Whirl Flutter Investigation of Hingeless Proprotors

Hingeless proprotor whirl flutter in cruise flight is investigated using comprehensive rotorcraft analysis codes CAM- RAD II and RCAS. Generic hingeless proprotor designs include conventional soft-inplane and stiff-inplane rotors operating at cruise tip speeds typical of existing tiltrotor systems, and a rotor which exhibits higher frequencies and operates at much lower cruise tip speed than existing rotor designs. The effects of blade elasticity, density, speed of sound, unsteady aerodynamics, and realistic airfoil tables on whirl flutter speed are examined. The US Army and NASA have been developing a new wind tunnel test system, TiltRotor Aeroelastic Stability Testbed (TRAST), and preliminary analysis for a notional TRAST hingeless rotor is also presented. The effects of precone, center of gravity, rotor rotational speed, and density on the TRAST whirl flutter stability are examined. CAMRAD II and RCAS show consistently excellent agreement with each other for wide variations of design variables and operating conditions.