The phenomenon of helicopter rotor blade sailing

Abstract

Blade sailing is an aeroelastic phenomenon affecting helicopter rotors when rotating at low speeds in high wind conditions. This is a potentially dangerous blade motion and the excessive flapwise tip deflections generated endanger the airframe, the flight crew and any personnel working close to the aircraft. This phenomenon is particularly applicable to naval helicopters or those operating off exposed sights such as oil rigs. The research covered an experimental investigation into the effect of an abeam wind flow over a simulated flight deck of a Rover Class Royal Fleet Auxiliary vessel. Blade flexibility and rotor hub mechanical features were introduced into the theory and the resulting method applied to the Westland Lynx and Sea King aircraft. The semi-rigid rotor of the Lynx is relatively well controlled, but the rotor hub construction of the articulated rotor of the Sea King and the interaction with the flexing blades allow blade tip deflections to be generated of an order to strike the fuselage. The research described in the paper has led to an improved understanding of the blade sailing phenomenon. The results concur with reports of blade sailing occurrences and the operational conditions that are likely to trigger this phenomenon. The development of theoretical models may be used to assess the importance or otherwise of this effect on future rotor designs or the operational limitations of the aircraft.