Droop Nose With Elastic Skin

Abstract

Morphing is a technology with high potential to reduce emissions in aviation by adapting the shape of the wings to varying external operating conditions. This paper is presenting results from the EU FP7 funded CHANGE project, where different concepts to adapt a UAV wing airfoil to different demands were investigated. The paper is concentrating on the design and experimental testing of a droop nose, which transforms the leading edge part of the 60 cm chord airfoil from a NACA 6510 shape for loiter and low speed to a NACA 2510 shape for a high speed mission. This paper is presenting the use of an especially soft skin, which reduces the needed force for morphing. That way the requirements for the servos driving the droop nose could be reduced significantly. This paper is showing the implications of such a soft design on the accuracy of the shape generated. For such a skin design, the driving mechanism of the system is designed as a compliant mechanism, which was generated by topology optimization, taking into account aerodynamic loads. For easy manufacturing reasons, thermoplastic polylactic acid (PLA) with zero warp property was used for the manufacturing of this compliant mechanism. Finally deformation measurements of the morphing skin were carried out in a series of lab tests. The match between measured and numerically derived section is quite good, especially in the root region of the wing. Finally an example of an alternative concept to the soft approach is presented. It is the metal based compliant mechanism with a rather stiff GFRP skin. A discussion on the use of different materials and the way forward towards 3D skin optimization is wrapping up the paper.

Conceptual-level evaluation of a variable stiffness skin for a morphing wing leading edge

“…The 'droop-nose' leading edge was investigated extensively in DLR (German Aerospace Center). [1][2][3][4][5] A process chain was proposed to design the leading edge structure, as well as the internal actuation mechanism. 6 A specific composite was developed for the leading edge skin, 7 which was a composite material based on a compliant matrix and embedded fibres.…”

“…For composite skins employed in the morphing leading design, the stiffness variation can be achieved by changing the lamination thickness (number of layers), such as in the droop-nose. 2,4 Alternatively, the variable stiffness skin may be introduced by changing the lamina angles, 21 although in the literature the stack sequence was encapsulated by axial and bending stiffnesses parameters to reduce the number of design variables. Varying fibre angle could lead to a continuous stiffness distribution of leading edge skin and varying the skin thickness would lead to a discrete stiffness distribution.…”