| Fire Detection |
| After a friends Velocity engine caught fire inflight, I started giving a lot of thought to a fire detection system. Just snooping around a little bit, I found out that all new light aircraft have fire detection systems. All the aircraft I investigated use the same type of system. They use a simple thermal switch to detect an over heat condition presumably caused by a fire. Purchasing a system from an aircraft maufacturer for a single sensor and a red light cost a staggering $4000. Holy Sh#t !! After speaking to knowledgable people on the subject, it was determind that the following was needed: The highest average cowling exhaust temp must be known. Then a buffer was added. The recommended value was 50 to 100 deg F. The switch needed to be a rugged normally open SPST device that closed at the desired temperature thus illuminating the FIRE light. FWIW, I decided 'ask) the highest exhaust temperatue to be 200 deg F. I had a switch custom made to close at 300 Deg F. This gave me a 100 degree buffer and makes me confident the thing will never give a false warning. The system had to have a closed loop test function to ensure all wiring to the switch and back was in tact. I added an aluminum heatsink to the sensor to insure it got the heat changes as soon as possible from the airstream. I even used some heat sink compound to reduce the thermal impedance. I want as quick of notification as is possible! Bottom line: 300 Degree sensor $0 free. Got it as an engineering eval unit. Heatsink $.75 Wire $3.00 Bright red FIRE LED $.55 Press to test switch $3.00 Total cost $7.30 Plus about 3 oz. weight for piece of mind. |
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| This is the switch and the heatsink |
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| Here the completed sensor assembly has been installed in the cowl air exhaust flow area. The sensor is held to the heatsink with two -8 stainless screws. Note wires heading for the cockpit. This allows closed loop testing of the entire system during preflight. |
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| A slightly different view showing the heatsink contact area. |