On Wednesday, August 28, 2013 3:52:39 AM UTC-7, Gilbert Smith wrote:




On Thursday, August 22, 2013 9:58:53 AM UTC-7, Squeaky wrote:



From Tom Knauff:





With few exceptions, what you will observe is the glider neither rolls



nor pitches, but yaws.







What happens is as the glider loses airspeed, the lift produced is not



adequate to hold the glider up and it begins to fall. Since the glider



is tilted, the falling glider causes the airflow to strike the side of



the fuselage, causing the tail of the glider to be pushed up, causing



the yawing motion.







There is no rolling. No pitching.







The wing is not stalled.







Because the wing is not stalled, the ailerons and rudder work properly..



This cannot be a technically correct explanation. And it isn't what any glider I have flown in recent memory does. If there is inadequate lift, and "the glider begins to fall" without pitching the AoA is very quickly going to exceed the stall angle. If it is sliding sideways enough due to falling that a large yawing moment is produced, the AoA is way past the stalling angle. A spin departure can produce pretty high yaw accelerations, but that ain't the mechanism.



Tom Knauf is right of course (as always), in a spin one wing is

producing lift, the other is not. This is not the case in the

"falling" scenario.



Whether the ensuing yaw changes this is debatable, but I find that

unloading the controls prevents any departure.

If the glider is "falling" without pitching down, the wing is stalled. The whole wing. The rudder and ailerons might still work a bit even above the stall angle. When he says "The wing is not stalled" - I just can't see that.

In a sustained autorotating spin, one wing is operating at a higher AoA than the other, above the max lift AoA for the section. Above that point, lift reduces and drag increases with increasing AoA. In a spin departure, both wings might be stalled, the wing going down is at a higher AoA and higher drag, therefore producing a net yawing component.