 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Windmills : windmill still runs backwards
Page 1 of 2   |
|||||
| Author | Message | ||||
GWatPE Senior Member  Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi all, I have witnessed an unusual site. I will not reveal the location. I have seen a 1kW chinese mill perform a feat of magic. The mill was enabled in moderate winds without a load. The machine got up to about 400rpm and when a lull in the wind came, the mill turned around and faced the wrong way. The rotor did not stop turning and go the other way as you would expect. The machine kept spinning the same direction. Would this indicate an issue with the blades, to still provide sufficient lift to rotate without much speed loss, even when spinning backwards? This would suggest that if the blades were assembled backwards, then the machine would spin the other way, and not just slowly the usual way. This was not a once off event, but was reproducible. Gordon. become more energy aware |
||||
philb Regular Member  Joined: 05/07/2008 Location: United StatesPosts: 96 |
Can't ever tell what the Chinese with think of next. 
Sounds like the surface area of the tail is too small for adequate control. The blades may also be backwards as you stated. I remember once, when one of my generator's lost it's tail. It turned around backwards and started generating power in the opposite rotation only after a full blade stop. It became an instant and very noisy downwind turbine!  philb |
||||
| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi phil, sorry, but the blades are on the correct way, duh. I used the if example, and did not state that the blades were actually installed backwards. On a load, the mill works fine. I was hoping someone with an aeronautical background may be able to shed some light on possible reasons. Gordon. become more energy aware |
||||
Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669 |
Gordon, Until you get an aeronautical experts opinion, you might consider 2 factors I suggest as contributing to your phenomena. Firstly. As the mill is unloaded it will spin faster then normal also when the wind drops off the stored inertia in the blades causes it to drive the wind instead of being driven. The drive together with the offset causes the mill to yaw. Secondly. The consistent fixed pitch of the Chinese blades with it's angle of say 3deg now becomes -3deg. This is still within stall limits considering the No Load and faster revs. Note: normally a root angle of say 45deg is 3deg on a Chinese prop so the angle of attack @ root is normally 42deg. Turned around it becomes 48 deg. Not a great increase when coupled with the increased speed of no load. For all their breaking of optimum design rules these blades still work well, causing very odd behaviour in out of design conditions it appears. 
Edit addition: When the mill yaws from wind drop off, I see the prop swept area drag with it's offset finding a balance with the backward facing tail. All goes well with wind speed variations until the wind changes direction. I forecast the tail to swing(slam) fully to it's furl position and cause the mill to yaw back to normal. Is this what happened, Gordon? was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
||||
| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi Gill, A 1kW chinese mill has a twisted tapered blade, with a flat mounting surface for the blades. [not the same as the 200W, or 300W, or 500W models] I have held a spare blade of similar dimensions that I have and looked at what has to happen to the airflow over a blade when what I have seen happens to the mill. The blade did not continue to spin with just inertia. The only way to stop the rotor was with the electrical brake. The tail did not slam around and push the rotor back into the wind. Just imagine your own windmill. The rotor is spinning normally with the blades on the correct way. The rotor continues to spin, but the windmill faces the other way, so the tail is into the wind and the rotor is now downwind. The rotor continues to spin the same way when looking at the nosecone, but it is now cutting the air the wrong way for the wind direction, but continues to keep spinning. The angle of attack is actually negative. The curved surface is somehow still able to generate lift, to allow rotation without a change in direction. I am not going to lose much sleep over it as the mill performs really well when loaded. These mills seem to be pretty well made compared to the smaller cousins. I have seen a another problem with a larger commercial downwind machine, that seems to get stuck facing upwind following a change in wind direction after a lull. These mills finally get it right when a gust comes suddenly from a different angle and the rotor swings around and all becomes good again. Gordon. become more energy aware |
||||
| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
Reading this and other stories about furling failures, I can't help but think about an active system for turning the turbine in and out of the wind. The advantages are obvious: no more long (and ugly, IMO) unelegant tail and vane needed; no need for sliprings, or ever unwinding the powercord. Easy 'push of a button' turning out of the wind of the turbine in case of strong winds, or it can be done even automated ('above nnn generator RPM, turn not into wind direction but direction + 90 deg') It shouldn't be too hard. A large cog at the yaw pivot, a small cog on a relatively small motor (windshield wiper motor?) with gearing, a few contactors or solid-state relays, an electronic windvane and some simple electronics to integrate wind direction and periodically drive the motor for corrections (once every 10 minutes?). A manual override (manual switch to power the motor in case of electronics failure). Or could even operate the contactors manually if need be. Am I the only one out there thinking about this ? I read very little about people experimenting with such systems, but I recall reading about such a system on FL a long time ago. It's doable. Reliability may be an issue as there are more components involved. But still... it would solve a few other problems. And yield a much more acceptable looking (more aesthetically pleasing, at least in my subjective view) windgenerator in return, without a long tailboom nervously moving about and introducing rapid direction changes with accompagnying large gyroscopic loads on the blades and tower. It'd probably only be worthwhile for larger windturbines anyway. (10 hp motorconversions ?  )
