REFLECTOR:Low fuel light
Scott Baker
reflector@tvbf.org
Sun, 27 Jul 2003 04:58:25 -0400
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John,
Something you just said in your previous post has me concerned.
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"I want to clarify something. Previously I said my tank vent faced
forward, but it is the tank overflow line and not the vent that faces
forward and should pressurize the tank. My manifold vent points to the
rear and should pull a little vacuum on the vent system."
John
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
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a) If your vent system is pulling a little vacuum, then you are =
"unpressurizing" the fuel tanks - which slows the fuel flow from the =
main tanks to the header tank. The fuel vent line should be installed =
so that it introduces pressure into the fuel tanks. The construction =
manual clearly shows the vent line pointing into the wind.
b) What tank overflow line? The Velocity schematic does not feature a =
"tank overflow line" (other than the vent line itself). It sounds like =
your system has more tubes - which may be just fine - however it is =
different from what is shown in the construction manual.
Short story - For a few years I owned a business to help composite =
aircraft owners build their aircraft. While I was working on the fuel =
system for a Velocity customer I had the "brainstorm" to redesign the =
fuel and vent system for a XL which would allow for a fuel selector =
valve. I consulted with Duane Swing at the factory - who was kind =
enough to review the facsimiles that I sent which outlined my new and =
improved fuel system. Duane patiently pointed out some possible =
pitfalls to the design. He offered a stern warning to be very careful =
when changing something like this (meaning - the fuel system needs to be =
100% reliable if the engine is going to stay running - if you're going =
to screw around (i.e.. alter the schematic or the installation) you need =
to be pretty sure of what you are doing - and to think through every =
possible situation that the change might affect. I went ahead with my =
improved fuel line/vent system - and later - when mimicking a ground =
fuel flow test to see if the system would deliver 25 gph (take off =
power) - I found that the fuel lines had too many curves and had too =
long a run to sustain this flow rate - which would have meant a partial =
loss of power about 2-minutes following takeoff. What a sobering =
discovery! Following this I removed the "new and improved" plumbing and =
reinstalled the system that was "in the book" - and the aircraft is =
operating without problem.
What I'm leading to is this - it looks like someone has changed your =
fuel system. If you have more than one vent line sticking out under the =
aircraft, then it is different from the Velocity schematic. Someone =
obviously felt a need to "improve" the fuel/vent system - what we don't =
know is this really an improvement - or is it the source of your problem =
(as in my true story above)?
As to your question as to why the low sump fuel light might come on in =
aircraft with the Velocity fuel schematic - in an earlier post I offered =
an opinion that the float switch might be culprit - causing a false =
signal. Have you had a chance to remove the float switch in order to =
test it? Is the float buoyant in avgas?
Best regards,
Scott B.
----- Original Message -----=20
From: "John Dibble" <aminetech@dixie-net.com>
To: <reflector@tvbf.org>
Sent: Sunday, July 27, 2003 12:42 AM
Subject: Re: REFLECTOR:Low fuel light
> Wayne, Scott,
>=20
> Methinks thou doest protest too much.
> I for one, do not consider a low fuel light being on for several hours =
of flight to be a
> mute point and I much appreciate the discussion and comments from =
others here. That's
> great that you trust the fuel schematic with your lives, but that's =
not a good enough
> reason for me to trust it. I would be more comfortable with a =
technical explanation as
> to why you think it's a good schematic and what is causing the fuel =
light to come on.
