Fuel tank balance

Roger (K8RI) writes:

Low wing aircraft generally have a set sequence or sequences of
drawing fuel from specific tanks to keep the plane balanced. If I
burn too much off one side (and it doesn't take a lot) the Deb will
get decidedly lop sided. A half hour to 45 minutes per side on the
mains is good. An hour on one side and the other wing will get heavy.
Were I to burn all the gas out of one wing tip tank while the other
was full I'd be in a heap of hurt and I'd want to get the major
portion out of the second tank before landing. The book says no more
than 5 gallons difference between the two.

That's what puzzles me: If you're not supposed to have a significant
difference between the two, why aren't the two tanks just connected so
that they always drain at the same rate on both sides? Why would you
_want_ one wing substantially heavier than the other?

I can see why one might want to change things for fore and aft tanks,
or between center tanks and wing tanks, but I don't see any utility to
having one wing heavier than the other, or to having wing tanks that
don't communicate with each other (provided there's a cutoff for
emergencies).

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"Mxsmanic" wrote in message
...

That's what puzzles me: If you're not supposed to have a significant
difference between the two, why aren't the two tanks just connected so
that they always drain at the same rate on both sides?

On a low win airplane, you need a fuel pump to get the fuel to the engine.
If you have one fuel pump connected to both tanks, and one tank runs dry,
the fuel pump will be sucking only air, and no fuel from the other tank.

If you put in two fuel pumps, and one tank runs dry, you will probably burn
out the fuel pump running it dry.

If you put in a way for the pump to shut down when it's dry, you run the
risk of a faulire that shuts down the pump when there is still fuel in the
tank.

The goal is relable and simple. One fuel pump (actually, mine has an engine
driven pump and an electric backup pump), and a valve to select tanks.


Why would you
_want_ one wing substantially heavier than the other?

When I fly alone, the left side of the plane is heavier. If I burn fuel from
the left tank, after about an hour the plane is more balanced.

"Steve Foley" wrote in message
...
"Mxsmanic" wrote in message
...

That's what puzzles me: If you're not supposed to have a significant
difference between the two, why aren't the two tanks just connected so
that they always drain at the same rate on both sides?

On a low wing airplane, you need a fuel pump to get the fuel to the engine.
If you have one fuel pump connected to both tanks, and one tank runs dry,
the fuel pump will be sucking only air, and no fuel from the other tank.

If you put in two fuel pumps, and one tank runs dry, you will probably burn
out the fuel pump running it dry.

If you put in a way for the pump to shut down when it's dry, you run the
risk of a faulire that shuts down the pump when there is still fuel in the
tank.

The goal is relable and simple. One fuel pump (actually, mine has an engine
driven pump and an electric backup pump), and a valve to select tanks.


Why would you
_want_ one wing substantially heavier than the other?

When I fly alone, the left side of the plane is heavier. If I burn fuel
from
the left tank, after about an hour the plane is more balanced.

Mxsmanic wrote:
why aren't the two tanks just connected so
that they always drain at the same rate on both sides?

Also keep in mind the need to isolate a fuel leak.

Mxsmanic wrote:
Is there any reason to drain fuel tanks in any way other than
symmetrically in normal flight? I notice that most aircraft have
complex controls for fuel flow from the tanks, and I wonder if there
are things one is suppposed to do during normal flight, or if this is
just to provide for possible equipment failures or a need to shift the
center of gravity of the aircraft in an emergency.

Not all tanks can be used in all flight regimes. My tip tanks
can not be used for takeoff or landing (well I don't think they
will make a difference on landing, but you want to be able to
do a go-around don't you). Also, the injected fuel system
returns fuel back to the main tank alone in my system, so
you don't start using the aux tanks until you have sufficient
headroom in the mains.

On Mon, 25 Sep 2006 08:29:10 -0400, Ron Natalie
wrote:

Mxsmanic wrote:
Is there any reason to drain fuel tanks in any way other than
symmetrically in normal flight? I notice that most aircraft have
complex controls for fuel flow from the tanks, and I wonder if there
are things one is suppposed to do during normal flight, or if this is
just to provide for possible equipment failures or a need to shift the
center of gravity of the aircraft in an emergency.

