|By damonv, zoggop|
a homemade fiberglass wind turbine. In 5mph winds it sits still. At 10 mph it's spinning at something like 100 rpm! also included: homebuilt permanent magnet generator.
It's 6 ft in diameter, so not too big. It works great though, and the shape came out nicely. Included are a bunch of pictures that basically show the construction technique. The only things it doesn't really show are:
1: that we used bearings inside the pivot box, which mounted around a steel rod.
2: that the turbine was made by hot-wire cutting pink foam around very carefully cut and sanded wooden airfoil cross sections
3: the fiberglass was layed all at once, with 5 layers at the base and 2 at the tip. Unidirectional was used for 3 layers, each slightly offset in direction to handle torque, and bid was used for the two layers over the whole surface.
4: we have a wooden block that all the magnets mounted into. This is what the picture with about a million clamps in it is about, laminating this wood block with layers of nice furniture grade luan, which made for a phenominally strong rotor. This is also how we made the mount plate for the turbine, which we just epoxied to the alternator, and then bolted to the turbine blades.
5: to make a flat mount of fiberglass for the turbine to mate with the alternator (now a PM generator), we carefully put the blades back in the jig we used to attach blades and hub, and put a carefully positioned flat peice of shelving with a nice lump of wetted out fiberglass on it, which squished out and bonded with the blades. This we drilled through to make screw holes. On the subject of screw holes, if you are using a weak sandwich material like pink foam, always make some kind of compression strut around where the bolts go, so that you don't crush your fiberglass shell! For this we drilled holes, wrapped foam cylinders with cling-wrap and then wetted fiberglass, and stuck it in the hole to dry. Then we drilled the foam out. This worked really well.
ask if you have any questions.
In terms of aerodynamic design, there's really only three things to consider at each station. One is how wide the blade should be, one how thick, and the last is what angle. You can figure the angle roughly by figuring out what angle each section has to be at in order to trace a no-alpha path with respect to the wind, given some reference angle. Usually the tip angle is used, in the form of a tip speed ratio, or TSR. If it's a low speed turbine, you might consider adding in a couple degrees since you expect some slight angle of attack during operation. (btw, alpha is angle of attack, or the amount the airfoil is tilted with respect to the wind direction).