|
In August of 2005 The Boeing Company conducted a full-scale flight test utilizing Shape Memory Alloy (SMA)
actuators to morph an engine's fan exhaust to correlate exhaust geometry with jet noise reduction. The test was
conducted on a 777-300ER with GE-115B engines. The presence of chevrons, serrated aerodynamic surfaces mounted at
the trailing edge of the thrust reverser, have been shown to greatly reduce jet noise by encouraging advantageous mixing
of the free, and fan streams. The morphing, or Variable Geometry Chevrons (VGC), utilized compact, light weight, and
robust SMA actuators to morph the chevron shape to optimize the noise reduction or meet acoustic test objectives. The
VGC system was designed for two modes of operation. The entirely autonomous operation utilized changes in the
ambient temperature from take-off to cruise to activate the chevron shape change. It required no internal heaters, wiring,
control system, or sensing. By design this provided one tip immersion at the warmer take-off temperatures to reduce
community noise and another during the cooler cruise state for more efficient engine operation, i.e. reduced specific fuel
consumption. For the flight tests a powered mode was added where internal heaters were used to individually control the
VGC temperatures. This enabled us to vary the immersions and test a variety of chevron configurations. The flight test
demonstrated the value of SMA actuators to solve a real world aerospace problem, validated that the technology could be
safely integrated into the airplane's structure and flight system, and represented a large step forward in the realization of
SMA actuators for production applications. In this paper the authors describe the development of the actuator system, the
steps required to integrate the morphing structure into the thrust reverser, and the analysis and testing that was required
to gain approval for flight. Issues related to material strength, thermal environment, vibration, electrical power, controls,
data acquisition, and engine operability are discussed. Furthermore the authors layout a road map for the next stage of
development of SMA aerospace actuators. A detailed look at the requirements and specifications that may define a
production SMA actuator and the technology development required to meet them are presented. A path for meeting
production requirements and achieving the next level of technology readiness for both autonomous and controlled SMA
actuators is proposed. This path relies strongly on cross functional and organizational teaming including industry,
academia, and government.
|
