REFLECTOR: FUEL FEED [heur]

[Scott Baker]

The Velocity factory position is that shown in the Construction Manual. 
Assuming that you are using the recommended fuel tank and vent line 
locations, the center sump tank should be vented with a check valve (flow 
towards the sump tank) that is "T'd" into the vent line.  The check valve 
allows the sump to continue venting if the main vent line were to clog (ice, 
bugs).

Short story - When I was in the business of being one of them-there 
professional "amateur" builder assistants, I toyed with the idea of 
modifying the Velocity fuel supply/vent system.  While doing so I consulted 
with Duane Swing to ask his opinion - and I vividly remember his reply - 
which was (paraphrased) "Don't screw around with the fuel system.  There is 
a lot 'there' that does not meet the eye - and it is easy to create a 
problem".  Following this I "screwed around" with the schematic anyway - and 
discovered (the hard way) that a) venting the sump tank without routing the 
vent line to the uppermost portion of the roof of the aircraft tends to 
siphon the fish tank dry (full tanks + high pitch angle during take off = 
beginning of fuel flow through the vent system being pumped overboard) ... 
"I say ... we're "burning" fuel at an alarming rate.  20-gallons in the last 
10-minutes.  Maybe it would be a good idea to land".  One of friends at the 
airport waved me off from approaching the hangar because of the trail of 
fuel that continued to be siphoned overboard during taxi.

On another occasion I did NOT vent the sump tank - opting to vent the mains 
only (sort of what Jim S. is suggesting).  This was a 260-hp engine 
installation with 0.375" diameter fuel lines and ... what were we using back 
then ...0.250" vent lines?  This system involved a fuel selector valve (near 
the pilot seat), so fuel was going from the mains, around the gear 
bulkheads, up the keel, short riser to the fuel-selector valve, back down 
through the keel, and into the sump tank.  Anyway, before the first flight I 
tested the fuel delivery by installing a flow restrictor after the electric 
fuel pump (a partially crimped aluminum tube) and turning on the electric 
fuel pump (dumping the fuel into a portable fuel can).  Everything went well 
...at first.  Fuel delivery was somewhere near 25-gph (using stopwatch and 
measured volume) for about 5-minutes - at which point ... and this is VERY 
IMPORTANT - PLEASE PAY ATTENTION - because of the small vent lines, and 
because of the long fuel line runs, the fuel pump was delivering fuel faster 
than the vent and feed lines could supply fuel.  The fuel pressure fell off 
as the system began to pull a vacuum on the fuel tanks - and the fuel lines 
literally filled with air bubbles due to cavitations - I could see the 
bubbles in the clear tubing I was using during the test.  The fuel flow just 
about stopped!  Just thinking about a loss of fuel flow at the 5-minute mark 
of flight (during takeoff and probably below 1,000' agl) gave me the 
shivers.  Why I decided to do a ground test to mimic the fuel flow during 
takeoff is beyond me.  I've never done this before and it has never been 
suggested by anyone in the Velo organization.  I came to the ongoing 
realization that I was not running a "one-man shop" ... that "Someone 
else" - without my thinking about it - was there to look over my shoulder. 
Sometimes divine intervention plays an important part in our lives!

Lessons learned:
a) Fix problems as they occur
b) Don't "fix" problems if they don't exist
c) Don't re-design the fuel system without giving it a lot of careful study!

Scott B.





----- Original Message ----- 
From: "Tom Martino" <tmartino at troubleshooter.com>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Wednesday, February 16, 2005 12:31 PM
Subject: RE: REFLECTOR: FUEL FEED [heur]


