just curious, are the blades set with an attack angle? or parallel to the plane of the hub?
The airfoil has angle of attack but the angle varies at each station along the airfoil because it has no twist. The GOE222 is a strange animal and it was originally developed by the Gottingen Aerodynamic Research Center in Germany and used for years on the Winchargers that powered many American farms before the Rural Electrification Act. It's a very high lift airfoil that appears to work well from zero angle of attack to over 17 degrees without a big change in performance. This will give you an idea of what it looks like:
http://www.ae.illinois.edu/m-selig/ads/afplots/goe222.gifThe best way I can describe its performance is that it's about as close to having variable pitch on a fixed pitch turbine as you're going to get. The TSR operating range where these blades will work is wider than anything I've ever run. I found out by accident that they'll quite happily spool up to 10+ TSR unloaded in the blink of an eye and they'll pull like a mule at 3 TSR. As far as "ideal" TSR I haven't really arrived at a conclusion on that. So I've been running them around 5 TSR at 15 mph wind speed and they seem to work pretty good on either side of that.
The rotor on this geared machine is running at 102 rpm at 25 volt cut-in at 6 mph, which works out to 7.4 TSR. At 12 mph it's pushing 330 watts and the rotor is at 140 rpm. At 20 mph the rotor is only up to 215 rpm and it's right at about 1,200 watts. At 24 mph where it starts to fold up and furl the rotor is running at 250 rpm and about 1,340 watts.
So the rotor only gains about 150 rpm from cut-in and hits 5 TSR right in there about 15-16 mph wind speed and only drops to about 4.6 TSR where it starts to furl. I tried a one-day experiment on the second turbine I built with a set of PowerMax 131's (13.1 foot rotor) on it and they wouldn't drive it. It would've even get above 12 amps with the PowerMax blades on it, and it struggled to get that far. The S809 airfoil used on the PowerMax blades is known as a high-torque airfoil with self-speed limiting capability in high winds, but they won't drive this beast.
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Chris
I'm going to modify this post to make a footnote here:
I designed this machine from the ground up to use these blades. I did a lot of research on the GOE222 airfoil, and I did a lot of testing with generators at the gear ratio I selected to arrive at what it takes to match the power curve of the rotor. I did my original testing with 12 volt stators and got a good match. But the machine was an animal in higher wind speeds and the amps on 12 volt was just ridiculous - I had hot wires, rectifiers with fans blowing on them to keep them cool, and all sorts of problems. So I took what I learned from the 12 volt testing and applied it to 24 volt and it still works. The machine is not near the animal on 24 volt because it cut the amps in half.
So, taking what I learned from the original, I can't recommend building a 12 volt version of this machine anymore. It works but no matter what I did to try to keep the power down it would still go well over 100 amps without even really trying, and start to fry everything hooked to it. So I finally had to give up on the 12 volt.