Effects of Flywheel Curvature on Aircraft Tire Footprint Behavior

Although aircraft tires are traditionally tested on external dynamometers, the effects of the curved test surface on normal contact pressure distribution and footprint area of a tire have not been previously addressed. Using the Tire Force Machine (TFM) at the Wright Laboratory Landing Gear Development Facility (LGDF), trends for pressure distribution and footprint area were investigated for concave, convex and flat plate surfaces. This evaluation was performed using the F-16 bias, F-16 radial and B-57 bias main landing gear tires at rated load and inflation pressures. The trends for overall tire footprint behavior indicate that the more convex the surface, the smaller the contact area and the larger the normal contact pressures. Conversely, the more concave the surface, the larger the contact area and the smaller the normal contact pressures. Based on these results, the study recommends a 168″ diameter concave (internal roadwheel) dynamometer for tire wear/durability tests. Additionally, after normalization of the results, the following were developed: 1) a potential load/inflation pressure adjustment technique for wear testing on curved surfaces, and 2) an analytical representation of the normal contact pressure distribution of the individual tire ribs.