DaveS,

Your analysis is fundamentally incorrect. All that you are claiming is that a high average wind speed will produce a higher average power. That’s obvious, and it does not speak to what I explained.

There is a simple way to test your assumption. Use a small model with the two ends of the tethers held by two people. Start downwind of a solid fence which is the height of the ends of the tethers. Once the blade is revolving, walk toward the fence until the lower half of the orbit is blocked from the wind.

According to you, the blade will produce more power -- because it is based on dynamic soaring, for which no wind speed on the bottom half of the orbit is ideal.
According to me, the blade will stop revolving -- because it is based on cycloturbine aerodynamics, so the advancing bottom half of the orbit produces more thrust, and without that thrust, the blade will be too handicapped to revolve.

I look forward to your finding your experimental notes.

PeterS

Hi Tallak,

As best I can determine, Active Lift upwind causes the blade to move downwind, which decreases the rotor radius to the blade. The elastic tethers contract some. Then, when the blade completes its upwind pass, the stored centrifugal potential energy is released. So during the downwind pass, that stored energy increases the rotor radius of the blade. Downwind, that stored energy is added to the normal centrifugal force on the blade. Also, Active Lift on the blade further increases the rotor radius of the downwind blade. So the downwind blade pulse is much stronger than the upwind blade pulse. That is why, in principle, the blade can be used as a short-pull kite.

However, as I mentioned, the TSR is limited to about 2, and that limits the power. Also, because the blade produces power by producing centrifugal force, it can produce more power if it uses a relatively small orbit that matches its solidity ratio and TSR. A small orbit will maximize the centrifugal force and increases the cycles per second (Hertz). The result is more power. But the swept area becomes rather small, more like a windmill than a kite.

So the blade/kite is far from an ideal short-pull kite. Given that limitation, and given the additional problems introduced by kites, it is probably more cost effective to use it as a windmill than as a kite. As a windmill, the orbit can be either vertical or horizontal. A horizontal orbit does not require orientation to the wind, so it should be cheaper to implement. In addition, a horizontal orbit allows the blade to self-start at a wind speed of about 2 m/s, whereas a vertical orbit requires a wind speed of 3 to 4 m/s. So a horizontal orbit will capture more wind energy annually.

But if a way to increase the TSR from 2 up to 3 or more can be devised, then the blade/kite might become competitive. That is because it requires minimal controls and is cheap to replace.

The reason that the TSR is limited to about 2 is the reliance of the pitch control on centrifugal force to create a resisting force to balance the aerodynamic pitching force. Upwind, the Active Lift on the blade reduces the centrifugal force needed for pitch control. So the blade pitches too much to produce strong thrust. The result is a bit paradoxical. The more lift the blade produces, the less the centrifugal force to resist pitching, the more pitching, the less lift. In other words, more lift causes less lift. Why that limit occurs at a TSR of 2 is not yet understood.

So my recommendation to inventors is to switch to a tail vane type of pitch control that does not rely primarily on centrifugal force. However that is easier said than done because there are many resonances to consider, and they are very difficult to analyze.

PeterS

Hi DougS,

          Thanks for your kind words. I’m still working away, but too slowly in terms of building things.

          Yes, DaveS is full of surprises….

PeterS

DaveS,

          You seem to not understand what I said. To repeat: DS benefits from no wind on the bottom, advancing side of the loop. The opposite is true for my blade/kite.

PeteS

Hi DougS,

          Yes, there is not enough information available yet about the Active Lift Turbine. So I concur with your skepticism and I expressed my own reservations when I first described it. However, the principle and the solution they present seem to me to be correct in terms of the physics. So to me the concept seems promising. But not certain. The reason I say that is that the use of gears and other parts that produce the increase in torque must be weighed against the added costs and the reduced reliability. They may achieve the most efficient VAWT, and it may be significantly more efficient than the best HAWT. But the bottom line is the lifetime cost of the energy, and HAWT currently set that standard.

          Personally, I found the concept of Active Lift to be most interesting because it finally explains to me why the Sharp Cycloturbine has such high torque at a TSR of 2. That is the TSR at which Active Lift should make the largest contribution to torque. So I think that my analysis is correct, based on studying diagrams of my VAWT’s pitching. Also interesting is that while other passive pitching VAWT researchers have predicted a Cp of .45 for my type of centrifugal pendulum pitch control, those other cycloturbines did not include Active Lift. So with the addition of Active Lift, the predicted Cp max. of the Sharp Cycloturbine should be close to .50, or about the same as the best commercial HAWT at present. I find that possibility to be encouraging. And I need all the encouragement I can get.

