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Forum Index : Windmills : Blade angles
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Rastus Guru  Joined: 29/10/2010 Location: AustraliaPosts: 301 |
Hi to all, The north eastern states are being hammered and it's a serious concern to everyone!  I hope the predictions are not realized. No offence or disregard is intended by this post, perhaps it will provide a momentary distraction.
I'm intending to use alluminium blades on my mill and read that the aproach angle can be varied from 8 to 15deg. Does the 8deg angle suite light wind aplications and the 15deg high winds? While I've posted some wind details on the spline angle thread, I'm unsure what catagory I'm in. Most likely low wind area. Can Aussie wind generators please give me guidelines. Cheers Rastus see Rastus graduate advise generously |
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JimBo911 Senior Member  Joined: 26/03/2009 Location: United StatesPosts: 262 |
Rastus I have tried changing the angle of attack with the GEO222 blades. In my experiences as the blades spin up and reach a certain RPM (RPM unknown)there is a noticeable and or very distinct jump or increase in RPM this I assume is when the lift affect takes hold or kicks in the angle of attack is set at a minimum or at a lower angle and they run very quiet. At a lower angle it takes a little breeze for them to start spinning from standing still. Increasing the angle of attack will cause them to begin spinning at lower wind speeds and will produce more low end torque. Running at increased angles will reduce lift affect and cause more drag which also creates more noise but helps keep RPM down. You can experiment with different angles to see what works best in your area. My anemometer has extra large cups and is designed to respond to light winds, more often then not my mill responds to varying wind speeds sooner the anemometer. When not loaded the blades will continue to spin with what seems to be very little or no wind at all but then responds quickly when a slight breeze comes in. My neighbor fly's a SkyStream 3.7 at 75 feet/22.86 meters and if the winds are out of the west my mill will almost always spin before his SkyStream does. Over all I am very pleased with there performance. My mill topped out at 690 watts, single stator F&P, neo mags, 2 meter blade set. Jim |
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| Rastus Guru Joined: 29/10/2010 Location: AustraliaPosts: 301 |
hi Jim, thankyou for the detailed and prompt reply! If I'm following the real life description, the 8deg aproach needs slightly more start up power,produces less noise and idles longer to catch slight pick up breese.The 15deg produces more noise, needs less power to start it and reduced rpm overall. Do you run 3,or more blades on your mill? When running 8deg does the head constantly furl/return? Do you find at 15deg the mill output is more constant because it still produces some power while furled? Does your head furl a full 90%? Not trying to bombard you with questions, just keen to learn! cheers Rastus see Rastus graduate advise generously |
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| JimBo911 Senior Member Joined: 26/03/2009 Location: United StatesPosts: 262 |
Rastus Questions are good. I am sure that most of the forum members will tell you that three blades is the best over all set up. I never flew two blades. There is very little or no real power to be had at low wind speeds so if it takes a bit more wind to get things going it's ok. With the ALUM GEO222 once they start to spin they want to continue spinning even at winds lower or around 4 MPH (no load)so even if it takes 10 to 11 MPH to get things going once they spin your good to go. My mill will start charging (battery system)at or around 6MPH once they ARE spinning, but again 6MPH will not get them spinning from standing still at a lower angle of attack. In my opinion a lower angle will out produce higher angles hands down, once the lift effect takes over they crank out PLENTY of torque. Furling (Hummmm) now thats a whole different subject all together. Furling is a balancing act that involves every aspect of milling wattage. Blade set, alternator off set, tail length and weight, clean air, turbulent air, furling direction verses blade rotation (CW CCW) etc. The wind is a very fickled thing just ask the BackShed Boys I would advise lower angles of attack for over all performance. When you build your blade hub make it so you can try different angles to best suite your situation. 'VERY IMPORTANT' Make SURE you have a way of being able to STOP or brake your mill or your doomed to failure. Given a chance Mother nature will tear your mill off it's perch guaranteed. Jim |
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fillm Guru Joined: 10/02/2007 Location: AustraliaPosts: 730 |
