Please could You recommended any blade profile(s) (naca,..etc) for home wind turbine? rotor diameter - 4m wind speed - 8 -10 ms-1 3 blades

Thank You for any advices.... I cannot make decision...

best regards michal"

I was taught to carve wind generator blades from wood by a NASA Physicist who has a sailboat and has carved his own blades, up to 9 feet per blade, for 25+ years, studied all kinds of model airplane wings, jet airplane wings, wind gen blades, shapes, tips, fences; undercuts, high and low aspects, you name it, he and I go over it all the time. Here is the plain truth:

ANY blade is fine. The better you balance and smooth the surface (except for a slight rough texture described at our website), the faster it goes. SOME designs are quieter than others. SOME are a little more powerful in LOW winds and some are much more powerful in HIGH winds. Some accelerate faster, some take a hit from a bird better because they are thicker, heavier, stronger. There are many many factors to choosing an air foil, the tip shapes, the coatings, the wood, the tools to make it with, the material (wood? fiberglass? metal? carbon fiber?)...not just power or 'air foil shape'.

And on top of all of the 'recommendations' from 'experts', there is a girl here at the harbor, nice girl; she designs HIGH SPEED TURBINE ENGINE BLADES for very very large jet engines. She does this everyday, all day, gets to play in wind tunnels and she and I and Jerry the NASA guy all argue about all kinds of things; even the experts do NOT know...

...but I do. I know because I carve and fly blades these 'experts' suggest; I am the little test guy and I know that a square tip vs. a round tip or a wide foil vs. a thin foil, high aspect or low aspect, inner curve or high camber...I know what they all do and I can tell you this...

1. Carve the blade with about an 8 degree angle of attack near the center that twists to about a 3 degree angle of attack near the tip. That will give you a good average powerband and be pretty quiet. If you want it quieter, reduce the 3 degrees down to 0, but this affects the lower end; you won't start as quickly.

An 8 degree angle of attack near the center is found by example: take a 1x4 inch finished plank (douglas fir, mahogany, teak, ash, birch etc.) and lay it flat. The board should actually measure about 3.5 inches across by 3/4 inch thick. A little variance of 1/8 will not matter that much, so relax. More important is to make sure if it has a 'wide/open' grain you can see, make sure it is VERTICAL. Look at the end. There should be a bunch of 3/4 inch long lines going up and down, the tighter and the more vertical the better. 20 lines per inch in fir is good, less is harder to carve and more is better.

To find 8 degrees near center, write the word 'flat' on the side facing up and near the center (about 3-5 inches towards a tip to accomodate the hub) measure down from the flat side exactly half an inch and get it right and make a mark. At the tip for the 3 degrees, measure down about 1/4 inch and inbetween these two marks, measure down to about 3/8 of an inch. You should have three marks along the edge facing you, the flat side 'up'; now connect them with a straight edge. If you are doing this on a blade longer than 7 or 8 feet, it will probably be thicker and wider etc., so you need to 'expand' these numbers using extrapoplation math, 1/2 inch becomes 1 inch if the board is 7 inches wide and 1.5 inches thick. Get it?

2. If you want to capture lower end power, increase the angles slightly and hollow out the flat side a little so it parrallels the round side and leave the tips wide and round. This doesn't buy you much power because there IS no power at the low end, but it will start up a little faster.

3. If you want the blade more powerful in medium and high winds, and to be quieter, thin it in every direction a little bit and thin the tips over a nice, long, even period. At all times make sure you match blades; use templates traced around 'the best looking' blade. As the Turbine Engine Girl says; '99% of the time if it looks like a good airfoil, it probably is a good airfoil.' Don't be too self critical. Balancing them is an art and getting them to match is part of that process; art is never perfect. Do your best and smile; it's scientific, functional, powerful art. Pretty cool stuff.

4. Once you have it done and coated (total weather/water proof paint), and balanced (more paint on one tip?) and centered on your 120 degree hub (three blades) and flying, perhaps you will wish you had started smaller, say a 5 or 8 foot blade because if your balance is out of wack you will regret it sorely in that large size. Be careful.

5. Then analyze the noise, power etc. and go carve another one. That's how you learn to do art well.

BTW, the complete 'blade carving class' is at our website http://windgenzen.com. Write anytime.

Sincerely,

Craig

at eduhosting.org/windgenzen.com"

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