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Step 2Making the blades
Blades and a hub to connect them to were the next order of business. More online research ensued. A lot of people made their own blades by carving them out of wood. That looked like an outrageous amount of work to me. I found that other people were making blades by cutting sections out of PVC pipe and shaping them into airfoils. That looked a lot more promising to me. This web site tells you how to make a set of blades for a small wind turbine using PVC pipe.
http://www.yourgreendream.com/diy_pvc_blades.php
I followed their general recipe. I did things a little differently though. I used black ABS pipe since my local homecenter store just happened to have pre-cut lengths of it. I used 6 inch pipe instead of 4 inch and 24 inches long instead of 19 5/8. I started by quartering a 24 inch long piece of pipe around its circumference and cutting it lengthwise into four pieces. Then I cut out one blade, and used it as a template for cutting out the others. That left me with 4 blades (3 plus one spare).
I then did a little extra smoothing and shaping using my belt sander and palm sander on the cut edges to try to make them into better airfoils. I don't know if it's really much of an improvement, but it didn't seem to hurt, and the blades look really good (if I do say so myself).
http://www.yourgreendream.com/diy_pvc_blades.php
I followed their general recipe. I did things a little differently though. I used black ABS pipe since my local homecenter store just happened to have pre-cut lengths of it. I used 6 inch pipe instead of 4 inch and 24 inches long instead of 19 5/8. I started by quartering a 24 inch long piece of pipe around its circumference and cutting it lengthwise into four pieces. Then I cut out one blade, and used it as a template for cutting out the others. That left me with 4 blades (3 plus one spare).
I then did a little extra smoothing and shaping using my belt sander and palm sander on the cut edges to try to make them into better airfoils. I don't know if it's really much of an improvement, but it didn't seem to hurt, and the blades look really good (if I do say so myself).
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Finding a solution for blade propellers that's both durable and efficient amounts to a fascinating engineering challenge. From my research, PVC blades (while cheap and easy to make) do not have the basic strength necessary to survive high wind speeds. (As Mdavis discovered).
Curiously, commericially made blades (for HAWT turbines) do feature connecting "tabs" that are placed centrally, rather than at the sides. Two main differences are apparent:
1. Carbon fibre is favoured over PVC as the blade material
2. A lamination process is used during blade manufacture (possibly strengthening the finished blade propellers and tabs).
Aerodynamically, the blades need to bulge at one side, then taper at the other. (A basic aerofoil). This reduces drag, as does a cambered blade. Since lift is produced once your aerofoil blade is in operation, this must be a contributory factor leading to blade failure (because the turbine is literally trying to "take off"!)
Personally, I think this "take off" factor amounts to a design flaw in HAWT turbines, since the primary objective is to capture wind energy and transfer it to the DC motor. I'd like to do testing on VAWT systems (Savonius) to see if the "lift" problem is minimized.
It's unlikely any comparison data (between HAWT propeller and VAWT savonius efficiency) exists. But you never know, the Internet is a big place... Any feedback welcomed.
NB