Claim: Kites in a MAWES need to be able to: CLAMP onto the tether and LATCH onto the previous kite + a discussion on how to do this + a first mention of stackable kites + a concept for automatic launch of a soft kite train

One could make the fuselages longer to increase the moment arm of the fuselage and with that have the tension in the TRPT ring have more of an effect in keeping the fuselage straight. Maybe with longer fuselages there is less of a need to keep the rest of the TRPT ring rigid.

I don’t know if this the most recent version of your system, but things that are somewhat surprising to me is that you’ve staggered the rotors, and with that doubled the number of lines and with that line drag. And the tethers going to the center of the TRPT ring seem to be under some tension, as they help keep the torque ring circular, seemingly reducing the torque carrying capability of the system.

The suggested changes might make the system floppier while the turbine isn’t spinning, so you could use the ground station to start the rotation, expanding it, perhaps.

Doing the bridle lines like this would probably make it less floppy again: https://forum.awesystems.info/uploads/default/optimized/2X/9/9c3f6b8d6230af254695a3acff2bcd804f39b230_2_375x500.jpeg

@Windy_Skies some questions on your post to make sure we’re on the same page…
you’re referring to this post Death to "Soft vs rigid" - #87 by PierreB
with this picture

The fuselages hold the blades and the rotor TRPT (Tensile Rotary Power Transmission) ring together.
Just to be clear, they are the black bands seen on the lower white rotor blades

1st paragraph - longer? - not sure I’m following you here, which dimension longer? spanwise radial out from centre, chordwise band path, or depth in line with the tether line
The TRPT rings for the rotor need to maintain enough rigidity to be able to launch and land.
Longer structures bend more easily.

2nd para - no that was not the most recent. we moved away from rings to using polygons. Interfacing with the fuselage had trickier shapes but overall we broke fewer TRPT tubes.

Doubled the (Number) of lines = wrong.
Why?, 2 rotors on 1 TRPT is more like halved the number of lines. = less drag per rotor.

The tethers to the centre are tensile yes. Most AWES suffer from not being able to maintain a small radius looping flight. These tethers prevent the rotor from exploding centripetally. They allow the rotor to spin a lot faster = more power with less torque = less material. Tensile design is an amazing thing use it where you can.

3rd para - which suggestions? and pre spinning the rotor is a great idea if you can maintain directional control of the rotor and your induced spin is results in upward thrust, however this needs the rotor to be spinning in a more horizontal orientation. For simplicity of launch we instead used a lift kite at the rotor head and stretched the rotor and TRPT out on the field (Please tell me you knew this already)

4th para from the picture I uploaded 10th International Airborne Wind Energy Conference (AWEC 2024) in Madrid - #67 by Rodread - I spoke with Franz about his concept at AWEC
As you pointed out earlier there’s a balance - you don’t want too many bridles going around at full diameter. We know that a rotor with effectively single line blades (Multiple bridles) works fine, and holds the blades well with respect to the plane of the rotor.
I do agree though
This softer ring rotor required more bridling


Than this more rigid ring rotor


And I also agree that a combination of lines up the centre of the shaft and up the outside of the shaft can likely make a larger TRPT more feasible see

In this concept (The OM stack) the blue outer tethers and red inner tethers support kite blades made using multiple smaller kites (shown as Blue soft kites) on an arch configuration.
It was assumed this would have to be launched vertically from a ~ fairground tilting centrifuge carousel style groundstation

Hope that helps

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Continuing the discussion from Windswept and Interesting Ltd - #180

Before in this topic I wrote about that:

Let’s explore the topic a bit differently now. You want to use (semi-rigid) wings to be able to put clamps inside the wings, and to reduce needed bridling. I also say you want to use multiple bridles to reduce the needed strength of the cantilever beam that the wing is to resist the lift forces.

To make an efficient system that generates some power, and is also able to transfer torque to the ground, you want a wing with a high Reynolds number, so flying fast, with a reasonable chord length, and a high aspect ratio. That all points to a single ring of kites on the outside of the shaft. You also can’t make the wing too long however. Let’s go for 3 meters like you described in your recent end rapport.

Previously, the highwind group probably, said a good looping diameter was 9-10 times wingspan. If I independently think about this, I want to say that the unachievable ideal is (Velocity _{ \ inner\ wingtip})^2 : (Velocity _{ \ outer\ wingtip})^2 = 1 This is anyway I think a metric that takes into account the lower flying speed of a soft wing and allows that perhaps to fly in a smaller diameter.

