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