r a t e d t o give t h e drag-brace tension loads r e s u l t i n g from t h e drag loads on the skids.
From t h e geometry of t h e main-gear system, t h e drag-brace tension loads were used t o c a l c u l a t e t h e drag reaction between t h e skids and t h e ground. No i n t e r a c t i o n e x i s t s between t h e drag-brace load and t h e main-gear shock strut, since pivot points a t the fuselage f o r t h e drag brace and t h e landing-gear l e g f a l l on a l i n e that is e s s e n t i a l l y parallel t o t h e longitudinal c e n t e r l i n e of t h e fuselage.
The s t r a i n gages on t h e l e f t and r i g h t h o r i z o n t a l - t a i l spindles were c a l i b r a t e d t o measure shear, bending moment, and torque a t t h e root s t a t i o n . Equations, which accounted f o r t h e i n t e r a c t i o n of t h e bending and shear gages, were used t o c a l c u l a t e t h e load normal t o t h e horizontal t a i l and were developed according t o t h e method of reference 1. The aerodynamic load was obtained by adding i n e r t i a corrections t o the measured forces. The i n e r t i a term was t h e product of t h e mass outboard of t h e spindle strain-gage s t a t i o n s (horizontal- t a i l panel) and t h e normal a c c e l e r a t i o n a t t h e t a i l of t h e airplane.
The nose-gear s t r u c t u r e of t h e X-15 number 2 a i r p l a n e w a s used as a strain-gage balance t o measure v e r t i c a l and drag forces on t h e a x l e .
The r e l a t i o n s h i p between t h e strain-gage response and t h e applied load w a s determined by c a l i b r a t i n g t h e nose gear i n a load-testing machine at North American Aviation, Inc.
The gages were c a l i b r a t e d f o r t r u n r i o n v e r t i c a l reactions and trunnion drag and down-lock drag reactions.
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gages were a l s o c a l i b r a t e d t o determine t h e e f f e c t s of side load a t t h e a x l e and t o e s t a b l i s h t h e i n t e r a c t i o n ( f o r example, t h e e f f e c t s of drag forces on t h e v e r t i c a l shear gages) under various combinations of v e r t i c a l , drag, and side load.
I n order t o determine if fuselage deflections during t h e landing touchdown induced axial compression loads i n t h e nose-gear trunnion which would i n t e r a c t with t h e drag gages, two additional gages were i n s t a l l e d and c a l i b r a t e d t o measure t h e axial load i n t h e trunnion.
The c a l i b r a t i o n showed t h a t these loads had a negligible e f f e c t .
The nose-gear ground-reaction forces, both v e r t i c a l and drag, a r e considered t o be t h e loads a t t h e nosewheel axle; no corrections a r e included f o r t h e i n e r t i a forces of t h e nose-gear lower mass (approx.
94 l b ) .
LANDING CONDITIONS The landings of t h e X - l 5 airplanes reported herein ( t a b l e 111) were made on designated, marked s t r i p s on t h e hard surface of Rogers Dry Calif., with t h e exception of one Edwards A i r Force Base, Lake a t emergency landing on an a l t e r n a t e landing s i t e , Rosamond Dry Lake. The landings, which were made following general research f l i g h t s of t h e X-15 airplane, resulted i n v e r t i c a l v e l o c i t i e s a t main-gear touchdown ranging from about 1.0 t o 9.5 f e e t per second and t r u e ground speeds between 145 knots and 238 knots. The t r u e ground speed a t touchdown w a s calculated by using t h e i n t e r v a l between t h e time t h e main gear and t h e nose gear i n i t i a l l y touched t h e ground (as obtained from oscillograph records) and t h e measured distance between t h e main-gear- and nose-gear- touchdown points on t h e lakebed. The angles of a t t a c k a t touchdown ranged from 4.7" t o 1 1 . 2 ' . The m a x i m u m wind velocity across t h e lakebed f o r any of t h e landings w a s approximately 20 knots.
The X-15 airplanes used i n t h e landings reported herein were flown by three experimental t e s t p i l o t s , designated A, B, and C ( t a b l e 111).
P i l o t s A and B had considerable experience with rocket research a i r c r a f t , and each of t h e t h r e e p i l o t s had performed numerous landings using operational a i r c r a f t modified t o simulate X-13 c h a r a c t e r i s t i c s ( r e f . 2).
Escort p i l o t s i n operational airplanes accompanied t h e X-15 through t h e approach and touchdown on t h e lakebed and informed t h e p i l o t of airspeed and a l t i t u d e .
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CONFIDENTIAL PRESENTATION OF RESULTS The flight-designation system ( t a b l e s I1 and 111) which has been established for t h e X - 1 5 research program c o n s i s t s of t h r e e terms: The f i r s t term indicates t h e X-15 airplane by number; t h e second term i n d i c a t e s t h e f r e e - f l i g h t number of t h a t airplane; and, t h e t h i r d term indicates t h e number of airborne X-l5/B-52 missions f o r a given X - 1 5 airplane. For example, t h e f l i g h t designated as 1-3-8 w a s made with t h e number 1 a i r p l a n e and was t h e t h i r d f r e e - f l i g h t and t h e eighth airborne mission of t h i s airplane.
A s s t a t e d previously, t h e i n i t i a l landings of t h e X - 1 5 a i r p l a n e ( f l i g h t s 1-1-5, 2-1-3, 2-2-6, and 2-3-9) were made with t h e o r i g i n a l main-landing-gear system.
A summary of t h e maximum measured q u a n t i t i e s f o r t h e main-gear touchdown, nose-gear touchdown, and runout i s given i n t a b l e 11.
Pretouchdown conditions of t h e X - 1 5 number 1 and number 2 a i r p l a n e s j u s t p r i o r t o ground contact are given i n t a b l e 111. The landing weights and v e r t i c a l v e l o c i t i e s are shown i n t a b l e I1 and t a b l e I11 f o r convenience i n comparing r e s u l t s . Some d a t a previously reported i n reference 3 f o r t h e landing following f l i g h t 1-1-3 and i n reference 4 f o r t h e landing following f l i g h t 2-1-3 have been corrected as a r e s u l t of more r e l i a b l e methods of d a t a reduction. true ground speed for t h e landing following The f l i g h t 1-1-5 i s 168 knots instead o f 158 knots, and t h e nose-gear v e r t i c a l v e l o c i t y a t touchdown i s 17.4 f e e t per second instead of 13.5 f e e t per second, as shown i n reference 3.
