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Firewall fuel shut-off (was: Re: glide ratios)

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brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Fri Apr 07, 2006 5:50 am Post subject: Firewall fuel shut-off (was: Re: glide ratios)

Rob Rowe wrote:



 	  Quote: 	
		   FWIW - a fellow -52 driver experimented with the fuel cut-off lever at ground idle a couple of years back. 

 

 To his surprise it idled for several minutes before cutting out due to the c. 1 litre fuel reserve sat in the downstream compensation tank (the yellow sphere on the firewall) ... so even at full throttle there could well be a (guesstimated) 15-20 seconds of full power available.

 

 Equally on re-opening the fuel cut-off afterwards would require the fuel pump & compensation tank to be re-primed before the pressure carb would function again ... this might take some time (and manual intervention!).

 

 So speculate that the power latency between fuel shut-off & restoration might not be conducive to the crisis at hand ... so maybe the mags are the more predictable control to use after all.


	


I wasn't thinking of actually cutting the fuel on and off but rather 

getting the valve into an intermediate position to reduce the flow of 

fuel without cutting it off completely. At that point we would be 

controlling power by starving the engine of fuel and running it way lean 

to where it almost won't run. It will be rough as hell but it should put 

out partial power.



And the more I think about it, the more I think that the mags are the 

easiest way to deal with this. My only concern would be the *bang* as 

the fuel/air mix in the exhaust lights off every time you turn the mags 

back on again.



 	  Quote: 	
		   As an aside - my understanding is that the fuel cut-off lever linkage is only engineered to shut off & is not to be relied upon to re-open again ... to be kept in mind even in an emergency.


	


There seems to be a *LOT* of supposition on this. On the CJ6A it is just 

an on-off valve with detents at both the on and off positions. The valve 

can be stopped at an intermediate position and is able to restrict the 

flow of fuel to the engine. I haven't played with this valve in the 

Yak-52 so I don't know if it behaves the same way. Someone (Dennis?) who 

knows this valve needs to speak up and explain how it works and whether 

it can be used to control the flow of fuel or whether it just cuts the 

fuel completely off (hysteresis in the linkage prevents putting the 

valve in an intermediate position).



-- 

Brian Lloyd                         361 Catterline Way

brian-yak at lloyd dot com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

- Antoine de Saint-Exupery

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_________________
Brian Lloyd
brian-yak at lloyd dot com
+1.916.367.2131 (voice) +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery

dsavarese(at)elmore.rr.co
Guest

Posted: Fri Apr 07, 2006 6:46 am Post subject: Firewall fuel shut-off (was: Re: glide ratios)

In the 52, the fuel shut off arm is pretty much like an over center type of 

mechanism and is very difficult if not damn near impossible to move and hold 

into a partially closed/partially opened position without physically 

manhandling the control arm.   I know that's true in my airplane.  If you 

haven't tried pulling the fire control/fuel shut off arm and place it in 

some arbitrary midpoint position, try it and you'll see what I'm talking 

about.  Add to that the fact you are still trying to accomplish the #1 item 

in the emergency checklist, which is to fly the airplane.



IMHO, try doing this on the ground with the brakes set and the airplane 

chocked when you are totally cool, calm and collected and see what happens. 

Then report your findings to the group.  I'd be extremely interested in 

reading about the results and your objective opinion as to whether you feel 

you could accomplish what has been suggested during a real emergency.

Dennis



---

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brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Fri Apr 07, 2006 8:58 am Post subject: Firewall fuel shut-off (was: Re: glide ratios)

A. Dennis Savarese wrote:

 	  Quote: 	
		   

 <dsavarese(at)elmore.rr.com>

 

 In the 52, the fuel shut off arm is pretty much like an over center type

 of mechanism and is very difficult if not damn near impossible to move

 and hold into a partially closed/partially opened position without

 physically manhandling the control arm.   I know that's true in my

 airplane.  If you haven't tried pulling the fire control/fuel shut off

 arm and place it in some arbitrary midpoint position, try it and you'll

 see what I'm talking about.  Add to that the fact you are still trying

 to accomplish the #1 item in the emergency checklist, which is to fly

 the airplane.


	


And that is a good point. It is going to be both sensitive and unstable,

not exactly the thing that will be easiest to use in flight. Add to that

the fact that the engine power output is going to vary hugely with only

a very small change in mixture and it will be even more sensitive.



Still, in an emergency it is good to know all the options.



 	  Quote: 	
		   IMHO, try doing this on the ground with the brakes set and the airplane

 chocked when you are totally cool, calm and collected and see what

 happens. Then report your findings to the group.  I'd be extremely

 interested in reading about the results and your objective opinion as to

 whether you feel you could accomplish what has been suggested during a

 real emergency.


	


I agree. Controlled experimentation would be useful before you have to

use it in real life.



I remember being told by just about everyone that I should *never*

attempt a turn-back to the airport if the engine quits. I remember

thinking that a blanket admonition might be wrong so I went out and

tried it for myself under controlled circumstances. I discovered that,

in my Grumman Tiger, it was safe to turn back to the runway from any

altitude above 400' if the engine quit while on upwind. I also

discovered that, in my Piper Clipper or Piper Comanche it was not safe

to turn back if the engine quit on upwind at any altitude.



So you really do need to figure some of these things out on an

airplane-by-airplane basis.



Brian

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