Ships, locks and potential energy

[russ_watters]

so your saying my post of an actual company being run by a retired nuclear designer is a perpetual motion gimic?

Yes, that sounds about right to me.

At best, it's a crappy glideer, but I doubt it is even that good. But the language used in the claims is so glowing, it implies much more.

hey i didnt design it...

What a coincidence, neither did he! A comic book illustration is not a design.

then tell me why it won't work

It's not so much that you can't lift a glider with a balloon, it's more a matter of there not being any good reason to. It just isn't a good idea. But by making it sound like a good idea, he has to exaggerate the claims so far as to make them laughable. And you've already had a couple of people point out some obvious flaws with his reasoning. I'd add another: balloons and gliders are both slow. And one more: The term "vacuum bag" is a self-contradiction.

 

[sophiecentaur]

It would be conceivable to make a helium balloon which carried a compressor to put the gas back 'in the bottle'. The energy for that would be what was effectively driving the balloon down again, once it had reached it operating height. (Very much like blowing and filling flotation tanks on a submarine).

I'm not sure that, on a total cost basis, it would be better value than just dumping the Helium when you wanted to descend. The gas cylinders and compressor would be a large extra payload. This proposal is, in effect, doing the same thing by doing work on a mass of gas.

If you want to use the Potential Energy due to your altitude to provide forward motion through the air, you would need to compress / expand more gas. The PE lost would need to be supplied by 'subtracting the bouyancy' which actually involves work equal to 'pressure times volume change'. This needs to be equal to the losses due to drag (at whatever speed you could actually go) over the length of the journey. The energy to achieve this speed with this amount of drag is the same as if you used a propellor / jet engine or tethered ducks. You are getting nothing for nothing. Certainly you aren't getting anything 'from gravity'. If you fully analyse the energy transfers in the situation there can be no inherent advantage - except that which any lighter than air machine can have (requiring no energy to keep it actually afloat).
Build yourself a Graaf Zepplin and do it better than they did nearly a hundred years ago and you could be on to something but don't go near "powered by gravity". Readers of these Forums are far too canny to take the bait, I'm sure. They aren't falling over each other to buy shares!

 

[mgb_phys]

I think the reason for recompressing the helium is more operational convenience.
If you want to operate like a Zeppelin between fixed airports then it's easy to just dump ballast to climb and dump helium to sink - then refill at the end of the trip.

If you want to use blimps as construction cranes, battlefield, or remote site delivery systems then having them entirely self contained might be a good idea. After all if you can truck in 10,000m^3 of helium to refill the craft for it's return trip you might as well truck in the cargo.

Composite gas tanks and solar powered pumps might make it practical, especially if you only need to adjust the pressure by a few % as a trim tank.

 

[sophiecentaur]

I think the reason for recompressing the helium is more operational convenience.
If you want to operate like a Zeppelin between fixed airports then it's easy to just dump ballast to climb and dump helium to sink - then refill at the end of the trip.

If you want to use blimps as construction cranes, battlefield, or remote site delivery systems then having them entirely self contained might be a good idea. After all if you can truck in 10,000m^3 of helium to refill the craft for it's return trip you might as well truck in the cargo.

Composite gas tanks and solar powered pumps might make it practical, especially if you only need to adjust the pressure by a few % as a trim tank.

But that's just not true in the quoted context. It may apply if you are just out for a pleasure trip but, if you want to lift a large payload and place it somewhere else, then you need to be changing a huge proportion of the total displacement.
But the original system proposes transport over large distances - implying the need for lots of energy - all of which would have to come from climbing then gliding. But, as I said before, doing it that way is not inherently better than towing it with a skein of ducks; same amount of energy needed.
It strikes me as an idea looking for an application. It's all down to the energy budget, in the end and shouldn't be led by the subjective appeal of a newly invented idea.

IFF we could get an extremely large, rigid structure that would stand large pressure differences and which had a negligible mass, then it would make a good air displacement vessel (lighter than air). You'd still have to get it from A to B, which is what is implied by the Buck Rogers craft in the picture.