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<< Lancair Builders' Mail List >>
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In a message dated 9/26/01 10:46:04 PM, Jim McKibbin wrote:
<<On September 23, 2001 Rob Wolf suggested drilling a hole in the standpipe to
vent it.....I must respectfully disagree with this suggestion. This is
tantamount to
venting the fuel system inside the cockpit! >>
Jim -
Thanks for your very detailed response on this issue. While reading it, it
became clear that y'all are talking about a standpipe EXTERNAL to the fuel
tank. I had thought that you were talking about a standpipe INSIDE the fuel
tank. With the standpipe inside the tank, there's no problem with fuel
vapors from the standpipe vent hole. Obviously, we can't vent the fuel tank
to the inside of the plane. Sorry for the misunderstanding and I hope nobody
follows that suggestion.
But you're absolutely right about one thing -- the top of the standpipe needs
to be vented to the same pressure as the ullage (gas space) in the fuel tank.
This can only be done by venting the top of the standpipe back into the fuel
tank or it's own corresponding vent line, since all the other approaches
introduce unacceptable errors.
The obvious solution (to me, anyway) is to vent the top of the external
standpipe back into the fuel tank. Hard to imagine how this could be done
without setting up a siphon. Maybe a bulkhead fitting on the inboard rib of
the fuel bay, with a long aluminum tube along the top surface of the wing out
to the filler cap area.
I suppose you could have one master fuel vent, plumbed to each tank and to
the standpipes, but that seems like a lot of complexity to me. Isn't the
standard system good enough? A capacitance probe angled upwards from the
inboard lower portion of the tank?
- Rob Wolf
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