Author Topic: Market for wooden windmill blades  (Read 14137 times)

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stofanel

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Market for wooden windmill blades
« on: May 12, 2015, 12:53:56 PM »
I was browsing through the Otherpower online store and noticed that they used to sell carved windmill blades for their machines. The web page shows the items to be out of stock. My guess is that there was no demand for the blades, or there was no way to economically mass produce the blades.

The reason I am talking to myself here is because I will have a set of prototype CNC cut windmill blades within two months or so. (the aerodynamic work is compete, but the CNC code to cut these blades will take some time to polish). Once all the design kinks are worked out, manufacturing these blades consists of strapping some wood to a CNC machine bed and pressing a few buttons.

My question is: is there demand out there for such products at the Otherpower advertised price (approx $300-$400 for a 10' dia machine), or am I just dreaming?

Bruce S

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Re: Market for wooden windmill blades
« Reply #1 on: May 12, 2015, 02:29:50 PM »
Most people on here carve their own blades these days.
There are several posts spanning the globe on how to carve blades even using a chain saw.

Hope this helps
Bruce S
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Mary B

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Re: Market for wooden windmill blades
« Reply #2 on: May 12, 2015, 05:41:15 PM »
I am sure there would be some demand for these from those who are not woodworkers and lack the tools. If offered in a variety of sizes to fit smaller DC motors like the GE ECM's, treadmill motors etc I am sure there would be buyers.

stofanel

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Re: Market for wooden windmill blades
« Reply #3 on: May 12, 2015, 06:46:03 PM »
The only reason I am contemplating this project is because I happen to have access to a rather large 3D CNC router. Such a machine can actually crave a much more precise airfoil profile than a guy wielding a chainsaw. Therefore, a well designed wooden blade that is CNC cut can outperform most of the so-called professional blades on the market today.

I noticed that hand carved 10' machines can produce  1KW at 25mph. A well designed CNC cut blade can easily produce 2kW-2.5kW of power.

niall2

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Re: Market for wooden windmill blades
« Reply #4 on: May 13, 2015, 03:11:00 PM »
Dreaming is good Stofanel  :).....nothing would be done without it

but you might have another thing to consider , that is ...matching the cnc blades to the load

for someone with the alt matched to the 10" axial , your blades would burn in out , so a specific alt matched to your blades would be needed ( i.e. a lot field testing )

a lot of people run their mills in kind of "under capacity" or deliberate high side stall mode , mainly for reasons of safety , longevity and low noise levels ...good props rarely fail on their own .............its the alt that usually lets go first

sounds like a great project though with lots of opportunity to cut quick profiles for field testing , good luck with it :)   

« Last Edit: May 13, 2015, 03:20:15 PM by niall2 »

stofanel

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Re: Market for wooden windmill blades
« Reply #5 on: May 13, 2015, 07:42:41 PM »
I have a feeling that I will be testing a lot of blades this summer. The trick is to somewhat automate the design process, where one can play with the main parameters (wind speed, rotor diameter, RPM), with the final output being chord and twist distributions for the blade that in turn will generate the CNC code to cut the blades.

So far I have written some Python code that solves the aerodynamic problem and outputs optimal chord distribution for a given Cl profile. The program solves the fluid mechanics equations using the methods outlined here:

http://www.ewp.rpi.edu/hartford/~ernesto/SPR/McCosker-FinalReport.pdf
and here:
https://community.dur.ac.uk/g.l.ingram/download/wind_turbine_design.pdf

The tricky part now is to choose appropriate airfoils and integrate that data to come up with the right blade twist. Once that is done, then write the Python code that generates the CNC program. My hope is that once all the programming is done, I will be able to test the blades against the theoretical predictions.

As far as matching the blades to the generator is concerned, having an accurate power curve for the blades will help.

Mary B

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Re: Market for wooden windmill blades
« Reply #6 on: May 14, 2015, 01:05:26 AM »
Depending on price I might be interested in a 3 foot diameter set... I have a GE ECM motor to play with(going to ignore the zoning that says I can't!)

richhagen

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Re: Market for wooden windmill blades
« Reply #7 on: May 14, 2015, 07:03:21 AM »
I can cut smaller wood cnc blades, and still do so occasionally for other folks.  I wrote a program to calculate the xyz coordinates based on a profile, diameter, and the desired tip speed ratio, based on the formulas of Hugh Piggot for optimum angle and chord length.  It was in Excel of all things.  Then I ran a crystal report against this to generate the g-code for carving the top and and bottom in two passes.  Not an ideal way to do this, as cutting close to the finish surface in one pass and then a second finish cut would probably yield a more accurate final result due to stress relief in the wood on the first pass.  Still, the results work. 

