>the only way to keep the fire out is to keep the air out
>being able to shut the cooling air flow, at the exit or intake will help a
lot.

I'm trying to put this in perspective.
Assuming no way to shut off the intake air, is firing a halon extinguisher
in flight going to have ANY worthwhile impact on an engine fire? Keep in
mind that the fibreglass cowl is likely to be breached early on, thus any
control of airflow is lost. I'm beginning to think that the most important
issues here are detection, and removal of the source (fuel) and that an
extinguisher would be useful to save the plane once landed, but worthless
(and wasted) if used while airborne.

Thinking of fire makes me glad I built a pusher.
John

Yes John, early detection is vital so a heat sensor, naked flame detector is
vital as is an ambient under cowl temp sensor. First one will detect the
fire, and the second one will tell you how hot things are getting, and most
important tell you when the fire has gone out.
    The very best strategy is in aircraft design. You need cowl flaps for
BOTH inlet and air outlet points, so that you have total control of the
airflow through the cowl. There are two main reasons for this.
1) If you can control the air flow, you CAN control the fire, you starve it.
Believe me it works. Why do commercial kitchens have fire blankets.
2) When you fire off your halon extinguisher, you want to hold that cloud of
halon under the cowl for as long as possible. If there is no air flow it
ain't going any where fast, and secondly and most importantly as long as you
have that halon cloud under the cowl, there is a very low probability of
re-ignition. this can buy you very valuable time to find a safe landing
area.
    Other design factors are, a decent size drip tray and hear barrier
between the fuel rail and the exhaust port outlets. Don't allow fuel to drip
or spray onto a hot exhaust. Second, shield the exhaust pipe/s from shooting
a hot flame onto any fibreglass surface. Easier said than done I know, but
if it can be done it should. Otherwise experiment with industrial fire proof
matting on the inside surfaces of your cowl.
    An extinguisher that you can control, and that has enough reserve so
that you can fire off 50% to 60% initially, and then two or three bursts
three or four minutes apart. This tops up the level of halon under the cowl,
and buys you very valuable time.
    Fires can be managed, but like everything else, its a lot easier if you
design for them in the first place, and have a sound fire drill to put into
action.
Safe flying guys
Michael Burke
Australia


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