a question for the aeronautical engineers among us

"BT" wrote in :

wrote in message
oups.com...
On Nov 2, 7:12 pm, Tina wrote:
OK, so the center of gravity (except for some airplanes with really
smart computers) is going to be forward of the center of lift for
stall recovery reasons -- that makes sense. The question I have is,
for a typical GA flying machine -- take a complex single for example
-- what really is the download (I'm thinking of it as induced weight
with fuel burn consequences) supplied by the vertical stabilizer? It
has a reasonable moment arm hanging way back there, but is it as
much as say 100 pounds if the CG is near the forward limit?

This isn't an aeronautical problem, its a basic mechanics problem.
The moment of the CG vs. the center of lift must equal the moment of
the tail plane.

If the airplane gross weight is 2500 lbs, and the CG is 1 foot in
front of the center of lift, that is a moment of 2500 foot-lbs. If
the tail plane is 10 feet behind the center of lift, the force on the
stabilizer is 250 lbs.

Dean


Now for fuel burn increases, factor in the induced drag created by the
deflected elevator to create the required down force.
Glider pilots attempt to maintain a CG at 75-85% MAC (some will go
farther aft), to keep the deflection to create the required down force
to a minimum to create the least amount of drag at cruising speed.


huh?
75 to 85% MAC? I began to build one years ago and it's CG was in the
"usual position" about 25% to 30%, depending on how much you had for
lunch
I can't see any of the competition gliders being able for a CG in that
position either. not with the stab area that they have. A model glider
with a massive stab, yes, but not any full size as far as I can see.
Anything with a CG that far aft on the main plane is leaning more
towards being a tandem wing aircraft than a conventional one.
Can you provide an example of one of these?


Bertie


Bertie