However, there is a down side. As the TSR of the Sharp Cycloturbine increases to 3.0 to 3.5 -- its normal operating range -- the contribution of Active Lift diminishes significantly because the blades no longer need to pitch much. In contrast, the Active Lift Turbine should be able to make best use of Active Lift at those higher TSR. At the lower TSR when the fixed-blades are partially stalled, Active Lift makes a much smaller contribution.

If and when the Active Lift Turbine is fully proven, and the same for the Sharp Cycloturbine, then the two concepts could be easily combined. The result would be a VAWT with a very high Cp max. and a very high and broad Cp curve. That should result in a large increase in annual energy capture, especially in turbulent and gusting winds.

But there is still a long way to go, and a lot to be tested. So your skepticism is warranted. If you find anything about the physics of Active Lift to be in error, or doubtful, I would greatly appreciate hearing your comments.

I’m also interested in how the concept might benefit HAWT, power kites, and sailboats. I think that Active Lift is used by the world’s fastest sailboat to reduce water drag -- by canting the sail to windward to create upward lift.

PeterS

DaveS,

I believe that you experimented. I am interested to know the details of what you did because you might have discovered something.

What is strange is that you did not discuss your experiments with me at the time. Not a single question, even though I had studied the concept for years. Apparently, you were supremely confident in your incorrect analysis of how it works. Did you even read my paper on the concept?

And now you want to sell me a model my own invention for $200, sight unseen (even after you’ve demonstrated that you don’t understand the concept), as a substitute for telling me the details of what you did? No, thank you. Just a copy of the report, please.

Incidentally, I sold plastic models for $10 when I was a street artist, and I gave away dozens of paper models for free to people who were interested in the concept.

If your record of what you did includes drawings, photos and videos, that would be helpful in spotting any unusual behaviors. I hope that you recorded details, such as the wind speed, blade weight, tip speed ratio, size and length of the shock cords, ratio of the length of the shock cords to the blade span, blade aspect ratio, counterweight placement and mass ratio, swivel types and sizes, wind speeds for self-starting, orbit diameters, supporting structures, etc.  

Of course, if you were just having fun playing with the concept rather than doing research, then I wouldn’t expect you to have detailed records. But you gave me the impression that you were trying to do research because you claimed to have analyzed the concept (however incorrectly).

PeterS

Hi Pierre,

          I don’t think I understand the question.

          I previously submitted a drawing of my Bird blade kite showing it supported by a pilot kite, and with a very long, horizontal rod above the revolving kite to as to provide tension for the outer ends of the shock cords.

The tension in the shock cords increases as the orbit diameter increases because centrifugal force is what increases the orbit diameter. But if the shock cords were too long for the orbit radius, then the blade would stall and stop, and wouldn’t self-start.

          The kite would remain dead downwind will revolving up and down, so I’m not clear on what the wind window might have to do with it.

Does that help to clarify?

PeterS

Hi PierreB,

There seems to be some confusion here. The videos you referenced show a horizontal blade orbit. But the blade/kite I showed has a vertical orbit.

Here is a similar video to what I showed: https://www.youtube.com/watch?v=RGm1cNSmDq0 

To fly that kind of blade/kite high up, the most obvious configuration is to use a horizontal rod above the orbit and another one below the orbit, and then connect ends of the upper and lower rods to each other using tethers. Then at the mid-point of those two tethers, attach the cords (elastic or non-elastic) that attach to the two ends of the blade. Then attach two tethers from the ends of the bottom rod to the ground, forming a shallow V.

If the blade/kite is high enough, the bottom horizontal rod can be eliminated, and the two vertical tethers can be extended down to the ground, forming a shallow V. The pilot kite attaches to the two ends of the upper horizontal rod.

The blade will self-start due to the tension in the tethers with pull the blade cords apart. As the blade begins to orbit, centrifugal force will cause the tethers to be pulled closer together. That will allow the orbit diameter of the blade to increase. The result will be a short-pull stroke, once each revolution of the blade.

