Toward the worst AWES

This comment is difficult to understand without a schematic.

Do you mean if you span a (untensioned) horizontal line and to that attach the (horizontal) rod, the orientation of the rotor doesn’t change from its original (horizontal axis) orientation?

Do you mean if you use your hand as a pivot point for the rod, and the other end of the rod (not) supported, the rotor only pulls in the direction of the wind?

I can’t parse this.

I held and tilted the rotor rotating around a rod like on the photo below, the wind coming from back:

The wind speed was about 5 m/s.

  1. When I let go of the set, the rotor flew a few meters high for a few seconds downwind thanks to its lift.

  2. But when I held and tilted the rotor for a while, the wind pushed the rotor in its direction, the rod pivoting between my thumb and my index finger to become appreciably horizontal as on the photo below, said rotor thus losing its lift.

Yes (see just above).

A windsock or a bol kite are also pushed in wind direction, without providing lift.

There is a curve down in the rod. Maybe between 10 and 20 degrees? So that would point the lift of the rotor more down than perpendicular to the rod, gradually lowering the angle of the rod. There’s also gravity.

The idea of using a rod and a bend in the rod, is that you can point the the rotor in every direction you want, independent of line angle.

There’s different ways you could test in which direction the lift goes with different rotor inclinations, and how strongly it pulls. I think I’d go with something like the below video. Instead of the pulley being at the top, it would be at the bottom with the weight hanging below it and the rotor pulling the weight up. The taut tether would be your hypotenuse – which your rod travels up and down on – , you would change the angle of that.

My assumption is that when the hypotenuse is flat, the most work can be done. But you want a higher inclination than that so you can raise the inclination and see if you can find an optimum, or where it breaks down.

I think then you’ve found an optimum rotor inclination relative to the horizontal. I guess the line angle has to be a little lower than that, because other than lift you also have drag and gravity which you have to counteract?

On my last experiments I tried to see if numerous rotors can fly under a small lifter kite. Indeed each rotor should generate its own lift once it is tilted. But the answer to my question would be negative with the tested rotor because of its low L/D ratio (once tilted in an optimal way as for the gyrokite) of about 0.7 :1 (elevation angle = 35 degrees as for the gyrokite of which the drag of the fuselage can be neglected as it is very low): so this (0.555 m diameter) rotor generates more drag than lift. In my previous experiments the 0.2 m² lifter kite allowed to implement only one rotor rotating at full speed by keeping a correct elevation angle compared to its potential.

As shown on the video below the wind tends to push the rotor in its direction even when it is tilted beforehand, this force being little overcome by the lift of this rotor which is relatively low. See also the short flight in the end of the video when the rod was kept tilted before releasing it:

The rotor being motionless on the concerned photo, the curvature is only due to gravity.

But on the photo below, the curvature is mainly due to the wind force on the tilted rotor which generates more drag than lift.

So I see three possibilities to fly a tethered tilted rotor:

  1. Passive control, using a large enough lifter kite.

  2. Passive control, using a gyrokite.

  3. Active control: Makani-like for one-bladed rotor, or Y configuration (dancing kites) and some other possibilities.

An efficient autogyro rotor could have a L/D ratio of 4 :1 and more, which would lead to a greater potential for the whole area swept by ​​the rotors compared to the area of the lifter kite.

Concerning “using a rod and a bend in the rod”, the wind force will push the rotor in its direction as for a rod without bend. For this configuration a large enough lifter kite (1) would be required, as for a straight rod within the line.

Your experiments are useful.

To offset the rotor angle to the line angle you would need, I think

  • A high enough line tension (above and below the rotor) (which is a given since here we are talking about a yoyo system)
  • Enough rod length below and above the rotor so that the moment from the wind pushing on the rotor does not overcome the moment from the line tension.

So that would have it pulling at roughly 18 degrees. You could try to experiment, for example with the setup I described above, if you can get it to pull more upwards than that with different rotor angles. That should be possible otherwise autogyros wouldn’t be a thing I think.

