Development of an SMA-based camber morphing UAV tail core design

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Abstract
This paper presents a new design for the core of a lightweight tail section of an unmanned aerial vehicle (UAV) with camber-morphing horizontal and vertical stabilizers. The core of each stabilizer is composed of an aluminum spar, two active end ribs, and multiple inactive ribs. Each active end rib is composed of a solid leading compartment connected to a flexible corrugated trailing segment. Thermally activated shape memory alloy (SMA) wire actuators along the length of the corrugated segment are used to control the camber of each active rib. The SMA wires are extended through the hollow spar to increase the amount of actuation and are guided using polycarbonate pulleys. A parametric CAD model was created to automatically regenerate the corrugated trailing segment geometry based on trough height, width and angle, as well as the used NACA airfoil. The locations of the vertical webs are adjusted with each parameter set so that the webs are always at the trough centers for consistency. COMSOL’s LiveLink was used to pass the generated CAD geometry to COMSOL, where finite element structural analysis is performed to study the effect of the geometric parameters on the camber deformation under SMA wire actuation and applied loads. The deformed shape of the trailing segment is then approximated as a third-degree polynomial and used to modify the four-digit NACA airfoil equation, generating a deformed shape for the airfoil. 2D computational fluid dynamics simulations are then performed to compute the lift-to-drag ratio for each structural configuration, from which the geometric parameters that maximize the performance of the stabilizer at the design speed can be selected. The proposed UAV SMA-based camber-morphing rear control section has been successfully manufactured and tested. Camber morphing up to 10.7° was successfully achieved and showed very good agreement with the numerical prediction.

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