For t h e landing following f l i g h t 2-1-3 ( r e f . 4 ) , t h e nose-gear v e r t i c a l v e l o c i t y a t touchdown i s 13.2 f e e t per second instead of 1 3 . 0 f e e t per second.
Some of t h e nose-gear shock-strut pressures measured immediately a f t e r each landing varied s l i g h t l y from t h e nominal value of 184 p s i because of leakage and temperature e f f e c t s . The pressure f o r t h e landing following f l i g h t 2-5-2 (330 p s i ) w a s t h e r e s u l t of overpressur- i z a t i o n during servicing .
Typical time h i s t o r i e s of shock-strut force, shock-strut displacement, and upper-mass acceleration f o r t h e present gear system are shown i n figures 6(a) t o 6 ( d ) f o r t h e X-15 number 1 a i r p l a n e from 0.2 second p r i o r t o contact with t h e lakebed through t h e main-gear- and nose-gear-touchdown period. Similar q u a n t i t i e s , as w e l l as main- gear and nose-gear drag reaction and nose-gear v e r t i c a l reaction, are presented i n f i g u r e s 7(a) t o 7(d) f o r t h e X-15 number 2 airplane.
Instrument malfunction during some of t h e landings r e s u l t e d i n some u n r e l i a b l e data.
For example, i n f i g u r e 7(d) no drag-reaction d a t a were obtained f o r t h e l e f t main gear or f o r t h e nose gea-, and i n f i g u r e 7(b) t h e measured nose-gear drag reactions p r i o r t o touchdown were t o o high CONFIDENTIAL 10 CONFIDENTIAL i n magnitude t o be considered as aerodynamlc drag. However, t h e incremental values of nose-gear drag reactions a r e considered satis- f a c t o r y .
Such q u a n t i t i e s as angle of attack, pitching velocity, center-of- g r a v i t y v e r t i c a l acceleration, h o r i z o n t a l - t a i l deflection, and h o r i z o n t a l - t a i l load a r e shown i n f i g u r e s 8(a) t o 8(d) and f i g u r e s g(a) t o 9(d) f o r t h e X-13 number 1 and number 2 airplanes, respectively. A photograph i l l u s t r a t i n g t y p i c a l main-landing-gear-skid marks on t h e lakebed i s shown i n f i g u r e l O ( a > , and landlng-gear t r a c k s during runout as obtained from measurements on t h e lakebed are shown i n f i g u r e s 10(b) and 1O(c). A photograph of landing-gear marks during t h e runout phase of a t y p i c a l landing is shown i n figure 11. The v a r i a t i o n of c o e f f i c i e n t of f r i c t i o n and true ground speed f o r t h e main-gear skids i s shown i n figures =(a) and 12(b) f o r t h e runout phase of one landing.
DISCUSSION The main-gear system located under t h e t a i l of t h e X-15 a i r p l a n e r e s u l t s i n a landing-impact maneuver d i f f e r e n t from that experienced on aircraf't with a conventionally placed gear. A schematic i l l u s t r a t i o n of t h e touchdown IS shown i n f i g u r e 13. P r i o r t o touchdown, negative h o r i z o n t a l - t a i l d e f l e c t i o n s established t h e nose-high a t t i t u d e during flare ( f i g . l 3 ( a ) ) .
t h e landing A f t e r i n i t i a l impact, r o t a t i o n of the a i r p l a n e about t h e main gear occurs, and t h e a i r p l a n e e s s e n t i a l l y "slams" d a m onto its nose gear ( f i g s . l 3 ( b ) t o l 3 ( d ) ) . A second Impact then occurs on t h e main gear as t h e r e s u l t of r o t a t i o n about t h e nose gear ( f i g . l 3 ( e ) ) . The gear system is then restored t o its normal s t a t i c height f o r t h e runout (fig. l 3 ( f ) ) . A more complete discussion of t h e e f f e c t of t h e l o c a t i o n of t h e r e a r landing gear on landing behavior is given i n reference 5.
Pretouchdown Conditions The a i r p l a n e a t t i t u d e j u s t p r i o r t o touchdown f o r a t y p i c a l landing is shown in figure 14. For a l l t h e landings reported herein, t h e v e r t i c a l v e l o c i t i e s a t main-gear touchdown ranged from 1.0 t o 9.5 feet per second; t h e latter velocity, occurred during t h e emergency landing on Rosamond D r y Lake ( f l i g h t 2-3-9). The angles of a t t a c k a t touchdown ranged from 4,7O, a t which t h e indicated airspeed a t touchdown was t h e g r e a t e s t (214 knots), t o 11.2", at which t h e indicated airspeed was 160 knots.
The lowest indicated airspeed (153 knots) at touchdown occurred on t h e first landing of t h e X-15 airplane ( f l i g h t 1-1-5) during which severe longitudinal o s c i l l a t i o n s were encountered just p r i o r t o touchdown ( r e f . 6 ) . The instantaneous a i r p l a n e lie a t touchdown, presented as CONFIDEmTlAL .........................
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COWIDENTIAL 11 center-of-gravity a c c e l e r a t i o n j u s t p r i o r t o first skid contact, varied from 85 percent t o 140 percent of t h e a i r p l a n e landing weight. There appeared t o be no consistent e f f e c t of l i f t on v e r t i c a l v e l o c i t y at i n i t i a l touchdown.
&in-Gear Touchdown Figures 6 and 7 present ty-pical measured q u a n t i t i e s from four landings of each X-15 airplane. The data a r e presented from i n i t i a l touchdown; zero time coincides with t h e time of t h e first contact of a skid t r a i l i n g edge with t h e lakebed. The time from t h e i n i t i a l t o t h e second skid contact was t h e result of one or more f a c t o r s , including a i r p l a n e roll a t t i t u d e and main-landing-gear-skid i n c l i n a t i o n . The data show t h a t t h i s time i n t e r v a l was small, with a maximum of 0.20 second experienced during t h e landing following f l i g h t s 1-3-8 and 1-7-12.
The s i m i l a r i t y of shock-strut force, shock-strut displacement, and upper-mass a c c e l e r a t i o n between t h e l e f t and r i g h t gear during t h e main-gear impact i s shown i n f i g u r e s 6 and 7. The landings, i n which both main gears equally absorbed t h e landing-impact energy, were ty-pical of most of t h e landings; however, two exceptions were experienced following f l i g h t 1-3-8 ( f i g . 6 ( b ) ) and f l i g h t 2-2-6 ( f i g , 7 ( a ) ) , For a l l t h e landings both t h e l e f t and t h e r i g h t skid were s o l i d l y on t h e lakebed. and had completed t h e i r respective landing impact before nose- gear touchdown occurred. Table I1 i n d i c a t e s t h a t , f o r a l l of t h e landings, only 5 t o 58 percent of t h e t o t a l shock-strut stroke of each main gear w a s used f o r t h e i n i t i a l impact. I n a l l landings w i t h t h e redesigned main-gear system, s u f f i c i e n t stroke remained f o r t h e main- gear system t o absorb t h e energy which was transmitted t o t h e main gear after nose-gear impact.
