NASA-TP-1080-1977 Friction characteristics of three 30 X 11 5-14 5 type 8 aircraft tires with various tread groove patterns and rubber compounds《带有多种胎面花纹沟和橡胶复合物三个30 X 11 5-14 5第8类型.pdf

1、NASA !EJ I 1080 c. 1 NASA Technical Paper 1080 -m 0-3 I+= P LOAN COPY: RETU !$ e g AFWL TECHNICAL -1 2f= x KIRTLAND AFB, ,f r= g -2 E - .- =2 =I- 4 I- 1 x_m - - Friction Characteristics of Three 30 x 11.5-14.5, Type VIII, , Aircraft Tires With Various Tread Groove Patterns and Rubber Compounds Thoma

2、s J. Yager and John L. McCarty - DECEMBER 1977 NASA Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,- NASA Technical Paper 1080 TECH LIBRARY KAFB. NY Friction Characteristics of Three 30 x 11.5-14.5, Type VIII, Aircraft Tires With Various Tread Groove

3、 Patterns and Rubber Compounds Thomas J. Yager and John L. McCarty Langley Research Center Hampton, Virginia National Aeronautics and Space Administration Scientific and Technical Information Office OL3427b 1977 Provided by IHSNot for ResaleNo reproduction or networking permitted without license fro

4、m IHS-,-,-SUMMARY A test program was conducted at the Langley aircraft landing loads and traction facility to evaluate friction performance and wear characteristics On Wet runways of three 30 x 11.5-14.5, type VIII, aircraft tires having two different tread patterns and natural rubber contents. All

5、three test tires had the standard three circumferential groove tread, but two of the tires had molded transverse grooves which extended from shoulder to shoulder. The tread rubber content of the two tires with transverse grooves differed in that one had a 100-percent natural rubber tread and the oth

6、er had a rubber tread compo- sition that was 30 percent synthetic and 70 percent natural. The third test tire (without transverse grooves) had the conventional 100-percent natural rubber tread. Results of this investigation indicate that the differences in tire tread design and rubber composition do

7、 not significantly affect braking and cornering friction capability on wet or dry surfaces. Braking performance of the three tires decreases with increased speed, with increased yaw angle and, at higher speeds, with increased wetness of the surface. Tread-wear data based on number of brake cycles su

8、ggested that the tire with a blend of synthetic and natural rubber experiences significantly less wear than the other two test tires. The unyawed braking test runs showed that the tires with transverse tread grooves experience less wear than the conventional tire without transverse tread grooves. IN

9、TRODUCTION In recent years, the aircraft tire has been the subject of considerable research aimed at improving tread wear life and traction under adverse weather conditions. As pointed out in references 1 and 2, tire replacement accounts for a high percentage of the overall landing gear maintenance

10、costs of current jet airplanes. Aircraft tire manufacturers have been trying to develop tread rubber compounds which resist cutting and to improve wear life without compro- mising design strength or traction capability. Correspondingly, studies (refs. 3 to 6, for example) have shown that aircraft br

11、aking and cornering capa- bility are reduced during wet-runway operations because of tire dynamic hydro- planing effects, and attempts have been made to eliminate or delay hydroplaning by providing improved escape routes for the water in the tire footprint. Both of these problems are being addressed

12、 in a United States Air Force (USAF) pro- gram directed toward increasing the wet friction and lifetime of tires designed for high performance aircraft. This paper presents the results of an investigation conducted at the Langley aircraft landing loads and traction facility, at the request of the US

13、AF, to determine wet-runway behavior of high performance aircraft tires hav- ing two different tread patterns and different natural rubber contents. Three 30 x 11.5-14.5, type VIII, 24-ply-rating tires supplied by the USAF were tested Provided by IHSNot for ResaleNo reproduction or networking permit

14、ted without license from IHS-,-,-to define their braking and cornering friction characteristics. These charac- teristics included the drag-force and cornering-force friction coefficients obtained for the tires operating on dry, damp, and flooded surfaces over a range of yaw angles from Oo to 12O at

15、nominal ground speeds from 5 to 100 knots (1 knot = 0.5144 m/sec). The objective of the tests was to compare on the basis of these friction characteristics a tire with conventional tread (labeled tire C in this study) with (1) a tire having a modified tread pattern to pro- mote water drainage in the

