In an earlier post I talked about installing an engine fire suppression system. The engine on my cat is very tightly cowled and would pose a serious problem should a fire develop inside. I have a 2.5 lb remote Halon fire bottle but I decided that would be overkill. (Plus, they are expensive and can only be used for whatever they are plumbed to. I had plans to use it on my new plane which would be a more effective use.) The total volume of the engine compartment on this cat is very small. I also had a 1-1/4 lb Amerex Halon unit so I mounted it up over the windshield. In order to access the engine compartment, I made a receiver that mounts on the angled part of the air duct. It is about .875 diameter and about 1" long. One end is threaded 7/16-20 to fit the union. The other end is bored about .005" larger than the outside diameter of the extinguisher nozzle. I then bored an o-ring groove in it for an MS29512-014 o-ring. The groove is bored just deep enough radially to provide about a .010 squeeze on the extinguisher nozzle when it is inserted into the receiver. This prevents any Halon leakage into the cab. I used an AN 815-4d union to connect the receiver through the cover and to a 1/4 stainless tube and AN818-4J coupling nut and sleeve on the inside. The tube is bent to direct Halon into the carburetor area which is the most likely fire point. 1.25 lb of Halon is enough to flood the engine compartment and the tunnel. The initial discharge pressure of a Halon extinguisher is 125 psi.
This setup has the advantage of allowing the extinguisher to be used elsewhere if needed.
The best buy on a 1-1/4 lb Halon extinguisher is from Aircraft Spruce and Specialty
http://www.aircraftspruce.com/pages/ps/fire_13/a344t.php This is an H3R A344T unit which is identical to the Amerex unit I have, and lists for $107.95. Amerex units are listed on ebay for $125.
About Halon: This is the best fire fighting agent known so naturally the EPA would outlaw it due to its ozone depleting properties. It has been illegal to make since 1998. All Halon available now is recycled and has gotten more expensive but can still be purchased in newly manufactured extinguishers. Halon 1211 is discharged as a liquid but turns to a gas rapidly. It is mainly used in handheld units so it can be directed at a fire. Halon 1301 is stored as a high pressure gas and is used in aircraft engine compartments and other enclosed applications.
I have always used Halon 1211 in my hangar and planes.
Halon agents extinguish a fire by interrupting the chain reaction between the fuel and oxidizer. This makes them very quick and effective. Other agents such a dry chemical or Co2 only remove the oxygen and are cheaper but less effective. Dry chem does not lend itself to enclosed spaces like engine cowls. Halon also has the advantage of not damaging your equipment once the fire is out. It just evaporates. (Into the Ozone layer I guess)
There is a Halon substitute available called Halotron 1. It can be manufactured until 2020, is a little cheaper but from what I have read, it is about half as effective as Halon 1211 but still better than dry chem. (sodium or potassium bicarbonate)
This would be a very inexpensive and effective fire suppression setup for any of the 1402, 1404 or 1450 Thiokol's and LMC's or any cat with the engine in the cab.
I was planning on taking the cat to it's new home this week but I had a problem with my defroster vents. They were a little too close to the exhaust manifold and melted. (Plastic) So I am going to use a Peterbuilt Semi-truck cab side air vent (all steel) mounted on top of the cowling. I'm waiting for the parts and will have a post about it when I get it done.
A little too close to the manifold I think. Good thing I found this out before I took it over to the mountains. So I made a couple of covers for the holes and found a horse trailer vent on ebay that is all metal. I like this better anyway because it will deliver much more air right onto the windshield and is fully adjustable from zero to a lot. It can also be opened the other way to blow hot air into the rear cab. Another advantage is that after engine shutdown, I can open it to vent hot air out of the engine cowl as this is the high point of the cowl. The engine can then cool more effectively through convective flow. This is the same type vent that Nikson used on the front of the cab for fresh air.
