Actual Logged data and Graphs 12ft machine

[Seekscore]

I am now getting data from my newly installed turbine. Looking at the data is fun so see what it is actually doing.

I have an APRS World data logger. I get RPM, Wind, Voltage, Current, Time.

It is pretty cool to see the real world data from the 12ft machine. Looking at the data, I am surprised to see some things. I am pretty sure from the data I am seeing that I need to change my air gap. I think it is too large. At least I can see actual performance changes. I was able to figure out how to adjust the efficiency calculation for my altitude and use that to measure how efficient the machine is.

I am trying to think of things that I can graph that would be meaningful, so if you have any ideas, let me know.

We have had some killer winds the last couple of days. The machine has spent a lot of time fully furled. I had a gust yesterday of 69 MPH with sustained winds around 44 for 10 seconds at a time. Some of these graphs are a cumulation of 3000 data records and some are 7000 records.

Below, you will see average power line graph, Efficiency graph, raw power scatter graph, RPM scatter graph, TSR graph

Average Power per MPH graph. Not what I was expecting to see, but the data doesn't lie   I averaged the wind speeds to try to get to the whole numbers. For example, I took wind from 24.5 to 25.5 and averaged the power readings to get an average power for 25.0 MPH. This is what made me decide that maybe my air gap might be too wide. I would have expected a little more power than what I see in the graph. I also would have thought I could see the power level off once furled.



This is the efficiency I am seeing. This was adjusted for my altitude of 6800 ft elevation. The image is kind of hard to read. The orange line is % efficiency and the Blue is what percent of Betz efficient I am.



This is the Raw power scatter graph with 7000 data points. The one point peak is 1553 watts. It also looks like it starts making power at around 6, so another indication my air gap may be too big.



This is the RPM scatter graph. Again, 7000 data points. This looks like 250 RPM is around the max RPM I am seeing. What I don't see is the RPM leveling off while it furls. That is what I would expect to see, but again, the data doesn't lie.



This was an interesting graph of TSR. I've heard that the TSR changes while under load and at different wind speeds. It's interesting to see how it does change.



Mike.

[Seekscore]

After looking at the data and consulting an expert (DanB) it looks like my air gap may be too small or my blades my have too high TSR. What this shows is that I am experiencing stalling. I am going to let this run a couple more weeks and then swap out the blades for another set I have. It will be good to compare data and see what it tells me.

Mike

[walp]

1. Where to get this APRS World Data Logger thingy! Its awesome! Very good work there Seekscore!


2. Whats air gap?


\walp

[B529]

Mike,

Thanks for the time and energy to you are putting into your data collection, it's good for all to see real-world data!

Will be interesting to see how your efficiency changes with your different blades. Your efficiency is very respectable now.

What blade profile are your running now? What profile is your other set of blades?

Kevin

[DanB]

A quick reply here - though I wish I had time for a long one.

It's wonderful to see such data.

I love the performance in low winds - it's obviously stalling pretty badly in higher winds.

If anything.. the airgap is too tight, not too wide - however, the cutin speed and low wind efficiency seems nice so I'm not sure I'd mess with that.

The blades on this machine are not quite what I would do - they're designed for TSR7, and quite slender compared to what I think might work better...  experimenting there might help in higher winds.

Also - adding resistance to the line would probably hurt very little in the low winds, but allow the blades to run faster in higher winds and probably improve efficiency on the higher end.

Great / fun stuff.  Thanks Mike!

[Seekscore]

I bought the logger from these folks. http://aprsworld.com/wind2/. They are excellent to deal with and make a great product. Very knowledgeable support as well.

The blades were a 7 TSR @ 12MPH from an online calculator http://windpower.org.za/bladecalcs/blades.php. The airfoil is a NACA4412. They were made on a CNC router so the human error in manufacturing should be minimal. I think the width at the tip is a little thin. The other set of blades I have are DanB design and manufactured. The airfoil on that set should be really close to the Clark Y.

The air gap is the distance between magnets where the stator is sandwiched in an Axial Flux machine.

[Flux]

My first impression is that at 10 mph the performance is about right. The rest seems to indicate a machine running in stall right up to 30mph. I see absolutely no sign whatsoever that it is furling at all and this confirms some suspicions I have had for some time.

Try increasing the air gap for a set of curves and also try adding some line resistance with the present gap. If you can increase the gap without loosing the low wind end then that is the easiest way but if you loose at the low end then adding resistance may be better.

