Effect of Tire Pressure on Aircraft Ground Handling

Abstract

Handling of ground vehicles is dominated by the ability of the tires to generate cornering and braking forces. Tire forces are primarily a function of the contact patch slip angle, the longitudinal slip ratio, normal load, and inflation pressure. As part of a program to assess the ground handling of a Navy trainer, comprehensive tire tests were conducted on a set of nose and main gear tires. The results of this testing indicated that improvements in ground handling may be seen by setting the nose tire pressure to the higher carrier service pressure, while the main gear tires remained at the lower field service pressure. Specifically, the nose gear tire data revealed a significant reduction in nose tire cornering stiffness at the higher pressure. To test for such an improvement, a flight test program was undertaken in which the proposed tire configuration was evaluated against the baseline aircraft configuration. Rudder pedal frequency sweeps were used to determine heading attitude bandwidth parameters at several speeds and a Runway Offset Capture and Hold maneuver was used to generate pilot handling qualities assessments. The frequency sweep data indicated a significant improvement in heading attitude bandwidth as a function of airspeed for the high pressure nose tire configuration. For one evaluation pilot, the Runway Offset Capture and Hold ratings indicated a one to two handling qualities rating point improvement and a one PIO tendency rating point improvement with the high pressure nose tire configuration. The ratings of the second evaluation pilot did not vary significantly between configurations, however his comments indicated a clear preference for the high pressure nose tire configuration. It was demonstrated through time history comparisons that the rating differences between the two evaluation pilots resulted primarily from differences in pilot technique, particularly in the level of aggressiveness.