Combined Preliminary Airworthiness Evaluation and Airworthiness and Flight Characteristics Evaluation of the UH-1H with Preproduction Hub Spring and Composite Main Rotor Blades Installed

Abstract : The Army has incorporated a main rotor hub spring on the UH-1H helicopter designed to reduce large main rotor flapping angles which occur during some flight maneuvers. Composite main rotor blades (CMRB), also incorporated, are intended to increase performance and to improve reliability and survivability of the UH-1H. A preliminary airworthiness evaluation was conducted to determine suitability of the combined preproduction CMRB and hub spring configuration for compliance with the CMRB Critical Item Development Specification (CIDS). Due to high vibration characteristics and the occurrence of cyclic control feedback contributing to loss of aircraft control associated with CMRB, additional testing was conducted for comparison with standard metal main rotor blades (STD) and composite main rotor blades constructed with production tooling (PROD CMRB). Flight testing was evaluated under a variety of operating conditions from field elevations of 2302 ft to 9980 ft. Some improvement was noted in out-of-ground effect hover performance with PROD CMRB compared to CMRB, while level flight performance of the CMRB and PROD CMRB was not significantly different. Performance improved for the PROD CMRB compared to STD, but did not meet CIDS requirements. Handling qualities are similar for CMRB and PROD CMRB, and deteriorated when compared to STD with regard to maneuvering characteristics and main rotor speed control during autorotation.