Mr. V -
If you are still there, here is what we are about to do and you can watch and decide how this fits your rig. I am using sheet metal blades 6 inch wide with the leading edges bent back with a radius bend resulting in about a 4 and a half inch wide blade chord. This will be a horizontals setup, while yours is a verticals. For this unit the rotor is to be fixed (with no yaw) on top of our 15 foot tall wooden tower. (If you haven't visited the website, please do so and you will see it.) We have a special shaft bearing using PVC pipe and two 1/2" ID, 1 and 1/8" OD bearings all available from local hardware stores. This will allow two 6 foot long threaded rods to be mounted on it as backbones for the blades - the blade leading edges just slip over them. They are to be about 3 inches apart axially, yours would best be a little less, maybe 2 inches. The blades themselves will be 22 inches long, while yours would be the full lengths. This gives us some 14 inches of radius around the hub with no blade coverage but there are plans to put something there that is wide and "flops" back and forth for startup. If you have followed this so far you will see that our blades will have no camber (will be symmetrical) and no pitch angle either, unusual for a horizontals but similar to your verticals. From what you see so far they will be doubled, the two rods supporting blades one behind the other. There will be a few flat connectors fastening the two blades of each pair together out along their lengths that help them support each other.
The tower is near a building which helps direct the wind flow in only two directions, west and east, naturally occurring here anyway in the mountain pass. The rotor will not yaw but this arrangement will allow the turbine to rotate the same rotational direction with wind from either of the two earth directions, also unusual but similar to how verticals work. The key is in using symmetrical blades and doubling them.
The smaller horizontals rotor we have now works well with its 3 inch wide, doubled, thin, sheet metal, 3/8 inch diameter leading edge, blades and zero pitch angle (but with a forward angled leading edge). It has a blade offset, the rear blade of the pair out ahead of the front blade about one inch. We are to do away with the offset and the forward angled leading edge in this new, larger rotor. I believe it will work well and there is room toward the center of the rotor face to do something about the startup, mentioned earlier. To see this in operation, no yaw, big blades, producing power with maybe a fan belt to a generator mounted on the top of the tower, running at a high rate with wind from either direction, and with an axis only 15 feet off the ground on the wooden tower with its ladder, will be a good demonstration. Certainly the smaller one has attracted attention.
Haven't yet decided about the diameter of curvature of the leading edges, i.e. what would normally be called the blade thickness. It will be in the range of about 1/4 inch to 1/2 inch and these are so easy to make we may make several sets of blades with different such leading edge diameters to try them all out.
You would best use wood and not sheet metal and it seems you have the ability to make good blade profiles with it. You will be happy to know that for thin blades like this you need not start with wood pieces that are very thick. They will need to support each other somehow with metal bracing between them along their lengths for strength.
I was never a believer in doubled blades like this until one day, after many futile efforts watching my small verticals projects refuse to start up no matter how thick and rounded the leading edges on them, I tried doubling them and they started up beautifully in even the lightest of winds. Ropatec and others use very thick blades and that is fine but it seems they have just never thought of doubling them.
Anthony C.
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