1、NASA N 0 N TECHNICAL NOTE LOAN COPY: RETI AWL (DOG KIRTLAND AfB D-6202 _4_ EXPERIMENTAL INVESTIGATION OF THE DIRECTIONAL CONTROL CAPABILITY OF 18 x 5.5, TYPE VII, AIRCRAFT TIRES ON WET SURFACES ? by Thomas A. Byrdsong Langley Reseurch Center Hampton, Va. 23365 NATIONAL AERONAUTICS AND SPACE ADMINIST
2、RATION WASHINGTON, D. C. 0 MARCH 1971 1 -_ Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-ERRATA NASA Technical Note D-6202 EXPERIMENTAL INVESTIGATION OF THE DIRECTIONAL CONTROL CAPABILITY OF 18 X 5.5, TYPE VII, AIRCRAFT TIRES ON WET SURFACES By Tho
3、mas A. Byrdsong March 1971 Pages 17 and 18: In the key for the three-groove, six-groove, and dimple tread tire data, the symbols were inadvertently omitted. They should be as follows: 0 Three-groove tread 0 Six-groove tread 0 Dimple tread NASA-Langley, 1911 Issued October 197 1 Provided by IHSNot fo
4、r ResaleNo reproduction or networking permitted without license from IHS-,-,-TECH LIBRARY KAFB. NM EXPERIMENTAL INVESTIGATION OF THE DIFtXCTIONAL - 1. Report No. NASA TN D-6202 4. Title and Subtitle 5. Report Date March 1971 . . 2. Government Accession No. I 3. Recipients Catalog No. 9. Perfaming Or
5、ganization Name and Address 10. Work Unit No. 126-61-12-01 - _ - - -. _ - ._ - 16. Abstract An experimental investigation was made to evaluate the free-rolling cornering capa- bility of a high-speed aircraft nose-wheel tire. Data were obtained for several 18 X 5.5, type VI1 tires with three tread de
6、signs (three-grooved, six-grooved, and dimple) at wheel yaw angles up to 30 and ground speeds up to 110 knots on various wet and flooded test sur- faces. angle and suggest a maximum cornering capability at an angle of approximately loo. surface texture, wetness condition, and ground speed are shown
7、to have a pronounced effect on the cornering capability of the test tires. and six-grooved-tread designs developed cornering capability that was comparable to and significantly greater than that of the dimple-tread tires. The results show a characteristic variation of cornering capability with wheel
8、 yaw The The results also show that the tires with three- - _ _ - -. - - . - . - 17. Key Words (Suggested by Authoris) Aircraft tires Wet runway surfaces Tire cornering ._ 19. Security Classif. (of this report) Unclassified . - 18. Distribution Statement Unclassified - Unlimited 1 20. Security Class
9、if. (of this page) Unclassified . For sale by the National Technical Information Service, Springfield, Virginia 22151 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-EXPERIMENTAL INVESTIGATION OF THE DIRECTIONAL CONTROL CAPABILITY OF 18 X 5.5, TYPE V
10、II, AIRCRAFT TIRES ON WET SURFACES By Thomas A. Byrdsong Langley Research Center SUMMARY An experimental investigation was made to evaluate the free-rolling cornering capa- bility of a high-speed aircraft nose-wheel tire. Data were obtained for several 18 X 5.5, type VII tires with three tread desig
11、ns (three-grooved, six-grooved, and dimple) at wheel yaw angles up to 30 and ground speeds up to 110 knots, on various wet and flooded test surfaces. The results show a characteristic variation of cornering capability with wheel yaw angle and suggest a maximum cornering capability at an angle of app
12、roximately loo. The surface texture, wetness condition, and ground speed are shown to have a pronounced effect on the cornering capability of the test tires. The results also show that the tires with three- and six-grooved-tread designs developed cornering capability that was com- parable to and sig
13、nificantly greater than that of the dimple-tread tires. INTRODUCTION A survey of incidents experienced by aircraft during landing or aborted take-off reveals that those resulting from a loss of directional control far exceed those resulting from a lack of braking capability. Stated concisely, more a
14、ircraft leave the side of the runway than the end of the runway. For directional control on the ground, an aircraft must produce a normal force or yawing moment which can be supplied by one or more of the following: rudder action, differential thrust, differential braking or nose-wheel steering. For
15、 operations on a dry runway, the steering or cornering capability of the nose-gear tires is the most convenient single force available to the pilot to control the direction of the airplane. However, tests have shown (refs. 1 to 4, for example) that the cornering capability of a tire deteriorates if
16、the runway surface becomes wet. This degradation in steering capability is of special significance to fighter-type aircraft which rely principally upon nose-wheel steering for directional control. The tests of refer- ences 1 to 4 were performed at various wetness conditions but only at one or two ya
17、w angles and, as such, do not completely describe tire cornering behavior. Particularly Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-I lacking is information which describes the variation of the available cornering force over a range of yaw angles
