Abstract:

The motion of a pneumatic tyre, when rolling freely through surface water, is resisted by two forces. These are a force arising from the flexing of the tyre as its circumference enters and leaves the footprint and a fluid dynamic force arising from the impact of the tyre with the water or slush as the tyre clears a path through the fluid. In this Data Item, the decelerating forces generated by aircraft type tyres when passing through a fluid medium are considered.

Experimental evidence can be drawn upon to show that, for a given style of tyre, fluid dynamic forces are affected by at least the following variables:

• speed,
• depth of contaminant,
• density of contaminant,
• tyre inflation pressure,
• vertical loading,
• tyre width,
• tyre diameter.

An empirical model for determining the decelerating force on rolling pneumatic tyres due to displacing water and slush is derived using a wide range of experimental data. Although limited to cross-ply construction, the range of tyre size includes all but the largest of tyres likely to be encountered in aviation.

The approach adopted is empirical, however, the theoretical framework that underlies the empiricism, although simple, is derived from rational, physical considerations. A strong correlation is observed between predicted and measured forces.