1、NASA TECHNICAL NOTE NASA TN D-7743 I M w h (NASA-TN-D-7743) EXPEEIHENTSI N74-34487 u cn INVESTIGATION OF THE BRAKING AND U COhNEhING CHARACTfRISTICS CF 3: X I Z 11.5-14.5, TYPE 8, AInChBFT Ti92L iiiTP Unclas CIFIER3NT (NASA) 24 p HC $3.ijC 2SCL “1C Hl/22 52Li17 EXPERIMENTAL INVESTIGATION OF THE BRAK
2、ING AND CORNERING CHARACTERISTICS OF 30 x 11.5-14.5, TYPE VIII, AIRCRAFT TIRES ,“ / WITH DIFFERENT TREAD PATTERNS / by Robert C. Dreher urrd John A. Tanner Langley Research Center Humpton, V 23665 NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON, D. C. OCTOBER 1974 Provided by IHSNot for Res
3、aleNo reproduction or networking permitted without license from IHS-,-,-1. Report No. 1 2. Gwtrnment Accession No. 1 3. Recipients Catalog No. NASA TN D-7743 I I 4. itle and Subtitle I 5. Repon Date EXPERIMENTAL INVESTIGATION OF THE BRAKING AND t October 1974 CORNERING CHARACIERISTICS OF 30 X 11.5-1
4、4.5, TYPE VIII, 6. PedomlngOrnizatlonCode AIRCRAFT TIRES WITH DIFFERENT rREAD PATTERNS 7. Author($) Robert C. Dreher and John A. Tanner 9 Pnfwmmg Organization Name and Address 6. Abstract 8. Perforrnng Orgnuation Report No. L-9687 10. Work Unt No. 501-3P-1.2-02 - 2. Sponsoring Agency Name and Addres
5、s National Aeronautics and Space Administration Washington. D.C. 20546 An investigation was conducted at the Langley aircraft landing loads and traction facility to study the braking and cornering characteristics of 30 x 11.5-14.5, Type VIII, aircraft tires with five different tread patterns. These
6、characteristics, which included the drag-force and cornering-force friction coefficients, were obtained on dry, damp, and flooded runway surfaces over a range of yaw angles from 0 to 12 at ground speeds from 5 to 100 knots. NASA Langley Research Center I 11. Contract or Grant No. Hampton, Va. 23665
7、13. Type of Report and Pwr:od Covered Technical Note 14. Sponsoring gmcy ode The results of this investigation indicate that a tread pattern consisting of transverse cuts across the entire width of the tread slightly improved the tire traction performance on wet surfaces. The braking and cornering c
8、apability of the tires was degraded by thin-film lubrication and tire hydroplaning effects on the wet runway surfaces. Also, the braking capability of the tires decreased when the yaw angle was increased. 7. Key Words (Suggested by Authorls) I Tires Aircraft Friction 18. Oistributon Sta:ernent Uncla
9、ssified - Unlimited STAR Category 02 19. Security Clamif. (of this report) 1 20. Security Clauif. (of this page1 Unclassified / Unclassified For mle by the National Tochnicrl Informtion Swlce, Springfield, Virginia 22151 21. NO. of PQUI 22 22. Rice $3.00 Provided by IHSNot for ResaleNo reproduction
10、or networking permitted without license from IHS-,-,-EXPERIMENTAL INVESTIGATION OF THE BRAKING AND CORNERING CHARACTEPJSTICS OF 30 X 11.5- 14.5, TYPE W, AIRCRAFT TIRES WITH DIFFERENT TREAD PATTERNS By Robert C, Dreher and John A. Tanner Langley Research Center SUMMARY An investigation was conducted
11、at the Langley aircraft landing loads and traction facility to study the braking and cornering characteristics of 30 X 11.5-14.5, Type VIII, aircraft tires with five different tread patterns. These characteristics, which included the drag-force and cornering-force friction coefficients, were obtaine
12、d on dry, damp, and flooded runway surfaces over a range of yaw angles from 0 to 12 at ground speeds from 5 to 100 knots. The results of this investigation indicate that a tread pattern consisting of transverse cuts across the entire width of the tread slightly improved the tire traction performance
13、 on wet surfaces. The braking and cornering capability of the tires was degraded by thin- film lubrication and tire hydroplaning effects on the wet runway surfaces. Also, the braking capability of the tires decreased when the yaw angle was increased. INTRODUCTION Researchers seek continually to impr
14、ove the traction of aircraft tires on runways under adverse weather conditions. After considerable research (refs. 1 to 6, for example), they have shown that aircraft braking and steering capability decreases during wet runway operations and that the problem becomes more severe with increased ground
15、 speed and fluid depth, M higher aircraft ground speeds and at a fluid depth defined by the runway surface texture and tire tread design, the phenomenon of dynamic hydroplaning occurs wherein the tire loses contact with the runway surface and thus its directional stability and braking effectiveness.
