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confused about props

Old 12-03-2007, 05:16 PM
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Join Date: Nov 2007
Location: Washington
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Default confused about props

I know that I am a long way off from upgrading anything, but as I look at parts I am confused.

I see 2 types of electric props available and I don't understand what their application difference is.

Cat 1- electric ie 10X5E
Cat 2- SF (slowflyer) electrics, ie. the 10x4.7SF.

can someone please explain to me what the differences are, because it seems to me that the difference in a 4.7 pitch and 5 pitch is insignificant and I don't understand what qualifies a plane as a SF plane vice a standard E plane
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Old 12-03-2007, 06:38 PM
John Canfield
Join Date: Oct 2006
Posts: 106

The slow fly props aren't quite as robust and are not designed for larger planes and faster prop speeds. All of my planes are around 16-20 ounces and my motors are all less than 1,000 kva and I use 3s packs. My planes are all suitable for SF props.

Once you get into the 30 and 40 ounce and up planes with larger props and 3 or 4 cell packs, using a SF prop would be risky due to the potential for self-destruction.

There are also some aerodynamic differences between SF and E props; maybe somebody else will point those out.
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Old 12-03-2007, 06:40 PM
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The basic difference is the slowflyer prop is wider.
The blade chord is much wider than a regular E prop.

This allows the prop to get more bite at low speed, more thrust, without going fast.

The slowflyer props require more power to turn them the same speed as an E prop.

So you will draw more current with the slowflyer prop.
The slowflyer props usually have an RPM restriction as well.

So the E props are a little better for higher speed planes.
The slowflyer props are better for the 3D types that are slow and a lot of thrust.
Yes the props you chose are very similar in pitch, there is some overlap in pitch amounts.

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Old 12-03-2007, 08:11 PM
Thread Starter
Join Date: Nov 2007
Location: Washington
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when you say higher speed, I assume you that you mean airspeed.

So my next question is when what breakpoints would be appropriate for shifting from SF to and E prop. Say for example I wanted to upgrade to brushless, how would I select SF over E, or vice versa.

next question- is there single source document (links or books) that covers all these basic design and building things that I could read up on. I am too much of an engineer (not aero though) to not at least attempt to fully understand why things are the way they are.
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Old 12-03-2007, 09:01 PM
Sky Sharkster
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Default Adding To The Confusion

Hello Meesier, Welcome to Wattflyer!
Paul and John have provided good infromation already, I will just add a link to APC Props that gives the suggested RPM limits;
As you can see, the SF props are not recommended for as high an RPM application as thin electric.
But (as with many electric questions) there's no hard-and-fast rule for exact plane size or motor output to define which prop to use.
One big difference between SF and thin electric-besides the blade shape-is the stiffness of the blade material. A SF prop is thin and can be easily bent in all directions. A thin electric is much harder, thicker material, and won't bend without snapping.
Now, we know that blades flex or "unload" at RPM. At a high enough RPM, a flexible blade will begin to straighten out in pitch, or "flatten".
For a slow-flying plane with (fairly) low RPM, this flattening is a trade-off. We are willing to give up a bit of thrust for the wider blades and the fact that these blades will absorb a landing shock (by bending) before they break.
On a faster model, we are not willing to make these compromises. SPEED is the criteria, and blade unloading, flex or flattening are unacceptable. Of course they break easier upon landing, but by then we've satisified the need to go fast, so replacing a prop is just part of the price!
Maybe it will be easier to determine which prop to use if you think of the props as "Slowflyer" and "Fastflyer".
Again, I know this doesn't answer your question, but perhaps provides another signpost along the way!
Good Luck,
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