A tapered twisted blade uses all of the blade in all wind speeds efficiently, that's why the blades look as they do.
Dave, these blades have 18° pitch at the root and 1.5° at the tip. They're an S809 airfoil, which is used on most of the commercial turbines today. The S809 is symmetrical except for a "cusp" on the trailing edge of the wind facing side of the blade. They like to run from 6.5-7.0 TSR, and will run quite well down to 6.0 TSR. Below 6 their Cp drops off pretty fast and they stall very easily.
I tweaked the power curve in the Classic's graphic editor today to let the turbine run at higher voltage and 7.0 TSR instead of 6.5. That got me another 120 watts @ 9 m/s.
This turbine is quite noisy at higher wind speeds. It sounds like somebody whipping three 1/2" cables thru the air at high speed. At 5-9 m/s it's not too bad. But at 10-12 m/s it sings pretty good - the rotor is running well over 500 rpm @ 12 m/s and I got just shy of 2.9 kW from it so far, which pushed the Classic to 95 amps output. Believe me, a 3.2 meter turbine @ 2.9 kW output is screaming like a banshee. I'm going to tune that back a bit by "clamping" the input voltage down a bit in the Classic's graphic editor to cut it back on the top end. But for now it's a new "toy" and I want to see what it'll do
We still got good wind tonight but it's tamed down a bit from what it was earlier. It's averaging 9-10 m/s right now and supposed to die down further tonight. But I'm happy with it - it had a good first day's run on the tower - 10.1 kWh since 10:00 AM.
What's really cool is that I ran a permanent ethernet cable from the Classic to my home network wireless router. I downloaded a thing off Midnite Solar's website that lets me access the Classic over my network with my laptop. I can sit right in my easy chair and watch my turbine's performance on gauges and stuff on my laptop. Never had anything like that before and it's cooler than hell.
Just kind of a sidenote on setting up the Classic 150 for your home computer network - when I first set it up I used DHCP but I couldn't find it on the network. Something either mucked up in my Workgroup or whatever, and it wouldn't show up. I gave it a static IP address and then it showed up and the Local Status Panel in my computer can find it. Don't know what the deal is with that. But it works.
Edit on the blade topic -
Dave, I got another set of these blades here and I measured them up this morning. I don't know if it would be possible to carve these or not. You'd have to use blanks that are 4" thick x 10" wide. These blades appear to be designed so the entire length of the blade runs at the same angle of attack.
The airfoils are almost perfectly symmetrical except for about the last 1/2" of the trailing edge where there's a slight "cusp" on the wind-facing side. This is the airfoil these blades use. It doesn't even look like it would work, or generate any lift, but it does:
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Chris