Structural Design, Optimization and Validation of the Integrated Active Trailing Edge for a Helicopter Rotor Blade

Active Trailing Edge (ATE) concept is studied in detail in this paper. An integrated active section is defined for the trailing edge of the rotor blade and finally optimized to achieve the strength requirements and the maximum aerodynamic efficiency. Similarly, the integration details, i.e. the construction of the transition section between the active and passive parts (i.e. the sections with- and without piezo actuators) of the blade are discussed. A structural optimization study coupled with the aerodynamic requirements is performed in order to determine the geometry and the stiffness of the bender with attached piezo ceramic actuators. Mass, stiffness and maximum trailing edge deflection are defined as target functions. Several constraints were defined by rotor dynamics and active material properties. The results representing the influence of the piezo thickness on aerodynamic performance and the benefits of the variable thickness are presented. The highest efficiency has been obtained for variable thickness of bender and piezo in chordwise direction. However, it is technologically quite difficult to manufacture piezo ceramic actuators with variable thickness. Piezo ceramic materials are quite brittle, the allowable tensile stress is very low and the Young’s modulus range is quite limited. Therefore, to reduce the normal strains transferred to the piezo ceramic material, the trailing edge geometry is further modified. It has been determined that it is mandatory to introduce cutouts into the blade structure in chordwise direction throughout the span. Finally, it is understood that the stiffness of the filling material has a remarkable effect on the trailing edge deflection and hence on the overall aerodynamic performance. Therefore, it is obligatory to choose a flexible, low modulus material to achieve the required aerodynamic efficiency. In parallel to optimization study, the interface outline is examined with different models to minimize the resetting influence on active trailing edge deflection. Afterwards, a finite element model has been created to determine the three-dimensional stress state due to operating loads (i.e. lead lag bending, flapping and torsional moments and centrifugal forces). Rotor blade segment with optimized active trailing edge and interface is modeled and analyzed with NASTRAN software. The resultant strains on piezos and blade structure, trailing edge deflections under the effect of operational loads and interface were determined. In addition, the effect of the aerodynamic loads on the transition area between the passive and active trailing edge along the blade span has been investigated.