The aerodynamics of the compound helicopter configuration

Abstract

AbstractA computational method has been developed to investigate the aerodynamic interaction between a helicopter rotor and the fuselage in steady-state level forward flight. In order to model a compound helicopter the fuselage is fitted with wings. The model uses deformable vortex rings for the rotor wake, a source panel representation of the fuselage and a lifting surface method for the wings which can handle arbitrary geometries. The wake representation is based on a free wake analysis, relaxing the nodal points on the vortex rings and wing wake elements according to the induced velocities in the flow field after every time step. In this way, neither wake is restricted to planar shape. At each time step the fuselage and wing forces were calculated. The trim attitude of the fuselage was determined by the pressure field surrounding it using a potential flow model for the external flow and a fully developed turbulent boundary layer model on the fuselage surface. Parametric studies were carried out to determine the influence of wing position, wing span, wing angle of incidence and advance ratio on the results. The computer program incorporates a graphical postprocessing output routine allowing the visualisation of the wake shape, the induced velocity and the angles of incidence on the rotor disc to be made, together with the velocities at various wing stations and the lift coefficients along the span.