Demonstration of adaptive wing

Shape memory wires contract into the austenitic phase at high temperature and they expand into the martensitic phase at low temperature. Thus a current set through the wire will make the wire contract, because of Joule heating, and no current will make it expand, because of the cooling through the surrounding air. This behaviour may be harnessed for adapting the shape of an air foil to the existant flight conditions. This has been done and a model is shown - consisting of a "slice" of an airfoil which bends so as to minimize drag of the airfoil under the constraint of a fixed lift force.
The optimal shape of the air foil for given angles of incidence and different speeds of the incoming air is stored in a data bank calculated from aerodynamics. The necessary current for the realization of the shape is calculated from the Müller-Achenbach theory of shape memory which was recently adapted by Seelecke for quantitative predictions.
Basically that theory is a statistical thermodynamic theory of activated processes, where the transitions between the austenitic phase and martensitic is singled out by the direction of the elongation. This theory combines rate laws for the phase fractions with the energy balance that governs the temperature of the wires.
The suitability of the theory for quantitative simulation of shape memory behaviour is shown by a feedback control problem which exhibits very good agreement between experiment and the prediction of the theory.
The airfoil exhibited during the session could be used interactively by the audience, because it responded to a change of the angle of incidence that could be adjusted by a joystick.