Hi DaveS,

Great tip! Thanks.

PeterS

Hi JoeF,

To me, tumbling implies a rolling/falling motion, as in “she tumbled down the hill” (as in Jack and Jill). That could be applied to two-sided rotors which do rise and fall twice each revolution and so they sort of look like they are tumbling.

But if the Sharp Rotor is tumbling when it is driven by a motor, then a Flettner rotor is tumbling when it is driven by a rotor. But that doesn’t seem descriptive or accurate. “Rolling” would be, but the rolling is upside down. (I’ve flown Sharp Rotor models such that they briefly roll along a ceiling.)

So why not just use “cross-flow rotary kite”, which is technically accurate and covers all cases? Then differentiate between types, such as two-side, three-sided, cylindrical (Flettner and Thom), and powered cycloidal rotors. Then two-sided can be further differentiated into Savonius, Lesh (oval), and Donaldson (highly cambered leading edge).

PeterS

Hi DaveS,

You misunderstood the article. In science, great effort must be made to guard against bias. Objectivity is possible only when biases are identified and rejected. You embrace your biases. That is not science. You claim to recognize your biases, but I have given you examples of your biases that you did not refute and did not reject. So you remain biased by choice, meaning that you choose to believe false information regardless of objective evidence that refutes it. That is not science. It is anti-scientific.

You are attempting to give bias a positive meaning, which I did not use, in order to continue to embrace your biases. You are trying to justify bias as motivation. That is something very different from what I am talking about, and you know it.

You also deliberately misrepresent what I say about bias against VAWT and take it to an extreme that I did not take it. That seems to be just another attempt to obfuscate the issue so as to avoid dealing with your biases.

If you find any biases (false statements) in what I have said about my windmills or other WECS, please state them, explain why they are false, and present the contrary evidence.

On the subject of neutral-party testing, which you insist upon, please show me your test results for the Flipwing. If you have none, then you are using a double standard.

PeterS

Hi DaveS,

I’m not sure what you are trying to say. The patent shows a wing kite supporting an H-Darrieus rotor with fixed blades (no blade pitching) that is horizontal and perpendicular to the wind.

As best I can make out, you are ignoring the VAWT, and you are pointing out that the wing kite is controllable with respect to its pitch angle. If that is what you are saying, then so what? Do you believe that pitch controls of all kinds and for all purposes -- there are a great many -- are all the same? And therefore any pitch control of kite anticipates any pitch control of a VAWT? That seems to be your point. If it is, it is obviously not true. It doesn’t make sense.

You are suggesting that I think that all other pitch control systems are inferior to the two new ones I invented strictly for VAWT. That is a bizarre over-generalization of what I have said. I said no such thing.

What I said was: The Sharp Cycloturbine -- due to its extremely simple, cheap, and efficient pitch control system -- is the best all-round VAWT. I also said that the Bird Windmill -- which uses pitch control, but which is not as efficient as that of the Sharp Cycloturbine -- may nevertheless produce energy more cheaply than other wind turbines because it is dirt cheap to make and because the blade sweeps a large area of wind for its size. I have also pointed out false statements about VAWT (myths) that I believe are retarding their progress, including the development of my two VAWT.

Whatever I say, you grossly distort it so that you can take issue with it. Gees, Dave….

PeterS

Hi JoeF,

The definition of “flip” includes the notion of something with a top and bottom turning over suddenly. A Flettner rotor does not turn over because it has no clear sides to turn over. It rotates. A Sharp Rotor rotates smoothly and does not suddenly turn over. The rotation is continuous and there is no vibration and no “flip”.  The rotation of two-sided rotors could be described as “flipping” if you like. But the Flettner rotor and the Sharp Rotor do not “flip”. They rotate smoothly all the time.

What is unique about the Sharp Rotor is that it both auto-rotates like 2-sided rotor, and it can be rotated by a motor, at a high spin ratio, like a Flettner rotor. It bridges the gap between auto-rotation and motorized rotation. It can do both. It also has a relatively large internal volume, so it can function as a balloon that has additional lift due to auto-rotation or motorized rotation.

Two-sided rotors depend upon the Kramer effect. Flettner rotors depend upon the Magnus effect. Sharp rotors can operate in both modes, the Kramer effect mode and the Magnus effect mode. They can operate in both modes at the same time when the spin ratio exceeds 1 and not much higher. A Sharp Rotor creates more lift than a Flettner rotor up to a spin ratio somewhere below about 2.

All of these rotors can function as windmill blades, both HAWT, and VAWT (if inverted on the downwind pass). All of these rotors can function as horizontal axis propeller blades.

Motorized cycloidal rotors also create lift by cyclically pitching the blades. So they function as propellers. All of the other rotors can also function as the blades of propellers.

A cycloidal rotor can also function as a vertical axis windmill.

PeterS

Hi PierreB,

Thanks for asking.

