Hi JoeF,

          Please let me clarify. The Sharp Rotor and similar rotors make use of the Kramer effect. VAWT make use of the Katzmayr effect.

PeterS

DaveS,

          You do not correctly understand the Kramer effect.

PeterS

DaveS,

          You did not understand what I said.

PeterS

DaveS,

          “PeterS recently wondered about the effect torque-loading of a rotor kite had on its flight performance, supposing it to be unknown.”

            That is not what I said. You missed the point.

PeterS

DaveS,

          That’s not what I said.

PeterS

DaveS,

          “Rotors” has more than one meaning, and you seem to be confusing them. So your comments don’t make sense.

PeterS

HI DaveS,

          Ooops! You are correct that I said “Kramer” when I should have said “Katzmayr”. To clarify: You do not understand the Katzmayr effect.

          Thanks for defining the Kramer effect. Now I can see that you also do not understand the Kramer effect.

PeterS

Nonsense

DaveS,

          The paper is about clap and fling flying by insects where they increase lift momentarily during each cycle by using the Kramer effect. It is not about how spinning rotors employ the Kramer effect. Yet you transfer a statements about insect flight directly to spinning rotors as if there are no differences.

          The Kramer effect is when a wing that it rapidly increasing its angle of attack delays stall, so that the lift can be as much a double the normal lift.

          That’s all. Don’t gum it up with confusing statements.

          Now you insist that I do not understand how the Kramer effect functions for a Sharp Rotor that is part of a VAWT, yet you give no evidence to that effect. We have already established what you know about VAWT, and it next to nothing.

          I have no idea what “radical claim” you think that I’m making, but I do know that you wouldn’t know if it were.

          The Katzmayr effect is typically understood to describe when a wing is subjected to an oscillatory angle of attack that varies between positive and negative, and thereby produces a net forward thrust.

          It can be applied to when an upward gust hits a glider wing so as to cause an increase in the angle of attack, resulting in a forward thrust. Whether or not a downward gust will have a slowing effect depends upon the resulting angle of attack. A large negative angle of attack, without stall, will also produce a forward thrust. But if the downward gust serves only to reduce or eliminate the angle of attack, then the glider may be slowed.

          I am left with the impression that no modern aerodynamicist understands me? No I’m not. What a bizarre thing to say. Now you read minds. No “modern aerodynamicist” has even read what I wrote about the Sharp Rotor VAWT Kite. You sound like you are thoroughly deluded.

PeterS

You are confused again. Dynamic soaring does not rely on the Katzmayr effect. Consider a model glider using dynamic soaring to achieve a very high speed by flying back and forth between a high speed wind blowing over a ridgeline, and a low speed wind behind that ridge line. The glider must maintain a high, positive angle of attack in order to resist the extreme G forces acting upon it. If it used a negative angle of attack at any time, it would be thrown outwards from it circular or oval orbit. So it can’t make use of the Katzmayr effect.

No, the error is yours for trying to transfer the effects of the Kramer effect in one context (insect flight during high lift situations) to all contexts.

When you say that “a wing is a wing is a wing”, that is precisely why you are confused. Wings of different kinds work differently, even though they may employ a common principle such as lift, drag, and the Kramer effect. You think that they all work alike just because they employ a common principle. They don’t. You can’t just transfer the behaviors of one type of wing to another type of wing without noting the important differences. If you do, it leads to a nonsensical analysis. That is why most of your analyses are nonsensical.

          I’ve noticed that you get misled when you see similarities because you ignore the important differences. That is something you do fairly consistently. For example, you think that dynamic soaring relies on the Katzmayr effect to produce forward propulsion. Why would you think that? My guess is that you see that a dynamic soaring model speed glider oscillates between flying between two air regimes, a fast one and a slow one, so you latch onto the “oscillation” and then say to yourself, “Oh, the Katzmayr effect relies on oscillation, so dynamic soaring speed gliders must be propelled by the Katzmayr effect.” You assume that oscillation is oscillation is oscillation. But it isn’t. There are different kinds of oscillation with important differences. But you often ignore the important differences. The result is nonsense.

