how about hinging the blades at the centre point? maybe having the blade split into 2 with a rubber section where the most stress is. thinking car spring bump stops or something simular. hate to think what the resonances would do to it at 300 mph,but i am sure aircraft engine designers have simular problems. personally i think there are better vawt designs but as an experiment it might be worth the time.

I think of your Darreus design every time I am driving down town & see some young bloke in a modded Torana or the like...with what looks like a length of standard aerofoil section bolted accross the boot for a spoiler...seems to me that stuff would be ideal for blades...its obviously ready made, can't be too expensive, & must have some strength..

Here is my take on it. The wind seems to be coming from behind the garage and the blades are being somewhat "pitched" by it, as though they are free to do so. One is pitched inwards a bit and the other outwards and this reverses as they go around. Is this right? This is certainly allowable and helps make it start up and run well.

My own experience is that otherwise with fixed blades something like this, begging to differ, would not start up or only do so slowly. What was done to make it better was to add a second blade about four inches or so behind each of the blades shown, i.e. it would have four blades instead of two on the two rotor arms. This then started up much easier and in the lightest of winds. However, it didn't run very fast even in strong winds. So the next thing was to make the four blades thinner, as thin as they could be made, still with the 0018 profile. They started up well and ran much faster but still didn't accelerate beyond a certain speed in gusts. Then the gap between the doubled blades was narrowed to only one and a half inches. Somewhere along the line an offset was made on the leading edges and some positive pitch was added to the trailing edges. As a result of all these mods, it now starts up and runs exceedingly well and I, like you, was thrilled by it and loved to watch it turn. It could be seen from about a half of a mile away and created much attention for itself.

When you go to make the larger unit you mentioned you wanted to make, pay attention to the blade thicknesses. The faster tangential velocities of the greater rotor diameter will create much more parasitic drag going upwind, out of all proportion, and it will not respond overall to the larger dimensions. So the blades must be much thinner, not thicker, and it will pay to consider the doubled blade idea as well. The Solwind people have been informed of this and it seems to me that they would also stand to profit from it with their large diameter rotors.

Like the Prairie Home Companion radio show host, Garrison Keillor, used to say, "Keep your feet on the ground, your hopes up high, pray for rain, and keep your vertical axis wind turbine blades thin". Did I get that right?

You may communicate privately and some pieces or assemblies here may very well be found to be useful.

Here I am again with a follow up comment to those posted previously. Here is a design that interests me. A couple of years back I uploaded an image to OtherPower of the little Wind Twister of which I made a hundred or so. I come now here to find it is still out there and so I have copied it below into this message.

It was fun and interesting just for a short while to make these and then give them out free to the thrift stores here in Tehachapi, who gladly accepted them for sale at a low price most usually to parents with small children, who loved them. They are just 6" x 6" and could be fastened with the string to something like a tree or porch overhang and would rotate in the wind. Being made of just some balsa wood and color construction paper from KMart, they were easy to make but didn't last very long out in the weather.

There is a market for these. Stores now sell wind toys for the yard along with kites and they have always had trouble trying to make these rotators spin on a vertical axis. So not many are available that can be hung from something with a string, an obvious and simple way to display them in the front of the home. Prices that are set at these stores range from $10 each to upwards of $40 or more and people come from great distances to buy them. See www.wind-toys-online.com .

So yesterday it finally occurred to me that these could be made out of the aluminum sheet with which I had been working and I set about making one this way. It doesn't produce any power and is purely for decorative purposes but it certainly spins fast, easily blur speed, and is practically always in motion. I added some colored adhesive contact paper to the blades and the possibilities of adding bright colors in this way are endless. Now it is built to last for years and through the worst weather. Other projects of mine I could say have the potential in the near term of being sold in the tens of thousands but this I would have to say could easily reach a million or more.

I just cut out each blade using a template from 4" aluminum sheeting, then bend them, and then fasten four of them together with pop rivets at the center. A small hole is drilled for the string which is then knotted through a nut. There is absolutely no doubt whatsoever that this small rotator can be readily sold in stores everywhere. Even Wal-Mart.

It is good publicity for the renewable energy technologies, isn't it? Seeing these in the yards of many homes certainly doesn't hurt the progress of windpower.

Millions. Making them takes time but as they are sold, improvements in how they are made would follow. Making them right now is something similar to craft projects, a labor of love. As fast as they are made, however, they can be sold. These aluminum ones really perform well in the wind.

A further comment about the NACA0018 blades is that I come to find that "0018" refers to the thickness-to-chord ratio directly and means 18%. This is equal to 1 : 5.5 and is far too thick. There are profiles that go all the way down to NACA0006 for a 6% ratio. These are much thinner and, once started, would rotate far faster due to a much lower parasitic drag. To start them better, several options are available, including the simple one of just making four blades rather than two. Another easy option is to staple a piece of "tail-wagging" paper (or vinyl or something) to the centers of the blades that extend the trailing edge out some 6" or so. These greatly facilitate startups and are easy to add to the completed assembly.

Thanks again for your time and I hope this information is of some use.