The Sharp Rotor is the one with the 3 sides. The Sharp Cycloturbine (Sharp VAWT) in the photo is the one with opposite blades. It is a cycloturbine VAWT. It doesn’t create lift if horizontal and perpendicular to the wind. (Actually, it doesn’t work if it is horizontal.)

They are both cross-flow rotors -- an inclusive category -- but they work entirely differently.

The address you gave me doesn’t open for some reason, so I am guessing at what you are referring to.

I hope that clarification helps.

PeterS

Hi DaveS,

I’m glad you like the general category of “cross-flow rotary kite”.

What you say about the physics of a cylinder in an airflow that is free to rotate doesn’t match with what I’ve read in research papers and textbooks.

So if you can refer me to some source that explains that, I would appreciate it.

What I’ve read is that a cylinder in an airflow creates a very strong Karman vortex street. That is common knowledge, not something obscure. That means that the air behind the cylinder oscillates a lot, and that would pull more air around once side of the rotor and then the other side. That’s why a cylinder can operate as a Flipwing. If the air is oscillating like that, then any tendency of the cylinder to rotate would be immediately cancelled as the air switched to flowing around the other side of the cylinder.

So I can’t figure out how a cylinder could be caused to rotate in an airflow. What would cause the cylinder to rotate?

Maybe if the cylinder were allowed to move from side to side like a Flipwing, the cycle rate could be slowed down enough to allow the cylinder to rotate a bit one way and then the other as the cylinder moved back in the other direction. But the inertia of the cylinder would be high relative to the net surface drag of the air on one side or the other, so it still seems unlikely that the cylinder would rotate more than a few degrees at most.

Does that make sense?

PeterS

Hi JoeF,

Obviously a cylinder can rotate so that a mark that was on the top could be on the bottom, so what was the top half of the rotor could become the bottom half of the rotor. But we typically say that “a cylinder rotated 90 degrees” rather than say that “it turned over 90 degrees” because that would be ambiguous. Would that mean that is rotated 90 degrees around a short axis or its long axis? It’s not that either term is correct or incorrect; it is that some terms have more common usage that others. So I’m just saying that it is more clear if we stick with common usage.

PeterS

Hi JoeF,

Well, I guess it would be accurate to say that a Sharp Rotor flips by not flipping, which means that it is smoothly flipping, but that sure is confusing. Why not keep it clear and simple and say that it rotates?

I’ve experimented with lots of Donaldson rotors and Sharp Rotors, and I’ve never noticed any vibration of the Sharp Rotors. There might be some variation in the lift due to having 3 lifting surfaces, but if there is, it is quite small.

It might be possible to change the surfaces to ones that would cause some vibration, but I’m not sure. For example, use a triangular column. It might rotate once started, and it might cause some vibration. Don’t know.

PeterS

Hi DaveS,

I see what you mean, but I don’t think that is quite true in all cases. Here is a counter-example: A proton traveling through space. It doesn’t proceed along its path by means of a series of jumps. The same is true for many other sub-atomic particles. But I guess if you wanted to regard a proton as a wave, then it would have to have some sort of oscillation. A photon travels in wave form, but I wouldn’t call those oscillations “tiny jumps”.

If all is ultimately strings that vibrate, could that be called “tiny jumps”?

PeterS

Hi DaveS,

You state that there is an optimal pitch for every part of any rotary wing cycle. That’s not quite accurate because spinning cylinders can function as rotary wings, and spinning cylinders have no pitch angle, as conventionally defined. By analogy with rotary kites that do have optimum pitch angles, we might say that spinning cylinders are always at their “optimum pitch angle”.

----------

In response to your request for technical information relevant to the Sharp Cycloturbine (1982, US Patent number 4,334,823):

The Sharp Cycloturbine’s pitch control system is a superior version of the Sicard/Bayly-Kentfield VAWT (S/B-K) that was patented in 1978 by Sicard (US patent number 4,048,947) and re-invented in 1978 by Prof. Kentfield at the University of Calgary. The 1981 paper by Bayly and Kentfield, based on Bayly’s Master’s thesis, is attached. Kentfield wrote 2 other papers on his VAWT in 1978 and 1985, and I can send copies, but most of the information is in his 1981 paper. I can supply a 50 page document on the Sharp Cycloturbine that includes a detailed comparison with the S/B-K VAWT’s pitch control, and also explains the flaws in other passive pitch control systems, such as cycloidal pitching.

A brief comparison of the Sharp Cycloturbine and the S/B-K VAWT, and why the Sharp Cycloturbine is superior:

The S/B-K uses a centrifugal-pendulum-spring for pitch control of each blade independently. The first full-scale model was predicted to reach a Cp of .45 (the Cp for efficient, small-scale HAWT). In tests outdoors, it reached .37. The discrepancy was attributed to the Reynolds number of the blades not being high enough. But it had other problems they did not address. My measurements of one of their drawings suggests that they did not use the correct, neutral, zero pitch angle, but instead used a toe-in pitch angle for their zero pitch angle in order to compensate for the lack of sufficient resistance to pitching by the blades.

