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Operation of advanced aircraft in the subsonic, supersonic and hypersonic regimes will require high degrees of propulsion and flight control integration. More sensors will be required for control and monitoring of the complex aircraft as well as more actuators to provide safe and efficient operation while at the same time providing for a high degree of maneuverability. Improved thrust to weight of these vehicles will be achieved through the use of high strength, low weight composites for the aircraft, propulsion system and control accessories (i.e., pumps, valves, actuators, etc.). The increased use of composites makes the digital control more susceptible to electromagnetic effects. In order to provide the protection to the digital control additional shielding will be required as well as protective circuitry for the electronics. This results in increased weight and reduced reliability. NASA and DOD have recognized the advantages that fiber optic technology pro-vides for advanced aircraft applications. The use of optical signals to carry information between the aircraft and the control module provides immunity from contamination by electromagnetic sources as well as other important benefits such as reduced weight and volume resulting from the elimination of the shielding and the replacement of metal conductors with low weight glass fibers. In 1975 NASA began work to develop passive optical sensors for use with fiber optics in aircraft control systems. Passive optical sensors require no electrical energy and operate with very low power optical signals. These passive sensors will result in less maintenance and improved reliability. Many interesting and innovative concepts for using optical signals to measure pressure, temperature, position, flow, speed, vibration, acceleration, etc. have been proposed and demonstrated in the laboratory. The problem now is to choose the best optical sensor concepts and evaluate them for use in the adverse environment of aircraft systems. In 1985 NASA and DOD entered into a joint program, called FOCSI (Fiber Optic Control System Integration), to look at optical technology specifically for use in advanced aircraft systems. The results of this program will be discussed. The objectives of Phase I of the FOCSI program were to conceptualize a fiber optic control system, define the environment in which the optical components must operate and define the specifications for the sensors. The environment issue is highly dependent on the location of the optical components (i.e, turbine region versus compressor inlet) and the aircraft flight envelope. Near term applications of fiber optics will be at relatively low ambient temperatures. Advanced aircraft such as the supersonic/hypersonic aircraft will present more of a challenge due to the higher temperature environment. The conclusion of the study indicated that the use of fiber optic technology in advanced aircraft systems is feasible and desirable. The study pointed to a lack of available sensors from vendors capable of operating in the adverse environments of advanced aircraft. In Phase II of the FOCSI program issues such as the electro-optic architecture required to service the sensors will be considered. Overall system analysis of the optical sensor and the electro-optic architecture will result in selection of the best systems for incorporation into advanced aircraft.
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