Sender: "Marvin Kaye" <marv@lancaironline.net>
To: lml@lancaironline.net
Date: Thu, 18 Nov 2004 22:13:34 -0500
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From: "Jabe Luttrell" <JabeLuttrell@comcast.net>
References: <list-536910@logan.com>
Subject: Re: [LML] Re: Halon fire extinquishers
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Hello Chris,

There is very likely way too much air entering the cooling inlets for a fire
to burn above the engine.  You only have fuel systems on the top of the
engine which will quickly become diluted in the cooling air to mixtures too
lean to burn.  Below and especially behind the engine the airflow is slowed
down, although continually refreshed with air flowing around the cylinders.
Behind the engine you have both fuel and oil sources.  Under the engine you
have hot exhaust jets (from cracked pipes) and composite cowlings.

On naturally aspirated engines there are few if any oil hoses to rupture or
chafe.  There are fittings and sensors that should be checked for security,
however.

On turbocharged engines there are oil supply and return hoses to the
turbocharger bearings and the waste gate controller.  All of which can
rupture and spray hot oil on very hot high mass steel parts that can ignite
the oil.

In airplane applications that have installed fire extinguishers the spray
nozzles are divided to direct the flow of extinguishant to the area behind
the engine as well as to the top of the engine.  The top nozzle won't
extinguish the fire on top of the engine in flight (it will when the fire is
on the ground, which does happen) but the extinguishant will flow under the
engine and mix with the air behind and below the engine.

Halon doesn't cool, smother, or remove oxygen as other extinguishants do but
rather preferentially participates in the chemical reaction causing the
fire, interrupting the process of reaction making the fire.  That's why it
stops the fire so quickly, IF it is not removed from the fuel source by
continued flow of the fuel source (oil or gas).

If you have an engine fire it is important to shut off the gas first (this
will quickly stop the fuel injected engine too), because the leak may be
upstream of you mixture control.  Then stop (ignition off and slow down) the
engine to stop the oil pumping.  Then extinguish the fire.  Do it all
quickly to limit the amount of burn.  More automatic systems in jet aircraft
do this in a single stroke of the fire switch.  Then get the plane on the
ground.

If you don't have an installed engine compartment fire bottle, the make sure
that all your fuel and oil fittings are torqued, secure, thread sealed, and
are not leaking. After first flight, at regular periods thereafter, and
every time the cowling is removed inspect all your hoses and flammable fluid
carrying fittings.  Be certain that all oil and fuel hoses are fire proof
(forget neoprene for fuel and oil) and are not under tension at any time;
i.e. both when the engine is at rest and when the engine is under load (it
moves both as vibration and in reaction to the propeller torque and thrust).
Secure (Adel clamps)all the hoses so there is NO chafing possible.  Replace
all hoses (cheaper than a fire) if any surface cracking is detected
(visually).  Be sure there are no holes in your firewall or fire blanket.
Painting the cowling with intumescent paint sounds like a good idea. (There
is an intumescent varnish used on military aircraft the char of which
withstands high velocity air and won't blow off
http://www.indestructible.co.uk/cat2/PL161_2.html).  Check for fuel leaks
from the fuel pump and pump tell tale. Check for leaks on the mixture
control unit (if you're unlucky enough to have one). Carefully check for
exhaust pipe cracks when you check your hoses.  The hoses feeding oil to the
turbocharger are most likely to degrade fastest because of the intense heat
they are near.  Install metal radiant shields between the turbo oil hoses
and the hot metal.  Check for cracks in the cylinder heads around spark
plugs.  Check for leaks in the push rod tubes. Don't hang anything on the
pushrod tubes or on the fuel feed lines.

Doing these things will minimize the possibility of fire and obviate the
need for a fire extinguisher in the engine compartment.  It also saves
weight.

Jabe Luttrell
Legacy N550JL


----- Original Message ----- 
From: "Christopher Zavatson" <Christopher.Zavatson@udlp.com>
To: "Lancair Mailing List" <lml@lancaironline.net>
Sent: Thursday, November 18, 2004 12:17 AM
Subject: [LML] Re: Halon fire extinquishers


> Ron,
> <<  If I shut of the fuel. Discharged a 2.5 pound bottle in the air
> stream  around the cowl openings. Would this from your experience have a
> chance at putting out the fire?>>
>
> I finally had the opportunity to run some numbers using the 360 as a
> baseline and found the chance of success with a 2.5 lb bottle to be very
> slim.  At cruise speed, there is no way to maintain the needed
> concentration for any significant length of time.  Slowed to 80 kts,
> with a metered discharge rate, you can only get half the duration I
> would consider the bare minimum to even have a shot.   A better approach
> might be to put the emphasis on detection.  I suspect that most engine
> fires are not detected for some time since the airflow naturally carries
> the fire underneath the plane and out of view of the pilot.  If the
> engine keeps running, melting floor board may be the first sign of
> trouble.
> Chris Zavatson
>
>
>
> --
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