1、Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-ERRATA NASA Technical Note D-7815 - EXPERIMENTAL INVESTIGATION OF THE CORNERING CHARACTERISTICS OF 18 X 5.5, TYPE M, AIRCRAFT TIRES WITH DIFFERENT TREAD PATTERNS By Robert C. Dreher and John A. Tanner D
2、ecember 1974 In both text and figures, all yaw angles mentioned should be multiplied by 1.36. Thus, the test yaw angles 4O, 8O, and 12O should be 5.4O, 10.9, and 16.3, respectively. Issued March 1976 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-I
3、nuyllltm. I- i -* l%a16. NASA TN D-7815 aT*lr.nd- EXPERIMENTAL UWBSTIGATION OF THE CORNgRJNG TIRES WITH DIFFERENT TREAD PATTERNS (XAFUCTERIsIlCS OF 18 x 5.5, TYPE Vn, AIRCRAFT 7. bttwsl Robert C. Dreher and John A. Tanner SRrtornirJOrpniaSianNnramtAWa NASA Langley Research Center Hampton, Va- 23665
4、12. SpDmmIy . Agncykllmd*dbar National Aeronautics and Space Administration Washington, D.C. 20546 5 fhm ar Bd. a-Orlnmon December 1974 Rm hb. 8. - L-9795 505-08-31-01 10. wak unir h. 11. Brrmc w Gmt Iya. 13. Typ of Rcpm rd Riad Cmmmd Technical Note 14. SDOnrai hgmw Cade 19. *uity Ckaif. (of this re
5、port) Unclassified For de by tho Nnionrl Tmchniul Intormoth %via, SpfinpfirW. Viwnir 22151 20. Sswity aisif. (of this -1 21. NO. ot P- n. Rice Unclasszied 19 $3.25 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-EXPERIMENTAL ETESTIGATION OF THE CORNE
6、RING CHARACTERISTICS OF 18 X 5.5, TYPE Vn, AIRCRAFT TIFtES WITH DIFFERENT TREAD PATTERNS By Robert C. Dreher and John A. Tanner Langley Research Center SUMMARY An investigation was conducted at the Langley aircraft landing loads and traction facility to study the cornering characteristics of 18 X 5.
7、5, type VII, aircraft tires with four different tread patterns. These Characteristics, which include the cornering-force and drag-force friction coefficients and self-alining torque, were obtained on dry, damp, and flooded runway surfaces over a range of yaw angles from Oo to 12 and at ground speeds
8、 from approximately 5 to 90 knots. The results of this investigation indicated that a tread pattern with pinholes in the ribs reduced the tire cornering capability at high yaw angles on a damp surface but improved cornering On a dry surface. A tread pattern which had transverse grooves across the en
9、tire width d the tread was shown to improve the tire cornering performance slightly at high speed; on the flooded runway surface. The cornering capability of all the tires was degrade! rt high ground speeds by thin film lubrication and/or tire hydroplaning effects. Alterations to the conventional tr
10、ead pattern provided only marginal improvements in the tire cornering capability; this would suggest that runway surface treatments may be a more effective way of improving aircraft ground performance during wet operations. INTRODUCTION A large percentage of wet runway skidding accidents involving h
11、igh-performance jet aircraft occur because the aircraft slides aff the side of the runway under the influence of a crosswind. During the approach md initial roll-out phases of the landing operation, the crosswind is usually manageable because the pilot can maintain directional control by tak- ing ad
12、vantage of aerodynamic forces. As the ground speed is reduced, hcwever, aerody- namic control forces become less effective and the pilot must rely more upon nose-gear steering to provide the desired aircraft heading 011 the runway. Past research (refs. 1 to 4, for example) has indicated that aircraf
13、t steering capability is decreased during wet runway operations by thin film lubrication and/or dynamic hydroplaning effects. One approach to eliminate or at least delay the deleterious effects attributed to hydroplaning is to modify the design of the tire tread. Tread pattern research (refs. 1 and
14、5, for example) Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-indicates that the friction level generated by a tire on a wet muray surface may be improved by an increase in the number of circumferential grooves or by the addition of transverse groo
15、ves in the tread. It should be noted, however, that tread wear and chunk- ing during high-speed ground operations are limiting factors to any tread alteration. The purpose of this paper is to present the results of an investigation to evaluate the wet runway cornering characteristics of 18 x 5.5, ty
16、pe VII, aircraft tires with four differ- ent tread configurations. These characteristics, which include the cornering-force and drag-force friction coefficients and the self-alining torque, were obtained for the tires on damp and flooded runway surfaces, with limited tests on a dry surface, over a r
17、ange of yaw angles from 00 to 120 and at ground speeds from 5 to 90 knots (1 knot = 0.5144 m/sec). The tires used in the tests were supplied by the U.S. Air Force (Rain Tire - Project 5549). SYMBOLS Measurements and calculations were made in U.S. Customary Units and converted to SI Units. Factors re
