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Forum Index : Windmills : Blade Shank Failure
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MacGyver Guru  Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Oops! 
You gotta know this puppy was haulin' balls when things let go! 
You know . . . I had every good intention of encasing these blade stand-offs in an aluminum channel this weekend. I just wasn't fast enough, eh? I'm reasonably sure this is why I call this little tower my "test" stand. I'm also reasonably glad I wasn't standing there watching; I'd likely have had to go change my britches! Now if this had been up in the air 30 or 40 feet, I'd be searching the neighbors' yards for the blade. These blades weigh in at only 4.1 ounces, so I'm pretty sure it would have sailed quite a ways had it not hit the grass as fast and as hard as it did. That's what it's all about, right? Gotta test stuff to make sure it's gonna work; back to the drawing board! 
. . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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JimBo911 Senior Member  Joined: 26/03/2009 Location: United StatesPosts: 262 |
Mac When in doubt over build. The wind loves to destroy anything it can. Just my thoughts but your components look a bit on the lite side. 
Looking forward to your up grades. Jim |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
JimBo911 The funny thing is, I wasn't going to leave this thing on the stand for more than a day. I was just testing how well the Coroflute blades flew and was going to take things down when I got distracted and just plain forgot. Mom (Mother Nature) reminded me today when I came in from having muscled a water heater into place all morning; ready to relax a bit -- NOT! I figured the wood shanks would have pulled through at the holes, since one on each blade was within only about 1/4" from the end. In all likelihood, that's where the crack started and centripetal force took care of all the little details! I'm sure yawing had some input as well. I'll be constructing a set of three high high aspect-ratio blades tomorrow and I'll throw them on the same stand to see 'if' or hopefully 'how much better' they fly. I read a great Link oztules sent me about Mr. Jacobs (Jacobs Wind Electric, circa 1920's - 1950's) and he said long, narrowing blades were the ticket. When I say "high aspect-ratio" all I really mean is they will taper and get narrower as the blade root approaches the tip. I don't want anyone to get the idea I've actually figured anything out mathematically. Heck, no; I'm a trial-and-error guy through and through. If it works, I leave it be; if it doesn't, I wrench on it a bit more. I'll be wrenching on blades all this weekend, be sure of that! I'm also going to try to fit together a single-bladed mill with a pitching device to throw into another thread here somewhere. I've built those kind before and they go scary fast, so I'm hoping to be able to do a youtube video of it before it self-destroys; hide and watch. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Follow-up On closer examination of the blade, it appears the spar cracked, letting the blade fly towards the tail and the final blow was caused by a tower strike. Here's the evidence: 
See that dent? It wasn't there when I built the thing. This method of construction I might add makes things nearly bullet proof! 
Here's another view of that same dent. This had to sound like a firecracker when it whacked the test stand; now I kinda wish I had been there! By the way, in the first picture of this thread, I dug a hole in the grass and stuck the blade in it so I could take a picture. It wasn't going so fast that it dug its own hole. Thought I should make that clear so nobody gets the wrong idea. I found the blade lying on the grass several feet away. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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wind-pirate Senior Member Joined: 01/02/2007 Location: CanadaPosts: 101 |
Hi Mac I know how you feel, I lost a 3 blade 3' "1 Meter" prop, My first one build. I so happy the way it turned, It hit tower too. But It lasted about an hour. Ron  THE Pirate. stealing wind & solar energy is fun |
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| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
Are we learning yet! My blades AKA Phillm aluminium jobs weigh in at best park of 4KG each. BULLETPROOF!! build the spars at the very least much much heavier. weight is not the enemy here. Karl Luck favours the well prepared |
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ChrisOlson Regular Member  Joined: 19/01/2010 Location: United StatesPosts: 60 |
That kind of reminds me of my 8.5 footer that blew up once. I lost the generator in it and had a runaway in 40+ mph wind. The blades held - got PowerMax 085's on it - but the magnets were a different story. The mags were scattered halfway across the county. Never did find four of them. That turbine hit well over 1,000 rpm and I just retreated to a safe distance and watched once I realized I didn't even have one phase left in it that could be used for braking. When the coils blew and the stator expanded it didn't even attempt to slow it down or lock it up - it just tore all the mags off the rotors. All due to my furling calcs being a little bogus. So that's when I invented my vertical hinge tail setup with an adjustable, spring-loaded power limiter. Every turbine since (I got five flying from 8.5' up to two 13 footers), I started pinning my mags to the rotors, using a vertical hinged tail with a spring-loaded power limiter, and put a half-wrap blast shield on the gen so if I get a runaway and it throws mags it directs them to the base of the tower instead of tossing them into the brush in the neighbor's back forty. -- Chris 
off-grid in Northern Wisconsin, USA |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
[Quote=KarlJ]Are we learning yet! A veritable "learning experience"! Yes, we're learning a lot. Like I said earlier, this was only put up in the first place to test the blade's reaction to wind and wasn't intended to be left there as long as it was. That's somewhat of the reason I started the thread out with "Oops!" I have yet another set of Coroflute blades to be tested and they have open tips. I'm comparing noise levels as I once did this with hollow, lifting-section aluminum blades and found that open tips were quieter. Where's all this leading? Well, it is my full intention to build nothing but Coroflute blades from here on out. I like them. They are easy to construct, quite robust, light and pretty. To me, lightweight and strong is a good combination. Pretty never hurts anything, so if given that option, why not take it? As for the spars; I intend leaving them wood, but actually decreasing their size. I'm going to thinner, which I'm sure will have a lot of folks scratching their heads. Be patient, I'm not done yet. When it's all said and done, everyone will see what I'm up to. To quell your anxiety, I intend encasing the root-end of the spar in aluminum channel and adding a flat bar to the open side, compressing the spar end between metal. I also have a plan to build an all-aluminum root insert, which will form-fit the root of each blade and be attached in several places. This will be part of the controllable-pitch system I've got on the bench at this very moment, All these little projects take time and money. I have each, but only have 12 hands if you know what I mean. I threw up some more videos this morning to give everyone a closer look-see at how I spent my Saturday. Had to attend a social event today (  ) -- would rather have spent the day in my shop.
