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????



Well, I'm not really an expert... but by moving the tank(s) from behind
the firewall to the wings, you create two main issues:

First, center-of-gravity changes. Moving them further aft will cause an
aft shift in CG. You will have to move other components forward to
compensate (or add ballast), and be VERY, VERY sure you analyze all of
the load conditions possible to make sure the CG is not out-of-limits.

Second, moving the tanks to the wings (assuming a low-wing aircraft)
means you will need an engine-driven fuel pump and an electric boost
pump. You can't simply use a gravity feed like you could with high-wing
tanks or (I'm assuming) a fuselage-mounted tank.

As far as changes in lift, assuming you don't change the outer mold line
of the wing, you won't generate more or less lift by putting the tanks
in the wing. However, putting them out there means the load
distribution will change; you have to make sure your wing structure can
support the tank. However, moving the tanks to the wings should reduce
the bending moment a bit.