An FPV drone!
It's kinda like racing a motorcycle and flying. Not talking about a DJI drone, but something that's amenable to hacking and fixing because you'll crash a lot when you start. It's a wide ranging hobby, and sounds like your brother could leverage some of the skills he already has.
Depending on the budget, could start with something like a tiny whoop [0] that fits in the palm of your hand or a 4" quad that has a 20km range [1].
There are a lot of sub-genres within the FPV community, from racing [2], to bandos [3] (acrobatic flying around/in abandoned structure) to long range cinematic flying [4].
You have to have quick reflexes (so it's kind of like racing) but ultimately you're flying and getting such a different perspective. Could expand into HAM radio to get truly long range flying.
The FPV industry is going through such rapid progress and it's really fun to follow.
To start, you'd need:
- goggles (to see what the camera on the drone sees)
- Transmitter (control your drone)
- The drone itself
- Batteries and charger
I recently destroyed a motor on my tiny whoop so I had to learn how to solder. Considering the motor is the size of a penny that was by far the most precise work I've done.
It's a bit daunting to figure out all the pieces, but something like a tiny hawk bundle [5] is a great way to start.
0 https://www.getfpv.com/happymodel-mobula7-1s-75mm-analog-who...
1 https://flywoo.net/products/explorer-lr-4-v2-analog?_pos=12&...
2 https://youtu.be/bZvNLuC12R0?t=659
3 https://youtu.be/wzwW5vuuK5w?t=374
4 https://youtu.be/dIP7wWY4Znw?t=89
5 https://www.getfpv.com/fpv-quad-kits/emax-tinyhawk-iii-fpv-r...