My VAWT Project II

[Tom in NH]

I was riding my bicycle feeling the drag my body was creating as the wind rushed past me. I decided part of my problem is the support post and the alternator assembly. It has to be creating all kinds of turbulence in the lower half of the rotor. I also was so impressed with the performance after I replaced the big 2x4 top crosspiece with a piece of half inch emt pipe, I decided to do something with the middle crosspiece (the rotor arms). I had some extra 8 inch wide aluminum strips so I placed strips on the top and bottom of the rotor arm and taped the ends temporarily together with duct tape, making pointy ends on the leading and trailing edges. I took some cardboard and fashioned a big cylinder to shroud the alternator and brackets. I also fashioned winglets a la windstuff ed's description out of thin plywood and attached them to the tops and bottoms of the blades. Now I just need some wind to see if these changes help or hinder my speed problem.

I have this setup in a sheltered place beside my house. I'm beginning to think I need to put it in a more exposed area to see if I can give it some real wind and get the rpms up to 60 or 70 instead of the 10-40 I'm seeing now.

Here's a link to a 15 second video .wmv file (It's about 300Kbytes long -- Sorry. ). If your computer tries to open the file in your browser like mine does, you can save the file, then open it from Windows Media Player:

http://files.blog-city.com/files/M05/102402/b/vawt15.wmv

[willib]

it played fine in winamp.

looks cool!

[windstuffnow]

  It worked fine in mine as well.  Pretty slick !  Do you know the windspeed it's running in?  I'm guessing around 3 1/2 to 4 mph.   Great work!   You'll get it!

.

[commanda]

820Kb.

Plays fine in mplayer on Ubuntu.

Amanda

[Tom in NH]

I don't know the exact windspeed. I'm waiting for an anemometer. That will help. The breeze was strong enough to feel on your skin. The tips of branches moved gently. Sorry about the underestimate of the filesize, Amanda (and all). Ed, do you think larger winglets would work better? --tom

[windstuffnow]

  Tom,   I've only experimented with versions that were a couple inches larger than the wing.  I'm sure there is a point of diminishing returns, it was significant enough in the wind tunnel to continue using them.  It was kind of hard seeing how large they were in the vid.   My 3x4 doesn't have them right now but I plan to modify it this summer as well as put a more powerful alternator on it, the one thats on it now won't hold up to the power it makes.  In a 30 mph wind with all the leads shorted doesn't slow it down much at all.

.

[Tom in NH]

The video does not show them well, but the winglets extend 1.5 to 2.0 inches beyond the wing. I was observing some crows flying playfully overhead and noticed several long primary feathers extending out from the end of the wing on the leading edge. By the angle these feather were at, I realized they probably serve a similar purpose as the VAWT winglets. The remarkable feature was that these crow feathers were only on the leading edge of the wing. Made me think maybe I should experiment with some leading-edge-only winglets, perhaps a half circle a few inches larger in diameter than the airfoil. Also, what would you think about adding two more winglets in the middle of the airfoil, one on each side of the rotor arm? It occurred to me that as the rotor arm cuts through the wind could create some eddy currents of air along the midsection of the airfoil. -tom

[electrondady1]

tom , your mill looks good!  in your other post you mentioned it responded to a reduction in dia. with increased rpm. but it still looks much wider for its height than eds. i'm thinking you will get increased torque(longer lever) but it would never approch the same rpm. as it is.  are you just being cautious? eds design is different than a drag unit as it can produce lift but whatever its tsr. the relationship to the wind speed would be the same what ever the dia.

 i'm not shure is what i just said is clear.

my little erma mill is only two feet in dia . i'm about to build a stacked up version . i want to keed the same rpm but get better torque .  but the next generation will be twice as big in dia.  

[vawtman]

Hello Tom

  Thats slow, 30rpms.Got a gen pic?Was the turbine under load?

 Good luck and keep playing with it.

[Tom in NH]

If I understand you correctly, I would disagree. Diameter affects rpms. Cut diameter in half and you double rpms, no matter what your design. It's like the spinning ice skater. Bring your arms into your body and your rate of rotation increases. If you make erma fatter she will slow down, other thing being equal.  

The problem I have is my air foils were originally designed for a 7 foot diameter rotor. Using them on a 3 foot rotor very likely introduces excess drag and other interfering forces that reduce rpms to less than what the math would suggest. I could make my airfoils much smaller to good effect if I choose to use a 3 foot rotor.

I'm not sure I want to go that way though. The video shows the airfoils attached to a 6 foot rotor which is probably more correct for the size of the foils. There is lots of torque. Right now I'm thinking I will wind new stator coils that will cut in at a lower rpm. I'm also thinking of gearing it up with a chain and sprockets. I'll try the windings first. Thanks for your kind remarks about her good looks. I gotta think of a name like you did. --tom

[Tom in NH]

Hey there Vawtman. The only pics I have of the alternator are what's on the web log. http://www.altenergyweb.com/vawt.htm

It was not under load when I shot the video. I've shorted out the coils just to see what happens. In a moderate breeze, there's hardly any decrease in rpms, but it wasn't generating much juice at the slow speed, only about 2 watts (2v, 1A). --tom