Wind Tunnel Investigations of a High Speed Stowed Rotor Aircraft 680280

Model rotor tests were conducted to investigate aeroelastic and aerodynamic behavior of a stowed rotor aircraft during stopping and stowing of the rotor. Results at various tunnel speeds, using rotors of varying stiffness, indicated the lower limits of blade stiffness necessary to provide adequate airframe clearance and manageable hub moments during conversion. The effects of blade pitch control during conversion were evaluated, and the control values required to minimize stress and moments were established. Various rotor stopping positions were examined and improved aircraft stability and drag were shown to result from initiating blade fold with one blade stopped over the nose. An oscillatory response phenomenon encountered during blade fold was thoroughly explored, and means to prevent the oscillation were successfully tested. The tests gave further evidence that the stowed rotor concept is feasible, but showed that stiff blades may be required for successful conversion in rough air.