Document
NASA TECHNICAL NOTE _NA SA TN D- 202 !,
64~14981 ~~
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CHARACTERISTICS OF A
LUNAR LANDING CONFIGURATION
HAVING VARIOUS MULTIPLE-LEG
LANDING-GEAR ARRANGEMENTS
by Ulysse j. Blanchard '-W~/;VA SA)
\
Langley Research Center
Langley Station, Hampton, Va.
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION • WASHINGTON, D. C. • . JAN . UARY 1964 ~ CHARACTERISTICS OF A LUNAR LANDING CONFIGURATION HAVING VARIOUS MULTIPLE-LEG LANDING-GEAR ARRANGEMENTS By Ulysse J. Blanchard Langley Research Center Langley Station, Hampton, Va.
Technical Film supplement^ L-803 available on request.
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION F o r sale by the Office of Technical Services, Department of Commerce,
Washington, D.C. 20230 -- P r i c e $1.25
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION TECHNICAL NOTE D-2027 CHARACTERISTICS OF A LTJNAR LANDING CONFIGURATION HAVING VARIOUS MULTIPU-UG LANDING-GEAR ARRANGEMENllS By Ulysse J. Blanchard SUMMARY
t4 Y f W
An experimental investigation has been made of some lunar-landing charac- teristics of a 1/6-scale dynamic model of a landing module having multiple- leg landing-gear systems. Symmetric four-point and five-point systems and an asymmetric four-point system were investigated. The landing-gear legs were inverted tripod arrangements having a telescoping main strut which incorporated a yielding-metal strap for energy dissipation, hinged V-struts, and circular pads.
The landing tests were made by launching a free model onto an impenetrable hard Landing surface (concrete) and onto a powdered-pumice overlay of various depths motion and acceleration data were obtained for a range of touchdown speeds, touch- down attitudes, and landing-surface conditions.
Maximum normal acceleration experienced at the module center of gravity during landings on hard surface or pumice was 2g (full-scale lunar value in terms Maximum angular of earth's gravity) over a wide range of touchdown conditions.
acceleration experienced was 1 2 . & radians/sec2 and maximum longitudinal accelera- tion was llg. The module was very stable with all gear configurations during landings on hard surface (coefficient of friction, p = 0.4) at all conditions tested. Some overturn instability occurred during landings on powdered pumice (p = 0.7 to 1.0) depending upon flight path, pitch and yaw attitude, depth of pumice, surface topography, and landing-gear configuration. The effect on sta- bility of roll attitude for the limited amount of roll-attitude landing data obtained was insignificant. Compared with the four-point landing gear, the five- point system with equal maximum gear radius increased landing stability slightly and improved the static stability for subsequent lunar launch. A considerable increase in landing stability in the direction of motion was obtained with an asymmetric four-point gear having two pads offset to increase gear radius by 33 percent in the direction of horizontal flight.
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INTRODUCTION Two of t h e important items f o r o v e r a l l success of t h e Apollo mission a r e a s o f t , s t a b l e landing of a manned spacecraft on t h e lunar surface and subsequent departure from t h e lunar surface. The landing-gear systems must arrest and sta- b i l i z e t h e landing module, provide a s t a b l e support on t h e lunar surface, and a l s o provide an adequate platform from which t o launch a return stage.
Proposed control and guidance c a p a b i l i t i e s indicate t h a t favorable module touchdown condi- t i o n s ( a t t i t u d e , o r i e n t a t i o n , and speed) can be achieved along with l i m i t e d s i t e s e l e c t i o n (hover). However, knowledge of d e t a i l e d lunar-surface c h a r a c t e r i s t i c s i s lacking and only generalized assumptions can be made from current l i t e r a t u r e and experimentation. Therefore, c u r r e n t l y proposed landing-gear systems a r e designed t o accomplish t h e t a s k f o r a f a i r l y wide range of landing-surface condi- t i o n s with minimum weight and operational complication. Multiple-point l e g sys- tems with simple nonviscous, low-rebound shock absorbers a r e promising with regard t o t h e s e general requirements and c a p a b i l i t i e s .
Results a r e presented herein of an investigation of a 1/6-scale dynamic model of a manned spacecraft f o r s o f t lunar landing ( a preliminary version of t h e lunar excursion module) employing a multiple-point, leg-type landing-gear system with yielding-metal shock absorbers and s e v e r a l contact-point arrange- ments. Lnpact a c c e l e r a t i o n and behavior were determined w i t h a 1/6-scale dynamic model over a range of touchdown speeds and a t t i t u d e s . The landing- surface configurations investigated included a smooth hard surface, various depths of dust overlay, and an integrated surface i r r e g u l a r i t y .
Motion p i c t u r e s of t y p i c a l landings were made during the t e s t s and film A supplement L-803 showing these r e s u l t s i s available on loan from t h e NASA.
request card and a description of the f i l m a r e provided a t the end of t h i s paper, on the page with t h e a b s t r a c t cards.
SYMBOLS A area, s q f t a acceleration, f t / s e c 2 a angular acceleration, radians /see P g r a v i t a t i o n a l rati 0, gearth/ $noon F force, lb 7 f l i g h t -path angle, deg I moment of i n e r t i a , s l u g - f t 2 2 length, f t h geometric model s c a l e m mass, s l u g d s t r e s s , lb/sq i n .
t time, sec P c o e f f i c i e n t of f r i c t i o n velocity, f t / s e c V horizontal velocity, f t / s e c vH v e r t i c a l velocity, f t / s e c VR r e s a t a n t velocity, f t / s e c DESCRIPTION O F MODEL The general arrangement of the 1/6-scale dynamic model i s shown i n f i g u r e 1.
