1、NASA Technical Paper 1917 TP 19 17 c. 1 I Cornering Characteristics of the Nose-Gear Tire of the Space Shuttle Orbiter William A. Vogler and John A. Tanner OCTOBER 1981 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-TECH LIBRARY KAFB, NM NASA Techni
2、cal Paper 1917 Cornering Characteristics of the Nose-Gear Tire of the Space Shuttle Orbiter William A. Vogler Kentron InternationaZ, Inc. Hampton, Virginia John A. Tanner Langley Research Center Hampton, Virginia National Aeronautics and Space Administration Scientific and Technical information Bran
3、ch 1981 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-INTRODUCTION The Space Shuttle Orbiter is the first space vehicle designed to land like a conventional airplane, and, as such, it is subjected to the same crosswind effects as commercial and mil
4、itary airplanes. As in the case of conventional airplanes, cross- winds during approach and initial rollout phases of the landing are usually manage- able because the pilot can maintain directional control by taking advantage of aero- dynamic forces. As ground speed is reduced, however, aerodynamic
5、forces become less effective, and the pilot must rely upon differential braking or nose-gear steering to provide the desired spacecraft heading on the runway. The response of the Space Shuttle to nose-gear steering input is defined, in part, by the cornering character- istics of the nose-gear tire;
6、thus, a need exists to establish these cornering char- acteristics under realistic operating conditions. The purpose of this paper is to present results of an investigation of the cornering characteristics of the 32 X 8.8 nose-gear tire of the Space Shuttle Orbiter on a dry concrete runway. These ch
7、aracteristics, which included side and drag forces and friction coefficients, aligning and overturning torgues, friction-force moment arm, and the lateral center-of-pressure shift, were obtained over a range of yaw angles from Oo to 12O and tire vertical loads from 22 kN (5000 lbf) to 133 kN (30 000
8、 lbf). This range of yaw angles and vertical loads spans the expected envelope of loads and yaw angles to be encountered during Space Shuttle landing operations. The tests were conducted at ground speeds that ranged from 50 to 100 knots (1 knot = 0.5144 m/sec). SYMBOLS Values are given in both the I
9、nternational System of Units (SI ) and in the U. S. Customary Units. The measurements and calculations were made in the U.S. Customary Units. Factors relating the two systems are given in reference 1. Fd FS FZ h Mx MZ 9 V YC drag force parallel to plane of wheel side force perpendicular to plane of
10、wheel tire vertical force axle height overturning torque aligning torque friction-force moment arm carriage or ground speed lateral center-of-pressure shift Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-B d S $ coefficients of curve-f itting equati
11、ons drag-force friction coefficient, parallel to plane of wheel side-force friction coefficient, perpendicular to plane of wheel tire yaw angle APPARATUS AND TEST PROCEDURE Test Tires The tires used in this investigation were 32 x 8.8, type VII, bias-ply aircraft tires of 20-ply rating with a maximu
12、m speed rating of 217 knots and a three-groove tread pattern. A photograph of two test tires having new and worn treads is pre- sented in figure 1. The worn tire is shown unmounted and thus unpressurized. The new tire which had an original groove depth of 0.25 cm (0.1 in. ) is shown mounted and pres
13、surized. During the course of this investigation, the test tire was changed when the tread was completely worn off and, thus, a total of three tires were used. Throughout the investigation, the tire inflation pressure was maintained at the nominal operational pressure of 2.07 MPa (300 psi). Test Fac
14、ility The investigation was performed on the 48 000 kg (106 000 lbm) test carriage at the Langley Aircraft Landing Loads and Traction Facility described in reference 2. Figure 2 is a photograph of the carriage with the test-wheel assembly installed, and figure 3 is a close-up view of the tire and wh
15、eel mounted within the instrumented dynamometer used to provide accurate measurements of the tire-ground forces. For the tests described in this paper, approximately 122 m (400 ft) of the available 366 m ( 1200 ft) of the flat concrete runway was used to provide cornering data. The concrete surface
16、in the test area had a light broom finish in the trans- verse direction that provided an average texture depth of 159 ym (0.00626 in. ), slightly less than that of a typical operational runway. The test runway was level (no crown) and, for all tests, the surface was kept dry. Instrumentation Tire fr
17、iction forces were measured with the dynamometer shown in figure 3 and illustrated schematically in figure 4. Strain gages were mounted on the five dyna- mometer support beams: two of the beams were used to measure vertical forces, two were used for measuring drag forces parallel to the wheel plane,
