Wind-turbine-tower-top-bent-again-2014

[Boss]

Wind-turbine-tower-top-bent-again-2014-north
From this angle it doesn't look too bad.

Yep Winter hasn't been much of a winter this year, and now Spring winds are already brutal, and Spring is 50+ days away.

Let me start at the beginning. Much like our neighbors in Colorado at Otherpower, here in northern New Mexico we're getting hellacious weather, years long droughts, forest fires, then floods and killer hail all last year in 2013. Golf-ball size hail tore the hell out of Kevin's sweet CNC router carved wooden blade set as well as reducing the tail to a nub. I pulled the machine down a couple months ago and replaced both. The tail is fabricated new by me, the blades we had, I gave those a tune up, stuck the whole mess back in the sky the next day. It worked well enough, but still wasn't putting out like it did before I built a new alternator a couple years ago; up to 10 amps from a breeze of 8mph and up. This machine has never furled properly. I've not really had the time to figure out why.

We've had steady 30mph winds recently with gust to 80mph, which happened in the middle of the night twice and I heard it and shut down the turbine.

Wind-turbine-tower-top-bent-again-2014-barely
2008-9 I guess is how long this sweet machine has been supplementing our power. I'm going to figure this out because this is a fabulous sustainable energy device. It seems like besides the issue with not furling, I'll need to completely remove and replace the tower top piece with something much beefier.


Wind-turbine-tower-top-bent-again-2014-barely-noticable
Now here is where you can really see the dent stubby


Wind-turbine-tower-top-bent-again-2014-looking-up-pole-zoom2

Wind-turbine-tower-top-bent-again-2014-looking-up-polezoom2
Just what I need; another can of worms project, but this is what it is

 

[birdhouse]

boss-
sorry to hear about the bent tower stub.  whats the dia. of the mill and what's the top stub (dia and wall)?

i was worried about such issues with my tower before fabrication.  i used a 2" sch 40 for the inner yaw bearing, but sleeved on another pipe as high as i could to beef up the tower stub.  so far i've been fine (knocking on wood).  but my mill is only 8.5' dia. 

i figured the small amount of blade tip to tower clearance lost by sleeving the pipes was well worth the added stiffness. 

adam

[Boss]

The tower is 3" think all square tube,  round stub is schedule 40 2" steel.  The fluting is 1/2"plate steel left over from another project.  The blades are 5' 2" each.  Boy howdy it sure was nice seeing it push 40 amps for a minute,  hehe

[Boss]

Supposed to have read "thin wall"
Brian Rodgers

[birdhouse]

yea, so we have the same stub size, but mine is sleeved w larger pipe right up to the bottom of the yaw pipe of the turbine. 

your turbine is larger as well.  do you have clearance (blade tips to stub) to sleeve your tower stub?  you can even drill large holes in the sleeve to weld the inner and outer along the way. 

adam

[Boss]

I think the stub would have been fine if the furling mechanism worked. Looking at the turbine in action I wonder if I  got the tab on the wrong side of the shaft the tail rotates on

[Boss]

Thanks Adam I like that idea of the holes for welding through too

[Boss]

My main concern at this point is the lack of furling.  I've never seen it furl.  The blades don't seem to fold away from the wind. Seems like the offset isn't enough.  Which is a pain because the fix is completely rebuild the turbine chassis

[JW]

Good to see you posting Brian.

[Boss]

Good to see you posting Brian.

thank you JW 2013 was a pretty awful year here, I hope to turn it around in 2014

[kitestrings]

Hi Brian,

Ya, the winds we've been having have been at times pretty brutal.  80mph, I'd shut it down too.  On a positive note, it's still standing.  Much more, the result would have been a mess.

From the first couple photos it looks like the guys are steep and could move up a bit to reduce the unsuspended length a bit.  Doesn't fix the bend of course.  Sleeve-ing it sounds simpler than other options.

Regarding the furling, are there any variables that you can adjust with less work, like the angle of the hinge, tail weight, or maybe the CL of the hinge moving closer to the pivot?

Good luck with it.

~kitestrings

[SparWeb]

I was just in the store this afternoon buying new ski poles.  Wiped out on some ice recently and as I went down I put way too much weight on a pole and bent it until it broke.  Kind of like what (almost) happened to your tower.

