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Old Jun 11, 2015, 06:56 PM
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What do the numbers mean on SF Props?

Ever since I got my Gamma 370 Pro, I've been trading off between the 8x6 and 9x7 props. I noticed the 8x6 gives a bit more torque, while the 9x7 gives more speed. Or is it the other way around... I'm not sure. So, here's my question. What do the numbers mean on a prop type? One of them has to be length...right? I'm a bit new to the hobby, and I wanna learn. Thanks

~GM
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Old Jun 11, 2015, 07:39 PM
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First is diameter, second is pitch. Larger diameter gives more thrust/acceleration. Larger pitch gives higher speed.
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Old Jun 11, 2015, 08:39 PM
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Thank you! I've always wanted to know...
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Old Jun 13, 2015, 05:00 PM
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for propeller information :

http://www.rcgroups.com/forums/showthread.php?t=2265005
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Old Jun 17, 2015, 07:51 AM
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Quote:
Originally Posted by GamerMitch View Post
Ever since I got my Gamma 370 Pro, I've been trading off between the 8x6 and 9x7 props. I noticed the 8x6 gives a bit more torque, while the 9x7 gives more speed. Or is it the other way around... I'm not sure. So, here's my question. What do the numbers mean on a prop type? One of them has to be length...right? I'm a bit new to the hobby, and I wanna learn. Thanks

~GM
I have the same Gamma Pro and you want to use the 8/6 prop with 3 cell batteries and the 9/7 prop with 2 cells. If you use the Larger 9/7 with 3 cells it could very well go over the 18amp rating of the ECS.
There are 2 Threads on the Ares Gamma in ParkFlyers forum with plenty of reading. The Plane flies Nice for the $$$.
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Old Jun 17, 2015, 09:58 AM
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The important thing to know is that depending on the manufacturer and model number, of a collection of 10x7 propellers of all sources will differ radically from each other in performance. Talking about a propeller by diameter and pitch only is about as informative as talking only about what color it is.
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Old Jun 18, 2015, 10:11 AM
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The important thing to know is that depending on the manufacturer and model number, of a collection of 10x7 propellers of all sources will differ radically from each other in performance. Talking about a propeller by diameter and pitch only is about as informative as talking only about what color it is.
An excellent example of exaggeration!

While it is true that performance does vary from manufacturer to manufacturer knowledge of diameter and pitch will at least get you in the ballpark with regard to the kind of performance you can expect.

I standardized on APC props many years ago. I was using Master Airscrew but once I tried a same pitch APC I realized the MAs make pretty good coffee stirrers. My favorite props back then were Rev Up but they got discontinued. The APCs perform very well without breaking the bank, a factor to me because I like to try lots of different size props until I find the one that flies a plane best.

Not sure how relevant tachometer readings are in this era of brushless electric motors and nnnn kV, but in the fuel daze they could be very enlightening. My tach fried after about twenty years of yeoman service around the time I got into modern electrics.

TP
AMA 59376

ps - APC props are grey.
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Old Jun 18, 2015, 11:44 AM
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Originally Posted by Tepid Pilot View Post
An excellent example of exaggeration!

While it is true that performance does vary from manufacturer to manufacturer knowledge of diameter and pitch will at least get you in the ballpark with regard to the kind of performance you can expect.

I standardized on APC props many years ago. I was using Master Airscrew but once I tried a same pitch APC I realized the MAs make pretty good coffee stirrers. My favorite props back then were Rev Up but they got discontinued. The APCs perform very well without breaking the bank, a factor to me because I like to try lots of different size props until I find the one that flies a plane best.

Not sure how relevant tachometer readings are in this era of brushless electric motors and nnnn kV, but in the fuel daze they could be very enlightening. My tach fried after about twenty years of yeoman service around the time I got into modern electrics.

TP
AMA 59376

ps - APC props are grey.
Holy cow, Tepid. You say my statement is "excellent example of exaggeration!" and then you support my statement, calling a MAS prop a "paint stirrer." I agree and I'm glad you agree that my "exaggeration" was spot on accurate. MAS was one propeller singled out in Professor Selig's UIUC study of propellers at low reynolds numbers for similar flogging.

I' ve also standardized on APC props as they seem to hit the price/efficiency curve perfectly.
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Old Jun 18, 2015, 12:07 PM
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MAS was one propeller singled out in Professor Selig's UIUC study of propellers at low reynolds numbers for similar flogging.
While I do ascribe to the teachings of Professor Longhair I find Doc Selig's representations to be entirely too scientifical for my poor, befuddled brain to comprehend.

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I' ve also standardized on APC props as they seem to hit the price/efficiency curve perfectly.
So, it turns out we a couple of wise guys.

TP
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Old Jun 19, 2015, 05:55 PM
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While I do ascribe to the teachings of Professor Longhair I find Doc Selig's representations to be entirely too scientifical for my poor, befuddled brain to comprehend.
Yeah, he gives density a whole new meaning, doesn't he? But just remember that academic is nothing but a foreign language. You gotta feel sorry for their inability to speak English!
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Old Jun 19, 2015, 08:57 PM
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But just remember that academic is nothing but a foreign language. You gotta feel sorry for their inability to speak English!
Depends on who you ask. I think my English is pretty good... but some of us DO feel sorry for those who can't speak science
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Old Jun 21, 2015, 04:08 PM
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Depends on who you ask. I think my English is pretty good... but some of us DO feel sorry for those who can't speak science
It's always best to be multilingual. Why was Carl Sagan the best? It was because he could translate scientificese into English without losing precision or content in a way that people only speaking English could marvel at. The best science popularizers are great translators.
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Old Jun 22, 2015, 09:02 PM
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"MAS was one propeller singled out in Professor Selig's UIUC study of propellers at low reynolds numbers for similar flogging. "

Who's Prof Selig? How low a Reynolds number are we talking about; and how does that relate to the rpm range we normally use these propellers for?

So, to get back to the thread topic; should there be a written warning on an SF propeller "do not use below a Reynolds number of 2, 500"?
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Old Jun 23, 2015, 09:11 AM
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Who's Prof Selig? How low a Reynolds number are we talking about; and how does that relate to the rpm range we normally use these propellers for?
Doc Selig: http://m-selig.ae.illinois.edu/people.html

The Study: http://m-selig.ae.illinois.edu/pubs/...Propellers.pdf

In case you really want to know.

TP
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