18、 and a single beam was used to measure side force perpendicular to the wheel plane. Three acceler- ometers on the test-wheel axle provided information for inertia corrections to the force data. An electronic interval timer provided a measure of the carriage speed. A slide-wire potentiometer was used
19、 to obtain a measure of drop carriage displacement and indirectly to provide a measure of axle height. All data outputs were fed into signal conditioning equipment and then into a frequency-modulated tape recorder. 2 Provided by IHSNot for ResaleNo reproduction or networking permitted without licens
20、e from IHS-,-,-Test Procedure The testing technique consisted of rotating the dynamometer and wheel assembly to the preselected yaw angle, propelling the test carriage to the desired speed, lowering the tire onto the dry runway and applying the selected vertical load, and recording the outputs from
21、the on-board instrumentation. The yaw angle of the wheel assembly, held constant for each test run, ranged from Oo to 12O in 2O increments with additional tests at a yaw angle of lo. The nominal carriage speeds ranged from about 43 to 104 knots and were measured when the maximum vertical load was at
22、tained. Tire vertical loading was varied hydraulically through a range from zero to 147 kN (33 000 lbf) and then back to zero during the course of a typical run, and the loading rate was approximately 133 kN/sec (30 000 lbf/sec). Data Reduction All data were recorded on analog magnetic tape filtered
23、 to 1000 Hz. The analog data were then processed through a low pass filter (cutoff frequency of 60 Hz 1, dig- itized at 250 samples per second, and used to generate time-history plots for data analysis. From these digitized data, direct measurements were obtained of the drag force (sum of two drag b
24、eams), the side force, the vertical force applied to the tire (sum of two vertical beams 1, the vertical displacement of the drop carriage, and the vertical, drag, and side accelerations of the dynamometer. The instantaneous vertical-, drag-, and side-force data were corrected for acceleration effec
25、ts and combined as necessary to compute both the instantaneous drag-force friction coeffi- cient parallel to the plane of the wheel and the side-force friction coefficient perpendicular to the plane of the wheel. The load transfer between the two drag- force beams (see fig. 4) provided a measure of
26、the aligning torque about the vertical or steering axis of the wheel. The load transfer between the two vertical-force beams (again see fig. 4) provided a measure of the overturning torque about the axis mutually perpendicular with the vertical and rotation axes. The lateral center-of- pressure shif
27、t of the vertical-load pressure distribution due to yawed rolling was defined by where h was the height of the axle above the runway surface. The friction-force moment arm q (see ref. 3 for definition) due to yawed rolling was defined by the equation A least-squares fairing technique (see ref. 4) wa
28、s used to smooth the digitized data from each run. In this application, seventh-order polynomial line segments were fitted to the data where each line segment was faired through 40 data points with a 10-point overlap between each segment. Linear interpolation was used to insure a smooth transition b
29、etween line segments within each overlap region, and eight line segments were necessary to fair the data for each second of test dura- tion. The effect of this smoothing routine was to limit the frequency response of the data to 24 Hz without introducing the phase shifts associated with electronic f
30、ilters. 3 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-The influence of the fairing technique on the data from a typical run is illus- trated in figure 5. Figures 5(a) and 5(b) are time histories of the unsmoothed and smoothed side force, respecti
31、vely, and figures 5(c) and 5(d) are time histories of the unsmoothed and smoothed vertical force, respectively. The side force is plotted as a function of the vertical force in figure 5(e) before smoothing and in fig- ure 5(f) after smoothing. The various cornering characteristics from each run were
32、 plotted as a function of vertical force, and discrete data points were chosen at pre- selected vertical-force values (dashed vertical lines in fig. 5(f) to establish the influence of parameter variations on tire cornering characteristics. RESULTS AND DISCUSSION Data from the yawed-rolling tests con
33、ducted on the nose-gear tire of the Space Shuttle Orbiter are presented in table I together with the corresponding test con- ditions. For purposes of discussion, these data are also presented in figures 6 to 13. The tests examined the effects of three parameters - tire vertical load, yaw angle, and
