Orval Fairbairn wrote:
In article ,
Brian Whatcott wrote:

This is a pointer to a home build 20 ft diam windmill on a 70 ft pole.
It features three 10 ft long laminated red cedar blades and nice looking
generator, tower couplings and gin....


http://www.otherpower.com/20page1.html

Brian W

(Thanks to Larry for the pointer on rec.boats)

I hope that you have good lightning suppression!


Ha! I noticed the maker specified a blade angle of 3 degrees at the
tips, increasing to (approaching) 9 degrees at the roots.
It took me a little while to get my head round this. The maker mentioned
the blades are set flat (undersurface) forward into the wind, and I
think he mentioned a target rotation rate of 65 rpm.
I imagine he was thinking of an AoA of 15 degrees at the rated wind. The
tips do a revolution in pi x 20 ft = 63 ft per rev - so the rotation
rate at 65 rpm would give a tip speed of 65rpm X 63ft/rev X 60 min/hr /
5280 ft/mile or 47 mph.

I guess the pitch angle for zero AoA at the starting windspeed 16 mph
would be atan 16/47 = 19 degrees from the plane of revolution, so for 15
deg AoA the pitch angle might be 4 degrees from the plane of revolution
at the tips.
And he mentions 3 degrees. But getting up to speed with stalled blades
would be an issue...
What's your take, Orville?


Regards

Brian W