A Simplified Approach to the Aerodynamic Rotor Interference of Tandem Helicopters

In any multi-lifting-rotor helicopter configuration, the problem of aerodynamic rotor interference and its influence on performance is of vital interest. Knowledge of its magnitude as well as understanding of the importance of various design parameters influencing this phenomenon may become an important element in shaping a decision regarding the basic concept of a new design. For this reason, the problem of rotor interference has been the sub)ect of both theoretical and experimental investigations. Attention has been focused first of all on the tandem as the most popular representative of the multi-lifting-rotor family. In particular, the sub]ect of the aerodynamic rotor interference in forward flight has been most intensely investigated, as, for the relatively large sub-group of tandems with non-overlapping rotors, performance problems in this regime of flight are most different than those of a single-rotored helicopter. But, when the lifting rotors are in a co-planar intermeshing, or an overlapping configuration, an additional problem of their aerodynamic interaction in hovering and vertical flight grows in importance. In the domain of analytical studies of the tandem in translatory movement, the works of Mangler, Squire, Meijer Drees, Castels and DeLeeuw contributed to the knowledge of predicting the downwash distribution and induced power of this configuration in forward flight.