Heave-Pitch Motions of a Platform Flying in Extreme Ground Effect

Abstract

High-payload platforms flying in extreme-ground-effect represent a promising concept for high-speed amphibious transportation. Their dynamics is governed, to a large extent, by unsteady airflow under the platform. A quasi-one-dimensional model for the underplatform channel-flow is applied to predict heave and pitch motions of a vehicle in the presence of external disturbances, such as nonuniformities on the underlying ground-surface. It is found that a complete nonlinear theory should be used instead of a linear model to accurately predict motions when ground nonuniformities are relatively short. A flat platform with a flap moving in extreme-ground-effect is intrinsically unstable. An aft-wing out of ground-effect can be added to the system to achieve stability. Movable control surfaces, such as a platform flap, can be also modeled by the nonlinear theory. It is demonstrated that an oscillating flap can reduce heave and pitch amplitudes in flight over a wavy ground-surface.