Good for a laugh or a cry (Gravity Plane)

[P-hack]

Underwater gliders are pretty cool, using thermal gradients to compress/expand the working fluid. Though 1/2 knot is slow, that isn't the point. UNDERWATER GLIDERS

I guess the problem can be simplified a bit (and water is probably a better test medium)

[niky]

My money says the idea works... And probably well, but it's enormously impractical. And the cost of helium!

And having a rigid airframe light enough to be bouyant... I wonder how fast you'd be able to get on the dive going into a headwind...

[ecomodded]

The narrator is the same guy who makes those hack videos that don't work , and hardly anyone tries them to find out.

He says in the video , the plane(now high in sky) reaches a equilibrium and lets in *new compressed air* where is all this compressed air coming from ? They never say, not the new compressed air not the original compressed air.

[ConnClark]

Its a scam folks. That is why I placed it here. They are just trying to suck money for development of something that will never happen.

Its fun to figure out why it can't work.

[P-hack]

Well I'm not talking about the narrators credentials, or the whole gravity plane either, nor the practicality of it, but the simplified problem in post 11. Assuming you recapture most of the compression energy when you release it into the balloon, and capture energy in the windmill on ascent and descent, is it feasible that the battery would "never" drain completely with the right equipment?

The whole FTTWDW debacle was eye opening enough that I don't want to dismiss it outright.

[niky]

Originally Posted by P-hack

Well I'm not talking about the narrators credentials, or the whole gravity plane either, nor the practicality of it, but the simplified problem in post 11. Assuming you recapture most of the compression energy when you release it into the balloon, and capture energy in the windmill on ascent and descent, is it feasible that the battery would "never" drain completely with the right equipment?

The whole FTTWDW debacle was eye opening enough that I don't want to dismiss it outright.

Nope. Most definitely not. But the idea of a gravity plane per se is probably workable.

With a paper thin unobtanium shell.

[P-hack]

Originally Posted by niky

Nope. Most definitely not.

"If not, why not?" This is the basic premise behind the gravity plane, and a small tank made of unobtanium seems more plausible than two blimps worth...

It'd be nice if you can get it up into the mesosphere, but that aint realistic. It might be possible to take advantage of the temperature gradient of the stratosphere somehow.

[niky]

One wonders... was Cloud City powered by thermal energy?

[P-hack]

It looks like it is supported by a column of some sort, that might be cheating or perhaps a space elevator?

[mort]

Originally Posted by P-hack

I guess the problem can be simplified a bit (and water is probably a better test medium)

Hello P-hack,
Naturally the design could be optimized to demonstrate the viability of the idea. For instance, make the gas envelope a torus with the wind generator-propeller in the opening and the various mechanicals underslung of the gas bag.
Consider the Goodyear blimp, Spirit of Goodyear. It has a gas capacity of about 200,000 cu ft which in helium provides 14,000 lbs. of lift (at sea level etc.)
The amount of power you can get out of the wind, that's during rapid descent, is:
P = 1/2 A*d*v**3
where v is the wind speed
d is air density
and A is the swept area of the blades
For modern designs, efficiency of the actual wind power mechanism is around
45% - that is 45% of the kinetic energy in the wind can be recovered as electricity.
A regular torus 120 feet wide with a hole 30 feet wide (R=45' and r=15') has a volume of 200,000 cu ft. The hole in the center has an area of 700 sq ft
Air density is 0.0023769 slugs/cu ft (sea level, 70 degrees F, etc.) The power produced is about:
P = .45 * .832 * v**3 (efficiency times area times density times speed cubed)
Now this gets a bit scary-
If you could descend at 125 mph (183 ft/sec) that would develop 9000 hp for 54 seconds (falling 10,000 ft) Assume a compressor-expander with round trip efficiency about 80% 9000 hp now is the difference between the power needed to compress the gas and the power you get back expanding the gas. You could run a compressor at 45000 hp for .91 minutes and compress 200,000 cu ft of helium in that time (3 stage compressor 15 psi to 215 psi helium adiabatic expansion coefficient=1.67). By the way that's about 8 Tesla S batteries worth of juice. That's about 100% of your gas bag volume. Assume the torus is actually streamlined for descent, and the Cd is just about the Cd of the windmill -- .5 at 700 sq ft. The drag on the airship falling at 183 ft/sec is 14,000 lb, so the ship is at terminal velocity for free fall.
The point is that you can fall fast enough to generate the power needed to recharge the battery. You don't need to completely deflate the bag to descend, but the faster you fall the better.

The airship could be scaled up to quite huge size so the load capacity would be sufficient to carry that big compressor and battery.
-mort