16、 tire footprint (tire A in this study) and (2) a third tire (tire B in this study) which like tire A had molded transverse grooves and wherein a percentage of the natural rubber in the tread had been replaced by synthetic rubber to reduce tread wear. SYMBOLS Values are given in both SI and U.S. Cust

17、omary Units. Measurements and calculations were made in U.S. Customary Units. Factors relating the two sys- tems are presented in reference 7. Pd , max Pd, skid Ps , max Maximum drag force Vertical force maximum drag-force friction coefficient, Skid drag force Vertical force skidding drag-force fric

18、tion coefficient, “ maximum cornering-force friction coefficient, perpendicular to Cornering force Vertical force direction of motion, APPARATUS AND TEST PROCEDURE Tires The tires used in this investigation were 30 x 11 .5-14.5, 24-ply-rating, type VIII, aircraft tires which are the same kind as tho

19、se used on a current high performance jet fighter. Photographs of the three test tires (A, B, and C) are presented in figure 1. All three tires had the standard three circumferen- tial groove tread currently in the USAF inventory, but tires A and B had molded transverse grooves which extended from s

20、houlder to shoulder similar to a “rain tire“ tread design evaluated and discussed in reference 8. The comparable tire of reference 8 had a conventional tread which had been modified by hand with transverse cuts. The tread rubber content of tires A and B differed, however, in that tire A had a 100-pe

21、rcent natural rubber tread; whereas tire B had a tread composition of 30-percent synthetic and 70-percent natural Tire C had the conventional 100-percent natural rubber tread and grooves. All tires were tested at an inflation pressure of 1827 and the vertical load ranged from 57.8 kN (13 000 lb) to

22、66.7 kN rubber. no transverse kPa (265 psi), (15 000 lb). 2 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Test Facility The investigation, conducted at the Langley aircraft landing loads and traction facility described in reference 9, utilized the

23、main test carriage pictured in figure 2. The aircraft test tire, wheel, and brake assembly were mounted as shown in figure 3 on an instrumented dynamometer which measured the various axle loadings. Figure 4 illustrates the dynamometer instrumentation which consisted, in part, of load beams to measur

24、e vertical, drag, and side forces, and links to measure brake torque, all at the wheel qxle. Additional instrumentation was provided to measure brake pressure, wheel angular velocity, and carriage horizontal displacement and velocity. Continuous time histories of the output of the instrumentation du

25、ring a run were obtained by tape recorders mounted on the test carriage. Test Surfaces Three approximately equal segments of a 183-m (600-ft) section of the con- crete test runway were maintained in dry, damp, and flooded conditions. For the damp condition, the surface was wetted to a depth of less

26、than 0.03 cm (0.01 in.); the water depth for the flooded surface ranged from 0.5 to 0.8 cm (0.2 to 0.3 in.). Photographs of the overall test runway and the three sur- faces are presented in figure 5. Texture depth values which provide an indica- tion of potential surface frictional characteristics w

27、ere measured by the grease sample technique described in reference 5. Results from these measure- ments indicated that the dry concrete test surface had an average texture depth of 91 l.Im (0.0036 in.); the damp concrete section, 114 pm (0.0045 in.); and the flooded test section, 145 pm (0.0057 in.)

28、 The damp and flooded runway sec- tions of this investigation are the same sections used in the tire program described in reference IO. That investigation used conventional tires of the size similar to the tires tested in this investigation. Test Procedure For most test runs the carriage was propel

29、led to the desired ground speed, the drop test fixture was released to apply the preselected vertical load on the tire, and the tire was subjected to controlled brake cycles on three sur- faces: first, on the dry surface; subsequently, on the damp and flooded sur- faces. The procedure was the same d

30、uring other runs except that the brake cycles were limited to the wetted surfaces only. A brake cycle consisted of actuating the brake-pressure solenoid valve at predetermined locations along the track (thus, braking the tire from a free-rolling condition to a locked- wheel skid) and then releasing

31、the brake pressure to allow tire spin-up prior to the next cycle. Nominal carriage speeds for these tests were 5 knots (obtained by towing the carriage with a ground vehicle) and 25, 50, 75, and 100 knots (obtained by propelling the carriage with the water jet). Evaluation of combined tire braking a