I don't know how much improvement you can really expect with a mill loaded in this way but I think there is more to be had.

You are seeing the real benefits of the large prop in low winds and you have respectable results in the higher wind but my 6ft machine with mppt converter produces over 1kW in winds approaching 30mph. I see no chance of you getting near the 4kW that ought to be available with direct loading but you may be able to improve things quite a bit in the 20mph region when you get away from the stall.

Keep up the good work, few seem interested in measuring performance.

Flux

[DanB]

Mike, what is the elevation at your site?

[Seekscore]

I am at 6800 ft.

Mike

[walp]

Ah, thanks for the reply from up in the sky! (6800ft!)

....oh my, it was actually air gap as in gap of air, not the generating wind speed spectrum as I believed

Pardon me, but Im not into the PMG mumbo-jumbo cause Im more of a capacitor\induction motor freak, but our mill happens to be about 12' as well, and with actually the same NACA-blade profile I think! Only with a slightly lower TSR and totally hand made in Swedish pine tree.

Im gonna get me one of those loggers, then we gonna battle like it's 1696!

I believe that PMGs are superior in the low end of the wind spectrum, while Induction Motor Excitation Generators (IMEG?) are better suited for high winds...
Correct me if Im wrong.

\walp

[Rover]

Excellent job at data collection, kudo's .

really good stuff!! 

[wooferhound]

....oh my, it was actually air gap as in gap of air, not the generating wind speed spectrum as I believed
\walp

walp
there is a definition of terms in the Glossery located in the FAQs area . . .
http://fieldlines.com/board/index.php/topic,144541.0.html

[Flux]

Walp

"I believe that PMGs are superior in the low end of the wind spectrum, while Induction Motor Excitation Generators (IMEG?) are better suited for high winds...
Correct me if Im wrong."

Tricky one to answer. Normally PMGs are made to suit the low wind at cut in, where they are quite efficient so they work well in low wind. Induction machines have magnetising and other losses that make them tricky to use in low wind and they are more restricted in speed range than the pmg.

If you match a pmg for low wind then the matching will be poor in high wind and it may not work so well. As the induction machine is not particularly good in low wind it is normally matched to higher wind speeds and in the speed range for which it is matched it does work very well.

If you ignore the low wind and match a decent pmg for high wind then the pmg will probably work better than the induction machine especially if you include the speed increase gearing needed for the induction machine.

The issue faced in all cases ( battery charging at least) is the difficulty of matching a machine efficiently over a 3 or 4 to one speed range.

If it's big power you want in a decent wind area then you can ignore the low wind and match for the big wind. This is the best approach with heating where a few watts is useless. For battery charging most people need the small amounts of energy that can be collected on low wind days and can't afford to ignore it and they are prepared to sacrifice some of the efficiency on very windy days to have a simple scheme that caters for both.

For grid tie the induction machine was basic and simple and reliable and was the choice for a long time although it is not very flexible in wind speed range.

With the present mppt inverters pmgs are capable of a better performance over the whole speed range and are definitely a better way to go for small installations.

It will be interesting to see any data you get from the induction machine and how it compares with various pmgs.

Flux

[Seekscore]

Flux,

I see absolutely no sign whatsoever that it is furling at all and this confirms some suspicions I have had for some time.

Can you expand on what you are saying about furling?

The machine spent most of the day in the higher winds fully furled. I watched it for some time. Isn't that was furling does? Change the angle in which the blades face the wind to make them inefficient and put them into a maximum power output "Stall" thus limiting the RPM?

Mike

[DanB]

hi Mike -
did you observe at roughly what wind speed the machine is starting to furl up, and at what speed is it 'fully' furled up?

Some other small things that may improve performance ~
there is no doubt that that machine doesn't run that square to the wind.  A larger tail vane would help with that - as would more angle outward with the tail boom.  I tend so far to make some compromise there because I think it looks goofy if the tail is sticking out too far to the side, and the size of the tail vane is perhaps a bit on the small side, according to Hugh Piggott anyhow.  I tend to believe him.

And - if the machine is starting to furl in very low winds, then just a larger tail, with more weight - may increase higher wind performance significantly.

So many variables and it's great to see such thorough data.

[ChrisOlson]

Can you expand on what you are saying about furling?

