1) have counterweights (e.g. as mentioned above for another similar concept Cargolifter which used water);
2) expand its volume during loading and contract after unloading. E.g. pumps compress gas while unloading and release it back while loading.
These two options are obviously the same thing - change the vehicle density to adjust the buoyancy but implemented with and without external weights. Submarines do this also by filling the ballasts tanks with either water or flushing them with compressed air.
I looks like they tether it to the ground with tension cables to weights or piles when they are lifting very heavy loads. If this was replacing a standard construction crane that would be economic as these things often have their own significant foundations. If it's a piled foundation for a building it's not uncommon to put extra piles in where you will have cranes. Maybe smaller loads can be done with bladders as others have suggested. You only have to lift 25 tonnes to beat the MI-26 which is the biggest heavy lift chopper and hard to get hold of.
I was wondering about the same thing. It doesn't seem to be explained on the company site.
The only thing I could come up with is to have neutral buoyancy air blatters that can expand/contract. These would be inside the volume of buoyant gas but connected to the outside air. Then pump the buoyant gas into a pressure tank to reduce buoyancy, or release it from the tank to increase buoyancy.
Yes, but the size of the blatter would be enourmous for 250 claimed tonnes: 1 m^3 of air weights 1.21 kg, so if to reach neutral buoyancy you use helium (0.18 kg / m^3) or vacuum (0 kg / m^3, best case), then to counteract lifting/releasing of just one tonne (1000kg) you need to offset 833 m^3 with vacuum and 970 m^3 with helium. Having blatter inside and having such high expension requirements means that the vehicle effectively needs two shells, which will add weight and complexity. Stretchable main "ballon" might be simpler.
That makes sense. It would indeed be simpler to make the buoyancy volume variable in that case.
I'm not sure though that fabrics exist which are both stretchable and can hold on well to small molecules like helium. (e.g. mylar can be stretched only 4% at most.) Maybe some type of "accordion" type connection between the bottom and top halves of the saucer-shaped balloon would work.
So instead of having to move your 25 ton cargo around, you now have to move your 25 ton ballast to be swapped for the cargo at the drop off point so the SkyLifter doesn't yeet itself into stratosphere.
The FAQ and literally everything else about this project is vague, disappointing and a little fishy.
Crane counterweights are a completely different matter. The crane doesn't have to drop the counterweight to take on load (the opposite really, unless it's a superheavy with active counterweighting the entire point is to be more stable once loaded).
So the issue with this thing is, any time you move an actual load from A to B, you need to have a weight waiting for you at point B. Or to offgas at which point you won't be able to make a second trip without regassing.
If the weights remain on the ground you can use a pulley system to load and unload weight, just put slack in the cable and lighten the load… Could even be automated with the right sensors.
1) have counterweights (e.g. as mentioned above for another similar concept Cargolifter which used water);
2) expand its volume during loading and contract after unloading. E.g. pumps compress gas while unloading and release it back while loading.
These two options are obviously the same thing - change the vehicle density to adjust the buoyancy but implemented with and without external weights. Submarines do this also by filling the ballasts tanks with either water or flushing them with compressed air.