REFLECTOR:Low fuel light

Chuck Jensen reflector@tvbf.org
Sat, 26 Jul 2003 12:34:27 -0400


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Brett,
 
I suspect the point is, why did the air get into the sump or how logical is
it that air is actually in the sump or, if that is not logical, then it does
point to a faulty instrument.  An investigation tree might look like:
 
Air in sump:
    1.    From the either tank?  
                No, both tanks were full and fuel outlets were always
covered
    2.    From the vent line?
                No, the sump vent line is open and there is no source for
the line to be pressurized to blow air into sump
    3.    Did the sump become starved for fuel from the tanks and pull air
in through the vent?
                No, flow paths open and if it was that starved, the engine
would have stopped.
    4.    Was air in the sump all the time and just hadn't been vented off
                No, the vent to the sump was always open and air should have
been displaced by gravity flow of fuel.
    5.    Do we know for sure that there is air in the sump?
                No, we only infer that because we are getting the low fuel
signal.
    6.    Is it logical that air is actually in the sump?
                No, not if it is vented off and there is not pathway or
mechanism for air getting into the sump
    7.   If air in the sump is not the problem, then what is?
                Then, it would seem to be a faulty instrument (float only
semi-buoyant) or a faulty signal. 
 
and so on.  Of course, if any of the answers in the question-path are wrong
or different than we think, then that limb breaks off the tree.
 
I don't mean to insult anyone's intelligence because this is pretty simple
stuff.  I've found difficult problems can be simple to solve with a
structured approach and simple problems can be difficult to solve with a
shotgun approach.  I've used both!
 
With that said, I'm still working on the unbalanced tank draw-down problem.
I have a long trip scheduled next week, so I'll be able to test the theory
that I'm unbalanced (which comes as no surprise to a lot of people) and that
I need to shim the rudder slightly.  
 
I just installed a new set of GAMInjectors this morning so I'm looking to
get some good "lean test" numbers to see if the balance has improved.  I was
confident that my engine was "pretty good" in that area because it does run
smooth.  NOT.  There was 2.1 gph difference between peak EGT across my
cylinders as I leaned out.  1.0 gph is OK, 0.7 is acceptable and and <0.5 is
an excellent target.  That's probably why the 540 started to run rough in
the LOP region.  In sum, mine numbers were kind of pathetic side.  
 
The single gph or two that are saved will probably never recover the cost of
the injectors but if running cooler and smoother increases TBO a hundred or
two hours, now we're talking real money.  And, like many things, it feels
good for it to be right!
 
Gotta go.  Have some OSH flight planning to do.
 
Chuck
 


min@tvbf.org [mailto:reflector-admin@tvbf.org]On Behalf Of Brett Ferrell
Sent: Saturday, July 26, 2003 9:06 AM
To: reflector@tvbf.org
Subject: Re: REFLECTOR:Low fuel light



Why would you jump to the assumption it's air in the tank?  Without a
sightglass, or replacing that run of tubing to the sump neoprene or
something, we don't have any idea what's causing the indication.  Could just
as easily be a defect inside the instrument.  My whole contention was that,
if air is entering the sump, it's probably for the best b/c the alternative
is most likely to pull a vacuum on the tank.  Air doesn't displace fuel
without a reason.


 Brett
 

----- Original Message ----- 
From: alventures <mailto:alventures@msn.com>  
To: reflector@tvbf.org <mailto:reflector@tvbf.org>  
Sent: Friday, July 25, 2003 5:56 PM
Subject: RE: REFLECTOR:Low fuel light


Al,

 

This thread started with Rene's problem with occasional low-fuel warning
with plenty of fuel on board.  How is the air getting into the sump tank if
the strake tanks have enough fuel to keep the strake-to-sump fuel lines
submerged?  The sump vent seems the most likely route.

 

Keith

 

Yes, I agree with that; assuming of, course, that the intermittent warning
is due to a low level in the sump tank and not a problem with the float
switch, or something else.

 

After giving the issue more thought, the valve in the sump vent seems to
make sense.  Although it is one more thing on the checklist, and not
convenient to get at.  And it doesn't preclude fuel exhaustion in the case
of a leaky fuel cap.  If we are going to keep a simple gravity feed system
from both tanks, we have to pay attention to the fuel caps, and be aware of
one tank level dropping faster than the other.

 

Let's see; if we could just find a different place to put the fuel cap;
someplace that doesn't happen to see about the maximum negative pressure of
anywhere on the airplane.

