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Forum Index : Windmills : 5 Blades vs 3 Blades
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| cobo351 Newbie  Joined: 18/12/2009 Location: United StatesPosts: 34 |
Hi All, I'm new to wind turbine hobby and from what I've read on other sites 5 blades will start turning with less wind than it would take to turn 3 blades. However 3 blades will turn faster than 5 in the same wind. Anyone know this to be true? Since Michigan doesn't get an overabundance of windy days I’m wondering if turning slower more frequently would be more efficient. I’m using a servomotor that starts making power at about 200 rpm (I’m guessing). I have not seen much about 4 blades any good reasons why? |
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KarlJ Guru  Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
Yes 5 blades will start turning earlier but if the turbine doesnt make power until 200rpm 3 blades is the answer. I cant see any good reason why 4 blades is not OK, check out the breezy 5.5 Having the mill blades matched to the generator is the answer, rotational speed is almost irrelavent as you know big mills turn slowly and make heaps of power and the Air X turns really fast and makes very little power. As far as I can tell its about matching the blades to the motor you're trying to drive. Without getting too complex, it looks to me like a 3m diameter rotor will make 700W-3KW at the same rpm, depending on what motor it is bolted to! If the wind resource is marginal, then the tower is critical, as a 3m increase in height will produce a significant increase in output as the windspeed increases with height. Looks to me like most windturbines on this site start out as hobbies and grow into something useful no matter what their size. some more info is the go, how big is this servomotor, what size rotor are you looking at etc etc Luck favours the well prepared |
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Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Have a read of a thread "Newbie - why 3 blades?" back a page or two in windmills as Oztules gave a very good explaination on this. Pete. Sometimes it just works |
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Bub73 Senior Member  Joined: 10/12/2009 Location: United StatesPosts: 116 |
Hi all; I'm new to the fourm here, a rather old newbie and from Michigan also. I am using a delco 10si with hyper spin 5's to help out my small solar system on our dark winter days and it seems a good match to me.12 volts at 160rpm useful voltage at 200+. I have tried several 3 blade sets including one set homemade, but I had very poor startup underload (battery's down lights on etc.) until I tried the hyper spin 5's. They come with a 90 day money back guarantee this is what got me to try them. I can't say they will work for you, as KarlJ pointed out your motor, load and wind maybe different than mine and your Blades need to match your motor,load and wind conditions. I must say I enjoy this site and its free exchange of ideas and info very much. Bub73 |
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MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Cobo351 I have not found oztules' article, but I can tell you a few things from personal experience: A spinning windmill blade array is much like a spinning bicycle wheel; it creates something called "angular momentum". When the wind direction changes, the yaw control (tail) changes the orientation of the windmill into the wind (up-wind machines). This horizontal rotation works against the angular momentum created by the spinning and must overcome the angular momentum before the thing turns about the y axis. That said, a 2-blade arrangement will fight the yaw when the blades are in the horizontal position and spin freely when they are in vertical. You will notice two-bladed, up-wind mills tend to "bounce" as they yaw. This is due to their position relative to the x-y axis as explained. A 4-blade array has more starting power, but again, there is a 'bounce' created whenever either of the (now 2) blades are in a horizontal position. The bounce will be less noticeable in a 4-blade arrangement. Remember the P-51 Mustang airplane? It used a 4-blade prop and it didn't seem to make any difference in the way the plane handled. My father owned a P-51 once, but I never flew in it, so I don't have any hands-on experience from that perspective. I've found that odd numbers of blades are best. A 3-blade arrangement puts only one blade parallel to the x axis at one time an does not bounce when the mill yaws. As far as the number of blades is concerned, the greater the number of blades, the more "compression" the thing will create. A 2-blade or 3-bade arrangement is able to spill used wind before the follow-up blade has a chance to compress it and therefore spins faster than a multiple-blade model. High-compression blade patterns (multiple blades) turn in less wind, simply because they present a greater wind-area (footprint) against the wind. These blades will create compression of the spill-air between consecutive blades and therefore are limited to their top-end speed, but like I said, are much more "powerful"in a start-up situation. A 3-blade mill will spin fast and depending on the pitch and blade length can also produce a great deal of power as well. Overall, the 3-blade design seems to be the way to go both from a starting torque position as well as a speed range and power point of view. The 3-blade design is the industry standard for the most part. Hope this helps you out. Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| cobo351 Newbie Joined: 18/12/2009 Location: United StatesPosts: 34 |
Thanks for the replies guys, that’s a lot of good info to get back from what little info I provided. I think I will try to make both a 3 and 5 blade. |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5124 |
Here's that post about 3 blades. http://www.thebackshed.com/windmill/forum1/forum_posts.asp?T ID=2168 Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| lichong712 Newbie Joined: 04/01/2010 Location: GermanyPosts: 8 |
I have ever find some tips on answer.yahoo, one says The most efficient wind turbine is one blade turbine. The less blades,the more efficient wind turbine is. If you are intent to reduce your power bills,why not pay wind power cost? |
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oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
No. The single blade is not the most efficient. The drag from the counter balance and higher TSR is an efficiency drag, but the main fault is shocking dynamic balance caused from uneven loading. The back loading is extreme on the blade side, and nil on the counter weight side. Add to that the tower effect, and it is dynamically difficult with cranky yawing characteristics. (teetering). But .... and there is always a but, the upside is that the alternator can be much smaller and more efficient electrically due to the higher RPM from the blade. So even with the big upside of electrical efficiency and smaller alternator and less blades to fabricate..... they still don't consider them a starter in the commercial power generating world..... tells you which one is efficient. Just follow the money trail of the people who generate electricity for a living..wind farms. How many blades do they use? Single bladers are just a curiosity and not contenders. ..........oztules Village idiot...or... just another hack out of his depth |
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Perry Senior Member Joined: 19/11/2009 Location: Posts: 190 |
I guess that's kinda one of the problems with the anonymous internet. Anybody can write something, right or wrong, and it gets perpetuated. Wikipedia/youtube/etc have done a tremendous job of dumbing us down. Perry |
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