Gliding: why pulling the stick back in a spiral dive would tighten the turn?
The effects of rudder and elevator get mixed when the aircraft flies at a roll angle. See it this way: When you pull the elevator at a roll angle of 60°, it will mostly (86.6%) work like a rudder would for a level airplane.
Why those 86.6%? When looking at the aircraft in an earth-fixed reference system, the additional tail force from an elevator deflection will produce a side load component proportional to the sine of the roll angle (which is 86.6% at 60°). The vertical component which would help to get the nose up is only 50% at a roll angle of 60° because it is proportional to the cosine of the roll angle.
Coordinated flight at higher roll angles is almost like flying a loop sideways. You will only lift your glider's nose in the reference system of the glider and tighten the loop. The reference system that counts more here is the one in which gravity acts, and you should lift the glider's nose up in this system.
Not knowing this subtlety ended the life of several early aviators until it was found out in 1912 that the rudder is what lifts the nose in a spiral dive. Of course, it is even more efficient to first roll wings level and make the elevator work properly again.
The horizontal-loop thing works in reverse, too: Rüdiger Kunz, the designer of the Standard Austria, was always fond of telling the story that happened on occasion of the first flight: At some point, the pilot started to fly loops. After the third, he asked Herr Kunz over the radio: &quot;Notice anything?&quot; - &quot;Yes, you're climbing&quot; was his answer. Thereupon the pilot replied: &quot;That's how you can circle in thermals, too!&quot;