Skywise wrote:

My not 100% educated guess would be that the blimp is trimmed to
neutral buoyancy just like a submarine. Then the engines and control
surfaces are used to 'fly' the vehicle.

Either AOPA Pilot or Sport Aviation had an article on flying the things a year
or two back. From what I read there, you are correct; they try hard to achieve
neutral buoyancy.

George Patterson
Why do men's hearts beat faster, knees get weak, throats become dry,
and they think irrationally when a woman wears leather clothing?
Because she smells like a new truck.