Photographs of t h e model with various landing-gear configurations are shown i n figures 2, 3, and 4. Details of t h e inverted t r i p o d landing-gear l e g assembly and yielding-metal shock absorber a r e shown i n figure 5 . Full-scale and model- s c a l e r e l a t i o n s h i p s applicable t o these tests are given i n t a b l e I. Pertinent model and f u l l - s c a l e dimensions a r e given i n table 11.
The model was a symmetrical body about t h e v e r t i c a l axis representing a l u n a r landing module consisting of t h e landing stage with attached landing gear and t h e lunar launch stage. The model was constructed of a s o l i d hardwood and balsa core containing appropriate c a v i t i e s f o r instrumentation and ballast. The model body was covered with a plastic-impregnated f i b e r - g l a s s skin. Landing- gear assemblies were made of 202bT3 aluminum a l l o y . The gear s t r u t s were Of tubing of 0.065-inch w a l l thickness with 5/8-, 1/2-, and 3/8-inch outside diam- eter f o r t h e main strut, inner s l i d e , and V - s t r u t , respectively.
The basic landing gear ( f i g s . 1, 2, and 3(a)) was a quadruped configuration with each of t h e four l e g s ( f i g . 5) c o n s i s t i n g of t h r e e s t r u t s mounted so as t o form an inverted tripod. The landing gear was designed t o provide stroke f o r a desired maximum acceleration and r e s i d u a l clearance f o r engine-nozzle protection and subsequent launch c a p a b i l i t y .
V e r t i c a l working stroke of t h e gear was approx- imately 2 f e e t full s c a l e and was designed t o give a m a x i m u m load of 2 e a r t h g f o r a f l a t impact a t a speed of 15 f e e t per second. A b a l s a block ( s t o p ) a t t h e t o p of t h e main s t r u t provided an emergency stroke of approximately 3 a d d i t i o n a l The main or upper strut telescoped during impact and the lower V-strut inches.
During impact was a hinged unit, which served to guide and stabilize the tripod.
the telescoping main strut yielded a metal energy strap in tension for impact attenuation. Also, as the main struts telescoped, the landing pads moved out- ward and thus increased the gear diameter as shown in figure 1. The pads were attached to the tripod assembly by a ball joint with no provision for shock absorption in the pads. Two footprint areas of the landing-gear pads were uti- lized, as indicated in table II.
The modified landing-gear configurations investigated are shown in fig-
ures 3(b) and 4. The asymmetric four-point gear (fig. 3 ( b ) ) was similar to the
basic symmetric four-point gear but with two adjacent pads offset radially 3 feet ( f u l l scale). This offset increased gear radius approximately 33 percent in the direction of offset. Gear height was held constant and the energy-strap shock- absorber configuration was unchanged.
The five-point landing gear shown in figure 4 was symmetrical with a 7 2 O cir- cumferential spacing. All gear and strut dimensions were the same as those of the symmetrical four-point arrangement. Therefore, maximum gear radius was the same and minimum gear radius was increased approximately 15 percent. The enerQy straps same design load as that of the four-point system.
were modified to provide the The model energy straps were made of pure nickel wire (Low-Carbon Nickel) a highly ductile metal which retains its mechanical properties over a wide range of temperatures. During impact, compression loads tending to telescope the main strut were opposed by the energy strap in tension. When the load exceeded the yield strength of the strap, it elongated and the gear stroked. Because of yield of the ductile metal, little energy was stored; and rebound was thus minimized.
Stress-strain characteristics of the strap material were similar to those described in reference 1, and a typical stress-strain diagram for Low-Carbon Nickel is shown in figure 6. The shock-absorber element used on the present model had desirable characteristics for the lunar-landing mission, but these characteristics could also be obtained by using other methods such as crushable materials, frangible tubes, or properly designed oleo systems.
The scale ralationships pertinent to the earth model tested are shown in table I. For geometric scaling the characteristic length was varied as the scale factor A. A 1/6-scale model was chosen, since this choice was suitable for I meeting construction, size, and weight requirements for test purposes. The same yield-strap material was assumed for the model and the full-scale configurations; hence, the stress relationship was held 1 to 1, so that exact structural scaling of shock-absorber forces was provided. The gravitational ratio j 3 is dictated by the fact that the force of the earth's gravity is 6 times that of the moon;
thus, accelerations experienced by the model are 6 times that resulting on the
moon. With these three relationships fixed, other pertinent scale relationships follow from laws of physics for a dynamically scaled model.
, APPARATUS AND PROCEDURE The investigation w a s conducted by launching the model as a f r e e body by means of a pendulum apparatus i n the Langley impact s t r u c t u r e s f a c i l i t y . The model i s shown on the pendulum launching carriage i n f i g u r e 7. Operation of the pendulum during landing t e s t s i s i l l u s t r a t e d i n figure 8. The pendulum with the model locked a t t h e desired a t t i t u d e was r e t r a c t e d t o t h e point A, from which it w a s released and allowed t o swing through an a r c of v e r t i c a l height AB. Model approxi- release occurred a t point B (dead c e n t e r ) a t a horizontal velocity VH After mately equal t o a f r e e - f a l l velocity f o r preset v e r t i c a l distance AB.
release the model dropped a preset height BC f o r desired v e r t i c a l velocity Vv.