Now this is a related topic: Bryan Roberts' Gyromill (Sky WindPower) the line tension and the rod replace the tethered autogyro. The question of interest is, have they found a rotor inclination that works for them?

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Indeed we are talking about a yoyo system. So the force (lift and drag) of the rotors is used, as for:
http://cdn.pes.eu.com/assets/misc_new/peswindissue17talkingpointskylimitpdf-891355291894.pdf
Unlike the previous system Sky WindPower rotor system is connected to a generator aloft that also assures VTOL.

Indeed, so on my previous comment I corrected the values that are rather L/D of 0.7, leading to an elevation angle of about 35 degrees, which is the elevation angle of the gyrokite from where the rotor comes. I don’t think a higher angle would be possible. Even this angle was difficult to achieve when I used the gyrokite by several wind speeds. Certainly a rotor of a gyro glider could have a better elevation angle by higher wind.

I put a sketch of trains of perpendicular rotors (as I use now), gyrokites, and rotors on their respectives rods with bends. For the last I don’t know if the sketch is correct.

For now I think the simplest way to obtain the desired angle of attack of rotors is by using the segment of the line with an appropriate tilting. The problem I see with rods with bends is the thrust adjustment which cancels the change of angle of attack. But I could be wrong. Perhaps also the bend rod system can be useful between the lifter kite and the first rotor, allowing to lower the angle of attack of said rotor thanks to the elevation angle of the lifter kite, while the lower part of the bend rod points on the lower part of the line with a lesser elevation angle, as we can see on the sketch.

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https://www.researchgate.net/publication/3270629_Harnessing_High-Altitude_Wind_Power
The page 2 mentions an angle of up to 50 degrees. This is likely due to the requirement of sweeping the larger possible frontal airspace. This system uses torque.

But the figure 18 of the following document about autorotation (like SkyMill Energy or what I try to do) shows that 30° is enough to optimize the force coefficient of the rotor, i.e. as if the swept surface was roughly a solid flat area.

https://dspace-erf.nlr.nl/xmlui/bitstream/handle/20.500.11881/1094/DY02.pdf?sequence=1

The force of a rotor of gyroplane increases when its rotor plane angle of attack (AoA) increases. But also its L/D ratio increases when its rotor plane angle of attack decreases when the airspeed increases. It is the reason why at low speed the AoA is high, while at high (translation) speed the AoA is very low.

I suggested on some previous post that my rotor of gyrokite has a low L/D ratio of 0.7 due to the low performances of this rotor. This is not quite accurate because an optimal thrust (lift + drag) is obtained at a high angle attack but not too high. And (roughly) 35 degrees elevation angle is an usual value for any AWES in operation. The problem is that the rotors are connected to the line and their respective angles of attack depend on said line: an elevation angle of 45 degrees imposes an angle of attack of 45 degrees, and the segments of less than 45 degrees correspond to an even higher angle of attack. This problem is not shared with the gyrokite. This explains why, at least from 2 rotors, the assembly can hardly go up because of a too high angle of attack, unless a solution such as that proposed by @Windy_Skies or myself can succeed. So to obtain a maybe desirable angle of attack of about 30 degrees, a lifter kite flying at an angle of elevation of at least 60 degrees would be required. But from a certain area of rotors the elevation angle would decrease significantly, leading to a too higher angle of attack…

According to Fig. 10, the L/D ratio of the MTOsport rotor is 2 at about 10 m/s speed then increases to reach 5 at 20 m/s. The angle of attack decreases and the thrust also, the L/D ratio of said rotor reaching approximately 11 at 33 m/s and a rotor plane AoA of 3.2 degrees (table 1), for approximately 0.1 of force coefficient according to Fig. 18. The maximum force coefficient of the rotor, then substantially perpendicular to the flow, is 1.2 or 1.4, even 2 for the parachutal drag coefficient of the MTOsport rotor, page 7.

