Author Topic: direction confusion (Read 6902 times)

dlenox · « **Reply #33 on:** March 17, 2010, 05:48:59 AM »

Chris,

It is pretty obvious that you have put a lot of time into experimenting with alternative designs.

One thing popped into my mind yesterday and was generated by the image that you showed with the tail on center with yaw bearing using a gas spring. I have to admit that I very much like having the tail in-line with the yaw bearing and not offset or using an angled hinge.

Now the tail serves two purposes 1) keep the turbine pointing into wind 2) help yaw the turbine out when the wind speed gets to some amount. But rather than a dynamic furling motion why not put in an electric actuator to yaw the turbine?

Obviously this is a slight complication as there has to be circuitry for control, an actuator and a power source. But it's pretty much guaranteed that when the wind is coming strong that the turbine is putting out power that can be tapped into. Not to mention that we already rely on a dump controller to operate or our turbines would easily burn themselves up.

Perhaps by using something like Ghurds dump controller, so that when a certain voltage is reached that it engages the actuator to initiate the yaw. Once the voltage drops below a set point (over a period of time) that the controller returns the actuator back to the 'normal' position.

There would have to be enough hysteresis in the circuit so that it would not act like a yo-yo, and yaw - unyaw - yaw - unyaw, but maybe to find some happy 'middle ground' and sustain this max turbine output voltage.

Perfectly honest you could use Ghurds 'auto-shutdown circuit' as well to initiate a mechanical brake for shutting down the turbine. This essentially gives you a back-up incase the yaw ceased to function.

As DaveB says that with these home built machines there are so many variables that either work for you or against you, that some sort of positive yaw control could 'fix' a lot of the furling issues that people are having. So it would not matter say which blade set you are using on a turbine, at a specific voltage it furls - end of story.

Dan

poco dinero · « **Reply #34 on:** March 17, 2010, 06:35:46 AM »

Hello Dan,

I'll be happy to take some pictures. Have to tell you though that I"ve never posted a photo, but I'll give it the old college try.

If I'm successful the pictures will show up in this thread.

poco

ChrisOlson · « **Reply #35 on:** March 17, 2010, 06:58:46 AM »

Dan,

That could definitely be done with a bit more complication to the system. All you'd have to do is replace the spring loaded cylinder with a linear actuator. The only problem I see is reliability - if the actuator failed, or you had a broken wire or some such, it could fail to furl in high winds when you need it.

I experimented with building an electric yaw drive and discarded the idea as being too complicated, and toyed with the idea of electric steering control but discarded it due to the reason I stated above. I kept going back to Jacobs' spring loaded double hinged tail system, which has worked well along with their variable pitch prop governor. The variable pitch governor would be nice, but I don't think required on a smaller machine of 20 feet or so.

--

Chris

TomW · « **Reply #36 on:** March 17, 2010, 07:03:47 AM »

poco;

If I'm successful the pictures will show up in this thread.

Get them uploaded to your files here, post a note that you did and I will either link to them or post them into this thread if you don't figure it out.

Tom

Royalwdg · « **Reply #37 on:** March 17, 2010, 07:06:38 AM »

Blade type has a lot to do with furling characteristics. So does the load as DaveB has said many times. The blades I build are long and slender. This requires a little more furling offset than the wider root blade that the Dans build. About ten percent more.

What the heck is WIND SEEKING. Was this term invented to act as a catch-all for "stuff" that is not understood. When these tail wagger machines furl they turn away from the wind and slow down because they are not "flying" efficently any more. When that happens the rpm drop and so does the work that is being done. Then it will try to swing back to the wind and get back to work. If it realises the same condition it will do it again. They are doing what they are supposed to be doing. It will never stay pegged fully furled if its working right. Has any experiencing these out of control "wind seeking" machines actually monitored the output during this "wind seeking" phenomenon. Tell us what you see. Unfurling in a strong wind does not always mean danger.

dlenox · « **Reply #38 on:** March 17, 2010, 08:14:43 AM »

Dave,

Yes what you mentioned is true that the yawing often times is a see-saw motion.

What I have experienced is that the machine furls successfully at say 28mph, but at 36+mph the turbine head apparently pulls itself out of the furling position, and refuses to furl until wind speed decreases.

