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Date: Thu, 24 Feb 2005 22:04:31 -0600
From: Charlie England <ceengland@bellsouth.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Vapor Lock
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Fuel vent positioning is one of the causes in Cessnas. Unequal ram air=20
pressurization of the 2 tanks in flight.

Charlie

Jim Sower wrote:

> Paul,
> Paul wrote:
>
>> Hi, Jim....is it possible there is a restriction in one of the fuel=20
>> lines? Are there any bends in the aluminum fuel line that might have=20
>> kinked during the bending process?
>
> This problem drove me NUTS for two years.  I tried everything.  For=20
> example, I checked the vents as best I could, leveled the airplane=20
> (checked the ball to ensure it was centered - it was), disconnected=20
> the fuel line from the engine side of the firewall and let it drain=20
> into a bucket.  I turned off one strake at a time (with manual=20
> maintenance valve) and timed how long it took for the other strake to=20
> gravity drain ten gal of fuel into the sump, out of the sump through=20
> the boost pump, through the filter and then through the firewall into=20
> the bucket(s).  Then I turned it off and did the same thing with the=20
> left tank.  They both drained 10 gal each  within 5% of the same=20
> time.  Then I reconnected all the plumbing, taped over the fuel caps=20
> so there's no possible way they could leak and went flying.  Right=20
> tank drained 20 gal while the left tank maybe 2 or 3.  Level balanced=20
> flight on a cross country.  All fuel lines, vent lines, etc. are as=20
> identical as I am able to make them.  To this day, I've not met=20
> anybody who can explain what happened.  I tried everything.  Back and=20
> forth on the Velocity list much longer than you've been inquiring=20
> after your vapor lock.  NOTHING.  I figured out a workaround - I=20
> installed electric shutoff valves in place of the manual maintenance=20
> valves between the strake and the sump.  Now, when one tank doesn't=20
> transfer, I turn off the tank that does and let the "reluctant" tank=20
> catch up.  The pump sucks it through the system just fine (the head=20
> pressure of 6" of fuel is about 0.16 psi - a problem that would=20
> inhibit that flow you can't even MEASURE.  Assymmetric transfer is=20
> 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=20
>> see if either had more restriction than the other?  Just looking for=20
>> possible reasons for your uneven fuel flow.  Even my Cessna 172 and=20
>> 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"=20
>> <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=20
>>> "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=92t think so: connect two tanks (one full with water and one=20
>>>> empty) to gravity feed Into Y connection. Than suck on the end and=20
>>>> try to breathe. Let me know how it works :)
>>>> Buly=20
>>>