Flight Tests of Fiber-Optic Interferometric Strain Gauges for Load Monitoring of Aircraft Structures

Abstract

A large number of fiber optic interferometric strain gauge concepts has been investigated during recent years (e.g. 1,2,3), however only little experience exists up to now with respect to aerospace applications under real world conditions4,5. In this paper we report inflight dynamic load monitoring of plates made from carbon fiber composites, which are screwed to the main wing spar of a Cessna C207A. Several flight tests have been performed with four different sensors since June 92. The fringe counting readout of passive quadrature demodulated double-polarization Michelson interferometers with balanced interferometer arms (OSG)3 is compared to the strain indicated by conventional resistive strain gauges (ESG). Of particular interest is the response of the interferometric sensor to the quasistatic maneuver-dependent load variations given strong simultaneous structural vibrations due to engine and aerodynamic effects.