I'm not Flux, but furling reduces the swept area of the rotor and limits the power.  It is not a situation where the machine comes up against a stop and absolutely limits power output.  At 65 mph the amount of wind power flowing thru even 50 square feet of swept area is sufficient to create a lot of power.  My 12 foot machines can push well over 100 amps in strong winds and can push the bus voltage to 39 volts at times and cause the inverters to kick out from over-voltage even with 3 kW load on the system, running fully furled.  They start to turn out of the wind at 1 kW, and at 1.8-2.0 kW are pretty much fully furled.  But if the wind is blowing 50+ they don't back down and I've seen spikes over 5 kW out of those machines in really strong gusts over 60 with the rotors turning 400+ rpm, fully furled.  They're down to 3 TSR at that point, but they don't give up and stop making power just because you turn them out of the wind.

I think a lot of people have the wrong idea about furling.  It is not a governor that absolutely limits power to some set value.  And the slower you have the rotor turning at the point where thrust overcomes the mechanics of the machine that keep it steered into the wind, the more power you're going to get in high winds.  The rotor never "stalls" in furl because if it does it stops making lift, stops making thrust, and steers itself right back into the wind and goes back to work.  All you do by furling it is reduce the swept area - you do not stall it.

Once you do the calculations at 65 mph and figure out how much total wind power you have flowing thru the reduced swept area, it's not too difficult to see that power surges of 3+ kW are possible with a well-designed 12 foot machine.  People who live in poor wind areas, or have their turbines installed in high turbulence zones and have never seen this don't understand it fully, and tend to think it's an absolute.  It's not.  When you go from 35-40 mph to 60+ with good clean laminar wind flow you're in a whole different ballgame, dude.

Maybe I don't understand your graphs, but my 12 footers (actually 12.3 feet) run at 5 TSR @ 12 mph wind speed and they're turning 136 rpm.  As far as I can tell your graphs indicate your 12 footer is running ~5 TSR @ 12 mph but the rpm graph shows about 175 rpm.  There seems to be somewhat of a discrepancy there.
--
Chris

[Flux]

Normally a well matched machine will level off power when it furls. I saw no indication of any levelling off on your graph, it may be that it did furl in the higher winds that you had, the graph only goes up to 34mph. Did it appear to be fully furled at that wind speed?

Machines vary in their behaviour when furling and much depends on the blade profile. The blades that Chris uses seem notorious for holding on to power even when almost edge on to the wind and at 60 mph they will still make a lot of power when almost edge on to the wind but most ordinary blades don't do this to the same extent.

I can only comment on what I saw from your graph and if you observed what looked like full furling in that 30mph wind then I would suggest you look at the blade axis with reference to an independent wind direction device such as a streamer. the fact that the tail is at right angles to the blade is no indication that the blade disc is almost at right angles to the wind.

All machines that I have built show a drop in power as they furl, ideally they ought to hang on at constant power but the theory is far from perfect.

Most commercial machines show this drop including Bergey and AWP although there are large variations. I have never run a machine hard into stall in high winds and tried to furl it because my loading schemes are intended to keep things out of stall so something strange may happen in this case. If the stall is bad enough the power will fall off from stall alone and it may be something of a gamble how much of the power limiting is from furl and from stall.

A lot of commercial machines in the past have failed to furl satisfactorily so there is no doubt that there is still something of a black art here and it is far from simple. There is little doubt that many machines have survived burn out by alternator reactance limiting the current and ineffective furling may have been overlooked except for the crazy noise, but air gap machines will continue to increase current if the speed keeps rising.

As you try differences in loading by changing air gap or adding resistance we may get a better idea of what is happening but for power measurements you need to look at the range below furling. it will also be instructive to see what the power does once it comes into furling but there is little doubt that this region will change rather drastically as you change the loading so just watch you don't burn things out during these data runs.

Flux

[Seekscore]

I haven't looked at what speed it starts furling. I just looked outside and it was in furl. Part way anyway. The wind speed is varying but as best I can tell from a low of 22 to as high as 35. If I had to guess what speed, I would say 25-27 is when it starts furling. Here are some pictures of about 25-27 I just took. I watched the anemometer for a bit and 25-27 seemed to be most consistent.









I'll post the math I used a little later to figure my TSR. Wife wants to run to town for a bit now. I am confident my results are accurate based on windspeed and RPM. I can not speak to the accuracy of the web page I used to figure out my stations for blade design. I compared to a couple different sources (blade calculators) and was very similar. I am not taking loading into account in my results. I am making decent power at 12 mph.

