The YAH-64A Composite Flexbeam Tail Rotor

A composite flexbeam tail rotor design (CFTR) is currently being refined at Hughes Helicopters (HH) for the YAH-64, Advanced Attack Helicopter (AAH). Advantages of the CFTR over conventional articulated (or teetering) rotors are reduced part count, less complexity, lower cost, less maintenance, and lower weight. This rotor is based on improvements over previous technology to avoid dynamics and loads problems, and uses modern composite manufacturing methods with particular emphasis on the wet filament winding, cocure process. The rotor design is being done under a U. S. Army AVRADCOMManufacturing Methods and Technology (MM&T) contract. This paper addresses the development of the CFTR design, a prototype of which was built and whirl tested as a company IR&D project. Uniqueness of the design is reflected in its patented hub design. The elastomeric shear attachment of the flexbearn to the hub results in a soft-inplane S-mode and a stiff-inplane C-mode configuration. The properties of the elastomer have been chosen for proper frequency placement and sta.ble damping of the inplane S-mode. The stress-critical pitch case/blade interface has been carefully designed to minimize loads. The flexbeam spanwise thickness and width distribution has been tailored for near-uniform corner stresses. The carry-through design of the flexbearn across the rotor hub allows the flexbeam to deform within the hub to reduce the hub loads to a minimum. Kinematic pitch-lag coupling is introduced to improve the inplane C-mode damping at high collective pitch.