REFLECTOR: fuel feed - my solutions
Jim Sower
canarder at frontiernet.net
Sun Feb 27 21:36:23 CST 2005
<...I suspect that an icing encounter sufficient to completely block ...>
I don't worry about ice. I don't go there. I do worry about "dirt
daubers" and other critters.
And I've heard DOZENS of anecdotal blockages from such critters ... Jim S.
KeithHallsten wrote:
>With 3/8" vent lines, plugging is not really a high-probability failure
>mode. It may well be that the check valve is "pink elephant repellent".
>(Since I put that check valve in, I haven't seen a single pink elephant!)
>Is there any verifiable history of plugging of a 3/8" vent line? Anyone
>have even anecdotal evidence that an alternate vent is really necessary? I suspect that an icing encounter sufficient to completely block the fuel system vent would also be sufficient to so alter the canard airfoil that flight would not continue anyway.
>Keith Hallsten
>
>
>----- Original Message -----
>From: "Brett Ferrell" <bferrell at 123mail.net>
>To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
>Sent: Sunday, February 27, 2005 2:25 PM
>Subject: Re: REFLECTOR: fuel feed - my solutions
>
>
>
>
>>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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