Soil/Wheel Interaction at High Speed

Tests of wheels towed through soft soils at high speed have revealed interaction phenomena that are important for design of various high speed vehicles, especially aircraft which are strongly influenced during takeoff and landing by the wheel drag loads. Available data shows that high drag loads are encountered upon starting, followed by a minimum at approximately 20 knots and then a second drag load peak in the 40-80 knot range. Recent tests at the NASA Landing Loads Track have shown that the rut depths have the same velocity relationships as the drag loads. Tests were conducted with a 29 X 11-10 8PR tire loaded to 5000 lb on buckshot clay at CBR 1.5, 2.3, and 4.4 and at CBR 1.5 on sand. An analytical model to predict wheel drag load and rutting is developed from a combination of currently used empirical drag load and rut depth prediction methods and high speed interaction factors which produces fair agreement with measured ruts and drag loads over the velocity range from zero to approximately 100 knots. Both the tests and analysis indicate that the interaction is most pronounced for soft surfaces and high tire pressures; it is reduced if either the tire pressure is reduced or if the soil strength increases.