I think it also heavily depends on what the longtime tests with the planetary gears are showing. Would anyone be willing to share how many hours of flying one particular gearbox has done?
Because I think for the gearbox to make sense, it would have to have a lifespan that is at least in the same order of magnitude as that of the batteries.
Also, I was doing this naive order of magnitude calculation estimating the numbers using Peter’s thread:
600Wh Battery, 600W average power drain, 70% battery usage ->42 min
assuming to save 1 kg in the drivetrain without the gearbox and investing this in more batteries and assuming an increase in current drain by one third due to lower efficiency of the jet drive :
800Wh Battery 800W average power drain, 70% battery usage ->42min
Of course, the increase in Wh is a bit optimistic but maybe with a normal battery size, the flight time can be about the same with a jet drive if the weight saved with the gearbox and larger propeller is invested in a bigger battery. Maybe someone can do a similar calculation with more realisitc numbers and prove me wrong.
The extra batteries are probably cheaper than the gearbox and getting the weight closer to the feet should be good as well. However, in case one would choose to go for much more range with a larger battery the comparison wouldn’t look that favourable for the jet drive anymore. Also if one wanted to have multiple battery packs to swap, it would comparatively get more expensive and disadvantageous to go with the jet drive.
I could very well imagine that the best compromise is in between a 25k rpm direct drive jet and the 25k reduced to 5 k geared drive.
I would guess that the 16k rpm you are proposing does not bring big weight savings compared to the 25k to 5k rpm geared drive because I expect that about 50% more motor torque is needed. But it should be simple and reliable and the decrease in efficiency should be far less compared to a 25 k rpm jet.
Have you already found a motor with enough torque for the 16k rpm direct drive?