Document
N A S A TECHNICAL N O T E
GROUND-RUN TESTS WITH A BOGIE
WATER AND SLUSH
LANDING GEAR I N
Lungley Reseurch Center
zdngley Stdtion, Hampton, Q.
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N A T I O N A L A E R O N A U T I C S A N D SPACE A D M I N I S T R A T I O N W A S H I N G T O N , D. C . JULYY966 TECH LIBRARY KAFB, NM 0130339 NASA TN D-3515 GROUND-RUN TESTS WITH A BOGIE LANDING GEAR IN WATER AND SLUSH By Robert C. Dreher and Walter B. Horne Langley R e s e a r c h Center Langley Station, Hampton, Va.
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i GROUND-RUN TESTS WITH A BOGIE LANDING GEAR IN WATER AND SLUSH By Robert C. Dreher and Walter B. Horne Langley Research Center SUMMARY Ground-run tests were made with a bogie-type landing gear on water- and slush- covered runways to obtain data on fluid-displacement drag, wheel spin-down, wheel spray patterns, and fluid-spray drag. Tests were made with the normal four-wheel (dual tan- dem) configuration and with configurations consisting of one and two wheels at different locations on the bogie truck. The ground speeds ranged from 15 t o 110 knots and the runway fluid depths ranged from 0.15 to 2.0 inches (0.38 to 5.08 centimeters). Tire inflation pressures were 25, 50, and 7 5 pounds per inch2 (17.2, 34.5, and 51.7 newtons per centimeterq, and the vertical load per t i r e w a s approximately 5000, 6000, o r 1 2 000 pounds (22 200, 26 688, o r 53 378 newtons) depending on the wheel configuration.
Some t e s t s were also made with a simulated wing flap mounted to the r e a r of the wheels in the take-off and landing positions. In addition, a few tests were made with a spray alleviator mounted between the wheels of the dual-tandem wheel configuration.
Results indicated that ground speed, vertical load, t i r e pressure, fluid density, fluid depth, and wheel location affected the fluid-displacement drag, the wheel spin-down characteristics, the wheel spray patterns, and the fluid-spray drag developed by this landing gear. Fluid spray impinging on the simulated wing flap in the landing position produced a maximum drag on the upper mass which w a s approximately 70 percent greater than that measured on the landing gear. The spray alleviator installed on the dual- tandem wheel configuration reduced the maximum fluid drag approximately 45 percent.
INTRODUCTION The National Aeronautics and Space Administration for the past several years has been studying the adverse effects of water- and slush-covered runways on the take-off and landing performance of airplanes. In 1960, the NASA performed slush tests on a single airplane wheel at the Langley landing-loads track. On the basis of these tests, a method for predicting airplane take-off distance in slush w a s developed and is presented 1. This method did not account f o r drag due t o slush spray impinging on the in reference airplane o r for t i r e hydroplaning effects, since only the drag due to displacing the fluid on the runway from the paths of the front wheels of the landing gear was considered. As a result of these t e s t s and of full-scale tests of reference 2, the Federal Aviation Agency instituted the “1/2 inch rule” which prohibits jet-transport airplanes from taking off on runways covered with slush or water greater than 1/2 inch (1.27 centimeters) in depth.
However, uncertainties such as t i r e size, tire pressure, number of wheels, high forward’speeds, and vertical load existed when the slush drag prediction method devel- oped with the single wheel was applied t o particular airplanes. Because of these uncer- tainties, it was believed that full-scale t e s t s on a jet transport operating in slush would provide results which would be useful in confirming or refining the slush drag prediction method. Such t e s t s were performed in the fall of 1961 by the FAA with NASA technical assistance on a commercial jet transport owned by the FAA. The results of these t e s t s were reported in references 3, 4, and 5; some of these results a r e shown in figure 1.
These results indicated that the effects on slush drag of slush-spray interference and impingement and of hydroplaning were large and, therefore, the simple theory of r e f e r - ence 1 was not adequate to predict slush drag.
In order t o obtain information on runway fluid-displacement drag, wheel spin-down, wheel spray patterns, and fluid-spray drag, the NASA conducted ground-run tests on water- and slush-covered runways at the Langley landing-loads track. A four-wheel (dual tandem) bogie landing gear was used in these tests. Seven separate wheel config- urations, six of which consisted of one and two wheels in different locations on the landing-gear truck and the normal four-wheel (dual tandem) configuration, were used during the tests. Tests were also made with a simulated wing flap mounted to the rear of the wheels and some t e s t s were made with a fluid-spray-drag alleviator mounted on the bogie landing-gear truck. The tests were made at various ground speeds, t i r e pres- sures, runway fluid depths, and vertical loads.
The purpose of this paper is to present the results obtained during this investiga- tion. These results show the effect of fluid-covered runways on landing-gear drag and wheel spin-down, the fluid spray patterns developed with the different wheel configura- tions, and the drag produced by fluid spray impinging on a simulated flap. In addition, the results show the possibility of reducing spray drag by means of an alleviator.
SYMBOLS Measurements for this investigation were taken in U.S. Customary Units and equivalent values a r e indicated herein in the International System of Units (SI). Details concerning the use of SI together with physical constants and conversion factors a r e given in reference 6.
I. . I
tire width, inches (centimeters) tire width, inches (centimeters), at inflation pressure of 75 pounds bst per inch' (51.7 newtons per centimetera) drag due t o fluid, pounds (kilonewtons) DS runway fluid depth, inches (centimeters) reference runway fluid depth, 1.0 inch (2.54 centimeters) vertical load on landing gear, pounds (newtons) tire inflation pressure, pounds per inch2 (newtons per centimeter2) ground speed, knots t i r e hydroplaning speed, knots ratio of wheel angular velocity on a wet runway to that on a dry runway Wdry surface APPARATUS Test Vehicle This investigation was made at the Langley landing-loads track.
The test vehicle of this facility is the carriage shown in figure 2 and weighs approximately 100 000 lb (444.8 kN). This carriage is catapulted by a hydraulic jet to speeds up to 120 knots along steel rails which are 30 f t (9.14 m) apart and 2200 f t (670.56 m) long. The carriage straddles a concrete runway which has a surface similar to airport runways. A vertical drop carriage to which the test landing gear is attached is incorporated within the main carriage. Further information on the operation of this facility is given in reference 7.
Landing Gear The dual-tandem bogie landing gear used in this investigation was equipped with
12.50 - 16, 38- inch-nominal-diameter (96.52 cm), type 111, 10-ply -rating, dimple -tread
tires. A schematic drawing of the test fixture and landing gear is shown in figure 3.
The oleo-pneumatic shock strut of the gear was replaced by an 8-inch-diameter (20.32 cm) bar. Due t o the geometry of the landing gear, 46 percent of the total static vertical load was carried on the front axle and 54 percent on the rear axle.
Wheel Configurations Seven configurations of the landing-gear wheels were used during the tests. These are shown by the sketches in table I. For configura- configurations, in order of testing, tions I, IV, V, and IA the landing gear was free t o pitch about the truck-beam pivot since the pitch snubbers were removed. A w i r e rope fastened between the front axle and the test fixture prevented the gear from pitching down to an excessive degree when it was air- borne. Configuration I w a s the normal condition in which all four wheels were mounted on the landing gear. In configuration 1 1 the two r e a r wheels were removed and replaced by steel b a r s which were attached from the wheel axles to the upper part of the vertical drop carriage. Similarly, in configuration III the two front wheels were removed and replaced by steel bars. A diagonal wheel arrangement w a s obtained in configuration IV by Configuration V consisted of two single removing the right front and left r e a r wheels.
wheels in tandem. Single wheel configurations VI and VII consisted of the left front and the rear wheel, respectively. A spray-drag alleviator was attached between the dual tandem wheels f o r some of the tests; this configuration was designated configuration IA.
W a t e r and Slush Trough Concrete dikes placed along the sides of the track runway formed a trough 9 ft (2.74 m) wide and 512 f t (156.06 m) long as shown in figure 4 . Temporary dams of a puttylike material were placed at each end of the trough t o retain the slush and water for testing.