A photograph of main-gear-skid marks on t h e lakebed for t h e landing following f l i g h t 2-4-11, for which t h e v e r t i c a l v e l o c i t y at touchdown w a s 6.5 f e e t per second, i s shown i n f i g u r e l O ( a ) .
Measure- ments of t h e main-gear t r e a d f o r t h i s landing, t h a t is, t h e distance between t h e c e n t e r l i n e of t h e l e f t and r i g h t skid m r k s , a r e shown i n figure 10(b) f o r t h e impact period. Also shown f o r comparison ( f i g , lO(c)) are t h e t r e a d measurements f o r t h e landing following f l i g h t 1-6-11, f o r which t h e v e r t i c a l v e l o c i t y a t touchdown w a s 1.0 f e e t per second. The figure shows t h a t f o r t h e higher v e r t i c a l v e l o c i t y t h e skids made s o l i d contact and stayed on t h e lakebed almost immediately a f t e r t h e trailing edge of each skid i n i t i a l l y scuffed t h e surf a c e.
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12 CONFIDEXI'TIAL Rotation About Main Gear Once the i n i t i a l main-gear impact has been made, t h e main-gear system encounters several s i z a b l e increases i n load. During rotation, t h e airplane i s losing l i f t , thus increasing t h e load on t h e main gear A s t h e and, consequently, increasing t h e shock-strut displacement.
v e r t i c a l velocity of t h e main-gear upper mass approaches zero, the angle of t h e horizontal t a i l with respect t o t h e free-stream flow i s increased ( f i g . 1.3). This angle f u r t h e r increases as t h e airplane r o t a t e s t o a negative a t t i t u d e a t nose-gear contact, resulting i n an increase i n h o r i z o n t a l - t a i l load. The records show a l s o t h a t t h e h o r i z o n t a l - t a i l angle s t e a d i l y increases i n a negative d i r e c t i o n during t h e landing due t o control inputs. The loads resulting from t h e high angle of a t t a c k of t h e t a i l increase t h e main-gear loads, since t h e main gear i s located close t o the forward and rearward center of pressure of t h e horizontal tail.
The d i r e c t i o n of all t h e loads--the down load on t h e tail, t h e negative wing l i f t , and t h e airplane i n e r t i a loads--results i n high values of t h e main-gear reaction during t h i s portion of t h e landing. A s can be seen i n figures 6 and 7, a i r p l a n e r o t a t i o n onto t h e nose gear appreciably increased t h e main-gear shock- s t r u t force, drag ground reaction, and upper-mass response over t h e values experienced during t h e main-gear phase of t h e landing. Also, t h e highest values of center-of-gravity v e r t i c a l acceleration occurred during t h e nose-gear touchdown.
The data of f i g u r e s 8 and 9 i l l u s t r a t e t h e v a r i a t i o n of a i r p l a n e angle of a t t a c k and pitching velocity with time during t h e landing period. The angle-of-attack data presented a r e indicated values and have not been corrected f o r pitching velocity. Because of t h e rearward location of the main gear, t h e pitching v e l o c i t i e s a t nose-gear touchdown a r e of high magnitudes, with a maximum of 0.445 radian per second.
Figures 10(b) and lO(c) show t h a t , as t h e airplane rotated, t h e maximum main-gear t r e a d w a s reached s h o r t l y a f t e r nose-gear contact, indicating t h a t t h e m a x i m u m v e r t i c a l reaction on t h e main-gear system occurred i n t h i s area. Comparison of t h e landings following f l i g h t s 2-4-11 and 1-6-11 shows t h a t t h e shorter distance and, also, t h e smaller i n t e r v a l of time f o r t h e nose gear t o contact t h e lakebed can be r e l a t e d t o such f a c t o r s as lower angle of a t t a c k and higher v e r t i c a l velocity during t h e main-gear touchdown.
The time h i s t o r i e s of f i g u r e 7 show t h a t t h e nose-gear v e r t i c a l reaetion reached an i n i t i a l peak 0.05 second t o 0.07 second a f t e r t h e start of t h e nose-gear impact, which was t h e end of t h e spin-up period.
A second peak occurred about 0.18 second a f t e r nose-gear impact following t h e springback period. For most of t h e landings i n which t h e nose-gear v e r t i c a l and drag reactions were measured, t h e maximum v e r t i c a l reaction was reached a t the end of t h e spin-up period.
CONFIDENTIAL Figure 15 compares t h e X-15 touchdown v e r t i c a l - v e l o c i t y and angle- of-attack design l i m i t s with similar data obtained from a c t u a l landings f o r t h e o r i g i n a l gear system and f o r t h e system now i n use.
A s a r e s u l t of t h e modifications t o t h e main-gear system discussed previously, t h e allowable angle of a t t a c k a t touchdown w a s extended, as indicated by t h e dashed l i n e . The s o l i d symbols i n d i c a t e t h e landings t h a t were made with t h e o r i g i n a l gear system. It w i l l be noted t h a t t h e most severe landing ( f l i g h t 2-3-9) w a s made outside of t h e present gear envelope.
Coefficient of F r i c t i o n of Main-Gear Skids The c o e f f i c i e n t of f r i c t i o n was calculated ( s e e appendix) f o r both t h e l e f t and r i g h t main skids and i s shown i n f i g u r e = ( a ) , along with t h e r e s u l t s obtained by using the t o t a l main-gear drag and v e r t i c a l skid forces, f o r a t r u e ground speed from 184 knots t o t h e end of t h e landing runout. The touchdown v e l o c i t y f o r t h i s landing w a s 198 knots t r u e ground speed.
