On Friday, June 26, 2015 at 7:57:19 PM UTC-7, Jim Lewis wrote:
On Friday, June 26, 2015 at 12:36:00 PM UTC-7, wrote:
Ditto the above question-- unless the L/D ratio is really poor, the stall speed in a 45-degree banked turn ought to be about 1.189* the stall speed in the same configuration in wings-level flight. S

This is probably an unneeded addition, but for the sake of completeness, I would change "45-degree banked turn" to "45-degree banked LEVEL turn in still air". Lots of us fly 45-degree banked turns in thermals without pressing the stick back much.

Is there some suggestion here that the glider behaves differently in an updraft? Surely not.

Re "level"-- in a glider? If the flight path is horizontal with respect to the airmass, you are decelerating, not in a steady-state situation. To maintain horizontal flight, you'll have to keep moving the stick aft at a certain rate, as the airspeed bleeds off. Will the glider reach the stall angle-of-attack at a different airspeed than if you just ease the stick ever-so-slowly aft, so that the rate of deceleration is negligible, and you stay very close to a steady-state glide?

At any given instant of time where the glider is at some given angle-of-attack, the L/W and Na/W values (Na=Net Aerodynamic Force) will be slightly smaller in the steady-state glide than in decelerating level flight, so the airspeed at the stall angle-of-attack will be slightly less in the steady-state glide than in decelerating horizontal flight, but the difference will be trivial for normal sailplane L/D ratios. In the decelerating level flight case, the L/W value will be the same as it is on the top line (infinite L/D) of the table I posted on June 25, and the Na/W ratio will be slightly larger. For any given glider at some given angle-of-attack, the ratio between L, D, and Na will be the same in the decelerating level flight case as in the steady-state glide case. Looking at the table I posted June 25, for glide ratios of 10:1 or better you can see that there is no discernible difference between L and Na. There's also no discernible difference between the value of L, or Na, at a 10:1 L/D, and L, or Na, at an infinite L/D. So I'd say there's no way you'll be able to tell the difference between the stall speed at the slow deceleration rate required to maintain exactly horizontal flight in still air, versus the extremely slow deceleration rate you'd use to reach the stall angle-of-attack while staying very close to a steady-state glide.

S