Speed 3 Blade Over 2. How to work out?

[lohring]

Propeller scaling is well understood. The power required varies as the diameter to the fifth power, the rpm cubed, and directly as the pitch and blade area. That's why two propellers with the same blade shape, pitch, and diameter will take 150% (3/2) times the power if one is a 3 blade and the other is a two blade.

Lohring Miller