This is an explanation of how motor ratings and the size of props come together to create a suitable package for your plane.
The kv rating is a theoretical ratio of what RPM the motor will run at per each Volt. So a 2000kv motor will achieve 2000 RPM at 1V, and 20,000 RPM at 10V, etc.
A motor will always try to achieve its kv rating in use, so think of a motor’s kv rating as an indication of the torque that motor can produce. High kv motors like small inrunners, generally have low torque, but can achieve very high RPM figures, where as large outrunners will have low kv ratings and as such, lower RPMs, but deliver a higher torque and will therefore turn large props. Think of motorbike engines and car engines, where you could have two 1000cc engines. They both roughly produce the same power, but one revs to 16000 RPM and the other 6000 RPM, but you wouldn’t want to carry five passengers, and tow a trailer using a motorbike.
But when choosing a setup for your aircraft, remember that the larger the prop, the more efficient it will be, so in that case a lower kv rating and a big prop is better. If your flying a souped up funjet, then a small inrunner with a 4000kv and a small square prop like a 4.5 X 4.5 will make it scream. But if you switch props, the large outrunner will simply be ‘underpropped’ and run very near its theoretical kv rating. The small inrunner when ‘overporpped’, on the other hand will simply do its best to achieve its kv rating and in the meantime draw more and more current until the motor simply burns out.
In simplified terms, prop diameter determines thrust, pitch is airspeed, so think of pitch like a car’s gears. Low pitch, low gear, high pitch, high gear. Those who’ve hand launched foam prop pusher jets with large pitches will know that they take a while to get going.
Remember, bigger the prop, more thrust, the higher the efficiency.
Here you can find one of many helpful motor/prop combos:-