Smart actuation mechanisms for helicopter blades : design case for a Mach-scaled model blade

Abstract

This work is part of the European project “Clean Sky”, which aims at improving the efficiency and the global transport quality of aircraft. The research, in this project, is currently focussing on active flap systems for helicopters to adapt the blade aerodynamic properties to local aerodynamic conditions. Fuel-efficiency, reduction of vibration and noise and increase of the helicopter maximum speed are the expected benefits. To validate this technology, numerical studies and wind-tunnel testing on reduced-scale rotor blades are necessary. This thesis investigates the selection process for actuators, the methods to design and optimise actuation systems and the procedures to validate them through simulations and testing. These methods are applied to the design of an actuation system to fold and deploy a Gurney flap for a Mach-scaled rotor blade. Integrating an actuation system in helicopters is especially difficult because of a combination of challenges: tremendous loads are caused due to rotation of the blade, the space inside a rotorblade is limited and durability constraints need to be addressed. Piezoelectric actuators mechanisms provide potential so- lutions to meet these challenges. The selection process and experimental testing of piezoelectric actuators showed the superior characteristics of Physik Instrumente patch actuators for the purpose of integration inside a rotor blade. The design procedure starts with the investigation of the aerodynamics loads on the Gurney flap using numerical solutions. Then, an algorithm is developed to generate and optimise geometries for actuation mechanisms that comprise of piezoelectric actuators and a deformable structure. The resulting structure presents the characteristic shape of a “Z”. It amplifies the strains generated by the piezoelectric actuator to operate the Gurney flap. A multi-domain numerical validation ensures the behaviour of the mechanism under loads from the airflow and the blade rotation. Finally, a z-shaped structure prototype is manufactured and its deformation is experimentally verified. This work provides methods for implementing actuation in the very demanding environments encountered in the aeronautic field and will help the next generation of smart rotorcraft to take off.