Richard Riley wrote:
There's a difference between a glider with a 30:1 L/D and a Cessna with
9:1. Doing a 180 in a glider from 400' is like doing it in a Cessna
from 1200'.

Yeah. Forget about turnbacks, a high performance glider can complete an
abbreviated circuit from 400 ft. Even lower performance gliders can
safely complete a 180 after a rope break from 200ft if you are react
promptly. In fact if you're lucky you may find some lift while doing
the 180 and who knows you may be able dump the rope and climb out of
your emergency and go soaring! (just kidding) The main problem with
gliders on 180s from rope breaks is not making the turn in time, it's
avoiding overrunning the field in the subsequent downwind landing.

For powerplanes, it would be prudent to go to a safe altitude and
practice 180s upon chopping power and noting the altitude loss with
optimum technique (although it's murder on the poor cylinders, best to
use a renter...). The least loss is with a hard 45 deg banked turn. If
with some practice you can confidently complete a 180 with say a 400 ft
altitude loss you can set a defined go-nogo limit of say 500 ft for
turnbacks and you've removed the guesswork from it.

John