@ onetrack: But how did they make the 1st propellor perfectly, to enable it to be used as the master on the copy lathe?
It's the same as shipbuilding there they made a drawing of half a hull then reversed the profiles to get the same shape on the other side.
There are if you look for them Profiles of aerofoils designed and tested by the RAE in the UK and NACA as was in America.
Somebody would sit down and work out the theoretical profile that should work and then they would draw that profile using standard drawing methods usually third angle projection. From this sections would be be taken at stations along the propellor and a jig made up with negative profiles which would allow for the twist in the chord to be included and a master blade would be made which would fit into this jig.This blade would then be used as a pattern to carve the next set of blades. These then would be tested to see if the actual performance matched the theoretical figures, the blade would then be tweaked until the desired performance was obtained and this would then be used on the aircraft.
Tis an arcane art but they've pretty much got it knocked these days. Not like the days when Sir Stanley Hooker joined RR and improved the performance of the superchargers by a large amount with a simple change to the shape of the rotors.