[rebel-builders] Re: Fuel Tank venting

[snowyrvr@mtaonline.net]

Ken,
Where did you put your header tank. It's just a gathering place for fuel
before it goes into the engine, right?

Original Message:
-----------------
From: Jim Cole jcole@rangroup.com
Date: Sun, 20 Apr 2008 14:56:05 -0400
To: rebel-builders@dcsol.com
Subject: [rebel-builders] Re: Fuel Tank venting



I have a "J" - tube that I built into both caps and it has worked great so
far (touch wood). I've been thinking a lot about installing a small header
tank the same as Ken and that another friend of mine has on his Kitfox.
I did have a hiccup in the engine one day when I was doing steep turns, when
I had less than a 1/4 tank in the right wing tank.
A header tank make sense to me now.

I also happened to be at Found Aircraft in Parry Sound yesterday and one of
the things I took pictures of was the fuel tank vents that they have on the
Bush Hawk. They are hoses cut on an angle protruding from the bottom of the
wing, designed to catch the wind. I posted a couple of pictures under Rebel
Fuel systems - 212.
I unfortunately uploaded a large file 2mb before I realized I had not
grabbed the low rez version - so have an eye - the 2mb version is the same
as one of the other two low rez shots that I up loaded.
I watched the new Found Expedition (trike gear) do some test flying -
they're still working towards their certification. More like a Cadillac than
a bush plane but nicely finished.

Cheers
Jim Rebel 333

On 4/19/2008 2:05 PM, "Ron Shannon" <rshannon@cruzcom.com> wrote:

The upper forward hole is for the cross vent, which is necessary to

equalize

pressure in the tanks, such as if one external vent (see below) is plugged
by bugs, for example. Imagine what happens if one tank's external vent is
plugged and there's no cross vent. The tank develops negative pressure --
and the fuel stops flowing down. That may result in fuel starvation and

ruin

your day -- whether you inline valves for each tank, or just one valve at
or after the junction of the fuel lines from the two tanks. Regardless,

the

cross vent is mandatory. I have some pictures of mine & will try to locate
them.

Of course, you also need the external vents, which could be snorkels

coming

up from somewhere in the cross vent, or snorkels in the gas caps. Both
locations will put some positive air pressure into the tanks, which is a
good thing. Putting snorkels in the gas caps may be a little better,

because

you don't run the risk of a blockage in the cross vent line between
snorkel(s) and tank(s), and snorkels in the gas caps are easily tested

with

a blow when you add fuel, etc.

Not sure about your descriptions of the other holes. The bottom-most hole

in

the root rib, about 7-8 inches forward of the torque tube, is for fuel

line

output. The hole in the bottom of the wing is for a fuel tester drain.

If you use capacitance probe gauges (or some float gauge type -- as far as
that goes) you'll need to cut a hole for them, per their installation
instructions. See the photo I linked to before, where the capacitance

probes

are shown as a roughly 2.5" dia. black "hockey puck" circle near the upper
forward part of the rib, about 2 inches forward of the cross vent
connection.

Ron


On Sat, Apr 19, 2008 at 10:20 AM, Craig Walls <snowyrvr@mtaonline.net>
wrote:

So, if I get this, the upper hole at the front of the root rib would be a
vent to the other tank, the lower hole at the front of the rib would be
for
the fuel gage, and the lower hole at the rear would be for the fuel
pick-up.


In my manual they show a cross vent between the two tanks with a metal
tube
that extends through the roof to get a ram air effect. Not sure if
that's
necessary, could probably do the same thing with those fuel caps with the
ram-air tubes built in.

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[Ken]

snowyrvr@mtaonline.net wrote:

Ken,
Where did you put your header tank. It's just a gathering place for fuel
before it goes into the engine, right?

In my case with Electronic Fuel Injection, it is a bit more -but since
you asked, here's a description and some answers from an offlist enquiry.


My header is just over 2 gal. and is behind the baggage curtain mounted
on the sidewall. It is large enough to contain 2 submersed fuel pumps
complete with automotive intake fuel socks and that is what determined
the tank size. It is in fact a large gascolator so I do not have a
separate gascolator. It is vented back to the crossvent line and has a
float switch to trigger a low fuel warning. It does take a bit of
structure to mount something that heavy back there and make it
reasonably safe in a crash situation. But I love the worry free concept
and consider it to be a much safer overall method. My tank is prosealed
together out of 0.050 aluminum although 0.040 would have been adequate.
All returned fuel goes back to the header.

Both my high pressure lines and also my return line run above the cabin
floor just under the aileron push pull tube that runs back to the mixer.
Less risk of rupture in a very hard landing I think.

Everything is a risk but there have been a number of downed EFI aircraft
due to poor fuel systems. I recommend a header but mount it carefully
such that impact and moving engine mount hard points don't immediately
cause a rupture. Anyone who thinks the fuel line to the engine is going
to survive a bad crash is dreaming, but good design will minimize the
risk. My header has a stronger mount than the engine. It is soft mounted
in rubber to survive significant airframe bending and the hoses in and
out are rubber for the last foot or so.

Anything you can do to minimize fuel management or supply risk will
greatly improve overall safety IMO. Fuel is still the biggest cause of
downed aircraft.

Bad design would be a welded tank with multiple solid mount points that
will move and rupture the tank as the airframe crumples. Bad design is
rubber hoses under the floor where they can't be inspected or
periodically replaced. Guys who haven't considered all the issues will
probably consider a header to be inherently dangerous but it also has
significant advantages.

Ken




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