It takes extraordinary circumstances for a combustible fuel/air ratio to be maintained "in an aircraft engine compartment" at flying speeds. If you think this is a rash statement, remember that within the engine compartment the only source of fuel is the fuel line FROM the fuel tanks or oil from the engine. The fuel line is capable of only a limited delivery of fuel and oil is even harder to burn than fuel. Since fuel has to be mixed with air (oxygen) within a fairly narrow ratio to be combustible, it would be difficult for a normal fuel line in a small aircraft to deliver enough fuel to bring that ratio up to the necessary point to establish or maintain flames.

On the ground, the story is very different. Without the high airflow, a fire can be sustained in an engine compartment very easily. From the standpoint of danger and potential loss, the risk on the ground is usually to the aircraft since the occupants of small aircraft on the ground experiencing an engine fire usually exit the plane safely. I myself experienced a small fire in my original Seahawk. The fire was confined to the throat of the carburetor and luckily didn’t last long enough to hurt anything, but it sure put a scare into me. The cover between the engine compartment and the baggage compartment was off and I could see the flames! In another instance, one of the Seahawks that lost a wing many years ago landed safely and the pilot and his passenger got out of the plane. The fumes from the open tank of the wing that had departed caught fire from the hot exhaust and the plane burned up totally. The fire didn’t even start until after the plane had been on the ground for several minutes! A firewall would not have saved that plane.

You may agree with some or all of this discussion or disagree. I do not claim that any of these points are set in stone. The potential variables preclude any absolutes concerning this subject. But it is interesting to consider some of these points and for those that have not yet had personal experience or any other reason to consider these things, maybe this discussion will shorten your trip.

After many years working with the Glass Goose, I firmly believe the answer to be YES, you do want the firewall material in your plane.

I have come to this opinion for several reasons. 1. To provide substantial protection you don’t have to line the entire engine compartment with the material. Only the bottom and the forward part. The side walls do not need the material. 2. If you should have a fire on the ground, just those areas covered in the material would probably save your plane. 3. In the unlikely event of an in flight fire, the material would give protection to the luggage/passenger compartment and to the back of the upper wing and the fuel tank located there. 4. The ACS material with the ceramic fiber core also serves as a very effective sound barrier that substantially reduces the sound levels in the cockpit. I feel these are enough reasons to justify the installation and expense of the material.

Aircraft spruce sells a very good material to use for firewall material in the Glass Goose. I do not have the name of it at this writing, but it is a sandwich blanket made up of a stainless steel foil on one side and an aluminum foil on the other with a sort of fibrous ceramic material in between. It is about 3/16" thick altogether. It’s in their catalog. The stainless steel side goes toward the engine of course.

The stainless steel "foil" on the material is a very "dead" metal. It acts a lot like lead. When you bend it, it has no springiness at all! Dead materials like that tend to absorb sound rather than transmitting it. Lead foil is used in larger aircraft and other applications as sound deadening material extensively. So the sound reducing capability of this material is sort of a freebie that goes along with the fire protection it provides. I consider that a pretty good deal and 2 birds killed with one stone!