2 blade vs 3 blade ?

[speed]

Can someone give me a brief explanation of the differences between a 2 or 3 blade prop.


Is there a reason I would use a 2 blade over a 3 blade ?

Thanks

[Mel]

Everything else being equal, a 2-blade prop is more efficient than a 3-blade. HOWEVER, seldom is everything else equal. On a fixed-pitch prop a 3-blade must be shorter than a 2-blade because of horsepower absorption. This makes the 3-blade quieter. 3-blades usually win in the take-off and climb catagory but suffer slightly in cruise. But this depends on the efficiency of the two props. In my situation (fixed pitch) my Sensenich wood prop worked great at altitude but my take-off suffered because at 640' elevation in Texas heat I could not turn up a good static rpm. I have searched for years for the right prop. My search ended with the Catto 3-blade. Craig worked with me to get the prop just right. Final result was a 17% shorter take-off. Noticable climb improvement and no degradation in cruise. And I won't even get into the sexy appearance and smoothness. This is my result...your mileage may vary.
Mel...DAR

[hngrflyr]

I don't know about you, but a biggie for me is price. Three blade props are said to be smoother, but very slightly slower than two blades. You would have to show me that they are smoother than the two blade Catto Prop on our RV-6.

Bob S

[speed]

What are your opinions on a 3 blade for a RV10 ? I like the appearances of the tri-blade, but with my lack of experience, I wonder about the rv10 size difference and the issues that will be presented.

Craig ? Does he work for Catto or is he a local here the DFW area ? Do you think he would possibly help or mind speaking with me about the tri-blade for an RV10?

[hngrflyr]

Craig is Catto. That's his name, Craig Catto. See: www.cattoprops.com Give him a call. Phone number is on the website. It's easier to communicate with him by phone than by E-mail. At least that's my experience. He'll discuss your needs with you. Very nice person to do business with. I've met him and spoken with him at Calavaras County Airport, in the Sierra foothills in central California.

If I were involved with a RV-10, I'd be looking harder at some kind of consant speed prop, but it depends on how you will use the airplane. I live in the west. We have lots of high elevation airports and lots of high density altitude days. For good safety margins, you might want all the performance your engine can give you. If all your flying will be lower elevation with wide open spaces, a fixed pitch prop might be satifactory. Fixed pitch propellers are always a compromise. You give up performance on one end of the range to get it one the other end.

As for two blade vs three blade, two blades are slightly more efficient. Three blade props are a little quieter due to lower tip speeds. They are smaller diameter. For that reason, three blades will give you more ground clearance. Three blade props cost considerably more than two blades and are generally heavier. From where I sit, that about it in a nut shell.

Bob S

[randylervold]

Originally Posted by speed

Can someone give me a brief explanation of the differences between a 2 or 3 blade prop.


Is there a reason I would use a 2 blade over a 3 blade ?

As with all things in aviation there are pros and cons to each. I have a layperson's summary of the physics about a third of the way down this page...
http://www.romeolima.com/RV8/Prop.htm

When I checked with Jim Rust, founder and designer of Whirl Wind, on the accuracy of my understanding he said "yea, that's a pretty good overview".