The c o e f f i c i e n t of f r i c t i o n immediately a f t e r nose-gear touchdown i s of t h e order of 0.35 f o r t h e main-gear skids, a f t e r which t h e values appear t o decrease somewhat with decreasing ground speed. The trend of decreasing c o e f f i c i e n t of f r i c t i o n i s evident t o a b m t 50 knots, corresponding t o t h e v e l o c i t y a t which t h e c o e f f i c i e n t of f r i c t i o n would begin t o increase t o i t s m a x i m u m value (impending f r i c t i o n ) a t t h e end of t h e runout. These values agree s a t i s f a c t o r i l y with t h e r e s u l t s , shown i n f i g u r e 1 2 ( b ) , obtained by using an a l t e r n a t e method and appear t o be similar up t o t h e m a x i m u m ground speed of lo3 knots, which w a s used i n t h e a l t e r n a t e method. Results from some X-15 lakebed trailer t e s t s , i n which t h e skid c o e f f i c i e n t of f r i c t i o n a t 6 1 knots w a s 0.35, comwre favorably with t h e values from t h e a c t u a l landing runout ( f i g . 1 2 ( a ) ) . For both methods, t h e mean value of t h e c o e f f i c i e n t was 0.33.
Nosewheel Shimmy I n f i g u r e 11 t h e absence of nosewheel shirmny i s i l l u s t r a t e d by t h e s t r a i g h t t i r e marks following t h e nose-gear touchdown.
N o nosewheel shimmy was observed i n any of t h e landings. Tests made previously by t h e National Aeronautics and Space Administration on t h e landing t r a c k a t Langley Research Center during some high-speed ground runs with t h e X-15 nose gear without a shimmy damper had indicated t h e absence of shimmy. A s a r e s u l t , t h e damper was removed p r i o r t o t h e first f l i g h t of t h e X-15 airplane.
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CONFIDENTIAL Directional S t a b i l i t y Figure 11 a l s o i l l u s t r a t e s t h e runout phase of a t y p i c a l landing during which no attempt w a s made t o s t e e r t h e a i r p l a n e a f t e r touchdown.
This landing w a s made i n t o a head wind estimated t o be between 3 t o 5 knots. The f i g u r e i l l u s t r a t e s the a b i l i t y of t h e landing-gear system t o provide s a t i s f a c t o r y d i r e c t i o n a l s t a b i l i t y during the runout by a c t i o n of t h e low r o l l i n g f r i c t i o n of t h e nosewheels i n combination with t h e high drag forces on t h e main-gear skids. Landings during which attempts were made t o s t e e r t h e X-15 airplane a f t e r touchdown show t h a t rudder input has l i t t l e o r no e f f e c t on a l t e r i n g t h e d i r e c t i o n of motion.
Because t h e nose-gear wheels a r e continuously a l i n i n g themselves with t h e a i r p l a n e d i r e c t i o n of motion, and because t h e c o e f f i c i e n t of f r i c t i o n of t h e main-gear skids i n a side d i r e c t i o n i s similar t o t h a t Roll i n a drag direction, mdder input alone simply y a w s t h e airplane.
input appears t o be more e f f e c t i v e than rudder input for a l t e r i n g t h e d i r e c t i o n of motion, since t h e v e r t i c a l ground reaction i s increased on one skid. The e f f e c t s are s m a l l , however, and surveys of some landing runouts showed t h a t , although f u l l control deflection was used, t h e only 523 f e e t i n a m a x i m u m l a t e r a l displacement on t h e lakebed was Results of t h e survey a l s o showed t h a t runout distance of 6,073 f e e t .
p i l o t inputs f o r controlled changes i n a i r p l a n e d i r e c t i o n must be induced immediately a f t e r touchdown.
CONCLUSIONS This paper presents some r e s u l t s of an analysis of landing-gear behavior and airplane-response c h a r a c t e r i s t i c s made during 17 landings of the X-15 research airplane. The data were obtained a t v e r t i c a l v e l o c i t i e s up t o 9.5 f e e t per second and forward ground speeds from 145 t o 238 knots. A summary of t h e principal conclusions follows: 1. The highest values of main-gear shock-strut force, drag reaction, and response of t h e a i r p l a n e upper mass occurred a f t e r t h e nose-gear touchdown.
2. Horizontal-tail loads increased t h e main-gear v e r t i c a l reaction and reached a maximum value during t h e nose-gear touchdown.
Nosewheel shimmy w a s not observed on any of t h e landings 3.
during t h e touchdown and runout phase, despite t h e absence of a nose- gear shimmy damper.
4 . The low r o l l i n g f r i c t i o n of t h e nosewheels, i n combination with t h e high drag forces on t h e main-gear skids far t o t h e r e a r of t h e center of gravity, provides s a t i s f a c t o r y d i r e c t i o n a l s t a b i l i t y during t h e runout phase of t h e landing.
CONFIDEWI'IAL CONFIDENTIAL 15 Landing results from t h e X-15 airplane have indicated t h a t roll 5 .
input i s more e f f e c t i v e than rudder input alone i n a l t e r i n g the a i r p l a n e d i r e c t i o n of motion during t h e runout. The e f f e c t s , however, are s m a l l , and t h e control inputs must be induced immediately after landing.
6. The mean value o f t h e coefficient of f r i c t , i o n for t h e main- This compared gear skids calculated f o r one landing runout w a s 0.33.
favorably with r e s u l t s obtained from lakebed t r a i l e r tests a t 61 knots t r u e ground speed.
F l i g h t Research Center, National Aeronautics and Space Administration, Edwards, Calif., January 10, 1961.
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**. * * * * * * * .= ._ CONFIDENTIAL APPENDIX METHOD OF COMPUTING COEFFICIENT OF FRICTION OF MAiN-LANDING-GEAR SKIDS DURING A RLJNOUT During the runout phase of some of the landings, data were of the coefficient of friction collected which permitted an analysis between the main-gear skids and the dry lakebed. The landing runout following flight 2-8-16 was chosen for this analysis, and that part of the runout which occurred between nosewheel touchdown and the end of the landing run was used. The data from the landing run showed only slight effects on longitudinal and vertical accelerations as a result of ground roughness. Roll motion through the runout was small, and a steering attempt caused the airplane to terminate the runout in a gradual left turn. This resulted in a slightly higher vertical reaction on the left main-gear skid than on the right skid. The analysis was made on the basis of the following simple relation for the skid coef- f icient of friction were determined from data recorded for The values of Qm and F , m each main-gear skid during the runout. The geometry of the main-gear system allowed the drag-brace loads to be resolved to the drag force % m between the skids and the ground. Since slight pitching, vertical, and rolling motions were encountered during the runout, the main-gear shock- strut reaction to the skid vertical load was regarded as equal to the strut airspring force; that is, the airplane was essentially riding on the airspring force of the shock struts. A calibration on the main-gear
system correlated the effect of skid vertical force Firm on shock-strut
cylinder reaction and shock-strut displacement.
True ground speed during the runout was determined by correlaticg the velocity obtained from Askania cinetheodolite information with the true ground speed at touchdown calculated from the time-distance relationship between the main-gear and nose-gear impact.
