What happened to the idea of a stable airborne cell tower? The only response I can find is "unlikely" or "unreliable" without any data.
What am I missing here?
You can also see this from conservation of momentum; it requires that, if something goes up, something else must come down. With an entire airplane going up, there isn't much else than air to come down (exhaust gases are another option, but then, you are talking rocket, not airplane).
And yes, gravity means the (airplane plus surrounding air) system isn't closed, but its effects only make matters worse; airplanes have to throw down air even to maintain level flight.
Why would a tailwind matter? That would cause it to go faster relative to the ground, but it shouldn't matter in terms of lift, right?
I'm waiting for someone to invent an extremely cheap lighter than air solid which can act like a battery.
Is this even possible at normal temperature? I can't imagine this at 1 atm. and room temperature...
after some googl-ing:
Lighter than air solids have the issue that if you remove the air from the spaces in those solids and try to hold it out you create a pressure differential that crushes them.
There was some speculation that given an ability to precisely manipulate carbon you could build dodecahedrons out of pentagons of diamond in a vacuum and then when you removed them from the vacuum they would have a net density lower than that of air, but the density ratio is so small (assuming you could build them) that you'r talking about a massive airship that ascends to maybe 3,000' on a cold day.
Exploiting air density is a challenging path that has not had much success of late.