High Winds up here this weekend!

[DanB]

It's been a windy week, last Wed and Thurs we had gusts over 60mph.  Last Friday night we clocked gusts up here close to 80mph (76.8 if I recall).  The house was shaking.. lots of trees blew down.  My 14' diameter machine was fine, with no problems... pegging the 150 amp meter frequently, although the heat sink for my rectifiers was getting pretty hot so I shut it down before bed.  

Matt's 15' diameter wind turbine would have been fine, except that he's precariously mounted his rectifiers on the wall, behind his couch.  Earlier in the evening there was a puppy fight on the couch, and one of the rectifiers got disconnected in the heat of puppy battle, and nobody noticed.  Each phase of his machine had 2 40 amp rectifiers in parallel, so with one unhooked, one rectifier was taking the full current and couldn't handle it.  His machine was pegging his 80 amp meter (it's a 24 volt system) when one of the rectifiers blew to short... and stopped the machine.  Easy fix, there was no real damage done.

Tims 10' diameter wind turbine, which we had just raised exactly two weeks ago today did a great job, producing steady current between 60 - 80 amps, and often times pegging his 100 amp meter.  I suspect it was producing at times over 1.5KW, which is not bad for a homebrew 10' machine.  I was happy to see this, because Tims is the first machine I'd made this way with slightly smaller magnets - and I have 2 more finished at my shop which are still untested.  I suspect they will work as well...

Toms, Georges Pigmill, Daves at the caboose, and even Wards old 7' machine with no furling system, and all the other wind turbines up here did fine through it all.

Poor Scott was not so luck with his Rooster wind turbine.  I think we put this up in April, and Scott's had a bit of a rough time with it all.  First, we put it on a 30' tower in a very turbulant site.  The alternator was too powerful for the 10' blades, so overall it performed poorly.  So we opened the airgap (in May) and that improved things some.  Then Scott decided to make a taller tower (50') and larger blades that would better suit the alternator.  (I think that was in June).  The tower was pretty precarious in my opinion, but he got it up there and it worked very nicely!  But, on a windy day, he noticed that the guy wire mounts (into rock) were not as strong as he'd thought - and one of the rocks moved slightly!  (we thought it was 'bedrock'... but it wasn't).  So he went to lower it, and about half way down the tower broke and the machine fell to the ground, smashing his new 11' blades.  So, he improved the tower, and built another blade set, and put it all back up.  It was down for 1 week.

Anyhow... the picture above is how it looked after the windstorm last Friday night... the blades are destroyed.

There's a picture from behind it, showing his tower.  Notice the tail is gone.

The tail was lying about 20' from the bottom of the tower.  This rooster had 'feet', and they both used to stick almost straight down.  Notice how one leg is bent up about 90 deg from where it started.  These chicken legs are made from 1/2" re-bar.

If you look closely at the tail boom pictured above, you can see lots of little marks where the blades (or perhaps the self destructing stub of a broken blade) was hitting the tail boom.

The picture doesn't show it real well, but the stops for the tail are spread out (especially for the furled position...  the normal unfurled position is still straight).  The gusset betweent the tail bearing and the tail boom is also bent.  My guess, is this happened in the process of the blades coming apart - I don't believe this was the 'cause' of the problem.

Here is a closeup of the chicken foot (the one that got bent back 90 deg).  Notice the wood which is impacted between its toes...  a blade hit squarely between the toes.  I bet this is what bent the leg back and bent the tail stops.

Here's a fun picture looking up at Scott's tower.  Lots of guy wires in weird places... this is what happens when you're on the side of a steep, unlevel hill - and you rely on the large rock outcroppings for guy wire mounts.  Evidently the tower is reasonably strong now, since it survived this storm fine.

Scott unhooks the guy wires so we can lower it with the winch.

George cranks the tower down.  This is one of those $20 harbour freight worm gear winches, it's welded to 3/4" re-bar which is hammered/epoxied into holes that were drilled in the rock.

A nice shot of a smashed blade...

There's another interesting picture, you can see how the chicken leg started in one place, and got bent back a little at a time.  My bet, is when all this started - we didn't have enough clearance between the leg, and the blades.  Even though it looked OK, I bet the blade flexed back enough near the tips to collide in a heavy wind, and started bending things one pass at a time.  Finally... once bent so far, the claw was in a position to lop off the ends of the blades.  Hard to say.. could be the stops for the furling postions simply were not strong enough.  The tail fell off, because Scotts blades turned counter clockwise - and with each little 'knock' (which you can see on the blade in the picture above - the little yellow marks) the tail moved up the pivot a little bit.  (you can actually see this  too, on the tail pivot!).  Once it got high enough, and a blade hit the claw square between the toes... then the tail bearing was easily bent and the tail was knocked off the top of the tial pivot.  Amazing the tail itself survived so well!

Back to the wood shop!

All in all, not a huge catastrophe... the alternator is fine, the tower is fine - and the tail is easily repaired.  I'm sure this will be back up in less than a week.  Today (now that Im almost done playing on the computer), we'll cut the tail bearing off and make a new, stronger one (even though I don't think that it was a problem to begin with).  Lots of fun guessing what happened here....  I blame the chicken feet poking down so low, I suspect if the feet were not there, there would have been no problem.  When this machine furls, the feet poke directly at the blade - probably not a good design.  They also add quite a lot of weight and keep this machine in higher winds than necessary I think.

