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Reduced Pressure Lighter Than Air Machine

Externally support reduced pressure structures.
  [vote for,

A ten percent reduction in pressure at ground level would allow a cubic metre of capacity to lift 130g but generates a frightening pressure differential of 1.5 pounds per square inch.

The lifting element in this machine would be a hollow cube of thin plastic sheet such as the aluminized PET used for snack bags. The actual size of the cube would depend on the manufactured width of the PET rolls. The cube would be supported from the outside by carbon fibre threads attached to a number of anchor points on each face of the cube designed so as to spread the load at the point of attachment. How these cubes would be constructed is a moot point but perhaps a balsa wood frame could be withdrawn through a small resealable hole on completion.

The overall machine would consist of three rigid carbon fibre poles anchored at the centre of each pole in an XYZ configuration. There are eight quadrants nesting in such a configuration e.g. : X+Y+Z+, x-Y+Z+ and so on. Each quadrant would hold one or more cubes in an even number. Tubes would connect the interiors of all cubes together so that they would be at the same pressure. Where a cube is adjacent to another, the cubes would be joined anchor point to anchor point by carbon fibre threads. Where the cube faces out towards the extremity of a carbon fibre pole then that cube would be attached to the pole with carbon fibre threads at intervals out to the extremity of the pole rather like a radio mast. The tensions at all anchor points should equilibrate and the machine would be completely symmetrical in all directions.

Air would be evacuated from the machine and if, (a very big if,) the structure would stand the enormous pressure differential then positive bouyancy would be achieved. There would not be a need to put much further structural stress on the machine as it could rise in height until internal and external pressures were in equilibrium and only then would more evacuation be applied to allow further height rise. Needless to say, the loss of a single cube would be catastrophic and the whole structure would collapse like an overstrung tennis raquet.

Successful construction of such a machine would be a notable first and would generate rather more than the proverbial fifteen minutes of fame. Beyond this there could be significant commercial potential depending on how light the device could be made and hence how high into the atmosphere it could ascend. Forget the lifting of humans and heavy loads and think rather of small electronic payloads such as those used in data transmission and broadcasting. If the device could use solar cells and battery storage to power the means to maintain a reasonably fixed position at a height above 50000 feet then broadcasting to state or country sized audiences might be a cheaper alternative to the use of satellites. It could revolutionize ham radio with the use of simple cross-band repeaters.

If all efforts to get the machine sufficiently light fail then there is a possibilty to flip the balance. Into each cube would be placed a sub container of hydrogen or helium in a partially collapsed bellows or Chinese lantern form filled so as to give some positive bouyancy. As the height increases and pressure decreases this vessel would expand and displace air from that particular cube.

A reasonable start could be made by creating one cube face with anchor points on a test rig and seeing how much reduction in pressure it could withstand and just how many anchor points are needed.

corvuscornix, Jul 23 2012

wind speeds at altitude http://www.classzon...02/es1702page09.cfm
[corvuscornix, Jul 23 2012]

Check out the first link on this idea. Inflated_20Shell_20for_20Vacuum_20Balloon
[2 fries shy of a happy meal, Jul 23 2012]

Short name! http://www.jstor.or...&sid=21101102233541
Description! [MaxwellBuchanan, Jul 23 2012]

Prior arts on the HB Wanted_3a_20Vacuum_...le_20Service_20Tech
Vacuum Dirigibles [sqeaketh the wheel, Jul 25 2012]


       hmm, okay so the frame + carbon fiber threads can be thought of as a solid rhombus... how are cubes the most effective packing material ?
FlyingToaster, Jul 23 2012

       So, suppose a cube 10m on a side. If the internal pressure is reduced by 1% (relative to outside, at seal evil), that's 0.15psi (I love to mix metric and imperial), giving a force of just over 10.5 tons on each face.   

       The lift provided by this pressure reduction will be 140kg (0.14 tons). I think a 10m cube supporting 10.5 tons on each face will weigh more than 140kg, but perhaps I am wrong.   

       Does this get better or worse as the balloon gets bigger? For a cube 100m on a side, the force on each face will be 1050 tons, and the lift will be 14,000 kg (14 tons). IE, force on the faces goes with the square of the side; lift goes with the cube).   

       So bigger cubes are better. But, then again, longer struts need to be thicker in order not to buckle.   

       As for bellows-like expansion, zero-pressure high- altitude balloons do this; they start out only very slightly inflated, and the fill out as they approach their maximum altitude.
MaxwellBuchanan, Jul 23 2012

       Cubes would not be optimum but the simplest shape to make.   

       The point of bellows idea is that as it expands it would displace much heavier air.
corvuscornix, Jul 23 2012

       Maybe I misunderstood your bellows.   

