"Louis L. Perley III" wrote:

Saw an article today about an aircraft that would change it's buoyancy, so
it would float up like a balloon and then change buoyancy and glide down.
Interesting stuff, although I doubt we'll see it anytime soon. Is something
like this even practical?

A similar technique that's been around quite a while is an internal air bladder
for LTA craft that use helium and hydrogen. Pump the bladder full of air, and
the buoyancy of the craft changes.

George Patterson
A diplomat is a person who can tell you to go to hell in such a way that
you look forward to the trip.