The combination of horizontal velocity a t release and v e r t i c a l velocity a t impact A photograph showing the determined flight-path t r a j e c t o r y a t model touchdown.
pendulum, support structure, and pumice box i n s t a l l e d i n t h e Langley 41-foot vac- uum sphere i s shown i n figure 9.
Pitch and r o l l a t t i t u d e s (about the axes shown i n f i g . 2) were obtained by a multiple platform and hinge arrangement mounted beneath the pendulum carriage 7). The model p i t c h a t t i t u d e was obtained by s e t t i n g t h e support release ( f i g .
R o l l a t t i t u d e was s i m i l a r l y mechanism t o the desired angle on the p i t c h quadrant.
obtained with a quadrant located on the side of the carriage. Yaw a t t i t u d e was obtained by r o t a t i n g the c l e v i s f i t t i n g i n s t a l l e d on top of the model ( f i g s . 2, 3, and 4 ) . Negative p i t c h a t t i t u d e was obtained by r o t a t i n g t h e e n t i r e carriage assembly 180~. Combinations of pitch, yaw, and r o l l could a l s o be obtained.
The landing surfaces used f o r the investigation a r e diagramed i n f i g u r e 10.
Hard-surface landings were made on smooth concrete and hardwood. The ledge simu- lated a dropoff o r crevice of about 2 f e e t ( f u l l s c a l e ) . Simulated landings i n - lunar dust were made i n t o a shallow box containing l3 and 3- inches of pow-
s ' r;' 2
dered pumice representing f u l l - s c a l e depths of 5 , 1 & , and 21 inches, respec- t i v e l y . The grain-size d i s t r i b u t i o n of the pumice material i s shown i n f i g - ure 11.
Average grain size of the powdered pumice w a s approximately 68 microns (400 microns f u l l s c a l e ) . Grain geometry was random, sharp edged, and jagged.
The pumice was disturbed and loosely struck off l e v e l (minimum compaction) before each landing. S t a t i c bearing strength of the pumice during model t e s t s was approximately 2 lb/sq i n . w i t h a bulk density of approximately 40 lb/cu f t .
Bearing strength was measured with a spring-scale penetyaneter provided w i t h a 1.0-inch-diameter c y l i n d r i c a l footing and a l/k-inch penetration i n a 4-inch depth of pumice. A few check landings were made i n pumice having bearing strengths up t o approximately 10 lb/sq i n . I n general, these surface conditions were similar t o those of the NASA Manned Spacecraft Center lunar-surface model.
Landing-impact accelerations were measured by strain-gage accelerometers r i g i d l y mounted i n t h e model as shown i n figure 12. The accelerometers were mounted on a common base which could be r o t a t e d i n l i n e with the axis of f l i g h t , depending upon model yaw a t t i t u d e . Normal acceleration a t the center of gravity was measured with a 20g accelerometer.
Longitudinal acceleration was measured with a l5g accelerometer mounted above the normal accelerometer. Angular acceleration was measured with a pair of matched 50g accelerometers. The natural frequency was about 180 cycles per second for the l5g and 20g accelerometers and about 310 cycles per second for the 5Og accelerometers. The accelerometers were damped to 65 percent of critical damping. The response of the recording zalva- nometers was flat to about l9O cycles per second for the l5g accelerometers and to about 135 cycles per second for the 20g and 50g accelerometers. A trailing cable, supported by an overhead guide wire, was used to transmit accelerometer signals to an oscillograph. Total gear stroke was obtained by measuring linear elongation of the energy straps after each landing.
Impact points, slideout, and penetration characteristics (in pumice) were visually observed and measured.
Motion-picture cameras recorded general behavior during landings.
The orientations of acceleration axes, attitudes, and the flight-path angles during landings are shown in figure 13. Landings were made at touchdown pitch attitudes of - 1 5 ' to +15O, yaw attitudes of Oo (one gear leg forward) and 36O or 4 5 ' (two legs forward), roll attitude of 1 5 ' , and combinations of the above. Ver- tical landing speed was varied from 5 to 15 feet per second and horizontal speed was varied from 0 to 15 feet per second (full scale). Combinations of vertical and horizontal speed result in touchdown flight-path angles ranging from approxi- mately 26O to goo. (See table in fig. 1 3 . ) The landings were made at a model weight corresponding to a full-scale lunar weight of 1,333 pounds (8,000 lb earth weight). The sliding coefficient of friction during hard-surface landings (con- crete or wood) was about 0.4 and was about 0.7 to 1.0 on the powdered pumice over- lay. In general, landing tests of the basic four-point gear were made over the entire range of parameters, whereas the asymmetric four-point and the symmetric five-point gears were investigated only at conditions where instability had occurred with the basic gear. The footprint bearing area of the landing-gear pad was varied by a factor of 4 during landings in pumice.
In order to determine the effect of entrainment of air and moisture in the powdered pumice on landing stability of the model a few landings were made in a During the landing tests under vacuum a vacuum of 0.20 millimeter of mercury.
mechanical shaker mounted on the chamber floor was used in an effort to settle the pumice during evacuation.
RESULTS AND DISCUSSION All impact data presented are converted to full-scale lunar values in terms of the earth's gravitational constant by use of the scale relations given in table I.
Symmetric Four-Point Landing Gear Hard-surface landings.- Oscillograph records showing typical impact charac-
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teristics during landings on a flat hard surface are shown in figure 14 for vari- ous landing speeds and attitudes with the symmetric four-point gear. Impacts were generally characterized by one or two main impulses, depending upon contact attitude, followed by secondary loadings due to very small rebounds which were damped in 2 or 3 cycles.