>=20
> John
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<DIV><FONT face=3DArial size=3D2>John,</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Something you just said in your =
previous post has=20
me concerned.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial=20
size=3D2>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>"I want to clarify something. =
Previously I=20
said my tank vent faced<BR>forward, but it is the tank overflow line and =
not the=20
vent that faces<BR>forward and should pressurize the tank. <FONT=20
color=3D#ff0000>My manifold vent points to the<BR>rear and should pull a =
little=20
vacuum on the vent=20
system</FONT>."<BR>John<BR>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>a) If your vent system is pulling =
a little=20
vacuum, then you are "unpressurizing" the fuel tanks - which slows the =
fuel flow=20
from the main tanks to the header tank. <U>The fuel vent line =
should be=20
installed so that it introduces pressure into the fuel tanks</U>. =
The=20
construction manual clearly shows the vent line pointing into the=20
wind.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>b) What tank overflow line? =
The Velocity=20
schematic does not feature a "tank overflow line" (other than the vent =
line=20
itself). It sounds like your system has more tubes - which may be =
just=20
fine - however it is <EM>different</EM> from what is shown in the =
construction=20
manual.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Short story - For a few years I owned a =
business to=20
help composite aircraft owners build their aircraft. While I was =
working=20
on the fuel system for a Velocity customer I had the "brainstorm" to =
redesign=20
the fuel and vent system for a XL which would allow for a fuel selector=20
valve. I consulted with Duane Swing at the factory - who was kind =
enough=20
to review the facsimiles that I sent which outlined my new and improved =
fuel=20
system. Duane patiently pointed out some possible pitfalls to the=20
design. He offered a stern warning to be <EM>very</EM> careful =
when=20
changing something like this (meaning - the fuel system needs to be 100% =
reliable if the engine is going to stay running - if you're going to =
screw=20
around (i.e.. alter the schematic or the installation) you need to =
be=20
pretty sure of what you are doing - and to <U>think through every =
possible=20
situation that the change might affect</U>. I went ahead with my =
improved=20
fuel line/vent system - and later - when mimicking a ground fuel flow=20
test to see if the system would deliver 25 gph (take off power) - I =
found=20
that the fuel lines had too many curves and had too long a run to =
sustain this=20
flow rate - which would have meant a partial loss of power about =
2-minutes=20
following takeoff. What a sobering discovery! Following this =
I=20
removed the "new and improved" plumbing and reinstalled the system =
that was=20
"in the book" - and the aircraft is operating without =
problem.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>What I'm leading to is this - it looks =
like someone=20
has changed your fuel system. If you have more than one vent line =
sticking=20
out under the aircraft, then it is different from the Velocity =
schematic. =20
Someone obviously felt a need to "improve" the fuel/vent system - what =
we don't=20
know is this really an improvement - or is it the source of your problem =
(as=20
in my true story above)?</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>As to your question as to why the low =
sump fuel=20
light might come on in aircraft with the Velocity fuel schematic - in an =
earlier=20
post I offered an opinion that the float switch might be culprit - =
causing a=20
false signal. Have you had a chance to remove the float switch in =
order to=20
test it? Is the float buoyant in avgas?</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Best regards,</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Scott B.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>----- Original Message ----- </FONT>
<DIV><FONT face=3DArial size=3D2>From: "John Dibble" <</FONT><A=20
href=3D"mailto:aminetech@dixie-net.com"><FONT face=3DArial=20
size=3D2>aminetech@dixie-net.com</FONT></A><FONT face=3DArial=20
size=3D2>></FONT></DIV>
<DIV><FONT face=3DArial size=3D2>To: <</FONT><A=20
href=3D"mailto:reflector@tvbf.org"><FONT face=3DArial=20
size=3D2>reflector@tvbf.org</FONT></A><FONT face=3DArial =
size=3D2>></FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Sent: Sunday, July 27, 2003 12:42 =
AM</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Subject: Re: REFLECTOR:Low fuel=20
light</FONT></DIV></DIV>
<DIV><FONT face=3DArial><BR><FONT size=3D2></FONT></FONT></DIV><FONT =
face=3DArial=20
size=3D2>> Wayne, Scott,<BR>> <BR>> Methinks thou doest protest =
too=20
much.<BR>> I for one, do not consider a low fuel light being on for =
several=20
hours of flight to be a<BR>> mute point and I much appreciate the =
discussion=20
and comments from others here. That's<BR>> great that you trust the =
fuel=20
schematic with your lives, but that's not a good enough<BR>> reason =
for me to=20
trust it. I would be more comfortable with a technical explanation =
as<BR>> to why you think it's a good schematic and what is causing =
the fuel=20
light to come on.<BR>> <BR>> John<BR></FONT></BODY></HTML>
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