Editorial Type:
Article Category: Other
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Online Publication Date: 01 Jul 2014

Experimental Friction and Temperature Investigation on Aircraft Tires

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Page Range: 116 – 144
DOI: 10.2346/tire.14.420301
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ABSTRACT

For modeling an aircraft tire using the brush model method, the friction coefficient μ between rubber and asphalt should not only be described in terms of the applied pressure and sliding velocity/slip ratio, but also by local temperature inside the contact area. Its influence cannot be neglected, since it leads to significant material property changes. Therefore, investigations on different test rigs are analyzed using thermal recordings of an infrared camera.

First measurements are done on a high speed linear tester (HiLiTe), a test rig at the Institute of Dynamics and Vibration Research (IDS) at Leibniz University Hanover, Germany. It allows testing single tread block samples with a constant slip ratio of 100%, that is, pure sliding, on a variety of surfaces such as dry and wet asphalt or concrete, as well as on snow and ice.

Results in this paper show that the convection has a smaller impact on tread block cooling than the actual contact between runway surface and sample. Since colder surface temperatures lead to higher friction, this effect antagonizes the excitation frequency, which heats up the rubber sample at high velocities. On long-lasting test sequences a quasi–steady-state friction coefficient might be achieved once these effects start to converge. Still, owing to permanent slip, the abrasion leads to cooling as the hot top layer of the rubber is removed occasionally.

In addition to these quasi–steady-state measurements on HiLiTe, the thermal behavior of an aircraft tire is investigated with an autonomously running test rig. It allows realistic testing on an airfield runway by altering load, speed, and slip angle of the tire within and beyond the regions of a passenger aircraft. During the measurements, new and partially unknown effects could be observed. The temperature is mostly influenced by the slip angle followed by speed and load. Furthermore, the contact between tire and runway leads to cooling of the tread but does not affect the temperature inside the grooves. They heat up separately and tend to transfer heat to the tread if the cooling by the runway becomes too low.

Keywords: aircraft; thermal investigation; friction; tire; tread block; rubber
FIG. 1
FIG. 1

(a) HiLiTe carriage in detail, (b) Complete view on HiLiTe with test track.

FIG. 2
FIG. 2

(a) Complete test setup and position of thermal camera, including the defined regions of interest for top of tire tread (ROI1x/ROI2x) and contact area of tire including surface (ROI1y/ROI2y), (b) Picture of recorded thermal movie with added ROI, (c) Example of warm tire tread moved out of camera field of view due to large slip angles.

FIG. 3
FIG. 3

(a) Side view of test setup, test rig moving forward, (b) Side view of test setup, test rig moving backward, (c) Front view of tire during forward movement, including ROI for top of tire tread (ROI1x) and ROI for contact area (ROI1y), (d) Front view of tire during backward movement, including ROI for top of tire tread (ROI2x) and ROI for contact area (ROI2y).

FIG. 4
FIG. 4

Tread sample on sample plate.

FIG. 5
FIG. 5

Coefficient of friction during test run.

FIG. 6
FIG. 6

Steady friction characteristics of tread compound at 20 °C ambient temperature.

FIG. 7
FIG. 7

Friction characteristics dry conditions vs. wet conditions at T = 20 °C.

FIG. 8
FIG. 8

Friction characteristics for dry conditions at two runway temperatures: −20 °C vs. +40 °C.

FIG. 9
FIG. 9

Friction characteristics dry vs. icy at subzero temperatures.

FIG. 10
FIG. 10

Static coefficient of friction in terms of the time of rest.

FIG. 11
FIG. 11

Test setup for contact temperature measurements.

FIG. 12
FIG. 12

Infrared image of temperature distribution in runway–tread contact.

FIG. 13
FIG. 13

Contact temperature in terms of pressure and velocity.

FIG. 14
FIG. 14

Coefficient of friction and contact temperature vs. sliding distance.

FIG. 15
FIG. 15

Complete test run with changing slip angle α at constant speed v and load L.

FIG. 16
FIG. 16

Lowering tire and staring to roll; temperature development on tire tread.

FIG. 17
FIG. 17

Temperature profiles across tire tread for different conditions.

FIG. 18
FIG. 18

Effects of cold contact patch on tire tread, leads to nonuniform temperature on tire outline.

FIG. 19
FIG. 19

(a) Assignment of ROI, (b) Temperature development of groove and tread during acceleration from v = 0 km/h to v = 70 km/h (α = 0°, constant load).

FIG. 20
FIG. 20

Temperature development of tread and groove while decelerating (v = 70 km/h to v = 0 km/h) and in standstill.

FIG. 21
FIG. 21

(a) Assignment of ROI, (b) Definition of different tread circumferences, according to direction of tire.

FIG. 22
FIG. 22

(a) S-shaped temperature profile across tire tread, (b) Bow-shaped temperature profile across tire tread.

FIG. 23
FIG. 23

(a) Evolution of temperature profiles across tire tread changing from a clear S-shape to bow shape, (b) with corresponding parameters load, speed, and slip angle.

FIG. 24
FIG. 24

(a) Evolution of increasing profile characteristics (difference of maximum and minimum temperatures), (b) with corresponding parameters load, speed, and slip angle.

FIG. 25
FIG. 25

Influencing potential of angle and load on tread temperatures.

FIG. 26
FIG. 26

Influencing potential of speed and load on tread temperatures.

FIG. 27
FIG. 27

Influencing potential of slip angle and speed on tread temperatures.

FIG. 28
FIG. 28

Overall combined parameter ranking.

Contributor Notes

2 Corresponding author. Email: linke@ids.uni-hannover.de
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