An alternate method for calculating the coefficient of friction of the main-gear skids made use of the following relation to determine the drag-reaction force at the skids CONFIDENTLAL 17 The nose-gear drag-reaction force % during t h e landing run w a s n The considered too high i n magnitude t o be used f o r r o l l i n g resistance.
nose-gear-loads c a l i b r a t i o n showed t h e drag due t o pure rolling resistance t o be unreliable. However, t h e values of v e r t i c a l around - was reaction were considered satisfactory, and t h e solution f o r Fhn obtained by using v e r t i c a l reaction and assuming a value o f c o e f f i c i e n t For an of f r i c t i o n between t h e nose-gear wheels and t h e lakebed.
w a s used with a analysis of t h e X-2 airplane ( r e f . 7), pn = 0.05 This value appears t o compare favorably s a t i s f a c t o r y degree of accuracy.
with an average of calculated r e s u l t s made by using t h e following r e l a t i o n i s t h e skid drag force obtained from t h e drag-brace loads.
where %m The aerodynamic drag DA was calculated by using t h e r e l a t i o n where CD i s t h e airplane drag coefficient corresponding t o extended landing gear and fill f l a p s and speed brakes. Flaps were f u l l down before landing and remained down during t h e runout, and speed brakes were deployed 15 seconds a f t e r i n i t i a l touchdown. Coefficient of f r i c t i o n w a s calculated for t h e landing from 17 seconds after touchdown t o t h e end of t h e runout (corresponding t o a t r u e ground speed of l o 3 knots). The dynamic pressure q was calculated by using data obtained from t h e s e n s i t i v e airspeed recording. The r e s u l t s of t h i s analysis a r e presented i n f i g u r e 12.
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18 CONFIDESPTIAL REFERENCES Skopinski, T. H . , Aiken, William S., Jr., and Huston, Wilber B.: 1.
Calibration of Strain-Gage Installations in Aircraft Structures for Measurement of Flight Loads.
NACA TN 2993, 1953.
2. Weil, Joseph, and Matranga, Gene J. : Review of Techniques Applicable to the Recovery of Lifting Hypervelocity Vehicles.
NASA TM X-334, 1960.
3. McKay, James M.: Measurements Obtained During the First Landing of the North American X-15 Research Airplane.
NASA TM X-207,
1959 -
4. Flight Research Center: Aerodynamic and Landing Measurements Obtained During the First Powered Flight of the North American X-15 Research Airplane.
NASA TM x-269, 1960.
Houbolt, John C., and Batterson, Sidney A,: Some Landing Studies 5 .
Pertinent to Glider-Reentry Vehicles.
NASA TN D-448, 1960.
6. Finch, Thomas W., and Matranga, Gene J. : Launch, Low-Speed, and Landing Characteristics Determined From the First Flight of the North American X-15 Research Airplane.
NASA TM X-195, 1959.
Walker, H . , Deutschman, J., and van Sunmern, J. : 7. Pitch Ianding Condition. Nose-Gear Loads. Rep. No. 52-941-010, B e l l Aircraft Corp., April 1953. (Rev. July 1954).
CONFIDENTIAL 19 TABLE I.- PHYSICAL CRARACTERISTICS O F THE AIR€’- wing : (Modified)
A i r f o i l section . . . . . . . . . . . . . . . . . . . . . . . . . . . NACA 66005
Total a r e a (includes 94.98 sq f t covered by fuselage), sq f t . . . . . . . . . . 200
S p a n , f t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.36
Mean aerodynamic chord, f t . . . . . . . . . . . . . . . ...... . . . . . . 10.27
Root chord, f t . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . 14.91
. . . . . . . . . . . . . . . . . . . 2.98
Tip chord, f t . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . 0.20
Taper r a t i o . . . . . . . . . . . . . . . .
. . . . . . 2.50
Aspect r a t i o . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25.64 Sweep a t 25-percent chord l i n e , deg . . . . . . . . . . . . . . . . . . . . . . .
Incidence, deg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
Dihedral, deg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
Aerodynamic t w i s t , deg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
Flap -
Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plain
8.30 Area (each), sq ft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.50 Span (each), ft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Inboard chord, ft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.61
Outboard chord, f t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.08
Deflection, d a m (nominal design), deg . . . . . . . . . . . . . . . . . . . . 40
Ratio f l a p chord t o wing chord . . . . . . . . . . . . . . . . . . . . . . . . 0.22
Ratio t o t a l f l a p a r e a t o w i n g a r e a . . . . . . . . . . . . . . . . . . . . . . 0.08
Ratio f l a p span t o wing semispan . . . . . . . . . . . . . . . . . . . . . . . 0.40
Trailing-edge angle, deg . . . . . . . . . . . . . . . . . . . .
.......
3-67
Sweepback angle of hinge l i n e , deg . . . 0
. . . . . . . . . . . . . . . . . . .
Horizontal t a i l : A i r f o i l section . . . . . . . . . : . . . . . . . . . . . . . . . . . NACA 66005 (Modified) Total a r e a (includes 63.29 sq f t covered by fuselage), sq f t 115.34 . . . . . . . . . .
S p a n , f t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.08 Mean aerodynamic chord, f t 7-05 ...........................
Root chord, f t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.22
Tipchord, f t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.11
Taper r a t i o . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.21
Aspect r a t i o . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 -83
.......................
Sweep at 25-percent-chord l i n e , deg 45 ..................................
Dihedral, deg -15 Ratio h o r i z o n t a l - t a i l a r e a t o w i n g a r e a . . . . . . . . . . . . . . . . . . . . . 0.58 . . . . . . . . . . . . . . . . . . . . . . . . . . .
Movable surface area, sq f t 51 77
Deflection -
.............................
Longitudinal, up, deg 15 . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Longitudinal, down, deg 35 Lateral d i f f e r e n t i a l ( p i l o t a u t h o r i t y ) , deg . . . . . . . . . . . . . . . . . .
*I5 L a t e r a l d i f f e r e n t i a l ( a u t o p i l o t a u t h o r i t y ) , deg . . . . . . . . . . . . . . . . * 30 Control system . . . . . . . . . . . . . I r r e v e r s i b l e hydraulic boost with a r t i f i c i a l feel Upper v e r t i c a l tail: A i r f o i l section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10’ single wedge
Total area, sq f t . . . . . . . . . . ...................... 40.91
Span, ft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.58
Mean aerodynsmic chord, f t . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.95
Root chord, ft . . . . . . . . . . . ...................... 10.21
Tip chord, f t . . . . . . . . . . . . ......................
