In which timeline would subsonic jetliners become as obsolete as airliners powered by radial piston engines?
I don't think that this approach would ever be cheap enough to be used by the masses (as opposed to the rich few). What would be needed to get ordinary people flying supersonic?But there's a way of having hypersonic/suborbital flight.
It's Burnside-Clapp Black Horse/ Black Colt/ Pathfinder way.
Have an aircraft with two jet engines, a non-cryogenic rocket engine, and in flight refueling.
Take-off using the subsonic turbofans only, and fly to a modified KC-10 Extender.
Transfer rocket oxydizer, light the rocket engine to accelerate to mach 12 or mach 15 and 500 000 ft.
Good thing with this method is, the rocket engine accelerate your machine so fast and so high that you have no sonic boom.
A TL with super advanced trains everywhere that makes medium haul flights pointless?
And piston airliners aren't obsolete, they're still used for a lot of short haul flights.