I think this will be pretty hard to do this in UE4. Now i’m not pretty sure how it´s done by other simulators.
When i was in-game FSX it doesn´t look like the world is shaped like sphere. but who knows…
I have an idea about a plane which will be the whole world and when player reaches the border of the plane, player seamlessly “respawn” on the beggining of plane.
(Umm… really don´t know how to explain this. take a look on my attached “high-tech” picture. 
and also forgive my english)