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kitestrings

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Re: Market for wooden windmill blades
« Reply #8 on: May 14, 2015, 08:36:10 AM »
Stofanel,

Welcome to the board.  My comments aren't intended to discourage you in any way.  I don't know how much demand for well made wooden blades there might be.  Wind throughout history has seen its share of ups and downs, no pun intended.  Now a days solar (PV) has put a pretty heavy crimp in the pace of small scale wind for all but a few of us crazy's.  Still there's opportunity and challenge, and sounds like you've got both experience and capabilities that many builders may not have/have access to.

Quote
I noticed that hand carved 10' machines can produce  1KW at 25mph. A well designed CNC cut blade can easily produce 2kW-2.5kW of power.

I would, however, be careful about statements like this without data to back it up.  First of all, 25 mph is a pretty high wind for most sites.  Instantaneous turbine outputs are often highlighted and overstated by commercial vendors, and mean very little in the larger scheme, and frankly they've only hurt the small wind "industry".

If you look at it purely form a physics perspective, the Betz limit on a 10' dia turbine at 25mph is 3,600 watts.  Real world results would suggest if you could squeak out over 2 kW with this size rotor you'd be above where most commercial efforts have demonstrated.  See:
http://www.ndsu.nodak.edu/ndsu/klemen/Perfect_Turbine.htm

Good luck, ~ks

stofanel

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Re: Market for wooden windmill blades
« Reply #9 on: May 14, 2015, 10:43:40 AM »
Kitestrings,

Right now I am just toying with the idea. The performance claims may seem bold, so I will have to test them. So far the BEM (blade element momentum) calculations seem to indicate that Cp's of 0.4-0.45 are possible with the right airfoil profile.

One thought about airoils:
Regular airfoils (airfoils made for general aviation) do very poorly on wind turbines. This has to do with the fact that the leading edge of the blade gets dirty over time. Bugs, dust (but mostly bugs) make the leading edge of the blades look like a car bumper that just drove through a swarm of insects at 100mph. This contributes to surface roughness which severely disturbs the airflow of regular airfoils and kills performance. That's why it is imperative to use airfoils specifically designed for such conditions. If you look at actual wind turbine arifois, they look really funky. Here is the S835, specifically designed for small wind turbines (<3m diameter):

https://wind.nrel.gov/airfoils/Shapes/S835_Shape.html

This is where CNC capability comes in really handy.

On a side note, my endgame is to design and eventually build a 10'-16' machine. Since the average wind is relatively low (15mph on a good summer day here in Texas), I am leaning towards the 16' option.

Bruce S

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Re: Market for wooden windmill blades
« Reply #10 on: May 14, 2015, 10:56:07 AM »
stofanel;

There has been a great amount of on-going discussions (wind section) about leading edge protection , the use of sticky foil and such.

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niall2

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Re: Market for wooden windmill blades
« Reply #11 on: May 15, 2015, 05:30:44 PM »
interesting Stofanel .....i,m not so sure about contamination on the leading edge effecting performance so much ...but i know there is an argument for that :)

i tried adding winglets to blades , but had no way to measure any extra few watts .......they did whistle a bit  ...maybe there was something in it ...who knows


if you get the cnc working you can test a lot of options ...i feel though maybe the simplest will be best ..:)

 
 

stofanel

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Re: Market for wooden windmill blades
« Reply #12 on: May 15, 2015, 05:43:11 PM »
The winglets on airplanes increase the effective aspect ratio of the wing. This translates into decreased induced drag. However, increasing the wingspan by the same amount has the same effect and makes the manufacturing process simpler. So everything else being equal, it's cheaper to just increase the wingspan by a few inches (or feet for big airliners). The reason winglets are becoming the norm on airliners is because they cannot increase wingspan. The overall size of the wing is limited by the size of the parking spot in the airport terminal.

