Adaptive-Twist Airfoil Based on Electrostatic Stiffness Variation

Abstract

Shape-adaptable airfoils with variable shear center location and torsional stiffness represent a promising solution for controlling the aerodynamic loads on a wing by continuous deformations instead of rigid-body attachments. In the present article, a structural concept for an adaptive-twist airfoil based on wing spars with variable mechanical topology is investigated. The integration of a smart material system relying on controllable electrostatic attraction forces in the spars allows for reversible opening of the wing box and thusfor controlling the airfoil's twist. While finite element simulations and static testing of an experimental airfoil demonstrate the concept's effectiveness, a numerical upscaling to the dimensions of a glider wing evaluates its potential with respect to a realistic application. Under the considered conditions, the upscaled adaptive-twist airfoil permits changes in lift coefficient by around 20% in such an implementation.

Multi-functional extremely anisotropic structural element

“…Additionally, the DCo displays negligible axial-bending coupling also when loads are not applied on the corrugation midplane (Previtali et al, 2014). The electro-bonded laminates (EBL) make use of electrostatic force for obtaining a reversible bonding (Bergamini et al, 2007;Di Lillo et al, 2011;Di Lillo et al, 2013;Raither, 2014). This results in the possibility of semi-actively modifying the stiffness and the damping characteristics of the laminate.…”

Stiffness control in adaptive thin-walled laminate composite beams

“…These materials have great potential for use in aerospace structures. For example, Raither et al [8], highlight the potential of shape adaptable airfoils for the control of the aerodynamic loads on wings by continuous deforma tions. Also, Gandhi and Kang [9] have studied the variation in the flexural stiffness of a multi layered beam when varying the tem perature of the polymer layers that formed it by applying heat with ultra thin electric heating blankets.…”

“…Raither [12] analysed a shape adaptable airfoil made of com posite material following an adaptive twist concept. The variable stiffness control in this study is based on two different systems: temperature control and voltage regulated control.…”

Interlocking electro-bonded laminates

“…This concept was extended, replacing the permanent adhesive between adjacent layers in a composite beam structure with reversible electrostatic bonding (Bergamini, 2009;Bergamini et al, 2006Bergamini et al, , 2007. The potential applications for EBL devices are numerous, including morphing structure applications (Previtali et al, 2015;Raither et al, 2012Raither et al, , 2013Raither et al, , 2014, vibration suppression (Bergamini et al, 2006(Bergamini et al, , 2007, or variable stiffness functionality (Di Lillo et al, 2013;Heath et al, 2016a). Significant progress has been made in increasing the level of electrostatic holding force generated, with greater understanding of thin film dielectrics used for EBL devices (Di Lillo et al, 2011) and improved close contact between structurally integrated electrodes through fabrication process enhancements (Heath et al, 2016a).…”

“…Strong electric fields generated from closely spaced electrode elements can generate significant electrostatic forces of attraction which can be utilised to control the structural coupling of laminated elements (Bergamini et al, 2006;Di Lillo et al, 2013;Heath et al, 2016a;Raither et al, 2014;Tabata et al, 2001). Figure 1 is an example of an EBL device, showing conductive elements attached to a host structure and separated by a thin dielectric layer.…”