Hi Rastus, As I sell the Aluminium GOE222 blades here in Aus and have done a lot of testing with different angles, as all my blade hubs I have are able to adjust the blade angle . The Recomended angle best suited to windmills is 8 - 10 deg through the cord or 11 - 13 deg on the flat . I usually always run at 8(11) and have found this to be the best. All is very dependant on where your alternator cuts in , as with any blade a cut-in below 70 Rpm can just lug them down too much too early causing a total loss of effiency. I like to have a cut-in of around 90 - 120 rpm and these bldes will get up to that easily in 5-7klm . A more "IMPORTANT" issue is that you do not skimp on mounting strength as many people do , the biggest killer of a set of ANY blades will be centrifugal force , the next biggest killer is un balanced blades . As Jimbo has said these blades can crank out big torque and can up in RPMs , I have seen a 3.1m set on my F&P Duals hitting 770+ RPMs in 12m/s+ for only 900w but in the same wind same blade set on my Ax Fx is 550RPMs @ 3200W. Furling is and to date has been an issue with these, but I also think that there has been a lot of misdirection with the angles recomended for good furling and hopfully soon I will have a bit more to say on this with real life testing and not just speculation. PhillM ...Oz Wind Engineering..Wind Turbine Kits 500W - 5000W ~ F&P Dual Kits ~ GOE222Blades- Voltage Control Parts ------- Tower kits |
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| Rastus Guru Joined: 29/10/2010 Location: AustraliaPosts: 301 |
Hi Jim, Your additional comments are persuasive to plan on lower blade aproach angles. The advise about stopping a mill is taken as critical. I've noted in other threads dead shorting is not a complete solution leaving me to contemplate mechanical alternatives. I don't have any knowledge specific to mills in this area at present. Hi Phill M, Thanks for confirming Jims advise. Due to circumstance I'm not looking to change the mill set up from construction/installation which with good planning I may not achieve maximum efficiency but nudge somewhere close. I do intend to purchase blades from you and now plan to set them at 8(11) on the hub. This post is a result of learning that a commercial 1.5kw unit has blades set that keep the mill producing power even when furled with no damage as a result. Due to the captured torque of your blades I've concluded its not feasible to aim for this feature. I would like to float an idea by you, and the forum. I'm considering adding an additional bearing between the front rotor and hub, using its centre as a bearing surface. This may reduce flex/vibration forces. What are your thoughts? see Rastus graduate advise generously |
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| JimBo911 Senior Member Joined: 26/03/2009 Location: United StatesPosts: 262 |
Ratus Furling is something that can be adjusted during field testing. After your mill is up and flying you can watch and make changes that will bring you closer to your goals. As you design and build keep flexibility in mind more then likely you will have to make several adjustments few people can build a serious mill and hit the nail on the head the first time. I've been at it for over a year now and feel that I am now getting close to what I like to call the SWEET spot (furling) for all around KWH production and over speed protection. At present my mill will furl so far as to turn the blades completely out of the wind which of course at this time she makes little or no power however this dose keep things in one piece. I to would like to see her crank out the KWH under VERY high winds but when a storm moves in and things really start cranken and you feel your heart skip a beat you will be thankful she's still one piece and willing to continue to to make power another day. You want your mill to furl early then as you gain more confidence you can keep her facing the wind a bit longer and work your way up. You will not go wrong buying these blades from Phill. Pictures and or some sort of drawings may help us with your build. Jim |
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| Rastus Guru Joined: 29/10/2010 Location: AustraliaPosts: 301 |
Hi Jim, I see I have a lot to learn yet. Once I start the build stage of this project I'll learn how to post pic's and be happy to get further help! I'm committed to summer tasks at present making research and planning manageable. It's probably wise to rope in some extra help for at least the first year to make adjustments as needed to refine the working mill. Again thankyou for providing usefull advise. cheers Rastus see Rastus graduate advise generously |
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| udsn Newbie  Joined: 15/12/2010 Location: JordanPosts: 9 |
Variable Angle of attack or pitch control First I would like to ask all, Is it better to start a new post or is this location good enough. What is best for these blades? Variable angle of attack system or fixed for a 3 meter per blad by 3 blades windmill. Since I want to make one that is 6 meters at least. What do you all think? Here are some pics of different angle pitch control systems. What do you think? 