There are probably further refinements that are possible, but that is the basic concept. I’ve already discussed its limitations.

The horizontal rod above the blade/kite could be eliminated by using two pilot kites pulling away from each other. But it is not certain if they could place enough tension in the tethers to keep the blade cords (attached to the tethers) under sufficient tension.

I hope that helps to clarify.

Hi Tallak,

Oh, you and Pierre seem to be asking if the Bird Windmill blade on tethers can be made to function like a regular windmill. If so, the answer is yes. I did it in 1978 to see if it could be done. I discuss what I did in my long paper on the Sharp Cycloturbine. The technique is called “centrifugal extension” or centrifugal expansion”.

What I did was to start with a two-bladed Sharp Cycloturbine 4 feet in diameter with 2 foot blade spans. Then I removed the blades. I placed long strings between the ends of the support arms and the ends of the blade’s rocking arms. (Assume two support arms per blade and two rocking arms per blade.) I had to manually start the turbine. But once started, it functioned well.

But I now know that the TSR was probably lower than for a pure Sharp Cycloturbine. That is because when the blades are connected only by cords, the pitch control system is altered. They pitch more easily. That lowers the angle of attack, which lowers the lift and thrust. The windmill becomes a hybrid between a Sharp Cycloturbine and a Bird Windmill. A Sharp Cycloturbine can reach about a TSR of 4, whereas a Bird Windmill is limited to a TSR of about 2. So the resulting TSR for the hybrid is somewhere in the middle.

To make such a windmill practical, the extension cords would need to extend to let the blade orbit expand. That could be done in a controlled manner to avoid unbalancing the rotor. All of the extension cords could unwind from a common reel under tension.

But for a windmill, I have ways to increase the size of the rotor that are simpler.

However, with respect to making a very large VAWT kite, centrifugal extension of the blades could be used to save a lot of weight because it could replace most of the support arms with cords. It should also be possible to eliminate most of the central shaft. If that were done, then the question would be how to best support the VAWT aloft and how to transmit energy to the ground.

I hope that clarifies what you were asking about.

PeterS

DaveS,

I could not possibly know what you missed on this forum. That is for you to decide. JoeF invited me onto this forum in response to his seeing some of my videos of the vertical orbit versions of the Bird Windmill, if I recall correctly. I described it as the first kite to fly above and upwind of its anchor point under its own power (which does not include falling or gliding into the wind, or a brief overshoot). If you don’t remember that, then maybe that is something you missed.  

I invented the Bird Windmill blade in 1978. I sold versions of it prior to 2000 to place it in the public domain. So any prior art must be earlier than those dates. Otherwise, its post art, like the Lebreque blade.

You claim there is lots of prior art. I look forward to seeing it because I haven’t found it. Please show me. But please don’t waste my time with silly examples like the Prism FlipKite.

The Prism FlipKite has nothing to do with the Bird Windmill. It is not prior art. You might as well claim the first airplane to do a back loop is prior art. Clearly, by giving that as an example of prior art you have demonstrated that you do not understand what constitutes prior art. You are once again making your usual logical error, which is that you regard any two devices that are at all similar in some way as variations of the same device. I’m hoping that those errors are due to careless analyses and not to something immutable.

PeterS

DaveS,

When it comes to the Bird Windmill, there is an exception to your assumption. That is because the Bird Windmill doesn’t need to produce torque. It can produce a pulsating pull-force using centrifugal force. As a result, the TSR remains at about 2 regardless of the load. If the load is a weight to be lifted, and the weight is increased, the heavier weight will not be lifted as far with each stroke, but the TSR will remain the same at about 2 (and the Hertz will remain the same). The stroke length varies with the wind speed. But the TSR remains constant.

This effect can be observed most easily when starting under a load. The load is not lifted at all until the centrifugal force is high enough to begin to lift it. The wind speed needs to be strong enough to begin to lift the load. But the blade will have a TSR of 2 even when the load is not moving at all.

