Prediction and prevention of aeroelastic risks for highly flexible HALE pseudo-satellites – FlexHALE

High-altitude long-endurance (HALE) pseudo-satellites are drones powered by solar energy. Their almost unlimited endurance makes them a green satellite alternative. Most past and actual drone prototypes have experienced major aero-structural issues. Their highly flexible wings are extremely sensitive to aeroelastic instabilities, which causes their design to be a major technological challenge. The codes developed so far to simulate and predict such instabilities focus more on the calculation of the critical flutter speed than on the dynamical behavior reached after the onset of flutter, such as limit cycle oscillations (LCOs). These phenomena, due to geometric nonlinearities of the structure and dynamic stall, are notably challenging to model. In particular, no reliable analytical model for the aerodynamic behavior of flexible wings at high angle of attack in 3D is currently available to simulate LCOs. A new strategy based on data-driven approaches combining modelling and experimentation emerges as a promising alternative.
In the context of safer and more robust designs of solar HALE drones, the main objective of the FlexHALE project is to develop a digital twin of highly flexible wings that will be the keystone of optimization procedures on the composite wing design. The creation of a nonlinear aeroelastic simulation tool for post-critical nonlinear analysis is the first step of the project. Results from wind tunnel experimentations on flexible composite wings under flutter conditions analyzed with medium speed cameras will be used to update, validate, and supplement the model with data-driven 3D aerodynamic force estimations. Finally, optimization algorithm will be applied for the aeroelastic tailoring of the wing box, optimizing its shape and the composite layups to influence the wing bending/twisting coupling directly involved in the flutter onset.