Need to build a HAWT - Starting w/ the blade

[Srinivasan Ravikumar]

I am a HS STEM teacher. I am going build a HAWT in Andover, MA w/ my students. I intend to document this entire process on this Forum from Soup-to-nuts; I mean the good, the bad and the ugly!

Chapter 1 - The Beginning

I have been reading for over 6 months various online documents and blogs for the best available information on how to go about doing it. I would like to generate about 1 kW power at the prevailing wind speeds (WS) of about 12mph with a 12 foot diameter Turbine w 5 blades. I would like to keep the pitch constant, minimize vibration but not concerned so much about the noise. I intend to construct the blade by cutting the station profiles out of luan boards on Laser Cutter, mount them on steel square tubing w/ the correct drop for the station, spaced about 6" apart w/ Craft foam filling, and eventually wrapping the whole thing in fiberglass cloth and epoxy, then bondo it smooth and paint it bright!

Two questions must be answered to get me going:


What profile should I use for the blades?
What should the Chord length, thickness and profile be at each of the 12 stations?


I see NACA 2412, 4412, 4415, 4418 etc., are all possible, and Stewart Corman mentioned in one of the blogs that the choice of profile isn't all that important for performance, but only for buildability. A confirmation from the Forum on this would be great, and would even be better if there is a consensus view on which one should I go w/ to achieve maximum probability of success.

There are profile generators like on airfoiltools.com but these generators are usable only after I get the Chord, thickness, and angle information for each station.

I even thought of using Hugh Piggott's calculator and use the "drop" in his calculations to back into the angle for each station.

Your answers would be much appreciated.

[Rob Beckers]

Hi Srinivasan,

Welcome to the forum!
I'd love to see the journey of designing and building a turbine. Thank you for posting here!

What age group are you students? If we're talking middle/high school why not let them figure out what blade profile to use?

A 1kW turbine, 12 ft, turbine is pretty ambitious! Building something smaller would be quite a bit easier, and you could build multiple smaller turbines for the same cost, have multiple 'teams' working on them, with their own design decisions, to test them all at the end.

Rather than focusing in the highest-efficiency blades and turbine, IMO it may be more worthwhile to focus on ease of construction. Pick a blade profile that is easy to carve and forgiving, rather than the one that produce the most energy. In the end the differences will be small.

-RoB-

[Srinivasan Ravikumar]

Rob:

Thanks for the prompt reply, and good to be talking to like minds.

The students are in their third trimester (yes, we go by trimesters instead of terms) on their Grade 11. I pondered the question you are posing a lot. We are working on a grant from Clean Energy Commission to make something w/ measurable "Clean Energy" impact to local community, which largely led to the decision to build a single HAWT than multiple smaller ones. Moreover, given that they have learned Statics & Structural design, Gears and transmission, and dynamics, albeit all at rudimentary level, I figured a single system w/ many teams working on it, is probably all that we could handle. Ultimately, I would like to have a HAWT on a tower w/ PTO (Power Take off) available at the bottom for a variety of uses.

That said, I read with great interest, again, that you have said that the profile makes little difference to HAWT efficiency. Is it certainly the case? Is there any firm recommendations on the right profile to use to satisfy the various attributes such as HAWT efficiency, torque, Low-wind performance, ease of start, vibration, and noise?

I am not too worried about the construction of the blade as I am not going to carve them out of wood, as Hugh Piggott says he does. Instead, I am going to build them up w/ square steel tubing running through the "thickest" parts of the profiles at stations w/ craft foam filling and fiberglass cladding. Placing the stations at 6 inches would allow be to carve the foam filling w/ hot wire foam cutter w/ the luan profiles on either side at successive stations as guides.

So, I am still looking for answers to my original questions:

What profile should I use for the blades?
What should the Chord length, thickness and profile be at each of the 12 stations?