7.56
Taper r a t i o . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.74
Aspect r a t i o . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.51
Sweep at 25-percent-chord l i n e , deg . . . . . . . . . . . . . . . . . . . . . . . 23-41 Ratio v e r t i c a l - t a i l a r e a t o wing area
. . . . . . . . . . . . . . . . . . . . . . 0.20
CONFIDENTIAL 0 . ......................... 0 . 0 . 0 . . ........
.
.
0 . . . . . . . . . . . . . . . . . 0 . 0 . . ..... . . . . . . . 0 . 0 . .
.................................
CONFIDENTIAL TABLE I.- PHYSICAL CHARACTERISTICS O F TRE AIRPLANE - Concluded
Movable surface area, sq f t . . . . . . . . . . . . . . . . . . . . . . . . . . . 26.45
Deflection, deg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +7.50
. . . . . . . . . . . . . . . . . . . . . . . . . . 0
Sweepback of hinge l i n e , deg Control system . . . . . . . . . . . . . I r r e v e r s i b l e hydraulic boost with a r t i f i c i a l f e e l Lower v e r t i c a l tail:
. . . . . loo single wedge
. . . . . . . . . . . . . .
A i r f o i l section . . . . . . . . . . .
. . . . . . . . 34.41
. . . . . . . . . . . . . .
Total area, sq f t . . . . . . . . . .
. . . . . . . . 3.83
. . . . . . . . . . . . . .
Span, f t . . . . . . . . . . . . . .
. . . . . 9-17
. . . . . . . . . . . . . . . . .
Mean aerodynamic chord, f t . . . . .
. . . . . 10.21
. . . . . . . . . . . . . . . . .
Root chord, f t . . . . . . . . . . .
. . . . . 8
. . .
. . . . . . . . . . . . . .
Tip chord, f t . . . . . . . . . . . .
. . . . . 0.78
. . .
. . . . . . . . . . . . . .
Taper r a t i o . . . . . . . . . . . . .
. . . . . . . . 0.43
. . . . . . . . . . . . . .
Aspect r a t i o . . . . . . . . . . . .
. . . . . . . . 23.41
. . . . . . . . . . . . . .
Sweep a t 25-percent-chord lfne, deg .
. . . . . 0.17
. . . . . . . . . . . . . . . . *
Ratio v e r t i c a l - t a i l area t o wing area
. . . . . . . . 19 - 95
. . . . . . . . . . . . . .
Movable surface area, sq f t . . . . .
. . . . . k7.50
. . .
. . . . . . . . . . . . . .
Deflection, deg . . . . . . . . . . .
. . . . . 0
. . . . . . . . . . . . . . . . .
Sweepback of hinge l i n e , deg . . . .
. . I r r e v e r s i b l e hydraulic boost with a r t i f i c i a l f e e l
Control system . . . . . . . . . . .
Fuselage: L e n g t h , f t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50.75
MaxhILXLIwldth, f t ................................ 7.33
lhdmumdepth, f t . . .............................. 4.67
lvlaximum depth over canopy, f t .......................... 4.97
Side a r e a ( t o t a l ) , sq f t . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215.66
Fineness r a t i o ................................. 10.91
bbin landing gear: Type . . . . . . . . . . . . . . . . . . . . . . . . . . Two (6 in. wide, 3 f t long) skids Oleopneumatic ( i n s i d e fuselage) Shock strut ........................
Original Present gear gear S t r u t - i n f l a t i o n pressure, ( f u l l y extended), p s i . . . . . . . . . . . . . 75 0 l.2 00
Shock-strut stroke, in. ........................ 2.577 3.58
Tread distance (no load), f t ...................... 7.03 7.34
Nose landing gear:
. . . VI1
T i r e t y p e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . 18 x 4.4
T i r e s i z e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . 8
P l y r a t i n g ................................
. . . 8
Rolling radius, in. ...........................
Dual, corotating Wheels ...................................
... 1.85
Tire pressure, p s i ............................
. Oleopneumatic
Shock s t r u t ................................
( f l i l l y extended)
Shock-stmt-inflation pressure, p s i . . . . . . . . . . . . . . . . . . 184
. . . 18
Shock-strut stroke, in. .........................
Moments of i n e r t i a (based on average landing weight, 14,500 l b ) :
Ix, slug-ft2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3,600
I ~ , s1w-ft2 .................................. 83,500
1 2 , siug-ft2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85,100
In, s l u g - f t 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500 CONFIDENTIAL e 0 . . .e . 0 . e . 0 .
.. ... e.. .*e e... e.. .e.. ..e
. e . . . . 0 . . e
. 0 . 0 . . . e e e .
.e .* e ..e . e.. e .
0.. ..e* e..
.. e . . e... . .
.* ... e... . e .e. *e. 0..
CONFIDENTIAL I !
f m r - m t , m n i n ?"??"!I "!I 0 0 0 0 0 0 0 0 3 A 4 A ,< r( 3 3 CONFIDENTIAL a a a am*. ma. a a a a a a am a
: a a a * a
m a a a m a a a a * a a a a a a a a o a a mea a a am CONFIDENTIAL m f 4 0 m t-f f + "?"t "?'4 59% N N N m N N N m N CONFIDENT I AL 23 u u m u m v m c u u u u < < u < e CONFIDENTIAL ••• • • • • .....
••• ...
... .
• • • •• • .
• •• • •• ~ • • • • • • • • •
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••• • · • • ~ .
• • • ~ •• • • • • • • • •
• · •
••• • •• • •• • • • • ••• • • •• • ••• • . ...
• •• • • • • • • • •••• •• • ..
• • CONFIDENTIAL co tr\ C\J tr\ I I f:iI I
•
CONFIDENTIAL CONFIDENTIAL
7 1
I cd l n rl t
z: R(
i
/
.d h
rl a, b i a , 5.d hi k a , k CONFIDENTIAL 2 6 CONFIDENTIAL & I O X F: H CONFIDENTIAL ......................... .
. ........ 0 . . 0 . . . . . . . . . . . . . . . . . . . . 0 . 0 . 0 . 0 .
...... ................................. 0 . 0 . . . . 0 . 0 .
.
. 0 . 0 .
CONFIDENTIAL CONFIDENTIAL I
I
.. ..
• ••
••• ... I
•••• • •• ...
• • • • •• A • • • • •• • • • • • • • •••
· · · • • •
• •• · •
• • • • • •• • •
• • • . •
... •
• •
... • ••
• • •• • • • •••• • • ••• • ....
•• • • • • • • • • •••• ". tt a8 • • CONFIDENTIAL .~ 3~ .... i~e '1 ~ • !l..!!.!'.er • ... !" .rlt.i r.
