Could something like this actually work?

"Louis L. Perley III" wrote in message
...
Saw an article today about an aircraft that would change it's buoyancy, so
it would float up like a balloon and then change buoyancy and glide down.
Interesting stuff, although I doubt we'll see it anytime soon. Is
something
like this even practical? The article says they take the aircraft up 10
miles to get 400 miles range, I would think ATC wouldn't like the idea of
a
free balloon (which is what it would be at that point) up in the flight
levels.


http://www.machinedesign.com/ASP/vie...PACE&catId=379



1) I wonder why a typical blimp has to use such a large volume (the ballon)
to provide the lift and a relatively tiny cabin attached underneath, whereas
this craft seems to use a much smaller volume (the wings). Has the inventor
calculated this correctly?

2) Where is the power source? Conservation of energy says that the plane
could not continue to ascend and descend without some input of energy. The
initial ascent would be powered by the energy required to separate helium
from the atmosphere, which is accomplished on the ground, but it should not
be true that the plane would "always land with its tanks fully pressurized",
since theoretically the amount of energy generated by the turbines during
the descent could not be enough to compress the gas used for the ascent.
Esecially if the efficiency of the turbines is 20%.

On the other hand I still think that Boeing 747s get off the ground by some
sort of magic. There is no way such a huge vehicle could be lifted by thin
air.

"Marc" wrote:

2) Where is the power source? Conservation of energy says that the plane
could not continue to ascend and descend without some input of energy.

A gas balloon can oscillate up and down by harnessing the
temperature differential with altitude. As it rises, it
cools, the gas contracts and the balloon then falls to
lower, warmer, altitudes, where the gas expands and the
cycle repeats. It could in theory have wings that allow it
to glide somewhat during each cycle.

I seriously doubt the practicality of such a craft.

A similar concept, alluded to in the text, is currently used
in extremely low powered ocean monitors that use a phase
change material for buoyancy control. The phase change
material has a larger volume when cold, so it rises when
submerged to a chilled depth. Winglike structures let it
"glide" towards the desired location to be sampled. They're
slow, but effective and can cruise for months. Electronics
are powered by solar energy at the surface during each
cycle.

The
initial ascent would be powered by the energy required to separate helium
from the atmosphere, which is accomplished on the ground, but it should not
be true that the plane would "always land with its tanks fully pressurized",
since theoretically the amount of energy generated by the turbines during
the descent could not be enough to compress the gas used for the ascent.
Esecially if the efficiency of the turbines is 20%.

Agreed.

Todd Pattist
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Todd Pattist wrote in message . ..
"Marc" wrote:

2) Where is the power source? Conservation of energy says that the plane
could not continue to ascend and descend without some input of energy.

A gas balloon can oscillate up and down by harnessing the
temperature differential with altitude. As it rises, it
cools, the gas contracts and the balloon then falls to
lower, warmer, altitudes, where the gas expands and the
cycle repeats. It could in theory have wings that allow it
to glide somewhat during each cycle.

I understood that as the balloon rises, the decreasing atmospheric
pressure allows the balloon to expand, displacing more air and
increasing lift to compensate. Some guy invented a black balloon some
years ago, really big, that was entirely solar powered. It worked.

Dan

"Marc" wrote in message
news:tXH0c.9865$ko6.197285@attbi_s02...


1) I wonder why a typical blimp has to use such a large volume (the
ballon)
to provide the lift and a relatively tiny cabin attached underneath,
whereas
this craft seems to use a much smaller volume (the wings). Has the
inventor
calculated this correctly?

Those two big pontoons are also being used for lift. The cargo/passengers
ride in the small section between the wings. Whatever else you can say about
it, this thing is enormous.

It is really just a huge double dirigible with wings. The wings double as
additional helium storage. If it were my design I would replace the wind
turbines with conventional blimp engines and use the wings and rudders for
directional control, folding the props to reduce drag during the glide
portion of the flight. This would give greatly improved range and
controllability during the climb. Right now his aircraft has a claimed range
of only 400 nm, hardly worth the effort given the costs involved.

It is not really a "perpetual motion machine" any more than any other
lighter than air aircraft. The compressed air stored by the turbines is not
used to provide lift. It can provide some thrust, but not enough to keep the
aircraft flying indefinitely, nor does the inventor claim any such thing is
possible. Obviously they are not able to store much air during the descent,
which is why the aircraft has such a short range. When you get right down to
it, I have to wonder why he is bothering with them at all.

Although it is short range and slow, it is expensive. People have been
fooling around with various winged blimp designs for years. Perhaps some day
someone will come up with something workable.