Mike

[Flux]

hi Mike -
did you observe at roughly what wind speed the machine is starting to furl up, and at what speed is it 'fully' furled up?

Some other small things that may improve performance ~
there is no doubt that that machine doesn't run that square to the wind.  A larger tail vane would help with that - as would more angle outward with the tail boom.  I tend so far to make some compromise there because I think it looks goofy if the tail is sticking out too far to the side, and the size of the tail vane is perhaps a bit on the small side, according to Hugh Piggott anyhow.  I tend to believe him.

And - if the machine is starting to furl in very low winds, then just a larger tail, with more weight - may increase higher wind performance significantly.

So many variables and it's great to see such thorough data.

Perhaps I can comment on a few things here as Dan has raised a few good points. For power curve measurements you can only make sense of things before furling but as I said earlier a power curve of what happens during furling is also a source of lots of other information, just don't get confusing the two separate cases.

Dan is again right in that these machines don't face the wind and with a big tail and it offset well to the side away from furling you still have a hard time getting it better than 30 deg to the wind. Fortunately this angle seems to have little effect on power.

I do agree with Dan that the tail looks goofy when offset enough to do much good and that is absolutely fine if you only have one machine. I regularly look at two machines with the offset on either sides and they are close enough to see both easily at once, the goofy tail offset is nothing compared with the fact that the prop axes are about 60 deg different, that looks even more goofy.

This is a feature of this type of furling that is difficult to overcome, I think you have to live with it or adopt a much more complex scheme where the alternator can pivot independent of the yaw axis ( as in mk 2 freelite or the SWWP angle governor which seems to be derived from it).

Flux

[ChrisOlson]

Most commercial machines show this drop including Bergey and AWP although there are large variations

The Bergey is really hard to compare to these homebrew machines because the R model battery charging machine has its power controlled by the OptiCharge controller and AutoFurl is the machine's overspeed protection when the controller unloads the turbine in high winds due to over-power situations.  The homebrew designs are trying to use half the Bergey's system for power regulation instead of just ultimate overspeed protection, and there's basic differences.

Besides me, this is one of the only other people I know who have actually studied this and experimented with it, and this experiment happened to be on a Bergey Excel-S.  There was only a drop of ~16% in total kWh power production of the machine over an extended period with the tail cranked fully vs flying totally unfurled.  And furthermore, the machine proved that even fully furled it could still overload the inverter and cause it to kick out and let the machine free-spin in high winds:
http://www.ualberta.ca/~mtyree/SWIEP/Docs/PowerOutputFullyFurledBergeyExcel-s.pdf

The designers of these homebrew turbines need to stop touting AutoFurl as a dead reliable method of power control.  It works reasonably well on turbines installed in poor wind zones and in turbulent conditions.  But it has limitations that people who build these machines need to be informed of.
--
Chris

[scoraigwind]

The designers of these homebrew turbines need to stop touting AutoFurl as a dead reliable method of power control.  It works reasonably well on turbines installed in poor wind zones and in turbulent conditions.  But it has limitations that people who build these machines need to be informed of.
--
Chris

Chris Olsen needs to stop making confusing statements about furling not working.

I live in a pretty high wind area, and have used furling (side facing with gravity tail) to protect all of my turbines over a thirty year period and it works well.  It's not perfect.  It's well known to be a 'black art' as they say.  you may have to make adjustments (especially in hot climates).   But all the other methods of power control (pitch control, stalling etc) are tricky too, so that's nothing unusual.

By the way I was using the side furling system long before Bergey started in business and I personally think that gthe geomtry of my system is better than the Bergey one (more stable).  It certainly produces a levelling off of the average power (unlike the graphs earlier in this thread).  I have done plenty of studies with dataloggers in addition to the simple observations of users over long periods of time.  There are surges of high power but the average is where I want it.  I never put a brake on my own wind turbine in high winds and neither do most of my neighbours.  Side furling is a good option for power control

Ok it doesn't seem to work out too well for everyone, but it has served me well for many years and it also works pretty reliably for people who follow instructions without being too creative on their own.  I am all for creativity but if you want to say that my furling systems don't work then you need to try them out first, and not extrapolate from your own rather different experiences.

Sweeping statements about it not working are just not helpful in my view.

[ChrisOlson]

Chris Olsen needs to stop making confusing statements about furling not working.