Landing impacts: Maximum accelerations experienced during such landings a r e p l o t t e d against flight-path angle f o r various p i t c h and yaw a t t i t u d e s i n The module experienced l i t t l e change i n maximum acceleration with 15.
f i g u r e change i n f l i g h t - p a t h angle from 33' (Vv = 10 f t / s e c ; VH = 15 f t / s e c ) t o 90' Maximum normal acceleration (2g) a c t u a l l y (Vv = 15 f t / s e c ; VH = 0 ft/sec).
occurred a t a p i t c h a t t i t u d e of 0 ' and a f l i g h t - p a t h angle of Po when a l l landing-gear shock absorbers yielded simultaneously and equally. Maximum accelerations a r e p l o t t e d against touchdown p i t c h a t t i t u d e i n f i g u r e 16 f o r landings a t a f l i g h t - p a t h angle of 4 5 ' on f l a t and ledged hard surfaces a t yaw angles of 0 ' and 4 5 ' . Normal and longitudinal accelerations d i d not change sig- n i f i c a n t l y with v a r i a t i o n i n p i t c h a t t i t u d e from - 1 5 ' t o + 1 5 ' . During landings a t p o s i t i v e p i t c h a t t i t u d e (+Yjo), t h e module with horizontal velocity underwent 13, and a p o s i t i v e longitudinal acceleration a t touchdown as noted i n f i g u r e s 14, 16. This acceleration resulted from t h e r e l a t i v e motion and f r i c t i o n between t h e t r a i l i n g pad or pads and t h e landing surface during t h e impact stroke, when t h e t r a i l i n g pad displaced rearward over t h e surface. A similar reaction occurred f o r a f l i g h t - p a t h angle of 90° and a p o s i t i v e o r negative p i t c h a t t i t u d e ( f i g . 15) M a x i m u m longitudinal acceleration w a s approximately &g during hard-surface landings.
a f l a t hard surface increased from a Angular accelerations during landings on maximum of approximately 61 radians/sec2 a t 0 ' p i t c h a t t i t u d e t o I 2 1 radians/sec 2 2 2 Angular acceler- with increase i n p i t c h t o + l 5 ' , as shown i n figures 1 - 5 and 16.
a t i o n a l s o increased s l i g h t l y with change i n yaw a t t i t u d e from 0 ' t o 4 5 ' during landing a t p i t c h a t t i t u d e . For landings a s t r i d e t h e ledge a t a p i t c h a t t i t u d e of 0 ' ( f i g . 16), angular accelerations were about t h e same as for landings a t p i t c h a t t i t u d e s of C l 5 ' on t h e f l a t surface.
The data p l o t t e d i n figure 16(a) f o r a landing astride t h e ledge a t p i t c h and yaw a t t i t u d e s of 0 ' were obtained during t h e sequence i l l u s t r a t e d i n f i g - ure l 7 ( a ) with t h r e e legs impacting on t h e ledge. I n t h i s case a l l four legs absorbed energy. Severe loading of a single l e g was obtained for t h e condition i l l u s t r a t e d i n t h e sequence of f i g u r e l 7 ( b ) . Essentially, only two legs were involved i n t h i s case and high accelerations r e s u l t e d when t h e leading-leg shock absorber was bottomed; t h a t i s , t h e emergency b a l s a stop was crushed.
The p o s s i b i l i t y of a l l impact energy being imposed on a single l e g suggests t h e d e s i r a b i l i t y of increased available stroke o r s t i f f e r shock absorbers f o r t h e present system. Maintaining low gear forces and increasing t h e stroke would be preferable from an overturn s t a b i l i t y standpoint. A varying-force shock-absorber system (pyramided force l e v e l s ) has been suggested i n an unpublished analysis made I n t h e suggested sys- by Charles C . F i l l e y at t h e NASA Manned Spacecraft Center.
t e m four force l e v e l s , increasing with stroke, are available i n each of t h e four l e g s and a single l e g has t h e same design energy-dissipating c a p a b i l i t y f o r f u l l stroke as four legs using one-quarter stroke. Such a system would be e f f e c t i v e and would reduce stroke requirements as compared with t h e present system f o r a single-leg impact.
Another system would l i n k a l l a r t i c u l a t i n g l e g s t o a s i n g l e shock-absorber unit o r element, and deflection of any number of l e g s ( s i n g l e o r multiple) would provide t h e same energy-dissipating c a p a b i l i t y f o r t h e same stroke. The shock absorber could be a constant- o r variable-force system.
Maximum accelerations obtained during hard-surface landings a t a roll a t t i - tude of 15' a r e presented i n t a b l e 111. When compared w i t h t h e data i n f i g u r e s 15 and 16, acceleration values and trends a t a roll a t t i t u d e of 1 5 ' were generally similar t o those a t a roll a t t i t u d e of 0'.
