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To:  lml@lancaironline.net
Date: Mon, 15 Jun 2009 07:06:17 -0400
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From: "Dan Schaefer" <dfs155@roadrunner.com>
Subject: Fuel Vent line test
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As a rough test to be sure the vent line will actually vent the header, one 
can run the transfer pump(s) until fuel begins to overflow thru the vent 
tube (be careful and stick a length of plastic tubing on the vent and run it 
back to one of the wing tanks to catch the overflow).

My LNC2 is an early 235 (first flight in '93 and still flown regularly) and 
I located the external tip of the vent according to the plans in effect at 
that time - just about straight down from the vent exit in the header. My 
external tube protrudes about 3/4 inch and has the 45 degree cut - so there 
must be a reasonably good pressure field under there - or 3/4 inch is long 
enough to get outside the boundary layer - whichever, mine works as 
required.

Also the plans called for plumbing all three fuel tank vents (wing and 
header tanks) with 1/4 inch tubing. One-quarter inch ID works OK as long as 
a mud dauber wasp (or some other big bug) doesn't take up residence where 
you can't see the plug (don't ask how I know) so keeping the vents clear 
should be added to your pre-flight check. A large diameter pipe cleaner 
stuck in the vent about an inch, with a red ribbon attached to the end that 
hangs out, works OK - as long as you are diligent in your preflight.

Dan Schaefer
N235SP 


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