Practical considerations for the design of an aeroelastic energy harvester

Achieving the optimal balance between weight and energy consumption during flight mission remains a challenge for the design of very efficient high altitude long endurance aircrafts (HALE). These aircraft are intended to have flight missions that can range from 30 to 90 days. Composite materials are used to provide the structural integrity of the aircraft while minimizing its weight. Typically composites are used in long and slender structural elements of the HALE and are the main drivers of dynamic aeroelastic instabilities, even at low speed. This is due to the higher structural flexibility they introduce. Therefore, in order to respond to the demand of HALE aircrafts of having a wider amount of energy on board, without any substantial weight penalization, an experimental piezoelectric wing have been designed with the aim of exploiting aeroelastic instabilities or any other type of induced vibrations to generate electric energy directly on board. The numerical model of the piezoelectric wing, presented in this paper, is built starting from the assumptions of the 3D Euler-Bernoulli beam theory and of the strip theory for the aerodynamic loads. A preliminary sensitivity study was carried out, over the flutter solutions, for the identification of a suitable experimental prototype, to be used for modal and wind tunnel tests. The test campaign showed a good agreement between numerical and experiments results, highlighting, above all, the encouraging results in terms of energy harvesting and in terms of the exploitation potential of the piezoelectric design in the dynamic of structures.