Slush w a s made by the ice-crushing machine shown in figure 5. Photographs and a description of a similar slush-laying operation a r e given in reference 5. The crushed ice was first leveled manually to the approximate test depth desired. Just before the start of a test run, the slush was trimmed to the desired test depth by the machine shown in figure 6. The crushed ice was allowed to melt to a slushy condition before a test.
The average specific gravity of the slush used in this investigation was 0.88.
TEST PROCEDURE The runway fluid depth d l and the slush density, in the case of slush tests, w e r e measured immediately prior to each test at the eight stations along the trough shown in figure 4 . Before each test, the vertical drop carriage w a s positioned so that the landing- gear wheels were approximately 2.0 in. (5.08 cm) above the runway surface. Then the test carriage was catapulted to the desired ground speed by means of the hydraulic jet.
In order to minimize landing-gear oscillations during the tests, the landing gear was l allowed to contact the runway well ahead o f the test section. Views of the slush bed before and after a typical test are shown in figures 7 and 8, respectively. All tests were made with freely rolling (unbraked) wheels.
In the investigation, a series of tests w a s made with each of the wheel configura- tions shown in table I. The ground speed VG ranged from 15 t o 110 knots. T i r e inflation pressures p of 25, 50, and 75 lb/in2 (17.2, 34.5, and 51.7 N/cm2) were used ranged from 0.15 to 2.0 in. (0.38 to 5.08 cm) for the and the runway fluid depth d l water tests and from approximately 1.0 t o 2.0 in. (2.54 to 5.08 cm) for the slush tests.
The vertical load per tire for the different wheel configurations is given in table I. In addition, a few t e s t s were made on the dual tandem wheels (configuration I) with a verti- cal load of approximately 12 000 lb (53 378 N). A simulated wing flap was mounted to the r e a r of the landing-gear wheels as shown in figure 9. This flap w a s mounted at an angle of 220 during t e s t s with all the wheel configurations and also at an angle of 55O Tests were also made with a spray-drag alleviator mounted on with configuration VI.
the dual tandem wheels (configuration IA) as shown in figure 10.
INSTRUMENTATION The drag load cell shown on the sketch in figure 3 was used to measure the drag forces developed between the landing-gear wheels and the runway whereas the upper m a s s drag dynamometer measured the total drag developed on the landing gear and the simulated wing flap (fig. 9). The difference between these two drag measurements gives the drag load experienced by the simulated wing flap alone. Instrumentation w a s pro- vided t o measure the angular velocity and displacement of each landing-gear wheel and the vertical displacement of the vertical drop carriage. The horizontal displacement and ground speed of the main carriage were obtained by means of a photocell. The light source from the photocell w a s interrupted at 10-ft (3.048 m) intervals along the runway and produced a pulse on an oscillograph-record trace. The electrical outputs of the instrumentation were continuously recorded during the t e s t s by means of an 18-channel oscillograph.
Several 16-mm motion-picture cameras operating at 200 f r a m e s per second and one 70-mm camera operating at 10 f r a m e s per second were mounted at various locations on the main carriage in order to obtain motion pictures of the landing-gear wheels during each test.
RESULTS AND DISCUSSION Previous research conducted on fluid-covered runways clearly shows that the phenomenon of tire hydroplaning can greatly influence the tire-ground forces developed _.. .. I l l 1 1 l 1 1 l l l l I I 1 1 l l 1 1 l 1 l 1 I II on aircraft. Available experimental data on hydroplaning were summarized in refer- ence 8 , in which the following simple expression was developed for estimating tire hydro- planing speed V P = 9 p where VP t i r e hydroplaning speed, knots t i r e inflation pressure, lb/in2 (N/cm2) P Since one of the main purposes of this investigation was to determine fluid drag effects on a landing gear under hydroplaning conditions, this equation w a s used to select t i r e pressures f o r study that would cause the test t i r e s to hydroplane well before the maximum speed capability (approximately 120 knots) of the test carriage w a s reached.
Fluid Drag Parameter When an unbraked tire rolls on a fluid-covered runway, as in airplane take-off, the moving tire contacts and displaces the stationary runway fluid. The resulting change in momentum of the fluid creates hydrodynamic p r e s s u r e s that react on the tire and runway surfaces. The horizontal component o f the resulting hydrodynamic pressure force is termed I'f luid-displacement drag" and the vertical component, "fluid-displacement lift."
Additional fluid forces termed "fluid-spray thrust or drag" and 'Yluid-spray lift" a r e created on aircraft when some of this displaced runway fluid in the form of spray sub- sequently impinges on other parts of the aircraft such as the tires, landing gear, and flaps.
The fluid drag parameter is defined as the incremental drag developed from all fluid-displacement and fluid-spray drag sources normalized to an effective water depth of 1.0 inch (2.54 cm). Values of this parameter were obtained by subtracting the dry- runway rolling resistance of the t i r e s from total drag values measured by the test instru- mentation. This incremental drag w a s then normalized to an effective fluid depth of 1.0 inch by multiplying by the ratio of a reference o r standard fluid depth (1.0 inch) to the test fluid depth. For the slush runs, this result w a s divided by the specific gravity of the slush to normalize the drag data to an effective water density.
This normalizing procedure was necessary because it w a s practically impossible to duplicate fluid depths from run to run because o f different slush melting r a t e s experienced at different times of day and from day to day. It w a s also found that water depths could vary considerably during some runs because of wind effects. Results of this investigation indicated that the The effect of several of these fac- fluid drag parameter is affected by various factors.
t o r s is discussed in the following sections.
The variation of the fluid drag parameter with ground Effect of ground speed.- _____- speed for the dual tandem wheels (configuration I) with t i r e inflation pressures of 25, 50, and 75 lb/in2 (17.2, 34.5, and 51.7 N/cm2) on water- and slush-covered runways is shown in figure 11. The fluid depths ranged from 0.5 to 2.0311. (1.27 to 5.08 cm). The curves faired through the data indicate that the drag parameter increases parabolically with V p is increasing ground speed until a speed near the predicted hydroplaning speed After this speed is attained, the drag decreases. This decrease is attributed reached.
t o the t i r e s riding up in the fluid and thus displacing less fluid from the runway and to the change in spray patterns.
Effect of fluid density.- Figure 11 also shows that there is very little difference in the values of the drag parameter obtained during tests through water (circles) or slush (squares). Therefore, normalizing the slush data to a standard of 1.0 in. (2.54 cm) of water tends to confirm the results shown in reference 9 that fluid drag is proportional to fluid density.
Effect of tire width.- At ground speeds before peak drag, the slope of the drag parameter curves increases as the t i r e pressure is decreased, as shown in figure 12(a).
bs increases from 10.1 in. (25.65 cm) at With the same vertical load, the t i r e width 75 lb/in2 (51.7 N/cm2) to 12.0 in. (30.48 cm) at 25 lb/in2 (17.2 N/cm2). The consequently greater t i r e frontal a r e a exposed to the runway fluid for the lower t i r e pressure causes more fluid to be displaced from the path of the wheel and thereby causes an increase in the drag parameter. When the values of the drag parameters obtained with t i r e pres- s u r e s of 25 and 50 lb/in2 (17.2 and 34.5 N/cm2) a r e normalized in t e r m s of bst, the t i r e width at 75 lb/in2, the curves shown in figure 12(b) a r e obtained. It can be seen from this figure that this normalizing procedure causes the three curves to be practically the same at ground speeds l e s s than the hydroplaning speed. This result tends to validate the assumption made in reference 1 that fluid drag is proportional to the width of the t i r e at the intersection of it and the fluid surfaces on the runway.
Effect ~~ of t i r e pressure.- Figure 12(a) also shows the large effect on the drag parameter created by changes in tire inflation pressure. For example, decreasing the t i r e pressure from 75 to 25 lb/in2 (51.7 to 17.2 N/cm2) reduces the maximum drag on the landing gear by 50 percent and changes the location of the drag peak from approxi- mately 78 to 45 knots. This effect is, of course, the result of tire hydroplaning and leads to the conclusion that reducing the t i r e inflation pressure w i l l in turn reduce the maximum fluid drag experienced by a landing gear. It should be pointed out that this reduction in t i r e inflation pressure will also decrease the ground speed at which the t i r e loses contact with the ground (tire loses its ability t o develop braking and cornering traction) as evidenced by the shift of the drag peak from 78 t o 45 knots occurring when the tire pres- s u r e is reduced from 75 t o 25 lb/in2.
