Here is an excerpt from an answer on aviation.stackexchange.com to the question of what is the maximum possible size for an airplane. I’d paraphrase but the answer was too good.

“An airplane flies because of the lift coefficient L=1/2pv2ACL, with v the airspeed, which is a combination of the speed of the plane and the wind speed, p approximetly equal to 1kg m to the -3 at a theoretical mimimum of 5 km height (remember that most planes reach 10km, but I took this a little more extreme to show an upper limit), A the area, and CL an coefficent with a typical value less than 2, that might change with technological innovation.

So the only factors we can influence are v and A. However, if we increase A, the mass m increases faster than the area A because there is more material needed to avoid the plane form breaking under the huge forces. Increasing A quadratically gives more than a quadratically in m, and hence in the needed L.

If we increase v, we need more fuel. The amount of fuel per distance unit increases linearily in v, because it increases quadratically per unit of time in v. Hence L increases quadratically where m only increases linearily. This means that we might do something with increasing v. That means that airplanes have to go faster before liftoff, which will need drastically longer takeoff lanes. Note that we can’t keep increasing v because we can’t lose control.

In summary, things we can improve are v, the speed, CL, with technological innovations and p by lowering flying height. However, it is not practical.”

*Reference: aviation.stackexchange.com*