Installation report: engine fire extinguisher system

pboyce · #1 09-19-2008, 03:23 PM

I decided to intall an engine fire suppression system in my RV-7A after reading an article about fire extinguishers in the August 2008 issue of Kitplanes. I was also inspired by another RV builder who kindly shared his ideas with me. Lots of hot-rod car builders put these engine compartment sytems in their cars, but interestingly, not a lot of homebuilders put these systems in their planes. Fortunately, it appears the likelihood of an inflight engine fire is very low, though I've never seen any statistics on it. Perhaps this is the reason we don't see many of these systems in small piston powered aircraft?

I called up Safecraft, a company referenced in the article, and ordered their AS model. This included the cylinder with 3 pounds of halon and all the hardware, including 3 identical spray nozzles. Each nozzle sends a spray in 3 directions, an arc of about 150 degrees. I dispensed with their supplied steel fittings in favor of AN aluminum fittings. Total weight with everything is about 4.5 pounds.

I chose to mount the cylinder horizontally on one of the panel ribs, adjacent to the firewall. This location meant it would be out of the way and from a practical standpoint not affect my CG. If you choose to mount in the same location, be sure to ask Safecraft for the old style head--their new style head is longer and will not fit in this location. Also, if you choose to mount the bottle horizontally, ask Safecraft to install an internal pickup tube in the cylinder.

Before mounting, I riveted a piece of 0.040 to the rib to act as a reinforcing doubler. Since my plane was already built, this mounting task turned out to be a lot more work than I expected. I spent countless hot hours on my back under the panel! On an under-construction RV, this task would be extremely easy.

After this task was completed, I ran aluminum tube to the engine compartment. Safecraft recommended 2 nozzles forward of the baffle and 1 nozzle behind the baffle. For the transition from the stationary engine mount to the moving engine, I used Aeroquip 303 hose.

I am pleased with the quality of the Safecraft product. I hope I never have to use it! By far the hardest part of this project was simply getting over the mental hurdle of adding more weight to my airplane. In the end it was $400 well spent, in my mind cheap insurance.

Paul

asav8tor · #2 09-19-2008, 04:06 PM

I think it's a great idea. The halon displaces air to put out the fire.

I'm wondering however, won't the halon be displaced by the ram air faster than it discharges rendering it ineffective? Kind of like throwing an ice cube in a river of lava?

Mike S · #3 09-19-2008, 04:14 PM

Paul, nice setup.

A word of advice from an old fireman.

Before you pull the pin on the extinguisher, be sure the fuel, and ignition, (or even the entire electrical system) are off.

Your Halon system is pretty much of a one shot deal, and you dont want the fire to re-ignite, and you to be out of extinguishing agent.

One more thing that could help, pull up steeply to almost stall speed first------less airflow through cowling.

pboyce · #4 09-19-2008, 05:24 PM

Mike,

That's good advice. You're right, it's a one-shot deal. Pull the cable and all the halon gets released.

As for the previous person's question about ram air displacing the halon, from the Kitplane article, apparently halon is extremely effective even at low concentrations because it "stops the chemistry of combustion", not just removing oxygen. Halon 1211 needs only a 2% concentration to put out a fire while Halon 1301 needs a 10% concentration.

RScott · #5 09-19-2008, 05:26 PM

I've wondered the same thing as Asav8tor--would the Halon be diluted by the incoming ram air as to be worthless?

Also, as one who admittedly knows nothing about engine fires, I wondered how serious a fire would be once the fuel and electrical were shut off? Insulation and hoses might continue to burn, but how serious would that be? Tefzel is supposed to be fire resistant, but will it burn after the flame source is removed, i.e., fuel flow is shut off? What about hoses and ducting? When the main fuel source is removed will these continue to burn in the presence of ram air flow?

L.Adamson · #6 09-19-2008, 06:28 PM

Quote:

Originally Posted by RScott

Tefzel is supposed to be fire resistant, but will it burn after the flame source is removed, i.e., fuel flow is shut off?

I had a "shorted" #4 wire that got red hot, and melted. The Tefzel just turned kind of liquid and fell off. It didn't even ignite. This wire was in a bundle with others, and they weren't even phased.

And no, this wasn't in a flying airplane...

L.Adamson

pboyce · #7 09-19-2008, 06:37 PM

Keep in mind that a fuel-related fire is not the only possibility. Oil-related fires are also a distinct possibility. Also, an exhaust pipe could crack, spewing hot air that could ignite something.

Kevin Horton · #8 09-19-2008, 11:34 PM

Quote:

Originally Posted by asav8tor

I'm wondering however, won't the halon be displaced by the ram air faster than it discharges rendering it ineffective? Kind of like throwing an ice cube in a river of lava?

Maybe. FAR part 25 aircraft halon system designs are validated by flight test - the system is discharged at various airspeeds, and the halon concentration is measured at numerous locations around the engine. It is quite normal to find that the location and orientation of the halon nozzles must be changed to achieve high enough halon concentrations. And this is often true even when the initial design was done by people who have done this many times before.

By all means, install a halon system if you wish, but don't assume that it will work when you need it.

asav8tor · #9 09-20-2008, 12:26 AM

Just a couple more thoughts (nice install by the way).

The AL feed lines and fittings might be melted by fire. Did you consider SS?

A shutter type ram air door or simply a door that closes off the ram air via the same cable that shoots the bottle could be built.

jetjok · #10 09-20-2008, 05:56 AM

The may be a dumb question, is there any protection for the bottom of the engine? As a previous poster stated, the ram airflow will likely disapate much of the halon in the top section. My concern is that there seems to be a much greater chance of fire under and behind the engine.
The exhaust system, fuel supply and metering, oil cooler and supply lines, and electrical wires and components, are all mounted behind and below the engine. There seems to be a greater chance of fire in these areas. I noted that you have one of the tubes mounted so as to discharge on the right aft side, nothing for the left or below.
All in all though a very nice installation, and certainly gives you much greater peace of mind.