Wind turbines don't have that problem. If I were to "unfold" the wingtip I would get much better performance just from the increase in swept area alone. 

niall2

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Re: Market for wooden windmill blades
« Reply #13 on: May 15, 2015, 06:02:19 PM »
erm ...but gliders use them , and they dont land at airports ?

i thought it was to do with reducing vortex,s at the wing tip and so adding lift ?

stofanel

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Re: Market for wooden windmill blades
« Reply #14 on: May 15, 2015, 06:40:20 PM »
Every case is different, and gliders are a special case. They have very thin (small chord) and long wings which produce high bending moments at the wing root. In such cases even small increases in wingspan require ever increasing structural reinforcements that add to the weight of the wing assembly. The tradeoff favors winglets.

niall2

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Re: Market for wooden windmill blades
« Reply #15 on: May 15, 2015, 06:57:19 PM »
"Every case is different" ...indeed , and its good to have a debate about windmills ....its in short supply lately ...it may come back stofanel...:)

stofanel

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Re: Market for wooden windmill blades
« Reply #16 on: May 15, 2015, 09:59:40 PM »
I am not totally discounting the winglet idea. As a matter of fact, wingtip losses account for a good part of the discrepancies between the Betz power limit and the real life power ratings of wind turbines. The wingtip vortices start to adversely affect the power production of the blade at about 70% of the radius and reduce the power production of the outer 5% of the blade by as much as 50%. So yes, anything that alleviates the problem is an improvement. However, the lazy solution is to just increase the blade size.

Now that you have peeked my curiosity, I am thinking of testing this idea a bit further. It should not be that difficult to create the wingtips in the CNC code.

dnix71

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Re: Market for wooden windmill blades
« Reply #17 on: May 16, 2015, 03:20:35 PM »
Winglets cause turbulence around the edge of the blade by breaking the laminar flow which swirls into a vortex. That reduces drag. Birds have small feathers in strategic places that do the same thing. On passenger aircraft they reduce the wingtip vortices that the aircraft behind them encounter and therefore make it safer to follow a big bird.

http://en.wikipedia.org/wiki/Wingtip_device
http://en.wikipedia.org/wiki/Wake_turbulence
http://www.pilotsofamerica.com/forum/showthread.php?t=79505 even a helicopter is capable of creating a lingering area of unstable air.

I use to live near an airport. The property bought in the landing zone was an old mobile home park. The trailers were gone but the area was unfenced. I would pick wild blackberries around the trailer slabs. When aircraft passed over and landed, there was a noticeable time delay before the wingtip vortex would reach the ground, but it was still quite loud.

niall2

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Re: Market for wooden windmill blades
« Reply #18 on: May 17, 2015, 04:45:14 PM »
the one thing i did find out about adding winglets is ....its "very" easy to knock them off   ???,  just one tap of something during assembly and its gone ......they might,nt  weather too well either ......but not a very scientific analysis

very nice cnc blades there Rich ...it must be a lot of fun to watch the process.....

the whistle sound with the winglets was actually fairly loud , and as these are Hughs blades (quiet) it seemed to detract from their design ....

i think Enercon use them on some of their commercial machines ......     

clockmanFRA

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Re: Market for wooden windmill blades
« Reply #19 on: May 17, 2015, 05:03:55 PM »
I have a good friend who lives just down the road, here in Normandy France, and his profession is wood cabins and the like. For years I have been prompting him, "Dimitri, don't forget now, Western Red Cedar please".

At the weekend, "Look what I found, they were going to burn it as its from a public park, so I shoved it all on my lorry, about 10 square yards."

But the nice thing with this lot is..... I can ensure its Quarter sawn properly during cutting/planking and knot free.  :)

Should get a few sets.

My youngest 8 year old and Dimitri's youngest at Dimitris Saw Mill.
Everything is possible, just give me time.

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3 Hugh P's 3.7m Wind T's (12 years) .. 5kW PV on 3 Trackers, (8 yrs) .. 9kW PV AC coupled to OzInverter MINI Grid, back charging AC Coupling to 48v 1300ah battery

niall2

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Re: Market for wooden windmill blades
« Reply #20 on: May 18, 2015, 05:28:14 PM »
 :) serious envy Clockman

is that all cedar? .....its crazy expensive here

i could only get it in small sizes and laminate .....your going to get a lot of nice timber out of that  :)

small blades.....

clockmanFRA

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Re: Market for wooden windmill blades
« Reply #21 on: May 18, 2015, 05:38:32 PM »
Yes Niall, all that collection/pile.

And er hmm I should have said 10 Cubic Yards of western red cedar. ::)

Mind you, I have been asking him nearly 10 years now.   ;D

Nice laminating on your blades.

I did one set for laminating, but the joint came apart  the following year.   :'(
 But now.........yippee!
Everything is possible, just give me time.

