Installation report: engine fire extinguisher system

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

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?

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.

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.

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?

RScott said:

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

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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

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.

asav8tor said:

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?

Click to expand...

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.

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.

Question

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.

While it's true I don't have a bona fide testing program to see if this system will really work when I need it, I am counting on a couple of things: 1) the amount of halon, 3 lbs, is A LOT of halon. As a comparison, a Boeing 747 has 6.5 lbs for each engine 2) the effectiveness of halon in stopping combustion 3) the fact that our engine compartments are very small relative to the expansion capability of halon gas.

Regarding stainless steel lines, yes that definitely would be an upgrade and is something I would like to do in the future. As you know, though, SS is hard to work with.

Regarding the fact that I only have 1 nozzle behind the baffle, the tech support guy Steve at Safecraft said given the small volume of this area, it would work. Keep in mind that each nozzle has 3 holes, ensuring that the spray pattern is quite wide.

Nice! Well, You never know if it will really work, but if I'm up there and that bad boy's on fire, I'd sure like a handle like that to pull! Hope you never have to report on it's effectiveness!

Bruce

jetjok said:

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.

Click to expand...

Ok - not to pick on the fire suppressant installation AT ALL here - but this is a very valid point. I would like to hear some data from some of the Reno racers (who regularly blow engines) or others who have grenaded engines in one fashion or another, to try to discern a pattern of what is likely to be the biggest problem area for an engine fire. In the case of catastrophic failure, you'll blow jugs, break the crank, or throw a rod - in which case you've got an oil fire, which means you would basically have to flood the entire FWF area with Halon because the engine case is no longer an engine case.

For a fuel fire (regardless of the ignition source) I'm thinking behind and under the engine is going to be your biggest problem. The cylinders aren't going to burn, unless the jug is blown off and oil is burning through that hole. I'm also thinking that we (non-racing pilots) are less likely to crack the case and make an oil fire, as we are to have a broken fuel or oil line and start a fire that way.

Anybody care to throw in any real data points that are not complete conjecture?

The natural tendancy would be for the air to be forced down through the cylinders via cooling flow. So you might as well have it there and let it flow down through the cylinders to the underside and back.

Bruce

nice install...

Hello Paul

The photos are great, the install looks good and that's a nice clean engine as well. A few comments from my certified perspective may be worthwhile though.
The distribution lines as someone had already said should be stainless steel. The engine fire extinguishing systems in the King Airs and Twin Otters I work on are all fed through stainless distribution lines with stainless fittings. Behind the firewall aluminum lines would be fine.
I have never heard of one of the systems being used and I guess that is a good thing. Hope you never have to use yours.
Firesleeve on the fuel lines is a good idea but consider the oil lines as well. All lines I've seen in turbine engine compartments are firesleeved. It's only a few ounces to add firesleeve to the oil cooler lines, the piece of mind added is worth a lot more.
A note about firesleeve installation though, the ends should be clamped to the hose end fittings just behind the B nut and coated in sealant. I have seen all to often the end band clamp come off and the fibers frayed and acting like wicks to soak up all the oil and fuel they can hold. I would think firesleeve is not very effective when it's saturated with flammable fluids. Lock wire can be used to secure the ends (I've seen ty wraps used!) and the red high temp silicone to coat the fibers and seal them.
The only fire related story I can think of is a Zenith CH200 pilot that credits the firesleeve on his fuel lines for saving the day when his exhaust cracked. It was directing very hot exhaust on the fuel lines in the bottom part of the cowl and they didn't burn.
Just my two cents. Have fun.
Phil

Use of Engine Fire Supression

I have a friend with a Glasair III that he planned to race at Reno (He never did). He had a very similar system with the nozzles arranged at the bottom of the engine, one forward of the gear retract system, one near the fuel servo. He said that his system was not intended to be used in-air, but on the ground, usually after a crash. A grisly thought, but there it is.

All of his lines were flexible stainless steel all the way back to the tank.

Paul...

I hate to ask a stupid question, but why do you want/need a fire extinquisher system in a single?

Are you concerned a fire may well disable you/ the aircraft before the forced landing? Or do you want an aircraft less damaged (by fire) after the forced landing (assuming the forced landing hasn't damaged the aircraft)?

I've flown various aircraft in my career, with varying numbers of engines, and on a single they usually aren't fitted because their usefulness is hard to determine. In a multi they enable continued (safe) flight, but in a single, you're going down anyway, and quickly

Last SE Mil type I flew removed the Fire Extinquisher in later models for exactly the above reason...

Just curious

Andy:

Your question is actually a good one.

My primary motivation is to avoid being burned to death BEFORE I have to land the plane. Also, to reduce/eliminate the amount of smoke coming into the cockpit from a firewall forward fire.

Data for inflight engine fires for piston singles is hard to come by unfortunately, so an accurate risk assessment of this sort of hazard is extremely difficult. Thankfully, we can all agree they are rare, though they can occur.

One incident that comes to mind involves an RV-8 engine compartment fire. The pilot decided to jump out of his burning airplane at low altitude. The jump resulted in his death. More details can be found at this NTSB link:

http://www.ntsb.gov/NTSB/brief.asp?ev_id=20001212X19358&key=1

Engine Fire

About 15 years ago a friend of mine hauling checks out of DAL in a Baron had the left engine get rough prior to rotation. Before he got it stopped there were flames coming out of every hole in the cowl. What happened was an injector line broke and sprayed fuel all over everything, including a very hot exhaust.