Off-topic for this discussion maybe, but a different metric that I think is useful for a controlled shaft is minimum orbit time. You want to probably increase that as much is reasonable while you are trying to learn how to control the shaft, so you have more time to control the kites, so you’d increase the diameter of the shaft as much as possible. It also conveniently should make it more difficult to collapse the shaft, as you need to spend a lot longer at mismatched speeds to achieve that, at the expense of more line drag.




Without the tethers you’d end up with a polygon with the same number of vertices as kites I think. To prevent breaking connectors I’d use live hinges instead of rigid connectors, although maybe for a triangle you wouldn’t need to.

I don’t remember seeing recent videos where you show the polygon rings, maybe those work at this scale. I remember thinking the rings wouldn’t survive very long even at this scale from all the flexing.

If you were to go for a larger ring, I’d go for a bicycle wheel construction, maybe add a tensairity ring, which could scale more I think. But at that point I’d sooner drop the airborne part I think as you’d hopefully have a cheap and light rotor you could attach to any wind turbine.

Assuming the use of the back bot and now gliders connected together like I describe above, you would use the lifter kite to lift everything up and preload the shaft. Then you would slowly start spinning the shaft and let centrifugal force expand the shaft. Because you now have two tethers going through the wings, they stay at a fixed bank angle relative to the shaft helping them to catch the wind. Perhaps you would also need to pre-expand the shaft from both sides, or only the bottom side, or maybe the rotation is enough to fix any potential tangles and expand the shaft.

You could of course add as much complexity as you want… I would put the generator on a tower for example…

I don’t want to add any

@Windy_Skies
I’m really struggling to understand where you are steering this discussion
How many threads do we have to tether this conversation to for efficient effective learning and common understanding?

So many of the points you just raised seem minimally relevant in the design of kite turbines

Saying “one” instead of “you” feels outdated. In the the first comment I did mostly mean “you,” in the second I mostly meant “one.” That comment was me thinking out loud, which I didn’t want to do in your topic and was more on topic here. My comment in your topic was on-topic though I think, so I put it there. I’ve now moved both comments here, with your replies.

In the first part I was thinking about rotary MAWES, mostly using bridled, possibly controlled, gliders/kites. Your OM stack falls within that. In the second and third part I was thinking about the ways to scale a rigid ring and the limitations of that, and on one way to launch a tensile torque shaft with the limitation that you can’t reel the lines in or out and that the gliders are not controlled.

Maybe.

You have a tether going through the inner and a tether through the outer wing in a glider that go from the ground station to the lifter kite attachment point, let’s call that the inner and outer bridle, and a tether going between the nose and tail between each glider in a rung, let’s call that the polygonal bridle, which is going to be slack whenever the shaft is not expanded.

You could increase the tension in the polygonal bridle by some function of the sine of the shaft elevation angle and the glider’s weight, when the shaft is not rotating, by doing the following: A polygonal bridle section is first connected to, say, an inner bridle, then enters the inner wing of one glider going around that bridle, is routed through the glider to exit at the the nose of the fuselage, enters the tail of the next glider, exits at an inner or outer wing of that glider, and is finally connected to the bridle of that wing.

When the shaft is not rotating the gliders are suspended from the connection point and the polygonal bridle. The sections of the polygonal bridle between consecutive bridle lines make a rough U shape, with tall sides when the shaft is not expanded. When the shaft starts rotating the tension in the bridle first decreases while the lift of the glider is lower than the weight of the glider, and then increases again as the lift becomes greater than the weight and now the polygonal bridle sections make an upside down U shape, with the lengths of the sides and top of the upside down U being some function of the relation between the different forces.

This ignores the centrifugal force from the rotating shaft and gliders. That force is partly or fully counteracted by the tension in the bridle lines from the lifter kite and the lift from the rungs of gliders above the current one. If that tension is greater than the centrifugal force from the shaft, the shaft doesn’t expand much and you still have the risk, although much reduced, of tangling lines.

You could reduce this tension by adding a central lifting line that goes through the center of the shaft from the ground station to the lifter line attachment point. If you add a winch to that line you can vary the relative tensions. If you add the central line, the winch is probably mandatory as you can’t do rotary launch while the bridles lines are slack while the shaft is not expanded because it is not rotating.

You could add control surfaces to the gliders or attempt ground control.

I previously wrote about earlier and different versions of this idea. See the first point in my first comment in this topic why I now think this version of the idea has limited usefulness; this would not allow for automatic launch and landing of the system by reeling the tethers in and out, and with that have limited scalability, or need a bigger footprint to suspend the tethers horizontally along the ground while not in operation.

