Hi friends,
I wonder what prop gives you best results for your 40cc... If possible, post your tach readings, static thrust etc. I've been told to move between 20-22" big props, preferably the smaller ones, with low pitch.
My engine will power a big scale RC hovercraft, so I guess I want traction rather than speed.
Another question is the number of blades. If I use a 3-bladed or even 4-bladed prop, what size? What things should improve/get worse? (I've been told they're a bit smaller and quieter)
Thanks folks!

Wood, Zinger 22x6 2 blade, rpms in the low to mid 7ks, 20-22lbs thrust give or take. All just a good guess. Lot depends on carb and muffler you use. The 3-4 blade props have pros and cons. Yes there quieter but they loose efficiency because one blade follows closely to the one before its' turbulence. They also have better braking affect on the plane, you dont need it.

For pulling power go big with flat pitch, for speed go with small dia. and high pitch.