Uh, Bert, what happens when a wing stalls? Lift decreases... drag
increases. Something needs to start the spin. Could that be... a
force? I suppose we could call it something other than drag. Gremlins
maybe?

Let's see, perhaps I can offer another explanation. Non-symmetrical,
differential lift across the wingspan produces roll. Non-symmetrical,
differential drag along the wingspan produces yaw (adverse yaw when
actuating the ailerons, for example). The vertical stablizer and
rudder are there to provide stability and yaw authority to counteract
the aileron drag effect (as well as the destabilizing effect of the
fuselage forward of the cg). If the stall (or partial stall) produced
no drag, the glider would simply roll. There would be no yawing
motion. And thus, no spin! (But lots of rolling.) Here's another way
to think about it... if you had an infinitely large vertical
stabilizer (that is, infinite directional stability), would it be
possible to spin? Since the infinitely large tail would produce an
infinitely large counterforce to any adverse yaw, then a spin is not
possible. What's the practical substitute for an infinitely (or very)
large vertical stabilizer? A moveable rudder.

It's all about the flippers, man.

And from a practical standpoint, spins are all about the drag. And
even though a partially stalled wing will display adverse yaw with
neutral control surfaces, so long as you don't move the flippers, the
vertical stabilizer will keep you from spinning. As noted before, I
prove this to myself with every modern model of glider I fly. But if
you move those flippers in an uncoordinated fashion, baby, all bets
are off!

Piggott: "Drag from the badly stalled, falling wing, pulls the glider
down into a steep spiral and the autorotation is speeded up."

There's a graceful way out of your dilemma... we could discuss the
torques brought into play by the rolling motion of a partially stalled
wing. That will introduce a rotation about the yaw axis (the
aerodynamicist's definition of autorotation), but you'll need to prove
to me that it alone is sufficient to overpower the vertical
stabilizer, even at very low airspeeds and relatively high rates of
roll. Since the vast majority of modern aircraft need an additional
yawing moment to enter a spin (pro rudder, counter aileron), it's
going to be a tough sell. But I'd be interested to see you work
through the problem.

Maybe we'll both learn something new.



"Bert Willing" wrote in message ...
That's nonsense. Spin/autrotation is all about one wing (partially) stalled,
and the other not. It's not about drag.

--
Bert Willing

ASW20 "TW"


"Chris OCallaghan" a écrit dans le message de
m...

Here's another argument. The vertical stabilizer provides a great deal
of yaw stability, even at very low speeds. To start autorotation, you
need a source of drag at the tip greater than the normal differential
to be expected resulting from span effect in a turn. That we don't