More as it happens. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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shawn Senior Member Joined: 30/03/2010 Location: New ZealandPosts: 210 |
Great post. Most of us have done this, that is the ones that have that "give it ago", mind set. Mine was a 4metre, 3 blade wooden set that hit the tower when it threw its chain drive causing free spinning. Just please use caution anybody getting hurt cannot look good for any of us mill heads. We all learn from these kind of posts. I suggest strength here and giving it a load to work on. |
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Don B Senior Member Joined: 27/09/2008 Location: AustraliaPosts: 190 |
Hi Mac I guess that you must have explained this before, somewhere, but what, exactly, is coroflute, and where do you get it, or how do you make it? I have tried to google the name, but all that I can find is corflute, which seems to be a different product. From what I can see of your blades, they appear to have a series of of bumps along the leading edge. I have a hazy recollection of reading somewhere that whales have similar knobs along the leading edge of their flippers, and this has been found to greatly improves their effectiveness in water. Is this what the coroflute lumps are for? Regards Don B |
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Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Don dont go giving Mac ideas or next we know he will have whale flippers bolted to a mill.
And lots of Japanese tourists hanging over his fence taking photos. 
Pete. Sometimes it just works |
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niall1 Senior Member Joined: 20/11/2008 Location: IrelandPosts: 331 |
hi Don its interesting about the bumps along the leading edge...i remember reading that topic as well ... i think the bumps on Macs blades are a by product off bending the coroflute ..the ribs inside the plastic deform a bit and so the bumps come in ? its used a lot on signage here ...during elections you could gather a load off the stuff as every pole seems to have 2 or 3 pondlife with their their well fed faces adorning it ps...Chris thats a very nice looking build ...maybe you could show us more off your work ? niall |
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| Janne Senior Member Joined: 20/06/2008 Location: FinlandPosts: 121 |
Chris, Nice work with the spring-loaded tail. One question if you don't mind,, how well the gas spring helps to dampen the movements of the tail? The furling speed on my axial flux machine is a bit on the low side, so I was thinking of increasing the power levels a little. But then also there is the problem of the tail slamming against the tail stop often quite violently.. So I started thinking, if I added a gas spring instead of more weight on the tail, would it also help to dampen the movements of the tail. A gas shock absorber could also do the trick, but small ones seem impossible to come by.. Or at least I've been unable to locate one. If at first you don't succeed, try again. My projects |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Don B et al Regarding "Corofute": Coroflute is what it's called in Australia, so since many of the 4m viewers are Australian, I used that term. In the USA, it's called "Coroplast". I use 2 mm; the election signs are usually 4mm and unless you're making an 8-foot blade that will be a foot or two wide, you'll find it's almost impossible to bend. Perhaps if you had access to a metal brake or bender or whatever it's called that bends sheet metal, you could use it to clamp and bend, but my thought is it'd mash it too severely. niall1 is correct about the bumps in the leading edge. They are merely a by-product of bending the stuff. Where the little, square cells bend, some of that material pushes up and out and together they form little bumps. As for adding to the aerodynamics, that's a coin toss, I dunno. One thing's for sure, if a blade were to hit you, it'd likely mash you rather than cut. When I said hese things are "bullet proof" I wasn't kidding. They are smooth, hard, lightweight and very robust. I purchased an 8' x 4' x 4mm sheet for around $12 at a sign shop in Orange, California. The sign shop in San Diego wanted $78 a sheet for the exact same thing. A little mark-up is fine and dandy, but that's out-and-out highway robbery! In Austrailia, ask for "Coroflute". By the way, the wooden spar that is CA-glued all the way up the bottom inside of the blade is there merely to discourage bending parallel to the cells in the plastic, which run fore-to-aft on the blade (or wing). As for creasing parallel to either the leading or trailing edge, I think that would be nearly impossible. Like I said, this stuff is robust with a capital "r". I intend using Coroflute (plast) for all my blade (wing) builds from here on out. Future blades will be long, narrow and tapered, with the tip length 1/3 the length of the root or slightly less. This is based on research conducted by Jacobs Wind Electric over a 40+ year study. I'm currently testing a set of hollow blades with open ends (tips). Back in the day, when I was building hollow aluminum (sheet metal) blades, I found that leaving the tips open caused the blade to "sling" or pump air up the inside of the blade and out at the open tip. This seemed to lessen the blade noise for some unknown reason. A friend suggested it might be spoiling any tip vortices (plural of vortex?) and might be the reason the blades run quieter, I dunno. When I get the new (tiny) blades up and flying, I'll post another youtube video. I kinda like living in this time, how 'bout the rest of the crew? Can you imagine being a serf in Medieval England or something like that where you couldn't build windmills? No youtube? That'd suck! 
. . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
[Quote=Janne]A gas shock absorber could also do the trick, but small ones seem impossible to come by.. Or at least I've been unable to locate one. I've seen small-ish ones used on the fold-up rear windows of SUVs and mini vans. I think they are pre-loaded with either gas or a spring or both and they assist lifting the weight of the rear-window glass, which also becomes a door just above the tailgate. Maybe check with the auto recycler or junk yard in your area to see if you could remove one from a mashed car, eh? . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| ChrisOlson Regular Member Joined: 19/01/2010 Location: United StatesPosts: 60 |
My first one was just a piece of pipe with stacked Hillman #62 springs in it (to keep the compression rate constant), an adjusting screw on one end, and a rod and piston pushing on the springs. My latest ones are oil dampened. I have the same setup with the stacked springs but I machined a piston that fits the pipe bore tighter, but not so tight that it doesn't let oil leak by it. Then I went to a stainless steel shaft so it doesn't rust and put an o-ring seal in the cap. When I assemble it, I fully compress the shaft with the cap screwed off and fill it with automatic transmission fluid. Then, holding the shaft fully compressed, screw the cap on. The oil inside dampens the rate at which it can extend and retract by how fast it leaks past the piston. Like on my 13 foot turbines, it takes 57 lbs of "push" to fully compress the cylinder for 1.5 kW power output. On the turbine when it gets hit by a powerful gust it takes about 2 seconds for it to fully compress. That 2 second delay can cause power spikes over 2 kW but it's only for a little bit. And once fully compressed, it takes about 2 seconds for it to extend again too, which limits how fast the turbine faces back into the wind and goes back to work. I've had really good luck with them - it costs about $17 in materials to build one. They're more easily adjustable than using an angled tail hinge working against gravity. When I fly a new turbine with one on it, I usually turn the adjusting screw all the way out and see where it peaks at. Then I turn the screw in (add preload to the springs) until I get the power I want out of the machine. I've used Century #2836 (I think that's the number) compression springs in my smaller turbines, and Hillman #62's in the bigger ones with pretty good success. Enclosing them in the cylinder, in oil bath, makes the whole setup pretty much weather-proof, and using light oil (ATF) doesn't change the viscosity enough so they dampen too slow in cold weather. I've run them at -20 degrees F and they still work fine. -- Chris off-grid in Northern Wisconsin, USA |
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Perry Senior Member Joined: 19/11/2009 Location: Posts: 190 |
Hey Mac, Couple thoughts here, take them for what their worth and realize I'm not being critical, just conversing. 1. I don't think these coro blades have that great of a profile. Understand it may be easy for you to work with but the profile you called 'perfect' in another post was quite lumpy and the trailing edge was extremely thick. Two material thicknesses. You want a TE that comes to a knife edge. This poor aero profile probably explains the lack of performance (rpm) shown in your vids. 2. I don't think these light weight blades will endure the ravages of the wind at all. You call them bullet proof but here we are in a thread where you first set failed pretty quickly. 3. You say they are extremely fast but all your videos show them not spinning or barely spinning. Do you have vids where they are actually cranking away? 4. Putting them under load (i.e. a generator) will only make things worse. If you are having troubles with a free-wheeling turbine then what is to come? 5. About your failure in this post. I noticed that your spar is not in line with the center of your hub. They look angled. As the hub rotates this causes a torque moment where they mount to the hub, causing the spar to split as shown in your picture. Have the spar radiate directly from the rotational axis of the hub and you will eliminate this troublesome moment at the base of your 'shank'where it split. Just some thoughts. We have traded posts for a while so I assume you won't take this as me being a jerk. Just know you good enough to start hitting you with the 'level 2' questions now. Perry |
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| Janne Senior Member Joined: 20/06/2008 Location: FinlandPosts: 121 |
Ok I actually tested a couple of gas springs, and it seems like the "damping" they provide is no good. It only takes under a second for them to fully extend. Not sure if the cylinders in SUV trunks differ from those? Chris, your damper / spring concept seems like it's pretty well thought out. With oil inside the cylinder it should eliminate any chances of the piston sticking to the cylinder and make the windmill not furl.. Overall I like it better than the original gravity driven furling. I will also look into oil shock absorbers to dampen the tail. I have a bunch of old pneumatic cylinders, they should easily convert into oil filled dampers. For added power I think I will just go with added weight in the tail end. If at first you don't succeed, try again. My projects |