Effect of wheel configuration.- Another factor which affects values of the drag parameter is the location a f the wheels on the bogie landing gear. Figure 13(a) sum- marizes the variation of drag parameter with ground speed in water and slush f o r the different wheel configurations at a tire pressure of 75 lb/in2 (51.7 N/cm2). This figure shows that the rear-mounted dual and single wheels (configurations 1 1 1 and VII) experi- ence less drag than the corresponding front-mounted wheels (configurations 11 and VI).
It is believed that these differences in drag a r e due to fluid spray. Spray from the front- mounted wheels is thrown rearward and impinges on various members of the landing- gear structure which are to the rear of the wheels and thereby increases the drag. The spray from the rear-mounted wheels does not increase the drag on the landing gear since none of the structure is t o the r e a r of these wheels. In addition, motion pictures taken during the tests show that spray from the bow wave of the rear-mounted wheels impinges on the landing-gear structure ahead of the wheels and produces thrust which decreases the drag parameter.
The effect of wheel configuration on the drag parameter is also shown in this fig- u r e by the curves representing the diagonal wheels and the single tandem wheels (con- figurations N and V). Even though these two configurations were similar, the maximum drag developed by the diagonal wheel configuration was more than twice that developed by the single-tandem wheel configuration. This result is also shown in figure 13(b) which gives the variation of drag parameter with ground speed f o r configurations I, 111, IV, and V at a t i r e pressure of 25 lb/in2 (17.2 N/cm2) and was due to fluid-displacement drag as well as fluid-spray drag. In the diagonal wheel configuration, both the front and the rear wheels were, in effect, leading wheels in that each had to displace runway fluid, whereas in the single-tandem wheel configuration the front wheel displaced most, if not all, of the fluid from the path of the r e a r wheel. The diagonal wheel configuration expe- rienced more fluid-spray drag since spray thrown t o the side and rearward by the front wheel impinged directly on the r e a r wheel.
The values of fluid drag factor given in table I also show the effect of wheel loca- tion on the drag parameter. This factor was obtained by dividing the maximum value of the drag parameter obtained with each wheel configuration by the maximum value of the drag parameter obtained with the single-rear wheel configuration corrected f o r verti- cal load. In reference 10, the prediction was made that landing-gear-wheel location might influence f h i d drag considerably. For example, this reference indicated that dual wheels (side by side) should experience more than twice the drag of a single wheel and single tandem wheels should experience considerably less. The values of fluid drag fac- tor shown in table I tend generally to confirm this prediction.
Effect of vertical load.- The effect of vertical load on the drag parameter can be seen in figure 13(a). The curves representing the values of the drag parameter for the two single wheel configurations (VI and VII) a r e near those obtained with the single tan- dem wheels (configuration V) and a r e apparently due to load per tire. As shown in the figure, the total vertical load was 12 000 lb (53 378 N) for all three configurations.
Hence, the load per t i r e f o r the single wheel configurations was approximately twice that f o r the single-tandem wheel configuration; this greater load produced a greater t i r e deflection and, consequently, a larger t i r e footprint width. Therefore, the wheels o f these two single wheel configurations displaced more fluid from the runway, which resulted in greater values of drag parameter.
Wheel Spin-Down On a dry An easily observed indication of tire hydroplaning is wheel spin-down.
surface the spin-up moment produced on the tire by surface friction and t i r e deformation is balanced by a spin-down moment which is created by a forward shift of the vertical ground reaction. When the tire rolls on a fluid-covered runway, a wedge of fluid detaches the t i r e footprint from the runway surface and makes the spin-up moment tend toward a zero value. This wedge of fluid also causes the center of pressure of the ver- tical ground reaction on the t i r e to move farther forward of the axle and thereby creates a larger spin-down moment. At some critical speed, usually near the hydroplaning speed, this spin-down moment exceeds the total spin-up moment from all the drag so that the t i r e slows down and under certain conditions comes t o a complete sources stop. Motion pictures of this phenomenon a r e shown in reference 11.
In order to determine the wheel spin-down characteristics on fluid-covered run- ways, the ratio of the measured wheel angular velocity on a wet runway surface t o that
on a dry runway surface - Wwet w a s computed for each wheel configuration and plotted
Wdry against the distance the landing gear traveled through the runway fluid at several ground speeds. These data and related data for the different wheel configurations a r e presented in figures 14 to 21. The ground speed at which the wheels enter and leave the fluid trough is given by the speed range shown in the figures. Several factors which influence wheel spin-down characteristics are discussed in the following sections.
Data obtained during this investigation indicate that wheel Effect of ground speed.- spin-down did not occur on leading wheels of the landing-gear configurations investigated until the ground speed either approached or exceeded the hydroplaning speed (determined from eq. (1)). Figure 14 shows this effect for the single tandem wheels (configuration V) and the dual wheels (configuration I I I ) at a tire inflation pressure of 25 lb/in2 (17.2 N/cm2) in approximately 1.0 in. (2.54 cm) of water. The wheels did not spin down until the ground speed was near the predicted hydroplaning speed of 45 knots. This
effect is shown more clearly in figure 15 where - wwet values obtained at station F
Wdry (see fig. 4), a point 352 f t (107.29 m) from wheel entrance into the water trough, for the V and VI) a r e plotted single-tandem and single wheel configurations (configurations V
against the velocity ratio A. The data shown in this figure suggest that wheel spin-
VP down begins at a speed equivalent t o 70 percent of the tire hydroplaning speed Vp.
Total spin-down (wheel stops) or maximum spin-down occurs between 80 and 120 percent of the t i r e hydroplaning speed and further increases in velocity ratio o r ground speed result in l e s s wheel spin-down. This latter effect (less wheel spin-down) w a s noted in references 3 and 5, and it is believed to be the result of: (1) l e s s tire-fluid exposure time in the trough due to the increased ground speed and (2) a more uniform hydrody- namic pressure in the tire-ground contact region under total hydroplaning conditions, which tends to reduce the wheel spin-down moment.
Effect of fluid density.- Figure 16 shows values of the ratio wwet - obtained f o r Wdry landing-gear wheel configurations 1 1 1 and V at nearly the same ground speeds f o r two runway fluids, water and slush. It can be seen from this figure that l e s s wheel spin- down occurs in slush than in water for both wheel configurations investigated. The average specific gravity of the slush used in this investigation was approximately 0.88.
Hence, the dynamic pressure of slush, if slush acts as a fluid, should be less than dynamic pressure of water and thereby should produce a smaller spin-down moment.
This effect is also shown in figure 17 by the data obtained with the single wheel config- urations since the wheel spun down more in water than in slush.
Effect of t i r e pressure.- The effect of tire pressure on wheel spin-down is shown Wwet This figure shows the variation of the wheel-angular-velocity ratio - in figure 18.
Odry with ground speed f o r the single tandem wheels (configuration V) at t i r e pressures of 25 and 75 lb/in2 (17.2 and 51.7 N/cm2). The vertical load F,,g was the same f o r both pressures. It can be seen that with a t i r e pressure o f 25 lb/in2 wheel spin-down began at approximately 30 knots and was greatest at approximately 50 knots. With a t i r e pres- s u r e of 75 lb/in2 spin-down began at about 55 knots and was greatest at about 72 knots.
The speed at which spin-down begins with each t i r e pressure is approximately 70 percent of the hydroplaning speed. It is apparent from these data that increasing the t i r e pres- s u r e increases the speed required for wheel spin-down to begin.
Another effect of tire pressure is indicated by figure 18. The wheel spun down to a complete stop with a t i r e pressure of 25 lb/in2 (17.2 N/cm2) whereas it did not with a pressure of 75 lb/in2 (51.7 N/cm2). This difference could be due to the tire footprint area which, at constant load, increases as the tire pressure is decreased. The larger footprint area with a pressure of 25 lb/in2 probably produced a larger spin-down moment than that with a pressure of 75 lb/in2 and thus caused the wheel to spin down t o a stop.