18、lating the two systems are presented in reference 6. TZ self-alining torque, N-m (in-lb) drag-force friction coefficient, parallel to the direction of motion, Drag force Vertical force pd PS cornering-force friction coefficient, perpendicular to the direction of motion, Cornering force Vertical forc
19、e APPARATUS AND TEST PROCEDURE Tires The tires of this investigation were 18 X 5.5, type VII, 14-ply-rating aircraft tires employed on the nose gear of several military and civilian jet aircraft A photograph of the test tires is presented in figure 1. Tire A has the standard three-groove tread con-
20、figuration currently in use. Tire B has seven circumferential grooves with a large num- ber of “pinholes“ in each rib. Tires C and D have a Circumferential groove pattern simi- lar to that of tire A, but modified with transverse grooves. These grooves are limited to the shoulder area in tire C and c
21、xtend across the entire tread in tire D. The dimensions of the various tread grooves and special features are listed in table 1. 2 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-All tires were tested at an inflation pressure of 1138 kPa (165 psi), a
22、nd the vertical load was varied with ground speed to simulate the effects of wing lift. This loading was determined from U.S. Air Force aircraft tests and varied from approximately 20.69 kN (4650 lbf) at 5 knots to 11.12 kN (2500 lbf) at 90 knots, as shown in figure 2. Runway Mace Conditions For the
23、 tests described in this paper, approximately 82 m (270 ft) of a concrete test runway were divided into two sections to provide tire cornering data on flooded and damp surfaces, The first 58-m (190 ft) section was maintained in a damp condition (no visible standing water), and the last 21-m (80 ft)
24、section was surrounded by a dam and flooded with water to a depth ad approximately 0.64 cm (0.25 in.). To define the effect of wetness further, a limited number of tests were conducted with each tire on a dry surface. A grease sampling technique, descyibed in reference 7, indicated that the average
25、tex- ture depth was 244 pm (0.0096 in.) for the surface in the damp test section and 99 prn (0.0039 in.) in the flooded test section, whereas typical texture depths for operational runways gene -ally vary between 100 m (0,0039 in.) and 400 p m (0.0157 in.). Test Facility The investigation was perfor
26、med at the Langley aircraft landing loads and traction facility, which is described in reference 8, and utilized the test carriage pictured in fig- ure 3. Presented in figure 4 is a schematic of the instrumented dynamometer which sup- ports the wheel and measures the various axle loadings. The instr
27、umentation consisted of load beams to measure vertical, drag, and side forces at the axle. Additional instrumen- tation was provided to measure wheel angular velocity, carriage displacement, and verti- cal, drag, and side accelerations at the axle for inertial corrections. Continuous time histories
28、of the output of the instrumentation were recorded on an oscillograph mounted on the test carriage. Test Procedure The test procedure consisted of either propelling or towing the test carriage across the runway test sections at the desired ground speed, releasing the test fixture to apply the desire
29、d vertical load on the tire, and monitoring the output from the onboard instrumen- tation. The tire yaw angle was held constant for each test run, and in a test series, was varied from Oo to 12O in 4O increments. Ground speeds for these tests ranged from approximately 5 to 90 knots. For a ground spe
30、ed of 5 knots, the test carriage was towed by a ground vehicle; for higher speeds, the carriage was propelled by the hydraulic water jet, as described in reference 8. 3 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-RESULTS AND DISCUSSION Time histo
31、ries of forces in the rerticd, drag: and side directions and of wheel angu- lar velocity were recorded on an oscillograph throughout each test. These time histories were used to compute steady-state values of the cornering-force friction coefficient p perpendicular to the direction of motion and the
32、 drag-force friction coefficient Pd pard- lel to the direction of motion. The self-alining torque Tz about the vertical or steering axis of the wheel was computed from the load transfer between the two drag-load beams shown in figure 4. The following sections discuss the variation of these cornering
33、 char- acteristics with yaw angle and ground speed for the different surface wetness conditions. Effect of Yaw Angle The effects of yaw angle on the cornering- and drag-force friction coefficients and the self-alining torque developed by the various test tires on damp and flooded surfaces at nominal
