Looks great Francesco.
Increasing the number of blades on a propeller is one way of improving power absorption through propeller solidity (the solidity of the spinning disc). When you consider that the Griffon 65 as seen in the Spitfire Mk.XIX could put out almost 2,000HP, that is nearly twice what the early war Merlins could produce. That is why you see an increase in blades as the type developed with more powerful engines. Later, contra-rotating propellers did the same thing, but also reduced torque effects as they turned in opposite directions. An interesting fact is that many pilots struggled to control the later aircraft on take off due to the massive torque produced from these enormous engines. More than one experienced Spitfire pilot came to grief because the Griffon actually turned the propeller the opposite direction to the Merlin (anti-clockwise as viewed by the pilot). Wrong pedal and full power = significant loss of ground control.
