Here's a video of the same blades but they are now turning on ball bearings and I used a better camera (30 frames per second instead of 15). I think the wind speed is about the same as the first video. YouTube - 100_0301.MOV

Hard to say since the first video FPS was so low, but I imagine the bearings made a big difference. What is the next step?

I've ordered a different router bit to help improve the blade shape.

In another test that I didn't video I rounded the lower front edge of the blades and set it back up on the pivot. They seemed to be more reluctant to start but when they did they were scary fast, nothing but a blur. I took them down because I didn't want the blades to fly apart and break a window or hurt someone.

I did quite a bit of research and adding the twist to the blades just doesn't seem to be worth the hassle. These blades are very easy to make once you get the tools set up and trying to add some "twist" to the middle half or third doubles or triples the work. I think greater gains could be had just by increasing the rotor diameter, which doesn't really increase the work.

I'm also trying to build a small turbine for the "5 watts for $25" challenge. It won't be a VAWT, but I think that's OK as long as makes some usable power.

Here's the shortened, streamlined prop on the new "P-47" pivot: http://www.youtube.com/watch?v=2qXSQ1nky8c

Its hard to tell. Does it appear to be an improvement?

Have you a design in mind for the two bladed props, i would like to have a go at carving them with a handheld router, or any step by step design using a router would be handy. No matter how much i search it always returns using a cnc router. At present i have a homemade affair made from scooter parts for the bearings,motor,gearing,chain etc and some homemade pvc pipe blades. Startup seems problematic along with the neighborhood kids throwing things at them,hence the move to a wooden design
many thanks

Prototype 3' 4-blade downwind prop for the 5W for $25 challenge. I have about $15 in materials in this one, mostly in the metal parts (bearings and bolts). Now I just need a 12V, 5W generator for $10. Anyone know where I can get one?

YouTube - 3' 4-blade Downwind Table Saw and Router Prop

Darin used a car fan blower motor for his bike... Something smaller would be better though. Search ebay for small PM motors I guess. Maybe a hair dryer motor or something...

Sorry I do not get on the interweb much in the winter, as I have to go to a hotspot. We used to call a blade with no "twist" a drag machine, as the wind hits it and turns the blade, the classic example is the American Agricultural water pump, with its blades that almost fill the circle, it will turn relatively slowly but quite relentlessly. If you are building a constant pitch blade, the more you fill the circle with muliple blades with a low aspect ratio the better.
If you want a blade that flies you need washout or twist.
My 4' blade was carved from a single 2x4 first drill a center hole to mount it, then about 2 inches out cut on the leading edge draw a diagonal line from the upwind side to within 3/8's of an inch of the downwind side. This will be the leading edge, grind or cut the wood off using the trailing edge (other edge of the 2X4) as a guide leave about 1/8" of wood at the trailing edge. Round the leading edge by eye so that the whole looks like an airplane wing, use a protractor every inch to keep left side = right side. this will give you a pretty good jumping off point to experiment from, keep it balanced by sliding it on to a shiny metal screwdriver shank. When I get home in the spring, I will try and post a drawing of the blades I used to produce.
Yesterday I saw a turbine blade made from what looked like 4" white plastic water pipe, it was cut in such a way that it had washout, and was turning in a modest breeze. It looked kind of easy once you cut the tube lengthwise in the right shape, each blade was bolted to the hub with two 1/4"(+/-) bolts, once you got the design right, you could easily make a three bladed prop.
cheers and sorry for being gone for the winter.

Prop with Twist
 

After Nibs latest post I decided to make a prop with twist. I used a bandsaw instead of the table saw for this one. If you want to duplicate it you will also need a rasp (rotary rasp optional), a hand saw, and some way to sand (I used a random orbital sander, but you could do it by hand). It took about 5 times as long to make this one as the one with no twist due to all the hand carving required.

Here's how to do it, step by step.

1) I ripped my board to 3" wide so it would fit in my bandsaw. You could go wider if your saw can handle it.

2) Mark the line for the leading edge on the top of the board (3/8" at the tip to full board width at the hub end. Flip the board end-to-end and do it again.

3) Set up a low fence on your bandsaw table. I used one of the cutoffs from ripping the board down to 3". Leave about 1/8" between the blade and the fence (this will form the trailing edge as the blade is cut).

4) Start with the line on the top of the board lined up with the bandsaw blade and the bottom edge of the board pressed against the fence. Turn on the saw and feed the board into the blade following your drawn line. Make sure you keep the bottom of the board pressed against the fence and the table and tilt the board as you feed it in. Stop when you reach the inside edge of the top of the board (where your drawn line ends). Turn off the saw and remove the board. Repeat for the other end of the board.

5) I used my router to get a start on the airfoil shape, but it's only good for the first few inches in from the tip of the prop on this design. You can do it all by hand with a rasp or a rotary rasp (see Step 7).

6) Draw a line squarely around the board where your bandsaw cut ends. Use the handsaw to cut into the board at an angle until you meet the bandsaw cut. This removes the waste piece. Repeat for the other end of the board.

7) Use the rotary rasp (or hand rasp) to carve the general airfoil shape into the back of the blade. You need to remove a lot of material near the hub, less toward the tip. When you get it roughed in, use the straight hand rasp to smooth it out.

8) Use the random orbit sander (or hand sanding block) to smooth out the rasp and saw marks.

9) Mark the center of the hub and drill the hole. I used a Forstner bit to fit 2 ball bearings to mine.

11) Balance it per Nibs' post.

10) Fly it.

I put mine up in the place of the 4-blade and it seems to fly well. I don't think the twist is right on this one, though (the blade angles don't match some online calculators that I tried). I'll post a video of it once I get some steady wind.

I can't upload all the pics in one post so I'll have a continuation . . .