REFLECTOR: fuel feed - my solutions
Brett Ferrell
bferrell at 123mail.net
Sun Feb 27 16:25:32 CST 2005
As soon as the pump pulls some fuel out of the sump with a blocked vent
line, the check valve will open and vent some air into the tanks. 1
atmosphere versus vacuum will open nearly any check valve. I've done some
process safety work and seen industrial tanks collapsed from under-pressure,
and I think it would be foolish not to install the factory-recommended check
valve and allow your tanks to routinely run under vacuum.
Brett
----- Original Message -----
From: "Jim Sower" <canarder at frontiernet.net>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Sunday, February 27, 2005 3:53 PM
Subject: Re: REFLECTOR: fuel feed - my solutions
My figures indicate that .5 psi is the equivalent of about 165 kias. Bad
news: they aren't going to vent a damned thing if the vent ices over.
Good news: the fuel pump will generate plenty enough suction to overcome
that (of course that underpressure would add to your chances of vapor
forming in the vent line and/or cavitation at the pump face).
Check valves are not the panacea some folks would have you believe ...
Jim S.
Wayne wrote:
> I'm using two of the .5 jobs for an alternate air source in the top of the
> loop before the vent line goes to the bottom of the fuselage. If the fuel
> vent iced over I hope they will provide cabin air to the fuel tanks. If
> the bird is upside down they shouldn't allow fuel to leak inside the
> cabin.
> Wayne
>
> ----- Original Message -----
> *From:* Brian Michalk <mailto:michalk at awpi.com>
> *To:* Velocity Aircraft Owners and Builders list
> <mailto:reflector at tvbf.org>
> *Sent:* Saturday, February 26, 2005 10:01 AM
> *Subject:* RE: REFLECTOR: fuel feed - my solutions
>
> McMaster has a lot of check valves.
> This one says less than .5 PSI cracking pressure.
> The image
> “http://www.mcmaster.com/catalog/111/gfx/large/47245kp1l.gif”
> cannot be displayed, because it contains errors.
> http://www.mcmaster.com/catalog/111/gfx/large/47245kp1l.gif
> This one says 0 PSI cracking pressure.
> The image
> “http://www.mcmaster.com/catalog/111/gfx/large/7909kp1l.gif”
> cannot be displayed, because it contains errors.
> http://www.mcmaster.com/catalog/111/gfx/large/7909kp1l.gif
> These came from this page:
>
> http://www.mcmaster.com/nav/enter.asp?pagenum=389
>
>
>
> Brian Michalk <http://www.michalk.com>
> Life is what you make of it ... never wish you had done something.
> Aviator, experimental aircraft builder, motorcyclist, SCUBA diver
> musician, home-brewer, entrepreneur and barely single
>
>
> > -----Original Message-----
> > From: reflector-bounces at tvbf.org
> [mailto:reflector-bounces at tvbf.org]On
> > Behalf Of Chuck Jensen
> > Sent: Saturday, February 26, 2005 4:27 AM
> > To: Velocity Aircraft Owners and Builders list
> > Subject: RE: REFLECTOR: fuel feed - my solutions
> >
> >
> > Jerry,
> > All check valves has some pressure differential which we can ill
> > afford to loose when the fuel head is measured in inches.
> > Probably the strongest reason for leaving them off is if you do
> > have a little non-uniform fuel flow during your flight, at least
> > when you land, the tanks will self level for your next
> > flight--assuming your on the level when you parked.
> >
> > Chuck
> >
> > -----Original Message-----
> > From: reflector-bounces at tvbf.org
> [mailto:reflector-bounces at tvbf.org]On
> > Behalf Of Jerry.Brainard at anthem.com
> > Sent: Friday, February 25, 2005 5:22 PM
> > To: Velocity Aircraft Owners and Builders list
> > Subject: Re: REFLECTOR: fuel feed - my solutions
> >
> >
> >
> > Just because I don't know - is there a reason not to put a check
> valve in
> > line on the strake feed lines? My thought is that this would prevent
> > retrograde flow into a tank that is on the low side (out of rig)
> or has a
> > leaking cap. I can think of many scenarios where one might be
> confused as
> > to what is happening, but it would seem to resolve any issue
> with pulling
> > fuel into a tank from the feed line. Of course there is also added
> > complexity and another failure mode to consider.
> >
> > -jerry
> >
> > 513-484-1328
> > 513-336-5949
> >
> >
> >
> >
> >
> >
> >
> > Don19dw at aol.com
> >
> > Sent by: To:
> > reflector at awpi.com
> >
> > reflector-bounces cc:
> >
> > @tvbf.org Subject:
> > REFLECTOR: fuel feed - my solutions
> >
> >
> >
> >
> >
> > 02/25/2005 04:38
> >
> > PM
> >
> > Please respond to
> >
> > Velocity Aircraft
> >
> > Owners and
> >
> > Builders list
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > As a result of my accident in June 1999, caused by a leaking
> fuel cap, I
> > made the following changes.
> > 1) Added the sump tank "low fuel" warning system per Velocity
> > plans, except
> > located float slightly lower. The "low fuel" warning would have
> allowed we
> > to reach an airport prior to fuel exhaustion from right tank and
> sump
> > tank.and thus prevented the accident.
> > However then during later flights, especially in turns would get
> flashing
> > "low fuel" warnings which made me very nervous. To trouble shoot the
> > problem I removed the rear seats and spar cover so I could
> visually see
> > sump tank in flight. Using "T" fittings I added a vertical clear
> > sight tube
> > between top sump vent port and bottom outlet port plus a light
> shinning on
> > the tube to see fuel level from my pilots seat. As Scott Swing
> suggested,
> > the sloshing of the fuel in the sump tank was causing the
> flashing "low
> > fuel" warning with little or no lowering of fuel level.
> > 2) In order to solve flashing "low fuel" warning, I added a time
> delay
> > relay set at 6 seconds, before warning light went on, and have
> > not had that
> > problem since.
> > 3) Installed a manual shut off valve in fuel line from each
> strake into
> > sump tank. These left and right shut off valves are actuated by
> cables and
> > small levers on each side of keel at pilots hip. These valves
> > could be used
> > in flight to isolate either strake tank from the sump if the
> fuel level in
> > one side or the other is seen to be dangerously low. If the sump
> vent is
> > closed, the fuel pump should "suck" fuel from the open fuel
> > strake. However
> > the argument for a closed sump vent is valid "to suck fuel" only
> if empty
> > tank is shut off, otherwise air is "sucked" from the empty tank,
> rather
> > than fuel sucked from the other tank. That apparently is what
> happened
> > prior to my accident. So far have never used my added valves in
> flight.
> > (However these valves are handy during servicing and I recommend
> adding
> > them for that reason alone)
> > 4) Added an instrument panel note: " Warning: at least every 30
> minutes,
> > check fuel level in each strake tank. If an unusual balance is
> > seen, ASSUME
> > fullest tank is unusable"
> > 5) After rebuilding the airplane, discovered the turn and bank
> > indicator in
> > the instrument panel, was not installed vertical, about 1/2
> bubble off
> > vertical. Once that was corrected, had to shim left rudder out
> 1/4 inch at
> > trailing edge. Plane now flies perfectly level and straight and
> have not
> > had any unusual fuel level problems since.
> > 6) Finally check fuel caps are tightly closed and properly
> lubricated.
> >
> > This may have been suggested to Jim already. During flight, have
> you held
> > slight pressure on one rudder or the other, to see if fuel tank
> levels
> > equalize? If that occurs, then I strongly suspect plane is not
> flying
> > perfectly level and straight.
> > Don White N19DW XL/RG
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