Peter. Edit: found the site I was looking for. Sorry, only Dutch, but still interesting to look at just the pictures. He solves the problems very differently from what's commonly done here. http://www.windmolensite.be/ Picture of the yaw mechanism: http://www.windmolensite.be/fotos/aktief/2006-04-04%2019-36- 50.jpg Also, this is an interesting gadget to connect induction gennies to the net. (in English): http://www.windmolensite.be/sturing-netkoppeling.html |
||||
| Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669 |
Gordon, I understand the blades are not as I related though the effect remains the same. The prop inertia is responsible for the yaw. Once gybed the relative wind is from the new direction as per the unchanged prop rotation. The angle of attack is larger not negative as you understand. The larger angle of attack promotes faster prop rotation though this is offset by the drag from the profile which is now reversed to normal. But it is nice to leave behind the meticulous diagnosis of wind turbines and just see magic. was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
||||
SparWeb Senior Member Joined: 17/04/2008 Location: CanadaPosts: 196 |
I suppose you could call me an aeronautical engineer, but I won't pretend that what you observed is "obviously" this or that. It sounds like the windmill doesn't have a lot of directional stability. This could be because of a small or short tail. Once the windmill is spinning in the normal direction, turning it around 180 degrees would make the airfoils work in reverse, and have an angle of attack reversed. There's no law preventing an airfoil from acting like an airfoil with the air flowing backward, you only incur a penalty on efficiency. I think the key to your observation is that there was no load on the windmill when you saw this. The blades probably don't have twist, and the angle of attack may or may not be small, too. In that case, the thing is free to run fast, and with straight blades, there isn't enough reverse-airflow angle of attack to actually stall. Just enough power was being produced to keep it turning. Without a load, the only thing it has to overcome is friction in the bearings, not to mention its own airfoil drag. Overall, you're darn lucky it did what it did. I know I don't have to tell you that an unloaded windmill can reach very high speeds of rotation. Steven T. Fahey |
||||
Bolty Regular Member Joined: 03/04/2008 Location: AustraliaPosts: 81 |
Hi SparWeb. I don't mond admitting that Gordon was referring to my installation. I am lucky that I live quite close to Gordon, and it is very rewarding to have his help! I am very impressed that Gordon observed this phenomenon and found it so interesting that he tried to explain it! I only saw it as magic!!!! I had been previously wondering about the directional stability. Even when under normal load conditions,I have noticed that it is slow to follow the wind in turbulent conditions. I guess that this is partly due to the wight of the tail arm, which is a very heavy piece of square galvanized tubing measuring about 4 X 2 inches. It also has a quite flexible sheet metal tail that is both above and below the arm. Gordon has suggested that I should replace the tail with a more elegant looking single wooden tail. I think that you are right with your explanation. You have summarized the blades characteristics very well seeing that you have not seen them. They don't have twist and the angle of attack is quite small! In fact there is some slight asymmetry in the blades. On slow rotation, you can notice that the end tip of one blade is virtually flat, where the other 2 have a slight forward attack (say 1 or 2 degrees) I was looking at a way of increasing the low end power from this turbine. The blades are each 1.3 metres giving an overall diameter of 2.7 metres. I have contemplated fitting spacers between the hub and extending each blade out by about 400 mm, bringing the diameter to 3.5 metres and increasing the swept area by 68 %. I realize that this is an imperfect design, but I could get up to 50% more power at lower speeds. I am not after a boost to top end power, as the wind regime here rarely produces the 1KW anyway. My average power is only around 200 watts so boosting this by 50% would be worth the effort. Dual electronic braking and furling should prevent overloading in high winds! I would welcome any opinions on this from anyone! One extra modification that I could easily do with these blade extenders, would be to slightly increase the angle of attack of each of the blades, and also eliminate the slight variation that now exists at the tips. Any thoughts? BTW when the turbine was free spinning we were testing the ability of the turbine to furl under no load, simulating an electronic brake failure. I might add that the wind was obviously not strong enough at the time, as it did not furl! I might also add that I had SWEATING, ITCHY fingers firmly place on the manual brake switch, ready for any eventuality! Regards! Bolty |
||||
| Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669 |
G'day Bolty, As I understand it the point of highest probability for stall is around 1/3 max revs. Now I'm not saying your mill is stalling, but if this is the area you would like to see more power, you could try a little resistance in the DC line to the battery. Try some stainless steel wire or thin threaded rod. This will reduce the load of the battery on the gen and cause it to spin faster. If the mill is a little to loaded in this range(designed for the impressive high speed powers they quote that sells machines), this may produce the desired result. If all is OK there is nothing much you can do with the existing setup and it's swept area to increase power. The beauty is, it costs so little to try and you need no modifications to existing structures. Worth a try? was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
||||
| Janne Senior Member Joined: 20/06/2008 Location: FinlandPosts: 121 |
