Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

APC prop hub numbers???

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Old 03-28-2014, 03:24 PM
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James c harrell
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Default APC prop hub numbers???

I was told on this forum to go to a APC prop over the MAS and it was great advice. One thing I would like to know though is what does the number on the hub of the prop mean. Most of the ones I buy have C-2 but I needed a 9-8 and bought one at the hobby shop and went to put it on at the field and noticed it said C-1. Looking at it I saw that it had a different sweep to it. What does these numbers mean?
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Old 09-08-2014, 02:36 PM
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The numbers are what the CNC program computes the pitch and length to. when the molds get worn out they re-machine the molds just by a little and the program sees that its a different shape and assigns a number to it. You will also notice on the C-2 and up props will have very small mold line on the prop edges that you can see.
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Old 09-08-2014, 04:33 PM
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I saw a big difference in the rpm between an APC 11x10 C-1 and C-2 props. The C-1 seemed to have more material in the inner 1/3 to 1/2 of the blade and would not turn nearly as many rpm as the C-2 11x10 on the same engine, same fuel with back-to-back runs.
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Old 09-08-2014, 04:44 PM
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yes i would think so and if you also notice the last number was more than likely higher also since it computed a slightly higher pitch on the prop. so you were running a 11x10.125 or some thing along those lines.
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Old 09-18-2014, 01:43 PM
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As I understand it, the increase in C-numbers simply represent the next version of the prop. It doesn't mean the pitch has changed. A 9x6 C-1 is a 9x6. A 9x6 C-2 is still a 9x6.

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Old 09-18-2014, 04:50 PM
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Kurt, I think you are correct, based on the props I have. The pitch on the 11x10 C-2 checks at 10" on Prather guage, as does the C-1. The C-1 just has a less efficient (more load for same pitch) blade configuration, as far as I can tell.
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Old 09-22-2014, 09:47 AM
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what you guys are not understanding is that the shape, width and length of the blade has changed. With this the pitch has changed ever so slightly. Some of the "C-1" props may have a for instance a 178 and the "C-2" props will have a 179 number for the pitch.

over time the molds of the props wear out and need to be cleaned up. when the clean up is dont on the CNC machine the props grow just a tiny bit. A larger wider cord will have a thicker airfoil hence the slight drop in RPM.

What ever number follows a letter is the next redesign of that prop. there are a few exceptions like on the 14x13N props that have the same C-1 but just have a redesigned hub.
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Old 09-22-2014, 12:03 PM
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airraptor, help me understand why, if the C-2 prop is the later version, the C-1 turns lower R's than the C-2.........
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Old 09-22-2014, 12:42 PM
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it could have been a complete re machine on the mold. They take a block of aluminum and machines the prop in it. Don't assume that they take every mold and re-machine them. It could be from a different airfoil. What prop you talking about and i will look at the numbers to see why it turns more.

If it is a new mold then he may have updated the airfoil to a more efficient one.
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Old 09-23-2014, 07:01 AM
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The prop in question is the APC 11x10; the "slower" one is marked C-1, the other is marked C-2.

I will try to make an accurate side by side camparison of physical features and post dimensions (if I can measure accurately enough) later.
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Old 09-23-2014, 07:26 AM
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Originally Posted by airraptor View Post
what you guys are not understanding is that the shape, width and length of the blade has changed. With this the pitch has changed ever so slightly. Some of the "C-1" props may have a for instance a 178 and the "C-2" props will have a 179 number for the pitch.

over time the molds of the props wear out and need to be cleaned up. when the clean up is dont on the CNC machine the props grow just a tiny bit. A larger wider cord will have a thicker airfoil hence the slight drop in RPM.

What ever number follows a letter is the next redesign of that prop. there are a few exceptions like on the 14x13N props that have the same C-1 but just have a redesigned hub.
I happened to be corresponding with a contact at APC when I saw this thread, so I asked him to clarify. Here is his response:

"Not sure who wrote this, but none of it is true. The hub lettering "C-1" etc. has nothing to do with the hub design or blade shape. It was an internal software version designator and is no longer used.
The number of the blade that is being referred to (178) is the metric equivalent of the pitch.
I.E. There will be a 9 X 6 E stamped on one blade and the other side will have the metric equivalent, 229 X 152 stamped on it.
There is absolutely no change to the propeller shape when the mold is resurfaced. It's like cutting a brand new mold that is identical to the previous."
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Old 09-23-2014, 02:31 PM
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Nothing like throwing facts into a dsiscussion..............
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