Landing s t a b i l i t y : During landings on a f l a t o r a ledged hard surface, t h e module appeared very s t a b l e with regard t o overturning f o r a l l landing conditione t e s t e d . Slideout distances i n t h e order of 30 t o 40 f e e t ( f u l l s c a l e ) r e s u l t e d a t t h e highest horizontal speed (15 f t / s e c ) . A t a yaw a t t i t u d e of 0 ' where one l e g i s forward, an undamped pitching o s c i l l a t i o n occurred during slideout as i l l u s t r a t e d by t h e oscillograph record i n f i g u r e 1 8 ( a ) . Greater stroking of t h e compared with t h a t of t h e s i d e and r e a r legs during impact a t 8 leading l e g as yaw a t t i t u d e of 0 ' was caused by a combination of pad f r i c t i o n and landing dynam- i c s . This phenomenon r e s u l t e d i n an unsteady or t e e t e r i n g platform during s l i d e - out and subsequently a t r e s t . Landing a t a yaw a t t i t u d e of 45' where two l e g s a r e forward generally a l l e v i a t e d t h i s c h a r a c t e r i s t i c . (See f i g . 18(b). ) Landings a t a roll a t t i t u d e of 1 5 ' d i d not a f f e c t overturn s t a b i l i t y . (See t a b l e 111.) Some t e e t e r i n g was noted during landing s l i d e o u t s f o r landings a t a roll a t t i t u d e .
Dust-surface landings.- Oscillograph records showing t y p i c a l impact charac- t e r i s t i c s during landings on a f l a t dust overlay 2 1 inches deep a r e shown i n f i g - u r e 19 f o r various landing a t t i t u d e s with t h e symmetric four-point gear. Impact events were generally similar t o those on a hard surface ( f i g . 1 4 ) . Inspection of f i g u r e s 14(b) and l g ( b ) shows t h a t i n t h e 21-inch depth of dust, a c c e l e r a t i o n onset r a t e was reduced.
Landing impacts: Maximum accelerations experienced during landings i n two depths of pumice dust a r e p l o t t e d against f l i g h t - p a t h angle f o r various p i t c h and yaw a t t i t u d e s i n f i g u r e 20. Normal and longitudinal acceleration d i d not change appreciably with change of f l i g h t - p a t h angle but angular acceleration increased i n some cases with reduction of f l i g h t - p a t h angle (increased h o r i z o n t a l speed) I The depth of dust had no appreciable o v e r a l l e f f e c t on maximum accelerations.
Compared with t h e accelerations encountered i n hard-surface landings ( f i g . 15) maximum normal accelerations i n dust were r e l a t i v e l y unchanged as a r e s u l t of t h e use of an e s s e n t i a l l y constant-force shock-absorber system. However, negative longitudinal acceleration (drag) increased by a f a c t o r of 2 o r 3 t o approximately 1 % because of increased r e s i s t a n c e t o horizontal s l i d i n g i n t h e dust.
During a landing a t a p i t c h a t t i t u d e of - 1 5 ' and a f l i g h t - p a t h angle of 3 0 ' ~ (Vv = 8.7 f t / s e c , VH = 15 ft/sec) with one l e g forward ( 0 ' yaw) t h e lower V - s t r u t of t h e leading l e g buckled a t i n i t i a l impact on that l e g as indicated i n f i g - u r e 20(a). A t t h i s landing condition t h e main strut d i d not stroke; t h i s r e s u l t i n d i c a t e s t h a t t h e r e s u l t a n t f o r c e of impact i n t h e dust was vectored along o r below t h e plane of t h e V - s t r u t , so t h a t excessive column loading and f a i l u r e occurred. The landing was similar t o stubbing t h e gear pad a t touchdown on an immovable obstacle (rock o r boulder). This r e s u l t i n d i c a t e s t h e d e s i r a b i l i t y of providing shock-attenuation c a p a b i l i t y i n t h e horizontal plane e i t h e r by incorporating stroke i n t h e gear pads (crushable pads) o r i n t h e lower S t r u t s ( t r i - s t r u t a t t e n u a t i o n ) .
Maximum accelerations a r e p l o t t e d against touchdown p i t c h a t t i t u d e i n f i g - ure 2 1 f o r landings a t yaw a t t i t u d e s of Oo and 4 5 O and a f l i g h t - p a t h angle of 45' on f l a t and ledged surfaces having various depths of dust overlay. A somewhat g r e a t e r change i n accelerations with change i n p i t c h a t t i t u d e i s noted f o r t h e dust landings, p a r t i c u l a r l y a t a yaw a t t i t u d e of 45', as compared w i t h t h a t obtained during hard-surface landings ( f i g . 16). This r e s u l t was l a r g e l y due t o g r e a t e r changes i n f r i c t i o n o r drag forces on t h e pads f o r impacts i n Pumice i n turn, a f f e c t gear actuation and stroking.
dust, and these changes, Maximum accelerations f o r landings a t a r o l l a t t i t u d e of 15' a r e presented A decrease of approximately 50 percent i n normal and longitudinal i n t a b l e 111.
acceleration i s noted f o r t h e landing a t a p i t c h a t t i t u d e of -15' as compared with t h e acceleration f o r t h e same p i t c h condition a t a roll a t t i t u d e of 0 ' ( f i g . 2 0 ( b ) ) .
Accelerations during limited landings i n t h e 41-foot-diameter vacuum sphere 0.20 millimeter of mercury were s i m i l a r t o those a t atmospheric pressure.
a t Landing s t a b i l i t y : Unstable landings a r e indicated by t h e s o l i d symbols i n f i g u r e s 20 and 21.
The module was s t a b l e over a wide range of landing conditions during landings on t h e dust overlay.