 

Al


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<DIV><SPAN class=704493215-26072003><FONT face=Arial color=#0000ff 
size=2>Brett,</FONT></SPAN></DIV>
<DIV><SPAN class=704493215-26072003><FONT face=Arial color=#0000ff 
size=2></FONT></SPAN>&nbsp;</DIV>
<DIV><SPAN class=704493215-26072003><FONT face=Arial color=#0000ff size=2>I 
suspect the point is, why did the air get into the sump or how logical is it 
that air is actually in the sump or, if that is not logical, then it does point 
to a faulty instrument.&nbsp; An investigation tree might look 
like:</FONT></SPAN></DIV>
<DIV><SPAN class=704493215-26072003><FONT face=Arial color=#0000ff 
size=2></FONT></SPAN>&nbsp;</DIV>
<DIV><SPAN class=704493215-26072003><FONT face=Arial color=#0000ff size=2>Air in 
sump:</FONT></SPAN></DIV>
<DIV><SPAN class=704493215-26072003>&nbsp;&nbsp;&nbsp; <FONT face=Arial 
color=#0000ff size=2>1.&nbsp;&nbsp;&nbsp; From the either tank?&nbsp; 
</FONT></SPAN></DIV>
<DIV><SPAN 
class=704493215-26072003>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
<FONT face=Arial color=#0000ff size=2>No, both tanks were full and fuel outlets 
were always covered</FONT></SPAN></DIV>
<DIV><SPAN class=704493215-26072003>&nbsp;&nbsp;&nbsp; <FONT face=Arial 
color=#0000ff size=2>2.&nbsp;&nbsp;&nbsp; From the vent 
line?</FONT></SPAN></DIV>
<DIV><SPAN 
class=704493215-26072003>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
<FONT face=Arial color=#0000ff size=2>No, the sump vent line is open and there 
is no source for the line to be pressurized to blow air into 
sump</FONT></SPAN></DIV>
<DIV><SPAN class=704493215-26072003><FONT face=Arial color=#0000ff 
size=2>&nbsp;&nbsp;&nbsp; 3.&nbsp;&nbsp;&nbsp; Did the sump become starved for 
fuel from the tanks and pull air in through the vent?</FONT></SPAN></DIV>
<DIV><SPAN class=704493215-26072003><FONT face=Arial color=#0000ff 
size=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
No, flow paths open and if it was that starved, the engine would have 
stopped.</FONT></SPAN></DIV>
<DIV><SPAN class=704493215-26072003></SPAN><FONT face=Tahoma><SPAN 
class=704493215-26072003><FONT face=Arial color=#0000ff 
size=2>&nbsp;&nbsp;&nbsp; 4.&nbsp;&nbsp;&nbsp; Was air in the sump all the time 
and just hadn't been vented off</FONT></SPAN></FONT></DIV>
<DIV><FONT face=Tahoma><SPAN class=704493215-26072003></SPAN><SPAN 
class=704493215-26072003><FONT face=Arial color=#0000ff 
size=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
No, the vent to the sump was always open and air should have been displaced by 
gravity flow of fuel.</FONT></SPAN></FONT></DIV>
<DIV><FONT face=Tahoma><SPAN class=704493215-26072003></SPAN><SPAN 
class=704493215-26072003><FONT face=Arial color=#0000ff 
size=2>&nbsp;&nbsp;&nbsp; 5.&nbsp;&nbsp;&nbsp; Do we know for sure that there is 
air in the sump?</FONT></SPAN></FONT></DIV>
<DIV><FONT face=Tahoma><SPAN class=704493215-26072003></SPAN><SPAN 
class=704493215-26072003><FONT face=Arial color=#0000ff 
size=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
No, we only infer that because we are getting the low fuel 
signal.</FONT></SPAN></FONT></DIV>
<DIV><FONT face=Tahoma><SPAN class=704493215-26072003></SPAN><SPAN 
class=704493215-26072003><FONT face=Arial color=#0000ff 
size=2>&nbsp;&nbsp;&nbsp; 6.&nbsp;&nbsp;&nbsp; Is it logical that air is 
actually in the sump?</FONT></SPAN></FONT></DIV>
<DIV><FONT face=Tahoma><SPAN class=704493215-26072003></SPAN><SPAN 
class=704493215-26072003><FONT face=Arial color=#0000ff 
size=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
No, not if it is vented off and there is not pathway or mechanism for air 
getting into the sump</FONT></SPAN></FONT></DIV>
<DIV><FONT face=Tahoma><SPAN class=704493215-26072003></SPAN>&nbsp;&nbsp;&nbsp; 
<FONT face=Arial color=#0000ff size=2>7.&nbsp;&nbsp;&nbsp;If air in the sump is 
not the problem, then what is?</FONT></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff 
size=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
Then, it would seem to be a faulty instrument (float only semi-buoyant) or a 
faulty signal.&nbsp;</FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2></FONT>&nbsp;</DIV>
<DIV><FONT face=Arial color=#0000ff size=2>and so on.&nbsp; Of course, if any of 
