Gravity Plane

[AWPrime]

To do this requires energy, and the indications here are that it is a considerable amount of energy.

Especially if you consider that it should be done in a very short time.

 

[Johnny Pneumatic]

I've done some more thinking about what you've said about the vacuum spheres and I don't get it. Once you had a shell that could hold up to 1 bar/14psi of air pressure the shell wouldn't need to be made any thicker as the volumes of spheres was increased would it? If so, why? The titanium sphere that is the cab where the people stay in DSVs when going deep in the ocean holds up to 14,000+psi without failing. If the sub were only less than a mile closer to the surface it would be possible to pump the air from the sphere and it wouldn't implode. What am I not getting? Titanium isn't nearly the
strongest know material

 

[CurtC]

I've done some more thinking about what you've said about the vacuum spheres and I don't get it. Once you had a shell that could hold up to 1 bar/14psi of air pressure the shell wouldn't need to be made any thicker as the volumes of spheres was increased would it? If so, why?

I think you're saying that if you have a 2 mm thick wall of "Krell metal" or whatever, which can hold a near-perfect vacuum around a 0.1 liter volume, could you scale up that volume to an arbitrarily large size, still with only a 2 mm thick wall. Is this right?

It doesn't work. The curvature of the container acts like an arch mechanically, and if it's scaled up, that arch flattens out so can't hold as much force without deforming.

Anyone remember what "Krell metal" refers to?

 

[Benguin]

I think you're saying that if you have a 2 mm thick wall of "Krell metal" or whatever, which can hold a near-perfect vacuum around a 0.1 liter volume, could you scale up that volume to an arbitrarily large size, still with only a 2 mm thick wall. Is this right?

It doesn't work. The curvature of the container acts like an arch mechanically, and if it's scaled up, that arch flattens out so can't hold as much force without deforming.

Anyone remember what "Krell metal" refers to?

Also, a more slender surface with shallower curve is much more prone to deflection, deflection is critical in this application from a point of view immediate failure under load and resonation problems (particularly from wind forces).

Edited to add: though reinforcing it with lightweight T section ribs with extended webs could probably negate the problem without adding nearly as much mass as thickening the membrane. I'm pretty sure the zepplins held their shape using a similar structural method. I'll look into it.

 

[MRC_Hans]

I've done some more thinking about what you've said about the vacuum spheres and I don't get it. Once you had a shell that could hold up to 1 bar/14psi of air pressure the shell wouldn't need to be made any thicker as the volumes of spheres was increased would it? If so, why? The titanium sphere that is the cab where the people stay in DSVs when going deep in the ocean holds up to 14,000+psi without failing. If the sub were only less than a mile closer to the surface it would be possible to pump the air from the sphere and it wouldn't implode. What am I not getting? Titanium isn't nearly the
strongest know material

Same problem as the double-walled container with pressure in the wall: The pressure perpendicular to the surface (air pressure) has to go somewhere and it is transferred to a pressure along the surface. So, the larger the surface, the more pressure along the surface that must be taken by the container. Therefore, the pressure anf thus the strength of the container must is proportional to the surface area of the container.

So, you may see small out here: The VOLUME of a container rises with the radius to the third power, whereas the surface only rises with the radius squared. Unfortunately, the volume, and thus the weight, of the container walls will also rise with the surface to the third power .

Hans

 

[Johnny Pneumatic]

So, you may see small out here: The VOLUME of a container rises with the radius to the third power, whereas the surface only rises with the radius squared. Unfortunately, the volume, and thus the weight, of the container walls will also rise with the surface to the third power .

Ouch! And I thought I had come up with a good idea for an SF story. Physics gets you every time.

 

[MRC_Hans]

Cool. Just got me a new sig.



Hans

 

[Crossbow]

I've done some more thinking about what you've said about the vacuum spheres and I don't get it. Once you had a shell that could hold up to 1 bar/14psi of air pressure the shell wouldn't need to be made any thicker as the volumes of spheres was increased would it? If so, why? The titanium sphere that is the cab where the people stay in DSVs when going deep in the ocean holds up to 14,000+psi without failing. If the sub were only less than a mile closer to the surface it would be possible to pump the air from the sphere and it wouldn't implode. What am I not getting? Titanium isn't nearly the
strongest know material

Ah, but the DSRV is an example of compressive loading.

Whereas in the vaccuum plane, one would have deal with tension loading. The problems to contend with are very different indeed!