h a l f b a k e r yIt might be better to just get another gerbil.
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A propeller inside the front end of a dirigible airship
pushes air in a vortex along the main mostly tubular
body of the airship. Extra fans in the middle or sides of
the internal airship can extend this turning air.
Excess air is pushed out (or rather pulled out) of the
airship at the end
and at the sides (or even sent to
wings in or around the ship) with extra propellers
The air does three things:
(1) The vortex shaped flow of air inside the dirigible
pushes out onto the external walls, assisting in
withholding the shape and structure of the ship.
(2) The higher pressure and density along the walls due
to the vortex shaped air flow leaves most of the
interior with air at low pressure and low density, thus
the airship becomes a lighter than air vehicle.
(3) The air leaving the ship propels it in the requested
direction, and can be used for upwards propulsion as
well.
An aerodynamic shape for high speed and winged flight
allow this ship to carry heavy loads at a lower expense
of energy than conventional aircraft.
Another one of HB low pressure gas airships, but this
time it works a tiny bit differently.
Prior art - see links
Inflated Shell for Vacuum Balloon
"Prayer Wheel" Vacuum Blimp
Centrifugal vacuum balloon
Centripugal force
Inflated Shell for Vacuum Balloon
[pashute, Nov 06 2012]
Centrifugal vacuum balloon
[pashute, Nov 06 2012]
Centripugal Force
[pashute, Nov 06 2012]
Pugal force
http://www.google.c...:429,r:5,s:23,i:172
[bungston, Nov 06 2012]
_22Prayer_20Wheel_22_20Vacuum_20Blimp
Working link [spidermother, Nov 07 2012]
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Annotation:
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There are some very talented engineers with seriously
sideways minds who are able to create minimal-turbulence
turbine ducts, but only with the assistance of large
corporations
andor military branches that can afford to pay them big
sticky gobs of cash. |
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If you can't afford to hire these rare and tormented
individuals (imagine if the voices in your head spoke
calculus), you end up with things like the DC-10. |
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I was *so* hoping that the propulsion would simply be air-flow within the balloon, so that we could re-explore the physics of the Rolling Goldfish Bowl. Futility, ahoy! |
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I wonder about the lighter than air piece. Would a vortex generated within a lightweight tube render the tube lighter than air? |
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That is what my claim is. Why not? I don't think it
would collapse. We are putting energy into the
system which is what is holding it up. |
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Think of it as a high pressure hose in the middle of it,
spraying the walls with water. You wouldn't need the
whole "balloon" to be filled with water to hold the
structure. |
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Same with air. The high pressure on the walls would
be caused by fast moving particles with high kinetic
energy, leaving the middle less dense and hence with
lower pressure. Think of a horizontal tornado or
hurricane pushing out. |
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Thinking about a simpler balloon (cylinder with one end open, propellor mounted inside that end) that would produce negative pressure within, one converges on the legendary vacuum balloon which must be light yet firm enough to withstand the crush of atmospheric pressure. |
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A vortex, as I understand, combines higher pressure on the outside and lower on the inside. |
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An interesting experiment would be to take one of those toy votex guns and fire the vortex thru a cylindrical tunnel made of cleaners bags. One outcome is that the bags puff out, absorbing the momentum of the vortex which does not emerge from the far side - if a tight fit this would happen a lot I think. But with a big cylinder and space for the votext to traverse the length - would the walls of the cylinder be sucked in or pressed out by the passing vortex? |
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If sucked in, the next experiment would be to hang the cylinder from a scale. Does the cylinder weigh less (= more buoyant) when the vortex traverses its length? |
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This could be a science fair project, but a pretty cerebral one. |
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[+] for furthering the cause. |
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In order to stay "inflated" radially, the skin has to centripugally weigh 14.7psi. You could do an ellipse but then the actual sp.gr. of the skin material would have to increase at the ends as the diameter of the object decreases. |
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The problem I think arises in that axially you're going to have 14.7psi, that's about 1 ton per sq.ft., pressure trying to squish the cylinder into a disk. I'm not sure pooling the air around the inside of the skin is going to make up for that. |
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[bungston] Interesting; a related question is whether a toroidal vortex is less dense than the surrounding air. But this idea seems to be about an ordinary (cylindrical?) vortex. |
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[FlyingToaster] And, as [caspian] pointed out on your "Prayer Wheel" Vacuum Blimp idea, you can, at best, redistribute the air, but to resist the axial load the average pressure, and hence the average density, remains the same or higher. The increased density around the outside offsets the reduced density in the centre. |
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This could work in a less compressible fluid (such as water), but not in a gas. |
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yes but I have a double-wall, internally joined, ie: the resistance to axial load is a boringly bog-standard inflatable cuff. The cylinder caps are convex hemispheres which distribute their load directly to the inner wall axially with no inward radial loading at the ends (such as you'd get with a flat cap). |
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However this is just one wall which would be an order of magnitude niftier than my solution... if it worked. |
