Airport size limits
How big landplanes can use existing airports?
There is some talk of 80x80 m box. Indeed A380 is built to have wingspan of exactly 79,8 m, and Airbus 380-900 is supposed to be exactly 79,8 m long as well.
But Cossack has wingspan of 88,4 m and is 84,0 m long. It is not restricted to hauling Buran between Ulyanovsk East and a few other Soviet Union airports built for it - it is happily running charters with outsize loads to sundry airports.
How can this be done? How come its nose or wingtips do not collide with something?
Also, there are the SST-s. While Concorde and Charger are manageable in size - 61,7 m long Concorde, 65,7 m Charger are both shorter than B747 - L-2000-7 is over 80 m long, B-2707 is over 90 m, ditto about Boeing HSCT and Airbus AST2, MD HSCT is over 100 m long, and JAXA NEXST is 104 m or so.
How is your airport going to handle the NEXST?
At least, SST-s have delta or swinging wings with modest spans (compared to subsonics) even when spread.
But then there are the ground-effect military transports. While most of them are seaplanes (no need for airport infrastructure), Boeing Pelican is supposed to be a pure landplane - with 147 m wingspan.
How can a Boeing Pelican be handled in an existing civilian airport?
How big planes could the existing airports handle at most? Be-2500, an amphibian, has slightly greater wingspan at 156 m.