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Venus is being paraterraformed with floating cities. Mechanical machines collect material from the surface and send it floating at an altitude of about 50 Km where conditions are more Earth-like. Here the material is assembled into building.

The "city" is not in one piece. Each building has its own floating mechanism independent of the others. The city is ring-shaped with buildings moving in a circular motion around an empty center.

Some buoyancy is provided by the internal atmosphere which is less dense than the venusian atmosphere. However I want them to use other systems as well, in particular wind. I was thinking in particular of the Vindskip concept (The video is short and gives an idea of how it works).

What shape/machinery can I give to the buildings to have them harness wind power for flotation?

EDIT: Maneuvering is available for the buildings, and some minor propulsion systems can be considered too

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  • $\begingroup$ Can you include direct description of the concept? And link to something that's not a video? $\endgroup$ – JDługosz May 10 '16 at 22:43
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A building, or any other body, floating in the air with no propulsion to move and direct it, will not experience any relative wind. There is no shape that will provide passive lift without relative wind.

If you can discover places where the wind varies significantly with altitude, and the wind patterns are reliable enough, you might be able to construct a flying object consisting of two bodies connected by a long cable and experiencing a strong relative wind between them.

This would look like two kites or wings facing each other but at different altitudes. The ground speed of the two connected wings would be the mean of the wind speeds, and each wing would fly on a relative wind half the difference between the wind speeds.

Here is a rough sketch: staying aloft on wind speed difference

On Venus this would be placed at high altitudes where the atmosphere is energized by the sun. The weather near the surface of Venus is very dark and very calm.

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  • $\begingroup$ Could the facing-off wings be supported by the building they support instead of a cable? $\endgroup$ – JordiVilaplana May 10 '16 at 13:35
  • $\begingroup$ The wings are the buildings. The altitude difference is probably 2 to 5 kilometers. The cable might be 10 kilometers long. $\endgroup$ – A. I. Breveleri May 10 '16 at 14:01
  • $\begingroup$ @A.I.Breveleri Thanks a lot for your answer. Very insightful! While the concept you describe makes perfect sense, my day to day thinking suggest there should be a way. How does a glider work then? Also I never said propulsion and maneuvering are not available $\endgroup$ – SilverCookies May 10 '16 at 14:57
  • $\begingroup$ A glider is constantly descending relative to the air around it. For a glider to stay aloft indefinitely it must find rising air. On Earth columns of rising air can be found on bright days where the sun heats some parts of the ground more than others. Gliders can stay aloft for a long time but must always descend at night. -- Rising air is also found on the windward side of mountains but this requires just the right winds and is less reliable than sunlight. $\endgroup$ – A. I. Breveleri May 10 '16 at 17:37
  • $\begingroup$ Perhaps there are permanent rising columns of atmosphere on Venus. Then your buildings could essentially be large gliders. Perhaps the upper atmosphere is transparent enough to allow the use of solar cells. Then your buildings could essentially be large airplanes. The scheme in my diagram was originally proposed for use in the Jet Stream (here on Earth). $\endgroup$ – A. I. Breveleri May 10 '16 at 17:37
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Spheres. No others need apply.

In particular, the enclosure wants to maximise the volume with minimal material, and the bubbles can be made with structural members in geodessy: that is, purely in compression or tension.

This is what I thought you were describing. But now (and the question still needs clarifying!) I think you're wanting what's essentially an airplane powered by wind: that's not possible. If you want a kite, it needs to be tethered.

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  • $\begingroup$ Indeed the sphere would maximise the volume per area. However consider that, unless you want to consider a person-size building (I don't), a sphere would still need additional internal structures that would make the area/volume ratio advantage pointless. As stated I am specifically looking for wind capturing designs. $\endgroup$ – SilverCookies May 10 '16 at 9:05
  • $\begingroup$ Doesn't it float by containing buoyant air? Have a link to your concept that's not a video, and maybe include a brief description directly? $\endgroup$ – JDługosz May 10 '16 at 9:22
  • $\begingroup$ Buoyant air provides only some of the lift. $\endgroup$ – SilverCookies May 10 '16 at 9:44
  • $\begingroup$ balloons full of hydrogen. btw if their are many separate buildings how do you move between them. $\endgroup$ – Donald Hobson May 10 '16 at 15:57
  • $\begingroup$ AIB made the point well: if you are thinking that wind can "power" the unattached building and provide lift, you are mistaken. $\endgroup$ – JDługosz May 10 '16 at 22:38
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Your spinning disc sounds a lot like the classic "Frizbee" toy. There are a lot of variations including ring shaped ones, so in terms of aerodynamics, a spinning ring with the proper airfoil shape should be able to fly in the Venusian atmosphere.

