Imbalanced fuel flow: was Re: REFLECTOR:Low fuel light

Brian Michalk reflector@tvbf.org
Thu, 24 Jul 2003 12:35:23 -0500


I've got a perfect solution.
Install a fuel gauge in each wing tank.

Feed the output from each gauge into a "rudder autopilot".  Let the
autopilot fly the airplane as needed to keep the fuel tanks level.

Kinda toungue in cheek.

> -----Original Message-----
> From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
> Behalf Of Chuck Jensen
> Sent: Thursday, July 24, 2003 10:11 AM
> To: 'reflector@tvbf.org'
> Subject: RE: Imbalanced fuel flow: was Re: REFLECTOR:Low fuel light
>
>
> Scott,
>
> Good idea.  I'll give that a look-see.  In turns, I feel lucky if
> I keep the
> ball anywhere near the lubber lines, but in straight and near-level, that
> should be easy to see.
>
> If a person thinks about the problem a little (which always gives me a
> headache), it would only take a wing being a couple inches low to
> make quite
> a difference in fuel feed between the tanks.
>
> I am still wondering if the left tank goes to 0, will I have to fly in a
> slight slip to keep my right tank feeding?  Or will the usual
> variations of
> flight continue to keep the sump filled as the right wing goes up
> momentarily?  If it will, then no problem....except, of course,
> when I turn
> a right base onto final with a quartering head wind from the right.  My
> rough calculations (and bad luck) indicate I would run out of
> fuel about 1/2
> mile short of the threshold.  My headache is getting worse.
>
> Chuck
>
> -----Original Message-----
> From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
> Behalf Of Scott Derrick
> Sent: Thursday, July 24, 2003 9:56 AM
> To: reflector@tvbf.org
> Subject: Imbalanced fuel flow: was Re: REFLECTOR:Low fuel light
>
>
> Chuck,
>
> I'd bet your plane is not trimmed correctly. I had imbalance tanks after
> flying a short while when I first bought my plane. I futzed with the
> caps. no change.
>
> The ball was not quite centered within the lubber lines when I was
> flying straight and level.
>
> So I tried this.  I flew a while until the tanks were 5-6 gallons
> different, then I held a rudder in to put the ball on the opposite side
> it was sitting on but all the way on the other side of the lubber line.
> Flew a very short while and the tanks evened out.
>
> If you shim out the correct rudder so the ball is exactly in the middle
>   I think your imbalance will be cured. Its a simple fix, just shim out
> the correct rudder to get the ball centered. Its an easy thing to try, I
> used a dab of JB Weld to shim it out.
>
> Scott
>
> Chuck Jensen wrote:
> > Good stuff on the vent system.  I've been greasing (petro jelly) the O
> > rings on the fuel caps but didn't even think about the O ring on the
> > locking lever.  During a long cruise, I'll get a 9 gallon indicated
> > differential between the tanks, so these efforts might reduce that
> > differential.  I wasn't too concerned as I understand some differential
> > is almost expected.
> >
> > Though I've never gone there, what happens when left tank is 0 and the
> > right is 9 gallons?  Will the rest of the fuel draw from the right tank
> > or will I have to pull off on the side of the road and hitch a ride for
> > gas? I'd hate to think I was carrying 9-10 gallons of useless
> ballast in
> > my tanks but I'm not (intentionally) going to find out.  Anyone been
> > there, done that?
> >
> > Chuck
> > XL RG 540
> >
> >     -----Original Message-----
> >     From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
> >     Behalf Of Ronnie Brown
> >     Sent: Thursday, July 24, 2003 7:46 AM
> >     To: reflector@tvbf.org
> >     Subject: Re: REFLECTOR:Low fuel light
> >
> >     I think the two primary reasons for the fuel tank imbalance are (1)
> >     airplane flying out of trim, i.e. one wing low; (2) a fuel tank cap
> >     leak.
> >
> >     Enlarging the vent system to 3/8" instead of the original 1/4" will
> >     greatly improve the impacts  from (2) a leaking fuel cap.  3/8
> >     tubing has double the area of a 1/4" tube and will pass twice as
> >     much air.  The reason this matters is that we are only talking about
> >     2 feet of fuel level from the bottom of the sump to the top of the
> >     tanks.  This is less than 1 psi.  It doesn't take much of a cap leak
> >     to pull a slight vacuum on that tank which causes that tank to fill
> >     up.  Keep those O rings vaselined and also make sure the cap is
> >     pulling all the way down (adjust the lock nut on the back side of
> >     the cap).  There is also a small O ring on the shaft of the locking
> >     lever that needs to be lubricated.  If you want to check how tightly
> >     your caps are sealing, connect a tube to the vent line, blow in it
> >     (keep the pressure less than 1 psi!) and spray the caps with a
> >     water-dish detergent mixture.
> >
> >     The original Velocity design had separate vents for each tank -
> >     which led to lots of problems.  It is impossible to create two vent
> >     outlets that have the same static pressure at 200 mph!!!  Hence the
> >     single vent system now used.  It is also important that the vent
> >     tubing slope upward to the manifold or you can trap some fuel and
> >     create a tank vent pressure imbalance which will lead to different
> >     fuel levels in the tank.
> >
> >     Ronnie
> >
> >         ----- Original Message -----
> >         From: KeithHallsten <mailto:KeithHallsten@quiknet.com>
> >         To: reflector@tvbf.org <mailto:reflector@tvbf.org>
> >         Sent: Wednesday, July 23, 2003 11:20 PM
> >         Subject: Re: REFLECTOR:Low fuel light
> >
> >         Yes!  Everything you say "SHOULD" be true.  Unfortunately, we
