Directionally Variable Stiffness to Reduce Actuation Requirement in Airfoil Camber Morphing

Abstract

This paper explores a new design for an airfoil whose chordwise bending stiffness depends on the direction of load. By designing the region aft of the spar to be very stiff under upward load, uncommanded camber deformation under aerodynamic pressure can be minimized. At the same time, a much higher compliance under a reversed load reduces actuation requirement to achieve a desired downward camber deformation. A rigid cantilever extending from the rear of the spar toward the trailing-edge, and flush with the lower skin, is used to realize this goal. Under upward (aerodynamic pressure) load the rigid cantilever engages and its added stiffness minimizes deformation. But under downward (actuation) load, the lower skin breaks contact with the cantilever, and camber deformation can be achieved at low actuation effort. ABAQUS TM finite element simulations were conducted for a variable camber NACA 0012 airfoil. For a cantilever extending over the entire length of the conformable section (between the leading-edge D-spar and the trailing-edge section), the effective stiffness under upward loading was calculated to be 15.43 times the stiffness under downward loading, but the maximum downward camber deformation was limited to 10 deg due to contact between the cantilever and the upper skin. Reducing the cantilever length increased the maximum downward camber deformation achieved but with a smaller increase in stiffness under upward load.

Abnormal stiffness behaviour in artificial cactus-inspired reinforcement materials

“…For example, a high bending to stiffness ratio would be useful in shape morphing applications in aerofoils, in which structures need to be stretched but the shape under bending needs to be preserved [34]. The different stiffnesses in stretching and bending also suggest different strain energy mechanisms being present in the same architecture; this could be used to design structures with tailored energy absorption capabilities that depend on the type of external loading provided [35].…”

Analysis, optimization and testing of morphing structures employing shape memory alloy actuators

“…The majority of the relative works considers application of the aerospace field. Therefore primary objective is the development of skin configurations that will favor the morphing by minimizing the required actuation energy while they will also be able to withstand the aerodynamic loads minimizing the respective deformation (DiPalma & Gandhi 2016). Early research conducted by Setoodeh et al (2006) aimed to design composite plates for minimum compliance considering both constant and variable stiffness designs where the lamination parameters were allowed to vary spatially over the structure domain.…”