enter image description here

There are a few factors to keep in mind. Unless the structure is very large (many kilometres in diameter), the spin rate will induce a lot of stresses on the people and buildings inside. In the extreme case, the ring is rotating so fast that the buildings are oriented with the "floor" pointing at the outside of the ring and the ceiling pointed towards the open centre, you are creating "artificial gravity" like a space station.

If, for simplicity and to keep the mass and maintenance to a minimum you have the buildings fixed to the floor of the ring, then the rate of rotation needs to be fairly low. People walking inside the ring will still experience forces induced by the spinning, but if it is low enough, they will be able to compensate.

The second issue is "how" the ring keeps spinning. The Frizbee gradually slows down as air friction steals the momentum of the toy after you release it. The colonists are not going top be too thrilled as the rotating forces are substituted for free fall into the depths of the Venusian atmosphere.....

Several ideas suggest themselves. The ring will need a series of motors around the perimeter to drive the rotational force. Since the atmosphere isn't too conducive to combustion (and sending fuel to keep such a large structure rotating will be an immense task in itself), you could have the upper surface being a microwave receiver and solar power sats in orbit are beaming electrical energy to the structure. Some is tapped to run the internal systems and the rest keeps the motors running (probably electric engines spinning huge ducted fans or propellers).

Another way to go about this is to consider a tether from the mining site on the ground. The tether is used to send mining buckets to and from the ring, but it might also be part of a thermocouple system, with the temperature differential between the ground and the ring being used to generate electrical energy. This avoids the complications of a solar power satellite, but the amount of energy will have an absolute limit based on the difference between the two temperatures, and the efficiency of any system to tap energy will always be less than 100% anyway.

For aerodynamic reasons, you want everything to be enclosed in the ring shaped airfoil, since protrusions and gaps between objects will simply induce drag and make spinning the ring much more difficult and energy intensive.

One other consideration for any sort of floating colony in the atmosphere is how are the people going to get too and from space? a spinning ring or a giant spherical balloon like a "Cloud Nine" is going to make a very tricky launch or landing platform.

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  • $\begingroup$ Thanks for the interesting idea. I don't want buildings in the kilometer range, but even if the rotational speed required is too fast you can have the "real building" inside the spinning "shell" right? Plus, remember that buoyancy provides some lift. What engines can be consider other than propellers and the like? $\endgroup$ – SilverCookies May 11 '16 at 15:54
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    $\begingroup$ Bouyancy simply means the mass of the structure is less than the equivalent amount of atmosphere being displaced. At the altitude you are talking about, the ring (or any other very large structure) could be buoyant if the air inside is warmer than the air outside, like a hot air balloon. A "Cloud Nine" takes this idea to an extreme, but a very light structure made of graphite or similar could also have buoyancy like a hot air balloon. If the atmosphere is electrically conductive, the shell could be energized to create an MHD engine. $\endgroup$ – Thucydides May 12 '16 at 15:26
  • $\begingroup$ What does the spinning achieve? In a frisbee you use it to give stability via the gyroscope effect but you don't need that in an actively managed building. $\endgroup$ – Tim B May 12 '16 at 15:33
  • $\begingroup$ For a structure the size being discussed (a floating city), having the entire structure gyroscopically stabilized is less resource intensive and much more fault tolerant than managing a "flock" of flying structures. It also incorporates the aerodynamic streamlining and provides the protective covering for the citizens and their property in the same structure, an elegant solution $\endgroup$ – Thucydides May 12 '16 at 15:39
  • $\begingroup$ @Thucydides sorry I don't get it then. Does the spinning provide lift or not? $\endgroup$ – SilverCookies May 13 '16 at 7:12

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