Effect of wheel configuration.- The spin-down characteristics in water of each wheel of the diagonal wheels (configuration IV) are shown in figure 19. The data show that neither wheel spun down at ground speeds below the hydroplaning speed of 45 knots.
However, at higher ground speeds both wheels spun down with the rear wheel spinning This characteristic is to be expected since, with down sooner and to a greater degree.
this wheel arrangement, a wedge of water is present under each wheel and causes the wheel to spin down. The fluid spray f r o m the front wheel impinging on the rear wheel as well as the water in front of the rear wheel being disturbed by the wake of the front wheel probably caused the rear wheel to spin down faster and to a greater degree. In configuration V the wheel arrangement is similar to that of configuration IV except that the r e a r wheel is mounted directly behind the leading wheel. With this single-tandem wheel arrangement, the rear wheel did not spin down at any test ground speed as shown by figure 16(a). Apparently, the front wheel of this configuration displaced enough water rear wheel so that there was not a sufficient amount remaining to from the path of the cause the rear wheel to spin down.
Effect of vertical load.- At the same tire pressure an increase in the vertical load causes the wheel to spin down to a greater degree. This effect is shown in fig- u r e 15. It can be seen that the single wheel with a t i r e pressure of 75 lb/in2 (51.7 N/cm2) spun down to a stop whereas the single tandem wheel did not. The vertical load on the single wheel was about twice that on each wheel of the single-tandem wheel configuration. Consequently, the tire footprint was larger for the single wheel and pro- duced a larger spin-down moment which caused the wheel to come to a complete stop.
Effect of water depth.- Some indication of the effect of water depth on wheel spin- down of each wheel of the dual front wheels (configuration II) with a tire inflation pressure of 25 lb/in2 (17.2 N/cm2) is shown in figure 20. The water depth varied from 0.15 to 1.25 in. (0.38 t o 3.18 cm) and the ground speed was in the neighborhood of 70 knots, a speed which is well above the approximate hydroplaning speed of 45 knots. The solid curves indicate that the wheels began to spin down as soon as they entered the water but spun up as the water depth decreased. A similar effect is shown by the dashed curves but t o a greater degree. At the greater water depths the wheels spun down to a complete stop. These data indicate that f o r this configuration a water depth o f approximately 0.40 in. (1.01 cm) is required to cause wheel spin-down. However, it should be kept in mind that other factors such as tire-tread pattern, runway surface texture, and fluid density may have large effects on the wheel spin-down characteristics. In addition, the spray pattern and fluid flow developed with this wheel configuration may also affect the wheel spin-down characteristics. Motion pictures taken during the t e s t s show that there is spray and flow interference with this configuration in which two wheels are mounted side by side.
Figure 21 also gives some indication of the effect of water depth on wheel spin- tests with the dual tandem down. The data shown in this figure were obtained during wheels (configuration I) in 0.5 in. (1.27 cm) of water with t i r e inflation pressures of 50 lb/in2 (34.5 N/cm2) and in 2.0 in. (5.08 cm) of water with t i r e pressures of 75 lb/in2 (51.7 N/cm2). In 0.5 in. of water, with a t i r e pressure of 50 lb/in2, and at ground speeds near and greater than the hydroplaning speed of 63 knots, the front wheels of this config- uration spun down but the r e a r wheels did not spin down at any speed. However, in 2.0 in. of water, with tire pressures of 75 lb/in2, and at a ground speed greater than the hydroplaning speed of 78 knots, the r e a r wheels as well as the front wheels spun down.
Evidently, in water of this large depth, the front wheels a r e raised high enough in the water s o that they do not displace all o f the water from the path of the r e a r wheels but leave an appreciable depth f o r the r e a r wheels to displace and thereby cause them to spin down.
Wheel Spray Patterns Motion pictures from the 16-mm and 70-mm cameras provided a means of studying the wheel spray patterns. Figures 22 to 28 show photographs from the 70-mm camera of typical fluid spray patterns attained f o r the test conditions with the different wheel configurations. In figures 23 to 28, the fluid depth and ground speed a r e given f o r each test condition. In addition, the ratio of the ground speed to the predicted hydroplaning speed (determined from eq. (1))is given. For values of this ratio l e s s than 1.0 the wheel is considered to be in a condition of partial hydroplaning. For velocity-ratio values of 1.0 and greater, the wheel is considered to be in a condition of total hydroplaning.
Types of spray patterns.- ~~ The photographs of figures 22 and 23, as well as the 16-mm motion pictures taken during this study, indicate that three distinct types of spray patterns a r e developed by the dual tandem wheels (configuration I) in slush and water; namely, (1) a bow wave formed at the intersection of the front of the t i r e s with the run- way, (2) side waves formed at the intersection of the outboard sides of the dual t i r e s with the runway, and (3) a "rooster tail'' or reinforced wave formed by the mixing of two side waves developed on the inboard sides of the dual t i r e s of the landing gear.
Different wheel configurations. - The motion pictures show that this reinforced wave also developed between the tires of the two other dual wheel configurations (con- figurations 1 1 and I I I ) . Figure 24(e) shows this wave during a test with configuration II.
A spray pattern similar t6 the rooster tail was also observed on the single-tandem wheel 1 2 configuration (configuration V) as shown in figures 25(d) and (e). It is believed that this particular spray pattern on the tandem wheel configuration arises from the side spray wave of the front tandem wheel impacting on and being deflected by the exposed rear The large amounts of spray surrounding the dual-tandem wheel axle a f the landing gear.
configuration prevented observations of the interference spray patterns developed between the wheels of this landing gear. Some assessment of this spray effect can be made by studying the photographs obtained of the diagonal wheels (configuration IV) shown in figure 26. Photographs 26(e) and (f) obtained at the higher ground speeds show that the side wave developed by the front wheel subsequently impinges directly on the opposite mounted rear wheel.
One other interesting wheel-spray-pattern effect w a s noted. Motion pictures taken of the rear-mounted wheel configurations (configurations 1 1 1 and VII) showed that the bow waves formed on the t i r e s of these configurations could impact with some forward veloc- ity on the r e a r of the landing-gear structure (strut and front wheel axles) that is ahead of the rear-mounted tires. This spray impingement results in some forward thrust being produced on the landing gear. Photographs illustrating this effect a r e shown in fig- u r e s 27 and 28.
The intensity or thickness of the wheel spray developed on all configurations appeared to increase as the fluid depth increased.
Figure 28, which shows photographs of the spray patterns developed by the single- r e a r wheel configuration, indicates that the spray patterns were about the same shape in slush o r in water.
on spray .- ~ patterns.- For all wheel configurations, the angle .
Effect of ground speed -- - -_I___. - ..
formed between the bow wave and the ground w a s quite large at ground speeds below the hydroplaning speed and large amounts of fluid spray were thrown nearly vertically into the air where it subsequently impinged on other parts of the landing gear and test car- riage structure. The maximum height reached by spray from the (See figs. 23 and 24.)
bow wave w a s estimated to be about 30 feet. As the ground speed w a s increased above the critical hydroplaning velocity, the angle between the bow wave and runway decreased progressively until at some high ground speed, the bow wave completely disappeared on the landing gear. The outboard side waves appeared to act in a manner similar to the bow wave just described except that at the higher ground speeds they did not disappear completely but did become much flatter. In contrast with the results observed f o r the bow and side waves, the rooster tail usually maintained a high angle with respect to the ground over the entire range of ground speeds.
Fluid-Spray Drag on Simulated Wing Flap References 4 and 5 indicate that minor fluid-spray impingement from the main gear o f the airplane when they were set at the take-off posi- wheels occurred on the wing flaps tion of 220. It would be expected that when the flaps were set at the landing position of 550, more fluid-spray-impingement drag would be experienced on the airplane since the flaps would be closer t o the ground and to the landing-gear wheels. Tests were made during this investigation with a simulated flap in the two positions. (See fig. 4.)