the answers in the question-path are wrong or different than we think, then that 
limb breaks off the tree.</FONT></DIV>
<DIV><FONT face=Tahoma><FONT face=Arial color=#0000ff 
size=2></FONT></FONT>&nbsp;</DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2>I don't mean to insult 
anyone's intelligen<SPAN class=704493215-26072003>ce</SPAN> because this is 
pretty simple stuff.&nbsp;&nbsp;I've&nbsp;found difficult problems can be simple 
to solve with a structured approach and simple problems can be difficult to 
solve with a shotgun approach.<SPAN class=704493215-26072003>&nbsp; I've used 
both!</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2></FONT>&nbsp;</DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2>With that said, I'm still 
working on the unbalanced tank&nbsp;<SPAN 
class=704493215-26072003>draw-down</SPAN> problem.&nbsp; I have a long trip 
scheduled next week, so I'll be able to test the theory that I'm unbalanced 
(which<SPAN class=704493215-26072003> comes as no surprise to a lot of 
people</SPAN>) and that I need to shim the rudder slightly.<SPAN 
class=704493215-26072003>&nbsp; </SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN 
class=704493215-26072003></SPAN></FONT></FONT></FONT>&nbsp;</DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN 
class=704493215-26072003>I just installed a new set of GAMInjectors this morning 
so I'm looking to get some good "lean test" numbers to see if the balance has 
improved.&nbsp; I was confident that my engine was "pretty good" in that area 
because it does run smooth.&nbsp; NOT.&nbsp; There was 2.1 gph difference 
between peak EGT across my cylinders as I leaned out.&nbsp; 1.0 gph is OK, 0.7 
is acceptable and and &lt;0.5 is an excellent target.&nbsp; That's probably why 
the 540 started to run rough in the&nbsp;LOP region. &nbsp;In sum, mine numbers 
were kind of&nbsp;pathetic side.&nbsp; </SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2></FONT>&nbsp;</DIV>
<DIV><FONT><FONT face=Arial color=#0000ff size=2><SPAN 
class=704493215-26072003>The single gph or two that are saved&nbsp;will probably 
never recover the cost of the injectors but if running cooler and smoother 
increases TBO a hundred or two hours, now we're talking real money.&nbsp; And, 
like many things, it feels good for it to be right!</SPAN></FONT></FONT></DIV>
<DIV><FONT><FONT face=Arial color=#0000ff size=2><SPAN 
class=704493215-26072003></SPAN></FONT></FONT>&nbsp;</DIV>
<DIV><FONT><FONT face=Arial color=#0000ff size=2><SPAN 
class=704493215-26072003>Gotta go.&nbsp; Have some OSH flight planning to 
do.</SPAN></FONT></FONT></DIV>
<DIV><FONT><FONT face=Arial color=#0000ff size=2><SPAN 
class=704493215-26072003></SPAN></FONT></FONT>&nbsp;</DIV>
<DIV><FONT><FONT face=Arial color=#0000ff size=2><SPAN 
class=704493215-26072003>Chuck</SPAN></FONT></FONT></DIV>
<DIV><FONT face=Tahoma><FONT face=Arial color=#0000ff size=2></FONT>&nbsp;</DIV>
<DIV><FONT face=Arial color=#0000ff size=2></FONT><FONT face=Arial color=#0000ff 
size=2></FONT><FONT face=Arial color=#0000ff size=2></FONT><BR><FONT 
size=2><SPAN class=704493215-26072003><FONT face=Arial 
color=#0000ff></FONT></SPAN><BR><B></B>min@tvbf.org 
[mailto:reflector-admin@tvbf.org]<B>On Behalf Of </B>Brett 
Ferrell<BR><B>Sent:</B> Saturday, July 26, 2003 9:06 AM<BR><B>To:</B> 
reflector@tvbf.org<BR><B>Subject:</B> Re: REFLECTOR:Low fuel 
light<BR><BR></DIV></FONT></FONT>
<BLOCKQUOTE dir=ltr style="MARGIN-RIGHT: 0px">
  <DIV><FONT face=Arial size=2>Why would you jump to the assumption it's air in 
  the tank?&nbsp; Without a&nbsp;sightglass, or replacing that run of tubing to 
  the sump neoprene or something, we don't have any idea what's causing the 
  indication.&nbsp; Could just as easily be a defect inside the 
  instrument.&nbsp; My whole contention was that, if air is entering the sump, 
  it's probably for the best b/c the alternative is most likely to pull a vacuum 
  on the tank.&nbsp; Air doesn't displace fuel without a 
  reason.</FONT></DIV><FONT face=Arial size=2>
  <DIV><BR>&nbsp;Brett</DIV>
  <DIV></FONT>&nbsp;</DIV>
  <BLOCKQUOTE dir=ltr 
  style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
    <DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
    <DIV 
