In a message dated 5/10/2007 8:49:27 A.M. Central Daylight Time,
MikeEasley@aol.com writes:
A couple comments on the vent lines. My super fastbuild has 3/8"
vent lines, but the original ESs had 1/4". I found this out AFTER
building my wingtips with the 1/4" tubing per the manual. There was also
an SB on the original tubing used in the vent lines.
I had a IV in my hangar for some interior work that had a wing tank fuel
leak. I had to drain the tank and wasn't sure I could keep up with the
flow after taking out the quick drain. So I put a piece of duct tape
over the NACA. The fuel practically stopped flowing after less
than 1 gallon. That's with 35 gallons of head pressure. I'm
thinking that a clogged vent would be impossible to overcome with the boost
pump.
If it was me, I think I'd do some more searching, very
mysterious.
Mike,
Not so mysterious..... Consider a mud dauber plugging a vent whilst
parked for a picnic. The failure to draw fuel is only one of the problems
as you can switch tanks. If you are down to the last tank and the vacuum
created by the engine/boost pump is great enough, consider the pressing
structural issues on the tank walls (pun intended).
You do inspect the vents before each flight, don't you? Did you
also install vented gas caps for vacuum relief? If so, the cap should
also contain a check valve to stop outflow while the tank is slightly
pressurized by the vent that's hanging out in the airstream.
Look at it this way - After sucking all that can be sucked and in the
engine out descent, the pressure differential is increased and the
probability of wing skin collapse may also increase. Remember that
bottle of Evian you sipped thru the flight at altitude? After closing the
cap, remember how it looked when you landed, all collapsed and shriveled
up?
Ah, the beauty of the 200/300 series. Wee Facet pumps, used to
push wing fuel into the header, do not make that much head. If
the crucial engine-feeding header tank vent gets plugged, pressure
relief is obtained by pulling fuel (or air if the wing is empty) from either or
both wings - a double backup.
Scott Krueger
AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL
(KARR)
Darwinian culling phrase: Watch
This!