The effect o f fluid-spray-impingement drag is shown by the curves in figure 29 which were obtained with the single-front wheel configuration (configuration VI). Fig- u r e 29(a) shows the upper m a s s drag to be slightly higher than the landing-gear drag with the flap set at 22'. Apparently some spray impinged on the flap. Since this wheel was more forward of the flap, the spray pattern was high enough to reach the flap. With the flap set at the landing configuration of 55O, an appreciable amount of spray evidently impinges on the flap as shown by the curves in figure 29(b). The maximum drag meas- ured on the upper m a s s was approximately 70 percent greater than that measured on the landing gear.
Pitching Instability of Bogie Landing Gear Some tests were made with the dual tandem wheels (configuration I) at a light weight of 12 000 lb (53 378 N) and a t i r e pressure of 75 lb/in2 (51.7 N/cm2) in 1.0 in.
(2.54 cm) of water. The landing-gear wheels were free to pitch about the truck-beam pivot since the pitching snubbers had been removed. Under these conditions, the landing gear was very unstable in pitch at speeds near and above the hydroplaning speed. Large pitching oscillations occurred as indicated by the photographs in figure 30. These photo- graphs are f r a m e s f r o m a motion picture made during a test in which the ground speed was approximately 100 knots. The oscillations can be seen by noting the relative posi- tions of the instrument covers mounted on the ends of each axle. In frames 17 and 24, the front wheels appear t o be completely above the water surface. This pitching insta- A s the front wheels began to hydroplane bility is believed to be due to hydroplaning.
they r o s e in the water and therefore less water was removed f r o m the path of the rear wheels. This allowed hydrodynamic forces to act on the rear wheels, raising them and forcing the front wheels down. With the front wheels down and in contact with the water, the hydrodynamic force on the rear wheels was removed and began acting on the front wheels again and the oscillation w a s repeated. These oscillations were s o severe that the wire rope used to prevent the truck beam from rotating to an excessive nose-down attitude when the landing gear was airborne failed.
I Fluid- Spray-Drag Alleviator The large difference in the drag parameter of the dual tandem wheels (configura- tion I) and the dual front wheels (configuration I I ) shown in figure 13(a) suggested that the drag due to fluid spray might be reduced by installing a spray shield o r alleviator between the dual tandem wheels. Therefore, t e s t s were made with each of three spray alleviators mounted along and under the bogie landing-gear truck beam as shown in the sketches in figure 31. The variation of drag parameter with ground speed obtained with the landing gear equipped with each of the spray alleviators is shown by the solid curve faired through the data whereas the variation obtained without a spray alleviator is shown by the dashed curve. Figures 31(a) and (b) show that the flexible rubber and the rigid metal alleviator increased the maximum drag parameter slightly. However, when the rigid metal alleviator was equipped with a curved top which almost closed the space
between the dual wheels (see fig. 10) , the maximum drag was reduced approximately
45 percent as shown in figure 31(c). The effectiveness of this alleviator is also shown by comparing the solid curve in figure 31(c), which represents the drag parameter obtained with this spray alleviator, with the curves in figure 13(a). It can be seen that the spray alleviator installed on the dual tandem wheels reduces the maximum drag parameter to The dual a value less than that obtained with the dual front wheels (configuration 11).
tandem wheels equipped with this spray alleviator is designated as configuration IA in table I. This table shows that installing the spray alleviator on the dual tandem wheels reduced the fluid drag factor from 3.33 to 1.86.
CONCLUSIONS Ground-run tests were made with a bogie landing gear in water and slush of depths T i r e inflation up to 2.0 inches (5.08 centimeters) over a speed range of 15 to 110 knots.
pressures of 25, 50, and 75 pounds per inch2 (17.2, 34.5, and 51.7 newtons per centi- Wheel configurations consisting of one and two wheels at different meter2) were used.
locations on the bogie truck as well as the normal four-wheel (dual tandem) configuration were used during the tests. Some t e s t s were made with a simulated wing flap mounted to the rear of the wheels. In addition, tests were made with a spray alleviator mounted between the wheels of the dual-tandem wheel configuration. The results of these tests indicated the following conclusions : Fluid Drag Parameter 1. Fluid drag increases approximately parabolically with increasing ground speed up to speeds near the hydroplaning speed after which there is a large reduction in drag.
2. Fluid drag appears to be proportional to fluid density and to the width of the tire at the fluid surface up t o the hydroplaning speed as predicted in NASA TN D-552.
3. Decreasing the tire inflation pressure reduces the maximum fluid drag but also reduces the ground speed at which tire hydroplaning will occur.
4. From fluid-drag considerations a tandem wheel configuration is preferable to a dual-wheel landing gear.
5. At the same inflation pressure, increasing the vertical load on a tire increases the tire footprint width which causes an increase in the fluid drag.
Wheel Spin-Down 1. Wheel spin-down begins at a ground speed near 70 percent of the t i r e hydro- planing speed and total spin-down (wheel stops) occurs between 80 and 120 percent of the hydroplaning speed.
2. The wheels spun down l e s s in slush than in water.
3. Decreasing the t i r e inflation pressure causes the wheel to spin down at a lower ground speed and to a greater degree.
4. The location of the wheels on the bogie landing-gear truck influences the spin- down characteristics of the wheels.
5. At the same tire pressure, increasing the vertical load causes the wheel to spin down to a greater degree.
6. The r e a r wheels as well as the front wheels o f the dual-tandem wheel configura- tion spun down in 2.0 inches (5.08 centimeters) of water.
Spray Patterns 1. Three distinct types of wheel spray patterns are developed by dual tandem wheels in slush and water; namely, a bow wave, a side wave, and a "rooster tail."
2. The intensity o r thickness of the spray patterns appeared to increase as the runway fluid depth increased.
3. The angle between the runway and the bow wave (and side wave) decreases as However, the angle of the rooster tail with respect to the the ground speed increases.
runway appeared to change very little over the entire range of forward speeds.
1 6 Fluid Drag on Wing Flap 1. With the single-front wheel configuration, drag due to spray impingement on a simulated wing flap w a s much higher with the flap in the landing position (55O) than in the take-off position (22O).
2. Fluid spray impinging on the simulated wing flap in the landing position produced a maximum drag on the upper m a s s which w a s approximately 70 percent greater than that measured on the landing gear.
Pitching Instability of Bogie Landing Gear 1. For a bogie landing gear undamped in pitch, a severe pitching oscillation due to hydroplaning can develop under certain combinations of t i r e inflation pressures and vertical load which produce small tire deflections.
Fluid- Spray-Drag Alleviator 1. A fluid-spray-drag alleviator installed between the dual tandem wheels reduced the total maximum fluid drag approximately 45 percent.
Langley Research Center, National Aeronautics and Space Administration, Langley Station, Hampton, Va., March 10, 1966.
REFERENCES 1. Horne, Walter B.; Joyner, Upshur T.; and Leland, Trafford J. W.: Studies of the Retardation Force Developed on an Aircraft Tire Rolling in Slush or Water. NASA TN D-552, 1960.
2. Sparks, Allan R.: Report on Effect of Slush on Ground Run Distance to Lift-off.
Doc. No. D6-5198, Boeing Airplane Co., Jan. 1960.
3. Anon.: Joint Technical Conference on Slush Drag and Braking Problems. FAA and NASA, Dec. 1961.
4. Shrager, Jack J.: Vehicular Measurements of Effective Runway Friction. Final Report, Project No. 308-3X (Amendment No. l), FAA, May 1962.
5. Sommers, Daniel E.; Marcy, John F.; Klueg, Eugene P.; and Conley, Don W.: Run- way Slush Effects on the Takeoff of a Jet Transport. Final Report, Project No. 308-3XY FAA, May 1962.
6. Mechtly, E. A.: The International System of Units - Physical Constants and Con- version Factors. NASA SP-7012, 1964.
7. Joyner, Upshur T.; Horne, Walter B.; and Leland, Trafford J. W.: Investigations on the Ground Performance of Aircraft Relating to Wet Runway Braking and Slush Drag. AGARD Rept. 429, Jan. 1963.
