Rotorcraft flight in interaction with obstacles

Abstract

Helicopter flight in time and spatially varying inflow environments sets special requirements for its designand it is closely linked to its utilization and operation envelope (classification). Commonly, definition of the abovementioned non-conventional inflow conditions in the standards relies on evidence coming from pilots’ reports while theoretical or experimental studies usually follow either to confirm or to revise or to update provisions of the standards. Such a non conventional flight scenario, which is the focus of the present paper, is when a helicopter performs hover flight in proximity to obstacles. Helicopters are largely employed in missions within confined areas, regions in which the flight of the helicopter is limited in some direction by the terrain or by the presence of obstacles. During approaching or landing under the above described circumstances an unsteady flow field is developed in the region between the rotor and the obstacle that has not been studied in detail. Moreover, interaction between the rotor and the obstacle is not yet well understood especially in cases that obstacles generate wakes. As a result of this interaction unsteady aerodynamic loads are developed over the obstacles and flight characteristics and controllability of the rotor might be affected.