Could something like this actually work?

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

--
Louis Perley III
N46000 - KBJC

"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.

From the article: "The aircraft, still in development, will be similar to a
submarine that changes its buoyancy, a form of gravity, to float on the
surface of the sea or cruise 300 ft below it. "

Since when is "buoyancy" a form of gravity? Since when does gravity have
more than one form usually known as, umm, gravity?

Cool idea, though.

--
Jim Fisher

Since when are Journalists actually responsible for articulating facts
accurately?

"Jim Fisher" wrote in
:

"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.

From the article: "The aircraft, still in development, will be similar
to a submarine that changes its buoyancy, a form of gravity, to float
on the surface of the sea or cruise 300 ft below it. "

Since when is "buoyancy" a form of gravity? Since when does gravity
have more than one form usually known as, umm, gravity?

Cool idea, though.

--
Jim Fisher

"Louis L. Perley III" wrote:

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?

A similar technique that's been around quite a while is an internal air bladder
for LTA craft that use helium and hydrogen. Pump the bladder full of air, and
the buoyancy of the craft changes.

George Patterson
A diplomat is a person who can tell you to go to hell in such a way that
you look forward to the trip.

Why? The added air has the same density of the outside air.

Mike
MU-2


"G.R. Patterson III" wrote in message
...


"Louis L. Perley III" wrote:

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?

A similar technique that's been around quite a while is an internal air
bladder
for LTA craft that use helium and hydrogen. Pump the bladder full of air,
and
the buoyancy of the craft changes.

George Patterson
A diplomat is a person who can tell you to go to hell in such a way
that
you look forward to the trip.

Mike Rapoport wrote:

Why? The added air has the same density of the outside air.

Good question. So I dug my books out. It turns out the internal bags (called
ballonets) are used for trimming and to allow the helium to expand and contract
without changing the shape of the balloon. They don't affect the buoyancy of
the craft.

George Patterson
A diplomat is a person who can tell you to go to hell in such a way that
you look forward to the trip.

"Louis L. Perley III" wrote in
:

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,

In theory, yes. In practice, probably not. G It's called a blimp...

One of the things that limits your aircrafts speed (or range - somewhat
interchangable for this discussion) is induced drag. That comes from
using part of the aircraft's power to create lift instead of forward
thrust. If we reduce the weight of an aircraft (keeping everything else
identical) then we can now lower the angle of attack and maintain level
flight at a much lower power setting (or higher speed at the higher powr
setting).

Nothing new here... You can see it in any C-172 that's either light, or
at gross.

So now we seal off part of the plane and replace the air in there with,
well, nothing would be best. We reduce the weight of the plane by the
weight of the air that we pumped out. We can go faster and/or farther
on less.

Now the problem... First off, we lost part of the volumetric capacity of
the aircraft. Second, we played great games with the CG. Third, by
having to seal the area, we increased the "empty" weight some (even if
we maintain 1 atmosphere by pumping back in helium). Fourth, we got
only minimal improvements... maybe a few pounds savings.

That last is the big problem. If we want REAL weight savings we have to
increase the volume. That's called a blimp, and to get useful weight
savings it must be BIG BIG BIG. Now we have a Bonanza that weighs 100
pounds ... but it's 400 feet long and 100 feet across. And NOW we have
to add back in the parasitic drag that all this increased wetted area
generates, and now we are down to 35 knots TAS at full power.


-----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
-----------------------------------------------

"James M. Knox" wrote in message
...
"Louis L. Perley III" wrote in
:


That last is the big problem. If we want REAL weight savings we have to
increase the volume. That's called a blimp, and to get useful weight
savings it must be BIG BIG BIG. Now we have a Bonanza that weighs 100
pounds ... but it's 400 feet long and 100 feet across. And NOW we have
to add back in the parasitic drag that all this increased wetted area
generates, and now we are down to 35 knots TAS at full power.

Since it is a glider, it does save the weight of fuel.

"C J Campbell" wrote in
:

Since it is a glider, it does save the weight of fuel.

Didn't notice the "and glide down" part until you pointed it out. Okay...
so change the above to reflect an aircraft with an engine of 1G thrust
rating. G

-----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
-----------------------------------------------

"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.

It is not a free balloon. Even if it was, free balloons climb to very high
altitudes now. They are the favored means of transport for space aliens
visiting Roswell. :-)