Ok you got me interested and I am brainstorming. So just pull me back in the line if necessary.
Maybe we should make a separate thread about this particular idea. Thanx to Pyro for throwing the bone.
The thing is supposed to be at the heights of tropopause where jet stream is. Apart from that I dont see many more advantages beside that there is almost no weather changes up there. No rain and no downdrafts
. So that puts the height at about 10-12km. Temperatures up there are somewhat stable at -56°C and the pressure is about 1/4 bar.
After some calculations I think that if you raise the average temperature of the air by 100K the lift at that height is 16m3/kg. Which is ofc proportional to temperature difference.
Another thing CraigD pointed out is insulation. One mile diameter balloon has 8 square kilometer area. So say 0.5 mm metalized film of the density about 1kg/l (Its about the same as water allright
) weights 4,000 tons. Films can be thinner and I guess multilayer approach gives better insulation.
Why is geodesic structure even needed? Balloons are easier to inflate if not rigorous, thinking that light-weight ball shaped geodesic dome would be hard to stand up without support. Balloon would support its shape on its own. Any faults would be negated by many layers. Repairs can be made by moving along meshes between layers. Did I miss anything?
As there is no to any kind of reactor, maybe there should be a big battery stack to storage energy for the night.
A big boost for this kind of flying vessel would be adaptive plastic solar cells, say being able to change the % of transparency/reflectivity on either side.
And by the way, using helium instead of air gives about 250% increase in lift. 600% for hydrogen
.
As far as electric planes go. Maximum thermodynamic efficiency of burning kerosene is about 90% (combustion temperature of about 2300K). As temperatures inside jet engines are somewhat comparable.And according to this:
http://www.transportenvironment.org/...nd_out/lid:398
the efficiency of airplanes rises now very slowly. I guess the energy efficiency is about 60-70%, correct me if I am wrong. So mechanical propulsion would improve that by maybe 30% at best.
As drag increases alot by increasing speed and density of air, I say that one would get a nicely low fuel consumption with a airplane traveling at 10km and with the speed of about 300 kmh. The thing is that you need very big wings to create enough lift. That in way create more drag, for which you need bigger engines etc...
