THE AERODYNAMICS OF THE COMPOUND HELICOPTER CONFIGURATION

A computational method has been developed to investigate the aerodynam ic interaction between a helicopter rotor and the fuselage in steady-s tate level forward flight((1)). In order to model a compound helicopte r the fuselage is fitted with wings. The model uses deformable vortex rings for the rotor wake, a source panel representation of the fuselag e and a lifting surface method for the wings which can handle arbitrar y 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 tim e step. In this way, neither wake is restricted to planar shape. At ea ch time step the fuselage and wing forces were calculated. The trim at titude of the fuselage was determined by the pressure field surroundin g it using a potential flow model for the external flow and a fully de veloped turbulent boundary layer model on the fuselage surface. Parame tric studies were carried out to determine the influence of wing posit ion, wing span, wing angle of incidence and advance ratio on the resul ts. The computer program incorporates a graphical post processing outp ut routine allowing the visualisation of the wake shape, the induced v elocity and the angles of incidence on the rotor disc to be made, toge ther with the velocities at various wing stations and the lift coeffic ients along the span.