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Date: Fri, 25 Feb 2005 11:02:41 -0600
From: Jim Sower <canarder@frontiernet.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: fuel flow
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Sadly, my airplane is set up exactly to Velocity plans. I modified it 
from there to make it work. Assymmetric flow is a very common problem 
with Velocitys. But that's not the purpose of my post. I was trying to 
point out that if Paul selects BOTH on his system and one tank runs dry, 
he will be sucking air into his plumbing. If he's venting his sump into 
one tank, that tank will likely be slightly more than the other and 
could transfer significantly faster, emptying significantly sooner, 
recirculating air/vapor into his main fuel line. I was merely trying to 
encourage him to monitor his fuel and select one tank or the other tank 
when either of them get low.
We've already discussed this too much - it's all been said more than 
once ... Jim S.

kenpowell@comcast.net wrote:

> Jim's problem description is the perfect example of the problems of 
> fuel system design - the flow just doesn't necessarily perform as we 
> would expect. Bill Freeman (a ME who works for Martin Marietta and no 
> longer contributes to ACRE - another Lamar victim) expounded on this 
> problem extensively with the high wing Cessnas and LongEZ's while 
> noting that even some of them still have venting and flow problems. If 
> you can't EXACTLY copy an existing system then you have to really test 
> for uneven fuel flow and vapor lock. I feel so little confidence in 
> deviating from a known design that I'm going to copy Tracy's system 
> EXACTLY for my RV-4. Even here you have to be careful because if the 
> system isn't EXACTLY the same you are again testing an unknown system.
>
> Ken Powell
> Bryant, Arkansas
> 501-847-4721
>
>     -------------- Original message --------------
>     Paul,
>     Paul wrote:
>
>>     Hi, Jim....is it possible there is a restriction in one of the
>>     fuel lines? Are there any bends in the aluminum fuel line that
>>     might have kinked during the bending process?
>
>     This problem drove me NUTS for two years. I tried everything. For
>     example, I checked the vents as best I could, leveled the airplane
>     (checked the ball to ensure it was centered - it was),
>     disconnected the fuel line from the engine side of the firewall
>     and let it drain into a bucket. I turned off one strake at a time
>     (with manual maintenance valve) and timed how long it took for the
>     other strake to gravity drain ten gal of fuel into the sump, out
>     of the sump through the boost pump, through the filter and then
>     through the firewall into the bucket(s). Then I turned it off and
>     did the same thing with the left tank. They both drained 10 gal
>     each within 5% of the same time. Then I reconnected all the
>     plumbing, taped over the fuel caps so there's no possible way they
>     could leak and went flying. Right tank drained 20 gal while the
>     left tank maybe 2 or 3. Level balanced flight on a cross country.
>     All fuel lines, vent lines, etc. are as identical as I am able to
>     make them. To this day, I've not met *anybody* who can explain
>     what happened. I tried *everything*. Back and forth on the
>     Velocity list much longer than you've been inquiring after your
>     vapor lock. NOTHING. I figured out a workaround - I installed
>     electric shutoff valves in place of the manual maintenance valves
>     between the strake and the sump. Now, when one tank doesn't
>     transfer, I turn off the tank that does and let the "reluctant"
>     tank catch up. The pump sucks it through the system just fine (the
>     head pressure of 6" of fuel is about 0.16 psi - a problem that
>     would inhibit that flow you can't even MEASURE. Assymmetric
>     transfer is common as dirt in the Velocity community (but not
>     nearly as persistent as mine). It was also a problem a long time
>     with the Vari-EZ.
>
>>     Lastly, have you tried blowing backwards into the two fuel lines
>>     to see if either had more restriction than the other? Just
>>     looking for possible reasons for your uneven fuel flow. Even my
>>     Cessna 172 and 150 had fairly even fuel consumption from the two
>>     gravity fed tanks.
>
>     I understand that Cessnas had a lot of trouble around this too.
>
>>     Just searching for answers. Paul Conner
>>
>>     ----- Original Message ----- From: "Jim Sower"
>>     <canarder@frontiernet.net>
>>     To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
>>     Sent: Thursday, February 24, 2005 5:57 PM
>>     Subject: [FlyRotary] Re: Vapor Lock
>>
>>
>>>     In my Velocity the strakes gravity feed to the sump. About a
>>>     foot of 3/8" Al / rubber fuel line on each side, downhill all
>>>     the way. I can run one tank plumb dry and have only a gallon or
>>>     two gone out of the other. Like when there's a slight leak in a
>>>     fuel cap or something.
>>>     If they're significantly uneven, you WILL get air if you select
>>>     "Both" ... Jim S.
>>>
>>>     Bulent Aliev wrote:
>>>
>>>>
>>>>
>>>>     If you're almost home and have "Both" selected, and one
>>>>     tank runs dry, what do you end up with in the fuel line? I
>>>>     believe mostly air. Late in the trip (traffic pattern?)
>>>>     where trouble shooting time is at a premium. Use L or R.
>>>>     Not B.
>>>>
>>>>     I don’t think so: connect two tanks (one full with water and
>>>>     one empty) to gravity feed Into Y connection. Than suck on the
>>>>     end and try to breathe. Let me know how it works :)
>>>>     Buly
>>>
>>>
>>>
>>>>>     Homepage: http://www.flyrotary.com/
>>>>>     Archive: http://lancaironline.net/lists/flyrotary/List.html
>>>>
>>>
>>>
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>>>
>>
>>
>>
>>
>>>  Homepage:  http://www.flyrotary.com/
>
>>>  Archive:   http://lancaironline.net/lists/flyrotary/List.html
>
>    
>