18、, including the angle at which maximum cornering is developed. The purpose of this paper is to present the results of an experimental study to evaluate the f ree-rolling cornering capability of a high-speed aircraft nose-wheel tire over a wide range of yaw angles on a variety of wet and flooded runw
19、ay surfaces. Also presented are the results from a comparative study to evaluate the effects of three tire- tread designs on the cornering force. Tests were performed on 18 X 5.5, type VII tires at ground speeds up to approximately 100 knots and at wheel yaw angles up to 30, and at zero caster and c
20、amber. The results of these tests are presented in terms of the cornering-force friction coefficient, which is the force measured perpendicular to the direction of motion divided by the vertical load on the tire. SYMBOLS Principal measurements and calculations were made in U.S. Customary Units and c
21、onverted to SI Units. V ground speed, knots W runway groove width, cm (inch) Cornering force Vertical force cornering-force friction coefficient, Q wheel yaw angle, degrees TEST APPARATUS Tire The test tires used in this investigation were size 18 X 5.5, 14-ply rating, type VII, aircraft tires which
22、 are used as nose-wheel tires on several current high-speed aircraft. These tires (see fig. 1) had three tread patterns: a six-grooved tread, a three-grooved tread, and a dimple tread. Several tires with each tread pattern were used during these tests. Each tire was tested with an inflation pressure
23、 of 1 MN/m2 (145 lbf/in2). The maximum tread wear was limited to approximately 50 percent of the original tread which, as indicated in reference 5, was considered to have a negligible effect on the test results. The worn appearance of the tires in figure 1 is due to the exposed fabric reinforcement
24、of the tread. i 2 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Test Surfaces Cornering data were obtained from nine test surfaces, each in a damp or flooded state. These surfaces were installed end to end along the test section of the Langley land
25、ing loads track and elevated 10.2 cm (4 in.) above the concrete base. Entrance and terminal ramps were installed to provide the tires with smooth access to and from the test surfaces. The test surfaces are pictured in figure 2 and identified and briefly described in the schematic of figure 3. Test s
26、urface 1 was a smooth finish concrete which contained very small aggregates and was painted to yield a very smooth finish. Surfaces 2 and 3 consisted of a mixture of a masonry sand and a commercial grade of (1/8 in.) over a concrete base. Coarse grain masonry sand was used in the mixture of surface
27、2 whereas surface 3 was prepared with fine grain sand. Surfaces 4, 5, and 6 were reinforced concrete slabs with transverse-flailed grooves 0.32 cm (1/8 in.), 0.64 em (1/4 in.), and 0.95 cm (3/8 in.) in width, respectively. The groove pattern for all three surfaces consisted of a pitch of 3.85 cm (13
28、 in.) and a depth of 0.32 cm (1/8 in.). Surfaces 7, 8, and 9 consisted of the MX-19 runway mat with coarse, medium, and regular size grain aggregate, respectively. Surface 9, the regular-size grain aggregate, is standard, whereas the other two mats were specifically resurfaced for these tests. Fig-
29、ure 4 is a photograph of a slab of grooved concrete (fig. 4(a) and a section of the MX-19 runway mat equipped with a regular-size grain aggregate (fig. 4(b). Some idea of the texture of each test surface may be obtained from the photographs presented in figure 5. I c , an epoxy compound (used to rep
30、air or patch concrete) spread to a depth of 0.32 cm Test Facility The investigation reported herein was performed at the Langley landing loads track with the high-speed test carriage. A description of this facility is given in references 6 to 8. A photograph of the test carriage is given in figure 6
31、. A closeup view of the test fixture with a six-groove tire installed is shown in figure 7. This fixture supported the test tire through a force balance which measured the vertical load applied to the tire and forces parallel and perpendicular to the wheel plane. The test fixture was designed to tur
32、e is given in reference 3. I provide the tire with fixed yaw angles as high as 80. A detailed description of the fix- TEST PROCEDURE The testing technique involved propelling the carriage to the desired velocity at which the tires rolled over the nine test surfaces, and recording the forces generate
33、d in the different tire-surface interfaces. Test velocities ranged from 8 to 110 knots and remained essentially constant throughout the test section. 3 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-The test wheel was set at a predetermined yaw angl
