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Third number in prop size??

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Old 03-09-2006, 01:29 PM
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Backwing
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Default Third number in prop size??

Trying to find an 18x10 prop at the LHS, they had an 18x8x4.
I've seen this on some other props, what does the third number mean?
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Old 03-09-2006, 01:44 PM
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Default RE: Third number in prop size??

Number of blades?
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Old 03-09-2006, 01:55 PM
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Default RE: Third number in prop size??

If it's a 18x8-4, it means 18" diameter and the pitch (angle of blades) progresses (regresses?) from 8 at the hub to 4 at the tips.
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Old 03-09-2006, 02:29 PM
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Don M.
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Default RE: Third number in prop size??

I don't think they make such a thing as a 18 - 8 - 4 I think you'll find it is a 18 - 8 - 14. Some engines respond very well to these multi pitch props, the old Quadra's were one of those engines.
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Old 03-09-2006, 03:37 PM
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Default RE: Third number in prop size??

Your right, I think it was 14.
Now I understand, so what would be the benefit?
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Old 03-09-2006, 04:17 PM
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Default RE: Third number in prop size??

In the case of an 18x8x14, the last number is how many times more expensive it is than a regular 18x8

I believe the idea is to get a big throw on the ends without making the prop hub too thick to mount.
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Old 03-09-2006, 04:27 PM
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Default RE: Third number in prop size??

Different bits of the prop work well at different RPM's & different airspeeds. There is always some portion of the prop that is doing it's thing fairly well at any one time. They are the ultimate compromise -- they don't do anything particularly well, but they don't do anything particularly badly either. The all-season tires of propdom.
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