asymmetric fuel feed was Re: REFLECTOR: Fuel Shutoffs

[Scott Derrick]

As I understand it, if you use the standard vent system of all tanks and 
sump tied into one vent line and your lines are unobstructed there are only 
two reasons for asymmetric fuel flow.

1.  leaking fuel cap. the low pressure over the cap pulling air out of the 
tank.  Get a new O ring or use fuel valve lube on the O ring to cure.

2.) Your airplane is skidding/slipping when in straight flight, ie not 
trimmed with the ball in the center.  This is the most common reason.   Fix 
the skid by adjusting the correct rudder outboard and the tanks will drain 
evenly within a couple gallons.

stepping on the fuller tank with the same rudder for a short period will 
equalize the tanks,
adding more valves and lights to fail is solving the symptom, not the 
problem......

Scott

At 11:06 PM 9/27/2004, you wrote:
>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: <mailto:reflector-bounces at tvbf.org>reflector-bounces at tvbf.org 
>>[mailto:reflector-bounces at tvbf.org]On Behalf Of v350tx
>>Sent: Sunday, September 26, 2004 8:31 PM
>>To: <mailto:reflector at tvbf.org>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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