Antitorque Safety and the RAH-66 Fantail

Tail rotors cause a significant proportion of mishaps during U.S. Army helicopter operations. They present potentially fatal hazards in different operational modes, including normal and low-altitude flight as well as ground operations. They were responsible for over 20 percent of single-rotor helicopter major mishaps. The RAH-66 Comanche development team established improvement in tail rotor safety as a design objective. In order to achieve this goal and to improve overall aircraft safety, Boeing Sikorsky designed the Comanche Fantail® shrouded tail rotor. This paper compares this design with the historical causes of conventional tail rotor mishaps. U.S. Army tail rotor-related mishaps that occurred between 1978 and 1988 were analyzed to determine their prime causal factors. They were categorized as being caused by several factors, the most noteworthy of which were tail rotors striking objects or personnel, loss of tail rotor effectiveness, and material failure or maintenance-induced component failure. Several safety features were developed to reduce the mishap probability caused by factors in the different mishap scenarios. The Fantail shroud is the major safety feature of the Comanche helicopter’s Fantail system. It is an essential component in preventing tail rotor strikes and is a contributing factor in antitorque thrust performance, the two most significant aspects of tail rotor design. Other safety features reduce the probability that other tail rotor-related mishaps will occur or provide redundancy in the event of failure of primary systems.