Linearly Variable Chord-Extension Morphing for Helicopter Rotor Blades

Abstract

A new morphing concept called linearly variable chord-extension was studied for its effectiveness in improving the efficiency of a helicopter rotor. Apart from chord-extension itself, an additional feature which is deflection of the extended part of the chord resulting in an effective camber and additional twist to the airfoil, is also studied for its effect on rotor efficiency improvement. Trim analyses were carried out for various chord-extended rotors for hover as well as various forward flight velocities using DLR in-house comprehensive analysis code S4. Chord-extension of up to 100% and chord-extension-deflection of up to 15 deg were considered. Results show that the linearly variable chord-extension concept is effective in reducing power requirement in both hover and forward flight. Deflection of the extended chord also helps reduce power requirement in hover, especially at higher blade loadings. However, the root torsional moments and hence, the pitch-link loads are seen to increase substantially for the morphed rotors.