16、 Most jet aircraft are susceptible to hydroplaning because of their high ground operating speeds. Attempts have been made to eliminate or delay the deleterious effects attributed to hydroplaning by developing techniques which would prevent the buildup of water pressure in the tire-pavement interface
17、. All these attempts tried to provide improved escape routes or drainage for the water in the tire footprint either by changing the texture of the Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-runway surface or by revising or modifying the tire tre
18、ad pattern. Changing the runway surface texture through the installation of transverse grooves or the application of a porous asphalt overlay can provide increased tire traction under wet conditions (see refs. 6 and 7). Research on tire tread patterns (ref. 1, for example) has indicated that the lev
19、el of friction developed by a tire on a contaminated surface is extremely sensitive to the tread design at least for fluid depths less than the tire tread depth. Traditionally, increasing the number of circumferential grooves in the tire tread, or adding radial or transverse grooves seems to improve
20、 the wet braking characteristics, particularly at the higher ground speeds. It should be noted, however, that other considerations, such as tread wear and tread integrity, during high-speed operation are limiting factors to any tread alteration. This paper presents the results of an investigation co
21、nducted at the Langley aircraft landing loads and traction facility to determine the wet-runway performance characteris- tics of an aircraft tire having various tread patterns thought to improve traction under all weather conditions. Five 30 x 11.5- 14.5, Type MJ, 24-ply-rating tires having differen
22、t tread patterns were tested to define their braking and cornering characteristics. This size tire is presently employed on the main gear of a high performance jet fighter aircraft. The braking and cornering characteristics included the drag-force and cornering-force friction coefficients obtained f
23、or the tires operating on dry, damp, and flooded surfaces over a range of yaw angles from 0 to 12 at ground speeds from 5 to 100 knots (1 knot = 0.5144 meter/second). The tires used in the tests were supplied by the U.S. Air Force (Rain Tire - Project 5549). SYMBOLS Values are given in both SI and U
24、.S. Customary Units. The measurements and calculations were made in U.S. Customary Units. Factors relating the two systems are presented in reference 8. Drag force drag-force friction coefficient, parallel to direction of motion, - Vertical force C(d ,max maximum drag-force friction coefficient Vd ,
25、o unbraked rolling-resistance friction coefficient, parallel to direction of motion pd ,skid skidding drag-force friction coefficient 8 unbraked cornering-force friction coefficient, perpendicular to direction of motion, Side force Vertical force Provided by IHSNot for ResaleNo reproduction or netwo
26、rking permitted without license from IHS-,-,-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 - the same type as ones employed on a current high performance jet fighter aircraft. A photograpl, of the test tires is p
27、resented in figure 1 which shows tire B mounted on a wheel and inflated and the remaining tires unmounted. Tire A had the stand- ard three-groove tread configuration currently in the U.S. Air Force inventory. Tire B also had a three-groove tread pattern, but the lands were equipoed with a large numb
28、er of “pin“ holes. For tire C, the basic tread of tire A was modified with narrow trans- verse cuts which connected the grooves and extended to the tire shoulders. Tire D had a four-groove tread pattern with transverse grooves in the shoulder area, and tire E was similar to tire D except for an addi
29、tional circumferential groove in each shoulder. The dimensions of the various tread grooves and special features are listed in table I. All tires were tested at an inflation pressure of 1827 kPa (265 psi), and the vertical load was varied with ground speed to simulate the effects of wing lift, The l
30、oading was determined from aircraft tests and varied from approximately 73.4 kN (16 500 lb) at 5 knots to 55.6 kN (22 500 lb) at 100 knots as shown in fipi-e 2. Runway Surface Conditions A concrete test runway, which was approximately 174 m (570 ft) in length, was divided into three sections so that
31、 tire braking and cornering data could be obtained on dry, damp, and flooded surfaces. The first section was kept dry to provide for full wheel spinup. The next section, 61 m (200 ft) long, was dampened (no visible standing water). The final 61 m (200 ft) section was surrounded by a dam and flooded
32、with water to a depth of approximately 0.64 cm (0.25 in). The concrete test surface had a light broom finish which was somewhat smoother than that of most operational concrete runways, By using the grease sampling technique described in reference 3, the average texture depth of the surface in the fl