34、 ground speeds of 5, 50, and 90 knots are presented in figure 5. Cornering-force friction coefficient.- The cornering-force friction coefficients p for all test tires operating on wetted surfaces are faired by a single curve for each test condition in figure 5. The cornering-force friction coefficie
35、nt for each tire is shown to vary with yaw angle ir an expected manner (refs. 1 to 3). At 5 knots ps increases with increasing yaw angle up to and including the maximum yaw angle tested on both the damp and flooded surfaces, whereas at the higher test speeds, ps peaks between 4O and 8O and then decr
36、eases with a further increase in yaw angle. The figure further shows that at 5 knots, ps is essentially independent of the surface wetness condition; but at higher test speeds, particularly at 90 knots, where the tire approaches its predicted hydroplaning speed of 116 knots (ref. 9), ps decreases mo
37、re rapidly on the flooded surface than on the damp surface, Of the tires examir-ed, one tire develops somewhat higher cornering friction and another tire develops somewhat lower cornering friction than the others. However, the conditions which provided these differences appear to be quite limited. A
38、s shown by the data of figures 5(b) and 5(c), tire D provides a slightly higher cornering capability than the other tires at high speeds on the flooded surface. The improved performance of this tire is attributed to the transverse grooves in the tread, *zhich ehtend from shoulder -0 shoulder, These
39、grooves apparently provide escape routes for the bulk of the water tn the tire footprint under flooded conditions and thereby delay dynamic hydroplaning el ects. Tire C also has transverse grooves, but only in the shoulder area; hence, their later tl drainage capability in the center of the footprin
40、t is negligible. This trend is in agrec meat with the results noted in reference 1 for similar tread patterns. Since the data of fig ire 5 suggest that only marginal imprwements in the cornering capabilitv can be gained through modifications to the conventional tread pattern, it appears that runway
41、grooving or other 4 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-surface treatments would be a more effective means for providing an airplane with direc- tional control on wet runways. Of the tires evaluated, tire B demonstrated the poorest corner
42、ing capability at the highest test yaw angle and on a damp surface. The reduced cornering friction provided by this tire, best illustrated L: the data of figure 5(c), is attributed to the numerous pin- holes in the tread, which apparently trap water in the tire footprint and thus reduce its wet corn
43、ering capability. This trend is similar to that noted for dimple-tread tires in reference 5. The results from the limited tests to ascertain the level of friction provided by each tire on an unwetted surface are presented in figure 5(c). These tests were conducted only at a nominal ground speed of 9
44、0 knots and examined tire A, with the conventional tread design, at all test yaw angles and the remaining tires at an arbitrarily selected yaw angle of 8O. The available data indicate that, except for tire B, all the tires provide essentially the same dry cornering capability. The higher dry corneri
45、ng friction provided by tire B is believed to be due to the numerous pinholes in the tread of that tire, which would tend to soften the tread rubber sufficiently to increase the size of the footprint and, hence, improve the dry traction. Drag-force friction coefficient.- Figure 5 shows that the drag
46、-force friction coeffi- cient pd angle and is essentially faired by a single curve for each test condition; hence, no major differences between the tires in terms of yawed drag are implied. The figure further shows that at 5 knots, is essentially independent of the surface wetness condition at all y
47、aw angles; but at the higher test speeds, the damp runway, particularly at small yaw angles. The higher values of I.(d on the flooded surface are attributed to fluid drag and are in agreement with the results from similar tests conducted on other tires presented in references 2 and 3. developed by a
48、ll test tires appears to increase linearly with an increase in yaw pd pd is higher on the flooded runway than on Data from tests on a dry surface (fig. 5(c) show that pd increases with yaw angle and, in general, is slightly higher than that developed on the damp surface, particularly at higher yaw a
49、ngles. feedback necessary to ensure a stable (self-centering) steering system. Positive torque values denote a stable steering system and negative values denote an unstable one. Data illustrating the effect of yaw angle on the self-alining torque T, produced by the four test tires are also presented in figure 5. The data indicate that for all test conditions, T, reaches maximum po
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