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

Abstract

Today's helicopters are the result of collaborative work in mechanical engineering and aeronautics. The European project "Clean Sky" aims at improving the efficiency and the global transport quality of aircraft. In the field of rotorcraft, the research in this project is currently focussing on active blade systems to adapt the aerodynamic properties of the blade to the local aerodynamic conditions. Fuel-efficiency, reduction of vibration and noise and increase of the helicopter maximum speed are the benefits expected from these new technologies. To envision the implementation of these innovative blade concepts, 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.Integrating an actuation system in helicopters is especially difficult because of a combination of challenges. To begin with, these include the tremendous loads due to the rotation of the blade, the limited space available, and constraints regarding durability. Secondly, the impact that the actuation system will have on the rotor blade behaviour has to be taken into account. And lastly, integrating the component inside the actual structure of a rotor blade should be feasible. A system based on piezoelectric actuators provides a potential solution to meet these challenges. A selection process has been established in Chapter 2 to match an actuation technology to application requirements. Among many of the smart blade concepts under development, the active Gurney flap is considered in the framework of the Clean Sky Innovative Technology Development project "Green Rotor Craft", for its potential impact on the blade performance and technology readiness. Actively deploying the Gurney flap on the retreating side of the helicopter increases the lift of the rotorcraft and its overall performances. To validate this technology, numerical studies and wind-tunnel testing on reduced-scale rotor blades are necessary. The procedures detailed in this work are applied to the design of an actuation system to fold and deploy a Gurney flap for a Mach-scaled rotor blade. Additional challenges arose due to the reduction in size: the centrifugal acceleration is increased and the space available inside the blade is drastically reduced.Computational Fluid Dynamic simulations are performed in the first step of the design procedure to obtain the aerodynamic loads on the Gurney flap for various realistic combinations of deployment levels, orientations of the blade in the flow and airspeeds (Chapter 4). Secondly, the design of the actuation mechanism is performed using a two-step approach: (1) computer generated topologies are analysed to find a suitable initial geometry; (2) an optimisation is carried out to maximise the displacement and force of the structure integrating a piezoelectric patch actuator. The resulting structure presents the characteristic shape of a "Z" (Chapter 5). It converts the strains generated by the piezoelectric actuator into rela...