I just want to share the thoughts I had on this topic.
I took a 6:1 4P Motorchief gearbox, TP4070 7Y motor (630Kv / 104A / 79V), Alu prop (have to look up the spcs.),Gong Allvator L foil .
My thinking behind this decision was:
• I have 12s Battery (so, the max voltage is fixed)
• I need between (rough number for my big prop) 2500 and 4000 rpm at the prop. (thats also fixed)(20-30%drop)
• I need as much power as possible. ( -> because voltage is fixed by battery, I need the possibility to draw some amps)
• High Kv motor is (normally) rated for more amps. (less windings -> thicker wire -> stronger for amps) (example TP motor: 440Kv 75A and 910Kv 150A)
• Reisenauer Motorchief is rated for max. 50000rpm and 5.5kW
So my thinking: -> take a gearbox with maximum reduction so you can take a motor with higher Kv rating which can handle more amps.
And after some calculations with Voltage/Kv/Amps/rpm(prop)/rpm(motor)/rpm(drop)/Power/reduction/Powerrating(gearbox), I made my decision.
Voltage is fixed by the battery so for more power you need more amps and as a higher Kv motor can handle more amps you need a higer gear reduction to take a motor with more Kv. ( but I guess that’s only a problem with the smaller motors)
That was my thinking. It may be wrong but my setup works and has lots of power. (I just need a better board)
Feel free to correct me