I'm not a beginner in flight, just a beginner in prop selection. I can do fine with 2-blade, but I start getting confused with more blades...

I have a P-51D that was designed for a .46 engine - I have a .91Surpass on it and I have been chipping a lot of props due to clearance issues. As soon as the tail pops up I sometimes hit the prop - I have to be very careful when I throttle up and reach airspeed...

I was planning on moving to a 4-blade prop anyways for looks, but I realized that the 4-blade would be shorter and would give me more clearance... (wish I had figured that out about 2 props or so ago)

I'm wondering what would be a perfect prop for this engine in a 3 or 4 blade prop (preferably a 4-blade)... Any ideas?

--Micah

Hi Micah,

Try www.bolly.com.au/book/content.html the info here applies to allbrands as to the conversions.

Cheers,

Colin

the rule of thumb for the 3 or 4 blade props is this, 3 blade -- run same pitch as the 2 blade ur using but just 1 inch shorter diameter. 4 blade --- 1 inch shorter diameter but 2 to 3 degrees less pitch on blades.


91 surpass; 2 blade == 12/12,13/6,13/8,14/6,14/8
3 blades == 12/6,12/8,13/6,13/8
4 blades == 11/8,11/10,11/12,12/8,12/10,13/4,13,6

these are just general prop sizes,you need to try a few and see what ones work best for you plane.

Good luck,Art

You will probably find that for engines that size (.46 - .91) 3 and 4 blade props are not nearly as efficient as 2 blade. The engine will turn it, but it may not give you the performance you want. But I'm no master on the subject. Experiment with some different props and let us know what you find out. Good luck!

Well, I'm more at a point where I don't have a choice... Sure, I'd love to stick with the 13/8 standard 2 bladed I have now.. but when the tail raises, the prop is only 1" from the ground... perhaps less... Just NEED to start preserving propellers at this point. Maybe I can go to a 12/10 or something and keep the performance?

--Micah

A 12 X 10 will make the plane faster in the air, but will require much longer take off runs, and the plane won't slow down as much when landing.

I'd suggest trying a 3 bladed prop first. Much easier to find, and will still help with the clearance issue. Maybe a 13 X 6 or 12 X 8 three blade.
Dennis-