8. Horne, Walter B.; and Dreher, Robert C.: Phenomena of Pneumatic Tire Hydro- planing. NASA TN D-2056, 1963.
9. Horne, Walter B.; and Leland, Trafford J. W.: Influence of T i r e Tread Pattern and Runway Surface Condition on Braking Friction and Rolling Resistance of a Mpdern Aircraft Tire. NASA TN D-1376, 1962.
10. Collar, A. R.: On the Drag Due to Slush. Aeronautical Research Council 22,491, E. P. 675, CN 644, Jan. 9, 1961.
11. Anon.: Hazards of Tire Hydroplaning to Aircraft Operation. NASA Langley Research Center Film Serial No. L-775, 1963.
. .
TABLE I.- WHEEL CONFIGURATIONS TESTED AND FLUID DRAG FACTORS OBTAINED [p = 75 lb/in2 (51.7 N/cm2); d l = 1.0 in. (2.54 cm) Configuration
J
d r a g Approximate Wheel arrangement tactor at load per tire, lumber Schematic of naximum 1b (N) De script ion vheels Xrection of motion d r a g > 3.33 Front: 5 125 (22 797) 4 D u a l tandem %ear: 6 025 (26 800) rotal: 22 300 (99 195) ..
2.04 h a 1 front Each: 6 000 (26 689) rotal: 12 000 (53 378) 1.59 2 Dual rear Each: 6 000 (26 689) Total: 12 000 (53 378) .. .
2.66 Front: 5 520 (24 554) 2 Diagonal Rear: 6 480 (28 824) J Total: 12 000 (53 378) 1.15 Front: 5 520 (24 554) 2 Single tandem Rear: 6 480 (28 824) Total: 12 000 (53 378) 1.08 Single front 12 000 (53 378) 1.00 Single rear 12 000 (53 378) Front: 5 125 (22 797) 1.86 4 Dual tandem with
fluid - spray -dr a€
Rear: 6 025 (26 800) alleviator Total: 22 300 (99 1951 h3
x io3 0
E x p e r i m e n t a l U ( J e t t r a n s p o r t , ref. 3)
- - - C a l c u l a t e d ( r e f . 1)
z 2 . 4 4 n
/ /
!-I a,
0 /
60 2
/ E 1 2 (d !-I (d a bD (d
/
40 4
7 /
a .d
/
/
r4
/
/ / I f 1 I I I 20 40 60 80 100 120 140 160 180 Ground s p e e d , k n o t s Figure 1.- Comparison of slush drag measured on jet-transport airplane (ref. 3) with drag pre- dicted by means of single-wheel method of reference 1 .
~~ ~ L-62-1048.1 Figure 2.- Test vehicle of Langley landing-loads track.
Upper mass d r a g dynamometer
s
S:atic v e r t i c a l load on f r o n t a x l e = 0.46 F ZYg S t a t i c v e r t i c a l l o a d on rear a x l e = 0 . 5 4 F Zag Figure 3 . - Schematic drawing of dual-tandem landing gear used i n tests.
Forward -
Dam A B C D
E F G H i
1 I I I I I I I 1
I 8 2 .75 f t m k 6 4 19.51 f t + 6 4 m 19.51 ft.+,64 m 19.51 f t - 1 ' 6 4 m 19.51 f t 4 - 6 4 m f t + 6 4 19.51 f t + 6 4 m 19.51 m a75 f t i m 19.51 m Figure 4.- Sketch of slush and water trough, showing stations at which slush and water depths were measured.
N W L-66-1179 Figure 5.- Ice-crushing machine used t o make slush i n operation.
L-66-1180 Figure 6.- Slush-leveling machine used t o t r i m slush t o desired t e s t depth.
Figure 7.- Slush bed before t e s t .
L-66-1181 Figure 8.- Slush bed a f t e r t y p i c a l t e s t .
L-66-1182 Upper m a s s drag dynamometer Figure 9.- Schematic drawing of dual-tandem landing gear, showing r e l a t i v e positions of simulated wing flap.
(a) Side view.
i (b) Front view. L-66-1183 Figure 10.- Spray-drag alleviator mounted on dual tandem wheels (configuration IA) .
27 i I11111 I11111111 II I I I I 1111111.1.111111. I I 1 I, 1 1 , 1 1 1 1 1 1 1 1 1 1 11111I 1 1 1 1 . 1 I 1 1 . .. ..
z 4 x io3 2 f: 0 Water $4 0 Slush U U a , E E
r
$4 10 2 d R M M a a P P *I P .rl
2 t
3 4 h w.
1- 100 0
Ground s p e e d , V k n o t s G ' ( a ) p = 25 lb/in2 (17.2 N/cm2).
. x lo3 L l $4 a , u a , E ! 4 rd a M $4 a a .rl b.
20 40 60 80 100 Ground s p e e d , V G , k n o t s ( b ) p = 50 lb/in2 (34.5 N/cm2).
1 2o !4 a , u a , ld rd R M $4 V P .rl h Ground s p e e d , V G , k n o t s ( c ) p = 75 lb/in2 (51.7 N/cm2).
Figure 11.- Variation of drag parameter with ground speed f o r dual tandem wheels (configwation I) i n water and slush.
FZ,g= 22 300 l b (99 195 N ) ; d l = 0.5 t o 2.0 in. (1.27 t o 5.08 cm).
...
T i re p r e s s u r e , p , T i r e w i d t h , b,, i n . (cm) l b / i n 2 ( N / c m 2 )
--
25 ( 1 7 . 2 ) 12.0 ( 3 0 . 5 )
----
50 ( 3 4 . 5 ) 10.8 ( 2 7 . 4 ) 75 ( 5 1 . 7 ) 1 0 . 1 ( 2 5 . 6 ) n $4 &I bo M a u c i u m L n v ) v) a a x X a a v) n n $4 a , U a , E cd a M cd Ground s p e e d , V G , k n o t s !-I n (a) Drag parameter in terms of tire pressure, with tire width not considered.
- 20
- x io3 x io3 n fl n X bst = 10.1 i n . bst = 10.1 i n .
( 2 5 . 6 c m ) ( 2 5 . 6 c m ) X
-
$4 2 a , a
I
M n k 0 20 40 60 80 100 Ground s p e e d , VG, k n o t s (b) Drag parameter in terms of tire width at 75 lb/in2 (51.7 N/cm2).
Figure 12.- Effect of tire width and tire inflation pressure on drag parameter for dual tandem wheels (configuration I).
I Approximate load p e r t i r e C o n f i g u r a t i o n l b N F r o n t Rear F r o n t Rear
----- --
I Dual tandem wheels 5 1 2 5 6 0 2 5 22 7 9 7 2 6 8 0 0
- -----
I V Diagonal wheels 5 5 2 0 6 4 8 0 2 4 5 5 4 28 8 2 4
- - _ - -
I1 Dual f r o n t wheels 6 000 2 6 6 8 9
- _ - -
111 Dual r e a r wheels 6 000 2 6 6 8 9 - V I 1 S i n g l e rear wheel 1 2 000 5 3 378
--- V I S i n g l e f r o n t wheel 1 2 000
5 3 378 V S i n g l e tandem wheels 5 5 2 0 6 4 8 0 2 4 5 5 4 28 8 2 4
-
z s 4 F X io3 P M --.
a, \ u \ / \ a, ' -\.
E
- 1 0 2
-
M bD a cd Li a a .4 3 --I a -4 h d - 0 w l 0 1 2 0 20 40 60 8 0 100 Ground speed VG, k n o t s ( a ) p = 75 lb/in2 (51.7 N/cm2).
0 2 20 4 0 6 0 8 0 100 1 2 0 Ground s p e e d y V G , k n o t s (b) p = 25 lb/in2 (17.2 N/cm2).
Figure 15.- Variation of drag parameter with ground speed for wheel configurations on water- and slush-covered runway.