You define “rotor” too broadly and therefore use the term in misleading ways. There are very different kinds of “rotor” that do not work the same way: cylinder-like spinning rotors that are passive or active, wind turbine and windmill rotors, helicopter rotors, auto-gyro rotors, cyclo-rotors used for powered flight, propeller rotors, etc. So when you use the term, you need to be clear about what kind of rotor you are referring too. “Rotor” merely indicates that the device rotates. Statements about rotors in general are likely to make no sense because there are so many important differences.

VAWT make use of the Katzmayr effect to produce forward blade thrust, not the Kramer effect. The blades see an oscillating apparent wind from ahead during normal operation.

For VAWT, the Kramer effect can sometimes occur when the angle of the apparent wind is increasing rapidly when the TSR is low, but VAWT are intended to keep their blades below the normal stall angle during normal operation. So they don’t try to benefit from the Kramer effect.

          You claim that “Its unrealistic that the Kramer effect is only helpful at all phase angles, that's the intended insight.” That is a nonsensical statement because VAWT don’t try to employ the Kramer effect. So there is no insight. There is only nonsense.

“Is a curved wing in a straight wind field relatively equivalent to a flat wing in a curved wind field?” Yes. In the case of VAWT, it is referred to as “virtual camber”. That is why VAWT with a high solidity use blades with a chord-line that matches the curve of the blade’s orbit. If the solidity ratio is low, it is not necessary to compensate for virtual camber. And it is even less necessary to compensate for virtual camber if the solidity is low and the blades are pitched.

          I commend you for asking a meaningful question. But be aware that it was asked and answered already by aerodynamicists a long time ago.

          I see that you are now off and running (in the wrong direction) with another of your grand unification schemes that ignore important differences. Have a nice trip.

Your first statement is reasonable. A sudden increase in the angle of attack due to a shift in the apparent wind can produce forward thrust, as for the glider example you cited. But it more commonly used to describe an oscillation of the apparent flow of a fluid, due either to the fluid itself or to the oscillation of a wing surface while the fluid flow remains steady. The interaction can be powered or passive.

Your second statement is meaningless. DS does not rely on the Katzmayr effect for forward thrust. Minor variations in the positive angle of attack, as is the case for high speed model gliders, does not produce forward thrust. DS model gliders are given a “kick” by a tailwind when the fly in the same direction of the faster and higher wind that flows over a ridgeline. It is the low drag of the slow air behind the ridge-line that enables the model gliders to return to the starting point near the back of the ridge-line, and then begin the cycle again, thus gaining another “kick” during each cycle.

Your statement is too fuzzy to have any meaning. Again, you seem to be reaching for a grand unification without noting important differences.

Why would you “assert” the all aircraft wings utilize the Kramer effect” Flettner rotors have been used for model aircraft wings. They don’t use the Kramer effect at any time. So you are talking nonsense.

You have fallen off the rails once again. VAWT blades do not experience a detrimental Wagner effect during normal operation. They are already moving at, for example, 3 times the wind speed on average. The Wagner effect describes what happens when the speed of the apparent wind starts at zero and then increases. It does not describe what happens when the angle of the apparent wind switches from one side of the blade to the other.  

Since VAWT can be more efficient than HAWT, it makes no sense to try to explain why they are less efficient by resorting to the Wagner effect.

You are making the biggest fundamental mistake that VAWT critics make: you are assuming that all lift-type VAWT are the same. They are not. There are big differences. Some are poor performers. Some are good performers. But as usual, you are ignoring the important differences.

          I forgot how little you know about VAWT, so I didn’t specify lift-type VAWT. It is the blades of lift-type VAWT that are subject to virtual camber, Not Savonius rotors. Whatever the “Sharp design space” might be, I have no idea. And I’m pretty sure you don’t either.

          Your preference for discovering things on your own explains why you are so far behind in understanding aerodynamics.

          I fully agree that there is a great deal to be learned about aerodynamic devices.