ORIGINAL: oldvet70
From Master Airscrew ;
To convert form 2 blades to 3 blades you want to decrease the total blade area and
increase the angle of attack (or pitch) to overcome the increased drag of the third blade.
The general rule is to DECREASE propeller diameter by 1-2”, and INCREASE by 1-2”
the propeller pitch. It is all right to keep the same pitch when going from 2 blade to 3,
however you will not want to decrease pitch.
http://masterairscrew.com/images/selecting_a_prop.pdf
Works very well for me.
This is what I was taught and what I do but today on some of the prop sites I keep seeing them drop the size and stay with the same pitch. From my own testing I find adding pitch worked best??
I was running the 13X6 APC on my OS .70 and tested the MAS 12X6 and 8, both worked out fine. Problem is I was flying a 66 inch Tiger Moth so it doesn't mean anything at all to Brett, apples and oranges but the different pitches are worth trying to see what you like. MAS props are cheap enough to test several and well worth the effort!!