Linearly variable chord-extension morphing for helicopter rotor blades

CEAS Aeronautical Journal ◽

10.1007/s13272-020-00477-4 ◽

2020 ◽

Author(s):

Rohin K. Majeti ◽

Berend G. van der Wall ◽

Christoph G. Balzarek

Keyword(s):

Reducing Power ◽

Comprehensive Analysis ◽

Rotor Blades ◽

Helicopter Rotor ◽

Efficiency Improvement ◽

Forward Flight ◽

Power Requirement ◽

Helicopter Rotor Blades ◽

Chord Extension

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’s in-house comprehensive analysis code S4. Chord extension of up to 100% and chord-extension–deflection of up to 15° 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.

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Helicopter Rotor Blade Chord Extension Morphing Using a Centrifugally Actuated von-Mises Truss

Volume 2: Mechanics and Behavior of Active Materials; Integrated System Design and Implementation; Bio-Inspired Materials and Systems; Energy Harvesting ◽

10.1115/smasis2012-8053 ◽

2012 ◽

Cited By ~ 1

Author(s):

Patrick Moser ◽

Silvestro Barbarino ◽

Farhan Gandhi

Keyword(s):

Leading Edge ◽

Rotor Blades ◽

Helicopter Rotor ◽

Design Solution ◽

Trailing Edge ◽

Power Requirement ◽

Helicopter Rotor Blades ◽

Final Design ◽

Von Mises ◽

Chord Extension

Previous studies have shown that chord extension morphing over a spanwise section of helicopter rotor blades can reduce main rotor power requirement in stall-dominant flight conditions while at the same time being able to increase the maximum gross weight, altitude, and flight speed capability of the aircraft. This study examines a centrifugally driven, fully passive chord morphing mechanism for helicopter rotor blades. It is based on a von-Mises truss situated aft of the leading-edge spar, connected to a rigid extension plate which deploys through a slit in the trailing-edge. When the rotor RPM increases beyond a critical value the chordwise component of centrifugal (CF) force on the von-Mises truss and plate assembly results in the deployment of the plate beyond the slit in the trailing edge, effectively increasing chord length. On reducing the RPM, a retraction spring pulls the plate back within the confines of the blade. This study presents the design process, iterations and the final design solution for a configuration that undergoes 20% chord extension. A prototype was fabricated and tested on the bench-top as well as on a rotor test stand at rotational speeds simulating 70% full-scale CF loads. The test results demonstrate that the concept works. However, effects such as friction lead to higher force (or RPM) requirements for deployment than predicted by simulation, and are present during retraction as well. The effects are more pronounced in the high CF field in the rotor test.

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