Rotor Loads Reduction by Dynamically Extendable Chord

Abstract

Dynamically extendable blade chord sections show promise for reducing helicopter rotor loads. A rotor model based on an elastic beam concept, and capable of predicting helicopter power, is used. A stiff in-plane four-bladed rotor with a shape similar to the UH-60A rotor is used as a baseline for comparisons. For the control of the 4/rev (per revolution) vertical hub force, it is not beneficial to actuate the extendable chord at hover and low-speed flight. At a high speed of , the extendable chord, with a width of 10% rotor radius and responded to an extension magnitude of 10% chord length, obtained a maximum force reduction of 89.4%. The magnitude of the dynamic chord needs to be optimized according to the flight state. The performance can be enhanced by increasing the extension or width of the dynamic chord. The dynamically extendable chord was not suitable for reducing the 2/rev blade flapwise root bending moment. However, a 3/rev dynamic chord extension showed great potential in reducing the 3/rev flapwise root bending moment and the 4/rev rotor rolling and pitching moments simultaneously. The effectiveness of a 5/rev dynamic chord in reducing the 4/rev rotor rolling or pitching moment degraded significantly as compared with a 3/rev actuation.