Ground speed r a n g e , k n o t s S i n g l e tandem Dual 24 t o 20 23 t o 19 f 3 1 t o 26
33 t o 30 i
< 4 3 t o 37 45 t o 4 1 56 t o 50 55 t o 48 63 t o 55 73 t o 64
--
I I 83 t o 78 85 t o 74 108 t o 101 106 t o 92
la0K- - - --
1.c
--La: ;heel
( a l l s p e e d s )
32 1
I .r(
'd U U rd rd .6 x Y 2r U .d .d U J 0 4 0)
s
L4 L . .4 a rd 3 M 3 M C C Gi a, . 2 Gi ar .c s wheel I I I 5 x lo2 1 2 3 4 0 1 2 3 4 5 x 102 D i s t a n c e t r a v e l e d through w a t e r , f t D i s t a n c e t r a v e l e d through water, f t 1 I I I I 1 I I I I I I 0 30 60 90 120 150 0 30 60 90 120 150 D i s t a n c e t r a v e l e d through water, m D i s t a n c e t r a v e l e d t h r o u g h water, m (a) Single tandem wheels (configuration V) .
(b) Dual rear wheels (configuration 111).
Figure 14.- Spin-down characteristics of single tandem wheels and dual rear wheels in water.
p = 25 lb/in2 (17.2 N/cm2); FZ,g 12 000 lb ( 5 3 378 N ) ; d l = 1.0 in. (2.54 cm).
w CL T i r e p r e s s u r e , p , l b / i n 2 ( N / c m 2 1 Sing 1 e tand em 25 (17.2) f r o n t wheel
--
whee 1 s 75 (51.7) f r o n t wheel
- 25,75 (17.2,51.7) rear wheel (configuration VI
-- - 75 (51.7) s i n g l e wheel ( c o n f i g u r a t i o n V I )
1 . 0 .8 Hydroplaning speed, Vp
/-
. 6 .4 .2 \
-
.4 .a 1 . 2 1 . 6 2.0 2.4
V, b
Velocity r a t i o , -
lJP Figure 15.- Variation of wheel angular velocity ratio with velocity ratio for single tandem and single wheel configurations.
Ground speed r a n g e , k n o t s S i n g l e tandem Dual rear
--
IJa t er S l u s h Water S l u s h
---
47 t o 41 55 t o 48 58 t o 52 53 t o 47 -- 80 t o 7 2 7 8 t o 7 1 79 t o 67 85 t o 73 106 t o 98 107 t o 101 105 t o 97 106 t o 93
- -----
1.0 Rear wheel, water and s l u s h ( a l l speeds)
-
.a . 6 - .-I m
-
!- .4 .4 a I \ / 3 M c
: .2
\water 1
S E F r o n t wheel Right and l e f t wheel I I
I I I I I I
1 2 3 h 1 2 3 4 5 x 102 D i s t a n c e t r a v e l e d through f l u i d , f t D i s t a n c e t r a v e l e d through f l u i d , f t L I I I I 1 I I I I r 0 30 30 60 90 120 150 60 90 120 150 D i s t a n c e t r a v e l e d through f l u i d , m D i s t a n c e t r a v e l e d through f l u i d , m (a) Single tandem wheels (configuration V) . (b) Dual rear wheels (configuration 111).
Figure 16.- Effect of fluid density on spin-down characteristics of single tandem and dual rear p = 75 lb/in2 (51.7 N/cm2); F , , g = 12 000 lb (53 3 7 8 N ) ; d l = 1.0 in.
wheel configurations.
(2.54 cm).
W W Ground speed r a n g e , k n o t s Water S l u s h 17 t o 15 29 t o 25
----
{ t h r o u g h 51 t o 46
64 t o 5 4 - - _ - - 6 8 t o 6 1 - - - - a 1 t o 74
- - - 8 4 t o 78
- - 96 t o 90 76 t o 70
99 t o 9 1 100 t o 96 1.0 1.0 .a .a .6 .6 .4 .4 . 2 . 2 I I I I I 0 1 2 3 4 5 x loa 1 2 3 4 5 x 102 D i s t a n c e t r a v e l e d t h r o u g h s l u s h , f t D i s t a n c e t r a v e l e d t h r o u g h w a t e r , f t - I I I I I I I I I I I J 0 30 60 90 120 150 0 30 60 90 120 150 D i s t a n c e t r a v e l e d t h r o u g h s l u s h , m D i s t a n c e t r a v e l e d t h r o u g h w a t e r , m (b) Single rear wheel (configuration V I I ) (a) Single front wheel (configuration 11) in slush; in water.
of single wheel configurations in Figure 17.- Comparison of wheel spin-down characteristics (51.7 N / c m 2 ) ; F , , g = 1 2 000 lb ( 5 3 378 N ) ; dl = 1.0 in.
water and slush. p = 75 lb/in* (2.54 c m ) .
T i r e p r e s s u r e , p , l b / i n 2 ( N / c m 2 ) 25 ( 1 7 . 2 ) f r o n t wheel
--
75 ( 5 1 . 7 ) f r o n t wheel
w
-- 2 5 , 75 ( 1 7 . 2 , 51.7) rear wheel
1.0 n *?I .iJ
I
cd L !
I
I
I
20 40 60 80 100 120 Ground s p e e d , VG , k n o t s Figure 18.- Effect of tire pressure on wheel spin-down of single tandem V).
wheels (configuration 3 5 w Q, Ground speed r a n g e , k n o t s 28 t o 23
_ _ _ _ _ _ 32 t o 27
'42 t o 36
- _ _ _ -
60 t o 52
-- --
65 t o 58
---
68 t o 6 1
--
8 5 t o 78 109 t o 100 1.0 0 .d .rl U U a d .6 2\ Y h Y .rl U d a , a , > > ! - a 3 M
\\\ \\
\ \ \ \ a - .. .
A a, a , . 1 a , a, s s I I I I 0 1 2 3 4 5 x 102 0 1 2 3 4 5 x 10" D i s t a n c e t r a v e l e d through water, f t D i s t a n c e t r a v e l e d t h r o u g h w a t e r , f t I I I I I 1 1 I I I I I 0 30 60 90 120 150 0 30 60 90 120 150 D i s t a n c e t r a v e l e d through water, m D i s t a n c e t r a v e l e d t h r o u g h water, m (a) Left front wheel. (b) Right rear wheel.
19.- Comparison of wheel spin-down characteristics of left front and right rear wheels of Figure diagonal wheels (configuration I V ) . p = 25 lb/in2 (17.2 N/cm2); FZ,g % 12 000 lb (53 3 7 8 N ) ; dl = 1.0 in. (2.54 c m ) .
Water d e p t h , Ground speed in. ( c m ) range, k n o t s 1.25 t o 0.80 (3.18 t o 2.03) 7 1 t o 63 --- 1.10 t o 0.75 ( 2 . 7 9 t o 1 . 9 0 ) 70 t o 62 -- 1.00 t o 0.40 ( 2 . 5 4 t o 1.01) 7 1 t o 63 0 . 4 5 t o 0.15 ( 1 . 1 4 t o 0.38) 68 t o 64 Decreasing water d e p t h j 1.0 0 .d U rd .6 h U .rl U 0 3 m $4 .4 rd 2 M rd m . 2 a, s 0 1 2 3 4 5 x 102 0 1 2 3 4 5 x loa Distance traveled through water, f t Distance traveled through water, f t I I I I I I 1 I I I I I 0 30 60 90 120 150 0 30 60 90 120 150 Distance traveled through water, m Distance traveled through water, m (a) Left wheel. (b) Right wheel.
Figure 20.- Effect of water depth on wheel spin-down characteristics of front dual wheels (con- figuration 1 1 ) . p = 25 lb/in2 (17.2 N/cm2); FZ,g % 12 000 lb (53 378 N).