34、ground speed - on the characteristics of side and drag forces, aligning and overturning torques, friction-force moment arm, and lateral center-of-pressure shift. The data are presented in the form of carpet plots to illustrate functional relationships between the characteristics and the test paramet
35、ers. In the carpet plots, each characteristic is presented as a function of both vertical load and yaw angle, and the ground speed is identified by test-point symbols. Lines of constant load and constant yaw angle were then fitted to the data in a weighted least-squares fashion to serve as an interp
36、olation aid. The coefficients of bicubic interpolation equations for each characteristic are presented in table 11. A glossary of terms used in the study of tire mechanical properties is presented in reference 3. Sub- sequent paragraphs discuss in detail the effects of tire vertical load, yaw angle,
37、 and ground speed on the cornering characteristics of the Space Shuttle nose-gear tire. Side Force The effect of the test parameters on the developed side force Fs is pre- sented in figure 6 where the side force is measured normal to the wheel plane (as opposed to cornering force which is measured n
38、ormal to the direction of motion). When yaw angle is held constant, side force increases with increasing vertical load and generally reaches a maximum at vertical loads between 89 kN (20 000 lbf 1 and 133 kN (30 000 lbf). This figure also shows that the effect on side force due to changes in the ver
39、tical load become more pronounced as yaw angle is increased. As expected, increasing yaw angle while holding vertical load constant increases the side force regardless of the vertical load. At low vertical loadings, however, the side force appears to reach a maximum around the maximum yaw angle test
40、ed. No dis- cernible trends are evident with variations in ground speed. Frequently, during high-yaw-angle tests, the lower vertical-load test points are reached in the loading process before the tire has fully spun up. When this condition exists, the side force and other cornering characteristics a
41、re negligibly small (see fig. 5(f), for example), and these data were not included in this report. Since side-force data are generally presented in dimensionless form, they were divided by the respective vertical load on the tire. This process yielded, by def- inition, side-force friction coefficien
42、ts us, which are presented in the carpet plot of figure 7. For fixed yaw angles, there is a decrease in 1-1, with increasing ver- tical load. The figure also shows that for most fixed vertical loads, us increases 4 Provided by IHSNot for ResaleNo reproduction or networking permitted without license
43、from IHS-,-,-as the yaw angle is increased. For the lightly loaded tire (44.5 kN (10 000 lbf ) 1, a peak value in us of 0.57 is observed at approximately 8O which is in close agree- ment with the value of 0.60 predicted by equation (88) in reference 5. As the tire vertical load increases, the yaw an
44、gle for maximum ps increases; and for tire vertical loads greater than 89 kN (20 000 lbf), the peak in ps is reached at yaw angles which are beyond.the range tested in this investigation. Again, no trends due to variation in ground speed are evident. These trends are similar to the trends observed i
45、n reference 3. Drag Force The effect of the test parameters on the developed drag force Fd is presented in figure 8 where the drag force is measured parallel to the wheel plane. When the yaw angle is held constant, drag force generally increases with tire vertical load. Increasing the yaw angle whil
46、e holding the vertical load constant generally decreases the drag force. For the lightly loaded case (44.5 kN ( 10 000 lbf 1, a minimum drag force is observed around 8O; and for the heavily loaded case (1 33 kN (30 000 lbf ) 1, a peak drag force is observed at approximately 6O. Dividing the drag for
47、ce by the respective tire vertical load produces the drag-force friction coefficient pd, and values of this coefficient are presented in figure 9. These coefficients represent rolling resistance values, and their absolute values are usually below 0.05. Con- siderable scatter is observed in the data
48、for small yaw angles (less than 2O), and no discernible trends are established in this yaw-angle range. For fixed yaw angles between 4O and 12O, pd increases with increasing vertical load. When the vertical load is held constant, pd generally decreases when the yaw angle is increased from 4O to 12O.
49、 For the 66.7-kN (15 000-lbf) vertical load case, a minimum pd value is observed between IOo and 12O; and for the heavily loaded case, a maximum pd value is observed between 4O and 6O. No trends due to variation in the ground speed are observed for either Fd or pd. Aligning Torque Aligning torque MZ is defined as the torque developed about the steering axis of a yawed tire. Positive MZ is considered self-aligning; that
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