Bi-Directional Stiffness for Airfoil Camber Morphing

Abstract

This paper explores a new design for an airfoil whose chordwise bending stiffness varies with direction of applied 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, lower stiffness under reversed load reduces actuation requirement to achieve a desired downward camber deformation. Rigid cantilevers extending from the rear of the spar toward the trailing edge, and flush with the lower skin are used to realize this goal. Under upward load the rigid cantilever engages and supplements the chordwise bending stiffness. But under downward load the lower skin breaks contact with the cantilever, and camber deformation can be achieved at low actuation effort. From twodimensional ABAQUS™ finite element simulations an upward-to-downward stiffness ratio of 13.82 was obtained with a cantilever extending over the entire length of the conformable section, but the maximum downward camber deflection was limited to 10 deg. Reducing the cantilever length reduced the stiffness ratio but allowed higher maximum camber deformations. A three-dimensional prototype was fabricated using "moderate-length" cantilevers and the measured stiffness ratio (under upward-to-downward loading) was determined to be 5.12. The corresponding stiffness ratio from a three-dimensional ABAQUS finite-element simulation was found to be within 6% of experimental results. Nomenclature EI = flexural stiffness, N ⋅ m 2 F, P = applied tip load, N L = length, m w = upward tip displacement, m

Efficiency Change of Control Surface of a Biomimetic Wing Morphing UAV

“…A large bending angle over 30 • has been achieved in the room condition. Dipalma and Gandhi [11] have explored and optimized the design for an airfoil whose chordwise bending stiffness varies with the direction of the applied load. Michaud et al [12] have proposed a morphing skin concept to improve the aerodynamic performance of a typical Bombardier aircraft wing while maintaining its structural integrity during flight.…”

Design, fabrication, and testing of an active camber rotor blade tip

“…These structural designs will not cause any discontinuity on the blade surface and as such will not suffer from an increase in aerodynamic drag or increased aeroacoustics noise due to gaps on the blades (Daynes et al, 2010). Several morphing concepts have been investigated for aerospace (Barbarino et al, 2011; DiPalma and Gandhi, 2018; Gandhi and Anusonti, 2008; Gandhi et al, 2008; Takahashi et al, 2016) application and their application to wind turbines is well summarized in a couple of review articles (Barlas and van Kuik, 2010; Lachenal et al, 2013). In (Ferede and Gandhi, 2018), the authors presented a study of vibratory load reductions on a 5 MW wind turbine using a new morphing concept that of a continuously conformable blade tip, where the outboard 30% span of the blade undergoes a linear variation in camber.…”