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Forum Index : Windmills : Vane tail length?
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The_Professor Newbie  Joined: 22/04/2007 Location: United KingdomPosts: 11 |
Progress is slow, but I am making steady progress 
Just wondering what the guys here thought on vane tail lengths? I'm going to use a three phase PM motor (a bit heavy, but it was the right price - free ) as my generator with a blade diameter of around 2.5 - 3.0 meters. I've set the tail hinge at 15 degrees (a figure found in one of Hugh's books). I couldn't decide on an off-set angle, so I've made that adjustable (0-45 degrees). What I can't decide on, it the length to make the vane tail? So does anyone have any suggestions please?
Thanks in advance of any help and guidance
Here is my set-up so far (the genny isn't bolted in position) 
The cable will eventually run down the centre of the mast. The genny body is 150mm (6")square. |
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Gill Senior Member  Joined: 11/11/2006 Location: AustraliaPosts: 669 |
G'day Prof, Nice compact design you have there. Looks good. You've pretty well echoed the needs of a fellow builder, philmountains, also from the UK. , just 6 topics ago. With the variety of generators you have to use, every project is a one off. At least in this part of the world we have the F&P that lets us compare dimension changes. Your furl pivot will need to swing out say to the max of your adjustment, 45deg. On my new mill in progress I have it set at 70deg(unproven Gill theory). The tail area,angle and length can all be calculated from prop and offset then furl data calculated, which ,more often than not, need you to go back to the start again. After a while you throw the pencil and calculator away and say this set of dimensions look good, lets go with that. Your design shows innovation so I reckon you have an eye for the overall proportions of components. And best educated guess builds dam near all DIY windmills. Check out the other post as I gave tips you may find useful. was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
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philmountains Newbie Joined: 17/01/2006 Location: United KingdomPosts: 24 |
Hi Prof Your design looks great,it makes me want to scrap mine and start again!!!I welded up the tail bearing the other night to gills recommendations,THANKS GILL, but my mount is huge like some Minny aircraft carrier. any Chance in posting some more pics please. See you Phil  |
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| The_Professor Newbie Joined: 22/04/2007 Location: United KingdomPosts: 11 |
The reason I started off at zero, is because the wind isn't too great round here, so setting at 70 deg may be a bit extreme. I'll have to get it up to see what it does. You'll find my energy related projects here http://www.sunandwindy.bitz.me.uk However the generator platform pickies can be found here http://sunandwindy.bitz.me.uk/mast_head/Mast_head.htm |
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| philmountains Newbie Joined: 17/01/2006 Location: United KingdomPosts: 24 |
Thanks Prof You sure have put allot of time and work into this design. I have found some 6"" plastic pipe at work which I intend to use for my blades,still have to get round to the problem of the fixing the hub for the blades to the motor ,I have a great Keyed taper block but it is cast steel and have made up the blade mounting plate out of 4"" steel plate ,I was just going to weld the blade mount to the block but I did a try weld on to a bit of scrap Cast steel (a section removed from the taper block with a peace of steel welded to) and did a break test on the weld(hit it with a hammer) and even though the weld looked great, there was little penetration ,I have scrounged a few low Hydrogen rods from a friend so i will give these a go. Sorry to ramble on. Great work Prof PS have you looked at Zubblys work on the other power site?
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| The_Professor Newbie Joined: 22/04/2007 Location: United KingdomPosts: 11 |
A way to have perfect profiles on your blade hub, try this.. Basically you cut yourself an equal triangle of about 12" along the flats and about 2" or 3" thick. This is the basic shape of your hub (will require the corners of the triangle being removed after this machining process). Mount the triangle on the edge of a bench with the side flat with the bench. Set up a router to cut circles the same diameter as your tube (blade). Then set up your router to cut a circle with the edge of the circle in line with the face of the triangle, then cut your perfect profile for the blade to sit in (don't cut a whole circle, as you only need enough to fit the blade). Perhaps not the best description, but I'm sure any hands on guy will get the general idea of what I'm trying to describe. Trying to weld cast is never very successful, unless your preheating etc. Do you have a link please? Thanks |
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| philmountains Newbie Joined: 17/01/2006 Location: United KingdomPosts: 24 |
Hi Prof Thanks for your reply will get to the blades idea soon I hope !!! Anyway I am going to try and past you a link to Zubblys gallery. www,anotherpower.com/gallery/zubbly/7-5baldo44 I hope it works he has made some great mills. Also I was reading Hugh's Windpower Workshop last night and hope it is OK to quote his words, "As a rule of thumb, the actual boom should be about equal to the length of one blade" This to me is not far short of what Gill was coming up with. Gill if you read this update how about posting some pics your new mill ? Thanks again everyone Phil |
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| dwyer Guru  Joined: 19/09/2005 Location: AustraliaPosts: 574 |
Hi philmountains philmountains wrote: I did a try weld on to a bit of scrap Cast steel. There is other way in weld is use stainless weld rod or can use special welding rod design use for cast iron to steel plate 
Dwyer the bushman |
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| Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669 |
G'day Prof, I understand what it is you are trying to do, and that's great. The trouble is that the range should have been 45deg to 90deg. Indeed I feel my 70deg is a general purpose setting then it gets harsher so that something like 20deg might suit Antarctic gale prone areas only. And that would need to be one mean, bullet proof installation. You see this angle does not effect the speed at which furling starts, rather it's effect is on the duration or harshness of the furl as it progresses from start to end. My recommendation is to try 45deg first, then I think you'll find trying lesser angles will perform worse, requiring stronger winds to complete the furl and this will stress your structure more. So many wonderful choices.. was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
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| The_Professor Newbie Joined: 22/04/2007 Location: United KingdomPosts: 11 |
I've not had much time to progress the generator mount much, however I've taken onboard your comments on angles. I must have been having an off-day  and can now see where your coming from, so I've made changes to increase the angle far more than what it was.
