Ground effect refers to the apparent increase in lift that an aircraft experiences when it flies close to the ground. For helicopters, this effect has been modeled since the 1950's based on the work of Cheeseman and Bennett, perhaps the most common method for predicting hover performance due to ground effect. This model, however, is based on assumptions that do not hold for small-scale rotorcraft because it was developed specifically for conventional helicopters. It is not clear if the Cheeseman-Bennett model can be applied to today's multirotor UAVs. In this paper, we compare the Cheeseman-Bennett model to experimental results for rotor performance due to ground effect in several small-scale multirotor and single-rotor configurations. Experimental findings suggest that some of the conventional thinking surrounding helicopter ground effect cannot be applied directly to rotorcraft using fixed propellers at variable speeds (e.g. multirotors), and that it is necessary to adjust the helicopter models to better reflect the differences in such aircraft. The experimental results for multirotors presented are for multiple propeller configurations, speeds and spacings. Ultimately, this work will facilitate the development of an improved UAV flight controller that can accurately account for ground effect to improve flight stability near surfaces and structures.

A semi-autonomous mobile self-leveling landing platform designed to launch, recover and re-launch VTOL UAVs without the need for human intervention is described. The landing platform is rugged, lightweight and inexpensive, making it ideal for civilian applications that require a base station from which a rotorcraft UAV can be launched and/or recovered on terrain that is normally unsuitable for UAV take-off and landing. This landing platform is capable of autonomously self-leveling on rough terrain and inclines up to 25°, and can operate in isolated remote locations for extended periods of time using large onboard lithium batteries and wireless communication. The unique design aspects of this landing platform are that it is mobile, self-leveling, and man-portable. A fully-operational prototype has been designed, constructed and evaluated. Design details and experimental results are presented to demonstrate the landing platform's functionality, and that all primary design requirements have been met.