33、ooded test section was measured to be 168 pm (0.0066 in.) and that in the damp section, 135 pm (0.0053 in.). A typical operational runway has an average texture depth of the order of 201 pm (0.0079 in.), Test Facility The investigation was performed at the Langley aircraft landing loads and traction
34、 facility, which is described in reference 9, and utilized the main test carriage pictured in figure 3. Presented in figure 4 is a schematic of the instrumented dynamometer which supported the wheel and measured the various axle loadings. The instrumentation con- sisted of load beam to measure verti
35、cal, drag, and side forces and links to measure brake torque. Ail t: !se measurements were taken at the axle. Additional instrumentation 3 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-was provlded to measure brake pressure, wheel angular velocity,
36、 and carriage displace- ment. Vertical, drag, and side accelerometers provided data for inertial corrections. Continuous time histories of the output of the instrumentation were recorded by an oscillo- graph mounted on the test carriage. Test Procedure The test procedure consisted of propelling or t
37、owing the test carriage across the runway test section at the desired ground speed, releasing the drop test fi.xture to apply the preselected vertical load on the tire, subjecting the tire to controlled brake cycles on the damp and flooded test sections, and monitoring the onboard instrumentation. I
38、n a test series the tire yaw angle was varied from o0 to 12 in 4 increments; however, it was held constant for each test run. Ground speeds for these tests ranged from 5 to 100 knots. To obtain a speed of 5 knots, the test carriage was towed by a ground vehicle; for higher speeds, the carriage was p
39、ropelled by the hydraulic jet as described in reference 9. The brake cycle consisted of energizing the braking circuit with “braking cams“ placed strate- gically along the test track, braking the tire from a free-rolling condition to a locked wheel skid, and then releasing the brake to allow tire sp
40、in-up. Time histories of the out- put of the instrumentation were recorded as the tire was braked on the damp and flooded test sections, In addition to the wet tests, one unyawed brake cycle was made with each tire on the dry section at a nominal ground speed of 100 knots. RESULTS AND DISCUSSION Tir
41、e-to-ground forces in the vertical, drag, and side directions and wheel angular velocity were recorded on an osciliograph throughout each test. These data were used to compute time histories of tk,e drag-force friction coefficient, parallel to the direction of motion, pd aid the unbraked cornering-f
42、orce friction coefficient, perpendicular to the direction of motion, ps. For each test condition, the unbraked (maximum) cornering-force friction coefficient ps measured just before braking was initiated, the maximum drag-force friction coeffi- cient PdmBx encountered during wheel spin-down, and the
43、 skidding drag-force friction coefficient pd, sldd measured at the instant of wheel lockup were determined from faired curves representing the time history data. These data for the five tes; tires are presented in table II. Also included in the table are the tire unbraked rolling-resistance friction
44、 coefficient gd,o, The following sections discuss the variation of pd,max, %,aid, and ps for the five test tires with respect to both ground speed and yaw angle. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Effect of Ground Speed The effect of gro
45、und speed on the braking and cornering characteristics for each of the five test tires is shown in figure 5 for various yaw angles and surface wetness conditions. Maximum drag-force friction coefficient.- The maximum drag-force friction coefficients kPmax for all test tires are faired by a single cu
46、rve in figure 5 for damp and flooded test conditions. In general, these fairings describe the coefficients for all , tires and thus the effect of tread design seems to be insignificant. However, the data indicate that tire C provides the best traction, although, in general, the improvement is not su
47、bstantial. The slightly improved performance of this tire over the others tested in this investigation may be attributed to the transverse cuts which extend across the entire width of the tread. These cuts may aid in breaking up the thin film of water on damp runway surfaces and also may help in rem
48、oving bulk water from the center of the foot- print on the flooded runway surfaces. Tires D and E also have transverse grooves, but only in the shoulder area; therefore, the lateral drainage in the center of the footprint is negligible. The data presented in figure 5 show that the maxinium drag-forc
49、e friLil m coefficient li.d, max decreases with increasing ground speed on both the damp and flooded test sur- faces. This trend, which can be attributed to thin-film lubrication and hydroplaning effects, is noted for all test yaw angles. Values of pd,mut at 0 yaw range from about 0.6 at 5 knots, which is in good agreement with that predicted (0.64) from the empirical expres- sion developed in re
