Model Tests and Analysis of Prop-Rotor Dynamics for Tilt-Rotor Aircraft

This paper presents some results of wind tunnel tests and analytical studies of a Grumman aircraft design called HELICAT which features a prop rotor mounted in a tilting pod at each wing tip. The rotor incorporates an offset flapping hinge with positive (pitch reducing) delta-3. The test program was divided between evaluation of the Helicat prototype design and investigation of a "research" whirl flutter configuration. Most of this paper is devoted to the whirl flutter investigation. One case of blade flutter was encountered in the Helicat configuration; 83 cases of whirl flutter were obtained in the research configuration. Forward, backward, and bimodal whirl flutter were encountered. The parametric study of whirl flutter included variations in blade pitch-flap coupling, hinge offset, rotor pod pitch and yaw stiffness, and damping. Analytical correlation studies showed good agreement with the test data. Testing of this semi-span dynamically similar model was performed in the 16-foot Transonic Dynamics Tunnel at NASA, Langley, under a NASA/Grumman cooperative program during the period 3 February through 8 April 1971.