Dinges, I think the scheme you are proposing for yaw mechanism would be a good idea in some larger installation, mayby grid tied, that gets constant attention. But on top of that, some other backup would be needed, like an automatically operated disk brake. But for these smaller machines, that mostly have to survive on their own sometimes for long perioids of time the KISS approach is the best. Too much to go wrong with all the fancy electronics and mechanics. Especially here, with the freezing conditions in the winter. I've had my share of problems too with the mechanical furling, but I'm going to keep banging my head onto it, as once set up well there's really no other part to go wrong with it except the tail hinge. One Finnish guy with his 6m diameter windmill ran into a lot of problems, with all this kind of fancy electonic controls. The whole system ended up taking so much power to run and maintain, that in the long run, it consumed more grid power than it made. He also had lots of problems with reliability. (Though the main problem was not with the yaw mechanism, but more with the overall complexity, like the hydraulic servo controlled pitch mechanism) So for a "minimum" size of machine, that I would try this would be somewhere in the region of 10-12m rotor diameter, where the regular "KISS" forms of control become difficult. If at first you don't succeed, try again. My projects |
||||
oztules Guru  Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Dinges, These things form the backbones of the two bigger mills down here. I am currently rebuilding these ones which are faulty..... they have their problems I'm afraid. 
..........oztules Village idiot...or... just another hack out of his depth |
||||
| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
Janne, I think such a system can be made to use very little power. Just a few mA for the electronics, and every 10-15 minutes a few seconds of several amperes as the yaw motor kicks in (or not, if it's not needed). With a relatively wide 'acceptance band' of angle-error (say, up to 30-40 deg) I don't think it'd even have to work often. No need to constantly track the wind within a few minutes of angle. I don't think it'd have to be very mechanically and electronically complicated and unreliable. BTW, I forgot to mention... a manual diskbrake for the 10 hp conversion is one of the plans/ideas too. Belt and suspenders security: 1) turn turbine out of the wind with yaw motor (or furling); 2) short the outputs electrically; 3) brake the turbine with diskbrake. There's no better kill than overkill 
Of course the above is still just mere fantasies and brainstorming at the moment. But I very much like how BruceDownunder implemented a diskbrake on his F&P generator. Just because no one else (in their attempts to simply copy Hugh P. or the Dans) does it doesn't mean it's not a sound idea. In the same vein, I'm seriously beginning to think about active yawing. I will *not* consider pitch control of the blades. That's one bridge too far for me. KISS is indeed an important design concept; but so are safety and reliability. I'm not sure that the standard furling method is either simple or reliable, at least, not as I usually see it implemented (think: tail held to bearing by gravity, 'hard' mechanical endstops (no damping to prevent slamming into the stops or other rapid movements), no manual furling override (exception: Southern Cross-like systems), rapid yawing resulting in large gyroscopic forces. If I'd build a furling mechanism it'd have to overcome these problems. Oztules, You're beginning to give me an inferiority complex here... Every time I have this brilliant new idea you pop in and say 'been there, done that, and now I'm repairing it'.
Anyway, if someday you decide to do a write-up of the problems of those two installations and how you solved them and/or repaired those particular control modules, you'd have at least one attentive reader. Peter. |
||||
| Janne Senior Member Joined: 20/06/2008 Location: FinlandPosts: 121 |
Pitch control in my mind also is problematic; especially with wear and tear problems. But thinkin about it, it pops into my mind, that a significant amount of the strain to the mechanism comes from the yawing action on the turbine, when working in high speed. The active yaw control would solve these kind of stresses, as with it the machine can be turned slow enough not to cause extra strain. That is one good side on the motor conversion; you already have an unused end of shaft, to mount a disk brake on. Even better, if one would be lucky enough to find a motor with a built in brake, with lever operation.. like the one in my tilt up tower winch ;). The brakes you usually find on these motors are not very big, but should propably handle an ocassional stop from full speed without cooking up. Yes, very much true with windpower  If at first you don't succeed, try again. My projects |
||||
| oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Dinges, I have been wrestling with the furling (standard gravity style) for a bit now, and am less than enamoured with it's natural characteristics. It bucks, kicks, wanders around, get's blanked by the main rotor and starved for air.... all up it seems to be a compromise between out of control, and no power at all. Having said that, it is important to remember that this installation (and I use the term very loosley) is only a few feet above the ground. It is very gusty and fickle with direction. This means the poor old furling has a devil of a job to stabilise. However, as it amplifies the shortcomings of the system, it makes it easier to see where it has difficulties. I like the idea of no tail and power yaw. It is not as simple granted, but in a poor wind site (close to the ground, or shadowed by trees perhaps), to stick to a direction unless over powered, or a true wind change occurred, then you would pick up a substantial increase on KWH over the current method. In it's current position, it spends a lot of time in the 300-700 watt area, when it could easily be in the 1kw area constantly if it had a dynamic pitch control, or a smart yaw system. So I am still waiting to see the Dingesman super yaw system.... so I can run out and copy it.... might even have welding gas by then.
