The blades arrived a couple of days ago. They only cost about $80 dollars + shipping. I think that is quite a good deal. They are not the highest quality but look pretty good for cheap blades from China. They are definitely much heavier than the cedar blades we carved last year at the sustainable living festival. I think they need to be coated with something to protect them from UV radiation as well.
Anyway, I built a couple of 12 inch wood disks to hold the blades together from the front and back. The back disk needed a 2 3/4 inch hole so it can slip over the hub and spindle. It needed 9 bolts (3/8 x 4 inches) to hold the blades to the disks. I think the roots on these blades are too small and the bolt holes too close together…I’m not sure how strong this could be in this arrangement. I guess we will see when it is flying.
After getting it all put together I measured it at about 9 1/2 foot diameter…so it is a bit smaller than the 10 foot diameter plans. This will definitely affect the power output since the power is related to the swept area of the blades. These blades have a higher tip speed ratio (TSR or 8 instead of ~6) because they are a more efficient airfoil. I will need to think a bit more about this but I think this higher TSR might cancel out the affect of a smaller swept area (and higher RPMs). I’ll have to make a posting on www.field lines.com and run this by the experts. I might be able to do a little math and figure this out too. Again, I can always reduce the efficiency of the alternator by making the air gap larger so it does not stall out at a low cutin speed (I think). Here are some pictures…
