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Old 06-04-2005, 12:45 AM   #1
IAR 80
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what prop?

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i'm building a WWII fighter, and wondering what 3 blades prop to use for a .91 4 stroke engine, i'm intending to use ?

any help is appreciated.
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Old 06-04-2005, 08:55 AM   #2
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First you need to find out what 2 blade it's supposed to be running, check the manufacturers web site.

I beleive the general rule for 3 blade props is 1" smaller in diameter and down 1 in pitch.

I was using an 11x8 on my T-34 with a Saito 56, I went to a 10x7 3 blade. The engine turns at 10,000 rpm and pulling about 3 1/2 lbs of static thrust with both props.

Hope this helps.

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Old 06-04-2005, 09:12 AM   #3
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try this after you know your 2-blade size:
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Old 06-06-2005, 07:31 PM   #4
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thanks for the informations.
manufacturer's recomandations are 13x8-14x6 for the prop.so, i should use like 12x8,13x5 for 3 blades.

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Old 06-07-2005, 02:00 AM   #5
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I full aggrement with Chris...this is waht i am told too by many..

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Old 06-07-2005, 05:40 AM   #6
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On the Master Airscrew 3-Bladed prop packages they recomend decreasing Diameter by 1 and increasing Pitch by 1.

Thus if you were using a 15 x 6 - 2 bladed you would go to a 14 x 7 three bladed prop.
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Old 06-08-2005, 12:31 AM   #7
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ooops, now i'm kinda confused.what i figured out, for sure, is that i have to reduce the size of the prop.about the pitch,....hmmm, dont know.

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Old 06-09-2005, 12:10 PM   #8
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Using the example of a 12"X 8 prop, the theory behind pitch is that under perfect ideal conditions, your plane will advance forward by 8" for every revolution of the prop.

Therefore whether its a 2 blade or three blade, the plane would still, theoritically, move forward by the amount of the pitch factor, in this case 8". So I cannot see having to change the pitch regardless of the number of blades. However, diameter does make a difference. So just follow the chart above for your conversion and you won't go wrong.

In your case, you would normally use a 13" X 8 two bladed prop, so just go down 1" in diameter and leave the pitch the same. Use a 12" X 8 three bladed prop. This is how I understand it anyway!
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