Overturning generally occurred at f l i g h t - path angles of 45' o r l e s s , depending upon module o r i e n t a t i o n (yaw a t t i t u d e ) and touchdown p i t c h a t t i t u d e during landings on f l a t dust overlay. The module w a s most l i k e l y t o overturn at 45' yaw a t t i t u d e (minimum gear r a d i u s ) asld at - 1 5 ' p i t c h a t t i t u d e . However, at a yaw a t t i t u d e of 0 ' (maximum gear r a d i u s ) where one l e g was forward, a misalinement r e l a t i v e t o t h e v e l o c i t y vector c o a d cause t h e module t o veer t o a two-legs-forward o r i e n t a t i o n ( 4 3 O yaw) with consequent over- turning as indicated i n figure a(&) f o r a p i t c h a t t i t u d e of 0 ' and a f l i g h t - p a t h angle of 33'. Some t e e t e r i n g c h a r a c t e r i s t i c s were noted during landings on pow- dered pumice at a yaw a t t i t u d e of 0 ' as was t h e case f o r hard-surface landings.
On t h e ledged surface, overturning occurred for a l l p i t c h conditions at 45' yaw with t h e symmetric four-point gear ( f i g . 21). The conditions f o r a y a w a t t i t u d e of Oo were not tested on t h e ledge t o avoid possible damage t o t h e model gear such as t h a t noted i n f i g u r e 20(a).
The e f f e c t s on landing s t a b i l i t y of depth of dust and pad s i z e a r e shown i n f i g u r e 22.
Data f o r two pad s i z e s and depths of dust a r e p l o t t e d a t t h e f l i g h t - path angles a t which i n s t a b i l i t y occurred. A t a touchdown p i t c h a t t i t u d e of -15O, t h e module was unstable regardless of pad s i z e o r depth o f dust t e s t e d . A t a p i t c h a t t i t u d e of 0 ' t h e module was s t a b l e i n t h e ?-inch depth and unstablt i n thc 21-inch depth of dust regardless of pad s i z e .
A t a p i t c h a t t i t u d e of l 5 ' , mixed r e s u l t s occurred with t h e l a r g e pads e i t h e r increasing o r decreasing s t a b i l i t y depending upon f l i g h t - p a t h angle and depth of dust. Although inconclusive, t h e I data i n d i c a t e t h a t i n t h e shallow dust ( 5 inches), t h e l a r g e c i r c u l a r pads b e s t e d I provided increased s t a b i l i t y , whereas i n t h e deep dust (21 inches) they we1.e d e s t a b i l i z i n g . Both s e t s of pads tended t o penetrate deeply and plow through t h e I Pumice during impact.
The l a r g e pads penetrated a t a f l a t t e r angle and not as deeply a s t h e small pads. The small pads tended t o penetrate through t o t h e sub- surface.
When overturning occurred t h e r e was i n most cases very l i t t l e horizontal ~ stroke o r skidding of t h e leading pads during landing impact.
Overturn stability was generally unchanged during landings at a roll attitude of l5O. (See table 111.) However, at a pitch attitude of -15' and a flight-path angle of 4 5 O , the module was stable whereas at a roll attitude of Oo, it was unstable (fig. 2 0 ( b ) ) . During rolled landings in the dust overlay the module tended to veer or rotate about the yaw axis at initial impact, but this effect did not seem to be a problem for these limited number of landings.
No changes in landing-stability characteristics were noted during landings in a vacuum environment of approximately 0.20 millimeter of mercury. It was observed that the pumice did not settle noticeably during evacuation of the sphere, and this result indicated that little compaction occurred. In this test dynamic penetration characteristics were not significantly changed because of the grain size and the vacuum pressure used. This is in agreement with the results presented in references 2 and 3 .
I
Asymmetric Four-Point Landing Gear Hard-surface landings.- Oscillograph records showing typical impact charac- teristics during landings on flat hard surface with the asymmetric four-point gear are shown in figure 23. Acceleration characteristics were similar to those for the symmetric four-point gear (fig. 14) except for small increases in acceleration pulse times and reduction in magnitudes due to the modified geometry. The change in geometry resulted in increased stroke during impact at the offset legs and the module generally came to rest pitched down in the direction of gear offset (for- ward). The maximum pitch attitude at rest was approximately 5 O for the conditions tested.
Maximum accelerations experienced during three landings on flat hard surface with the asymmetric four-point gear are plotted in figure 16. Normal and longi- tudinal accelerations were the same as for the basic gear, and angular accelera- ~ tions were reduced slightly.
Dust-surface landings.- Data obtained during landings with the asymmetric four-point gear on flat dust overlay are plotted in figure 24. Landing stabil- ity was increased considerably with the asymmetric gear as compared with the sym- metric gear (fig. 2 0 ( b ) ) . Likewise, stability was improved during landings on ~ the ledged surface. See figure 21(b).
Maximum normal and longitudinal accelerations experienced with the asymmetric gear (fig. 24) were reduced relative to those experienced with the symmetric gear.
Longitudinal accelerations during dust-surface landings were reduced as much as 50 percent. These reductions are attributed to the change in geometry of the off- I set legs which resulted in less "jELmming" and more horizontal stroking of the leading pads through or over the dust during landing impact.
This phenomenon is illustrated in figure 25 by typical oscillograph records showing landings on the ledge and dust overlay with the symmetric and asymmetric four-point gears. Par- ticularly noticeable is the large change in time and magnitude of the longitudinal acceleration pulse at impact of the leading legs (which are labeled 2 to 3) and the associated change in horizontal displacement between the two gear configura- tions. Normal-acceleration pulses were similarly affected. The increased gear radius and reduced pad loading of the asymmetric four-point gear were very effec- tive in increasing landing stability.
