Assume you enter a cloud with no visibility of the horizon. Your glider is not equipped with an artificial horizon, turn speed indicator or the like.
You must fly within safe limits, using air speed, ball, yarn, compass, variometer, altimeter and what basic instruments are available.
Is this possible, and how difficult is it? Can most "normally skilled" pilots do that without extensive previous training?
For example, if you just correct the yarn with the ailerons, the speed with the elevator and keep rudder neutral or fly a fixed compass heading, is that likely to keep you flying safely until you're out of the cloud?
Edit: I now remember an old "story". I am not sure I remember it correctly though. What is certain is that in the "old days" some instruments were sometimes sealed before a competition, in order to (try to) make it impossible to go into clouds. I think it was the turn speed indicator and also the compass? But some pilots were caught cheating by bringing a small compass in their pocket. OK, I am not sure I am telling this story correctly. (Nowadays they check GPS logs and compare to cloud base altitude.) If I remember correctly, these pilots were willing to fly in clouds and also curve using only primary instruments.