ORIGINAL: DaveFlynn

Mostly true. The max prop size depends on ground clearance and the min on the thrust required. I try to choose the lowest Kv for a given frame size then choose the cell count to get the pitch speed I want or the maximum rpm rating for the prop. Pay close attention to the numbers, too many watts will cook the motor, too many amps and the weakest link (batt, ESC or motor) will be damaged.

I recently changed the motor on one of my planes from a Kv=650RPM/Volt to a Kv=380RPM/Volt motor of the same weight and size. The prop was changed from 12x6 to 14x6 and the battery from 6S2P to 9S1P. Flight times are unchanged at around 10 min and the plane is much faster and 5.5oz lighter. I'm getting slightly more thrust for fewer amps at a lower rpm and lower wattage. This is a big slow trainer, so no 3D stuff here.