Which airfoils to use?

[amiklic1]

Hello!

I am trying to us esome NACA airfoils to build the frame of my future blades.

Somewhere on the web I found that NACA 4412 airfoils are good for windmill purpose.

I am just wandering do I need to recalculate some blade angles ( front side angle), as the one that is drawn on the template seems too small to me.

Any other suggestions on airfoil templates??

I've downloaded Profili 1.2 program , and there are many airfoil templates in it( NACA, and also the other types), so it wouldn't be problem to build the frame.

I plan to do the frame of thin steel plate, and then to give it a shape by using some cloth and polyester. Steel shaft would be inside, connecting all the templates on 10 sections.

Not small job, but sure a good and secure blades in the finish.

[finnsawyer]

It probably doesn't matter.  The NACA 4412 is a good choice, though.  Tables exist that show the lift and drag as a function of angle of attack.  Note that these are for airplane size (width) airfoils that exhibit laminar flow only over a small part of the span, whereas your blade may have laminar flow over its entire width and perform better.  You do have to vary the twist or pitch over the length of the blade.  You can also vary the width of the blade and the angle of attack (up to about 12 degrees).  So, you have a great deal of freedom in your design.  Unless you are trying to reach the Betz limit don't get too tied up in the design.  If you are trying to reach the Betz limit you need to work for a University with deep pockets.  In any case, have fun.

[amiklic1]

OK now. I guess I understand a little of what you write, but still not enough to start working.

I understand how to change blade width and angle of attack. But how to make twist or pitch changed?

[rotornuts]

Amiklic,

here's an image of an NACA 2414 it's a nice tip profile and would go well with a root (or hub) of NACA 4412 or 4414. Note the heavy blue line I drew through the center of the profile. This is considered the cord line and is the line that is used to set the angle of attack by rotating the entire profile clockwise to increase or counterclockwise to decrease the AOA(opposite for a wind turbine). Modifying the profile itself would result in you creating a new profile that is no longer a 4412.

Pitch and angle of attack are are both used to describe blade angle in two different ways. Pitch is actually how far forward a propeller will travel in inches or mm in one rotation if it were to perfectly follow the direction the cordline was pointed. The direction the cordline is pointed is the Pitch angle which is the same as AOA and that's how the two get confused, poeple drop the word angle after pitch and use it to describe AOA. I mean no offense but I suggest a bit more research may be needed yet.

The tip angle and twist and diameter(everything in fact) are dependent on the power output of the alternator and the average wind speed in your location or you could just use a default kind of setting such as tip 6 degrees and twist 12 degrees but these should be set from the maximum expected apparent wind direction. Or again you could just use the plane of rotation as a default.

As was allready posted above it's all much more forgiving than one would think.

Start small, don't get wild, and each set you build will teach you something new.

[finnsawyer]

You need to get a book on Aerodynamics.  I recommend the one of that title by H. C. .Smith.  No calculus.  It's a good read and easy to follow.