To my eye, it's more a combination of the thrust on the rotor (pretty high in that wind you've had) and the compression on the column when the guy wires are tightened.  How did you tighten them?  If you have turnbuckles, do you crank until most of the slack is up, plus a few more cranks... or are they guitar tight?  If you rap on the guy wire with a wrench does it make a sound like humming or a metallic "zooh"?  It may be a moot point, though - I think the main problem is something else.

Square tubing is not as resistant to column buckling collapse as round tubing or pipe.  The flat faces of the square tube can develop little waves that let it flex more than a round tube would.  Since you are going to be removing a segment of your tower, you should use at least 3" Sched 40 pipe.  More if your turbine is 12' diameter or larger.

[SparWeb]

A temporary fix?
Add another guy-wire station mid-way between the upper ones, maybe.  You can use it to straighten out the big bend, and it will give the tower less length over which to develop a curve. 
Won't help that kink in the top stub - have to replace that one.

Unfortunately it will also add another series of tight cables pulling down on the tower, not helping the column-compression scenario.  Think temporary - just to keep you going as you build a bigger tower.

[fabricator]

I'm pretty sure your tail vane is to heavy for the length of the boom, not enough leverage, you need a longer boom and a lighter vane to furl right.

[Boss]

I'm pretty sure your tail vane is to heavy for the length of the boom, not enough leverage, you need a longer boom and a lighter vane to furl right.

Thank you all for the input. I'm thinking along similar lines. Although my long-term observations coupled with a short attention-span for any particular project of the half dozen I've had in the shop in the last few months, seems to now suggest that the blades are not ever pushing back from the wind. I've noticed this lack of furling since the turbine was first installed damn near six years ago.

Not trying to be contrary, as a small scale professional electro-mechanical trouble-shooter I know how difficult it can be to get a handle on what is happening at a remote site with only the client's description to work with.   

I may be completely wrong, but this is what I think I'm seeing, The tail folds up to the blades. The blades are not folding back toward the tail. There is no dynamic effect between the weight , length and thus leverage presented against the offset of the blades. While it looks like the tail is moving separately from the blades it is not rotating the turbine head.  This is why I tried a heavier tail this time. Trying to make enough weight to rotate the turbine around. No change in angle of attack to wind.

Also while I have 10' 4" blade diameter it was barely 10 foot with the last set which I took down last month. I realize I have added another variable making it more difficult to troubleshoot, sorry about that. What I am saying is none of the three or four blade sets has ever furled, even slightly.  For some reason the force against the blades is not turning the turbine head  away from the wind. When we built the turbine head mechanism Dan and Dan  hadn't completed the book. We used a pre-first edition if you will. I still have it and can look at the numbers for offset and whatnot that we went with.

If it is determined the turbine housing needs to be replaced, we're in better financial shape now than back then and I would consider a purchase. But there is no rush, I want to figure this out first. The information about the square tube tower was spot on. I'm always amazed and impressed at the  experience found here.

With my little LED flashlight in the pre-dawn light I witnessed the tower flex exactly as you said. You guys know what you're talking about.
Thank you all
Lots of info about my setup can be found on my site http://outfitnm.com/wind-power/ 

[just-doug]

here is how i would tune the tail.first,length of the tail boom is the key factor in getting it to point up wind.second factor in pointing is tail surface area.to get the thing to fold up out of the wind,the tail hinge is the course adjustment.45 degrees is late furling 22ish is early furling.tail weight is a fine tune for furling.heavy tail is later furling ,lighter tail is early furling.let us lnow how it goes.

[Boss]

thank you for this information. Perhaps as well, I'll make a new turbine stand which is tall enough to let the blades spin freely where I can reach the tail so I can better get an understanding of these relationships between turbine offset, tail length and weight: 
"... first, length of the tail boom is the key factor in getting it to point up wind.second factor in pointing is tail surface area.to get the thing to fold up out of the wind,the tail hinge is the course adjustment.45 degrees is late furling 22ish is early furling.tail weight is a fine tune for furling.heavy tail is later furling..."
Are you all mostly in agreement that my trouble is the tail, not the offset? I was thinking the wind force was always pushing the blades back, but I am hearing the tail moves the blades back

[fabricator]

If you put it up without a tail it will just turn out of the wind, the tail holds it into the wind until the force of the wind pushing on the rotor is too much for the tail configuration you have to hold it into the wind. The tail keeps pointing into the wind and because of this the rotor is rotated away from the wind.
If you have any offset at all it should work fine, my machine has a six inch offset and it furls fine but my tail is very light.

