Hello
Main problem will be make good ai. I have flying drone, my AI is based on heavy modified youtube totorial, but this is up to you how your ai will work. Most important is flying navigation, below:
- here is good for start ai tutorial Creating AI in UE4 Part 1 - AI Components - YouTube you can easy modify it for flying drone too
- here is http://www.drunkonnectar.com/3d-pathfinding-ue4/ 3d pathfinding plugin with tutorials and samples.
I believe, here is no simpler way, and my flying drone works exactly as expected. Most of time you will spend with general behavior ai, up to you it need maybe few days if you will follow this tutorial and have some skills. Flying is just installing plugin, is easy to use (10 min to much longer if you stuck).
Here is test scene where it flying:
https://i.imgur.com/k2cwq04.png
But have no problem inside buildings with many floors and rooms, windows etc too.