Even if the blade is used to create torque by attaching the lower blade cord to the end of a crank arm below the blade, the blade will quickly accelerate to a TSR of 2 even if the crank arm does not turn. As the centrifugal force increases, with an increase in the wind speed, the blade begins to pull hard enough on the crank arm to begin to pull it forward in jerks. Then a further increase in centrifugal force will cause the crank arm to move in complete circles and follow the blade. However, as can be seen in this video, the torque still https://www.youtube.com/watch?v=EdDaRMr4dwg varies.

https://www.youtube.com/watch?v=EdDaRMr4dwg  

The torque is stronger when the blade is downwind than when upwind, due to Active Lift.

To achieve a more steady torque, multiple blades can be linked to a common shaft using one-way clutches.

There is still a lot to learn about the Bird Windmill. That’s why I’m interested in the record of your research. For example, a heavier blade (plywood) seems to lower the TSR. If so, why?

PeterS

DaveS,

Sadly, you just confirmed that don’t understand prior art. I don’t doubt your sincerity. Your habitual error of over emphasizing minor similarities while under emphasizing major differences appears to be a permanent handicap. So explanations are pointless. It’s like talking about art with a guy who is color blind. All I can tell you is that you often talk nonsense and that you will never understand why it’s nonsense. But I know that you can’t understand that either. You’re an intelligent person, but you have a conceptual blind-spot.

PeterS

DaveS,

Nonsense. The same gibberish.

PeterS

Hi Tallak,

For a VAWT, the whole blade moves at the same speed as the tips of the blade. So the tip speed ratio (TSR) of a VAWT is the ground speed of the blades divided by the true wind speed. For example, if the ground speed of the blades is 30 mph, and the true wind speed is 10 mph, then the TSR of the VAWT is 30/10 = 3. The blades are moving at 3 times the speed of the true wind.

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It’s also useful to know about the “local TSR” of the blade, which changes at each azimuth angle along the blade path. It is the speed of the apparent wind acting on the blade at any given azimuth angle. For example, if the blade is heading directly into the wind, the apparent wind speed will be the ground speed of the blade plus the true wind speed, and that sum divided by the true wind speed. Using the example above, the calculation is (30 + 10)/10 = 4. The local TSR is 4 when heading directly into the wind (when the TSR is 3).

If the blade is moving directly away from the wind, the apparent wind speed will be the ground speed of the blade minus the true wind speed, and that remainder divided by the true wind speed. Using the example above, the calculation is (30 – 10)/10 = 2. The local TSR of the retreating blade is 2 when heading directly away from the wind (when the TSR is 3).

So what that means is that the average TSR of a VAWT blade is actually the mean of all of the local TSRs. For example, the mean of the maximum and minimum local TSRs in the example above is 4 + 2 = 6; 6 / 2 = 3.

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The blades of a cycloturbine have to be able to adjust to the velocity (speed and direction) of the apparent wind at all azimuth angles. That’s hard to do. Different flow models produce slightly different local TSRs. So it’s hard to calculate the exact local TSR at any given azimuth angle. Plus, the true wind speed is constantly changing, which constantly changes the TSR. So it’s hard for any pitch control mechanism to sense the changes and react quickly enough to capture the most energy.

The advantage of passive-pitch-control is that the blade can do its own sensing of the changes and adjust itself to those changes so as to maintain close to the optimum pitch angle (which is usually just below the stall angle of attack). That’s very hard to do and most passive pitching systems don’t do it well. So far, based on all of the available research, and informal testing, the Sharp Cycloturbine seems to be the most accurate of the passive systems, and reasonably close to optimum. (Plus it also includes Active Lift to produce additional torque.)

The most accurate active-pitching uses wind sensors, a computer, and motors to adjust the pitch angle of the blades. But that’s expensive and complicated. Different all-mechanical systems are being developed. They should be less complicated, but still expensive. There are lots of active-pitch systems, but most of them are not accurate. An example is the original cycloturbine patented by Darrieus in the US in 1931. It uses the same pitch angles regardless of the TSR, and it uses the same pitch angles upwind and downwind, so it’s not accurate. So far, there are more than a dozen types of pitch control for VAWT, but most of them are not accurate.

PeterS

DaveS,

I have told you how to test your assumption that the vertical Bird Windmill is explained as DS. To repeat, use a small model and block the wind from the lower half of the orbit. If the blade is explained by DS, then it will work better when the lower half of the orbit is blocked. If it works worse, or stops, then DS cannot be the explanation. That is because DS works best when there is little or no wind acting on the lower part of the wing’s orbit.

Do you understand this test?

PeterS