Hamish,
The proposition is that, on the ground and tethered, the wind will spin the turbines which will compress air and charge batteries (for instrumentation etc.)
Once there is enough of it you can take off.
But, assuming there is no compressed air to begin with then the helium bags are fully expanded and the thing is going to be free floating somewhere or floating on the mooring lines.
My immediate concerns are about the air compression.
Compressed air has to do three things:
[il][li]compress the helium to take away lift[/li]
[li] provide ballast[/li]
[li]provide propulsion aids (its not all gravity gliding)[/li][/ul]
These are going to have to be pretty efficient turbines.
This won't work, we are told, with to small a vehicle because of the weight of the structure. To create something that will not only support its own weight, and carry a significant cargo it has to be very large to contain enough helium.
That requires a correspondingly large volume of air and it needs compressing.
But, how much compression to deflate the helium, how much to run propulsors (and while the turbines flap OK in a wind, how efficient will they be using stored compressed air?)
In a gravity glide, how fast do you need to go to and how long a glide is necessary to develop any realistic air compression? and, how fast can you go in a giant +/-neutral buoyancy vehicle?
It'll probably end up that this would work fine on a low G low density planet with a deep atmosphere but will it work on earth?
I would hope this guy Hunt has done his sums time and again and had them checked by a sceptic.
There would appear to be a hell of a lot of things that have to add up for it all to have the faintest chance. The higher the compressed air storage pressure, the stronger the tanks and the more weight. But if you compress more, you need less volume and that means less weight...
But, if we assume that the turbines/compressors work well in any reasonable air flow then yes, they can harvest wind energy even when sitting idle on the ground and that is what starts to make some sense, this isn't a closed system.
Any airflow that will turn the turbines will generate electricity for instruments and thence for controls which means compressing air between the shell and the helium bags.
But while it doesn't present as a true perpetual motion machine, what worries is that it is a great balancing act of various factors and it all depends on being able to compress enough air into a small enough volume and at a high enough pressure, fast enough to do any good.
So we have to start either up in the air or on the ground. If on the ground and tethered, then the turbines will run in the wind. Of course, up in the air held aloft by helium buoyancy and with no compressed air, its only source of energy is air flow through the turbines and if this is a free floating object the vehicle will tend to go with the wind so the available differential could be quite low. To have any hope of compressing enough air to provide propulsion, to wing the wings, and compress the helium bags, it is going to have collect and compress air pretty quick before someone shoots it down as a hazard.
I'd guess free floating with no compressed air reserve would be a pretty tough situation.
JMW
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