Assuming that you get a brushless with the right Kv rating you should be
able to turn the prop a bit higher speed at the same power as the
current brushed motor. Geared brushless motors seem to really shine
when you run them _fast_, which would indicate using a higher voltage
(or lower Kv motor) and a smaller prop or more reduction in the gear box.
It all depends on what you want. If you want to go straight up forever
with that poor little Cessna then you probably need to gear down more
and put a really fast motor & powerful in there. If you just want
sustained inverted flight then the right motor with that gear/prop
combination may be just the ticket.
If your LHS is really good you could just ask there.
Yes, provided it physically fits, the brushless is an inrunner and will
work at an appropriate RPM when geared, and you take account of the
likely different motor characteristics when selecting the pack/prop.
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