~"'t r",' ..... 0 'r~ib;!, .'S.rrarJ.t-""emef,t j' r l ' e~r'l'l"! y\,;o Hi 1.
r Figure 4.- X-15 nose gear-extended position.
CONFIDENTIAL ••• • • •• • • •
.. . •• • •
••• • • • • • • • •• • • • •• • •
• •• • •• • . •
• •• • • • • • • • • ••••• •• • • • • • • • • ••• • • • • • • •• • ••••• • •• Ii'. • ...
• • •• • •• • • • • • • • • • • • • • • • • ••• CONFIDENTIAL ,. j ' .1 r ,.
' " " ., ,,/ } ' ", ...J , ~ ,
. /
I I • J / f .
• I , ' ~' ,..
r' !
,..j
', I~, .,.I I
' I ' ' /" j r ...
" 1'/' I , '",,', .. .,J . , ,. A, , k I , .' I ' ."
{r • r.' ,' '; / ' :. J r I .
t t . 4' .. ( I' ,.
. , t' r.' ,..# : I
;.r
.. , I ' t , , I 'I , .1 I '/ ,') ~ f" • J.
I , I
. ~
'.
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!
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I) "" " t, : j 1 -
r ·
/-.
:v
.,J- ;!
.,I
) . J:r
,I , . i .
~ • I " " ' . , ' ~
, /
' ..
, ' • • ~ 1 CONFIDENTIAL CONFIDENTIAL IO,.- ~ Left main gear _ _ _ - Right main gear Nose gear
8 L
6 1 --
o v . 9 Nose 0 - Right main gear / 0 - Left main gear -2-
4 1 = 1 2
6Ox1O3 A , ?, \
4 '
\ \ \ I' , .
, '.
/ , -I' ___
4g 20
~- -<.-- I -.2 0 Touchdown Time after initial touchdown, sec ( f l i g h t 1-2-7).
At, = 0.730 second (a) Nose-gear touchdown occurs at Figure 6.- Variation with time of shock-strut force, shock-strut dis- placement, and upper-mass acceleration during some landings of t h e X-15 number 1 airplane.
CONFIDENTIAL 0 . 0 . 0 0 . 0 ... .... 0.. o... 0 . 0 0 . 0 .
0 .
0 .. 0 0 . 0
. ..
0 0 . 0 0 . ..
0 0 0 . .. 0 0 . 0 . 0 . 0 0 . 0 .
0 0 .
0 . 0 0 . . .
0 0 . 0 0 .
0 .. 0 0
.a ... 0 . 0 0 0 0 0 0 . 0 . 0 0 0 . . 0 . 0 0 . 0 . 0 . 0
CONFIDENTIAL Left main gear _ _ _ _ Right main gear ~~_ - Nose gear Nose Right main gear L e f t main gear -
- - - .. - l i _ -- - -
, : c = - - % --
asn, in. IO a s , , in. 2. -- I r 4 [ + 2 ! 2 0 .4 .6 .8 I O 1.2 1.4 1 . 6 Touchdown Time after i n i t i a l touchdown, sec ( b ) Nose-gear touchdown occurs at At, = 0.385 second (flight 1-3-8).
Figure 6.- Continued.
CONFIDENTIAL ......................... . 0 . . 0 . .
.
0 . 0 . 0 . 0 . .
........
.
0 . . . . . . . . . . . . . . . . . 0 . 0 . . ......
e ....
.
0 . e . .
.................................
CONFIDENTIAL av,. 9 Nose Right main gear Left main gear
2ol
sSn, in. 10: ssm, in I ' 0 ' Touchdown Time after initial touchdown, sec touchdown occurs at At, = 1.410 seconds ( f l i g h t 1-6-11).
( c ) Nose-gear Figure 6.- Continued.
CONFIDENTIAL C OW1 DENTIAL 33 IO Nose 0
---__
Right main gear 0- Y Left main gear 0 -2 SSn, in. 1 0 6 s , , in.
(d) Nose-gear touchdown occurs at A t , = 0.960 second (flight 1-8-13).
Figure 6.- Concluded.
CONFIDENTIAL 34 CONFIDENT I AL
,i"
16' Fhm. Ib Right m i n gwr main gwr - 1 0 ?2 0 .2 .4 .6 8 i o 1.2 14 1.6 Touchdown Time after initial tcuchdcwn, sec (a) Nose-gear touchdown occurs at At, = 0.455 second ( f l i g h t 2-4-11).
Figure 7. - Variation with t i m e of shock- s t r u t force, nose-gear v e r t i c a l
ground reaction, drag ground reaction, shock-strut displacement, and upper-mass acceleration during some landings of t h e X-15 number 2 airplane.
CONFIDENTIAL CONFIDENTIAL 35 Nose 0 Right main gear L e f t main gear - 2 2 0 4 .
I ‘ h. ---------- e BSn, i n . I O Ssm, in. 2 , , --’ I f 2 0 .2 .4 .6 .8 1.0 1.2 1.4 1.6 Touchdown Time after initial touchdown, sec ( f l i g h t 2-6-13).
(b) Nose-gear touchdown occurs at Atn = 0.928 secoxd Figure 7. - Continued.
CONFIDENTIAL 0 .
......................... . 0 . . 0 . .
. . . . . . . . . . . . . . . . . . . . . a 0 . 0 . .
........
0 .
.
.
0 . ....
..........
. 0 . ...... 0 . .
.......................
CONFIDENTIAT; av, 9 Nose Right main gear Left main gear I I I I I I I 1 - - - _ _ I I -10
- . 2 4 m Touchdown r L I O 12 1 4 1 1 6
Time after initial tcuchdown, sec 2-8-16).
( c ) Nose-gear touchdown occurs at At, = 0.795 second ( f l i g h t Figure 7.- Continued.
CONFIDENTIAL CONFIDENTIAL
!A I 1
Nose Right main gear Left main gear Fvn 9 : * In 1.2 1.4 1.6 -02 0 2 4 6 8 10 1 2 14 16 Touchdown Time after initial touchdown, sec' ?c' nds ( f l i g h t 2-9-18).
touchdown occws at Atn = 1.090 seconds ( f l i g h t Nose- gear Figure 7. - Concluded. Figure 7. - Concluded.
CONFIDENTIAL 0 .
......................... . 0 . . 0 . .
.
. . . . . . . . . . . . . . . . . . . 0 . 0 . 0 . .
........
0 .
.
.
0 . ...... 0 . . 0 . .... .
.................................