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| ChrisOlson Regular Member Joined: 19/01/2010 Location: United StatesPosts: 60 |
Those power limiter cylinders have gone thru a few changes since the first one I built. The latest thing I'm testing is a detent on one of my 13 foot machines. I machined a groove in the shaft and it has a detent plunger that engages the groove. The detent plunger is spring loaded with an adjusting screw to set the "breakaway" force to bring it out of the detent. I have the detent groove machined in the proper place to hold the tail perpendicular to the rotor. What it does is prevent partial furling, and subsequent loss of power in higher winds because the rotor is running oblique to the wind. The peak pressure in the cylinder is 57 lbs and I have the detent set to break away at 50 lbs of "push" on the shaft. It seems to work pretty good - I keep hand written logs of the amp-hour output of my turbines, logging the output with Doc Wattson meters and my recording anemometer. It appears, after five weeks of testing with the detent, that I've gained an average of 6% more power into the batteries in wind speeds over 18 mph. That turbine gets to about 1,400 watts before the detent "lets go" and then the yawing turbine head works against the spring pressure in the cylinder. It has to get down to about 18 mph wind speed before the return spring pressure is sufficient to latch the detent again, locking the tail perpendicular to the rotor. I assume the additional output is due to more precise steering control and not running the rotor partially stalled (oblique to the wind) until the max rated power is reached. I've been pretty happy with it - a lot of guys are afraid to try it because it's different and doesn't follow the homebrew plans. I've been running these cylinders for quite awhile now and haven't had one fail, or fail to work, yet. In the mean time there's been lots of guys that have built turbines and had angled hinge tails working against gravity fail to work due to the weight of the tail being off, or some other reason. The cylinder adds a little complexity to the furling system, but not really because the concept is simpler than an angled hinge working against gravity - and if you know how much thrust your rotor makes the spring pressure can be set in the shop using a simple spring scale pulling on the rotor head while holding the tail. It eliminates having to worry about how heavy the tail is, how long the boom is, and whether or not you have that angled hinge welded on the turbine frame at the right angle. -- Chris off-grid in Northern Wisconsin, USA |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Perry To answer your 5 thoughts, I must reproduce a quote from the movie Bruce Almighty: "Yes to all." That was from the part where he (Bruce-who had taken God's job for a few days) was faced with answering about a billion prayers (emails) many of which were to have the winning lottery number. First off, there's virtually no wind where I live. It's here, then it's there; little spurts. Great place for small birds. Not so great for serious windmills. I have a little test stand that I could load up and take down to the coast where there's lots of wind. Maybe I'll do that and take a video there too. I'm having great fun with the videos, ya know! Ain't technology great? In fact, "fun" is 99.9% of why I do this; I enjoy it whether it works well or not. When something seems to go right I post the results. When things awry, I post those results too. I don't mean to be a pest, but I know I likely am; sorry! As for the Coroflute blades, I like 'em. I'm going to build them whether they're "perfect" or "bullet-proof" or not. In my opinion, they are. If the rest of the crew wants to build them too, that's cool. If not, I'm okay with that too; no worries. The fact that the blade spars are not centered on the hub is due to my laziness. I stole the hub off another windmill. When I get the time, I'll build a real hub and clean things up a bit, but for now, I'm happy with what's spinning out in my backyard. If it comes apart, it'll make a dandy story. That's not to say others should follow my lead and I try to make that clear in my postings. In fact, I just posted an "Alert" in that regard, having discovered closing the blade ends encourages rain water to partially fill the blades, throwing them way off balance even having been nearly perfectly static-balanced before letting them fly. The generator is in the works and if the mill won't turn it, I'll cross that bridge when I get there. For now, I'm just taking things as they come down the pike and not worrying much about anything long range. I'm like a kid (big kid!) in a candy store. Please excuse my exuberance! Wish I had some "level-2" answers to your questions, but I don't. No worries though; I'm working on it! . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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