A Review of Active Blade Twist Technology: Part I – Actuation Concepts

Abstract

Marques P. (2014). A review of active blade twist technology: Part I – Actuation concepts. International Journal of Unmanned Systems Engineering. 2(S2): 16-25. Helicopter rotors operate in a complex unsteady aerodynamic environment. Variations in aerodynamic loads on the rotor caused by phenomena such as shock waves, dynamic stall, stall flutter, blade-wake interaction, and blade vortex interaction generate vibration and noise. Suppression of rotor vibration and noise has several advantages, particularly enhanced forward flight performance and less environmental impact. Active blade twist attenuates noise and vibration, and improves helicopter performance through a better spanwise distribution of loads. Rotor-based active control systems that attenuate vibrations and noise at their source, at the rotor blade, are considered superior. This paper reviews actuation concepts for the active twist of the rotor blade and provides a valuable reference in the design of rotors for advanced rotor-UAVs. The simplest method to modify the rotor blade pitch is to apply harmonic frequencies above the rotor rotational frequency using Higher Harmonic Control (HHC). Individual blade control (IBC) is superior to HHC, however IBC necessitates high hydraulic power. The Smart Spring concept provides IBC by actively altering the blade dynamic stiffness, rather than the aerodynamic characteristics, and overcomes the limitations of piezoceramic actuators. The SMART system integrates piezoelectric actuator materials into the rotor blade. There are different means to obtain active twist, including relatively-simple discrete flaps, Smart Tabs, and the Active Trailing Edge which twists the blade aeroelastically. © Marques Engineering Ltd.