Design and control of a proof-of-concept variable area exhaust nozzle using shape-memoryalloy actuators

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There is no reported research in the literature of using shape-memory alloy (SMA)actuators for variable area exhaust nozzles for a jet engine, to the authors’ best knowledge.SMA actuators have the advantage of a high power-to-weight ratio and can resultin dramatic weight reduction as compared to hydraulic systems. However, thedifficulty of using SMA actuators for controlling variable area exhaust nozzles liesin the fact that the temperature near the exhaust nozzle is far higher than thetransformation temperature of an SMA actuator. Due to the flexibility and smallvolume of SMA wire actuators, they can be remotely replaced in a region where thetemperature is lower than that of its transformation temperature. By exploitingthis fact, this paper presents a novel design of a proof-of-concept variable areaexhaust nozzle using shape-memory alloy wire actuators. The SMA actuators areremotely placed away from the exhaust nozzle area so that the environmentaltemperature is below their transformation temperature. By electrically heating theSMA actuators, the exhaust nozzle will experience an area reduction of up to40%. Bias springs will apply forces to return the exhaust nozzle to the open-upconfiguration. A feedback controller based sliding-mode method is used to regulate theSMA actuator position. Experimental results demonstrate that the proposeddesign meets the desired area variation specifications and shows the promise of alightweight and simple exhaust nozzle design by using shape-memory alloy actuators.