Headhunter70

Gents, I am having problem where I would need your expertise.

I am using a Webra 91 P5 with a 12x10 prop which turns 12600 RPM. In theory gives that a speed of 118 mph.

The question here If I would reduce the prop size to 10x10 and maybe gain another 1400 RPM that would give in theory a speed of 132 mph. Does it make sense ? Should I expect a significant increase in speed ?

What would be the limit of the prop diameter. I do not believe it is possible to reduce the diameter without taking the airplane into consideration....how to find the best setup without experiementing with a lot of props (which I do not have yet).

The plane is about 4 kg and has a wingspan of 1,70 m

rgds
Gordon