Wing flexibility is critical to flapping rotary wings (FRWs), and in that the deformation is bilaterally coupled with aerodynamic forces and thus determines the performance. Conventional solutions to this fluid–structure interaction (FSI) topic require considerable computational resources. In this paper, an efficient FSI model is proposed to calculate the aerodynamic force and passive twisting of FRWs. The passive pitching is regulated by a torsional spring, and the twisting is simplified as a quadratic distribution. A well-verified quasi-steady model is employed to estimate the aerodynamic forces. Our results show that the performance of rigid FRWs is superior to twistable FRWs within an upper limit of the wing-root stiffness [Formula: see text], which is around [Formula: see text]. At higher [Formula: see text] values, the twistable FRWs generate comparable lift to rigid FRWs at a higher efficiency. An increase in flapping frequency can remarkably reduce the efficiency of twistable FRWs despite the lift enhancement, while a concomitant reduction of flapping amplitude can moderate the loss of efficiency at higher flapping frequencies. Our model provides an efficient tool for the quick estimation of the aeroelastic performance of twistable FRWs and can thus contribute to the wing stiffness design.
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