SMAs have been demonstrated for many actuation applications and found a few commercial applications, generally for small components with ambient temperature actuation. A study into their use for an adaptive geometry exit nozzle for a large aero gas turbine started around 2001. SMA mechanisms offer significant advantages in weight, complexity and aerodynamic form which can be achieved. It quickly became clear however that virtually all aspects of the material, form availability, mechanism, design methods, actuation and application assessment would need significant further development. This paper will describe the work which has been done on those aspects which have been necessary to move the concept towards a practical reality and wind tunnel demonstration of a prototype component. A relatively simple structure has been pursued, but this has led to the unusual need for large sheet materials at higher temperatures than the materials which were available at the time. Unique processing and characterisation methods have been developed in parallel with the materials to provide a practical process which can be applied to provide predictable stable operation within a structure where the loading is predominantly in tension. The structure also allows more rapid cooling of the SMA which has been identified as an issue in many studies, although our solution does require increased heat input for actuation. The design of any engineering component is a series of compromises around parameters such as weight, efficiency and cost. SMA seems to offer a major opportunity in all of these areas. Safety is clearly paramount in any aircraft application and the compromises must be made without any detrimental effect on this. All of these issues are covered by standard industry procedures. The characteristic of SMA which are different to conventional actuation offer major advantages, but also significant challenges in achieving acceptance.
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