Symmetric Five-Point Landing Gear Hard-surface landings.- Maximum accelerations experienced during landings with the symmetric five-point landing gear on a flat hard surface are shown in figure 2 6 at various flight-path angles and landing attitudes. A s expected, nor- mal and longitudinal accelerations were approximately the same for this configura- tion as for the symmetric four-point gear. Angular accelerations at pitch atti- tudes were reduced slightly as a result of the reduced shock-absorber force of individual legs of the five-point system. For all landing conditions investi- gated, this configuration was stable. Slideout oscillations and static teetering encountered with the four-point system were generally eliminated, so that a more stable platform for lunar launching was provided.
Dust-surface landings.- M a x i m u m accelerations experienced during landings with the symmetric five-point landing gear on flat dust overlay are shown in fig- ure 27 at various flight-path angles and landing attitudes. In general, maximum accelerations were similar to those for the symmetric four-point system. The mod- ule was somewhat more stable during landings on dust overlay because of the net increase of approximately 15 percent in minimum gear radius, additional footprint, and reduced gear force.
CONCLUSIONS Results of the dynamic-model investigation indicate that landing character- istics of a lunar landing module having multiple-point leg-type landing systems and yielding-metal shock absorbers were satisfactory over a considerable range of touchdown parameters and landing-surface conditions. The principal conclu- sions indicated by this investigation are as follows: 1. Maximum normal acceleration obtained during landings was approximately 2g (earth value) at the center of gravity. Maximum longitudinal acceleration on 1 3 hard surface was approximately -g and increased to approximately l-g on powdered
2 4
pumice overlay. Maximum angular acceleration was approximately 12l radians/sec2
E
during hard-surface landings.
2. The module was very stable with regard to overturning with all landing- gear configurations during landings on an impenetrable hard surface (coefficient of friction, p = 0.4) at all conditions tested.
3. Some overturn instability occurred during landings on powdered pumice ( p = 0.7 to 1.0) depending upon flight-path angle, touchdown attitude, depth of pumice, surface topography, and landing-gear configuration.
4. An asymmetric four-point gear configuration with two pads offset to increase gear radius by 33 percent in the direction of horizontal flight improved landing stability considerably on powdered pumice overlay.
5. A symmetric five-point gear configuration was slightly more stable than
a four-point system with equal maximum radius and provides a nonteetering launch platform for lunar departure.
6. Shock attenuation capability in the horizontal plane would be desirable for extreme impact conditions.
Langley Research Center, National Aeronautics and Space Administration, Langley Station, W p t o n , Va., August 16, 1963.
1. Blanchard, Ulysse J . : Landing Characteristics of a Winged Reentry Vehicle With All-Skid Landing Gear Having Yielding-Metal Shock Absorbers. NASA TN D-1496, 1962.
2. Rowe, R. D . , and Selig, E. T . : Penetration Studies of Simulated Lunar Dust.
Trans. Seventh Symposium on Ballistic Missile and Space Technology, Vol. I, U.S. Air Force and Aerospace Corp., Aug. 1962, pp. 53-72.
3. Clark, Leonard V . , and McCarty, John Locke: The Effect of Vacuum on the Pene- NASA TN D-1519, tration Characteristics of Projectiles Into Fine Particles.
TABLE I.- SCAT-IE RELATIONSHIPS FOR EARTH MODEL OF LUNAR LANDING MODULE h = Geometric model scale P = Gravitational ratio, 6 (gearth/%noon) Quantity Lunar full scale Scale factor Earth model scale Length A2 Stress (energy strap) a Acceleration Pa Area Force Mas s Velocity Time Inertia Angular velocity Angular acceleration TABLE 11.- PERTINENT D I h B N S I O N S O F MODULE 1/6-scale model Full scale General : Gross weight. l b . . . . . . . . . . . . . . . .
37- 0 1. 333 Moment of i n e r t i a (approximate) : 4. 666 0.6 Roll. slug-ft2 . . . . . . . . . . . . . . . .
0.6 4. 666 Pitch. slug-f t2 . . . . . . . . . . . . . . .
0.50
yaw. slug-ft2 . . . . . . . . . . . . . . . . 3. 888
2.56
Overall height. f t . . . . . . . . . . . . . . . 15.35
Overall diameter (basic gear) : 19.62 Small pads. f t . . . . . . . . . . . . . . . .
3.27 3.46 20.76 Largepads. f t . . . . . . . . . . . . . . . .
1.50 Center of gravity above ground line. f t . . . .
9.00 Landing gear: Symmetric four-point (four legs 900 apart) :
M a x i m u m radius. f t . . . . . . . . . . . . . . 1.54
9.25
Minimum radius. f t . . . . . . . . . . . . . . 6.55
1 . og
2.10
Vertical stroke. f t . . . . . . . . . . . . . 0 - 35
Shock-strut energy strap (each): 6.28 x 10-4
Cross-sectional area. sq f t . . . . . . . . 1.75 x 10-5
3.62
Length. f t . . . . . . . . . . . . . . . . . 0.60
Asymmetric four-point (four legs 900 apart) : M a x i m u m radius :
Basic legs (2). f t . . . . . . . . . . . . . 1.54 9.25
12.25
Offset legs (2). f t . . . . . . . . . . . . 2.04
Minimum radius : . . . . . . . . . . . . .