[Flux]

His description is the classic one of wind seeking ( something that some people refuse to accept exists)

If you put it up with no tail and it has a small offset it will turn out of the wind but if you get it to face the wind long enough to get it up to speed it will hold head into the wind and go flat out. There is a critical offset that has to be exceeded before it will come out of the wind.

If the offset is too small it will not furl and it will push the tail round towards the prop and convince you all is well until you check the prop axis against an independent indicator of wind direction.

The critical offset depends on the type of prop and the operating tsr, some machines such as Bergey will run with their prop and very little offset. If you change to a different type of prop it will hold upwind even without a tail.

If the offset is above the critical you can tune things with boom length and tail weight to get the furling where you want it. If you are below critical offset it will just not work no matter what you do with the boom, tail weight or area.

From the description of what is happening I suspect the offset is too small for that prop.

Flux

[fabricator]

That is possible, it would be nice to have an offset number.

[letERblow]

Flux     I can see how spinning blades could seek the wind, with gyroscope action and wanting to have equal forces all around the circumference. This is where  the critical offset is necessary to overcome these forces. But where is the force coming from that holds the tail at 90deg to the wind? Wouldn't it want to take the easy path and ride down the incline and stay parallel with the wind flow?

[Flux]

This question indirectly came up in the next post, I have answered it there as best as I can.  I think we have to assume that at best the wind behind the prop disc is very disturbed and when the seeking force takes over the wake is so tubulent behind the prop that the tail vane has no real idea of the true wind direction.

It seems as though the tail will line up along the helical vortex direction rather than the true wind.

Flux

[ChrisOlson]

If the offset is above the critical you can tune things with boom length and tail weight to get the furling where you want it. If you are below critical offset it will just not work no matter what you do with the boom, tail weight or area.

Flux, been gone for awhile here and this thread is a little old.  But basically in my experience the reason a lot of these homebrew turbines don't furl correctly is because the efficiency is too low and they don't produce any real power.  So the homebrew designs have gone to lots of offset to try to get them to furl.

In order to generate thrust with the rotor you have extract the energy from the wind.  That's what makes your thrust.  You can't let the kinetic energy in the wind slip thru the rotor's swept area without being harnessed and expect to make any serious thrust.  A 3.0 meter turbine should be running at 2.2 kW output @ 28 mph and few of the homebuilt 3.0 meter machines make much better than 750-800 watts, maybe spiking at 1,100 every now and then.  That's only half of what that size rotor should be producing.  The rotor thrust is so low, and so unpredictable, that they don't furl right.  If you get the overall efficiency of the machine at 30% or better, with the rotor at Cp .40 or better, then you need very little offset to get it furl correctly.  That's why the Bergey Excel-R, which has about 5.5" of offset with a 7 meter rotor, furls very reliably.  And why the Jacobs 23-10, also with a 7 meter rotor that has no offset at all, furls very reliably at ~40 mph even with the governor running with the blades partially feathered, just from the torque on the gearbox output shaft to the generator.

[Flux]

Chris
I think you are right, I have had little experience operating machines stalled and it took me a while to puzzle out why many of these machines fried in high wind.

I believe they normally protect by stall and although the tail moves round they are not furling. If a really big wind comes and it pulls out of stall then the thrust will rise and it will furl. If this happens within the capabilities of the stator then all is well but if the furled current is too high it will burn out.

The snag with this scheme is that until the big wind comes you don't know how it will behave and it could be several years of running before you find out.

Flux

[ChrisOlson]

For a machine that seems to not want to furl properly I would stick a quarter to half ohm of resistance inline to let it spin.  That's not going to get any more power to the battery because it will dissipate the additional power produced in the resistance.  But it will improve the efficiency of a turbine that is running too slow by letting it run at higher voltage.  If it then seems to furl properly the problem is simply a generator that is over-wound and trying to produce too much voltage at low rpm, causing the blades to run inefficiently at higher rpm.

