Velocity effect of vehicle rolling resistance in sand

Vehicle rolling resistance is important to vehicle and aircraft ground movement in loose soil and sand conditions, especially in military operations. Off-road rolling resistance measurements have been taken at relatively low velocities, 2.1–4.6 m/s (meters per second) (7–15 ft/s) (4–9 knots), which has precluded studying any potential velocity effect on rolling resistance. With the emergence of aircraft designed to be used on unimproved soil runways and the military’s proposed new vehicles, especially the lighter-weight, 23–500-kg (50–1100-lbs) robotics, capable of high-velocity off-road movement, it is important that the rolling resistance be measured at velocities closer to the expected operating conditions. This paper presents data from rubber tire rolling resistance measurements in three depths of uniform-density dry sand at velocities from 2.1 up to 18 m/s (7–58 ft/s) (4–34 knots) and three load ranges from 4534 to 10,266 N (1020–2308 lbs). In dry sand the rolling resistance increases with velocity until the tire starts to “plane,” where it levels off or decreases and it is modified by load. Limited past work in this area is presented along with some existing analytical descriptions of rolling resistance versus velocity. Limited agreement between the published equations and the test data, along with contradictory published results, indicate that additional work on this topic is needed.