REFLECTOR:Looking for suggestions about fire detection
Jim Agnew
reflector@tvbf.org
Tue, 20 May 2003 18:41:54 -0700 (PDT)
I don't believe that they would be anywhere as effective
for the following reasons.
First you must accommodate two extremes no or low airflow
like idling or taxing and high-speed large airflow and
everything in-between. Then you have up or downdraft
cooling that must be considered. Given these parameters we
can assume that most fires are going to be burning liquid
so we will concentrate on those first.
At little airflow the burning liquid will (personal
experience) flow forward and collect at the low point of
the cowl producing a lot of hot gases that will rise and
heat the upper cowl near the rear the most. Thus the high
mounted rear cowl sensors will most likely trip. With low
airflow the heat will also travel rear to exit following
the upper cowl and most likely trip the top rear sensors.
As airflow increases you will get more of a blowtorch
effect out the rear and depending on up or downdraft
cooling the upper or lower rear sensors should trip.
No lets look at a fiberglass fire where the cowl is
burning, it would most likely be caused by an exhaust pipe
breaking and burning a hole thru the fiberglass, which will
burn. The flame will probably burn both inside and outside
the cowl and hopefully burn thru the wires or trip a
sensor.
Given the airflow thru the cowl I don’t know how effective
a Halon system will be. You will have to flood the cowl
very quickly and with plenum cooling the plenum as well.
When I was Flag Marshall for the SCCA I taught fire
fighting in racecars and fought a lot. I can tell you that
it takes a lot of almost any firefighting agent to put out
a gasoline fire and flashbacks are common.
Jim
--- Paul Calhoun <paul@med-amb.org> wrote:
> Jim,
> Would not your eight thermal fuses work just as well
> attached to the
> engine mounts forward of the engine and attached to the
> plenum and
> engine bolts in the rear of the engine near the cowling
> exhaust? This
> would avoid problems arising when the cowls are detached.
> The 22g wire
> {perhaps 18g)would be suspended in space between
> attachment points. Each
> fuse would possibly need to be anchored at both ends of
> the fuse.
>
> Just thinking aloud.
> Paul
>
> -----Original Message-----
> From: reflector-admin@tvbf.org
> [mailto:reflector-admin@tvbf.org] On
> Behalf Of Jim Agnew
> Sent: Monday, May 19, 2003 7:32 AM
> To: Velocity Reflector
> Subject: Fwd: Re: REFLECTOR:Looking for suggestions about
> fire detection
>
>
> Will have to post the picture on the Galery later, it is
> too big.
>
> Jim
> --- Jim Agnew <jim_agnew_2@yahoo.com> wrote:
> > Date: Mon, 19 May 2003 05:03:08 -0700 (PDT)
> > From: Jim Agnew <jim_agnew_2@yahoo.com>
> > Subject: Fwd: Re: REFLECTOR:Looking for suggestions
> about fire
> > detection
> > To: Velocity Reflector <reflector@awpi.com>
> >
> > Added a low res copy of the picture.
> >
> > Jim
> >
> >
> > Wayne,
> >
> > This is exactly the circuit I used several years ago
> and
> > it
> > works well. You need to keep the sensors in the 140
> > degree
> > C (284 F) range or a little lower since that is very
> hot
> > for fiberglass. I used 4 sensors on each cowl half 2
> > front
> > about 18" apart under the area behind the engine in
> case
> > gas or oil ran back burning and two in the rear of the
> > cowl
> > just forward of the reinforcing ridge about 12" apart
> to
> > get fire exiting the cowl. The upper cowl has the
> > sensors
> > in the same place. Obviously this should be looked
> upon
> > as
> > a "possible fire warning" circuit since a sensor or
> wire might fail.
> > I used #22 tefzel wire and covered all of the
> > wire on the cowls with one fine bid leaving the sensor
> > body
> > exposed.