38 CONFIDENTIAL . .
i
I
a n , 9
-
up . 4 - q, rad i anslsec
.4 L
6 - L
( f l i g h t 1-2-7).
(a) Nose-gear touchdown occurs at At, = 0.730 second Figure 8.- Variation with time of angle of attack, pitching velocity, h o r i z o n t a l - t a i l deflection, center- of - g r a v i t y v e r t i c a l acceleration, and h o r i z o n t a l - t a i l load during some landings of t h e X-15 number 1 airplane.
CONFIDENTIAL CONFIDENTIAL 39 I /--- F+, Ib - - Left .
, .
.
.
...- deg R i g t i L --7- 1.6 Touchdown Time after initial touchdown, sec Atn = 0.385 second ( f l i g h t 1-3-8).
(b) Nose-gear touchdown OCCUTS at Figure 8. - Continued.
CONFIDENTIAL . 0 . . 0 . . .........................
.
0 . 0 . 0 . 0 . . ........
......
.*. .
...... 0 . 0 . 0 . .
....
.
0 . 0 . .
.................................
40 CONFIDENTIAL
Down .10x103 I
.-
e
I E L I 2.0 2.4 i
sec ( f l i g h t 1-6-11).
At, = 1.410 seconds ( c ) Nose-gear touchdown occurs at Figure 8.- Continued.
CONFIDENTIAL CONFIDENTIAL (d) Nose-gear touchdown occurs at A t , = 0.960 second (flight 1-8-13).
Figure 8. - Concluded.
CONFIDENTIAL m m m m o m 0 0 0 . m o o = 0 0 . o m 0 .am ma 0 a 0 0 0 0 o m a 0 a 0 o m a 0 o o o o m 0 0 0 om. 0 0 0 a 0 om 0 m o o 0 0 0 moo o o o m 0 0 0 0 0 0 m o o m o o 0 ommo 0 0 . 0 0 mo a 0 0 . m m m mmoo o m o m CONFIDENTIAL Touchdown Time after initial touchdown, sec ( f l i g h t 2-4-11).
At, = 0.455 second (a) Nose-gear touchdown occurs at Figure 9.- Variation with time of angle of attack, pitching velocity, center-of-gravity v e r t i c a l acceleration, h o r i z o n t a l - t a i l deflection, and h o r i z o n t a l - t a i l load during some landings of t h e X - 1 5 number 2 airplane.
CONFIDENTIAL . . . . . . . ......................... .
........ 0 ................ 0 . 0 . 0 . 0 .
0 .
0 .
. . . . . . . ................................. .
. . . . . ..... . . .
CONFIDENTIAL shn deg Airplane nose up Touchdown Time aftw initial touchdown, sec (b) Nose-gear touchdown occurs at A t , = 0.928 second (flight 2-6-13).
Figure 9. - Continued.
CONFIDENTIAZ; 44 CONFIDENTIAL
UP +--
.2 I
q, radianskec .2 Touchdown lime after initial touchdown, sec (c) Nose-gear touchdown occurs at A t , = 0.795 second (flight 2-8-16).
Figure 9.- Continued.
CONFIDENTIAL ......................... .
. 0 . . 0 . . 0 . 0 . e *
........ . . . . . . . . . . . . . . . . . 0 .
.
......
. ................................. 0 . 0 . .... 0 . .
. . 0 . 0 .
CONFIDENTIAL 45 Time after initial touchdown, sec (d) Nose-gear touchdown occurs at A t , = 1.090 seconds (flight 2-9-18).
Figure 9. - Concluded.
CONl?IDENTI AL • • • • • •
.. • • •
• • • :of. • • •• • • • • • • • •• • • • •• •• • • • ••• • • •• ....
• • • •• • • ••• •••• •• • • • • ••••• • ••• • ~ •••• •••
..... • • • •
• • • • •••• • • • • • • • • •• •• • "
~ '":<j ~ ~
+- 0\ (") 0 H H E- .
touchdown 11) - the 2-4 for (flight .
, lakebed ng i on land ft/sec -1 marks R_J X 6 . 5 = an sktd 1:1.
Vv of gear - phase main , airplane.
j" X-
, Typical
. - a) ( .,: Figure
(") 0 ~ H ~ ~ ~
......................... .
. 0 . 9 . e . 0 . 0 . 0 .
........ . 0 .
.
...... . * a 0. e.. 0 . 0 .
. ................................. 0 . . e .... 0 . .
.
CONFIDENTIAL 47 II/ I 1 I, V N I IN d CONFIDENTIAL ••• •••• ••• • •• • ••• • •• • • • .
• • • • ..
• ~ • 0
• • 0 . 0
0 • • 0 0 • ••• • 0 0 • ••• • • • • • 0 • 0 •• • • • • • • • • • • • • • • ••• • • ••• •••• ••• • ... ... ..
• ••• • • • • ....
• • ••• ..
• CONFIDENTIAL ..
-
( / Nose-g ear - iouchdown ., '-- J I r' , I ,; .'
.
( r , .t' /'
\
.; <' j I E- 52 33 Figure 11.- Landing-gear marks during runout phase illustrating direc- t ional stability and lack of nosewheel shimmy of the X-15 airplane (flight 2- 4 -11) .
CONFIDENT IAL CONFIDENTIAL
I I
E 3- CONFIDENTIAL 50 CONFIDENTIAL
&&
c
I
I
cd c, a 3 a I' I
r C
-
.........................
0 . 0 . . 0 . . 0 . e a
.
........ . . . . . . . . . . . . . . . . 0 .
. . 0 . 0 .
......
. ................................. 0 . 0 . .... . . .
CONFIDENTIAL 51 Lift Tail load Relative
wind /
Z////,,,///,////,/,,/,/////,,/,,,/,,,,,/,,/, ,- (a) /-/ / // , , , I / / ,/ , ////////////,/,/// / /// /, , ,, I, // ( c ) m
-
/,//////,///////,,/,/,,,,,,,,,,,,,,,,, , ( d) Figure 13.- Landing sequence of X-15 airplane showing conditions leading to second main-gear impact.
C O W I D E N T I AT-, •• • •• • • • •• • •• • •• • • • • .
• •• •• • •• • . .
• • .
• • • • • •• • •
· · • • • • • •
· •••
• •• • • • • • • •• • • • • • • • • • • ••• ...
• ....
.. . ... .
• .. ..
• • ..
•
· · · · • •• •
• • CONFIDENTIAL CONFIDENTIAL CONFIDENTIAL I' I / I', I
b
I I I ------- L
b a b
h d
v
C O N F I D r n I A L