How does this explain the behaviour of non-radio-controlled model
gloiders that return to level flight anytime? They are built perfectly
symmetrical, have a smooth polar and no controls at all...

They have a lot more dihedral or polyhedral to help them return to level
flight.

Interestingly, a well trimmed hand launch free flight glider will climb almost
straight up, "flop" into a glide without stalling, and then start turning in a
stable, constant circle. Great fun!

Jim Vincent
CFIG
N483SZ
illspam