On Thursday, May 8, 2014 12:00:45 PM UTC+12, 150flivver wrote:
Someone wrote:

"Turns do not cause stall/spin accidents. In fact, the steeper the turn, the greater the stall margin. That's because elevator authority is progressively used up making the glider turn as the bank gets steeper until the angle of attack can't be raised above stall. Try it. You'll find many gliders will run out of up elevator before they can be stalled at bank angles over 45 degrees."



Any comments on the above statement. Steep turns offer a greater stall margin--really?

Sure.

If you have a glider that stalls at 35 knots then in a 60º banked turn (2 Gs) at 49.5 knots your turn radius is about 38m.

If your glider has 6m (20ft) between the wing and the tailplane then they are 9 degrees around the circle from each other and will see 9º different angle of attack to each other compared to straight and level flight. That 9º comes off your available back elevator movement.

In a corresponding 5G turn the numbers are 78.46º of bank, 78.3 knots, 33..8m radius and over 10 degrees of difference between wing and tailplane airflow. Plus you're going to need a lot more back elevator to pull those Gs.

Can you stall your glider in straight and level flight if you don't use the last 9 or 10 degrees of elevator deflection?

Another factor is that in a high G steep turn the two wingtips are seeing more more nearly the same airspeed and same angle of attack. So even if you do manage to stall, the spin tendency is much less and the merest easing of back pressure will stop it instantly.