[richhagen]

I was looking at the photos for a while and thinking about it.  I know you don't feel that the stops or the gusset were likely bent before the impact, but if they were, and had started to fail before the catastrophic failure, the result would have been that the tail would be able to furl closer to the blades, making an impact with that foot more likely.  It looks possible that the tail may have been getting periodically slammed into the full furl position, spreading the stops a little further each time, and allowing the blade to scrape it a little further each time, causing the line pattern of scrapes on the blade.  This could have occurred over a long period of time. Then, when the tail was able to furl enough, with the blades deflected slightly towards it in the strong gust, catch the chickens foot, shattering a couple of blades, and lifting the tail off of the post in the process.  The impact would have placed a force upon the tail near the imacts, lifting it towards the machine. (Is the damage to the stops and gusset consistant with this or with the tail slamming into a full furl position?)  If this is what happened, some sort strengthening of the furling stops and gusset might prevent it in the future. If the stops were spreading prior to the catastrophic failure, then it was likely only a short matter of time before the furling system failed anyway.  If this was not the cause, strengthening those parts shouldn't hurt anything.  Have you ever seen spreading of the furling stops, or damage to the gusset connecting the pivot on any of the other similar machines?  Of course, it could be just the wind deflecting the blades back enough to catch the mill with two left feet.

Keep having fun, Rich Hagen

[Ungrounded Lightning Rod]

One thing that bugs me is that the stops are very near the center of the tail's furling axis - creating a horrendous leverage.

I'd be inclied to build a strong support inches out from the axis (as far as possible) and put a rubber bumper on it (like a doorstop or a foot from a machine like a typewriter, or better yet a limit bumper {whatever they call 'em} from an automobile front suspension).  Something non-bouncy by preference.  Let the tail boom hit the bumper rather than coming down hard metal-on-metal.

[DanB]

I do always reinforce the stops, but more so on the 'normal' running side, not on the furling side.  In watching mine, and others - I cannot say I've ever seen it slam (or even go lightly) into the fully furled position - I've never seen one go that far.  It takes a good bit of force to lift the tail into that position and Im not sure it would ever happen under normal conditions - hard to say.

I've never seen one flare out like this before on the fully furled stop - I have seen it on the 'normal' running stop, and I always reinforce that pretty heavily now.

On this one - there is a little bit of noticable wear on the stop for the normal run position, but there is no wear or any indication that it ever even reached the stop on the other side.  Im pretty sure we just didnt have enough clearance here and the blades hit the feet.  I think the tail bearing got bent because it was getting lifted off the tail pivot, and my guess is that when the blades finally did hit hard, the tail was allready partly lifted off so it was easily bent.

Just guessing!  At any rate, we've replaced the tail bearing and it's much stronger than it used to be.  We also amputated the feet.

[DanB]

yes, there would be no harm in that...

On some machines I have made the furling stop on the tail boom itself, and it hits the yaw bearing (that's how Matt's 15' machine is).  The greatest force is on the normal run stop, I see them slam into that position sometimes and I have seen them get damaged when not reinforced.  It might be wise to change this part of things a bit...  although I've not seen problems lately.  I guess my 14' machine will probably be the 1st to fail, it's about the same as Scotts but the tail is longer and heavier.

I hate to complicate things if not necessary, but it does make me wonder about a shock absorber on the tail.  I suppose such a shock should probably only act one way - so that it can still furl quickly, but it would not allow the tail to move too quickly back into the normal position.  I know slamming back into the stops has got to be a bit hard on things - I wonder how hard it is on the blades!  Such a jolt to the machine while the blades are moving quickly has to put some stresses on them.

[BT Humble]

I hate to complicate things if not necessary, but it does make me wonder about a shock absorber on the tail.  I suppose such a shock should probably only act one way - so that it can still furl quickly, but it would not allow the tail to move too quickly back into the normal position.

I'll say it again - Motorcycle Steering Damper.  That's what they're made for (and yes, they're bidirectional too).

They're pretty expensive new, but there's an awful lot of sports bikes that end up at the wrecker's...

BTH

[Gary D]

Hi Dan, It could be a few things here coming into play here. The standard wood can flex more, allowing the blades to head back towards the furled tail. The tilt slightly upwards of the rotor while keeping the blades from hitting the tower automatically puts the blades on their top part of the swing closer to the furled tail. And the tilt of the tail raising to the furling position puts the tail closer to the blades? The larger the diameter of the blades and the longer the length of the tail might exagerate this requiring a slight adjustment to the furling stop? Just glad no one was hurt, and more wood is available! I think a shop to manufacture the new blades is nearby too! ;-)  Not worth 2 cents tho... your village idiot, Gary D.

[Ungrounded Lightning Rod]

I hate to complicate things if not necessary, but it does make me wonder about a shock absorber on the tail.

Naw, don't use a shock absorber.  Use an energy-absorbing rubber and/or shape for the bumper.  It will absorb part of the energy and the rebound will be much smaller than the impact.  That, plus the wind resistance of the tail, will cause it to settle against the stop fairly quickly (and do the right thin meanwhile) rather than bouncing back-and-forth.

That's why I suggested noise-suppressing machine feet or automotive suspension limit bumpers (rather than captive superballs B-) ) for the rubber stops.  Automotive door bumpers should work, too.  Such rubber is designed to absorb the energy from the impacting metal and bring it to a stop, rather than bouncing it back.