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Date: Tue, 23 Aug 2005 13:08:28 -0500
From: Jim Sower <canarder@frontiernet.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Fire extinguishers
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<... I'd have no idea what cut the wire ...>
True

<...  but I'd know something was amiss, be it a fire or parts leaving 
the engine ...>
Not necessarily true at all

<... Either way the alarm would mean, "Get on the ground. NOW!!" ...>
You've NO assurance that anything significant broke the wire.  GIGO (see 
above).

I'm going on the assumption that the death rate on precautionary 
landings is very low ...>
A VERY dangerous assumption IMO.  Particularly with the mindset that 
it's a FIRE alarm.
I do believe you'd kill yourself a dozen times over attempting emergency 
landings in unfavorable circumstances in response to "false positives" 
before you ever experienced an actual fire.  Examine all the "emergency" 
landings executed by folks on this and similar lists.  Nearly all were 
precautionary landings in response to deferrable situations with no 
compelling time line.  Two flat out emergencies come to mind - Paul 
Connor's - and he's one for two.

Practically any affordable system would be too unreliable.  Ejection 
seat would be nice - you don't have to make any precipitous decision 
until you've confirmed how bad the problem is.  A parachute by itself is 
not much good since it only works under very favorable circumstances.

There just aren't any good choices in this area ... Jim S.


Ernest Christley wrote:

> Bulent Aliev wrote:
>
>> I was just thinking: a sensor from a house smoke alarm positioned at 
>> the cooling air exit point, can give a first alert signal? Any smoke 
>> has to come out there.
>> Buly
>
>
> They're smoke detectors, and the smoke has to reach a certain 
> threshold before the alarm trips.  There won't necessarily be a lot of 
> smoke in a gas fire.  Any smoke that is made will be heavily diluted 
> by the fresh air used for cooling.
>
> There was a recent thread on the Aerolectric list that discussed 
> detection techniques. Infra-red detectors were recommended, and 
> they're supposed to be fairly cheap and will feed into one of those 
> miniature monitors so that you can see what is happening.  In my 
> opinion, it's more weight and complexity than it's worth.  
> I didn't like the first idea that was offered; run a twisted pair of 
> thin wire all around the engine compartment.  The theory is that a 
> fire will burn through the insulation, shorting the wires and tripping 
> an alarm.  My theory is that the wires would get oxidized and covered 
> in melted plastic before they could short, preventing a good contact 
> and defeating the alarm.  I would modify the design to be a single 
> wire of the thinnest possible gauge, made from that cheap twisted 
> aluminum stuff instead of real copper.  It would always be powered 
> when the engine was running, and if anything cut the wire for any 
> reason an alarm would go off.  I'd have no idea what cut the wire, but 
> I'd know something was amiss, be it a fire or parts leaving the 
> engine.  Either way the alarm would mean, "Get on the ground. NOW!!"  
> I'm going on the assumption that the death rate on precautionary 
> landings is very low.