In the development of electric aircraft, due to the use of Distributed Electric Propulsion (DEP), not only the classic wing flutter but also the propeller whirl flutter needs to be considered for wing structural design. To this end, this paper proposes an aeroelastic optimization method within the framework of an in-house tool named PROTEUS, which enables the preliminary design of DEP wing laminates including propeller whirl flutter effect. In this method, a new aeroelastic model is developed for the coupled propeller-wing system, based on a classic whirl flutter analysis model and the wing aeroelastic model implemented in PROTEUS. Further, the required sensitivities of aeroelastic stability constraints are derived and implemented by making use of these implemented in PROTEUS for conventional wing design. The objective of the optimization is to minimize wing mass by aeroelastically tailoring the lamination parameters and thickness of wing laminates, subject to given aerostructural design constraints. The features and usefulness of the proposed optimization approach are demonstrated through two numerical case studies (with and without whirl flutter constraints) focused on sizing the wing structure of a reference DEP aircraft. The necessary inputs regarding propeller mounting stiffness and damping for the case studies are determined through parametric studies of isolated propellers. The results indicate that including whirl flutter effect in wing sizing slightly increases wing mass, and introducing a flexible-mount-propeller leads to the decrease in wing flutter speed. Additionally, a parametric study of investigating propeller mounting stiffness is conducted, which confirms that the propeller mounting properties have a large influence on aeroelastic instability of the coupled propeller-wing system.

In the development of electric aircraft, the use of distributed electric propulsion introduces a potential occurrence of propeller whirl flutter, which needs to be taken into account for wing structural design. To this end, this work extends an in-house aeroelastic optimization tool by means of including a post-processing procedure on whirl flutter analysis. In aeroelastic optimization, propellers are modeled as concentrated masses, and the wing mass is minimized by tailoring the lamination parameters and thickness of wing laminates subject to aerostructural design constraints. For the whirl flutter analysis of the optimized wing, a new aeroelastic model is built by coupling propeller motions and aerodynamic loads into wing aeroelastic model. The usefulness of the purposed approach is demonstrated using a numerical example, where the required inputs on propeller mounting properties are determined via a parametric study. The result indicates that flexibly mounting propellers on a flexible wing leads to the decrease of wing flutter speed, and it also confirms that the propeller mounting properties have a large influence on aeroelastic instability of the coupled propeller-wing system.