An alternative to clamps might be something like this, although to me that looks worse, heavier and more complex and much more draggy, than using clamps. Maybe it still needs winches and clamps to avoid slack lines while the shaft is folded in: From Paper to Bionics: Origami’s Incredible Impact on Science | FD Engineering

The shaft would start as a folded in helix, for example. You would start the rotation of the arms of the ground station, that would allow the kites to also start rotating and catch the wind. You then let the kites rotate more quickly than the arms of the ground station, which would unfold the shaft, in theory. You would probably need winches to fold the shaft back in.


Or there’s this:

The interfaces between different dominoes could look a bit like those of the wing sections here:


Maybe related: ASME JMR - Wrench estimation and friction compensation tether units augmented to remote TDCRs

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Where you mentioned folding
and the video had leaf mirror folding deployment patterns

there’s a similarity with the other video you linked with the string toy… It also has at the end
A folding carnival crown toy
That looks more like one possible key to larger scale rigid ring unfolding of a turbine rotor

A folded crown rotor would be depowered
An unfolded one would be very powered up
The design skill would be do you attach the blade at the single pivot point or across the dual expanding pivots for more rigidity (might not be necessary with bridling)

Yes, and in a similar way with a soft kite, as discussed in the forum.

Several foldable kites could maybe form a foldable crown rotor.

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There’s the question maybe if you can control your shaft with a rigid rotor, or support the extra weight from a relatively heavy shaft and rotor. It’s like attaching an autogyro to a tether and powering it from the wind, but instead of the rotor pointing mostly up, it now is pointed mostly downwind if you can find a way to angle it up a bit relative to the shaft, or perfectly perpendicular with the shaft if you can’t. So you’d then have to build a significant bank angle into the rotor, I think, and do cyclic pitch variation and/or control surface deflection, to increase the vertical lift at the top of the loop. You’d compare the extra vertical lift you’d get from that at your desired cut in speed to the weight of the system, and add some significant safety margin to that to reliably keep things in the air, and also take into account system drag and desired tether tension.

Easier to start with a rotor where you can do both that and also cyclic roll variation, but maybe also uses a bridle for the weight saving. Maybe you can do that with blades on a ring, but at that point you’re adding so much control that you have to wonder what the point of keeping it rigid is.


I don’t think this folding crown makes for a very good collapsible rotor. You’d attach the blades to the two points that come together upon expansion, for the shorter cantilever arms and the assumed easier control from the two fixed points, but now you can’t expand the rotor as now those points can’t come together. Attaching the blade to the single point doesn’t give you the benefit that connecting to the two points give, and also still gives you the drawback of using double the number of rods that you want, so then you’re better off choosing a different geometry that does give those benefits. A quick example could be a ring that doesn’t use this scissor mechanism, but is just rods or dominoes in a ring connected with hinges that pivot. The blades could be attached to fuselages with two longer pivoting rods between consecutive fuselages. Or if you use the dominoes from before you could use the same post-tensioning trick here. That would probably also allow you to expand the shaft with the expanding rotor instead of the other way around and make a complex, rigid, rotor, to which you could add control surfaces.

If you want to make a complex shape then the question is probably what shape do you make the mating surfaces of each domino and how many channels does each domino have, and how do you design the shape so the lines going through the dominoes do as few wraps as possible to minimize line friction.

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Thanks Pierre
The way I looked at it
The opened crown rotor has the blades set more flat to the plane of rotation
The crown rotor compression action banks (rolls) the blades to be flat to the shaft

All this of course plays havoc with bridling
But maybe

For the coiled/uncoiled helical shaft idea you’d maybe use a channel and mating surfaces for the coiled state and a channel and mating surfaces for the uncoiled state. Assuming you can do no more than 4 or 5 wraps before the friction inside the dominoes becomes too much, or you’d have to use more motors along the length of the shaft, the length of the uncoiled shaft would be optimistically limited to something like 5 times the circumference of the ground station rotor, so perhaps 150 meters for a 10 meter diameter rotor.

If you don’t use these internal channels to coil and uncoil the dominoes, instead using the kites to unreel the tethers from a drum for example, that particular limit probably goes away.

Ignoring the shaft, a nice image of a ground station with segmented blades would be like a weeping willow when there is no wind and then when the wind picks up the branches slowly stiffen, start rotating, and take off. Or they don’t necessarily need to take off. Or maybe the image of a flower bud opening is also good.

Related: Would blades inspired by palm trees be suitable to AWES?

Maybe related: FROW - The first rotary-wing drone that changes its wingspan mid-air


Also for transforming or folding wings for example. You could have a motor that tensioned a number of lines when it rotates one way, and tensions different lines when it rotates the opposite way. Or it can just tension and untension lines. You’d probably use a latch so that it doesn’t have to be holding the tension constantly.

