"Yossarian" wrote
I don't understand how you can pull a 180 from only 400' with no engine
power.

More easily than you might imagine. Most singles in that class have a
power-off descent rate of about 800 fpm (give or take a bit) in the
normal takeoff configuration at normal glide speeds. It will be a
little more in a steep turn. That gives you a little less than 30
seconds to work with - tight but doable. Generally glide speeds tend
to be 70 kts give or take a bit, and that means with 45 degrees of
bank you're doing more than 3 times standard rate - which means a 180
takes less than 20 seconds. So from 400 ft you have enough time to
make a 180, do a minor correction to line up with the runway, and
flare.

Part of glider training is an intentional tow release at 200 ft or so,
with a return to the field. This means making more than a 180 -
sometimes as much as a 270 - plus another turn to get lined up,
sometimes as much as 90 degrees. The turns are made at normal glide
speed and 45 degrees of bank. Glider sink rates being what they are,
this gives the pilot a little more than a minute to work with - which
isn't even tight. It's a presolo maneuver that a pilot with less than
10 hours total time is expected to perform correctly, and in my
experience most pilots get it right on the first or second attempt.

Michael