Mailing List flyrotary@lancaironline.net Message #18033
From: Jim Sower <canarder@frontiernet.net>
Subject: Re: [FlyRotary] Re: Vapor Lock
Date: Sat, 26 Feb 2005 21:55:51 -0600
To: Rotary motors in aircraft <flyrotary@lancaironline.net>


WRJJRS@aol.com wrote:
In a message dated 2/25/2005 8:54:52 PM Pacific Standard Time, canarder@frontiernet.net writes:
What does the path of least resistance look like for 10 gal per hour of air through a 3/8" line?  If we were talking honey or motor oil or something ... but AIR?
I don't think we can measure anything that small ... Jim S.
True Jim,  but don't forget you are dealing with positive pressure when flying so the whole system comes into play.
120 kias = 7.13" H2O = 8.79" Avgasl = 0.273 psi
150 kias = 11.17" H2O = 13.17" Avgas = 0.428 psi
How big a leak (like fuel cap) does it take to dump that much pressure?  Suppose it only dumps one third the pressure?  How you gonna' tell that you've got 0.273 psi in one tank and 0.18 psi in the other?  What are you going to measure that with?  Attempting that, how do you determine ow much of the 0.09 psi difference is caused by the measuring device (whatever that might be)?

One tanks pressure head may end up marginally higher. This could be caused by so many things that are small and hard to measure. Just an example, you could have a gas cap that leaks a bit more AIR on the side that drains slow. 
You may recall I tried it several times with Al foil-tar duct tape over the fuel caps.  Nothing changed
So then the fast tank sees a bit higher positive pressure. Not being critical here but you did mention that one tank ALWAYS drains faster.
Nearly (virtually) always.
Could be a couple of sharp edged fittings in the delivery line...no way to be sure.
EXACTLY.  So how do you find these burrs?  How do you fix them?

How do we solve a problem we cannot quantify or even identify? ... Jim S.

Bill
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