The structure of the gyrokite allows to disconnect the angle of attack of the rotor plane from the elevation angle of the tether. If the bend rod system allows the same by using less material than for a gyrokite, that would be interesting. I think also that the curvature of the tether maybe could be used to settle the rotors at an appropriate place.

After some experiments and analyses I don’t see a better way to stack rotors for yoyo system than:


The figures 4 and 18 represents a stack of rotors with their respective fuselages or frames which are essential to obtain a suitable angle of attack of each rotor plane, without depending to the elevation angle of the tether. And also a lifter kite is not needed. But strong winds are required I think.

Perhaps an alternative would be to stack the rotors under a gyrokite or a lifter kite at a high elevation angle (about 70 degrees) in order to allow said rotors to have a reasonable angle of attack (AoA) of the plane of the rotor, of the order of only 15 degrees (the AoA of a gyroplane can vary from 0 to 18 degrees), losing in force coefficient but winning in elevation angle, unlike the rotors I experimented but in a similar system.

In all cases this seems to be a marginal kind of AWES, but we never know.

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Today I made some other tests, using the same 0.2 m² kite lifter, and only one gyrokite rotor of 0.555 m diameter as always, but in a different way, with a wind speed of 3-8 m/s. Previously the rotor 1 was 5 m from the bridle point. I put a stop 1 m from the bridle point. I launched the rotor 15 m from the kite, then it went up like a messenger until the stop. When it yet rotated at low angular speed, the pull was low, and the elevation angle was a little lesser than that of the kite. But when it rotated at full speed, the pull was strong and the set went down quickly, also losing stability.

That confirms what I thought in the message above about complete gyrokites as a better solution.

I can see several problems with that bottom drawing. I won’t comment on the top two drawings.

  • A bend in the rod like that will cause the line tension to want to break the rod. Better to have a straight rod and only have a bend, or a pivot point, right where the rotor bearing attaches to the rod, so that only the rotor wants to break the rod, not also the line tension.

  • The rotor at that position on the top of the rod will put the center of gravity of the rod+rotor assembly close to that point. I think you’d want it at the middle so line tension will have the least effect on rotor inclination, or closer to the bottom if that results in a higher rotor inclination with very low line tension.

  • Your rod now only helps resist the moment from the rotor from the bottom.

  • It’s easier to hit your line with your rotor.

  • Like tallakt says, that lifter kite is not to scale

I think what you’d want is to be able to set rotor inclination independent of line angle. For that I think you’d need a pivot point instead of a bend and either passive or active control of the pivot point.

Here is an updated sketch. The red circle is now a pivot point, that would need a way to control it. And also missing here is a way to keep the rod, and pivot point, right side up.

I think only the complete gyrokite on the second sketch is more or less workable. it corresponds to the patent figure 4 which is mentioned above.

I don’t know where he indicated this it but that looks correct. I intended to implement the smallest possible lifter kite compared to the rotors. Experiments showed limits as expected.

Rotor à roulement non parallèle à l'axe formé par la corde

Whatever the configuration (comprising that with the pivot point) excepted with gyrokites, a large enough lifter kite would be required. It is a problem shared by all passive rotating devices where the lift is mainly assured by the lifter kite.

Non sunt multiplicanda entia praeter necessitatem.

You probably don’t need the complete autogyros. You’ll save money, time, and weight if you don’t.

I can’t verify your experiments or conclusions. I like the tests I suggested above better:

We don’t have the information, as we have not yet seen all possible “configurations”, to make that statement.

I’m beginning to think that the pivot point might be mandatory, so that the rotors really pull as little as possible when reeling in and as much as possible when reeling out. Or you have to have another way to vary lift.

Please See Images from My U.S. Patent 6616402:





On a gyrokite there are several points in order to change the centre of gravity, as for any kite where the bridle can be modified to change the angle of attack. After all a gyrokite can be only a long stick + a stabilizer + a mast + the rotor whose the weight is equivalent to all other gathered elements. It is the only known way to fly a rotor without a lifter kite or without automated control.