It is my understanding that in the short time it was burning there was enough structural damage done that the wing was scrapped. He continues to be very happy all this took place prior to rotation and figures if it happened a minute or two later he would have been part of*one smoking hole in North Dallas and the wing in another.


*

Why I want a fire suprresion system

The temperature of an open gasoline fire is approximately 1500F. Aluminum in the immediate proximity will be melted Aluminum in the vicinity will reach a temperature where its structural properties are greatly compromised.

In the event of an engine compartment fire, it is a certainty that the plane will be lost. The important thing is to dive toward the ground as rapidly as possible, pulling out close to the ground, and hopefully having suppressed the fire to the extent that I don't have a complete structural failure pulling out of the dive.

This is what I was taught during a BFR conducted by a friend who is a United Airlines check pilot, among other accomplishments:
1. Time is of the essence.
2. Get on the ground as quickly as possible, by which he meant push over, exceed Vne and risk moderate structural airframe damage pulling out of the dive. Bleed off the speed once close to the ground.

To that I would add, carry hull insurance so you don't have any second thoughts about doing this.

In flight fire is a rare occurrence and a very unpleasant topic to talk about. During all the years I raced cars, I only personally witnessed two crashes that involved fires that injured the driver. In the second crash, the driver wound up permanently disabled. His car was pitted next to mine and it could have been repaired and raced the next week because steel does a lot better than aluminum. The day following that race, I ordered Simpson's top-of-the-line quilted nomex driving suit. I still remember that poor fellow's name 35 years later.

In summary, I think a fire suppression system is a great idea because it buys a little bit of time to get on the ground (and our emergency procedure should call for getting on the ground in as little time as possible) and I sincerely hope none of us ever has to use it.

Larry

pboyce said:

The pilot decided to jump out of his burning airplane at low altitude. The jump resulted in his death. More details can be found at this NTSB link:

http://www.ntsb.gov/NTSB/brief.asp?ev_id=20001212X19358&key=1

Click to expand...

This was just discussed in another thread last week, and it is not an accurate statement. Von did depart the aircraft in flight sans chute, but whether he did so intentionally or accidentally is a matter of some debate. We will never know for sure. Just want to set that record straight.

http://www.vansairforce.com/community/showthread.php?t=34116

Starting at about post #20.

Time at concentration

pboyce said:

Mike,

Halon 1211 needs only a 2% concentration to put out a fire while Halon 1301 needs a 10% concentration.

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We did about a year's worth of engine compartment fire suppression testing for the military several years ago. The number one most critical factor in achieving success was stopping the airflow first. Yes, Halon works at very low concentrations, but only if one can maintain that minimum concentration long enough. Suppression of the fire is not instantaneous and if it is not extinguished 100%, it comes back to life.
The graph below shows what we are up against (mass flow through my engine compartment). You've got a lot of fresh air coming in. One would have to meter the discharge and completely mix the Halon for 10 to 20 seconds.
On the ground, a system like this should work really well and plenty of planes have burned up while on the ground that could have otherwise been saved.

Chris:

Thanks for posting this data.

It certainly points to the difficulty of assessing how effective a halon system will be in a flying (and burning) airplane.

You state that the 'number one most critical factor in achieving success was stopping the airflow first.' I'm concluding that this is because stopping the airflow allows the concentration of halon to get high enough to stop the fire. So this would argue for slowing down the plane during an inflight engine fire, right?

What's interesting is that this runs counter to 'conventional' wisdom. Many people on this forum have said to speed up in order to get more airflow, thus putting out the fire. Maybe this makes sense only if you DON'T have a halon system?

Chris, I think you've stirred the pot a little.

btw: I called up Safecraft to find out how long the halon discharge lasts for in their 3 lb system. He said about 20 seconds.

pboyce said:

Chris:

Thanks for posting this data.

It certainly points to the difficulty of assessing how effective a halon system will be in a flying (and burning) airplane.

You state that the 'number one most critical factor in achieving success was stopping the airflow first.' I'm concluding that this is because stopping the airflow allows the concentration of halon to get high enough to stop the fire. So this would argue for slowing down the plane during an inflight engine fire, right?

What's interesting is that this runs counter to 'conventional' wisdom. Many people on this forum have said to speed up in order to get more airflow, thus putting out the fire. Maybe this makes sense only if you DON'T have a halon system?

Chris, I think you've stirred the pot a little.

btw: I called up Safecraft to find out how long the halon discharge lasts for in their 3 lb system. He said about 20 seconds.

Click to expand...

You are correct. Stopping the airflow gives the Halon time to build in concentration and get into every little corner of the engine compartment.
More ariflow turned the flames into a blow torch

I was a little critical of the installation at first but don't discount it. I have read of total hull losses on the ground from an engine fire so even if all the halon blows out in flight there is merit to the idea from real risk losses that have happened on the ground. My gut feeling is fire is perhaps more likely on the ground. Sure would be worth a whole lot to have that handle to pull in that case. If you could get the insurance to lower your cost a few bucks the system could pay for itself.