VTOL Downwash / Outwash Operational Effects Model

A hovering Vertical TakeOff and Landing (VTOL) aircraft produces hazards due to downwash / outwash in the ground environment. Downwash is the downward flow of air from the thrusters of a hovering VTOL aircraft. When the downward flow of air meets the ground plane, it turns and spreads as outwash. This paper presents the development of a semi-empirical math model of the outwash velocity profile. The math model represents the shape and magnitude of the outwash. Using the derived math model, a computer code predicts the effects (heaviest object moved, how far baseline object moves, danger areas around aircraft, etc.) of different hovering aircraft on rocks, branches and personnel in the ground environment. The aircraft consist of helicopter, tilt rotor, tilt wing, and fan-in-wing VTOL concepts, each sized to 20,000 lb gross weight. The effects of the outwash on the different objects are then compared to determine some of the operational characteristics of different aircraft configurations.