To increase the compression between the dominoes discussed above and here: Tensioned soft shaft, but now made semi-rigid with dominoes for example, you could use motors with gearboxes at various points, or in limited cases you could maybe only use gearboxes, if I understand the physics of that correctly.

You’d have your slack structure sitting atop the ground station. If it keeps sitting atop the ground station even in operation, you can just use motors in the ground station to tension the lines in the structure. The ends of the arms of the ground station act as the stoppers. If not, and the structure is meant to go airborne, you’d need a stopper on each line to prevent the structure from going slack again from the unreeling of the lines.

That stopper could be [1] a clamp in the bottom dominoes, clamping the domino to the line, [2] a motor with a drum in selected dominoes, keeping the tension in the lines that the motor acts on, or, I think, [3] a gearbox in the bottom dominoes, multiplying the tension in the line coming from the ground station to the gearbox by the gear reduction of the gearbox, and dividing it by the number of lines coming from the gearbox going into the structure.

I’d like to see experimentation, modelling, diagrams, performance data etc of the “dominoes” before being able to comment on their likelihood of being integrated into an AWES. I think I know roughly how they’re meant to work. ( Internal tension pulling beams together. ? ) The closest analogue I can think of is tent poles.
Which aren’t far off what I used on kite rotors previously

It is an application of post-tensioning. A well-known example is post-tensioned bridges. In this case the tensioning cables would be dyneema, which leaves the material and design of the compressive elements, which are ideally as wide as possible in the direction of the main force. For wings a thick a wing as reasonable, with the tensioning cables mostly along the underside, for shafts as long a chord as reasonable, with the tensioning cables mostly along the trailing edge. Maybe for both bracing between neighboring elements. Maybe you’d use a genetic algorithm for example to minimize drag, weight, and number of wraps, and maximize lift and buckling resistance.

My previous comments about this were mostly just brainstorming. I don’t think I gave an opinion on the viability yet.

We don’t have enough information to make conclusions, but my preliminary opinion is that for torque transfer you only want to use these fairings to resist the torque, and not any gravitational or centrifugal force, as that is for the tether tension. I think that means thin airfoils with a longish chord, and the thickest section very close to the leading edge to have enough cross-section there to resist compression. You can then analyze or test that, does it increase the torque transfer capability enough that it more than makes up for the drawbacks? Testing it, like I say in the other topic, can start out simple: make a few sections and test to failure. The folding/unfolding idea I don’t think makes sense as you’re adding weight and complexity that is not useful in production. I think this idea is probably less viable than adding compressive rings, possibly constructed in the same way.

For wings, if you think it makes sense to make very long wings, which I don’t necessarily, it could make most sense. For shorter wings it could make sense too.

One design could be for example a bridle line every few meters, like the poster I linked to before, mimicking an upside down suspension bridge, and then this construction method mimicking a post-tensioned bridge.

One of or the lightest beam possible is a tensairity beam:

You could use a tensairity beam as a spar and then surround that with these post-tensioned compressive elements. Or you could design these compressive elements to withstand some internal pressure and use an inflated bladder as a core.

The goal with these ideas; thicker wing, bridling, internal spar(s), is to lower the compression needed as that is the likely limiting factor in the strength of the wing; how do you make wing sections that can withstand lots of compression and are light.

To expand on this:

You want to do torque transfer; you want to have kites circling in the air turn a wheel on the ground. Your tethers can’t be too long and your wheel can’t resist the circling kites too much or the kites get too much ahead of the wheel. To allow you to use longer tethers you want to add additional wheels that you space along the tether. They need to be light and strong.

Best would be a bicycle wheel-like construction that has a central hub that gives lateral stiffness to the wheel with the tensioned spokes going to the rim, the wider the hub the greater the lateral stiffness. The spokes distribute the single-point load from the road (now tethers) along the entire rim.

If you don’t want to use a central hub, maybe because the attachment to the tethers already might give some lateral stiffness, among other things, you can mimic some of the load distribution of the spokes in your compression ring by using bridling, or by making a taller rim.

In the likely case that the possible increase in lateral stiffness from the tether attachments points isn’t enough, another way to increase that would be to make the rim wider. To still be able to stack the rings and decrease the height of the stacked rings, you would angle the rim.



