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National Advisory Committee for Aeronautics, Technical Notes - Low Speed Yawed-Rolling Characteristics and Other Elastic Properties of a Pair of 40 Inch Diameter, 14 Ply Rating, Type VII Aircraft Tires

The low—speed (up to h miles per hour) yawed—rolling characteristics
of two #0 x 12, lh—ply—rating, type VII aircraft tires under straight—
yawed rolling were determined over a range of inflation pressures and
yaw angles for two vertical loadings. One load was approximately equal
to the rated vertical load and the other load was approximateLy equal to
twice the rated vertical load for these tires. Static tests were also
performed to determine the vertical, lateral, torsional, and fore—and—
aft elastic characteristics of the tires. The quantities measured or
determined included lateral or cornering force, drag force, twisting
moment or self-alining torque, pneumatic caster, vertical tire deflec—
tion, lateral tire distortion, wheel twist or yaw angle, rolling radius,
and relaxation length. Some supplementary tests which included measure—
ments of tire footprint area and the variation of unloaded tire radius
and width with inflation pressure were made.

During straight—yawed rolling the normal force generalLy increased
with increasing yaw angle within the test range. _The pneumatic caster
tended to decrease with increasing yaw angle. The sliding—drag coeffi—
cient of friction tended to decrease with increasing bearing pressure.

Measured lateral and torsional spring constants appeared to
decrease with increasing amplitude of tire lateral distortion or twist,
respectively.

In order to cope with airplane landing and taxiing problems such as
landings with yaw, wheel shimmy, and ground handling, designers of
landing gears must have reliable data on many elastic properties of air-
plane tires under such conditions. Until recently, the experimental
data on such tire elastic properties, most of which are summarized and
discussed in reference 1, were limited in both scope and quantity.
Recently, a program was initiated by the National Advisory Committee for
Aeronautics to alleviate this lack of experimental data by determining
experimental values of some essential tire parameters for a range of
tire sizes under static, kinematic (low—speed steady—state), and dynamic
(transient and high-speed) conditions.