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I want to try 3 blade prop. Am I getting the right size?

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Old 09-24-2012, 09:05 AM
  #1
Sherv
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Default I want to try 3 blade prop. Am I getting the right size?

Hey guys I've been doing some research online about switching from 2 to 3 bladed props.

I hear the rule is to drop 1 size in diameter when you go 3 bladed prop but keep the pitch. And then I've found a simple formula to calculate prop load to figure out what size to use.

This is the simple formula i've found.

D x D x D x P x Square root (N-1), where N = the number of prop blades

My plane is a 1.8meter Cessna 182 with a G32 600kV motor (similar to eflite power 32)
http://www.hobbyking.com/hobbyking/s...dProduct=19025

The stock prop on this cessna is 14x7.
Based on this formula the load factor of the stock prop is 14 x 14 x 14 x 7 x 1 = 19208

If I were to drop diameter by one going 3 blade then it would be 13x7 3 blade
13 * 13 * 13 * 7 * 1.41 = 21749

and a 3 blade 13x6
13 * 13 * 13 * 6 * 1.41 = 18642


Should I just buy a 13x6 and a 13x7 prop? Or is the formula wrong, should I be calculating this differently?

Any help would be appreciated.

I dont have to go 3 blade, I just felt the cessna would look nicer with a 3 blade.
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Old 09-24-2012, 12:11 PM
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jetmech05
 
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Default RE: I want to try 3 blade prop. Am I getting the right size?

I've always heard down a size in diameter up a size in pitch
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Old 09-24-2012, 01:59 PM
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Default RE: I want to try 3 blade prop. Am I getting the right size?

It is down an inch in length then up one inch in pitch. This used to be posted on manufactures web pages but in recent years some of them just state to go down one inch in length. I still go down in length and one up on pitch when going from a two blade to a 3 blade. Most people can't tell the difference anyway so either or. Finding the size you want in a three blade is difficult in most hobby shops so I tend to pick them up if I can get close to what I want. If not, then I have to go on line. No one stocks three blade spinners either so I have to mail order for them.
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Old 09-25-2012, 05:01 AM
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Default RE: I want to try 3 blade prop. Am I getting the right size?

Sherv,

Since you are experimenting you can't do it with just 1 prop.
I would by the three recommended here; 13x6, 13x7 & 13x8.
Now you can see which one makes your plane fly the best.

Tell us how it goes.

Good Luck,
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Old 09-25-2012, 05:13 AM
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Default RE: I want to try 3 blade prop. Am I getting the right size?

G'day

A mate recently bunged a Saito 100 in a Kyosho Calmato (60 size). Normally I would have suggested a 14 x 6 as a starting point but this had too little ground clearance so we put a three bladed 13 x 7 on the motor. It works well and flies the model as I would have expected the 14 x 6. The old tried and true formula ( down one in length and up one in pitch) worked for us.

Mike in Oz
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