FATIGUE AND COST IMPROVEMENTS IN PRODUCING TITANIUM LEADING EDGES FOR HELICOPTER ROTOR BLADES

Prototype titanium leading edge caps for the helicopter composite main rotor blades, have been fabricated by hot forming processes using ceramic dies at 1,450°F. Extensive chemical processing is required to remove the contaminated alpha case formation. There is evidence that the fatigue characteristics of the material are degraded by the high forming temperatures. The preliminary work reported herein, conducted by Boeing Vertol Company and Kaman Aerospace Corporation, indicates that significant cost reductions can be made by the utilization of a cold stretch forming process, using low cost epoxy coated aluminum-steel dies. This process results in minimum alpha case formation and can significantly reduce tooling costs and capital investment for equipment. There is also evidence that the structural, static and fatigue properties of the cold formed material have improved over those reported for hot formed leading edge cap sections.