       Shape-wise, a tetrahedron is better, no?
MaxwellBuchanan, Jul 23 2012

       // Any balloon compresses the lifting gas, whereas just a gas barrier can exploit 1 atmosphere or a bit less [link]. //   

       There are "pressure" dirigibles (blimps) where the envelope maintains its shape via a modest overpressure. However, the rigid-framed airships of the 1920's and 30's had "gas bags" enclosed in netting, which were at local atmospheric pressure. As the airship rose and the external pressure dropped, the bags would expand until any slight overpressure was vented via relief valves. At QFE (MSL), the lower portion of the bag appears "pinched in".   

       Hence [MB] is correct when he points out that //zero-pressure high- altitude balloons do this; they start out only very slightly inflated, and the fill out as they approach their maximum altitude. //
8th of 7, Jul 23 2012

       // start out only very slightly inflated, and the fill out as they approach their maximum altitude//   

       I do the same. The catering in First is often very good.
MaxwellBuchanan, Jul 23 2012

       Of course it is. Ridiculous. Your own private jet, yet you still insist in having two seats at the back marked off as "Business" and "Tourist" so that you can gloat.   

       And the whole pathetic business of issuing "boarding cards", too ... Yes, yours is hand-written on vellum and illuminated with gold leaf, very nice BUT IT'S THE SAME ONE EVERY TIME AND THERE'S ONLY YOU BOARDING. Mind you, your Senior Stewardess does have a very nice, errr, smile ...   

       One of these days your chair-men are going to damage themselves getting your Sedan chair up the steps, too.
8th of 7, Jul 23 2012

       Don't be ridiculous, [8th]. Vellum would crack with the repeated humidity changes between the UK and Saudi. It's straightforward parchment. <link>
MaxwellBuchanan, Jul 23 2012

       [corvuscornix] has passed the secret HB entry test, which consists of reinventing yet one more time the Vacuum Blimp. Its a baked, warmed-over, and refried idea, yet beautiful. Well done! [+]
sqeaketh the wheel, Jul 24 2012

       //tetrahedron// It might just be the way I picture it, but I think if you take a caltrop and string it from point to point (ie: make a tetrahedron), applying pressure to the middle of one of the strings will simply bend the string.   

       Whereas it won't happen on a rhombus.
FlyingToaster, Jul 25 2012

       See the many prior arts here: <link>
sqeaketh the wheel, Jul 25 2012

       The prior arts seem to be mainly about proposed vacuum devices. My proposition is about a reduced pressure device and I have in mind some 90% of atmospheric pressure which would be in the same order as that obtaining in hot air balloons. Even this modest reduction in pressure would involve a load of one and a half pounds per square inch on any vessel containing it and I contend that the concept of external support to the vessel walls transmitted via filaments to the compressive strength of, say, carbon fibre rods in an XYZ configuration is worthy of consideration.   

       The term 'vacuum blimp' is surely misleading. Any vessel containing reduced pressure will have to be rigid and a blimp is essentially a gas bag and non rigid.   

       I suggest that it would be an excellent project for an aeronautical student to set up a test rig with a one metre square face of aluminised mylar film supported by, say, nine nylon fishing line filaments attached to a single external anchor point and see just what pressure reduction can be achieved before implosion. Achieving a 90% reduction would be a clear signal to extend the experiment to a one and half or even two metres square. Success at this stage would justify the construction of a cube supported on all six faces by filaments radiating out to fixed anchor points. By this time there would be a much better indication of the ultimate viability of the concept.
corvuscornix, Aug 15 2012

       Somebody once said that a vacuum-dirigible could be made using modern structural components, but it would be the size of a small city. Along those lines, you could be right that a decreased-pressure system could be more effective, ie: a much larger structure provides better lift:weight. Bun.   

       //Any vessel containing reduced pressure will have to be rigid and a blimp is essentially a gas bag and non rigid.// But I do take exception to that comment (see "Prayer Wheel Vacuum Blimp").
FlyingToaster, Aug 15 2012

       If you're the size of a small city, you just make the top of the envelope clear, and use solar heating to get the pressure down. I'm blanking on the accepted name, but it's a serious proposal to produce floating habitats that way.
MechE, Aug 15 2012

       // //Any vessel containing reduced pressure will have to be rigid and a blimp is essentially a gas bag and non rigid.// But I do take exception to that comment (see "Prayer Wheel Vacuum Blimp").//   

       Apologies if that came over badly and I should have phrased it better. I do think that for many the word blimp does conjure up a picture of something non rigid with Goodyear on it.
corvuscornix, Aug 16 2012

       I went to the first link on that idea. Then read the idea. Then noticed it was my idea in 2002. I wonder if there is research about affects of too much web surfing on the brain.
pashute, Dec 04 2012

       A reduced pressure lighter than air machine will always be even more difficult than a vacuum one. I have devised an elegant proof of this, but can't be arsed typing it out.
spidermother, Dec 06 2012


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