This paper deals with the investigation of performance and stability characteristics of a two-seater, two-bladed, lightweight helicopter developed in the framework of VLR certification specifications. The main rotor features a gimballed hub with elas-tomeric bearings equipped with a Bell-Hiller bar to improve stability, while the fixed pitch, rpm controlled, five-bladed tail rotor is a fenestron design. The main technical drivers of the novel design are to reduce the high level of 2/rev vibrations occurring in teetering rotors, to retain adequate control power in low-g maneuvering and to improve handling qualities using the stabilizing bar to increase roll and pitch damping. A specific aspect of the gimballed rotor is the presence of a sustained wobbling motion of the hub, even in steady-state conditions. A nonlinear model of the vehicle is developed that includes, among other aspects, a detailed model of main rotor, nonlinear, quasi-static blade aerodynamics, inflow dynamics, a simple fuselage aerodynamic model and a tail rotor model derived from experimental wind-tunnel tests. Periodic trim conditions are evaluated using a shooting method in order to assess the impact of rotor wobbling motion on helicopter steady-states. Results on performance and controllability are presented and discussed. Finally, the stability characteristics are assessed in order to gain some preliminary insight on the handling qualities of the helicopter.
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