With my 17' turbine it has put out anyware between 4.5 - 7kw of power, and the last time the stator burnt as a result.

Hope this helps.

Dan Lenox

dlenox · « **Reply #39 on:** March 17, 2010, 08:20:51 AM »

Chris,

thanks for the info, as Tom says - I just throwing things out there and see what sticks...

trying to see if there is some sort of active furling could be incorporated rather than relying on a whole series of circumstances having to be near 'perfect' to accomplish furling.

Dan

ChrisOlson · « **Reply #40 on:** March 17, 2010, 08:51:06 AM »

What the heck is WIND SEEKING.

Dave,

I have never seen what Dan refers to where a machine furls and then unfurls itself in high winds, generating dangerous amounts of power. However, I have no reason to doubt that this phenomenon exists because he's not the only person who has described it. I have a theory on how this could happen, but it's a theory and therefore probably mostly conjecture, so I won't go into it. "Wind seeking" is the term that has been applied to this phenomenon.

I do think "wind seeking" is an isolated thing based on the fact that people who have had it happen usually describe situations where the machine appears to furl normally later on - without changing anything.

What I have seen is that changing blades on my own machines has caused them to fail to furl due to the new blades developing less thrust and more rotational power - and the furling point has to be reset to compensate for it. Your GO222 blades are a blade of this type (very similar to what I've gone to on my smaller machines) - they develop more torque, and require more offset/less furling resistance, than the common homebrew blade style. Because of this they WILL burn up generator stators if the generator isn't matched to the blades and the furling system set properly. But this is not "wind seeking" - it's merely a different setup.

--

Chris

ChrisOlson · « **Reply #41 on:** March 17, 2010, 10:08:10 AM »

Dan,

I can whip up some drawings of my cylinder later tonight (I never made any) and send the specs on it to you by private email if you'd want to look it over closer. I am fairly confident it removes some of the "what if's".

The day we got enough wind to furl my 8 footer with this tail on it, it was super-smooth. I wish I could've caught a video of it but my wife was gone to Minnesota and had the video camera with her. The tail never moved when it furled - it was like the tail was tied to an anchor with a rope. The head started turning out of the wind at about 400 watts (this is a 12 volt system on this one). A few stronger gusts came and I never got a chance to record the wind speed on my chart because I was outside watching the thing to see how it was going to work. I watched the head turn so it was slammed right up against the stop from the wind, the rotor slowed down slightly then it slowly turned back into the wind and rotor sped back up.

I ran back inside once to look at the ammeter and it was right on 28 amps - just where it was when I ran outside to see how it worked. So I threw the shutdown switch, clambered up the tower quick and gave the screw 9 turns with a 3/4" wrench. Then I let it go and this time it went to 62 amps and the voltage went over 15 volts (I don't have a controller or load diverter on this machine). I ran outside to see where it was and it was running fully furled with the cylinder compressed all the way and the rotor had stalled and was already turning itself back into the wind. So it peaked at 62 amps at right around 15 volts (or maybe a bit more) into the batteries, which is right around 930-950 watts.

So I left it there because the generator in that machine can't be hurt by anything less than 90 amps.

I have to admit I was pretty happy with it after several weeks of scheming and dreaming about how to build something that's easily adjustable, and that only really depends on one variable - how much thrust does a rotor make to actually apply the force to the offset and steer it out of the wind?

Take a good look at what I did here - it's really very simple - if the rotor makes 21 lbs of thrust you don't have to do 3 pages of mathematical calculations to figure out the moment of the rotor and the counteracting moment of the tail. You just apply that same 21 lbs of counteracting force to the same offset point that the rotor is applying it to, with a spring cylinder.

It works and I was pretty impressed with it. A lot of my experiments don't turn out as expected. This one did. The biggest unknown is how much thrust does that rotor actually make? I elected to set it on the low side after doing some in-shop measuring on my angled hinge setups, then crank it up when I found out how close I was. As it turned out I was WAAY below - and I found out it don't take very much to increase the power output because that cylinder only changes the pressure required to compress it by 8 lbs at peak. And cranking it 9 turns over doubled the power output.

