REFLECTOR:Low fuel light

Mon, 28 Jul 2003 10:03:11 -0500

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Chuck Jensen wrote:

>  John,It's agreed that the sump would react with more gain than the
> tanks but there are probably a couple factors going on here that would
> mitigate that factor.  1st, any change is so slow, that if the vent
> system has decent sized lines (1/4" may be too small) that our rate of
> descent/climb is really pretty subtle change rate.
>
> I don't know, at low altitude the outside pressure changes 0.25
> psi/500 ft.  A 0.026 psi difference in tank/sump pressure will change
> the sump fuel level by 1".  The question is - How quickly will the
> vent system transfer air to an nearly empty tank.  Has anyone ever
> pressurized their empty tank and measured the time it takes for the
> pressure to go to zero?
>
> Unless, of course, you're going to rolling over on your back and going
> into a vertical dive for a strafing or high speed bombing run.  You
> know, the more a person flies, the more that I'm astounded at the
> piloting skills of our Air Force pilots.  Mind-boggling, and some of
> them are just past being teenagers; but a little off subject.And, 2nd,
> there really shouldn't be any air space in the sump, if it's properly
> vent to a static condition with the tanks, and so it may not make a
> difference that the change-rate for the sump is slightly different
> than the mains.
>
> I agree that there shouldn't be any air space in the sump under static
> pressure conditions, and in this case the pressure change rate for the
> sump is instantaneous so it makes the biggest difference.
>  All these nice things people were posting about mutual respect,
> understanding and sensitivity, heck, it made me want to go hug
> somebody!!
>
> Sorry, Chuck, you're not my type.
>
> John
>
> Chuck

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Chuck Jensen wrote:
<blockquote TYPE=CITE>&nbsp;John,It's
agreed that the sump would react with more gain than the tanks but there
are probably a couple factors going on here that would mitigate that factor.&nbsp;
1st, any change is so slow, that if the vent system has decent sized lines
(1/4" may be too small) that our rate of descent/climb is really pretty
subtle change rate.&nbsp;&nbsp;
I don't know, at low altitude the outside pressure changes 0.25 psi/500
ft.&nbsp; A 0.026 psi difference in tank/sump pressure will change the
sump fuel level by 1".&nbsp; The question is - How quickly will the vent
system transfer air to an nearly empty tank.&nbsp; Has anyone ever pressurized
their empty tank and measured the time it takes for the pressure to go
to zero?
Unless,
of course, you're going to rolling over on your back and going into a vertical
dive for a strafing or high speed bombing run.&nbsp; You know, the more
a person flies, the more that I'm astounded at the piloting skills of our
Air Force pilots.&nbsp; Mind-boggling, and some of them are just past being
teenagers; but a little off subject.And,
2nd, there really shouldn't be any air space in the sump, if it's properly
vent to a static condition with the tanks, and so it may not make a difference
that the change-rate for the sump is slightly different than the mains.
I agree that there shouldn't be any air space in the sump under static
pressure conditions, and in this case the pressure change rate for the
sump is instantaneous so it makes the biggest difference.
 &nbsp;All
these nice things people were posting about mutual respect, understanding
and sensitivity, heck, it made me want to go hug somebody!!&nbsp;
Sorry, Chuck, you're not my type.
John
Chuck&nbsp;</blockquote>
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