Hugh, please read again and show me where I make this sweeping statement that said it does not work.  I said it's not dead reliable as a method of power control and I said it works reasonably well where most of these turbines are being installed.  Reading comprehension is the key here.

The issue for Seekscore here is whether or not the machine is furling.  What he's seeing as an increase in power output at wind speeds well beyond where the machine mechanically furls is completely normal in my experience with certain generator and blade combinations, and I didn't start flying turbines just last week either.

If you read thru the posts you'll see where Seekscore said:
"The machine spent most of the day in the higher winds fully furled. I watched it for some time. Isn't that was furling does? Change the angle in which the blades face the wind to make them inefficient and put them into a maximum power output "Stall" thus limiting the RPM?"

The machine is running furled -fully.  He says so.  He watched it.  The power and rpm continues to increase anyway.  What more proof do you need that turn to the side furling is NOT an exact science where you can just limit the power to some arbitrary value?  A good portion of the swept area of the rotor is still exposed to the wind with it furled.  And that's a fact.

We all know you've never burned a stator out, right Hugh?  And anybody that does - it was always something else that caused it.  The tail is too heavy - let's saw the boom off a bit.  The hinge is welded on wrong so let's whack that off and re-weld it on at less angle.  The stator was too light duty - lets throw a couple more strands in 'er.  The rotor was stalled - lets bolt some resistors inline and see if that works.  And all the while the real problem was that you throw a little 3 foot prop in a 100 mph wind and you still got over 8 kW of power.  The limitations of the design were exceeded.  Period.
--
Chris

[DanB]

Mike -
one other thing to play with I forgot to mention, but it's been more on my mind lately...
if the studs on your alternator are extra long (and I seem to recall they are) - you could play with pushing the blades forward further.  I don't think this will affect when it starts to furl, but once it's on the way - it should cause it to furl more... how much, I don't know.  It's definitely a simple adjustment you can play with though.

Im less worried about the furling at this point than I am about tweaking things to get a bit more power in higher winds.

Flux suggests that not running square to the wind should not affect power output too much.  Todd H from Bergey was talking about this with me (bergeys have a similar problem - they don't run square to the wind) and he suggested that it was costing them almost 20% ~ at least that was my understanding.

At any rate though - I think you have lots to experiment with...
- try the other blade set
- add some resistance to the line, again - I would start with about half an ohm on the DC side of the rectifier
- maybe open the airgap a bit
- play with furling, although getting the TSR up in higher winds may affect furling quite a bit.  Pushing the blades forward on the studs may also help.

[ChrisOlson]

one other thing to play with I forgot to mention, but it's been more on my mind lately...
if the studs on your alternator are extra long (and I seem to recall they are) - you could play with pushing the blades forward further.  I don't think this will affect when it starts to furl, but once it's on the way - it should cause it to furl more... how much, I don't know

Dan (and Mike) - I've played with what I called "forward lead" of the rotor extensively, and it takes a BIG change to make that adjustment or design change make much difference at all.  And by big, I mean moving that rotor out there another 6-8" before you'll even start to notice any real difference in how it furls, and how aggressively it wants to steer back into the wind, after it starts to turn to the side.

There's so many other forces at work there that that just really doesn't even work.  LOL!  At one time when I first started experimenting with it I thought it was the cat's meow.  But after playing with several different configurations I found out it's more theory than practical application.

The biggest advantage with moving the rotor further out front is in how much tower clearance you get.

The biggie, in my experience, is how FAST that rotor is turning when it starts to turn to the side.  If you're turning a rotor designed for high tip speeds at too low of rpm, it's going to aggressively steer back into the wind after it turns to the side and it's just going to keep right on making power, the faster the wind blows.  A rotor that's running too far below it's design tip speed just does not make reliable thrust to furl one of these machines.
--
Chris

[DanB]

We all know you've never burned a stator out, right Hugh?  And anybody that does - it was always something else that caused it.  The tail is too heavy - let's saw the boom off a bit.  The hinge is welded on wrong so let's whack that off and re-weld it on at less angle.  The stator was too light duty - lets throw a couple more strands in 'er.  The rotor was stalled - lets bolt some resistors inline and see if that works.  And all the while the real problem was that you throw a little 3 foot prop in a 100 mph wind and you still got over 8 kW of power.  The limitations of the design were exceeded.  Period.

I saw a good bumper sticker last summer.  'You are entitled to your own opinions but not your own facts'.

