Rotor Without Reaction Torque - Historical Review of H.G. Küssner's Rotorcraft Research

As early as 1934, Prof. Dr. Hans-Georg Küssner from the Aerodynamische Versuchsanstalt Göttingen (AVA) in Germany was thinking about an alternative to helicopter rotor torque compensation, that was tried experimentally already in 1921 by Passat in England. Based on the theoretical work about two-dimensional unsteady airfoil aerodynamics, especially combined plunge and pitch of an airfoil that revealed a propulsive force as is used by bird flight, he was tempted to try this concept on driving a helicopter rotor via forced flapping of its rotor blades. Experiments have been carried out in the mid-30ies and patents applied for the concept which were granted a long time later after an intense and controversy dispute with the responsible officials. This paper describes Küssner's efforts regarding the forced flapping concept and experimental results he obtained in the AVA wind tunnel in hovering condition.