34、e which ranged from 0 to 30, and the pneumatic loading system (ref. 3) was adjusted so that a nominal vertical load of 14.7 kN (3300 lbf) was applied to the wheel when the tire was in contact with the test sur- faces. Tests were made when the surfaces were in the damp and flooded states. Damp surfac
35、es were obtained by first flooding the surface and then sweeping the excess water from the surfaces with a stiff brush. In the flooded state, dams (noted in fig. 2) were installed on either side of the test surfaces and the surfaces were kept flooded with water depth was greater than the groove dept
36、h of the tires. Immediately prior to launch, a recorder on board the carriage was started to provide a history of forces parallel and perpendicular to the test-wheel plane throughout the test run on the different surfaces. to a depth of approximately 0.8 cm (1/3 in.). This depth was selected so that
37、 the water 6 Tests were made with the three-grooved tread tire freely rolling on the test sur- faces at various yaw angles and two ground speeds. Tests were made with all tires at one selected representative yaw angle for a broad range of ground speeds. RESULTS AND DISCUSSION The cornering force as
38、defined herein is the force developed in the tire-surface interface perpendicular to the direction of vehicle motion. This force was computed from the data recorded as the tire traversed each of the nine test surfaces and was con- verted to coefficient form by dividing by the vertical force acting o
39、n the tire. Thus, all data from the cornering tests are presented in terms of the cornering-force friction coef- ficient py. In the sections which follow, data are presented to show: the effects of yaw (cornering) angle on the cornering capability of the test tire with a three-groove-tread pattern,
40、a widely used tread design for this tire; and the effect of tread design on the tire cornering characteristics, accomplished at a fixed yaw angle. Effect of Yaw Angle The variation in the cornering-force coefficient with wheel yaw angle on the differ- ent test surfaces under damp and flooded conditi
41、ons is presented in figures 8 and 9 for tires having a three-grooved-tread pattern. Data are presented at ground speeds of 38 and 75 knots for the damp surfaces (fig. 8) and at 8, 25, and 69 knots for the flooded sur- faces (fig. 9). The figures show that for all ground speeds the cornering coeffici
42、ent increased to a maximum as the yaw angle was increased and thereafter, where data are available, decreased gradually with further increases in yaw angle. This variation with yaw angle was characteristic for all test surfaces under both wetness conditions. The faired data from the damp test surfac
43、es suggest that the maximum cornering capability for the three-grooved tires is developed at a yaw angle of approximately loo, regardless of the ground speed. This yaw angle also appears to define the maximum cornering 4 Provided by IHSNot for ResaleNo reproduction or networking permitted without li
44、cense from IHS-,-,-coefficient on the flooded surfaces except for the low-speed test data where the maximum coefficient is seen to occur at somewhat higher yaw angles. Figures 8 and 9 also show that the cornering-force coefficient decreases with increases in ground speed over the test range of yaw a
45、ngles and corroborates the results from cornering data obtained at a limited number of yaw angles as presented, for exam- ple, in references 1 to 4. A comparison of the data of figure 8 with that for corresponding surfaces in figure 9 gives an indication of the loss in cornering capability attribute
46、d to hydroplaning. The critical hydroplaning speed for this tire, defined in reference 9, based on the tire inflation pressure of 1 MN/m2 (145 lbf/in2), is approximately 108 knots. On the flooded grooved surfaces a lower cornering-force coefficient was obtained than on the damp grooved surfaces, whi
47、ch is an apparent contradiction of the concept that grooved surfaces postpone the effects of hydroplaning. However, these data confirm the results of reference 10 for grooves of comparably shallow depth, 0.34 cm (1/8 in.) deep, and a relatively heavy flooded surface condition, 0.51 cm to 0.76 cm (0.
48、2 in. to 0.3 in.). r An examination of the relative cornering capability of the tire on the different test surfaces suggests several general comments. The epoxy-finished concrete having a coarse-grain sand aggregate provided the largest cornering-force coefficient of all sur- faces tested in both th
49、e damp and flooded states. The cornering-force coefficients asso- ciated with the medium-grain runway mat were the lowest for all surfaces tested. Fin- ally, the figure shows that there is no pronounced effect on the cornering-force coefficient due to changes in the width of the flailed grooves ranging between 0.32 cm (1/8 in.) and 0.95 cm (3/8 in.). Effect of Tire-Tread Pa
