Since we're on this subject, just one more caution about possible engine coughing due to air in the fuel lines. It's happened to me, so this is first hand experience.
If your fuel system has the shut-off valves at the top by the tank outlets, you need to be sure to use the correct sequence of opening and closing the two valves if you run one tank dry while in flight.
If you are running on one tank, and it runs dry, you must first open the other tank, before closing the empty one. If you close the empty one first, and then open the good one, your engine will quit. The reason is that air is trapped in the lines, and can't escape. If you keep the empty one open until you are sure the fuel is feeding from the good tank, the air will escape up to the empty tank, and then you can close it after that.
You can easily test this on the ground, but don't try it in flight. When on the ground, close both tanks, then drain all the fuel from the lines out the gascolator. It will take a while to drain, as the air slowly bubbles up to replace the fuel in the lines, so give it time. Then open one tank only and start your engine. After a few minutes running it will quit. Give it a minute, and then it will start again, but continue to quit because the air can't purge itself up the new feeding tank, and there is not enough gravity feed to push it through to the carb. Open the empty tank, and it will stay running.
Again, this is only a potential problem with the fuel valves up top. If your valves are at the bottom by your seat somewhere, you should always have enough prime to push any air through to the carb, no matter which sequence you use.
We've talked about this a few times before on this list, but thought it worth mentioning again, for those planning their fuel system, and those flying with the valves up top.
As for the fuel venting, I just have a ram air tube in each cap facing forward, with the old rear filler drilled holes plugged as Wayne mentioned, and then a "plastic" tube through the cabin at the top joining the two tanks, with tees to my sight gauges. Never any problems with this set-up. I also don't like the possibility of any insects plugging my vents, so two is a good. There was another plane in a hangar near mine that didn't have his pitot tube covered, and sure enough he found out the hard way after take-off one time, so I know it happens.
Walter
----- Original Message -----
From: "Wayne G. O'Shea" <
oifa@irishfield.on.ca>
Date: Friday, April 7, 2006 10:57 am
Subject: Re: [rebel-builders] Fuel crossover venting
As you know Drew...first thing I do to every Rebel I refurbish is
stickrivets in the filler neck holes drilled by builders per the
manual to plug
them up and add tank to tank cross over with Ram air in a wing
root fairing.
I have never had a fuel flow issue on ANY Rebel that has left the
yard...even ones where the builders took the fuel line forward
over the door
post. I've flown circuits in every configuration and darn near
upside down
and never had an engine cough for fuel.
Everyone is welcome to play with their experimental....but I gotta
ask why F
with fate when you know there are proven systems flying flawlessly
for over
a decade!?
Cheers,
Wayne
----- Original Message -----
From: "Drew Dalgleish" <
drewjan@cabletv.on.ca>
To: <
rebel-builders@dcsol.com>
Sent: Friday, April 07, 2006 1:43 PM
Subject: Re: [rebel-builders] Fuel crossover venting
At 08:24 PM 4/6/2006 -0400, you wrote:
Ready to do venting.I have installed the standard crossover as per
manuel.Was advised by a rebel builder to drill a 1/8 hole just
below the
fuel cap in each filler pipe facing firward,has been installed
on two
other
reb els and works fine.One difference the other two rebels have
fuel> pumps,mine do not.Has anyone tried this,do you guys think
this will be
ok.Trying to avoide ram air pipes.
Regards; alvin adams
R 776
I flew my rebel for a couple years with vent holes in the back
of the
filler pipe as per murphy instructions at that time. The problem
was that
when flying with low fuel any sloshing that let a gulp of air
into the
fuel
line would take a looong time to purge itself. Very unnerving at low
altitude. Also if flying one tank dry it would take quite a
while for the
engine to restart after switching tanks. I took the advice of
Wayne and
others on this list and added one ram air vent through the wing root
fairing and all my fuel flow problems have been solved.
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