HYTEM DEMONSTARTOR: DESIGN AND ANALYSIS OF A MORPHING TRAILING EDGE DEMONSTRATOR USING HYPERELASTIC ADHESIVE

Abstract

The biggest challenge of our time is the transition of aviation to climate neutrality and the move away from fossil fuels. Alternative fuels and energy storage systems go hand in hand with lower energy densities. This directly leads to higher fuel or system masses for the same range. The quotient of payload to required energy is dropping. As a result, aerodynamic efficiency is the focus of future aircraft designs. One way of achieving this goal is to use morphing trailing edges that improve L/D, especially in off-design conditions. However, the deformation of a morphing trailing edge changes the circumferential length of the airfoil section. This problem was often solved by slitting the pressure side of the wing, which cause a gap on a local section of the wing. Elastomers or sliding mechanisms are used to close this gap. Both lead to a deviation from the target shape and higher maintenance effort. Pressurized solutions for camber morphing are in equilibrium between aerodynamic loads and internal forces. Therefore, additional measurement devices are required to determine the position of those systems. In this work, a new approach is pursued by avoiding the slitting of the aerodynamically effective surfaces and using a compliant mechanism in the trailing edge. A conventional kinematic is introduced to drive the lower skin directly. Actuator moments are limited by use of non-linear transmission ratio of the kinematics. The design and pre-dimensioning by analytical and finite element method (FEM) approach are presented. Based on this, a demonstrator was derived on the basis of the unmanned aerial system (UAS) PROTEUS from German Aerospace Center. PROTEUS has a span of 2950mm, a root chord of 595mm, an aspect ratio of 6 and Vd of 300 km/h. The demonstrator represents a 100 mm span morphing trailing edge section. To evaluate the prediction methods, drive forces and moments were calculated and compared using finite element method (FEM) as well as analytical methods. In the comparison of both analysis methods, a very good correlation with a deviation of 0.5% was found for the actuator loads. The rod forces deviated from each other by approx. 5%. Based on these results the prescribed demonstrator will be build and measurements on the kinematical loads and fatigue will be carried out to verify this concept for the implementation on PROTEUS. Additionally, the wing demonstrator will be designed to determine internal loads performing spanwise differential deflections. The UAS PROTEUS will then undergo flight tests determine L/D improvements using morphing trailing edges. Keywords: Morphing, Wing, Trailing edge, Hyperelastic material, Compliant mechanism, HyTEM, Camber variation, Unmanned aerial system.