What Tree

Is there a chart that would tell me what three blade propeller woud replace a 12-6 2 blade prop?

Sorry if this has been brought up before, Ilooked, I really did! LOL

Thanks in advance.

MinnFlyer

My Feedback: (4)

General rule of thumb is to drop one size in pitch or diameter.

So you would replace a 12x6 with either a 12x5 or 11x6

TimBle

I generally agree with Minnflyer but this 2 to 3 conversion thing is not that simple.

You need to go back to basics. At what sort of rpm does your particular engine work best? Not easy to establish but you probably did some rpm tachometering to establish which prop gave you the best rpm's for the best power output.

the same principle applies to 3 blade propellers. You need to buy a couple andtacho them.

Remember a 3 blade is heavier and less efficient but produces more thrust. SO I'd start where Minn has advised you to but also consider a 12x6 three blade and everything inbetween.
I believe those would be 11x6, 11x7 11x8, 12x6, and 12x7 even a 12x8.

We recently (yesterday infact) tried a OS55AX with a 11x7 3 Graupner which was supposed to reduce the speed of the trainer. Wrong it went like a scalded cat and thats with a 55AX at nearly slobbering rich high speed setting. It behaved likea 11x7 two blade prop bu with more pull on the vertical.
My conclusionis that its not as simple as drop inch in diameter and increasing one inch in pitch.
I'm tempted to try a 12x7 3b on my Extra

Trail and error

What Tree

I appreciate the wisedom. I have 2 issues, ground clearance and my plnae is 123.4 grams tail heavy. The engine is a OS 64LA on a Nexstar 60 Select. I am figuring that in the snow the clearence will really be an issue, and, if I am going to swap out the spinner to a metal one (to reduce need for lead weights for balance) I might as well try a 3 blade prop too.

As I run chainsaws for a living, I have always wanted a tach. Hmmm, this sounds like a great excuse to get one of those too!

thunderwolve61

Go to masterairscrew.com and read the article on selecting a prop.
                                                                                                                           jerome

Gray Beard

My Feedback: (-1)

Yep, most manufactures have some sort of chart but the rule of thumb is to drop the length one inch and raise the pitch one. So, going from a 12X6 single blade to a three would be 11X7 or 8. Again, testing the plane with the new props is a must and there is no magic number anyone can give you, just a close idea.

Lnewqban

You can also increase ground clearance more than the 1/2" (that 2 to 3 blade switch will do) by extending the landing gear.

Those additional 123 grams (4.3 ounces) on the nose are no much weight and may be achieved by increasing the battery pack and/or relocating it.

During training, you will break several propellers; I would stick to 2-blade.

Regards

Campy

My Feedback: (1)

In addition to the above suggestions on the plane being tail heavy, here are a couple of others.

Go to a larger battery - instead of the typical 600 mah battery, go to an 1800 mah or 2200 mah battery moved as
far forward as possible (I have relocated batteries to just in back of the firewall and used an extension to get to
the receiver).

They also have "Crankshaft Weights". They come in 1 oz and 2 oz sizes and replace the thrust washer. They
NORMALLY will fit inside the spinner so no one sees them.

carrellh

Every engine and airplane is different so the "rules" are nothing more than a starting point.

The reality is: Three blade prop selection is limited. Your decision likely will be based more on availability than optimum performance.

Zinger says 'keep the pitch' and 'drop the diameter' http://www.zingerpropeller.com/_2_blade_.htm

What Tree

Thanks for all the info, much appreciated.

Gray Beard

My Feedback: (-1)

Good point Carr. I did find a better selection from Graupner {spelling} but it's almost always mail order. They are as tough as MAS too.