    style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B> 
    <A title=alventures@msn.com href="mailto:alventures@msn.com">alventures</A> 
    </DIV>
    <DIV style="FONT: 10pt arial"><B>To:</B> <A title=reflector@tvbf.org 
    href="mailto:reflector@tvbf.org">reflector@tvbf.org</A> </DIV>
    <DIV style="FONT: 10pt arial"><B>Sent:</B> Friday, July 25, 2003 5:56 
    PM</DIV>
    <DIV style="FONT: 10pt arial"><B>Subject:</B> RE: REFLECTOR:Low fuel 
    light</DIV>
    <DIV><BR></DIV>
    <DIV class=Section1>
    <DIV>
    <P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face=Arial size=2><SPAN 
    style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Al,</SPAN></FONT></P></DIV>
    <DIV>
    <P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman" 
    size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT>&nbsp;</P></DIV>
    <DIV>
    <P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face=Arial size=2><SPAN 
    style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">This thread started with Rene's 
    problem with occasional low-fuel warning with plenty of fuel on board.&nbsp; 
    How is the air getting into the sump tank if the strake tanks have enough 
    fuel to keep the strake-to-sump fuel lines submerged?&nbsp; The sump vent 
    seems the most likely route.</SPAN></FONT></P></DIV>
    <DIV>
    <P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman" 
    size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT>&nbsp;</P></DIV>
    <DIV>
    <P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face=Arial size=2><SPAN 
    style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Keith</SPAN></FONT></P></DIV>
    <DIV>
    <P class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman" 
    size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT>&nbsp;</P></DIV>
    <BLOCKQUOTE 
    style="BORDER-RIGHT: medium none; PADDING-RIGHT: 0in; BORDER-TOP: medium none; PADDING-LEFT: 3pt; PADDING-BOTTOM: 0in; MARGIN: 5pt 0in 5pt 3pt; BORDER-LEFT: black 1.5pt solid; PADDING-TOP: 0in; BORDER-BOTTOM: medium none">
      <DIV>
      <P class=MsoNormal style="MARGIN-LEFT: 0.6in"><FONT face="Times New Roman" 
      color=blue size=3><SPAN style="FONT-SIZE: 12pt; COLOR: blue">Yes, I agree 
      with that; assuming of, course, that the intermittent warning is due to a 
      low level in the sump tank and not a problem with the float switch, or 
      something else.</SPAN></FONT></P>
      <P class=MsoNormal style="MARGIN-LEFT: 0.6in"><FONT face="Times New Roman" 
      color=blue size=3><SPAN 
      style="FONT-SIZE: 12pt; COLOR: blue"></SPAN></FONT>&nbsp;</P>
      <P class=MsoNormal style="MARGIN-LEFT: 0.6in"><FONT face="Times New Roman" 
      color=blue size=3><SPAN style="FONT-SIZE: 12pt; COLOR: blue">After giving 
      the issue more thought, the valve in the sump vent seems to make 
      sense.&nbsp; Although it is one more thing on the checklist, and not 
      convenient to get at. &nbsp;And it doesn't preclude fuel exhaustion in the 
      case of a leaky fuel cap.&nbsp; If we are going to keep a simple gravity 
      feed system from both tanks, we have to pay attention to the fuel caps, 
      and be aware of one tank level dropping faster than the 
      other.</SPAN></FONT></P>
      <P class=MsoNormal style="MARGIN-LEFT: 0.6in"><FONT face="Times New Roman" 
      color=blue size=3><SPAN 
      style="FONT-SIZE: 12pt; COLOR: blue"></SPAN></FONT>&nbsp;</P>
      <P class=MsoNormal style="MARGIN-LEFT: 0.6in"><FONT face="Times New Roman" 
      color=blue size=3><SPAN style="FONT-SIZE: 12pt; COLOR: blue">Let's see; if 
      we could just find a different place to put the fuel cap; someplace that 
      doesn't happen to see about the maximum negative pressure of anywhere on 
      the airplane.</SPAN></FONT></P>
      <P class=MsoNormal><FONT face=Verdana color=blue size=2><SPAN 
      style="FONT-SIZE: 11pt; COLOR: blue; FONT-FAMILY: Verdana"></SPAN></FONT>&nbsp;</P>
      <P class=MsoNormal><FONT face=Verdana color=blue size=2><SPAN 
      style="FONT-SIZE: 11pt; COLOR: blue; FONT-FAMILY: Verdana">Al</SPAN></FONT></P></DIV></BLOCKQUOTE></DIV></BLOCKQUOTE></BLOCKQUOTE></BODY></HTML>

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