Studies of convertible turboshaft/turbofan engines for high-speed rotorcraft

Abstract

Rotary wing aircraft require auxiliary thrust to fly at speeds higher than current helicopters. One approach is to use the turboshaft engine to drive both the vehicle rotor and a variable geometry fan which allows independent variation of shp and thrust. Various convertible engine configurations including variable pitch fans, variable inlet guide vane fans, and clutched fans are described and their suitability for two types of aircraft is examined. One is a 225 knot U.S. Army combat rotorcraft in which the rotor operates in high-speed flight. The variable inlet guide vane fan with or without a clutch is shown to be a viable approach. The second aircraft is a 400 knot X-wing commercial transport in which the rotor is stopped in flight. The variable inlet guide vane fan and prop/shaft systems are shown to be competitive.