> Can the factory weight in on this?  It is a very obvious conflict!  Should 
> the sump be vented or not?
>
> -----Original Message----- 
> From: Jim Sower [mailto:canarder at frontiernet.net]
> Sent: Wed 2/16/2005 10:17 AM
> To: Velocity Aircraft Owners and Builders list
> Cc:
> Subject: Re: REFLECTOR: FUEL FEED [heur]
>
>
>
> <... there is the potential of fuel vapors coming through the vent ...>
> Someplace I thought I heard that fuel vapors (not to be confused with
> raw fuel) would asphyxiate you long before there was a combustible
> mixture.  With raw fuel OTOH there would be a combustible mixture at the
> surface of the puddle.  That said, an overpressure in the sump (from
> heating the wings or some other very unusual condition) can push fuel
> out of the sump vent if it is open.
> Again, NEVER vent the sump tank in flight ... Jim S.
>
> Scott Derrick wrote:
>
> > Yeah, I thought about the ice free environment thing after thinking
> > about it.
> >
> > But the potential for igniting the fuel system scares the crap out of
> > me.  Even without being upside down, there is the potential of fuel
> > vapors coming through the vent!
> >
> > Scott
> >
> > Alex Balic wrote:
> >
> >> Not that I condone that design change in any way, because I agree
> >> that it is
> >> a bad idea- especially if the aircraft ends up on it's back from some
> >> accident (fuel pouring into the hot engine compartment and all) but I
> >> could
> >> see where some might think that it was a good idea to place the vent
> >> in a
> >> high pressure area where it would not be exposed to ice or water
> >> ingestion.
> >>
> >> -----Original Message-----
> >> From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On
> >> Behalf Of Scott Derrick
> >> Sent: Wednesday, February 16, 2005 10:14 AM
> >> To: Velocity Aircraft Owners and Builders list
> >> Subject: Re: REFLECTOR: FUEL FEED [heur]
> >>
> >>
> >>
> >> I think it is extremly dangerous to vent the fuel system into the 
> >> engine
> >> compartment!
> >>
> >> Why would anybody do that???
> >>
> >> Scott
> >>
> >> Ron Brown wrote:
> >>
> >>
> >>
> >>> Tom,
> >>>
> >>> I don't think it is a good idea to vent the fuel system into the
> >>> engine compartment, especially if you happen to flip upside down
> >>> during a crash landing.  You will have lots of fuel draining out the
> >>> vent system into the hot engine compartment.
> >>>
> >>> With the factory designed fuel vent line routed up to the top of the
> >>> firewall then back down to exit the bottom of the fuselage, fuel will
> >>> not leak out of the vent system when the airplane is upside down.
> >>>
> >>> One other thought on uneven fuel flow, even if the vents are tied
> >>> together and the plane is flying level/ball centered: there is a
> >>> possibility that an air bubble trapped in the vent line with fuel on
> >>> either side of the bubble can cause an uneven venting of the tanks.
> >>> This wouldn't happen if the vent lines always slope upward to the
> >>> manifold.  I think this may be the scenario that Jim Sower is seeing
> >>> from time to time.  I have had it happen a couple of times on long
> >>> trips after filling the tanks nearly full.  After landing and parking
> >>> in my hanger, the fuel tanks were 5 or so gallons different and
> >>> remained that way until I opened the fuel caps.  STRANGE!  Wings are
> >>> level when parked in the hanger.  Another experiment - I placed a 2 x
> >>> 6 under one main tire, simulating a wings down.  Guess what - the fuel
> >>> level difference was MUCH LESS than I have seen in the air.
> >>>
> >>> But again, it could be fuel caps that are not always sealing perfectly
> >>> for every flight.
> >>>
> >>> Ronnie
> >>>
> >>> ----- Original Message ----- From: "Tom Martino"
> >>> <tmartino at troubleshooter.com>
> >>> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
> >>> Sent: Tuesday, February 15, 2005 12:23 PM
> >>> Subject: RE: REFLECTOR: FUEL FEED [heur]
> >>>
> >>>
> >>> My plane flies perfectly.  Not my opinion, it is the assessment of my
> >>> test pilot.  The ball is in the center and the plane flies "hands off"
> >>> straight and level.
> >>>
> >>> I will keep looking.
> >>>
> >>> -----Original Message-----
> >>> From: Scott Derrick [mailto:scott at tnstaafl.net]
> >>> Sent: Tuesday, February 15, 2005 9:18 AM
> >>> To: Velocity Aircraft Owners and Builders list
> >>> Subject: Re: REFLECTOR: FUEL FEED [heur]
> >>>
> >>> A leaking gas cap can cause uneven fuel flow but is not the prime
> >>> culprit. A bit of fuel valve lube applied to the O ring once a year
> >>> will
> >>>
> >>> insure this doesn't happen.
> >>>
> >>> A miss-rigged airplane is most likely the cause. Shim your rudders so
> >>> the ball is right in the middle and you will get perfect fuel flow.
> >>>
> >>> To test, be sure your turn and bank is installed correctly first,
> >>> garbage in garbage out. Then fly, this is the fun part.. Once you
> >>> see an
> >>>
> >>> uneven condition, press on the rudder that will put the ball in the
