REFLECTOR: Re: Reflector Digest, Vol 9, Issue 68-Fuel Feed-blinking low fuel warning

Tom Martino tmartino at troubleshooter.com
Fri Feb 18 08:51:26 CST 2005


Isn't there a simple on/off fuel sensor that can be installed?  "ON"
when fuel touches it, and "OFF" when fuel drops below a certain level?
Like the sensors in RV water tanks?

 

-----Original Message-----
From: Carruth, Joel L [mailto:joel.l.carruth at lmco.com] 
Sent: Friday, February 18, 2005 7:34 AM
To: Velocity Aircraft Owners and Builders list
Subject: RE: REFLECTOR: Re: Reflector Digest, Vol 9,Issue 68-Fuel
Feed-blinking low fuel warning [heur]

 

Jeepers!  I've been listening to the problems with unporting, greasing
the o-rings, false sump indications over 10K, and "no way" of knowing
what situation your fuel is in, and frankly it leaves me a little
worried about my future fuel system!!!  On one hand, I tend to agree
with Scott Baker and don't change the design, but on the other, you all
have convinced me that there is room for some tweaking!  I just don't
believe in guessing about my fuel condition.

 

In particular, I plan to do away with the float switch and install a
fuel-level sensor in the sump. Secondly, a simple flow switch in each
line from the mains would give you vital information about which way the
fuel is going! This wouldn't be an expensive flow meter, but a simple
flow switch with indicator. I think Omega sells these for around $130
each. Two switches, plus the fuel-level sensor would take the guess work
out of fuel management and allow the pilot to make corrections as
needed... before the fan goes quiet!!  

 

'96 SEFG

 

Joel Carruth

Lockheed Martin 

JSF - Pilot System Software

W: (817) 763-4337

Fax: (817) 777-8378

joel.l.carruth at lmco.com

 

  _____  

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Jim Sower
Sent: Thursday, February 17, 2005 9:02 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Re: Reflector Digest, Vol 9, Issue 68-Fuel
Feed-blinking low fuel warning

 

<... The only way I could see that happening is if the flow from the
mains is somehow restricted due to inadequate venting, and that the fuel
pump is pulling fuel out the sump tank and the sump vent line is letting
in air into the sump lowering the fuel level. ...>


Bingo!!


And once your sump fuel level falls low enough to light the low fuel
light, you never know how much usable fuel you have until that light
goes out.  The mains might be providing 95% of demand in which you'll
make it home with a gallon or two in the sump.  Then again, they might
be only providing 50% of demand in which case you flame out in under an
hour.  If the strakes are only providing 25% of demand, you've got about
half an hour of fuel.  
And you have NO WAY of knowing which situation you're in until either
you get where you're going and LOOK at the sump, or the fan goes quiet.

Go ahead and ask me how I know this ... Jim S.


Chuck Harbert wrote:

To John Dibble: 

This is very strange that it only occurs intermittingly at high
altitudes, unless it is just a intermittent bad electrical connection or
switch. Do you have the same type of low fuel switch that I have ( mine
is green and floats in the sump tank)? I installed mine on the pilot
side of the sump near the top. I didn't quite understand your
description and thot maybe it was a different type switch. Are you sure
the warning light itself isn't just loose in it's socket? 

I'm trying to understand what changes at higher altitude that would
affect the low fuel switch. The only thing I could think of was that
atmospheric pressure drops, so the sump tank could possibly expand a
little I guess. Do you have a sump tank vent line and the main tank vent
lines per plans? 

I'm assuming that you have pretty much ruled out the possibility that
the sump tank is partially emptying and that the low fuel switch is
working properly? The only way I could see that happenning is if the
flow from the mains is somehow restricted due to inadequate venting, and
that the fuel pump is pulling fuel out the sump tank and the sump vent
line is letting in air into the sump lowering the fuel level. 

Chuck H 



-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.tvbf.org/mailman/private/reflector/attachments/20050218/cf76dc7c/attachment.html


More information about the Reflector mailing list