Autorotational Entry Improvement Program TH-55A Helicopter

The TH-55A helicopter was tested as part of a development program to improve the autorotational entry characteristics. Previous tests indicated that the TH-55A exhibited excessive nose-down pitching and left rolling motions following simulated power failures. The autorotational entry characteristics of the standard helicopter and the characteristics with a reduced-chord horizontal stabilizer configuration were investigated. Test data indicated that other minor stabilizer configuration changes could also improve the autorotational entry characteristics. An experimental development program was conducted to determine an optimum stabilizer configuration. This program resulted in the development of a reduced-span stabilizer with an upper-leading-edge spoiler which improved the nose-down pitching characteristics without seriously degrading other handling qualities. A second phase of the test program was conducted to verify the structural adequacy and basic airworthiness of the new stabilizer for the entire flight envelope contained in the 1967 Hughes TH-55A owners manual. Improvement was achieved in the autorotational entry characteristics and other flying qualities. As a result of this test program, the active fleet of TH-55A helicopters was converted to the horizontal stabilizer configuration developed by the United States Army Aviation Systems Test Activity.