How do I figure what size 3 blade for a particular engine ?

I have a North Star that will not allow a full 10x6 prop and thought I should go to a 3 blade for clearance . Just dont know how much pitch . I can only have a 9 3/8 dia .

Thanks , Jim B.

Most people will suggest this one: http://www2.towerhobbies.com/cgi-bin...&I=LXVJ18&P=SM (9 X 7)

According to MAS--on the back of their 3 bladed packages, you go down one inch in diameter, and UP one inch in pitch. Most say down one inch on both, but I've used MAS's suggestion before and it works great.

well that gives you a 9-6 or 9-7

That Balsa USA Northstar is a cool design! I'm sure you'll have a blast flying it. Using a 3-blade prop to overcome clearance issues is usually quite helpful. I've flown 3-blade props for the same reason on my Tiger Stick .40, and always liked the way it flew with the 3-blade.

Most folks think that 3-bladed props are less efficient than 2-bladed props, but I had a guy with a PhD in physics who used to work for NASA write me a four-page long proof about why 3-bladed props are better. I don't care either way really, I'm just happy to be flying.

thanks one and all, I appreciate your replies