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Forum Index : Windmills : Using those chinese blades
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5116 |
Thinking about these Chinese blades while I wait for a set to arive. I want to make a blade extender hub arrangement to suit the F&P. This will let me move the blades out from the center to gain a larger turbine diameter, and adjust the angle of attack. Did some maths and thought I would share the results. Now I think these blades are about 1.05 meters long and if mounted on the chinese hub, give a blade diameter of 2.2 meters, meaning they are mounted about 50mm from dead center. If I extend the blades out 200mm, this will give a diameter of 2.6 meters. We gain some swept area on the outside diameter, but loose near the middle of the turbine as the blades no longer sweep this area. But this is not worth worrying about, the root area of the blade makes very little power, while its also the most difficult to shape correctly. We can work out the area lost in that first 250mm from the center using Pi*sqr(radius), our radius is 0.125m ( 125mm ) so 3.14 * 0.125m * 0.125m = 0.049 square meters. The area gained on the outside diameter = (Pi*sqr(New Radius)) - (Pi*sqr(Original Radius)), so ( 3.14 * 1.3 * 1.3) - (3.14 * 1.1 * 1.1 ) = 1.507 meters squared. All up, by moving the blades out 200mm we have gained 1.507 meters squared and lost 0.049 meters squared, giving a net gain of 1.458 meters squared. The total area for the standard 2.2 meter blade was 3.8 meters squared, moving the blades out 200 gave a area of 5.3 meters square ( minus the 0.049 we lost near the middle ). The other advantage is the blades need less twist the further they are from center, so by moving the blades out and adjusting the angle of attack to suit, should give a big performance increase and less noise. The mill may spin slightly slower, but would have much more power. Glenn  The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5116 |
Now that I have a set of the blades, I can get stuck into mounting them on the F&P windmill. The hub I've designed up will give a diameter of 2.6 meters, and will let me adjust the blades angle of attack. With any luck I'll get these parts laser cut by the weekend. 
Now to the reshaping, these drawings may not make sense, but I will cut a wedge out of the leading edge of each blade, and then reshape the leading edge where it was cut. This should be a 10 minute job for each blade ( a power file helps ) and will give twist over the blade length. 
This photo of the end section should explain how I'll reshape the leading edge. 
Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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Gill Senior Member  Joined: 11/11/2006 Location: AustraliaPosts: 669 |
Hi Glenn, Just a thought from lookin at your last photo. Propellor blades or wing tips that end abruptly as in the photo generate more noise and ineffiencies through the equalising of pressures around the tip instead of the airfoil creating a vortex. For me, the natural tendency is to get engrossed in the profile and angle and forget to consider the losses around the tip which make that portion of the prop usless and noisy. There are several ways to overcome/reduce this vortex on a wing, but on a propellor the only one I know of is rounding off. Say like the shape of a Spitfire wing tip. I reckon trimming to this shape will add to your improvments and further reduce noise. 
was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5116 |
Yes for sure, I agree. Rounding of the tip will help. I was also thinking of adding a small cigar shaped winglet, but bonding could be a pain and I wanted to keep the modification simple. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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Trev Guru  Joined: 15/07/2006 Location: AustraliaPosts: 676 |
Hi all post added here http://www.thebackshed.com/Windmill/FORUM1/forum_posts.asp?T ID=424&PN=1 Trev @ drivebynature.com |
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| dwyer Guru Joined: 19/09/2005 Location: AustraliaPosts: 574 |
hi tev i just ask gimzo other day about chinese blades and so l will wait and see how Glenn finish modification on the chinese blades 
dwyer the bushman |
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rotorhed Newbie  Joined: 29/01/2007 Location: AustraliaPosts: 36 |
Hi glen I notice that you refer to having your metal parts laser cut. Do you have some one else do it or do you have your own laser cutter. P.S. My farther works for a company called Advanced robotic technology (ART) they make computer controlled routers and plasma cutters. Apparently plasma cutting is a lot cheaper than laser cutting. ( if you live anywhere near Brisbane I know a few of the customers with plasma cutters). Let me know if you want any details. Cheers Christian Marge the Winds are here Ah McCaine............. |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5116 |
Hi Christian. Yes we have a laser cutter here at work, big 5kWatt unit, so I tend to design with laser cutting in mind. Plasma would work just as well for most of the parts. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Magooly Newbie Joined: 25/01/2007 Location: AustraliaPosts: 4 |
If you are going to use the Chinese blades, take care, see photo. The bolts were still in place but blade was not. I am thankful it didn't go thru one of my solar panels.  |
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| windman Newbie Joined: 02/12/2006 Location: Posts: 19 |
the bergey people use straight pultred blade with success those china blades look very similar, should work without too much tampering |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5116 |
Thanks Magooly, I am a little worried about water ingress into the fibreglass. Trev, could you suggest a way to seal these blades once they are ready to mount on the windmill? I was going to paint them, but I wonder if there is something I should do to those mounting holes first? Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Trev Guru Joined: 15/07/2006 Location: AustraliaPosts: 676 |
Glenn, It is not necesary to do anything? nothing is going to change its strength. Water will not effect it. However the resin will no doubt be polyester which will deteriorate is sunlight, so a coat of paint to stop the sunlight getting to the resin will make them last longer. The best (longest lasting) paint is two pac and possibly should have an etch primer underneath. Anything will do though. Mogooly, any ideas why it broke?? Trev @ drivebynature.com |
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windstuffnow Newbie Joined: 30/06/2006 Location: United StatesPosts: 31 |
Glenn, You can use a UV protecting paint made for the ole rag wing aircraft or newer composite kits then paint over the top of it with any color you need. A cloth covered or composite wing without the UV protectant will last 2-3 years in sunlight where the protected cloth/composite will go 15-20.... big difference! I only know of a few places here in the states that sell it, wicks aircraft or aircraft spruce and specialty but I'm sure there are a few places over there that carry the stuff. I've used it on quite a few planes I built using the stits process of covering the wings. Never leave the runway without it! Have Fun Windstuff Ed |
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wind-pirate Senior Member Joined: 01/02/2007 Location: CanadaPosts: 101 |
Hi all Could you use a gel coat like they put on boats? you can put colour dye in the resin and make it permanent. Ron THE Pirate. stealing wind & solar energy is fun |
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| Trev Guru Joined: 15/07/2006 Location: AustraliaPosts: 676 |
Gel coat is thick and impossible to spray real smooth. The best is kind of like orange peel texture. Gelcoat also remains sticky for proper adhesion of glass laminating. It needs wax in styrene to get it to set dry. I once had to resurface a 25 foot ocean racer with flowcoat (gelcoat with wax in styrene), all over. It was somewhat rippled. Sanded for proper adhesion, and 5 layers with a roller. Sanded off again to get it straight. Then one fine spray of flow coat (orange peel finish). Sanded with finer paper and then with finer paper again. Finished of with the buff and cutting compound. Not exactly an exciting exercise. Paint is by far easier to cover the blades. Trev @ drivebynature.com |
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