--

Chris

Royalwdg · « **Reply #42 on:** March 17, 2010, 10:18:23 AM »

Chris , I also agree that direction of rotation and which side we furl to. Gyroscopic procession is real and has serious effects on fast spinning things. we have found that if the rotation is not right it will fight furling. I would suspect that it could reverse the direction that you want to go. we have first hand experience with this force. Lets try to see if any or all of these machines exhibiting this condition is set up to improperly(in my opinion) clockwise rotation furling to the right or counterclockwise furling to the left looking from the upwind direction. DaveM

ChrisOlson · « **Reply #43 on:** March 17, 2010, 11:18:43 AM »

Dave,

General consensus is that if you have a clockwise rotating machine (viewed from the upwind side), then the offset should be to the left (viewed from upwind). I've never done that. All my machines are clockwise rotators with the offset to the right, which goes against "conventional wisdom".

Any time I've had one fail to furl it was only because it wasn't set up right - too much tail hinge angle, too much tail weight, tail too long, generator not matched to the blades, or not enough offset. Once corrected, they have all worked fine.

--

Chris

Dave B · « **Reply #44 on:** March 17, 2010, 12:11:02 PM »

I don't want to generalize so I will only state what I have found to be true with my 16' when I basically started with trying to scale up the 10' plan.

#1 and most important is that the blade profile was huge with the effect on furling.

#2 the direction of rotation with respect to the offset side was huge with the effect on furling.

#3 the electrical load, battery charging or resistive heating etc. was huge with the effect on furling.

It took a considerable amount of time and fabricating (thanks Dave M) to get this machine working as great as it is now.

It is a system of components that must work together. Anyone not willing to or those who don't have the resources to work with the design of their own machine will soon realize it's not a plug and play thing.

Good luck to those working on several different ideas with the larger machines. I like simple, the gravity tail has been around a long time and it works. Funny, we don't hear too much from the Dans on problems with this either ?

For those fighting with this furling thing I sure would think there would be more interest and questions to those who appear to have it nailed but then maybe that's just me.

Dave B.

ChrisOlson · « **Reply #45 on:** March 17, 2010, 12:21:48 PM »

#2 the direction of rotation with respect to the offset side was huge with the effect on furling.

IIRC DaveM's blades are counterclockwise rotators so you have your offset to the right now?

--

Chris

Dave B · « **Reply #46 on:** March 17, 2010, 01:09:06 PM »

Chris,

Yes, looking from upwind at the face of the machine my offset is to the right of the yaw axis and my blades turn counter clockwise.

I burned up a couple stators and smashed an 18' set of blades during the "tweaking" of my machine. Powerful blades was and now certainly is a good problem to have once under control.

We lessened the tail angle as well as carved a new set of blades to rotate counter clockwise. I guess I felt it too obvious to mention the air gap is also a huge contributer to how and when the machine furls, this of course is directly related to the load, RPM and power curve.

I am sold on not changing the gravity furling tail. When the most successful machine out there is over 20' diameter and has been flying for millions and millions of miles for how many years ? That's the Bergey Excel 10K of course.

By the way, we always seem to hear that a properly fully furled machine will reduce the output. Agreed. My machine seeks the wind in high speed winds too even when fully furled.(the blades lose lift, the RPM drops, the machine is doing less work and WA LA, the machine seeks the wind) that's what I designed it for.

I'm sorry to chuckle when some are convinced their machine is possesed by the wind seeking curse. Don't be scared, it's really nothing more than getting things right.

Here's a pretty photo of my machine.

http://www.royalwindandsolar.com/index.php?option=com_content&view=article&id=52&Itemid=
63

Dave B.

Flux · « **Reply #47 on:** March 17, 2010, 03:42:21 PM »

There are so many issues being observed here that not all may be the same problem.

When I refer to wind seeking, the best example I can give is a 8ft machine with an offset of just under 3". This one refused to furl under any condition and the message was finally driven home when part of the tail mechanism fell off, leaving the machine with no means of steering it into the wind. The fact that it had an offset and there is thrust on the prop it should have turned round and stopped or faced the other way. In fact it held directly into the wind for about 15 minutes at full power.

