REFLECTOR: RE: asymmetric fuel feed

Wed Sep 29 13:22:46 CDT 2004

Larry,

Your point is not just well taken, but even better, well-proven.  Even the
IO-540 on takeoff won't gobble quite that much fuel.

My earlier reference regarding concern about adequacy of fuel flow through a
single, 3/8" line was from a somewhat impeachable source, who was quoting
another source...who had once dated Carmen Electra's, sister's cousin.  

When I balance the quality of information from the two sources, you may know
your's is somewhat weightier.  Are there any other data points out there
showing adequate fuel flow through a 3/8" line?

Chuck

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On
Behalf Of Laurence Coen
Sent: Wednesday, September 29, 2004 11:51 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: asymmetric fuel feed was Re: REFLECTOR: Fuel Shutoffs

Scott,

I agree with your statements regarding asymmetric flow.  As a point of 
interest, fuel flow problems due to leaking fuel caps are not unique to the 
Velocity.  I have a friend with a Debonair that had a bad "O" ring on the 
left tank.  He pulled enough of a vacuum to collapse the fuel bladder.  This

in turn held the fuel sender float up, indicating 3/4 full when the tank was

empty.

As to the fuel flow being marginal with the standard venting system I will 
pass along the results of some tests I ran.  I have a standard RG with 3/8" 
fuel lines and both tanks and the sump vented from a common manifold.  I 
have a carbureted Franklin engine.  I disconnected the fuel line at the 
carburetor.  This was to insure that I was indeed measuring fuel delivered 
to the engine with any restrictions to flow still in place.  I delivered 
fuel from the left tank and the lines from the right tank plugged.  Ten 
gallons in the left tank plus the sump (2.4 gal usable).  I ran the electric

(Faucet) fuel pump and measured flow with my fuel flow meter.  Initial flow 
was 33.4 gal/hr and dropped to 30.5 gal/hr just before the pump ran dry. 
The Faucet pump is rated at 30 gal/hr.  The fuel totalizer indicated 12.4 
gal total.  This shows that you can get at least 30 gal/hr from a single 
tank till the system runs bone dry.  I see nothing marginal about that.

Larry Coen
SE/RG Franklin
N136LC

----- Original Message ----- 
From: "Scott Derrick" <scott at tnstaafl.net>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Tuesday, September 28, 2004 6:07 PM
Subject: asymmetric fuel feed was Re: REFLECTOR: Fuel Shutoffs

> 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.)
>>
>>_______________________________________________
>>To change your email address, visit 
>>http://www.tvbf.org/mailman/listinfo/reflector
>>
>>Visit the gallery!  www.tvbf.org/gallery
>>user:pw = tvbf:jamaicangoose
>>Check new archives: www.tvbf.org/pipermail
>>Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
>
>
> "Those who sacrifice freedom to get security, deserve neither."
> - Benjamin Franklin
>
> _______________________________________________
> To change your email address, visit 
> http://www.tvbf.org/mailman/listinfo/reflector
>
> Visit the gallery!  www.tvbf.org/gallery
> user:pw = tvbf:jamaicangoose
> Check new archives: www.tvbf.org/pipermail
> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
> 
_______________________________________________
To change your email address, visit
http://www.tvbf.org/mailman/listinfo/reflector

Visit the gallery!  www.tvbf.org/gallery
user:pw = tvbf:jamaicangoose
Check new archives: www.tvbf.org/pipermail
Check old archives: http://www.tvbf.org/archives/velocity/maillist.html