I like the pinion and gear system but I need the calculations but also it needs something to back up the rack, I also like the? Scotch Yoke Leaver system simplest also has self limiting property. I still need to do lots of math/engineering. Any help there? Please all comment want real scince |
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| Rastus Guru Joined: 29/10/2010 Location: AustraliaPosts: 301 |
Hi udsn, Your post is a unique addition to this post. Some of the forum members know about large/commercial wind turbines and may be able to provide guidance for you. The topic is active so allow some time for replies, if these do not follow within your time frame try a new post "variable pitch Blades" or "large scale mill" reposting your current info! Your preferred designs both have parts moving within the hub, lubrication and hardened faces will postpone early wear and binding. Taking into account abrasive airbourne particles may also need to be considered depending on location along with the temper and compatibility of component materials to reduce maintenance down time. I hope you are provided with the guidance you're looking for, all the best Rastus see Rastus graduate advise generously |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi udsn The scotch yoke in your last picture is the simplest to do, but is better with a round pitch plate than a triangle as it is easier to combine into a governor system. However the engineering of a device such as this would require a machine shop and the skills to use it otherwise the cost would be to great. For our size mills it is better to stick to something simple like a furling mill or even a high speed non furling mill, if you are thinking of a multi KW mill then the pitch control may be a proposition, but will be a high maintenance device. KISS is the word. All the best Bob Foolin Around |
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| udsn Newbie Joined: 15/12/2010 Location: JordanPosts: 9 |
Hi all Thank you all Thank you and hi both Rastus and VK4AYQ The Scotch Yoke is the first three pics. I am working (theoretical) on 5 Kwatt system 6 meter long diameter. I only have the aluminum blades. What do you mean high maintenance? Why? I think the best to lower maintenance is the ball joint system. Something that is engineered for outdoor use in the first place. for dust ,water, extreme conditions, also ready off the shelf. Do I need a range larger than 90 degrees? What is the optimal for GOE222 ?? Best regards want real scince |
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| Rastus Guru Joined: 29/10/2010 Location: AustraliaPosts: 301 |
Hi udns, your preferred blades have a usefull working range between 8(11)deg to 10(13)deg, results odtained by Pill M through feild tests. He has a post in this thread.The blades where 3mt in size but the results would be comparable to larger swept areas. I wondered why you were specific about the blade type, when the variable pitch designs could work equally well with numerous blade profiles,including aircraft type profiles. Are you planning to rely on governing pitch angle, more so than furling, in your design. If yes! another type of blade may yeild substantialy better results. By buying an of the shelf hub and gov/pitch control, guality should be High, however with so many moving parts prone to wear scheduled maintenance would have to be a prudent inclusion. If you exspand on the calculations you are interested in further help may be offered! Best wishes Rastus see Rastus graduate advise generously |
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| udsn Newbie Joined: 15/12/2010 Location: JordanPosts: 9 |
Dear Rastus Thank you for replying. Thank you for the blade angels. 8(11)deg to 10(13)deg. I bought the Aluminum blades from the site The black shed from china . So I have some stock that I am stuck with, I need to sell or build one. I live in a third world country. No market here for such stuff. So there are not ready made rotors. I thought it is an easy task to build a windmill, if I had known its so hard I wouldn’t have done so. I am planning on using pitch control to maximize efficiency. And Furling or braking for protection, PIC controllers. And yes I need help in the calculations I asked for that quit a lot. I want to put the equations in the PIC controller so it would actively provide best efficiency- maximum power extrication- and load dump. I actually cannot imagine how would that work , I think need differentiation or integration and reversal of the power equations. I also would like to make the design and equations for free as a manual for those blades or any other blades so other half handy people would just copy and past every thing . I wish to sue excel sheet and move info into the pic. For example --for this wind speed with this load then = move blades to this location loop— too much energy? Then dump power. Any help is most welcomed. Thank you and best regards . want real scince |
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| Rastus Guru Joined: 29/10/2010 Location: AustraliaPosts: 301 |