Rather than working on the mount, I've been welding brackets for the mast, plus I've bought some blades (see alternative post for info), so putting the home brew blades to one side for the time being. |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Please excuse my ignorance, after all, I'm new here  but I seem to have trouble following what you are saying. When you refer to angles, angles of WHAT exactly?? 
I have gleaned from the messages that the tail fin rotates on a 20 deg. inclined (from the vertical) post. This is to raise the end of the vane as the offset rotor blades get rotated offwind by the force of the wind. The lot will come to some equilibrium with the rotor running no longer square to the wind - did I understand this theory right? So, what are all the other angles you were mentioning above? Thanks, Klaus |
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| The_Professor Newbie Joined: 22/04/2007 Location: United KingdomPosts: 11 |
Hi, I have the generator shaft off-set from the centre of the mast bearing by about 80mm. So when the wind pushes against the blades, it will push the generator around the mast and out of the flow/path of the wind. To counteract this mast rotation we use the tail fin. At 90 degrees the tail fin would be at a right angle to the generator drive shaft. So at zero degrees the tail fin would be in line with the generator drive shaft (directly behind the blades). In the zero position, the wind would push against the blades, thus pushing the whole generator out of the path of the wind until the side of the tail fin has an equal amount of wind pushing against it, to keep the blades in to the wind. So by increasing the fin angle, you push the blades in to the wind. The ideal set-up will keep the blades square on to the wind flow direction. Now... when the wind gets too strong, the blades get pushed out of the wind flow because the tail fin starts to 'furl' on its own angled support, so reduces the angle between the generator/blade shaft and the tail fin. I've just re-read this, and it seems fine to me, however it still may be as clear as mud to someone else. Perhaps some pickies would help, but I haven't got any, sorry. |
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| Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669 |
G'day tinker, OK you seem to have grasped the idea that the tail is not fixed and can rotate about a furl pivot that is inclined off vertical. You would also realise this tail keeps the prop shaft pointing into the wind until the winds force reaches the start of furling where 'the knuckle cracks' from the tail's weight being overpowered. Now this off vertical furl pivot has 2 spots in 360deg where the tail has no ability to resist the knuckle cracking. That is at it's lowest and highest points. It's Maximin countering force is at 90deg to those points. The second angle we refer to is where we place these two points in relationship to the alignment of the prop shaft axis. The most common assumption and greatest error is that the tail furl pivot leans 20 deg directly to the rear. Unfortunately there it has little to no potential force to counter furling at all. But what angle is best???? The furling geometry is quite complex when examined closely. Consider the increasing force of wind against a rotating surface area that reduces as it turns into furl. You need to be Einstein to do this other half. I'll have to do a course one day, if I can find one. I hope that's shed some light on the discussion for you. was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Thanks Professor and Gill for your comments. These have the effect of telling my old brain that this whole furling affair is far more complex than observed at a first glance .
It now looks like a good idea if I mock up something in my shed and see if I can get the hang of that tailfin mystery .
Meanwhile, while I'm tinkering with the supporting hardware, what is a reasonable offset of the horizontal rotor axis to the vertical windseeking axis? 80mm was mentioned above, is 50mm too little? Considering that I'm thinking of a smaller (<2m) propellor which would look less threatening in my suburban lot. Might even disguise it with palm fonds, now there is an idea.... Klaus |
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