Although it would not furl when the tail was intact it could be stopped by using a manual control to turn the tail at right angles. Using this manual control it held virtually full power until the tail was at about 75 deg and then suddenly the prop turned at right angles to the wind and it stopped. I tried a rope attached to the tail at one point with the tail fixed and it took a large force to pull the prop to about 45 deg to the wind then suddenly the force vanished and it then turned 90 deg to the wind and stopped.

The simple furling theory suggests that the thrust is proportional to the power extracted and so a scheme that breaks the tail away from the stop and maintains a constant restoring force should produce furling at constant power. Whatever you do in practice the thrust appears to be less than it ought to be and it always furls at a higher speed than predicted. This discrepancy varies drastically with the type of blade and to a lesser extent on the loading. Some furl at nearly constant power but at a higher speed than predicted. Others seem to hold into the wind until the blades are at a significant angle with the wind and then suddenly go into furl and the power drops dramatically. The first type will run with the blades at virtually any angle to the wind and the angle changes just sufficiently to keep the power near constant. This is surely how it should work.

The second type will drop power drastically when it furls and will not pull back into the wind until it drops speed considerably. This method of operation is safe and some may like it but it is a sure indication that something other than thrust is acting on the blades.

The disaster case is one where the offset is too small and the thing never does furl and power never drops, the blades never get at a sufficient angle to the wind to prevent the power rising with wind speed.

I am not sure about the described cases where things are claimed to furl at one wind speed and then loose control at a higher speed, I have never experienced this condition but I have never used a machine working stalled . I still believe that these don't really furl but stay near constant power from stall operation until the blades break stall. It's no good looking at tails, you need to see the angle of the blade disc to the wind and that is the only way you can see that it is furling and until the blade disc is at something well over 45 deg to the wind there is no reason to believe it is furling at all. I suspect that these large machines with drastically under powered alternators for the very high wind speeds can produce enough power to burn the alternator with the blade disc at 80 deg to the wind.

You really have to get the blades at this angle or greater in winds within half the maximum rating of the alternator.

Several people have said that they can't imagine how a tail can be at right angles to the wind and the prop be flying at high power into the wind. To be honest I can't imagine how this happens either but I have seen it and that is why I emphasise that you must compare the blade disc angle to the wind to be sure you are furling and forget looking at tails.

I really can't imagine what a mess the air flow is behind the prop and short tailed machines in particular may have their tails in an air flow that bears no resemblance to the true wind direction.

I suppose the conclusion from this long ramble is that what I call wind seeking is the difference in thrust along the alternator axis between the theoretical value and the real thrust. I am only considering the thrust as that which acts along the alternator axis the other forces such as drag and others from phenomena I don't understand don't produce rotation about yaw from the alternator offset. They certainly exist but are not those considered in the basic furling equations.

Flux

dlenox · « **Reply #48 on:** March 18, 2010, 05:47:07 AM »

Flux,

This is a bit off topic from the original intent of this thread, but since it was my thread to begin with - I'm going to hijack my own thread...

My property is literally ridge top and the turbine is literally at the top of the ridge. I've always thought that this was an optimal situation as it's known that as wind comes through the valley below and goes up the ridge that the wind speed at the top of the ridge can be as much as 2x what it was in the valley below. So I had thought that my property should have been ideal!

However this may explain why I for one am having furling issues!

In doing some searches last night I came across a Bergy XL1.24 Owners Manual v2.2 and in it it states:

"There is one situation in the field, however, that

we have found can disrupt the operation of Auto-

Furl. If the wind turbine is installed on a sharp hill

or next to a cliff so that the wind can come up

through the rotor on an incline (e.g., from below;

as opposed to horizontally) we know that this will

affect furling and can produce higher peak outputs.

We strongly recommend avoiding this situation."

I believe that this condition directly relates to my location and issues with furling! Up until now I don't think that I have ever heard this statement.

Since the wind angle of attack is coming from essentially below the turbine I believe that I can help remedy this situation by putting a small horizontal 'flap' on the tail vane. This should help create additional lift and help maintain furling.

I wanted to throw this out to you and get your opinion, as well as informing others of what I have found.

Dan Lenox

ChrisOlson · « **Reply #49 on:** March 18, 2010, 06:08:28 AM »

I'm sorry to chuckle when some are convinced their machine is possesed by the wind seeking curse. Don't be scared, it's really nothing more than getting things right.

