Early Fire Warning
 2006.01.13
 

Two wires
Hopefully current interest in early fire warning will result in offering a few good options for us.

While building I heard of an EZ that had a fuel line fire in the cowl.
The way I heard it he flew in the pattern unaware of the fire for some moments while his friends on the ground saw it and scrambled to get to a radio, unsuccessfully.

It seemed reasonable to me to have some clue in the cockpit as to a cowl fire. My intent was to get an early warning. There was no expectation to create the best or most comprehensive system ever, only to improve my EZ’s situation in a practical manner. This resulted in a simple design that provides about 30 detection points around the engine compartment.

Components
-A cockpit light and two unconnected ground wires.
The light is mounted high at the top of the panel with a hot wire.
The ground wire is in two long separate pieces; one bare, one insulated. In a fire they can touch, completing the ground connection and illuminating the light. My tests resulted in appreciation and confidence pretty quickly.

The insulated ground wire goes from the light, aft and through the firewall plus about ten feet. The second element of the ground wire is a used bare ten-foot long rudder cable attached to the ground point near the firewall.

These two wires are twisted together with about three twists per foot. They wrap around the engine with a loop around the carb and fuel pump and a couple of other places that seem logical. At the end they are held together with a piece of shrink wrap. The end of the cable can be bent and touch-tested to the end of the insulated wire.

Logic
The insulated wire is stranded automotive type so the insulation is not as heat resistant as aircraft wire. The gauge is thick to withstand burning in two too quickly.

The bare rudder cable is used because it is stiff and provides a nice combination of resistance and contact with the insulated wire. When testing and playing with different wires I liked this combination best.

The three-per-foot twists provide about thirty contact points along the ten foot length around the engine and cowl. Springs could be used at various points to pull on or improve tension and contact between the twisted pair.

During preflight, bending the cable to touch the end of the insulated wire confirms that the light is working. It’s fun to demo.
There is a push-to-test button on the dash, un-needed. A ton of other little tweaks and gizmos were left off.

In-flight fire extinguishing agent
There is a fire extinguisher accessible in the cockpit. The nozzle can be fitted into a flexible tube that goes along the fuselage side, back to a metal tube that goes through the firewall aimed at the carb.

Should I ever be so desperate to use the extinguisher, ventilation from the two fresh air vents can blow air directly into the face of the pilot and passenger, with a vent that pulls air from the cockpit.

So if the fire warning lights up in flight and I think my rear end might be about to be on fire there is an option to use the extinguisher to keep the airplane’s rear end from distorting. Also not a bad in-cowl extinguishing capability to have on the ground.

De Light! De Light!
So, what’s the first item on the Fire Warning Checklist?
Step 1- Fly de Airplane.
Step 2- Land as soon as practical.
Step 3- Options:
- Try to see if there is a fire.
- Close the fuel shutoff.
Step 4- Fly de Plane
- Extinguishing agent? At least there is the option.
Step 5- Fly de Plane

Some single engine fighters have a fire warning from the engine compartment but no extinguishing capability installed. I guess they figure that even after doing the emergency checklist, you’re better off not relighting it and you’re still going to be walking home. Until we come up with a foolproof 5 lb ejection seat, I’ll just keep the two wires. Even with the seat.

At my first mention of using the two wires several years ago there were a couple of negative comments made on the Canard-Aviators group. There was a concern that the light might come on when there was actually no fire and cause pilot distraction, loss of reasoning and probably a rushed crunched landing. Another observation was that adequate development of this system would require years of testing and millions of dollars.

They always bring a smile and more importantly nudge me enough to wake up out here and hopefully not do something really stupid that could be somehow attributed to those two wires. I enjoyed the comments and since they pop into mind during most preflights I just had to mention them.

Bill James, Fort Worth VariEze 
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