A multi-stable spanwise twist morphing trailing edge

Morphing structures have received growing interest from the engineering community, owing to potential for enhanced aerodynamic efficiency and scope for reducing weight. Many morphing concepts focus on development of conformal trailing edge flaps with associated chord wise aerodynamic effects. However, the lateral ends of such flaps can also induce spanwise aerodynamic discontinuities thereby increasing drag force and noise emission. As such, to address this issue, we introduce a novel spanwise twist morphing trailing edge design utilizing structural multistability with minimised actuation energy requirements. The spanwise morphing trailing edge consists of carbon fibre reinforced plastic laminate spars and ribs which are assembled in a grid pattern. The composite laminate spar strips are manufactured in a stress free state with a deliberate curvature and are prestressed by flattening before assembly. This way, initial strain energy is stored in structural components that can later be released during structural deformations. The prestress effects in spar strips are exploited in the design to adaptively tailor the the structural strain energy state and also the structural torsional stiffness thus minimising the actuation requirements. With an analytical structural model, design parameters including laminate layups of spars and ribs and the initial curvature in spar strips are investigated. Results show that by selectively changing the structural design, the stable equilibria configuration of the spanwise morphing trailing edge can be set over a wide range of twist angles. Particularly, a zero torsional stiffness spanwise morphing trailing edge design has been observed. Finite element method results are provided to verify the analytical model and good correlation is found. Furthermore, the spanwise trailing edge deformation shape of the developed morphing device features a desirable torsion behavior, so providing spanwise conformality without gaps, where a constant torsion angle variation is observed along the span. Comparison with a nominally deformed shape of a flap transition design from the literature indicates that further optimization of the profile can lead to improved aerodynamic performance. The morphing structure concept and the simple analytical model developed in this paper can be used in future for a detailed morphing structure design.