..........oztules PS There is an sinister looking dude where Catweasel was.... I can't help but think something untoward has occurred to the weasel. Village idiot...or... just another hack out of his depth |
||||
| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
Don't hold your breath. At the rate I'm progressing lately you'd end up blue in the face (or worse) before I had something to show for. But it's reassuring to see I'm not the only one who isn't 100% satisfied with the current furling system. Catweazle had a little run-in with some elektrickery and won't be back soon. Something about 380kV distribution lines and flying kites. ... but what do you mean by 'sinister' ?... That's my happy face! Had to scan the passport photo for something else but thought it'd also make a nice avatar for this site. Blame the guy who made the passport photos. First batch got rejected because of the presence of a smile. But yes, I think I overdid the 'must not smile!' routine in the above one. If I get enough complaints I may revive Catweazle...
|
||||
| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Oztules, dare I suggest that much of the bucking and kicking one sees in a HAWT is gyroscopic forces at work. The mill yaws suddenly and the turbine tries to tilt up or down and everything we build has to be strong enough to accommodate these forces, plus of course these same forces resist the mill yawing to catch the latest wind. Maybe a non-rigid turbine is worth looking at? Fully teetering or even fully articulated. Wind turbines and helicopter rotors are bound by the same laws of physics and it makes good sense to consider which solutions in one may be applicable to the other, IMHO of course.  |
||||
| SparWeb Senior Member Joined: 17/04/2008 Location: CanadaPosts: 196 |
Hi again, If I could interject a few more comments here... The topic of this thread has zigzagged a bit and settled on "what's wrong with folding-tail furling". A popular topic, these days. I think the biggest problems people are having with it are that A: they expect too much and B: they don't understand what's happening. Fear what you don't understand. Folding tail furling is an equilibrium of forces. A couple keeps it facing the wind, a different couple takes it out of the wind. Once one exceeds the other, the furling goes into action. If built correctly, and used away from significant turbulence, this system will work VERY WELL. Mine has remained furled and protected in very strong winds. I should add that I have an engineering background and went to a lot of trouble to understand what was happening when I first built it. But I never found the perfect "formula", but I filled in the blanks by gradually increasing weight in cautious small steps. Anybody could do it that way, and succeed. Figuring out this furling is really tricky, and the average builder is not interested in pursuing the minutiae of trigonometry. Some of us were called "nerds" in high-school, but some of us weren't. Abandoning something that is mechanically simple because it is mathematically complex, though... Back to the thing I said about equilibrium. Some turbulence won't shake it, but a lot will upset that equilibrium. When the opposing forces are strong, the turbulence required to upset the equilibrium must be high. If the forces only marginally cancel each other out, then very little turbulence is needed to bump the tail back down. Face up to the fact that the more turbulence your windmill experiences, the bigger the margin has to be on the furling limit. Since turbulence is nasty on bearings, towers, guy wires, and blades, you're doing yourself a favour in all respects by furling early. Since it's so hard to "get it right" the first time, nobody should expect to. I certainly didn't. So plan to tweak it several times at least, and whenever other changes to the windmill affect its power, speed, or TSR, then expect the tail to need tweaking, too. Steven T. Fahey |
||||
| mbombay Newbie  Joined: 17/09/2008 Location: IndiaPosts: 5 |
- You don't have to be an aeronautical engineer to understand the phenomena. It possibly is happening due to the symmetrical design of the wind blades where the blade can face the wind any which way but continues to get the lift or the drag.... It could also happen if the design is inspired by steam-powered locomotive design that ensure the driving wheel moves frontwards no matter how the piston shoots... We all know a piston provides power through a connecting rod directly to the driving-wheel in a steam powered locomotive. But do we know how the driving wheel moves only frontwards and not the other way-round? Thanks - |
||||
| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
I don't think you have visualized what I described. Gordon. PS: steam locomotives uses use valving to control the steam to the driving cylinders. I think this has no bearing to a windmill operation. become more energy aware |
||||
| Page 1 of 2 |
|||||
 Print this page |
 |
The Back Shed's forum code is written, and hosted, in Australia. | © JAQ Software 2025 |
