If the assumption is made that both the front and the back take the load equally there is still a problem in that when the blades are near the outer fringe of their circuits (like a sailboat sailing nearly directly upwind or downwind) they are not as able to convert energy as when they are at the points where they are crossing at right angles to the wind (helped by the fact that the entire blade is at work at the rotor arm length rather than a declining amount over its length as with the horizontals blades).

To do the math for this, some calculus is necessary but it works out surprisingly well. Here is my cut at it:



I know it is a great disappointment for the fans of the verticals to hear that a factor of 2/3 should be applied to the rotor front aspect area, i.e. the rotor diameter times the blade length, but a serious look at what is involved leads to this conclusion. Just think that the horizontals have not done much better, few to none of them being able to produce even half of the energy that their swept areas indicate is possible under Betz at rated conditions and able sometimes to meet only 75% anytime other.

The 10 watts at 15 mph was found this way. The rotor diameter of the project in the message is 12" and the blade length is 18". This aspect area, 12" x 18", is 1.5 square feet. In square meters this is = .13935 m^2. This divided by a standard factor of .114 yielded the energy in kilowatts at the Betz limit for 30 mph winds = .1222 kws = 122.2 watts. Divided by 8 for 15 mph winds this came to 15.3 watts. But then the factor of 2/3 derived above was applied and this then resulted in 10.2 watts. For a device as small as this, that is quite good energy. For your device, 42" diameter x 34" blade length, this same calculation for a 15 mph windspeed yields 67.3 watts.

My verticals device shown on the IntegEner-W website has a blade length of 22" and rotor diameter of 36" resulting in a potential at 15 mph windspeed of some 37.4 watts.

Watch your blade thickness-to-chord ratio. I prefer thin blades that, even so, have difficulty starting up. With two blades, some "hemming and hawing" will take place when stopped but they will eventually start. Mine with the four doubled blade configurations shown starts up in winds almost as light as the crow's aforementioned gaseous emission and certainly hardly even sensed by observers, some 3 mph.

This has been fun writing this and I hope your project turns out well.

The verticals need something thin like those mentioned above for their own purposes. The thickness-to-chord ratios must be less than 10% for them to avoid the terror of high air drag to which all verticals are subjected when traveling on the part of their paths heading straight into the teeth of the oncoming wind. This factor is often not given its due as if it doesn't exist and everyone finds out, sooner or later, sometimes after spending a lot of money and time on their projects, that it does. Look at what has happened to Mass Megawatts (www.massmegawatts.com/index.htm) on the East Coast with their drag-based verticals. They even built their own wind tunnel to test out their designs, all without a satisfactory understanding of basic physics and vector algebra. It is a shame some of these efforts are not better directed.

The foundations are now in place in wind energy. One of the problems that need to be solved is the problem of blade parasitic drag, which exists everywhere, even on the multi-megawatt turbines of the big wind energy companies. It is hard to imagine but true that 50% of the power in the wind seen by these big machines, thousands of kilowatts, is being wasted in blade parasitic drag as revealed by a check of their power curves. It also can be seen in the efforts to go out on a limb with blades bending back as far as they do and with high stresses when under load. This is serious business.

I would also have to say that the small horizontals, the Bergeys and the like, tend to spin too fast as if they must give a good accounting of themselves visually. I would imagine that they only are creating more noise than necessary and it comes as no surprise that it is due to the power wasted in the parasitic drag of the fast moving blades. The energy produced has never been highly satisfactory, either. Four kwhs a day at the 7 cents we used to pay for electrical power in Minnesota comes to just what it used to cost to buy the daily paper before the price went up. Something better is possible.

New ideas are welcomed but it is easy to avoid responding to those who clearly do not have a good conception of what all this is about.

Just wanted to preclude an opportunity to point out a trivial error in terminology.