> >         continue to get these reports from the flying population
> >         regarding odd behavior of the fuel/vent system!
> >
> >         I think that at times the vent system supplies air to the sump
> >         tank just a TINY bit more easily than the longer path through
> >         the strakes supplies fuel to the sump tank.  It's probably a
> >         transient event, just persisting long enough to actuate the "low
> >         fuel" warning and scare the bejesus out of the pilot.  I see
> >         little risk in shutting the vent line to the sump tank, thereby
> >         assuring that the flow into the sump tank must come from the
> >         strake tanks.
> >
> >
> >
> >             ----- Original Message -----
> >             From: Ronnie Brown <mailto:romott@adelphia.net>
> >             To: reflector@tvbf.org <mailto:reflector@tvbf.org>
> >             Sent: Wednesday, July 23, 2003 6:55 PM
> >             Subject: Re: REFLECTOR:Low fuel light
> >
> >             If the vent lines slope upward to the manifold from the
> >             three tanks, there shouldn't be any problems trapping air or
> >             fuel.  The fuel should go down and the vent air goes up.
> >             And the fuel in the sump tank vent should seek the same
> >             level as in the fuel in the main tanks, thereby keeping the
> >             sump tank full and the alarm off.
> >
> >             Ronnie
> >
> >                 ----- Original Message -----
> >                 From: KeithHallsten <mailto:KeithHallsten@quiknet.com>
> >                 To: reflector@tvbf.org <mailto:reflector@tvbf.org>
> >                 Sent: Wednesday, July 23, 2003 8:51 PM
> >                 Subject: Re: REFLECTOR:Low fuel light
> >
> >                 Rene',
> >
> >                 I'm not flying yet, so my comments can be discounted
> >                 accordingly.  I plan to install a manual vent shut-off
> >                 valve between the sump tank and the vent manifold.  The
> >                 result will be that the vent system can allow the main
> >                 strake tanks to drain, but can't introduce air into the
> >                 sump tank.  I have a theory that the vent line to the
> >                 sump tank causes more problems than it solves, once the
> >                 initial "burp" of air is allowed to escape from the sump
> >                 tank (before engine start).
> >
> >                 Keith Hallsten
> >
> >
> >                     ----- Original Message -----
> >                     From: Rene Dugas <mailto:rdugas@bayou.com>
> >                     To: reflector@tvbf.org <mailto:reflector@tvbf.org>
> >                     Sent: Wednesday, July 23, 2003 4:00 PM
> >                     Subject: RE: REFLECTOR:Low fuel light
> >
> >                     Thanks Jack,
> >
> >                     I felt that maybe the boundary layer was causing a
> >                     vacuum allowing air to enter the sump but not the
> >                     tanks.  I don not want to over pressure my tanks and
> >                     rupture them at high pressures.  I can splice a gage
> >                     into the line but wanted to glean info from the
> >                     informed (flying) few.  Since all three tanks are
> >                     connected to the manifold I remain perplexed.
> >                     Thanks for the info on the Vision.  Two engine
> >                     builders told me significant fluctuations with the
> >                     engine pump are common but no pressure numbers were
> >                     available.  I talked to Lycoming.  He air might be
> >                     in the line but I don't see how.  Thanks
> >
> >                     Rene'
> >
> >
> >
> >                     -----Original Message-----
> >                     From: reflector-admin@tvbf.org
> >                     [mailto:reflector-admin@tvbf.org] On Behalf Of Jack
> >                     Sheehan
> >                     Sent: Wednesday, July 23, 2003 4:35 PM
> >                     To: reflector@tvbf.org
> >                     Subject: Re: REFLECTOR:Low fuel light
> >
> >
> >
> >                     Rene'
> >
> >                     I can not say much about the low fuel light except
> >                     that I have not had that on my XL-RG and I am not
> >                     extending the vent. Mine is as you described in the
> >                     plumbing except the vent line under the belly is cut
> >                     off almost flush with the fuselage. I have tested my
> >                     sump warning light durin the test flight period by
> >                     getting pretty low on fuel and then pushing the nose
> >                     over and maintain a dive for enough time for the
> >                     sump light to start to flicker The low pressure
> >                     warning from the VM1000 is a common indication. I
> >                     have spoken with Vision micro about it and the good
> >                     news is the VM1000 is working fine and the bad news
> >                     is the lack of pressure is real. it is the way the
> >                     lycoming pump works and if you have an analog system
> >                     with low sensitivity you never see it. They have
> >                     sent me a snubber to install in the sensor line
> >                     which will in theory reduce thesensitivity. ther is
> >                     a similar snubber device in the manifold pressure
> >                     system. I will let you know when I get some free
> >                     time to install it.
> >
> >                     Jack
> >
> >                     N55XL
> >
>
>
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