SMA Actuated Mechanism for an Adaptive Wing

Abstract

A preliminary study of an adaptive unmanned aerial vehicle (UAV) wing actuated by shape memory alloy (SMA) devices is presented. The wing consists of a sandwich box substructure, flexible ribs, and a flexible laminated skin. The adaptation capability to the changing flight conditions is obtained via airfoil shape adjustments. Torsion SMA tubes are employed for wing camber control, while levers powered by SMA wires are employed for local shape control. A new architecture is proposed: the downward or upward actuation torque is provided by counterrotating concentric tubes connected through a clutch and a positioning piezoelectric motor to the flexible ribs. These actuator tubes are heated one at a time while the other is made free by the clutch in order to obtain any wanted shape without waiting for cooling. The capability of the wing to bear the aerodynamic loads, the power required by the actuators, and their force and torque are assessed by finite-element simulations. An improved version of a recently developed element is employed that accurately and efficiently captures stresses and deformations in the composite structure. The wing requires a peak power of 1,223 W that is compatible with the UAV considered here, i.e., with a maximum take-off weight of 1,000 kg and jet engine. It can smoothly deform with a camber mean rotation of 22° and rotation at the tip of 40° with a load factor of 5, a differential camber rotation of 10°, and a profile variation from 40 to 55% of the chord (4.5% increase and 3.9% decrease of thickness) at cruise speed.