Experimental testing of spanwise morphing trailing edge concept

Abstract

Aircraft wings with smooth, hinge-less morphing ailerons exhibit increased chordwise aerodynamic efficiency over conventional hinged ailerons. Ideally, the wing would also use these morphing ailerons to smoothly vary its airfoil shape between spanwise stations to optimize the lift distribution and further increase aerodynamic efficiency. However, the mechanical complexity or added weight of achieving such a design has traditionally exceeded the potential aerodynamic gains. By expanding upon the previously developed cascading bimorph concept, this work uses embedded Macro-Fiber Composites and a flexure box mechanism, created using multi-material 3D printing, to achieve the Spanwise Morphing Trailing Edge (SMTE) concept. The morphing actuators are spaced spanwise along the wing with an elastomer spanning the gaps between them, which allows for optimization of the spanwise lift distribution while maintaining the continuity and efficiency of the morphing trailing edge. The concept is implemented in a representative section of a UAV wing with a 305 mm chord. A novel honeycomb skin is created from an elastomeric material using a 3D printer. The actuation capabilities of the concept are evaluated with and without spanning material on a test stand, free of aerodynamic loads. In addition, the actuation restrictions of the spanning elastomer, necessary in adapting the morphing concept from 2D to 3D, are characterized. Initial aerodynamic results from the 1'x1' wind-tunnel also show the effects of aerodynamic loading on the actuation range of the SMTE concept for uniform morphing.

Spanwise morphing trailing edge on a finite wing

“…Accordingly, the span of each individual flap was the size of one active and inactive section on the SMTE, so as to prevent gaps between the control surfaces of the articulated wing. For further description of the internal construction methodology, refer to Pankonien et al 2014 12 .…”

“…As previously detailed by Pankonien et al 2014b 12 , analyzing the change in aerodynamic forces between different wings and configurations beyond basic trends can be difficult due to many different factors including: the interplay of spanwise actuation with the tip vortex, the inboard flap vortex, and positioning errors for the individual actuators. The lift control derivative was derived from the measured experimental values as:…”

“…The Spanwise Morphing Trailing Edge (SMTE) concept improves control of aerodynamic forces such as lift, roll, and pitching moment for a Low to Medium Altitude Long Endurace (LALE to MALE) 10 UAV by reducing the associated drag penalty while adapting to off-design conditions 11 . The SMTE achieves smooth, complex, spanwisevariation of the trailing edge of a wing or tail while eliminating traditional gaps and discontinuities, as shown in Figure 1b …”

“…The experimentally measured control derivatives were derived with spanwise-uniform actuations in the method presented by Pankonien et al 2014 12 . The control derivatives were approximated by dividing the change in nondimensional forces from the unactuated configuration (i.e ΔC L , ΔC l , ΔC m, ΔC D ) by the spanwise integral of effective flap angle as defined by the tip deflection from the previous section.…”

“…Generalization of the effects of "higher-order" control surfaces for the motivation of morphing concepts have previously been investigated by Sanders et al 17 . The mean camber line, z, of an equivalent Nth order symmetric airfoil was expressed by: (12) where θ provides the appropriate coordinate transform for chordwise position. These control derivatives were utilized for comparison with experimentally measured values and were summarized in Table 3.1.…”