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National Advisory Committee for Aeronautics, Technical Notes - Low Speed Yawed Rolling and Some Other Elastic Characteristics of Two 56 Inch Diameter, 24 Ply Rating Aircraft Tires

The lowespeed (up to h miles per hour) cornering characteristics of
two 56 X 16, type VII, extra—high—pressure, 2h~ply—rating tires were
determined for a range of vertical loadings, yaw angles, and tire infla-
tion pressures. Locked—wheel drag tests were also made for one vertical-
load condition. The quantities measured included cornering force, drag
force, self-alining torque, pneumatic caster, vertical tire deflection,
rolling radius, and relaxation length. Some supplementary tests were
made which included measurements of tire footprint area, vertical—load-
deflection characteristics, and the variation of tire radius and width
with inflation pressure.

Results indicated that the normal force reached a maximum at between
1&0 and 18° yaw. The self—alining torque increased with yaw angle up to
between 5° and 8° yaw where a maximum was reached. Increasing the yaw
angle beyond this point tended to decrease the self-alining torque con—
siderably. The pneumatic caster was a maximum at small yaw angles and
tended to decrease in value with increasing yaw angle. The yawed—rolling
and sliding drag coefficients of friction both tended to decrease in mag—
nitude with increasing average bearing pressure. In general, the test
results indicate that the relaxation length decreases with increasing
vertical tire deflection and increasing inflation pressure.

Existing experimental data on aircraft tire behavior under static,
kinematic, and dynamic conditions, most of which are discussed in refer—
ence l, are limited in both scope and quantity particularly for large
tires. This lack of scope has hindered those engaged in design problems
concerning landings with yaw, ground handling, and wheel shimmy. A pro—
gram was therefore undertaken to determine values of the essential tire
parameters for a range of tire sizes under static, kinematic, and dynamic
conditions.