My fuel system is standard per Europa Mark 1 latest mod except
that the gauge vent line from the panel to the vent is 1/4 OD
nylon. This was done to allow the vent line to fit between the
side of the panel and the cockpit interior covering providing a
continuous rise from the footwell to the lower corner of the
windscreen.
Recently, I left the aircraft in the sun for a couple of hours
with the tank about 3/4 full. I had checked the fuel in level
flight prior to landing since I don't use the sight gauge for
judging fuel level on the ground, other than when filling the
tank. I drained fuel samples prior to departure so the tank
filler was opened and vented temporarily prior to departure.
After takeoff I noted that the fuel gauge was reading full, i.e.
the level in the sight gauge was out of sight behind the panel.
This condition persisted for about 10 minutes until I leveled for
cruise when the gauge read correctly. This is opposite to the
normal situation where the sight gauge reads low during climb.
After landing again I noted streaks of fuel from the fuel cap
area toward and around the fin and onto the rudder on both sides
of the fin. At the base of the fin the streaking was about 4
inches wide on each side a couple inches above the tailplane stub
with similar width in the dorsal area between the fuel cap and
the fin. On the stbd side there is some additional streaking
toward the fin which then runs down forward of the tailplane stub
suggesting that the tank vent was involved while parked or while
taxying.
My present theory is that there was some fuel in the tank vent
line after landing and that while parked the fuel in the tank
expanded. For unexplained reasons the fuel in the gauge vent
then was forced up and into the line where it passes overhead in
the area between the doors probably filling this downward sloped
area of the line. It is unclear how this is actually possible
since the tank vent is lower than the high point in the gauge
vent line so it should have released the pressure before this
could occur... In climb, with the gauge vent line filled with
fuel, the fuel siphoned and/or was vacuumed out of the vent.
However, checking the low point of the gauge vent line (just
below the vent itself) showed no fuel trapped there so this
theory may be incorrect.
Anyone else seen this? Which vent actually emitted the fuel?
Any other theories on what caused it?
To avoid this in the future will blowing into the tank vent to
clear it be effective? What about when the tank is filled such
that the tank end of the vent is submerged?
Has anyone measured the pressure produced by the tank vent system
in flight? Is the fuel tank at a positive pressure with the
forward facing vent plus two holes in the rear side of the vent
or could it siphon fuel in flight? Should one of the two holes in
the rear of the vents be covered to ensure positive pressure to
the fuel system in flight? Any info or theories gratefully
accepted.
John N44EU
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