Unreal’s rotations are by default Quats internally.
You can convert a X,Y,Z rotator to quats via the kismet library
You can make Quaternions directly to via “Make Quat”
Code wise some extensive examples
As for the forces you won’t find many calculations. You’re going to have to either use a plugin or implement the formulas yourself. It’s first and foremost a game engine not a simulator.
Project Borealis implemented it’s own air drag calculations:
