The Challenger aircraft fleet of the Canadian Forces will fly demanding missions, requiring the implementation of a fatigue management program based on the monitoring of in-flight aircraft load conditions. Conventional sensing techniques experience problems arising from severe electromagnetic interference (EMI). This paper describes the development of an EMI- insensitive smart-structure sensing concept for loads monitoring. Fiber-optic strain sensors, incorporated at critical structural locations, are used to monitor the fatigue life of the aircraft wing, fuselage, and empennage. A fiber-optic accelerometer is also incorporated in the system. A long-term plan is presented for the development of an advanced smart-structure concept which can support the continuous monitoring of fatigue-prone components, and provide the aircraft with near real-time damage location and assessment.
A variety of glass waveguide devices, including passive components (splitters and couplers), active network components (waveguide switches, lasers and amplifiers), and sensors for the measurement of pressure acceleration, position, rotation, etc, are in various stages of development, or have reached the production stage, at various companies. These components are expected to have a major impact on the implementation of fiber-optic (FO) systems for aircraft. Many new functions and applications can be realized with their introduction. This paper examines factors which have so far delayed the introduction of these products. Applications of FO and integrated-optic (10) technologies, and the potential of glass waveguide devices in aircraft systems, are discussed.
This paper considers two important application issues of fiber optic sensors in aircraft structures. The first concerns the interfacing of optical fibers with composite material structures: concepts have been developed for realizing a reliable exit point for the embedded fiber from a composite aircraft component, by means of single-mode connector assemblies embedded in composite material structures. The second issue relates to the temperature stability of the sensors: temperature characteristics of two-mode fiber optic strain sensors were investigated, sensors made of elliptical core and bow-tie fibers are compared, and the trade-offs among strain sensor range, sensitivity and temperature stability are discussed.
A strain sensor system for smart structures and skins has been developed. The sensor system uses a two-mode elliptical core fiber sensor and two diode lasers, operating at nominal wavelengths of 750 nm and 780 nm, respectively. The lasers are frequency-modulated such that periodic mode hopping is induced. Data is sampled for each laser mode. A least-absolute-deviation method has been devised for calculating the sensor phases at both wavelengths. The ambiguity arising from the periodicity of the interferometer response is resolved by comparing all possible optical path differences corresponding to the sensor phases at the two wavelengths. The system is able to measure 0.01 of a fringe over a range of ten fringes.