 Lots of these types of machines hold up quite well on very good wind sites.  Any 'new' design will surely involve some tweaking here and there - and yes, that could involve all of the 'tweaks' you mention above.  Nobody every said that when a stator burns out it was always something 'else' that caused it - although often times that is the case, or...  some other change could've prevented it.   Here I think we have a machine with a pretty stiff alternator (and we knew that going in) that can produce sustained output in a simple battery charging system of probably 1500 Watts without danger of burning it out.  We knew the power curve of the alternator was too steep for the blades to keep up with it and the data confirms this.  There are ways to improve that ~ it has been my thinking for a while that I'd rather have heat in the line, or in a resistor ~ than heat in the stator.  My thinking may change on that some day.  Overall, for a simple 12' turbine with a robust alternator and not much tweaking done yet I am not unhappy with the performance and I know that some simple changes will improve that and we'll all learn along the way.  

Chris - I love the work you do and the stuff you post.  Your sometimes arrogant attitude towards folks who are just experimenting, and seemingly moving forward with this stuff gets tedious though.  

Perhaps I should just give up here, go back to chain driven machines, wired in Delta,  with spring loaded furling systems and start buying blades from China ~ you seem to have it all working perfectly!~  

(really I'm joking there to some extent - you do fine work and I think everyone here is grateful that you share your projects, please though try to be a little less certain about what you *think* you know because sometimes the stuff you state as 'facts' here... are a bit off, they are strongly believed opinions and they can be misleading to folks who don't know much about this stuff)

That is my opinion anyhow.

[DanB]

one other thing to play with I forgot to mention, but it's been more on my mind lately...
if the studs on your alternator are extra long (and I seem to recall they are) - you could play with pushing the blades forward further.  I don't think this will affect when it starts to furl, but once it's on the way - it should cause it to furl more... how much, I don't know

Dan (and Mike) - I've played with what I called "forward lead" of the rotor extensively, and it takes a BIG change to make that adjustment or design change make much difference at all.  And by big, I mean moving that rotor out there another 6-8" before you'll even start to notice any real difference in how it furls, and how aggressively it wants to steer back into the wind, after it starts to turn to the side.

There's so many other forces at work there that that just really doesn't even work.  LOL!  At one time when I first started experimenting with it I thought it was the cat's meow.  But after playing with several different configurations I found out it's more theory than practical application.

The biggest advantage with moving the rotor further out front is in how much tower clearance you get.

The biggie, in my experience, is how FAST that rotor is turning when it starts to turn to the side.  If you're turning a rotor designed for high tip speeds at too low of rpm, it's going to aggressively steer back into the wind after it turns to the side and it's just going to keep right on making power, the faster the wind blows.  A rotor that's running too far below it's design tip speed just does not make reliable thrust to furl one of these machines.
--
Chris

Thanks for that Chris - that is all of what I expected  I guess.  I do wonder if part of Mikes furling issues have something to do with it just really being in stall - and really, I had not expected that this machine should flatten out much (furl) before output is over 1kW, which he is barely achieving.  I have a feeling that if performance is improved in higher winds, we will see it furling better.  Time will tell though.  How far the blades are pushed forward on the alternator - it is interesting to hear your results.  It's something I've not played with much.

[fabricator]

One thing that needs to be remembered here is that its it KWH that power a home not the rated output of the machine and NOT 20 days a year when you have higher than normal winds, what ever you do DO NOT tune your machine so you gain a few amps in high wind situations at the expense of those day after day normal wind conditions when KWH are made, bragging amps are fun to see but other than that they can cause more trouble than they are worth.

[97fishmt]

I was having the opposite conditions tuning my furling in.  I put the rotor ahead
19 inches in front of the tower and 6 inches offset from the yaw tube.  With my initial setup the machine would turn out of the wind and the blades would actually stop.

My fix was to change the top and bottom stops on the tail swing points and add more weight and a larger vane to the tail.  It is tunable to dial it in.  It is better to start out with a lite tail or it could all go up in smoke before you even get to play with it.

Just remember to have fun and keep the scary moments to a minimum.

[fabricator]

The one glaring problem with the gravity furling tail is the experience of the builders, Hugh and Dan have good success because of experiences with many machines, especially Hugh probably hundreds of machines? Whereas many of the folks here have experience with ONE machine, they often don't know exactly how or where the angles or lengths should be measured from, a few degrees and a few pounds can mean the difference between a smoked stator and a machine that runs on the razors edges but lives to run another day, if every one here were to be brutally honest as we should be, they should be willing to admit a perfectly functioning gravity furling tail is a black art that takes experience and a little luck to make them work properly because there are SO many variables.
And, the larger a machine gets it appears the less likely it will be to ever get a gravity furling tail to work in fool proof manner.