That said a correct angle of attack (until 45 degrees for a glide number of 1 for a large static rotor (not a toy like my rotor), preferably 20 to 30 degrees, and only 15 degrees for a crosswind gyrokite) (see page 45) could allow to increase the total rotor area compared to the lifter kite area.

The maximal elevation angle of my small rotors is about 30 degrees, corresponding to an angle of attack of about 30 degrees when the complete gyrokite is used. But as a lifter kite with an elevation angle of about 40 degrees was used, the angle of attack of the rotor was 50 degrees close to the kite, and still more when the rotor was far to the kite, leading to an elevation angle still much lesser.

So a device to lower the angle of attack is needed, such like I attached the sketch, or preferably the pivot system you describe, allowing an individual adjustment according to the curvature of the line. But that remains in a certain limit (which?) due to the requirement of the lifter kite.

The figure 72 and the figure 73 mention a pivot (26) but I think this is related to a collective mechanism that is not applicable for individual rotors used in yoyo mode.

Some bad designs but not yet the worst: two for yo-yo kites and a fly-gen:

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For the last design above (and below with light modifications), a special fabric could be used, allowing to keep the heat:

This information link, among other links, is also on Is an electrically heated balloon lift support for AWES possible?.

However using heating from generator can be questionable unless it contains a tube bringing fresh air from outside the balloon. Moreover if it is cooled, it will not be able to heat the air contained in the balloon. Indeed a wind generator should be cooled: https://www.ifm.com/fr/fr/applications/060-windenergie/1010/2090/refroidissement-du-generateur.html (in French):

Refroidissement du générateur

Pour des éoliennes à transmission directe ou sans multiplicateur, le générateur est le cœur du système. Dans la production d’énergie, de la chaleur est générée sur les bobinages. Cette chaleur doit être évacuée afin de refroidir le générateur. Pour les grandes éoliennes multi-mégawatts, un refroidissement par air/eau est utilisé pour refroidir les générateurs.
Outre la surveillance de température du générateur et du fluide de refroidissement, il est également important de surveiller la pression et le débit de refroidissement. Si le système de refroidissement tombe en panne, la centrale doit être arrêtée afin d’éviter une surchauffe du générateur.

Translation:

Generator cooling
For wind turbines with direct transmission or without a gearbox, the generator is the heart of the system. In power generation, heat is generated on the windings. This heat must be removed in order to cool the generator. For large multi-megawatt wind turbines, air / water cooling is used to cool the generators.
In addition to monitoring generator and coolant temperature, it is also important to monitor cooling pressure and flow. If the cooling system fails, the power plant must be shut down to prevent the generator from overheating.

So maybe a cooled generator could be used for power generation, as well as a device that converts energy into heating.

I have tried flying ring discs: this works very well, perhaps better than solid discs.

I tried taping a three-bladed propeller inside the 33 cm diameter orange model (see photo): no rotation with my fan as opposed to the propeller alone. On the throw, the whole thing went 3 to 4 times less far than the ring alone.

Not very promising, at least if the blades are inside. Perhaps it would be better with many thin blades like spokes, providing both rigidity when scaling up, and rotation. See perhaps with outer blades in addition.

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The objectives of the rotating flying rings were (are?) to provide additional lift and gyroscopic stability, as well as structural strength.

Better (in front of the same fan as previously where there was no rotation) for this counter-rotating helicopter rotor: about 200 rpm for both annular rings (see the photos below: orange 0.33 m diameter, blue 0.25 m diameter), so less (but not far less) than 3.9–6.14 rps when a rotating disk is launched, and far less (half) than the rotor alone.

Another configuration with the same blue ring and another 56 cm diameter propeller:

The 25 cm diameter rotating ring for launching considerably slows down the rotation of a 56 cm diameter two-bladed rotor.

Generally the ring slows down the rotation, regardless of the configuration. Its annular band should be much less wide, but then you lose lift and gyroscopic effect…

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