> >>> middle. If you want to even up the tanks fast, press on the correct
> >>> rudder so the ball is on the other side for a couple minutes, you'll
> >>> see
> >>>
> >>> the fuel even up and even go into the opposite imbalance if you keep
> >>> the
> >>>
> >>> rudder depressed. Then hold the rudder so the ball is centered, fuel
> >>> will flow as it was designed to.
> >>>
> >>> Scott
> >>>
> >>> Tom Martino wrote:
> >>>
> >>>
> >>>
> >>>> Well, now that I'm in my test flying mode ... I will really be asking
> >>>> a lot of questions.
> >>>>
> >>>> Here are some of them, as they relate to my fuel system:
> >>>>
> >>>> 1. What makes the fuel tanks feed unevenly to the header tank/engine?
> >>>> (My right tank is feeding twice as fast as my right tank.)
> >>>>
> >>>> 2. Will that cause a problem when the fast-feeding tank runs out?
> >>>>
> >>>> 3. I used the larger vent lines for my tanks and tied them al 
> >>>> together
> >>>>
> >>>
> >>>
> >>>
> >>>> with a manifold, then vented the entire system out through the top of
> >>>> my firewall in the engine compartment (about four inches below my 
> >>>> naca
> >>>>
> >>>
> >>>
> >>>
> >>>> duct). Do you think the system gets enough venting there?
> >>>>
> >>>> 4. Is there a need for a "whistle" hole in any of the tank vents ...
> >>>> for additional venting (like we do with the crankcase breather?
> >>>>
> >>>> Any help is appreciated from my more experienced Velocitologists J
> >>>>
> >>>> Tom
> >>>>
> >>>> N173EX
> >>>>
> >>>> (A mere 6 hours)
> >>>>
> >>>> -----------------------------------------------------------------------
> >>>>
> >>>>
> >>>
> >>> -
> >>>
> >>>
> >>>
> >>>> _______________________________________________
> >>>> To change your email address, visit
> >>>>
> >>>
> >>> http://www.tvbf.org/mailman/listinfo/reflector
> >>>
> >>>
> >>>
> >>>> Visit the gallery!  www.tvbf.org/gallery
> >>>> user:pw = tvbf:jamaicangoose
> >>>> Check new archives: www.tvbf.org/pipermail
> >>>> Check old archives:
> >>>> http://www.tvbf.org/archives/velocity/maillist.html
> >>>>
> >>>>
> >>>
> >>> _______________________________________________
> >>> To change your email address, visit
> >>> http://www.tvbf.org/mailman/listinfo/reflector
> >>>
> >>> Visit the gallery!  www.tvbf.org/gallery
> >>> user:pw = tvbf:jamaicangoose
> >>> Check new archives: www.tvbf.org/pipermail
> >>> Check old archives: 
> >>> http://www.tvbf.org/archives/velocity/maillist.html
> >>>
> >>>
> >>> _______________________________________________
> >>> To change your email address, visit
> >>> http://www.tvbf.org/mailman/listinfo/reflector
> >>>
> >>> Visit the gallery!  www.tvbf.org/gallery
> >>> user:pw =vbf:jamaicangoose
> >>> Check new archives: www.tvbf.org/pipermail
> >>> Check old archives: 
> >>> http://www.tvbf.org/archives/velocity/maillist.html
> >>>
> >>> _______________________________________________
> >>> To change your email address, visit
> >>> http://www.tvbf.org/mailman/listinfo/reflector
> >>>
> >>> Visit the gallery!  www.tvbf.org/gallery
> >>> user:pw = tvbf:jamaicangoose
> >>> Check new archives: www.tvbf.org/pipermail
> >>> Check old archives: 
> >>> http://www.tvbf.org/archives/velocity/maillist.html
> >>>
> >>>
> >>>
> >>>
> >>
> >> _______________________________________________
> >> To change your email address, visit
> >> http://www.tvbf.org/mailman/listinfo/reflector
> >>
> >> Visit the gallery!  www.tvbf.org/gallery
> >> user:pw = tvbf:jamaicangoose
> >> Check new archives: www.tvbf.org/pipermail
> >> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
> >>
> >> _______________________________________________
> >> To change your email address, visit
> >> http://www.tvbf.org/mailman/listinfo/reflector
> >>
> >> Visit the gallery!  www.tvbf.org/gallery
> >> user:pw = tvbf:jamaicangoose
> >> Check new archives: www.tvbf.org/pipermail
> >> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
> >>
> >>
> >>
> >>
> >>
> > _______________________________________________
> > To change your email address, visit
> > http://www.tvbf.org/mailman/listinfo/reflector
> >
> > Visit the gallery!  www.tvbf.org/gallery
> > user:pw = tvbf:jamaicangoose
> > Check new archives: www.tvbf.org/pipermail
> > Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
> >
> >
> _______________________________________________
> To change your email address, visit 
> http://www.tvbf.org/mailman/listinfo/reflector
>
> Visit the gallery!  www.tvbf.org/gallery
> user:pw = tvbf:jamaicangoose
> Check new archives: www.tvbf.org/pipermail
> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
>
>
>
>
>


--------------------------------------------------------------------------------


> _______________________________________________
> To change your email address, visit 
> http://www.tvbf.org/mailman/listinfo/reflector
>
> Visit the gallery!  www.tvbf.org/gallery
> user:pw = tvbf:jamaicangoose
> Check new archives: www.tvbf.org/pipermail
> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html