> >
> > Now for the real trick, I originally used locking plugs
> > on
> > each cowl to connect the wires. I quickly found that
> > this
> > was a real pain and decided to make an automatic
> > connector
> > so I could just install the cowl haves without worrying
> > about the connections. I settled on alarm system
> window/sliding door
> > Foil Take-off Contact switches (example picture
> attached) that you
> > should be able to get inexpensively from alarm system
> installers.
> > They have high
> > pressure wiping nickel contacts with one or more
> > "fingers",
> > depending on the make, and are very dependable.
> Install
> > the fixed portion on the engine bulkhead and the moving
> > contact on the cowl. It will take some trial and error
> > in
> > placement and mounting. Mine are mounted on the side
> > curve
> > of the cowl.
> >
> > Hope this helps those planning to use this type of
> > system.
> >
> > Jim
> >
> >
> > --- Wayne Owens <wamowens@bellsouth.net> wrote: Woops.
> > What
> > Digi-Key calls them now is Thermal Cutoffs. They list a
> > bunch from Panasonic for various temperatures in
> degrees Centigrade.
> > Part numbers are similar to P10925-ND.
> >
> >
> > Flashing LEDs show up in a couple of places L20691-ND
> has
> > a
> > built in resistor for 13 volts 671499-ND requires a
> > 1000 to 2000 ohm 1/4 watt resistor in series according
> to
> > how bright you want it on the panel. Don't go much
> below
> > 1200 ohms.
> >
> > If the attachment is too large I will post it to the
> > Jamaican goose thingy. Wayne
> >
> > ----- Original Message ----- From: Ronnie Brown To:
> reflector@tvbf.org
>
> > Sent: Sunday, May 18, 2003 8:53 AM
> > Subject: Re: REFLECTOR:Looking for suggestions about
> fire detection
> >
> >
> > Wayne.
> >
> > How about a part number? I did a search on Thermal at
> Digikey and got
>
> > no response.
> >
> > THANKS! Ronnie
> >
> > ----- Original Message ----- From: Wayne Owens To:
> reflector@tvbf.org
> > Sent: Saturday, May 17, 2003 6:12 PM
> > Subject: Re: REFLECTOR:Looking for suggestions about
> fire detection
> >
> >
> > I used Thermal fuses (from Digi-Key) in a string
> > (series) around likely hot spots. One end is grounded
> and
> > the other end is tied to the anode of a flashing red
> LED
> > (also Digi-Key)on my annunciator panel. The LED anode
> is
> > fed from a resistor tied to positive voltage (cathode
> is
> > grounded) but the fuse string keeps the anode low until
> > one
> > of them blows (overheats). That allows current to flow
> > through the flashing LED to ground. You should insert a
> > normally closed "press to test" switch in the string
> > also.
> > Wayne ----- Original Message ----- From:
> PVTPIL8@aol.com
> > To: reflector@tvbf.org Sent: Saturday, May 17, 2003
> 4:18
> > PM
> > Subject: REFLECTOR:Looking for suggestions about fire
> > detection
> >
> >
> > I've got the fire suppression worked out now were
> looking
> > for the early detection. Anyone have some suggestions.
> > Wayne or Scott??
> >
> >
> >
> >
> >
> > =====
> > James F. Agnew Jim_Agnew_2@Yahoo.Com Tampa, FL Velocity
> > 173
> > Elite Aircraft Completed
> >
> >
> >
> > =====
> > James F. Agnew
> > Jim_Agnew_2@Yahoo.Com
> > Tampa, FL
> > Velocity 173 Elite Aircraft Completed
>
> > ATTACHMENT part 2 image/jpeg name=Takeoff Contact.jpg
>
>
>
> =====
> James F. Agnew
> Jim_Agnew_2@Yahoo.Com
> Tampa, FL
> Velocity 173 Elite Aircraft Completed
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=====
James F. Agnew
Jim_Agnew_2@Yahoo.Com
Tampa, FL
Velocity 173 Elite Aircraft Completed