Basic legs (2). f t 1 . og 6.55
8.65
Offset legs (2). f t . . . . . . . . . . . . 1.44
Vertical stroke:
. . . . . . . . . . . . . 2.10
Basic legs (2). f t 0.35 2.80
Offset legs (2). f t . . . . . . . . . . . . 0.47
Shock-strut energy strap (each) : 6.28 x 10-4
Cross-sectional area. sq f t . . . . . . . . 1.75 x 10-5
3.62
Length. f t . . . . . . . . . . . . . . . . . 0.60
Symmetric five-point (five legs 720 apart) :
M a x i m u m radius. f t . . . . . . . . . . . . . . 1.54 9.25
Minimum radius. f t . . . . . . . . . . . . . . 1.25 7.50
2.10 . . . . . . . . . . . . .
Vertical stroke. f t 0.35 Shock-strut energy strap (each) : 5.30 x
Cross-sectional area. sq f t . . . . . . . . 1.47 x 10-5
3.62
Length. f t . . . . . . . . . . . . . . . . . 0.60
Gear pads: Small pad (each): 1.13 0.19 Diameter. f t . . . . . . . . . . . . . . . .
1.00
Footprint area. sq f t . . . . . . . . . . . 0.03
Large pad (each): 2.25 Diameter. f t . . . . . . . . . . . . . . . .
0.38
Footprint area. sq f t . . . . . . . . . . . 0.12 4.32
I I 'z - O f f c u "0' Gc-r A i - o!
'" 0' -f 4 9 9
-
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-
In 0 ln f a
-
ln I 2 2 4 t 4 H
-
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-
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-
4 4
-
- - Maximum gear r a d i u s Minimum g e a r r a d i u s - / / .
. -- ( + ) -
-
I I
t6V
Maximum stroke
I
Figure 1.- General arrangement of 1/6-scale dynamic model.
All dimensions a r e i n Inches.
Pit ch Fig~re 2. - Photograph of model with symmetric four-poin t landing gear.
L- 63 -5 53 ·1 . .I.
(a) Symmetric .
L- 63 - 554 (b) Asymmetric .
L-6 3-555 Figure 3 .- Photographs of model showing symmetric and asymmetric four -poin t landing gears.
L-6;-1559 (a) Side view.
(b) Top view. L-6;-1557 Figure 4.- Photograph of model showing symmetric five-point landing gear.
Figure 5 .- Landing - gear assembly . L- 6) - 47)'7 L-3616 .
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L- 62 - 4270 . 1 Figure 7.- Model on launching gear .
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J .
, Tnstrumen cg,ble L- 62 - 7386 .1 Figure 9. - Model and landin g- test apparatus in 41-foot - diameter vacuum sphere .
h h c d a rl l-l k k a .
a , 0 0 u w VI f 3 b e , c . .
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I, I I I I \ I I \ I I I I I I I I I I I 1 1 I I I I I I 1 0 20 40 60 80 100 120 140 Grain s i z e , microns Figure 11.- Grain-size distribution of powdered pumice used for dust overlay.
'-0r~2l ------- '] cc "'1 Figure 12 .- Instrument installation in model . L-62-4271.1
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i t c h a t t i t u d e , 00 (a) Yaw attitude, 0'.
L I * i r , , 10 -ft/seC; vH; 10 f t / s e c P i t c h a t t i t u d e , + 1 5 O 7 ( b ) Yaw a t t i t u d e , 45'.
Figure 14.- Typical oscillograph records of a c c e l e r a t i o n s during landings on f l a t hard surface at various speeds and a t t i t u d e s with s y n r e t r i c four-point landing gear. R o l l a t t i t u d e , 0 ' .
OQ c,m d r l
a + 1
e A, OOA M 0,
U 4
c, n A 0 do A Q
I , ; N
0 0 0 0 0 0
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a J rl m a >x t O a 0 I + . ..
1 I P i t c h a t _ t l t u d e , -15"
P i t c h a t t i t u d e , + 1 5 O
. I l I I I I
(a) Yaw attitude, Oo.
1-1 L L . 1 1 1 1 I I I I 1 I I 1 L . I . L I A , I (b) Yaw attitude, 450.
Figure 19.- Typical oscillograph records of accelerations during landlngs on flat dust overlay at varioue attitudes with symmetric four-point landing gear.
45O; VV, 10 ft/eec; Flight-path angle, VH, 10 ft/eec; roll attitude, Oo; depth of dust, 21 inches.
0 0 OD
+ +
0 0 O N 2 N rl cu m 0 0
-
cu 0 “ l o 3 cu 0 0 4 I N cu r( r( I N eo0 cJ3D 0 .
d rl
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a
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t sec Vv, 15 ft/sec; VH, 0 ' Pitch attitude, 0' Pitch attitude, O o Pitch attitude, -15'O Figure 23.- Typical oscillograph records of accelerations during landings on flat hard surface at Yaw attitude, 450; roll various speeds and attitudes with asymmetric four-point landing gear.
attitude, 0 ' .
rl co u3 A 00 0 0
p”, 1
f cu 0 cu 0 N I 1 Normal acceleration at c.g.
l ' ~ : l l ! l ~ l l l l l
(a) Symmetric four-point gear.
(b) Asymmetric four-point gear.
Figure 25.- Typical oscillograph records of accelerations during landingr on ledged surface and dust overlay with symmetric and asymmetric four-point landing gears. Pitch attitude, t l 5 O ; roll atti- tude, 0 ' ; yaw attitude, 45'; flight-path angle, 45O; VV, 10 ft/sec; Va, 10 ft/sec; depth of dust, 21 inches.
ri o co a N r- 0 0 M co V n a, V .!2 d \D V O W 0 0 E O A +i f
-
- 3
N rl m rD b f d- f (v 0 ( u o 0 0 0 I N rl ri I d d ..
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