Too much offset is not good.  It causes the machine to not track the wind properly.  And it will still not make a poorly performing turbine furl correctly because without the rotor facing the wind and producing the proper power for its size the thrust it produces is unpredictable.  I did not learn this relationship until I started building high-voltage turbines with MPPT.  I found that very little offset is needed with them.  As an example, this is the head frame for a 3.5 meter machine that produces 3 kW @ 30 mph.



The offset, from the yaw centerline to the mainshaft centerline, is only 4.7 inches.  The tail is very long (86 inches) and very heavy at the tip (41 lbs).  With that little offset I had to keep adding weight to the tail tip to keep it from furling too early.  It furls at 35-36 mph producing around 4 kW on a 48V system.  It starts furling at about 30 mph but its power output doesn't level off until the rotor gets past ~30 degrees from true wind, and it is still producing 4 kW @ 60 mph with its output only being regulated by how much the effective swept area is reduced from furling.

The tower shown in this thread that has the stub bent would not hold my 3.5 meter turbine even in 20 mph wind because it develops over 300 lbs of side thrust and approaches 580 lbs of thrust at full output.  That's because the rotor is catching 44% of the kinetic energy in the wind that passes thru its swept area instead of only about 20%.  The rest of the thrust is pure drag coefficient on the mechanical bits of the machine.  If I built this machine with 6" of offset it would barely run and be tracking 45° off true wind all the time, and then it would not furl reliably at all.  I know that because I already been there and done it, and it didn't work.

[Flux]

Yes, again I agree with this. I similarly never managed to sort out some of the quirks before I tried mppt. I always thought that the gain would only be in high wind. I was very surprised to find that direct coupled machines go into stall just above cut in and there is a fair bit to gain here from mppt as well as the spectacular gain in high wind.

The furling idea is based on the thrust being proportional to power out, but this all goes wrong when the prop is sliding right down the stall side iof the power curve.

I similarly have found that up to 30deg there is virtually no drop in power which is good as most machines track way off the true wind direction. Many assume that this first 30 deg of tail movement is an indication of furling and are forming the wrong impression.

I know that you didn't get any more power into the battery when adding resistance but your machines were never stalled as hard as many are. With very hard stall I have found that the gain from the prop exceeds the electrical loss from the resistor and there is a net gain. Even with no gain the resistor can be worthwhile if the heat can be used usefully in an immersion heater  and it does sort out much of the furling problem.

Flux

[ChrisOlson]

What happens with a turbine blade is that when it running too slow it runs at a very high angle of attack.  That reduces lift and increases drag, so the blade is running very inefficiently.  Then a wind gust comes along and now the tip speed of the rotor is too slow for the relative wind speed and it stalls the airfoil.  The rotor cannot increase its speed to match the wind because the generator is too "stiff".  So now you have a rotor that is not tracking the wind, running badly stalled, and creating no thrust.  Suddenly the wind switches directions in the next gust so the relative wind is head-on with the rotor.  This pushes the rotor out of what you think the wind direction is and makes it look like the machine is furling, when it's really not.  It is simply stall regulating itself.

These kinds of machines are dangerous because if a really strong gust comes along and pushes the machine to a higher output, then the gust dies down a little, now the rotor comes out of stall and the blades start making decent lift because of the rpm vs relative wind speed.  When the rotor gets "boosted" like that and brings it out of stall, now it can easily overpower the generator.  If the wind conditions remain such that the rotor continues to run at a more efficient speed, overpowering the generator, it will burn the stator.  That's why I don't particularly like stall-regulated designs.

[midwoud1]

Simulation of variable blades.  250 -330 Rpm.
 With a programmable switch ,Arduino m-controller and a Rpm chip LM 2917 as we have in all our cars.
At high wind and  high propeller speed an actuator pulls the blades in ,  4 degrees.
After 3 steps ( 12 degr. ) blade stall start . Slim blade tips is low noise.


http://www.youtube.com/watch?v=Y6CEBIzXdmc

[Smithson]

Hi Boss:  I don't see how it would be to hard to fix the offset on your turbine.  Just cut the turbine support near where it joins the yaw.  Then slip a black iron collar over the two ends and weld to the length you want.  You could also fix the problem where the blades are to close to the tower by tiling the whole unit out at the bottom before you weld.

http://outfitnm.com/wind-power/bmn-painting-the-wind-turbine-housing/

I realize that by this time you have probably fixed the problem.  Just a thought.  Arch