Hi udsn, Once you have the information you need the project will seem less daunting. Please start a new post "5kwatt AXFX?" asking what magnets, wire size and coil count can deliver the output you are aiming for. If you can obtain some local wind speed data, forum members can help you calculate the wind power you need to drive the machine. Also a new post on "PIC logger! help" descibe what you need and if any of the sites units can be exspanded to suite your application. By doing so you can have a number of subjects being developed simultaneuosly saving you valueable time. It's possible that you already have knowledge on these subjects, I'm not discounting that probability instead looking for a starting point for international discussion, I do hope these suggestions generate satifactory results! all the best Rastus see Rastus graduate advise generously |
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Oscar4u Regular Member  Joined: 23/02/2011 Location: New ZealandPosts: 42 |
Hello there I have toyed with the idea of variable pitch angle partially to protect against overreving. My dreams are to make a sevenish meter diameter three bladed mill. Safety of the mill is a big concern to me. My thoughts were to make a govenor. Ideally I would find the front of an aeroplane but they are difficult to get hold of. I live a couple of km from the coast so everything needs to be salt and weatherproof. I figured hubs and stubs would be ideal for pivoting the blades. I have wrecked a few David Brown tractors over the years hence having these stubs to spare. Being taper rollers and only one oil seal I figure they will last forever in this job. Also with the wheel nuts it would be very easy to attach and remove the blades from the mill. On the inside of the wheel rims I thought of welding a short piece of 100mm pipe and fixing the blades at the end of that. Pretend that the long skinny bits of wood are the blades. The 20mm piece of pipe would be the shaft the windmill turns on. My thoughts were of using a car diff and facing the center part down with a length of 50mm pipe as driveshaft so that the generator would be close to ground level vertical. Again using a rim and wheel nuts to attach the blades to the diff. Possibly use the brake at the other end of the diff. The red box would be a counterweight so the govenor could be adjusted. On the opposite side of the rim to where the govenor is fixed I would make a set of linkages so that the three blades have to swivel together the same ammount.I struggle to explain myself well. Sorry.Does all this sound like a mad idea? Would welcome suggestions. Thanks very much Oscar 
Oscar4u - for all your rotary cowshed repairs |
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| Rastus Guru Joined: 29/10/2010 Location: AustraliaPosts: 301 |
Hi Oscar4u, You seem to have a lot of ideas about your mill,but I'm struggling with the connections.Aeroplane blade pitch controls can have hydraulic actuators adding complex and exspensive gear to a home made mill.The axles you have will be usefull components in your build.Unfortunateley I can't follow the description about the governor and its levers so I'll have to leave that to others, cheers Rastus see Rastus graduate advise generously |
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| Oscar4u Regular Member Joined: 23/02/2011 Location: New ZealandPosts: 42 |
Hello Rastus I do not blame you for not understanding. You have possibly seen the govenor on a pre WWII stationary engine where round balls fly round and by centrifugal force regulate motor speed. Well I thought of making three of these in the front of the mill, one for each blade. As the blades speed up it throws out the steel weight and causes the blade to feather more (or less am not sure which) by two linkages each. Is that still clear as mud ? In general I beleive in the kiss (keep it simple stupid) idea but figure this might be a good safety mechanism. It would be trial and error but by changing linkage lengh and weight amount should be possible to get it fairly good. At very high wind is it safer to tie a mill up or keep it spinning out of the wind? Cheers Oscar Oscar4u - for all your rotary cowshed repairs |
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shawn Senior Member Joined: 30/03/2010 Location: New ZealandPosts: 210 |
Guys i strongly recomend building a small cheap mill to start with and let mother nature play with it for a while you will learn heaps and understand why we avocate the KEEP IT SIMPLE aproach. nothing is new in wind power and otherpower make up to 20 foot diameter wooden blade mills successfully buy the kiss aproach!!! On that note Rastus have you considerd wood blades? I think the alloy ones sold here may start up in slower winds but there furling has been contraversal and I know of a few that have burnt stattors this will get sorted im sure and it might not matter with a f&p but wooden blades are tryed and tru with proven mills for years and the angles are all sorted in the making just sandwich the hub end together and your humming. |
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| Oscar4u Regular Member Joined: 23/02/2011 Location: New ZealandPosts: 42 |
Hello Shawn. Thanks for that advice. I sometimes struggle to know what is good for me. A large part of me certainly agrees. I would like the challenge of the feathering but probably have other more important things to do. Cheers Oscar Oscar4u - for all your rotary cowshed repairs |
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