[DanB]

I have no data aquisition left on my turbine that works...
here are observations about my 20' machine though -

originally we made the blades for it, they were quite wide and heavy - my best guess at what my be appropriate, and it seemed to work pretty well.  Decent low, and high wind performance and it furled nicely right around 4 -5 kw.  (I would see peaks upwards of 10kW at times)

I took those blades off (gave them to somebody else) and fit some old jake blades that I cut down to 20' diameter - they're more slender, designed to run faster.  Now - much like Mike, I have decent low wind performance (I still get more energy than I need) - but it stalls badly in higher winds, it's rare ever to see more than 3kW and it barely furls - I've not seen it fully folded up since I made that change.

I suspect, that getting mikes blades running faster - or - fitting slower blades to it, might help a lot.

[ChrisOlson]

I took those blades off (gave them to somebody else) and fit some old jake blades that I cut down to 20' diameter - they're more slender, designed to run faster.  Now - much like Mike, I have decent low wind performance (I still get more energy than I need) - but it stalls badly in higher winds, it's rare ever to see more than 3kW and it barely furls - I've not seen it fully folded up since I made that change.

Well, like Fabricator says, low wind performance is more important for somebody who lives in a marginal wind area.  But it appears to me that Mike possibly lives in a pretty decent wind area and he would benefit from opening that turbine up and letting it flat out run rather than switching to slower blades.

I prefer slow turning rotors to fast ones because they're less maintenance over the long run and tend to have less leading edge wear on the blades, and less stresses on the machine.  But they're also a little trickier to control in high winds.
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Chris

[Seekscore]

Thanks for the information and pretty good discussion. I really have no need for the power. Just learning something new. Right now I am just charging some batteries and heating my shed with the wasted power. I realize that my blades may be the cause of some of the issues I am seeing. I got a perfectly good set from Dan but I made a set on a CNC router. Its a shame that they are causing some issues. They sure are pretty...

It seems that everyone has different opinions on what works best. There are a lot of variables that make a particular turbine perfect for the user. What works great for one person may not be the best for the next. Like Flux said, its all about kWh energy generated. I also think there is a lot of pride that gets in the way of reality. One thing I have noticed, and I don't mean this in a bad way, is that a lot of people who post on here are touting their successes and how great their particular machines are. Who wants to brag about their hard work when it doesn't work right? While some probably do have great machines, I would be willing to bet it didn't happen on their first attempt. This leads to the advice they share with others. Those that have been there and done that are the best sources for advise. I know that I learn a lot more from my failures than I do my successes. Trying to learn from you folks that have been there and done that is why I come here. There are a lot of different perspectives on how to solve a particular problem.

I am going to let the turbine run for a couple weeks and collect data. I need to lower the tower to do my initial maintenance and I will swap out the blades. I'll collect more data and see what happens to efficiency and performance. My normal wind speed is around 12. I am on a pretty good wind site with the turbine about 40ft above anything within a mile or so.

What would be a good target RPM to shoot for? 250 seems to be my max now. What would be reasonable?

Mike

[ChrisOlson]

What would be a good target RPM to shoot for? 250 seems to be my max now. What would be reasonable?

Well, I'll put it this way - my 12 foot machines are actually a bit bigger than 12 feet, have a lot slower design blade profile than I think you got there, and mine are running at 260 @ 24 mph, and I consider that pretty slow.  I seen it over 400 rpm a few days ago in really high winds.  So it's just my opinion, but I think 250 rpm on the top end is pretty slow to get any real performance at all from the machine.

I really don't think as slow as you appear to be running that machine right now that you're going to see any loss at all in even low wind performance by opening it up a bit and letting it run.  It might raise the cut-in from like 6 to 6.5 or something, but the rotor will spool up faster after that and you might even see better performance at 12 than you get now.

Slow turning rotors are really tricky to get to furl right.  So if it was me on the first one, and still experimenting, I'd opt to run it a bit faster until you get kind of a handle on things and get it figured out a bit better.  And it's really easy to do - whatever you got the air gap set at now, just open it up about 1/10" of an inch.
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Chris