I'm sure it always has something to do with setup, for sure. But I've run many different sets of blades, testing them for no-load running ability so I can record the data in my chart and compare it to loaded rpm data later. I have a small test stand that I run them on - sometimes in the shop, sometimes outside in real wind. Typically I don't even put the tail on them for doing that - I tie a rope to the tail hinge and secure the rope to one leg of the stand.

I've found that an 8 foot rotor will swing right into the wind and run at 400 rpm with no tail on it if it's not driving a generator - with 8.5" of offset. The rope isn't even needed in most cases. And I've also found they'll run with no speed reduction at 45° to the wind and it takes a pretty good tug on the rope to pull it around far enough to stop the rotor.

Flux describes this below too, with a machine driving a generator and having a small offset. So this I HAVE seen, and believe me, you'd be surprised at the force it takes to pull the thing out of the wind when it's spun up.

--

Chris

TomW · « **Reply #50 on:** March 18, 2010, 06:38:26 AM »

Dan;

I keep saying The devil is in the details.

Since we cannot "see" the wind itself it gets hard to understand what is going on.

Bergey seems to be on top of things so I tend to believe their information.

It kind of makes sense once it is said. The wind is experiencing both a direction change and compression / decompression as it tops the hill.

Thanks for finding that!

As a wild thought, I wonder if a lower tower would help?

Might find more consistent air conditions where the wind is still "stuck" to the hill top?

Just spitballing.

Tom

Flux · « **Reply #51 on:** March 18, 2010, 07:04:15 AM »

Thanks for bringing this up Dan, I had seen that warning long ago and completely forgotten it, it may well be one of your problems. If the prop can produce power when at a fair angle to the wind in the horizontal plane then wind approaching at angles in the vertical plane seem likely to have very strange effects. It would be interesting for Russell ( Hiltopgrange) to let us know if he is in a similar position.

Flux

dlenox · « **Reply #52 on:** March 18, 2010, 07:09:25 AM »

Tom,

I Thought that this was a good piece of information and that others should at least be aware of it! I also tend to believe it since it came from Bergy as they obviously have come across it - hence the statement.

I'd doubt that unless you were a long time seasoned professional that you might not have this tidbit of information, that obviously can have large consequences!

It's going to be a while before I can get around to getting the 17'er back into operation as currently I have a plate-full of things that have a higher priority.

As to lowering the tower, well it's a fixed lattice tower, so that is pretty much out of the question.

But that's why I think that I probably need to attack this problem with tail modification, and if the wind is coming from 'underneath' that I though my idea of putting horizontal flap would help increase lift for the tail and possibly to help maintain the furling position.

Dan Lenox

Dave B · « **Reply #53 on:** March 18, 2010, 07:47:10 AM »

I'll post this again. No tail here either. http://www.youtube.com/watch?v=iJCtN_-di6k&feature=related This is counter clockwise blade rotation. If the offset were to the left of the yaw axis (oh my, it's not that wind seeking curse is it ?) Dave B.

Flux · « **Reply #54 on:** March 18, 2010, 08:12:46 AM »

If the furling speed is only modified by the effect of the wind coming at a vertical angle then your flap may be ok, it really comes down to lightening the tail.

On that 8ft machine I described tried a similar trick but it didn't do any good. The critical thing seems to be whether the thrust on the rotor will overcome the seeking force, nothing you do to the tail has any direct bearing on the seeking force. You can reduce the restoring moment when things are right and it alters the furl point but if the seeking force is greater than the thrust component rotating the yaw from the alternator offset you can reduce the restoring force to zero and probably take it negative and it will still stay right into the wind.

In this case the only hope for any vane helping is one sticking out sideways past the prop and attached to the alternator not the tail as I suggested to Russell. This gives an additional force due to wind thrust independent of where the centre of pressure of the wind on the prop acts. This was an old idea used before the offset was thought of and I am beginning to suspect it has some merit. It will work without the offset if the vane is big enough.

Flux

Dave B · « **Reply #55 on:** March 19, 2010, 09:03:05 AM »

And of course we can wind seek the other direction with clockwise blade rotation as well. http://www.youtube.com/watch?v=Ms3M1rs5jf8&feature=related Dave B.

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Author Topic: direction confusion (Read 6902 times)