Model Forum / Radio Controlled / Air Models / April 2007

Blunt, rounded leading edges and fat airfoils are better for avoiding
snaps than sharp leading edges on thin airfoils.

Check the incidence of the wing against the incidence of the
horizontal stab.  Your need for up-elevator may come from
having them working against each other.

Go ahead and try some nose weight.  If it helps stabilize the
plane, that's good.  Planes that are too nose heavy can often
be landed OK; planes that are tail heavy often can't.

You might want to try putting a little washout in the wing
tips or using stall strips on the inner 1/3rd of the wing.
This sometimes makes tip stall less severe because different
parts of the wing stall at different angles of attack.

Don't slow down too much on landing until you figure out
the problem.  A touch plane like yours is a prime candidate
to stall, snap, and spin while attempting to land.

                    Marty

Sounds to me as if you have too much elevator throw.

Can you tell us the incidence angles of the engine, wings and tail?
Also, what is the wing loading?  If you don't know that, how much does
it weigh and what is the wing area?

Those sound like classic symptoms of a too-rearward GC.

Have you done the dive test?  Assuming that you can get the thing high
enough in a steady wind, get it trimmed for a slow glide.  Then nose
down into a fast glide and let go of the sticks.  If it tends to zoom up
when you let go then the CG is forward.  If it tends to tuck under into
a steeper dive then the CG is definitely too far back.  If it stays the
same then the CG is right on the knife-edge stability point.  For sport
flying, you probably want to go about 1/4 inch ahead of the neutral CG
point; if you're a hot rodder then leave it right there and learn to be
gentle with the elevator (and enjoy the flick rolls).

If you don't like the dive test, then check to see how it flies inverted
compared to upright.  If you can use the same elevator trim in
canopy-down flight as canopy-up then you're definitely at the neutral CG
point.  If you have to stick close to the slope this may be an easier
test to do.

The other suggestions that you've gotten will all help to tame the plane
down when you get a sudden excursion in pitch, except for reducing the
elevator throw which will compensate for the CG position somewhat.
Don't discount them, but I'd get the CG right.