Demonstration Projects
You Saw These First Here On The Integrated Energies Site!

- The Half Square Meter Verticals MicroRotator -
and
- The Half Square Meter Horizontals MicroRotator -

Both Featuring Newtonian Deflection and UltraThin Profile Ratio Blades

- - The "Double Thins" - -

These are more views of projects which have now been taken down after completion of their demonstrations as prototypes. The Verticals MicroRotator was rotating in the wind at a retail store featuring wind products near Palmdale, California and the Horizontals MicroRotator was rotating in the wind near steel buildings at a small airport not far from Tehachapi, California.

Both MicroRotators incorporated generators on them, a 3.5" diameter axial flux generator for the Verticals Demo and an ordinary 12 volt bicycle rim generator on the Horizontals Demo ( image close-ups ) that has a friction drive 2:1 speed multiplier. The "loads" in both cases are a few bright colored LED lights which are frequently seen to light up.

Q and As follow:

Q: Are the blades on these wind rotator considered to have innovative features?

A: Yes. While doubled blades have been considered before, the use of doubled blades in such a way as to allow a much lower thickness-to-chord ratio on each blade profile appears to be new. Previously, doubled blades were thought to increase parasitic drag while here they are applied instead to the problem of reducing parasitic drag. The blades are ultra-thin, even sail-like and provided with a specific configuration as key elements of the design. The concept has been and continues to be documented as an innovation for which patent protection may be sought in the near future.

Q: Doesn't the classic streamlined, raindrop profile of the blades reduce the parasitic drag?

A: Streamlined profiles are known to eliminate turbulence in the flow but drag occurs even in laminar flow due to the viscosity of air. It is the combination of thin blades and blades with greater chord widths, i.e. greater lift to drag ratios, that is important. Blades with wide chords see greater lateral forces on their surfaces and hence normally a need for greater blade thickness to support these loads. Doubling blades in this manner with bracing between them gains mutual self-support strength without the need for blade thickness. Certain blade profiles with their thicknesses are sometimes thought to have desirable aerodynamic properties but testing with these small models here has shown that it is more the camber of blades that is important rather than their thicknesses.

Q: What are some typical thickness-to-chord ratios?

A: Most horizontal axis wind turbines tend to adhere to a standard of about 1 : 8. Vertical axis turbine experience is limited but it is clear that it should be less for them - maybe 1 : 10 or even 1 : 12. Today the straight bladed verticals are not meeting this low a standard. Some even have higher ratios, about 1 : 6, since they follow a design pattern of making both blade surfaces convex curved. The same principles can be made to apply to the horizontals blades since it may provide benefits for them as well.

Q: What is the gap between the two doubled blades on these rotators?

A: In earlier trials with the verticals test rotator the gap was set to be about 6" or so but it was found that a narrower gap worked best. As can be seen in the view to the right, the gap is narrower and was set to be about 1.5". The explanation for the improvement is conjectured to be that, according to Fluid Dynamics theory, the Reynolds Number is reduced with a narrow gap, thus achieving attached flow on the blade surfaces and better lift characteristics. This same gap was applied to the horizontals rotator as well as can be seen in the views.

Q: How were all these blades made?

A: They were made by bending aluminum sheet metal into a special shape that has a thickness-to-chord ratio of about 1 : 12.5 for the verticals rotator and about 1 : 8 for the horizontals rotator.

Q: Anything else of importance about their blade configurations?

A: Yes. The verticals rotator blades make use of a special "offset and pitch" system for obtaining wind deflection, which has been found to work well even at low rotational speeds. On the upwind side of the rotor, the leading edge of the outside blade is set a short distance behind or "offset" from the leading edge of the inside blade and, on the downwind side of the rotor, the windflow bypasses the blade gap entirely while the back of the inside blade makes use of a positive pitch bent into it. The same doubled blade offset system was provided for the horizontals rotator and was found to provide good results for it as well.

Q: How do these micro rotators perform?

A: Unlike most verticals style wind devices, the verticals rotator starts turning readily in winds so light as to be not even noticeable to anyone standing nearby, about 3 mph. It is almost always rotating. It accelerates as the wind increases and appears to maintain a blade speed ratio (to the wind) that is constant up to quite strong winds. In other words, its upper limit rotation rate, if there is one for ordinary ground level winds, is rarely if ever seen with this blade design as it continues to accelerate at blur speed. Although not directly viewed during recent storms involving gale force winds, it has survived all winds it has seen so far with no ill effects. The horizontals rotator with this doubled blade configuration, though, runs clearly better than this, starting up quickly and often rotating at blur speeds in winds that are lighter. In some of the views here the blades appear to be bent but that is only the digital imaging of the fast moving blades (noting that strong steel rods form the backbone of each blade). It is immediately apparent to observers that both rotators can be used in winds of 25 mph or more for a dozen or more watts of micro power production, the horizontals rotator being the more powerful.

Q: What are the advantages of each of the two rotators?

A: This horizontals rotator has a blade swept area of close to one half of a square meter. The verticals rotator here also has a blade swept area of about one half of a square meter but its effective blade swept area is less since a standard factor derived by means of mathematics of 2/3 should be applied to it, thus making it about one third of a square meter effective and so requiring that it have a larger rotor to be as powerful. The verticals rotator, however, allows the generator to be mounted more securely in the tower and the blades have simpler, constant profiles that can be decorated with colorful patterns. The blades on both here are thin aluminum sheet and quite light and sail-like being only about two or three ounces each, contributing to a rotor assembly that is light in weight.

Q: What is the "Bent Air Law" and how does the "doubled, ultra-thin blade" concept relate to it?

A: One of the most cogent applications of the Newtonian Principle, the use of which has been gaining momentum in aerodynamics work ( The "Newtonian Principle of Flight" was mentioned several years ago in a paper which can be found at the University of Washington website and in which a basic force equation similar to the one in this website for the case of wind energy was presented ), is in reducing the blade airfoil to a fixed system wherein the airflow seen by it is the apparent wind as opposed to the actual wind. Technological development of wind turbine blades in gaining more efficiency and higher TSRs is then seen as a matter of increasing or even just maintaining the blade driving force F with increases in the airfoil velocity and reductions in the angle alpha (see graphic on right) to ever lower values, even to values as low as 15 degrees or so. Focusing attention on such efforts in this way should assist in the development of wind energy and concepts such as the ones proposed herein can be said to be the result of it. Testing will determine to what degree this "Law" holds as TSRs are increased in this manner for the new blade configurations. If nothing else, this graphic makes a great T-shirt iron-on transfer!

Q: Has this project been of value and interest?

A: It has and these two rotators are fun to watch, creating a certain amount of low level attention from a distance, like shrubbery tossing in the wind. The ultra-thin blade designs even reduce the blade "swish" sound that is normally attributed to the blade parasitic drag when near by to that just barely audible. The high rotation rate along with the silence is remarkable.