when low on fuel, in turbulence, or sideslipping. I put a float switch
in the header tank to tell me if it is not full. I do find that I have
started to keep more fuel in the right tank for balance. An aileron trim
would probably be a better solution for me.
However when optimizing range or performance, one usually likes all
remaining fuel in one tank with an accurate quantity gauge so you have
confidence in how much is really there. Sometimes that avoids an extra
fuel stop for me. Kind of pointless having large tanks and carrying
extra fuel weight if you don't have confidence in how much is useable.
I don't like guessing and my Rebel performs noticeably better when I do
not carry excessive fuel. I have over 8 hours of fuel with full tanks.
In machines with multiple fuel tanks, it is not uncommon to watch a fuel
pressure gauge for fluctuations and then switch tanks before the engine
coughs. An amusing incidence of this (not in a Rebel) was accompanied by
a major aircraft pitch up which quite surprised me. What happened was
that when the engine coughed a group of parachuters all immediately
moved to the rear door to get out... Imagine trusting silk more than an
aircraft just because of a momentary hiccup ;)
I also recall an interesting night ferry trip on a newly purchased
aircraft. The destination had a curfew and the new owner was quite
nervous. It took me awhile to realize that he had previously rented
aircraft and had never actually flown with tanks less than half full.
I suspect that some specific Rebels may push air through the lines and
vent it through the carb float bowel. But many do not. One fellow used
transparent lines to prove that on his machine the air was being trapped
at the top of the vertical line. The air would not travel the last few
inches of horizontal tube back into the wing tank. Air in the line does
restrict fuel flow. He constructed a vapor separator at the top of the
vertical tubing to vent that air bubble. Fortunately when an engine
coughs, the first thing most pilots do is to switch on a tank that they
are sure has fuel in it which I think avoids the problem being discussed
below. With a header tank, I never give any of this a second thought.
Ken
Kevin & Nancy Mayville wrote:
I am going to jump in here because I don't understand why any one needs to
drain one tank completely, I can understand burning one tank down to say 3/4
or so for balance, I would never run a tank down until the engine coughs !
I run both my tanks at the same time and I don't have any balance problems
with or without a passenger.
My fuel system is a little different I have a ball valve at each aft wing
root ( which I can reach ) and then each tank flows in to a small tank like
a header tank ( aprox 2''x3'' x 16'' long mounted vertically ) aft of the
pilots seat. then the main shut off valve is just forward of the pilots door
.
This header tank eliminates any chance of air being trapped in the fuel
line. I believe this was the fix for the first generation of Glass Stars
because the fuel sloshed in the tanks and allowed air to block the fuel
lines like Walter stated, which caused some unscheduled landing .
Kevin C-FRFP
----- Original Message -----
From: "Walter Klatt" <Walter.Klatt@shaw.ca>
To: <rebel-builders@dcsol.com>
Sent: Tuesday, December 22, 2009 6:34 PM
Subject: RE: [rebel-builders] Fuel slector valves
I am quite sure it will happen to any tank valve top mounted gravity feed
set up in a Rebel or Elite. I have my tanks cross vented, plus a snorkel
vent on each cap.
It has to do with trapped air in the lines below the valves. The fuel is
trying to flow down, while the air is trying to vent upwards to the tanks,
which slows the fuel flow enough to stall the engine.
Think about it. When you shut one tank off run to run the other one dry,
all
the fuel will run out of both lines when the empty one finally drains.
When
the engine runs out of fuel, there will be nothing but air left in both
lines right up to the valves. Then if you close the empty tank valve, you
trap the air there. When you open the full one, the flow has to fight the
air coming up.
If you keep the empty one open, the air has a place to get pushed out and
vented, and no problem.
Again, if you use the right sequence, with opening and closing the valves,
everything is fine. But with the wrong sequence, your engine will quit,
and
you will not get it started in time before you hit the ground, guaranteed.
Trust me, I have been there, and I know this issue very, very well. And I
can replicate it on my plane on the ground any time, and I am sure I could
do it to yours if you have the same set up.
Walter
-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of Ron
Shannon
Sent: December 22, 2009 3:04 PM
To: rebel-builders@dcsol.com
Subject: Re: [rebel-builders] Fuel slector valves
I believe the tank venting design will have an influence on this switching
procedure. Not to reopen a subject that's been covered quite a bit (see
archives) I think with dual vents and full cross vent (and perhaps other
configurations) it may be possible to run one tank dry before switching as
Drew suggests -- if you're so inclined. Personally, I wouldn't
intentionally
cause an in flight shutdown except in an emergency scenario where fuel
reserves absolutely had to be managed that tightly. Your mileage may
vary --
literally. :-)
Ron
254R
On Tue, Dec 22, 2009 at 2:41 PM, Drew Dalgleish
<drewjan@cabletv.on.ca>wrote:
everHi Walter I wonder if that problem could be unique to your plane cuz I
often run the pilots side tank empty to help balance my plane and get
maximum range. I think I usually turn off the empty tank before turning
on
the one with fuel in it and I've never expreienced any delay in the
engine
restarting.
As for floor mounted valves consider where you place it so that if youtheinstall floats you will be able to easily crawl through to the other side
for docking, pumping out, refueling etc.
At 11:27 AM 22/12/2009 -0800, you wrote: running one tank dry while flying. The sequence for closing and openingkeepvalves is very critical to avoid an air lock. I know this from first hand
experience and am able to replicate the issue on the ground. run one tank dry, with the other full tank closed, you must first open
the
full tank before you close the dry one. Otherwise, your engine will quit,
and you will not be able to keep it running. It will restart, but thenthequitting on you.engine,full one can't flow fast enough. It flows just enough to start yourtobut it will keep quitting on you. If you keep the empty one open, the
locked air will vent up through it, and allow the good tank to feed downthethe carb. Once it is feeding OK, and the air is out, then you can closeempty one. the ground when I first did it. locked in the lines above to the tanks. Drew
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