Not all tanks can be used in all flight regimes. My tip tanks
can not be used for takeoff or landing (well I don't think they
will make a difference on landing, but you want to be able to
do a go-around don't you). Also, the injected fuel system
returns fuel back to the main tank alone in my system, so
you don't start using the aux tanks until you have sufficient
headroom in the mains.

On the Deb the tip tanks are...well...just tanks. You have to pump
the contents of the tip tanks into the mains before you can use that
gas. Of course the mains need to have enough room to take that 15
gallons each. Typically I don't bother with the tip tanks as it takes
a good 3 hour plus trip to make them useful.

When transferring fuel I run both transfer pumps at the same time to
keep things in balance. The engine burns 14 GPH. The tip tanks
carry 15 gallons each and the transfer pumps will move all 15 gallons
in 45 minutes. Running an hour on one main will make the plane
decidedly lopsided. 45 minutes is stretching the balance comfort
factor. You do not really want to burn off 15 gallons out of both
mains as there is 11 gallons considered unusable and they are 25
gallon tanks. Just to complicate matters when running off the aux
tanks (10 gallon on each side) they return to the left main only.
About 30 to 40% of the fuel ( 6 to 8 gallons) is returned to that left
main. Oh, and it feeds from both aux tanks at the same time.

As you can see, keeping in balance, keeping at least one main with
useable fuel and not over filling when transferring from the tip
tanks, or over filling the left main when running off the Aux tanks
can make keeping track of how long you are feeding from where, when
can be vital.

If I switch mains at 1/2 hour intervals, turn on the transfer pumps at
2 hours (one hour on each main) I will stay balanced and not over fill
either main. That will also leave the left main down far enough to
take the return fuel from the aux tanks without over filling OR
getting out of balance IF I continue to follow the proper sequence of
feeding.

I carry about 4 1/4 hours of useable fuel between the mains and aux
tanks. I carry about 2 hours and 10 minutes worth in the tips.

In an emergency I could use *all* of that fuel considered unusable but
I'd not want to have to do a go around or any steep climbs and all
turns would need to be right on the ball for coordination. IOW
depending on those 11 gallons would not be smart at all.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

"Roger (K8RI)" wrote in message
...
In an emergency I could use *all* of that fuel considered unusable but
I'd not want to have to do a go around or any steep climbs and all
turns would need to be right on the ball for coordination. IOW
depending on those 11 gallons would not be smart at all.

So, you could basically use the 11 gallons to get you over the airport and
plan for a deadstick landing from that point... Interesting...

On Thu, 28 Sep 2006 19:03:14 GMT, "Grumman-581"
wrote:

"Roger (K8RI)" wrote in message
.. .
In an emergency I could use *all* of that fuel considered unusable but
I'd not want to have to do a go around or any steep climbs and all
turns would need to be right on the ball for coordination. IOW
depending on those 11 gallons would not be smart at all.

So, you could basically use the 11 gallons to get you over the airport and
plan for a deadstick landing from that point... Interesting...

I was thinking on having the engine quit on roll out, but one is just
a foolish as the other. :-)) The amount of adrenalin might be
different though.





Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

Roger (K8RI) wrote:
I was thinking on having the engine quit on roll out, but one is just
a foolish as the other. :-)) The amount of adrenalin might be
different though.

One could argue that having the engine quit when you're 2000 ft over
the center of the runway is preferable to having it quit unexpectedly
while you're trying to fly a normal pattern and trying to get that last
drop of fuel out of the tank by making your turns "just right"... At
least you *know* what is about to happen and you don't have to consider
much in the way of alternatives...

Roger (K8RI) writes:

I was thinking on having the engine quit on roll out, but one is just
a foolish as the other. :-)) The amount of adrenalin might be
different though.

See

http://www.alexisparkinn.com/photoga...bob_hoover.avi

He apparently prefers to fly without engines.

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