Lou wrote:
Ok, a question or 2 about the wings. I'm building a wooden aircraft
that could go either fixed tri-gear or retract. I choose fixed seeing
how this is my first plane to build and I wanted to keep it simple. The
fuel was supposed to go behind the firewall but I choose to build tanks
in each wing where the wheels where to go.
What will this do to the loading of the aircraft? Does this effect
the useful load and how? Does it raise my useful load or lower it or
niether? Since the wings create lift, and the fuel was in the fuselage
and now in the wing should it screw up the center of gravity? Anybody,
Anybody, Anybody????


You have to worry about 3 axis. With now knowledge of the airplane, it
is possible that the fuels position may not have not changed fore or
aft. If that it true then your CG is safe. If not, then you will have
to be very careful in your weight and balance calculations. The nice
thing about wing tanks is that the fuel tends to sit on the center of
lift. When this is the case, the draining fuel doesn't cause your trim
to creep.

Next is the vertical axis. If you move a lot of weight from up high to
down load, but leave the center of thrust untouched, then you've created
a situation where adding thrust will cause the plane to tend to nose
over. You're trying to move a filing cabinet by pushing the top. So,
you're on short final, just before the flair, all trimmed out and
smooth. A deer jumps on the runway. You firewall the throttle. Do you
have enough elevator to keep from eating a mouthful of dirt.

The other issue is lateral loading. Move all that weight to the wings
and you've modified your roll response. Just like an ice skater that
changes her spin by extending her arms or retracting her arms (moving
weight in and out.) When you try to start a roll, you have to have
enough differential lift in the ailerons to get everything moving...and
THEN get everything stopped. Moving the tanks could make the plane
difficult to control.


The upshot is that the wing ROOT doesn't have to carry the bending
moment of the fuel load. If the wing root was the limiting factor in
your load allowance, then this move very well could increase your
plane's usefull load. Airplanes have to be light, though. It's
doubtful that the designer cut the wing root to the bare minimum and
then beefed up everthing else, like landing gear, tail surface area,
elevator surface area, etc. I wouldn't bet MY life on an increased load
allowance from moving the fuel tank.


--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."