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Date: Wed, 02 Mar 2005 19:53:24 -0600
From: Jim Sower <canarder@frontiernet.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: fuel cutoff valve necessary?
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<... A throttle with a cutoff switch wired into it that would cut power 
to the pump after being pushed past a detent would accomplish three 
disjointed operations in one intuitive step, and leave the pilots
throttle hand on the throttle ...>

I think we're kind of gilding the lily here.  Fuel pump switch(s) are 
used enough to be pretty easy to reach and fumbling for them cannot 
reasonably be classified as a significant distraction.  OTOH automatic 
cutoff switches (hidden behind a detent or not) add several failure 
modes and a lot of complexity and expense - but no measurable benefit. 

I think we've got another one of those ten-cent tails wagging our 
forty-dollar dog ... Jim S.

Ernest Christley wrote:

> Ed Anderson wrote:
>
>> Ernest, I could be wrong, but seems I recall somewhere that FAA 
>> requires a
>> fuel shut off valve.  Someone else may know whether that is correct 
>> or not.
>> For the reason you stated - Safety.
>>
>> Ed A
>>
>>  
>>
> I don't doubt that it is so, Ed, but putting the edicts from Federal 
> agencies aside, I'd like to raise the question of whether it is safer.
> I mentioned two instance where a valve for a single tank system would 
> be useful, an inflight fire and emergency landing prep.  In both 
> instances, the pilot is required to remember to throttle back, turn 
> off the boost pump and then turn off the manual valve under the worst 
> of circumstances.  Unless it is very well practiced, most pilots will 
> have to look around for the switches and knobs, taking their attention 
> away from other duties.  If you're going in under partial power, you 
> may not be wanting to give up that power until very short final, 
> moving the list of task to the most dangerous times.  A throttle with 
> a cutoff switch wired into it that would cut power to the pump after 
> being pushed past a detent would accomplish three disjointed 
> operations in one intuitive step, and leave the pilots thottle hand on 
> the throttle.
>
> Assuming that connections will be the weakest spot in any system, and 
> that there actually is a pump that blocks flow when there's no power 
> applied (I haven't tried to determine if there is),  I would argue 
> that the pump IS the cutoff valve, and that adding a pilot operated 
> manual valve actually reduces safety by needlessly increasing 
> complexity and pilot workload.
>
> Marc, is quite right that the fuel system is a pain to work on when 
> the fuel can't be contained in the tank.  But does this argue for a 
> pilot accessible fuel valve, or one directly at the tank exit?  I 
> think it might be different issue from what I was first asking about, 
> but interesting nonetheless.
>
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>>
>
>