Wanting to keep the apperance up on this one, I decided to go with 3 blade MAS 9/7 props. I will be using 2-Supertigre 40's. Are these all right for the 40's? I will normally use a 10x6 on a 40 and a 10x7 on a .45. I think the rule for 3 blade is to drop and inch and keep the same pitch. Alas, I could not find 3 blade 9x6. Do you get a better idle from a 3 blade, I would think you get better momentum. Thanks, Al

3-blade props at high RPM's like we have in model engines actually loose some of their efficiency. The higher the RPM may not be the rule with a 3-blade, try to keep your RPM around 9800 and you will get the most thrust out of it. The 1 inch rules doesn't always work because of it. If you are using a 2-stroke the power band may require you to run at a higher RPM than 9800 but I would give it a try. I use 14x7 3-blade MA props on my .91 4-strokes and they turn at 9800+ with 15% fuel. Plenty of thrust! I ran 8-6 3-blades on my .30 4-strokes and got 11,000 rpm from them but they stopped giving anymore thrust at around 9800 just like the bigger props. Hope that helps a little.

Have you checked Hobby Lobby for Graupner 3-blade props? That's what I'm running on the B-24. I also had 3 blades on the TF DC-3/AC-47 I had. I used the 3 blades for more scale appearance, plus to take away some of the thrust for more scale flight. OF course, the A-26 was a pretty fast airplane to begin with.
Randy

Don't limit the RPM. The 9x7 MAS is perfect for the ST40. Keep in mind the ST40 is a little heavy. I've run the 9x6 Zinger plastic and the 9x7 MAS on 40 Super Tigres. Great sound and about 13,000 RPM with 9x6. I think that inefficent 3 blade hype is nonsense till you get way up in the RPM range. If prop makers made more sizes , you'd see more used. The zingers aren't as strong as MAS .