"As we see above our motor runs at 6660 RPM at NO LOAD. But when you mount prop on it, RPM will be reduced. Here we will take example of two props 10x3.8 and 10x6. When you mount 10 inch diameter prop RPM of motor will be reduced to 3600 RPM"
How did he know after mounting 10 inch diameter prop RPM of motor will be reduced to 3600 RPM ??
Replies
Reduction in prop speeds cannot be estimated accurately, the only way to see what the prop speed is is to measure them. The reduction in speed also depend on what motor you are running as well as the type of prop. Lower KV motors should in theory reduce less than high KC motors since the torque of the high KV motors are more, but then again the dimension of the props on low KV motors is greater. The number of cells on the Lipo will also have an influence. 6S lipo packs have a lot more kick to them than 3S packs to on the same motor and prop setup, speeds reduction from a 6S pack will be much less than on the same motor and prop setup with a 3S pack.
I think the only way you can "guess" by how much prop speeds will reduce is with experience.