REFLECTOR: Fuel Shutoffs

[Jim Sower]

If you don't vent the sump, the [marginal] gravity feed will be enhanced 
by the fuel pump sucking the fuel out of the strakes into the sump.  
That said, if you have assymmetric feeding of the strakes (a common 
occurrence in these airplanes) once one tank gets empty, the sump will 
vent through that strake vent and the strake that still has fuel will 
have only gravity feed (which it has demonstrated is not working for it 
very well) available. Isolation valves would solve that problem.

<... a turn the wrong direction on take-off (away from the fuel outlet) 
could all contribute to less than adequate fuel flow ...>
 Of course if you're in balanced flight (ball centered) the fuel has no 
way of knowing you're turning so fuel flow would not be affected.

I had assymmetric fuel transfer from the strakes to the sump for the 
LONGEST time.  I tried everything (except 1/2" lines) to no avail.  
Finally solved the problem with electric "de-selection" valves that 
light a LED on the panel when they are closed.

If you vent your sump, all bets are off .... Jim S.



Chuck Jensen wrote:

> Regarding a dual fuel shutoff, I understand there was some 
> work/testing done on this years ago that raises an issue that is worth 
> thinking about.  It seems Velo (or someone) did flow tests from a 
> single tank (with a low level of fuel in it) through the 3/8" fuel 
> line and found the flow rate was marginally greater than the expected 
> fuel consumption of an IO-540 engine at max power.  Given that some 
> installations are non-standard and less than optimal, there was 
> thought that with low fuel, a turn the wrong direction on take-off 
> (away from the fuel outlet) could all contribute to less than adequate 
> fuel flow unless both tanks were feeding.  Since then, most have gone 
> to 1/2" fuel lines, which should resolve the flow capacity from each 
> tank--but not the exposed outlet from a flight turn.
>  
> So, 1) I don't know if there is anything to it!, 2) on the side of 
> caution, item #86 on the checklist would be to confirm both tanks are 
> on line.  With all that said, I wish I had dual isolation valves!
>  
> Chuck 
>  
> -----Original Message-----
> *From:* reflector-bounces at tvbf.org 
> [mailto:reflector-bounces at tvbf.org]*On Behalf Of *v350tx
> *Sent:* Sunday, September 26, 2004 8:31 PM
> *To:* reflector at tvbf.org
> *Subject:* REFLECTOR: Fuel Shutoffs
>
> I have run into more than case when I wish I had put individual fuel 
> shut-offs in each tank.  I have one that shuts off the fuel after the 
> sump tank, but if you have a leak in the sump tank or any of its 
> fittings individual shut-offs would be handy.  Dave Bertram  ( hop to 
> have my velo V-8 flying in a couple of weeks.)


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