Glide distance is determined by the glide ratio (L/D ratio for the
airplane as a whole) and the altitude. If you're 1 mile up, and your
L/D is 10, you can glide 10 miles. Since the best L/D ratio for an
aircraft doesn't change with weight (although the SPEED to fly at best
L/D goes up with increasing weight), the distance you can fly isn't
dependent upon weight.

The heavier you are, the faster you'll get there, but where you get TO
is the same :-).

Howzzat?

That's what they do in gliders. Put on 400 pounds or more of water
when conditions are strong and dump it when it gets weak or before
landing.

Glide ratio is a function of the design and doesn't change with weight
so with no lift, the glide range is the same but you'll get there
faster. Since glider records are all speed over distance, that's what
you want.

BTW the Boeing 707 glide ratio is 19 to 1, about the same as an old
Switzer glider. The best 25 meter glass ships are around 53 to 1.