Crash Lander writes:

If a "normally" poowered a/c was not designed to fly without power, it
would drop like a stone when the engine is cut.

Why? The same aerodynamics that help it to fly with power help it to glide
without power.

The only difference is that a glider is usually much lighter, and the
wings longer. The glide ration, due to these differences is different
to a powered a/c. The principles are the same.

The difference in glide ratio is pretty important.

I imagine that trying to turn around in a glider isn't particularly smart,
either, just as it is extremely unwise in a powered airplane. But I don't know
much about gliders.

If a powered a/c loses power on take off, it lacks sufficient forward
motion and altitude to maintain flight. When a glider loses power (it's
tow plane), on take off, it lacks sufficient forward motion and altitude
to maintain flight.
Same same.

In that case, the glider pilot should behave like the pilot of the powered
aircraft, and look for a place to land ahead of him, instead of trying to turn
around.