The fundamental configuration and design of the compound helicopter

Abstract

The compound helicopter has much to offer as a means of expanding the flight envelope of rotorcraft. There have been significant amounts of research performed, albeit disjointed, and many flight demonstrator compound helicopters produced and trialled since the end of the Second World War mainly with the aim of increasing the helicopter's maximum forward speed. This paper aims to pool this knowledge, along with relevant developments in other fields, not only to state the current level of understanding of the compound helicopter configuration but also to use it to predict likely configurations and technologies that would be best suited to future compound helicopter designs. From this basis it is suggested that the most likely configuration will be a low wing of minimized area to alleviate retreating blade stall at a minimum hover blockage, with plain flaps for blockage reduction and control of the rotor-wing load share. In terms of propulsion a ducted fan or propeller are deemed most suitable, driven by either an advanced mechanical drive or variable cycle engine. The areas of rotor-wing interaction and advanced rotor design are also noted as subjects of significant interest in the optimal design of a compound helicopter.