Fiber-Optic Shape Sensing and Distributed Strain Measurements on a Morphing Chevron

Boeing has recently flight tested a Variable Geometry Chevron (VGC) system which used shape memory alloy (NiTinol) actuators to drive changes in shape. At take off, the VGCs immersed into the fan stream to reduce jet noise; at cruise they were actively morphed to investigate shock cell noise and performance losses. A set of three strain gages mounted on each chevron provided estimates of its tip position (shape) and feedback to the on-board control system. During the development of the VGC flight system, Luna Innovations instrumented two VGC test articles with shape probes, a new technology in which multi-core fiber provides distributed and axially co-located differential strain measurements to generate complex shape data. This technology shows promise of providing a more direct correlation of NiTinol actuation to chevron shape and tip immersion. Additionally, Luna Innovations instrumented each VGC with high density distributed strain fiber to provide hundreds of discrete strain measurements over the surface of the chevron.