Tony,
Kitplanes did a nice review of fuel tank vent types.
On the Europa, drilling the base was for plugging concerns. With two forward
facing
vents (one vent and one sight gauge) on top of the Europa with holes at
the base, the tank will vent in the event of plugging on the front as air can
enter the holes at the base, and the sight gauge vent could also vent the tank
if needed at the loss of a fuel gauge. Because the Europa designed vents are
located in a low pressure area on top of the fuselage, in a steep turn to the
right, with the tank nearly full of fuel, some fuel will be sucked out and down
the fuselage staining the back. The same problem exists if the fuel tank is
full to the neck and then expands. There is no concern with ram air pressure
---From the forward facing vent on our system. At Vne, a vent tube only adds a
tiny fraction of pressure and bursting is not a concern. If you follow the
build
manual you will be OK, but if you leave the plane outside, consider the issue
of rain entering the top side tubes unless covered. Jaxida aircraft covers
made a hump for the vents. Very nice. In my experience, the Europa vent
design
accumulating water from rain, has not been an issue.
I place my vent on the bottom facing forward to get some pressure, but primarily
to prevent fuel staining and allow a drain if accidentally overfilling. Then
as the fuel warms, the expanding fuel has somewhere to go rather than staining
my paint. It is imperative that the bottom vent be drilled at the base with
two holes as mud or debris coming off the nose wheel could plug the tip. In
my design, there is no other way to vent the tank as in the Europa design. Not
a concern for me as I have a wheel panted trigear operating off of hard surface
runways. For guys flying off of muddy runways my system may not be
advantageous.
A vent can be just a straight down pipe also if ice or debris is a concern.
This would be true for the Europa also. At the slow speeds of our aircraft
and a fuel draw of less than 12GPH (.2 gallons per minute) tank venting
requires a very small diameter vent to prevent fuel starvation as the engine
draws
fuel from the tank. A vent of only 1/8 inch ID is sufficient in my calculations
for fuel delivery.
When filling the tank, venting is a different story. If filling from a
commercial
fuel hose at full rate, expect to get wet with fuel. (If the one inch filling
hose is flowing at 5 gallons a minute under pressure, clearly a vent of the
same flow rate would be needed. Fill the Europa slowly from the commercial
pumps. Aircraft fuel trucks can flow at 10 plus gallons per minute and many
a line boy has been drenched.) Larger vents up to 3/8 ID have been tried, but
flow into a necked tank inlet hose to the tank can still be an issue of fuel
burping back. If fuel goes in rapidly, air must rapidly escape the tank. A
fill
vent that comes back into the filler neck as on my design will still burp
back at you at a high rate of fill.
A fuel vent design can also be pointed down, horizontal or aft. Testing is the
key. Some positions would create a vacuum and the fuel delivery system
(aircraft
pumps) must compensate. Icing can be a problem for some doing IFR ops.
The Europa doesn't do ice well so avoid it obviously. In my observations, those
aircraft using forward facing or angled forward pressure vents tend to have
gravity feed issues from the wing tanks. So, design of the fuel vents takes as
much planning sometimes as the fuel delivery to the engine. The older aircraft
often had vented caps only on their gravity feed fuel system and the low
pressure
area over the wing was high enough that fuel was restricted from flowing
to the engine on takeoff.
In any case, never take your fuel vent for granted. Our Europa fuel cap is
sealed
fairly tight, therefore the only way the engine can draw fuel out of the tank
is if there is a way for air to replace the fuel used at a rate higher than
the feed. On preflight, check the vent is clear. Don't assume that the fuel
fumes will keep an insect from building a nest in your vent(s). If operating
off of muddy runways, think about the affects on your fuel vent on the bottom.
If it is damaged or clogged, fix it. If the engine sags on takeoff, reduce
power and return to land. Checking the engine is a must, but don't fail to
check your fuel vent. When refueling, fill the tank slowly if your tank venting
system is not capable of the flow rate of your fuel filler nozzle or you
will get a fuel bath.
Just my opinion,
Bud Yerly
-----Original Message-----
From: owner-europa-list-server@matronics.com
<owner-europa-list-server@matronics.com>
On Behalf Of tonyvaccarella
Sent: Thursday, June 24, 2021 7:28 AM
Subject: Europa-List: Is Mod 38 a good idea?
I only just became aware of this Mod that drills 2 x 1/8 holes at the rear of
the
fuel vent. From what I read, its intent is to prevent too much pressure being
developed in the forward facing vent and therefore within the fuel tank.
Having some pitot pressure, I would have thought, would be desirable.
Im interested to know who has incorporated this Mod and would you recommend it?
Europa lists it as desirable.
Thanks
Tony
Sydney Aust
--------
Tony Vaccarella
Mascot NSW 2020
Sydney Australia
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