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niall2

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Re: Market for wooden windmill blades
« Reply #22 on: May 18, 2015, 06:06:33 PM »
nice .... :)

the cedar i got ( 4 by 2 rough lengths) were soaking wet .... the cheapest option

but seasoned very fast ...about 6 weeks in room temp to be ready to work on

you wont have to wait too long  i think .... :)   

MattM

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Re: Market for wooden windmill blades
« Reply #23 on: May 18, 2015, 09:10:50 PM »
I would love to have the money to CNC wax mold patterns to create molds for vacuum-injected casts.  Definitely spend more than three passes to make the mold.  It might not be as stiff as lumber, but it will reach higher tip speeds.  One can always dream.

I'm curious why one would stick to conventional airfoils if you're using CNC.  Airbus wings use underwing airflow to create lift and I'd think the conventional airfoil shape actually is putting added stresses on your blade.  Instead of creating bending stresses away from the wing origin - deflection with the wind - why not use supercritical underwing shapes to maintain a level blade in high winds?  Intentionally creating a shape to bend with the wind seems counterproductive.

I can understand hand carved supercritical wings would be a very tough act to get consistent from one blade to the next.  But CNC offers excellent consistency.

stofanel

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Re: Market for wooden windmill blades
« Reply #24 on: May 18, 2015, 11:08:46 PM »
I can cut smaller wood cnc blades, and still do so occasionally for other folks.  I wrote a program to calculate the xyz coordinates based on a profile, diameter, and the desired tip speed ratio, based on the formulas of Hugh Piggot for optimum angle and chord length.  It was in Excel of all things.  Then I ran a crystal report against this to generate the g-code for carving the top and and bottom in two passes.  Not an ideal way to do this, as cutting close to the finish surface in one pass and then a second finish cut would probably yield a more accurate final result due to stress relief in the wood on the first pass.  Still, the results work. 
(Attachment Link)
(Attachment Link)

rich,

Have you done any tests on the blade and motor setup you have pictured?

acme12

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Re: Market for wooden windmill blades
« Reply #25 on: May 20, 2015, 11:01:35 AM »
I use to live near an airport. The property bought in the landing zone was an old mobile home park. The trailers were gone but the area was unfenced. I would pick wild blackberries around the trailer slabs. When aircraft passed over and landed, there was a noticeable time delay before the wingtip vortex would reach the ground, but it was still quite loud.

https://www.youtube.com/watch?v=E1ESmvyAmOs

stofanel

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Re: Market for wooden windmill blades
« Reply #26 on: May 20, 2015, 02:26:31 PM »
I would love to have the money to CNC wax mold patterns to create molds for vacuum-injected casts.  Definitely spend more than three passes to make the mold.  It might not be as stiff as lumber, but it will reach higher tip speeds.  One can always dream.

I'm curious why one would stick to conventional airfoils if you're using CNC.  Airbus wings use underwing airflow to create lift and I'd think the conventional airfoil shape actually is putting added stresses on your blade.  Instead of creating bending stresses away from the wing origin - deflection with the wind - why not use supercritical underwing shapes to maintain a level blade in high winds?  Intentionally creating a shape to bend with the wind seems counterproductive.

I can understand hand carved supercritical wings would be a very tough act to get consistent from one blade to the next.  But CNC offers excellent consistency.

There is ongoing airfoil research regarding supercritical profiles, but they are more useful on propellers than windmills. The main benefits of using wind turbine airfoils are (1) immunity to turbulent boundary layer transitions due to leading edge roughness (explained in the introductory posts) and (2) noise reduction. And no, these airfoils cannot be carved by hand.

richhagen

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Re: Market for wooden windmill blades
« Reply #27 on: December 09, 2015, 02:51:21 PM »
This is an old thread and a late reply, but Stofanel, I have not specifically, a few folks have used different variants of them, and a graduate student of Professor Battle Brown at Carnagie Melon University used two identical 9 inch diameter sets in a wind tunnel study of different power capture schemes in a study for his thesis.  I do not have a copy of his thesis however.

That said an old saying is that the difference between good blades and reasonable blades is less than 5% added to the diameter in terms of energy capture.  Of course a larger diameter puts more mechanical stress on everything, but everything is a compromise, that is the difference between the theory and the engineering.  An alternator optimized for low wind speed will cook at high wind without furling or braking.  Most of the big home built machines are optimized for the dominant windspeed, not the highest energy and used off grid, because the batteries are the limiting factor, you have to find uses for the extra power in times of high winds, and extra power there doesn't generally help much unless you can shove it into the grid, which for a remote site is not possible.   Therefore such machines are generally optimized for lower wind speeds.  Rich
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