The main advantage of the Sharp Cycloturbine over the S/B-K VAWT is that the Sharp blades have less inertia and more stiffness (resistance to pitching) because the entire blade and its counterweight function as the bob of the centrifugal pendulum. The S/B-K does not use the blade as part of the centrifugal pendulum bob. So its blade-units must be considerably heavier to produce the same resistance to pitching; or, the moment arm of the pitching force must be reduced to compensate for a lighter pendulum bob, which causes the blades to pitch more slowly. So the Sharp blades can pitch more quickly in response to changes in the velocity of their apparent wind. They can also store more energy for rapid pitch reversal on the retreating side of the rotor. The Sharp blades also have a higher natural frequency of pitching (19% based on simulated tests with pendulum weights). And Sharp blades pitch more during the downwind pass than the upwind pass in order to compensate for the slower air reaching the downwind blades. The Sharp VAWT reaches maximum torque at a TSR of about 2 (based on my informal testing using a variable load), which is quite useful for maintaining power during wind gusts, since the operating TSR is 3.0 to 3.5. In contrast, the S/B-K VAWT produces maximum torque at close to it normal operating TSR of about 3.7, which is a disadvantage because gusting will lower the TSR and drop the power considerably. In contrast, the low TSR for maximum torque of the Sharp Cycloturbine should enable it to maintain power when gusting drops the TSR. Accurate cycloturbines can capture up to 35% more energy, annually, than fixed-blade Darrieus rotors due to their ability to capture gust energy more efficiently. They also have strong starting torque which makes them far more versatile. Computer control is more accurate than passive pitching (Cp of roughly .50), but prohibitively expensive, and so not suitable for small-scale VAWT. The blades of the Sharp Cycloturbine experience low stress because the blades are free-floating. Straight blades, curved blades, and V-blades can be used. V-blades can withstand very high bending forces. Cords that twist can be used as the blade-pitch bearings. So construction can be very inexpensive.

https://www.youtube.com/watch?v=LXUiDx-F6FI&feature=youtu.be 

A disadvantage of the Sharp Cycloturbine is that it must operate at no more than about 20 degrees from vertical or gravity will degrade the pitch control. However, that same characteristic can be used to achieve simple and reliable overspeed control by letting the VAWT tip or swing away from a high wind.

Kentfield abandoned his VAWT because he could not obtain a Canadian patent. The patent examiners saw no advantage to passive pitch control for VAWT! (That is the sort of ignorance that I run in to frequently.) He discovered the Sicard patent many years later.

PeterS

Hi Dave,

Instead of trying to create a category that includes very different devices, why not stick with smaller and more accurate categories? What is to be gained by claiming tenuous similarities?

The Flipwing is an oscillating foil (wing) cross-flow windmill, More specifically, it produces an amplified flutter. There are many types of oscillating foils, some based on flutter and some based on control linkages.

They don’t work the same as rotary windmills or rotary kites. The basic principles are different. So putting them in the same category gets confusing.

“Tacking” could be used to describe the motion of an oscillating foil relative to the wind, but “tacking” is predominantly used to describe the back and forth motion of a sailboat heading upwind, and relative to the surface of the water. So tacking is a very slow cycling. But oscillating foils typically cycle fairly rapidly, and some cycle very rapidly (the WindBelt).

PeterS

Hi PierreB,

Thanks for your comments.

I think what you meant to say is that a L/D ratio of 2 is low, rather than high.

Well at the size I’m testing, the glide ratio of Sharp Rotors and Flettner rotors, with an aspect ratio of about 6, and end-discs on both, is about the same. They both travel roughly twice as far as they fall. As I recall, that is a glide angle of 60 degrees relative to the ground. Savonius rotors glide with an L/D of 1, so the glide angle is 45 degrees relative to the ground. So I am assuming that larger Sharp Rotors will still have the same L/D as Flettner rotors of the same size. So if the application could make use of a Flettner rotor, it might also be able to use a Sharp Rotor.

Making models with a CNC is a good idea, although I’m not sure if the skin could be thin enough. Maybe.

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Yes, partnering with a scientific partner is what I am trying to do. I have contacted hundreds of engineering professors around the world, and a large number of alternative energy organizations and aid organization.  Most don’t know enough about cycloturbines to grasp why mine are superior. As I mentioned previously, a professor of wind engineering in Malta, with a PhD from Delft, considers both of my windmills to be worth testing and analyzing, but at present he does not have money to pay graduate students. Both windmills, while very easy to make, have a large number of variables that make analysis and optimization extremely difficult. They need to be optimized before testing or the testing wouldn’t be accurate. So I will be making more and bigger models if and when I can (arthritis), and that may spark more interest. Amateurs have a hard time grasping the basic principles because they cannot be seen by just looking at the windmills.

The address you gave me didn’t open.

PeterS