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Old Jan 29, 2009, 10:58 AM
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A unique request - 3 blade prop as wind turbine

Hi.
I run the renewable energy company gotwind

I am looking at making a small wind turbine and need some help in finding the correct 3 blade propeller, used in reverse to power a home made alternator, swept area diameter of around 12"

I have seen good results with the Graupner 11" x 7 (I don't actually know what these numbers refer to, diameter i assume??)

I have also tried a 'Master Airscrew' 11" x 6 two blader which caught the wind better, Im assuming the second number refers to pitch?

So I guess a 12 x 6 three blade propeller would be a good step forward?
I'm looking for 1000 rpm in a 10 m.p.h windspeed.

Any help appreciated.

Thanks

Ben.
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Last edited by gotwind; Jan 29, 2009 at 11:08 AM. Reason: Newbie
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Old Jan 29, 2009, 12:14 PM
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Ben,

The first number is diameter in inches, the second is Pitch (6 shoudl signify that the prop would move 6 inches forwar per revolution if their wsa no slipage)

You might need to go to a 16x?? prop (I dont use props above 12" for my planes)
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Old Jan 29, 2009, 12:40 PM
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You could use something like this:
http://www.hobbycity.com/hobbycity/s...idProduct=4351
4 blade
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Old Jan 29, 2009, 01:14 PM
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Model props are rather inefficient at being turned by the wind. You'd want to get a "SF" style and re-pitch it to a higher pitch. (if they make a SF style 3-blade at 12 inch dia)

As to the desired RPM... "Pitch speed" is appx rpm/1000 * pitch. So aiming for 1000 rpm at 10 mph. 10 inch pitch is pretty close. The drag of whatever you are driving will give you a bit less actual rpm.

So you will want appx 9.5 inch pitch.

A "glow style" (probably easier to find) will not be as efficient for your purpose as the SF style electric prop.

APC would make the props to order, and would be cost effective if you want a lot of them.
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Old Jan 29, 2009, 01:46 PM
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Great answers, thanks.

Wow this is an active forum, I run my own forum on renewable energy DIY ideas, but it's not as busy as this one.

From what I can gather, the lower the pitch number, the more angle at the root of the blade, that was why the number '6' started up quicker than the '7' pitch prop? - I know diameter has a huge impact on performance (with wind turbines), so maybe a 14" or 16" diameter might be better.

I am U.K based, and am completely new to RC, so terms like "SF" and "glow style" prop are a little lost on me.

Thanks again.
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Old Jan 29, 2009, 02:58 PM
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SF is slow fly prop...the blade tips are wider for more thrust which in turn should turn with less wind.

glow style props are heavier and thicker so that would be bad in terms of weight.
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Old Jan 29, 2009, 04:23 PM
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Take a look at these GWS slow fly props. They are very light weight and are very wide and go up to a 15 x 10. They are two bladed but maybe two 90 off might work.

http://www.bphobbies.com/view.asp?id=V576658

Maybe something like a toy pinwheel might also suit your needs.
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Old Jan 29, 2009, 04:43 PM
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I think the 'slow fly props' are the way to go, maybe..

I guess, I am after the reverse of thrust, let the wind take care of that - the airofoil section with ready made props appeals to me, 3 bladers in particular - it reduces gyroscopic forces in yaw (turning out of the wind) from an even bladed prop - 2/4/6 e.t.c

Odd numbers of blades is the norm with wind turbines, 3 or even 5 blades.
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Old Jan 29, 2009, 08:54 PM
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Basically, SF is Slow Flyer. Glow Power is, well, glow power, or basically IC (Internal Combustion) engines, that require fuel to run. Glwo is different then gas, as it's octane level is higher then gasoline.

SF props work excellent on slower turning motors, which is important for slow flight for models. They grab the air pretty good, when being powered. The air should grab them well on a ball bearing supported shaft.
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Old Jan 29, 2009, 11:15 PM
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another two cents

Not that I am an expert, but wouldnt a "squirl cage" work better on a small power generator? wind direction ceases to be an issue and the surface area to the wind increases dramaticly.

Squirl cage: like the blower inside of a hairdrier.
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Old Mar 29, 2009, 10:12 PM
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Lower pitch will be better for a prop that is pushed by the wind. Prop with a 6 inch pitch at 1000 RPM will have a pitch speed of 5.68 mph A prop with a 7 inch pitch at 1000 RPM will have a pitchspeed of 6.628 mph So in a 10 mph wind, with a perfect world & no prop slip, you would see 1508 rpm the 6 inch prop would turn at 1760 rpm. You'll see less than that on a generator because of the friction of bearings & the load from generating electricity. Pitch should be quite low for wind turbines, whereas the diameter of the swept area is the more important factor. That gives you the torque to generate more current. The pitch gives you the RPM to generate a higher voltage.

Never have looked into micro turbines before since the amount of electricity being generated is very small, but it would be an interesting school science class project.
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Old Mar 29, 2009, 10:14 PM
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Oh, one other thing, assuming you can't find a commercially made propeller to suit your need, you can always take 3 props & make this.


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Old Mar 29, 2009, 11:01 PM
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Actually, you can make the 3-blade prop from just 2 props... and have one blade left over.

Works OK for relatively low RPM and electric drives. Don't do it for a glow engine. Should be fine for the wind powered application.
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Old Mar 29, 2009, 11:35 PM
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Ok, heres a couple of things that i'll throw in.

HC has some 3 blade props in RH and LH rotation although the bigest one is 9 x 7 so may be a bit small for what you require.


There are also several 'variable pitch' set up's available which would allow you to 'tune' the pitch for what you are trying to achive.



you could also run through a gearbox which may help
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Old Jul 23, 2015, 08:16 PM
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Quote:
Originally Posted by Nathan Schmoekel View Post
Not that I am an expert, but wouldnt a "squirl cage" work better on a small power generator? wind direction ceases to be an issue and the surface area to the wind increases dramaticly.

Squirl cage: like the blower inside of a hairdrier.
That's what came to mind to me. If I were to do any DIY wind generator I would go vertical.

http://www.remnet.com/Wind%20Energy/Hesperia1.jpg

Neighbor down the street has one of these on his garage:

http://cleangreenenergyzone.com/wp-c...nd-turbine.jpg
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