Flight dynamic-aeroelastic response of highly flexible aircraft with distributed propellers

ifasd2024 Tracking Number 182

The increased concern about climate change has driven an international effort to develop zero-emission air transport. Within the emergent clean electric aircraft market, Distributed Electric Propulsion (DEP) is a promising concept. The freedom in the disposition of the propellers allows higher aerodynamic efficiency and enables new capabilities in vehicle control [1]. However, distributing rotary devices along the aircraft can promote traditional aeroelastic instabilities or result in unconventional instabilities like whirl flutter. Furthermore, propellers enhance couplings between rigid flight dynamics and aeroelastic effects. Moreover, maximizing the lift-over-drag ratio leads to high-aspect-ratio wings, which undergo large deformations and exhibit geometrically nonlinear behaviour. This also reduces the typical frequencies of elastic modes, enlarging the flight dynamics-aeroelasticity coupling. To achieve actual implementation of DEP technologies in the market, it is critical to develop methods to evaluate these effects since the early design stages. Efforts have been made to propose purely aeroelastic frameworks capable of analyzing the interaction between propellers and wings, considering classical wing flutter and whirl flutter [2], [3]. They consist of rigid propellers flexibly attached to a wing undergoing out-of-plane bending and torsion. The wing aerodynamics is modelled with a DLM performed on the rigid wing and propeller aerodynamic with Blade Element Theory, with no interaction between them. None of these methods consider the free motion of the aircraft and they are not valid for very flexible wings. There is the need for the development of frameworks capable of analyzing the coupled non-linear flight dynamic-aeroelastic response of free-flying aircraft with distributed propellers. This proceeding aims to present a method capable of this, while still being computationally efficient. The aircraft structure is modelled with a non-linear beam formulation and a lumped mass model. The unsteady aerodynamics are modelled with a Vortex Particle Method, coupled with an enhanced Doublet-Lattice Method for the wing and Blade Element Theory for the propeller. Geometrical non-linearities are considered both in the structure and aerodynamics. Propeller slipstream effects are taken into account. Finally, a synthetic test aircraft is analyzed to showcase the capabilities of this framework and demonstrate the importance of considering the coupling of non-linear flight dynamics and aeroelasticity in the design of highly flexible Distributed Electric Propulsion (DEP) aircraft. [1] H. D. Kim, A. T. Perry, and P. J. Ansell, “A Review of Distributed Electric Propulsion Concepts for Air Vehicle Technology,” AIAA, no. 2018–4998, Jul. 2018, doi: 10.2514/6.2018-4998. [2] N. Böhnisch, C. Braun, S. Koschel, and P. Marzocca, “Whirl flutter for distributed propulsion systems on a flexible wing,” AIAA SCITECH 2022 Forum, Jan. 2022, doi: 10.2514/6.2022-1755. [3] N. Böhnisch, C. Braun, S. Koschel, P. Marzocca, V. Muscarello, P. Marzocca, “Dynamic Aeroelasticity of wings with distributed propulsion system featuring a large tip propeller”, IFASD 2022 Forum, Jun 2022