INTRODUCTION OF THE M-85 HIGH SPEED ROTORCRAFT CONCEPT

A new high-speed rotorcraft concept, designated M-85, is proposed. It is a helicopter that reconfigures to a fixed-wing aircraft for high-speed cruise. The concept enables smooth, stable conversion between fixed-wing and rotary-wing flight while retaining the hover and low-speed flight characteristics of a low-disk-loading helicopter. The M-85 designation reflects a 0.85 Mach Number goal at altitude. To be viable for most missions, the concept must have cruise efficiency competitive with fixed-wing aircraft. The M-85 has a unique large circular hub fairing capable of generating sufficient lift to support the aircraft during conversion between rotary-wing and fixed-wing modes. With the aircraft supported by this hub fairing, the rotor blades are unloaded during the 100% reduction in rotor rpm. With the blades unloaded, the potential for vibratory loads is lessened. In cruise, the large circular hub fairing becomes part of the lifting system with the blades becoming additional lifting panels for better cruise efficiency. In hover, however, the circular hub fairing slightly reduces rotor thrust and hover efficiency of the rotor system. This report describes the M-85 concept and presents estimated forward flight performance characteristics in terms of thrust requirements and L/D versus airspeed. The forward flight performance characteristics reflect recently completed wind tunnel tests. Hover characteristics, rotor power, and thrust characteristics from test data are discussed. The report discusses other technologies pertinent to the M-85 concept, such as the passive control of inplane vibration during starting and stopping of the rotor system, the aircraft control system, and rotor drive technologies. Also presented is a control system technique that is critical to achieving low oscillatory loads in rotary-wing mode.