…Or a different idea: let’s say you use as many rods as tethers, and you want to increase the compression they can take before buckling without making them too thick on the ground station, and generally reducing their weight. You could replace the individual rods with 3 or more thinner rods. You pre-bend them in the direction you want them to under compression - outward - and connect them together at the ends, and by spiraling a tether around them through rings attached to the rods. Now when you compress them and they bend outward, the tether gets taut and prevents any further bending. Because you used a single tether the tension in the tether is equalized. Now the limit becomes how much compression can the shorter sections/spans between the tether attachment points take before buckling.

You would make this construction stronger by increasing the angle the spiraling tether makes with the rods, making it more effective at resisting the bending rods, in the same way that guy cables are more effective then, and by reducing the length between spiraling attachment points, reducing the length of individual rod sections/spans.

You do that by allowing the rods to bend more under compression and by increasing the number of times the tether spirals around the rods. You’re probably looking for an ideal shape of the egg this new column makes under compression, so a ratio of the minor to the major axis, or something more elaborate that adds hinges to the rods.

A failure mode is probably that the rods bend outward, but come together somehow, so you end up with an arch instead of an egg. This is likely because the tether is under the highest tension when the rods make the egg shape and the rods are free to slide from this highest stored energy state to the lowest one, the arch, like a ball rolling down the top of a hill. This makes my original idea of only fixing the tether at the ends of the rods and allowing it to slide through the rings wrong. I liked that because of its less finicky construction. Now you have to compress the column and tension the tether segments like the spokes of a bicycle wheel while it is compressed. You can mitigate the difficulty of that somewhat by adding some elasticity somewhere, or by increasing the safety factor.

Maybe this is something like a Space frame - Wikipedia using different materials. I’d be interested in finding examples of this principle, but I can’t find something at the moment, except maybe this: Veritasium - World’s Highest Jumping Robot, but it’s not really. It’s probably a variant of Stressed skin - Wikipedia.

There is also this: Ali Clarkson - We Made Our Own Rope Spokes! And here someone saw that video and reached out to demonstrate the FEA software they developed to analyze and optimize structures like that: We Used Computers To Really See How Good Rope Spokes Are!

Continuing with the idea, if you only spiral around the rods in one way, when you compress it, it will probably fail from shear stresses. So you’d do something like X-bracing - Wikipedia. With that, now the metaphorical ball from the previous comment is also prevented from rolling down the hill, so that again simplifies construction, you’d make something like a bracket that you attach to the rod that has 2 (or 4) rings for the two tethers that must pass through them (or the four that terminate at them), and again worry a bit less about tensioning the tethers. If you do still worry about that, you can wrap the tether around the ring a number of times, and clamp the wrappings to the ring.

I don’t know if this is Tensegrity - Wikipedia. Here the compressive elements are connected together and are pre-bent. If they are not, the structure would sag while not in compression and then I don’t know if it would take the correct shape when it gets compressed.

You can help the pre-bending, by pre-bending, and then running a taut tether from one end to the other. That tether would become slack under compression unless you prevent that somehow. The brackets could also be spacers between the rods.

Sounds like you’re evolving your ideas along nicely Windy.
You should probably be playing with sticks and string now, taking picktures of measurements of various configurations so we can literally see what you are talking about.
There are plenty further framing methods to rigidise a TRPT ring to prevent buckling.
e.g. triangulating an inner longer (axially) frame or even adding a tense inner line loop fixed to the mid points of the main polygon rods
Then for rigidising the torque transmission (torsional rigidity of the overall shaft not just the ring unit) you could add an anti chiral rod between rings in advancing node order between subsequent rings with the normal straight node 1 to node 1 TRPT lines

Plenty options to make it heavier than what has been shown to work on small scale
And probably stack designs can use that
But normally with scale we want to make it lighter still though.

Oh that video - the guy with the dyneema spokes - from Tarty Bikes… waaay back he made me a bright steel stub axle with a circlip to retain a thrust bearing for the ground station PTO hub. The axle was welded to a square tube section for options

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That’s a reasonable suggestion. I’m a bit tempted to make sketches maybe, and maybe try to compare it to alternatives, but nothing else for now. Or maybe even not that, as I tend to do initial thought experiments in my head. The basic idea that a lattice tower should be much lighter than a tubular tower for the same resistance to bending should be sound I think, so maybe I’ll explore that a bit. Whether and how that is useful in AWE isn’t a priority for me to find out, how to make a ground station or a kite would sooner be. You’d perhaps try different options after you already were flying kites and decided you wanted to pursue torque transfer and found that you really do need some rigid components.

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So the title of this thread is
Claim: kites in a MAWES need…
Is this claim based on more than thoughts of imagined MAWES systems?
Surely you have some sketches to support your musing.
An idea translated into a pen swiped curve can save you hours of low bandwidth written communication

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