This paper deals with the investigation of performance and sta- bility characteristics of a two-seater, two-bladed, lightweight he- licopter developed in the framework of VLR certification spec- ifications. The main rotor features a gimballed hub with elas- tomeric bearings equipped with a Bell-Hiller to improve stabil- ity, 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 derived that includes, among other aspects, a detailed model of main rotor, nonlin- ear, 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 mo- tion on helicopter steady–states. Results on performance and controllability are presented and discussed. Finally, the stability characteristics of the vehicle are assessed in order to gain some preliminary insight on the handling qualities of the helicopter.
Performance Analysis of a Lightweight Helicopter Featuring a Two-Bladed Gimballed Rotor
AVANZINI, Giulio;
2011-01-01
Abstract
This paper deals with the investigation of performance and sta- bility characteristics of a two-seater, two-bladed, lightweight he- licopter developed in the framework of VLR certification spec- ifications. The main rotor features a gimballed hub with elas- tomeric bearings equipped with a Bell-Hiller to improve stabil- ity, 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 derived that includes, among other aspects, a detailed model of main rotor, nonlin- ear, 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 mo- tion on helicopter steady–states. Results on performance and controllability are presented and discussed. Finally, the stability characteristics of the vehicle are assessed in order to gain some preliminary insight on the handling qualities of the helicopter.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