32、nd cornering traction was achieved by rotating and locking in place prior to each run the entire test fixture dynamometer to yaw angles of Oo to 12O in 4O increments. No combined braking and cornering test was undertaken on the dry pavement because of the extensive wear associated with braking a yaw

33、ed tire on a high-friction surface. The instrumentation 3 I Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-measurements were recorded on tape and provided a complete time history of the test tire behavior during the course of a run. RESULTS AND DISC

34、USSION Tire-to-ground forces in the vertical, drag, and side directions and wheel angular velocity were recorded throughout each test and were used to compute time histories of the drag-force friction coefficient parallel to the direction of motion and the maximum (unbraked) cornering-force friction

35、 coefficient per- pendicular to the direction of motion. For each test condition, the maximum cornering-force friction coefficient pStmax measured just before braking was initiated, the maximum drag-force frlction coefficient pd max encountered during wheel spin-down, and the skidding drag-force fri

36、ction coefficient I.d,skid measured at the instant of wheel lockup were determined from faired curves of the time history data. These data for the three test tires are presented in table I. The following Sections discuss the Variations Of pd,max, pd,Skid, and ps,max for the three test tires with res

37、pect to both ground speed and yaw angle and conclude with comments relative to the wear characteristics of the different tires. Effect of Ground Speed on Friction Characteristics The effect of ground speed on the selected tire braking and cornering char- acteristics developed during operations on dr

38、y, damp, and flooded surfaces is shown in figure 6 for each test tire at yaw angles of Oo, 4O, 80, and 120. The data for all three test tires are faired by a single curve for each surface and yaw angle condition; in general, these fairings describe the coefficients for all tires. Thus, it would appe

39、ar that there is no significant effect on brak- ing and cornering friction, wet or dry, attributed to differences in the tread design and rubber composition of the tires evaluated in this program. The data of figure 6 agree well with results from tests on similar tires in earlier pro- grams. (See re

40、fs. 8 and 10.) Maximum drag-force friction coefficient.- The data of figure 6 indicate that the values of maximum drag-force friction coefficient pd,max decrease with increasing ground speed. The decrease is observed under all runway sur- face conditions although it is much less pronounced on the dr

41、y than on the two wetted surfaces. This decrease corroborates the trends observed in refer- ences 3 to 6 for aircraft tires in general and in references 8 and 10 for tires of the same size as tires used in this study. The figure also shows that pd,maX in the unyawed condition is essentially the same

42、 on all three surfaces at very low speeds. The magnitude agrees well with the prediction (0.64) from the empirical expression developed in reference 11 for maximum friction under nearly static conditions. In general, values of pd,max on the flooded surface are the same as those on the damp surface f

43、or similar test conditions. The similarity is per- haps due to the following reasons. First, the texture depth of the flooded surface is approximately 25 percent greater than that of the damp surface. 4 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,

44、With all the test speeds of this program well below the computed dynamic hydro- planing speed of 147 knots for the test tire (ref. 4, this difference in sur- face texture should affect tire friction. Second, the flooded surface, because of its water depth, induces a significant fluid drag on the ti

45、re whereas on the damp surface (no standing water) such drag can be considered negligible. Skidding drag-force friction coefficient.- The skidding drag-force fric- tion coefficient pd skid developed by all three tires is essentially the same as whereas on the wetted surfaces a more rapid deteriorati

46、on in ps,max is observed as the speed increases. At high speeds, this deterioration appears greater on the flooded than on the damp surface. No recognizable difference in the maximum cornering-force fric- tion coefficients is caused by the tread rubber compositions tested, but the available data do

47、suggest that the conventional tread pattern (no transverse grooves) generates slightly higher friction under the flooded condition at the higher speeds. Effect of Yaw Angle on Friction Characteristics The effect of yaw angle on the drag-force and cornering-force friction coefficients developed by th

48、e test tires under the three surface conditions at nominal ground speeds of 5 and 100 knots is illustrated in figure 7 where the data are again taken from table I. The two drag-force friction coefficients were available only at a yaw angle of Oo on the dry surface because of the excessive wear which

49、 would result from braking a yawed tire on a high-friction surface. The data for a11 three test tires are faired by a single curve for each surface and ground speed condition which suggests little or no differences in the friction characteristics of the tires. Maximum drag-force friction coefficient.- The data of figure 7 indicate that the maximum drag-force friction coefficients pd,max are highest for the unyawed tire