W c o Ground speed r a n g e , k n o t s Ground speed r a n g e , k n o t s 33 t o 28 --- 35 t o 31
- - - ( 52 t o 45 --
55 t o 50 97 t o 85 9 1 t o 83 r e a r wheels Rear wheels ( a l l s p e e d s )
3 3 " .8 -
:I
.rl U cd Right r e a r wheel 2, U .d U m m > >
.4 -
$d cd cd F r o n t w h e e l s ,- F r o n t w h e e l s 3 3 M M L e f t r e a r wheel a ,
. 2 -
- 2
b
I I I I I 1 - 1 I I I I 0 1 2 3 4 5 x 10" 0 1 2 3 4 5 x loa DFstance t r a v e l e d through w a t e r , f t D i s t a n c e t r a v e l e d through w a t e r , f t I I I I I I 1 I I I I I 0 30 60 90 120 150 0 30 60 90 1 2 0 150 D i s t a n c e t r a v e l e d through w a t e r , m D i s t a n c e t r a v e l e d through w a t e r , m (a) Water depth = 2.0 in. (b) Water depth = 0.5 in.
(5.08 cm); (1.27 cm); p = 75 lb/in2 (51.7 N/cm2) . p = 50 lb/in2 (74.5 N/cm2).
Figure 21.- Comparison of wheel spin-down characteristics of front and rear wheels of dual tandem wheels (configuration I) in water. F , , g = 22 300 lb (99 195 N ) .
L-66-1184 Figure 22.- Typical f l u i d spray patterns developed on dual tandem wheels (configuration I).
(b) VG/VP 0.32; (a) Entrance into water; VG = 25 knots. VG = 25 knots.
(e) vG/vP 0.32; (d) Vc/Vp 0.64; VG = 50 knots.
VG = 25 knots.
(f) VG/VP = 1.23; VG = 96 knots.
L-66-1185 Figure 23.- Spray patterns developed by dual tandem wheels (configura- tion I) at subhydroplaning and superhydroplaning velocities.
F z t g 22 300 lb ( 9 9 195 N); p = 75 lb/in2 (51.7 N/cm*); 0.5 in.
(1.27 em) water depth; oblique front view.
( b ) V G / V ~ % 0.29; ( a ) P r i o r t o entrance i n t o water; VG = 23 knots; VG = 23 knots.
Water depth = 1.0 i n . (2.54 cm).
(a) VG/VP = 1.01; ( e ) vG/vP z z 0.72; VG = 79 knots; VG = 56 knots; Water depth = 1.0 i n . (2.54 cm).
Water depth = 2.0 i n . (5.08 cm).
( e ) vG/vP 0.69; ( f ) v G / v p CZ 1-01; VG = 54 knots; VG = 79 knots; Slush depth = 1.0 i n . (2.54 cm). Slush depth = 1.0 i n . (2.54 em).
L-66-1186 Figure 24.- Spray patterns developed by dual f r o n t wheels (configura- t i o n 11) at subhydroplaning and superhydroplaning velocities.
(51.7 N/cm2); 1.0 and FZtg = 12 000 lb (53 378 N ) ; p = 75 lb/in2 2.0 in. (2.54 and 5.08 c m ) water depth; 1.0 in. slush depth; oblique f r o n t view.
( a ) Entrance i n t o water; VG = 20 knots.
( e ) v v = 0.93; ( d ) V G / v p 1.29; G I VG = 42 knots.
VG = 59 knots.
L-66-1187 Figure 25. - Spray patterns developed by single tandem wheels (configura- t i o n V) at subhydroplaning and superhydroplaning velocities.
FZ,g = 1 2 000 lb (53 378 N ) ; p = 25 lb/in2 (17.2 N/cm2); 1.0 i n .
' (2.54 em) water depth; oblique f r o n t view.
( a ) P r i o r t o entrance i n t o water; VG = 24 knots.
( d ) V ~ p p 1.29; VG = 54 knots.
VG = 59 knots.
L-66-1188 Figure 26. - Spray patterns developed by diagonal wheels (conf igura- t i o n I V ) at subhydroplaning and superhydroplaning velocities.
(17.2 N/cm2); 1.0 in.
FZ,g = 1 2 000 lb ( 5 3 378 N ) ; p = 25 lb/in2 (2.54 em) water depth; oblique f r o n t view.
(a) Prior to entrance (b) Entrance into water; into water; V c / V p E 0.47; VG = 37 knots.
VG = 37 knots.
(d) VG/Vp 0.87; VG = 68 knots.
(e) v G / v ~ 1.00; (f) vG/vP 1.23; VG = 78 knots.
VG = 96 knots.
L-66-1189 Figure 27.- Spray patterns developed by dual rear wheels (configura- tion 111) at subhydroplaning and superhydroplaning velocities.
F z t g = 1 2 000 lb (53 378 N ) ; p = 75 lb/in2 (51.7 N/cm2); 1.0 in.
(2.54 cm) water depth; oblique front view.
Water death = 1.0 in. (2.54 cm) . - ( d ) V G / V ~ E 0.80; (a) P r i o r to entrance (b) VG/Vp = 0.25; VG = 63 knots. into water; VG = 20 knots. VG = 43 knots.
VG = 20 knots.
Slush depth = 1 ..o in. (2.54 cm) L-66-1190 Figure 28. - Spray patterns developed by single rear wheel (configuration VII) at subhydroplaning and superhydroplaning velocities. FZ,g E 12 000 lb (51.7 N/cm*); (53 378 N ) ; p = 75 lb/in2 oblique front view.
Landing-g ea r drag (single front wheel) -- Upper mass drag 40 6 0 80 100 120 I 0 20 Ground speed, VG, knots (a) Flap angle = 2 2 ' .
-.I z .A
5 4 - x io3
n $4 !4 aJ a , u u aJ a , E E cd cd $4 ! 4
- 1 0 2
cd /\ a 2 - M bD
/
c d E !4 a -Q a a .rl .rl =I h Fy I I Ground speed, VG, knots (b) Flap angle = 55'.
Figure 29.- Comparison of drag parameter with ground speed for single front wheel (configuration VI) with simulated wing flap at different angles. = 12 000 lb (53 378 N ) ; p = 75 lb/in2 (51.7 N/cm2); dl = 1 . 0 in. (2.54 c m ) .
F i l m speed = 10 frames per second 6 1 2 Frame 1 1.4 16 ( a ) Frames 1 t o 17.
L-66-1191 Figure 30.- Pitching i n s t a b i l i t y of bogie landing gear developed during t e s t at l i g h t weight a n d high t i r e pressure ( s m a l l v e r t i c a l t i r e deflection) at superhydroplaning speed.
VG VG = 100 knots; FZ,@; = 1 2 000 l b (53 378 N); - = 1.29; p = 75 lb/in2 (51.7 N/cm?); 1.0 i n .
VP (2.54 cm) water depth; bogie gear not equipped with p i t c h damper.
1 8 2 1 29 30 3 2 (b) Frames 18 t o 32.
L-66-1192 Figure 30. - Concluded.
- C - With alleviator
- - - _
Without alleviator 20 2 3 $d $d Y U (u E m $4 10 g a
M \ M
$4 $4 -0 -0 alleviatox, Spray P d Q d 1 4 h Ir 1 1 I I -/ ) 40 60 80 100 20 Ground speed, VG, knots (a) Flexible rubber a l l e v i a t o r .
zu s w m u 01 $4 m E u (u E Em 10 a m n 00 \ E M P w P .A P P d Ir, k 1 I I 20 40 60 80 100 Ground speed, VG, knots ( b ) Rigid metal a l l e v i a t o r .
D z 3 x io3 $4 $4 m u m u 0 E m E ! d 10 g
\
M M E $4 Q P P .A Q d 21 4 Ir, crr n
120 -
0 2 0 4 3 6 0 80 100 Ground speed, VG, knots ( c ) Rigid m e t a l a l l e v i a t o r with curved top.
Figure 31.- Variation of drag parameter with ground speed i n water f o r dual tandem-wheels with and without spray-drag a l l e v i a t o r s .
p = 75 lb/in2 (51.7 N/cm2).
L-3415 NASA-Langley, 1966 I “The aeronautical and space activities of the United States shall be
conducted JO as to contribute . . . to the expansion of hziman knowl-
edge of phenomena in the atmosphere and space. The Administration shall provide for the widest prdcticable and appropriate dissemination of information concerning its activities and the resrdts thereo f .” -NATIONAL AERONAUTICS AND SPACE ACT OF 1958
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