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//water// err... sqrt2 * (disk area / (disk area - water area)) * 14.7 = centripugal pressure ? |
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//An interesting experiment would be to take one of those toy votex guns// |
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Well [Alterother] has shown a remarkable flair for experimentation and seems to have quite a few types of gun... |
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// //water// // I just meant that the property of gases (their inverse pressure-volume relationship) that rules out this idea does not apply to liquids. So it should be fairly easy to create a vacuum-filled vortex in water with a density less than that of the surrounding water; but you can't - even in theory - do the equivalent with air, because the compressed air around the outside masses more than the air the vessel displaces. |
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Using spinning water to create a lighter than _air_ vessel is another problem again; I can't see immediately why it would be impossible, but it would certainly be difficult. |
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I don't see the problem theoretically: |
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As long as you have a lip at each end to prevent spillage then you should be able to spin it up, thus compressing the air and hold the structure radially using the combined "weight" of air + skin. There won't be a vacuum inside but given enough rotational velocity it may be rareified enough not to matter. |
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Holding it axially means the squished air has to push against the ends as well (which it will) but instead of just holding back 14.7 psi, it has to hold 14.7 psi times the entire area of the disks at the ends divided by the outside circle at the ends where the air is (and some calculus here and there because the pressure won't be constant). |
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That's precisely the problem. The average pressure must equal or exceed external air pressure. Since density is directly proportional to pressure (ideal gas law), the average density must also equal or exceed that of air at the external air pressure. Q.E.D. |
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ah right, it'd hold but wouldn't fly. |
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Aha! I've thought of a simple way to test this. Take a piston and cylinder, full of air, at atmospheric pressure. Spin it axially at high speed. Measure the force exerted on the piston. |
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I'm suggesting that there will be no significant axial force, because the pressure and density distributions will exactly match - the average density has not changed, nor has the average pressure. On a molecular level, the same number of molecules will strike the piston, with the same momentum, regardless of whether they are uniformly (radially) distributed, or centripugally concentrated against the curved cylinder wall. |
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Clearly the radial force will be greater, but the axial force (I suggest) will not. |
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But its not indefinitely pushing air out and therefore
this is idea is not about creating a vacuum balloon. |
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There is a certain amount of air entering the tube. In
the initial state the is a larger amount of air leaving
the tube.
Once reaching its steady state, there is a constant
amount of air inside the tube, of a lower mass than
air of the same volume outside. |
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So rather than a vacuum balloon, this is equivalent to
a less-than-outside-pressure balloon. In a different
form, with high kinetic energy added to the air, this
kind of system is known to exist . Its called a hot air
balloon. |
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/Take a piston and cylinder, full of air, at atmospheric pressure. Spin it axially at high speed./ |
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I like this very much. From the safety of my armchair I offer more musings and advice. It would be good to try an iteration with a little water inside as well as I think the drag of the spinning water would help entrain the air. That internal water piece I think has been around here before. |
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I wonder if the result would be different for a piston that completely occludes the circumference of the circular cylinder face, versus a more centrally placed piston which occludes only the center of the circular cylinder face. I can imagine that within the spinning cylinder there is a pressure differential: greater on the outside, less in the central "eye". It will probably average out and so not be detected by a completely occlusive piston. A piston only at the center might be drawn into the relatively lower pressure at the eye of the vortex. |
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Now, as is my wont, I am thinking about tornadoes. Those we see must be perfectly balanced as regards outward high pressure from the spin at the edge and low pressure at the center. Too low an internal pressure and the atmosphere will compress - as the circumference of the tornado gets smaller velocity increases, pressure increases and there is a balance. Or the thing implodes. Too high an external pressure causes the tornado to expand with slowing of windspeed and lessening pressure, again until internal and external balance or it flies apart. |
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Confined in a cylinder (as opposed to loosey goosey atmosphere) with external spin one could increase the external pressure from the wind: the volume will not increase because of the confinement. Instead external pressure will increase and internal pressure will drop. One might want relatively robust ends of the cylinder as I am not sure the external pressure will be as great there at the "eye" as above. |
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[bella], interesting point but I checked myself and am
correct. |
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Wikipedia for Cyclon. You'll see that there is
"intense" low pressure in the middle and high
pressure at the circumference. |
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The reason it does not collapse is because of the
kinetic energy of the air (and condensed water
droplets) |
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