A flueric circuit for sensing afterburner light-off was designed, built, and successfully demonstrated on a GE J79-15A engine. The sensing principle took advantage of the fact that the kinematic viscosity of air increases with temperature to the 1.71 power. Therefore, laminar flow resistance of a capillary is very sensitive to temperature changes. This resistance change characteristic was utilized in a pneumatic bridge circuit, the output of which is proportional to temperature. The Flueric Light-Off Detector (FLOD) output was 1.5 psi for minimum afterburner light-offs and the time constant was about 0.3 sec which exceeded predicted performance. Output at max A/B was 15 psi. The FLOD functioned equally well as a blow-out detector. This circuit can also be utilized for main combustor light-off or blow-out indication and has the additional potential of absolute temperature sensing. The FLOD does not have a single moving part and required no filtration or pressure regulation.

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