Darrell R. Schmidt
B-58 Hustler Web Site URL (below)
http://members.cox.net/dschmidt1/

"Jay Beckman" wrote in message
news:%5eQg.39$La2.35@fed1read08...

"Michelle P" wrote in message
ink.net...
Mxsmanic wrote:
Bob Moore writes:


In order to reduce the bending moment on the wing spar at the
juncture with the fuselage. Longer airframe life.


But wouldn't putting weight inside the wings cause them to flex
_more_, since the weight is now outside the wing root instead of
within it? That's the part I don't understand.

Think of it this way, Bob. In level flight the wings basically support the
aircraft total weight thereby tending to bend the wings upward at the wing
root. Fuel in the wings make them heavier which tends to bend the wings
downward from the wing root. If you put all the fuel weight in the fuselage
it adds to the first situation only, tending to bend the wings upward. Fuel
you place in the wings adds to the weight but also adds to the 2nd situation
which fights the upward bending movement because of the weight of fuel in
the wings themselves. (Some fancy aircraft like the SR-71 produce
considerable lift from the fuselage which changes the situation somewhat)

In many commercial jets the fuel is first burned from the center tank
(within the fuselage) and then the wing tank fuel is burned. Sometimes, due
to Center of Gravity (CG) situations it becomes necessary to retain some
center tank fuel for CG purposes. That fuel is considered unuseable and it
the only time that all the center tank fuel is not burned first. In the
MD-80, fuel in the wings that is in contact with the upper wing surface
contributes to ice forming on top of the wings. Because of that many users
burn the wing tanks down a little before burning the center tank fuel.

You were correct in your statement below that the stress at the wing roots
is what is the most important consideration. You are also correct to state
that fuel in the wings reduces roll authority, but you can just use more
aileron/spoiler input and it is normally not a controlling element.

I guess that if the weight is in the fuselage, and the wings have to
move the fuselage, there might be more stress on the wing roots; is
that what you mean? In that case, I can see where putting the weight
in the wings might reduce the stress at the point where they join the
fuselage; although it still seems that it would put the wings under
more stress when landing, and it would make the aircraft slower to
respond to roll commands (which I presume isn't desirable).

One reason weight and balance. Another if you put a non compressible
(realtively) fluid in a confined space it gets stiffer. Think full soda
can vs empty. Try to crush a full one.

Michelle P

Be sure to shake it vigorously first...

Jay B