Study on Aerodynamic Interaction of Rotor and Fuselage in Hover and Its Application to Flap Width Determination of Winged Helicopters

The vertical drag or download on the structure under the rotor of a helicopter caused by the downwash deteriorates hovering performance. On the other hand, the partial ground effect provided by the structure under the rotor improves hovering performance. The design of the fuselage planform should simultaneously consider these aerodynamic interactions, namely the effect of download and the ground effect. This is more important for winged helicopters, which have a large planform area. In this research, as a first step, the download and the partial ground effect of a disk-like structure are investigated to obtain general knowledge of aerodynamic interaction. Experimental parameters are the disk radius, the distance between the rotor and the disk, and the root cutout of the rotor. It is revealed that when the root cutout is relatively small, if the disk radius is up to about half the size of the rotor radius, hovering performance does not deteriorate. Then, as a second step, it is shown that this general knowledge of the disk can be successfully applied to the problem of determining the flap width of winged helicopters.