DESIGN VERIFICATION AND FLIGHT TESTING OF A BEARINGLESS SOFT INPLANE TAIL ROTOR

A composite experimental tail rotor has been developed with the objectives of improved aerodynamic efficiency, gains in simplicity and reduction in weight and cost. To reach these aims a four-bladed bearingless soft inplane rotor was selected. The design uses a fiberglass bending-torsion-flexbeam to accomodate bending deflections and collective pitch control. Theoretical studies are presented dealing with dynamic characteristics, aeromechanic and aeroelastic stability problems, and load and stress aspects. An extensive ground testing program using a whirl tower with precession capability to generate dynamic loads is described. In addition the ability to simulate ground resonance conditions to test aeromechanic stability was investigated. Finally, basic ground and flight testing on a BK117 helicopter is presented. These tests were performed to verify ground and air resonance stability and to check the rotor loads as well as the aerodynamic and flightmechanic characteristics.