After reading a lot on the fpvlabs leaderboard, it became clear that a limiting factor for pushing really high alt is that the air at high altitude is so thin that props have to spin extremely fast to produce enough thrust (the other is the ambient -30°c but thats something else)
so I decided to make a variable pitch prop using folding prop blades, I havent started CAD work yet but theorically a simple ceramic bearing and a few printed parts could do the job. Could also help for planes like the mini talon that are hard to launch but can aquire a good high end pitch, provide lots of static thrust at launch then increase the pitch angle to produce less static thrust but more pitch speed for more efficient cruising.
In short, like real airplanes do.
I will have to work on that, it could be useful.