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Ultralight aircraft are popular with many flying enthusiasts because of their relatively low cost to own and fly. One of the most common designs is the high wing cable supported ultralight. Because of its simple shape and method of construction owners like to modify the structure and aerodynamic surfaces to attempt to improve the performance of the aircraft. One of the more common modification requests is for the conversion from a cable supported to a strut supported aircraft. The objective of the modification is to reduce the drag and improve the performance of the ultralight. The purpose of this study is to determine the structural performance of the cable supported aircraft and compare it to the structural performance of a strut supported version of the same aircraft and to provide an estimate of the change in drag associated with the conversion from cable supported to strut supported.

Presently, there exist two classical analytical results that provide information regarding the lateral stability of car/trailer systems. These results are the directional stability equation for the automobile and the frequency and damping relationships for yaw oscillations of a trailer towed by a vehicle of infinite mass. Neither of these classical results provides an adequate description of car/trailer dynamic behavior because the associated classical models do not allow for any car/trailer interaction. In this paper, basic analytical results for car/trailer lateral stability are developed. These results are validated by comparing critical speeds predicted by the new analytical solution with those obtained numerically using a standard eigenvalue technique. General observations based upon the analytical results are then presented.

Comparisons are made between a three wheeled vehicle with two wheels on the front axle, a three wheeled vehicle with two wheels on the rear axle, and a standard four wheeled vehicle. Each vehicle’s lateral stability, rollover stability during lateral acceleration, rollover stability while braking in a turn, and rollover stability while accelerating in a turn are determined. It is shown that for lateral stability, the three wheeled vehicle with two wheels on the rear axle is more stable than the four wheeled vehicle, which is in turn more stable than the three wheeled vehicle with two wheels on the front axle. For rollover stability the four wheeled vehicle is always stable as long as the vehicle’s track width is greater than twice its center of mass height. The three wheeled vehicles are less stable than the four wheeled vehicle in terms of rollover stability.