Carving your own wooden wind turbine blades
There are lots of articles out there that discuss the merits and disadvantages of sizes number of blades, what length you need to power this or that. We'll start from the position that you have had a flick through them and know what size you need for your purposes. Since you know what size, we'll just go through how with a saw, chisel and a plan you can make your blades. For our example we will use three, one metre blades.
- Pick out some wood.
Once you have decided on your length (1 meter in our example) and the number of blades (3 in our example), you will be looking for 3 bits of wood a little bit over 1 metre long (here wood is sold in lengths increasing by 30cm so 1.2 meters is the closest for this example). Now for the width and depth. Try and get between a 2:1 ratio and 3:1 ratio (see diagram below) and try to get the width at about 10% of your length. We have 1 meter so we'll try to get about 10cm by 5cm lets say. Now try to find that in a light wood, pine is great. And look through the pile of wood there to get a piece without any knots (know as 'clear' wood). So we have the length, width, depth, type and picked out the clear ones. Get them!
- The shape from the top.
For each blade, place it on your workbench and divide up the wood with pencil markings dividing it evenly into 5 as shown. Mark one end as the tip and one end as the base. Also mark one side as the fround and one as the back.
Now mark the half way point along the width on the tip and draw a line connecting it to the back end of the line before the base.
Cut Along that line so we now have something that should look like this.
- Top side.
Ok now turn it on it's side so the back is facing up (the side we just cut) and the front facing down. And we are going to mark this shape along it.
Now cut along this red line, don't cut all the way through, don't cut into the front top line! Be Careful!
Imagine a flat surface that runs from the front edge to the grey line we drew. Now we need to plane and chisel the top bit away until we have a smooth surface that runs between those two line. Just to make sure, if you plane into the front top line or the grey line you have gone too deep :( Hopefully we will end up with something like this. And you should be able to run a ruler between the two lines and get a flat surface.
Have a bit of a sand and sit back and appreciate it's beauty because one side is done.
- Bottom side.
Ok this bits gets a bit curvy and difficult to draw so I'll go over what we are try to achieve first. We want to achieve that nice plane wing shape all the way along the bottom, with it thin at the tip and thicker and thinker till we meet the base.
For Example near the base.
And near the tip.
So lets make it happen. Since it would be a hell of a lot of planing at the tip lets make some cuts to make it easier. Place it on it's edge front down and cut out the sections indicated below.
Now we have to get out the plane and make the bottom into the shape we spoke about above. Try not to cut into the front or back top edges. On the front we want that round areodynamic shape and on the back edge we want it tappering down to a point. And the tip should be quite thin and get slightly thinker to meet the base. So it should look something like this.
- The Base!
Depending on how many blades you have you will want to divide that number by 360 degrees and cut that angle into the base. We have three blades so we need an 120 degree angle into the base like below. And then they all go together.
Ok now get out that sand paper and finish any rough bits and make it a smooth as you can.
There are many painting options to preserve them against the elements. I like to fiberglass the front edge for some strength and then use a coat or two of epoxy and a coat or two of boat paint.
All that is left is to attach it to your system.