Design Improvement and Test Evaluation of FBR Bearingless Main Rotor

A new main rotor system has been developed and tested in flight at Fuji Heavy Industries Ltd. (FHI) The rotor system, designated the FBR (Fuji Bearingless Rotor), is an all composite, four-bladed, soft in-plane bearingless main rotor for 10,000 to 12,500 lb gross weight helicopters. Based on the advanced composite technology at FHI along with the extensive research on aerodynamics, noise, and vibration, the rotor system was designed and developed for new generation helicopters with challenging design objectives. The prototype FBR was tested on a Bell Model 412 helicopter in 1996 (Ref. 1 and 2). After the flight test, the FBR was improved in the fatigue strength of the hub, manufacturing cost of the blade and the blade folding provision. This improved FBR was evaluated by the flight test in terms of flight loads, performance, noise emission, vibration level, handling qualities and aeromechanical stabilities. This paper describes the FBR rotor system, the structural features, the structural substantiation, the ground test and the flight test. The rotor system has shown improvement in high speed performance, a significant reduction in noise emission and a remarkable reduction in vibration levels. In conclusion, it was confirmed that the design objectives have been achieved or surpassed for the FBR rotor system.