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Forum Index : Windmills : pvc extruded blades - vawt
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| Rubes Newbie  Joined: 01/05/2009 Location: Posts: 36 |
I seem to remember someone on the forum trialing the pvc extruded blades on a vawt, I have searched the site extensively and cannot find the thread. Anyone remember this? I am trying to put together a f&p vawt using these blades Basically I am a bit vague on attack angles for the vertical orientation Thanks for any reply's |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5119 |
Here it is here... http://www.thebackshed.com/windmill/forum1/forum_posts.asp?T ID=1703&PN=2. It works ok, but I've not put any load on it yet. It will self start, sort of, some of the time. If I give it a spin by hand, its goes like the clappers, typical H rotor stuff. Very little startup torque, you you would need a smaller Savinous in the middle to get it started. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Rubes Newbie Joined: 01/05/2009 Location: Posts: 36 |
excellent thats the post, thanks Glenn |
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SparWeb Senior Member  Joined: 17/04/2008 Location: CanadaPosts: 196 |
[quote] you you would need a smaller Savinous in the middle to get it started.[/quote] I experimented with that once. I put the savonius on a clutch bearing so that it wouldn't slow down the H rotor once it got going. Steven T. Fahey |
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| Rubes Newbie Joined: 01/05/2009 Location: Posts: 36 |
Hi Glenn, what diameter did you end up with, I am trying 4 blades x 1 meter and starting with a 1.6m diameter. I realise that this is probably way to large (small solidity)but easier to take off than to add. Did you end up using wooden insert? and what sort of screws would have enough holding power. Regards Rubes |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5119 |
Hi Rubes Mine was 650mm diameter, 3 blades. I ended up using aluminum pipe as the insert, it was lighter AND cheaper than a timber dowel. So I didn't use screws, I used rivets. Will be interrested to see how your's goes. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Rubes Newbie Joined: 01/05/2009 Location: Posts: 36 |
Bugger, well its up in a less than ideal spot, self starts some of the time but is painfully slow in a reasonable breeze, I am guessing that 1600mm diameter is way to much, any suggestions appreciated. 
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5119 |
Can you try it without the stator, ie free wheeling? Also if you give it a spin up by hand, will it go faster. I found on my little one it will self start, but only in "drag mode", very slow. If I spin it up by hand, its then in "lift mode" and goes fast. On a couple of occasions I've seen it spin up into lift mode by itself, but usually it needs a hand to get going. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Rubes Newbie Joined: 01/05/2009 Location: Posts: 36 |
Well I have shortend the diameter to 1200mm, now it does not self start nor maintain momentum. Tried a fast hand spin but it eventually slows and stops in a wind speed about 5 - 10 knots, no load on genny, but stator only partially decoged, will try without the stator. and also need to move it to cleaner wind |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5119 |
Its possible the Darrieus is not a good match for the F&P. At your original diameter of 1600 by 1000mm, your wind capture area is only 1.6m2. If you used the blades in a HAWT, and ended up with a diameter of 2.2 meters, your wind area is 3.4m2, over twice as much wind and power. Using your Darrieus's dimensions, its good for maybe 150 watts, which is a bit low to make good use of a F&P. It could still work though, you just need to help it along with a Savinous to give it some startup torque, and have a high cut in speed, so its not loaded until it gets up to speed. This is why you need to do a free wheeling test, to see if it can spin up to a fast speed. Darrieus windmills have bugger all torque until they get up to speed. Watch your head  , they do go fast!
Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Jarbar Senior Member Joined: 03/02/2008 Location: AustraliaPosts: 225 |
Rubes,well done on assembling your VAWT,it looks fantastic.Now the fun bit trying to make it do what you had hoped.I was reading this thread on another site and thought it might help.A bit like a Biplane wing it might develop more lift/power. http://www.vawts.net/index.spark?forumID=125317&p=3&topicID= 28013934 Anthony. "Creativity is detirmined by the way you hold your tounge".My Father "Your generation will have to correct the problems made by mine".My Grandfather. |
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| Rubes Newbie Joined: 01/05/2009 Location: Posts: 36 |
Ok, the saga continues. Finally got some wind, around 15knts, with the stator removed it will self start over about 5 minutes, reaching approx 120 rmp (bit scary up close with no braking system) . Have tried again with the stator in place but will not maintain speed even with a hand start and no load. Have fitted a small dc perm mag motor which chugs along at around 5v @ 100rpm but not much power obviously. Conclusion - 1m x 4 Extruded blades with 1.2m diameter vawt is like Glen suggests probably not suitable with F&P Genny. Just wondering if instead of scrapping it, would increasing the air gap take enough load off but still enable some generation, and if so how much gap should I try? Thanks for any input. |
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