Fly-By-Hire Tail Rotor Controls

The purpose of the program described in this paper is to develop fly-by-wire (FBW) controls uniquely applicable to helicopter tail rotors. Single failoperate redundancy is provided by three electric motors mounted at the tail rotor gearbox. Each motor drives through a simple mechanical torque breakout device into a single gear attached to a control quill, which converts rotary motion to linear motion. The torque breakout devices provide failure management in the mechanical components; therefore, the electronics can be kept simple and inexpensive. Three independent electrical circuits provide serial summing of signals from the pilot's position transducer, tail rotor pitch-change position transducer, and the Stability and Control Augmentation System (SCAS) to command the motors. A dual monitor warns the pilot of a failure in a specific channel. Three types of concept validation tests were conducted by Bell Helicopter Textron (BHT) under contract with the U. S. Army Applied Technology Laboratory (ATL), AVRADCOM, Fort Eustis, Virginia. Tests included simulated lightning tests, motor performance tests, and life tests. Simulated lightning strikes in the 96 percentile rank (120, 000 amperes in the fuselage) caused no damage to the FBW controls and no blade pitch change resulted from the impluses. Motor performance tests proved that the motors met the design requirements. Life tests simulating severe maneuvers and cruise flight for a period of 500 hours were completed successfully. A second contracted effort, funded by ATL, provided for the design and fabrication of flightwozthy hardware. The current phase of the program, gzound and flight test, is being funded by BHT Independent Research and Development. The FBW control components have been installed in an AH-1G helicopter, and ground tests are in progress.