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Forum Index : Windmills : down wind turbine
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shawn Senior Member  Joined: 30/03/2010 Location: New ZealandPosts: 210 |
Ok as I still consider myself A newby I will ask what must have been debated before! My mill is all good after two days of punishment so furling works! BUT can not help think why should tail beat the living sh..... out of A mill when RPM dos not hurt f&P mills. my blades were made out of cheap soft pine with nots in all the wrong places and they servived no problem! I spent many hours working out furling and killed mills with blade contact if I had spent half of this time building laminated blades I think they would handle the RPM of A downwind mill. Not to mention all the lost power when furling or if you do not get it facing the wind which is harder than it sounds. My mill has A big tilt away from the tower there are loses in this also I know everybody will say your mill lived why change? how many F&p mills have not lived and downwind must be easyer to build for the beginer? ALL coments welcome |
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| brucedownunder2 Guru  Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
Yes Shawn , I agree with your points.. But ,for some reason ,we, in this forum have ,sort of, concentrated on the furling tail principle. There was recently a posting of someone interested in the downwind developement, I hope he comes back . You are right , you can throw everything at the F@P dual set or even quad , as PhillM did. With success. I've been lazy lately for a year or more , but am now getting excited again with windgennies.Was going to give the whole thing away .. anyhow ,I'll be watching for a reasonable design and will be going that way for a bit of fun Bruce. Bushboy |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Shawn Glad to hear your mill survived, on your comment, I don't believe in furling as part of normal operation, I believe that more damage is done by violent uncontrolled furling than by over speed, the gyroscopic forces the mill is subjected to with the mill wobbling in and out of furl cause structural loading beyond the limits most mills and tower top mounts can stand on a long term basis. I have seen more mills destroyed by furling than anything else. In saying that manual or controlled furling during high wind events can be a desirable thing. Furling to control maximum power out means the whole design is wrong in the first place. I am making my F&P stronger by doubling the bearings and using minimum overhang on the turbine mount, I have spun it to 1500 rpm and there was a little vibration from rotor imbalance so balanced those and now it spins like a top. I do have reservations on the use of ply wood for blades, you are better and cheaper to use ordinary timber as it is twice as strong, if you must use ply then I would suggest that you bias cut it before lamination and use light glass cloth to cover the outside. Balance carefully and it will last for years. All the best Bob Foolin Around |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Hi Shawn I did run a downwind turbine about 12 months back, just for a few weeks. It wasn't my design. Instead of mounting the blades swept back at 10 or more degrees, they were mounted flat, like a conventional upwind design. This meant it struggle to stay, well, down wind! To fix the problem, the manufacturer added a tail behind the turbine, it was a odd setup, but at least it would tract the wind, mostly. The thing that most surprised me was the noise. Standing down wind it was pretty silent, but stand upwind and it made a whop whop noise as each blade passed behind the tower. The tower leaves a wake, and as each blade passed through this wake it lost its clean air and stalled for a fraction of a second, making a whop noise. If the blades were angled back correctly as they should for a down wind turbine, this noise may have not existed. The F&P will generally survive a lot of abuse, it wont burn out thanks to its air cooled coils and high impedance, or fly apart as it is after all a washing machine motor designed to run at over 1000RPM in the spin cycle. But its downfall is it cant be relied on to pull up a wind turbine in strong winds, which is why we depend on a furling system to keep things under control. Yeah a F&P could spin at over 1000 or 2000RPM all day, but the rest of the mill wont last long at such high RPM. The turbine will make a lot of noise, and will eventually fly apart. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| shawn Senior Member Joined: 30/03/2010 Location: New ZealandPosts: 210 |
Thanks for your reply bruce/bob Bruce maby the tri stator should be revisited as A very cheap 1500 watt downwind turbine? Bob I agree with you on blades would only ever laminate with grain going long ways together I would never consider plywood. |
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