Another laddermill concept

Recent talk about laddermills got me thinking about them. Here’s a concept I came up with today:

Your rope drive is now rotating around its longitudinal axis too. The kites are flying (crosswind) in a circle around it, in a large radius going up, in a small radius and minimal drag mode going down.

Further development is left as an exercise for the reader.

Benefits include: crosswind operation possible with a relatively simple and light kite; low total line drag compared to single kite yoyo awes; (variable) strength in numbers, not size.

Drawbacks include: ground station design still a black box.

To begin testing and thinking you would need at least: 2 fixed points some distance from each other, a loop of line, a number of pulleys, a kite (optional), a motor (optional), an image in your head of your design.

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I was thinking about a wing travelling upwards while reeling out. If geometry is chosen carefully, the kite could fly directly in the direction of the tether. If this were the case you could have multiple kites on the ladder.

This would be somewhat similar to @PierreB’s suggestion for a reversable kite.

Could be this was laddermill all along and I didnt understand.

Anyways, its a mix of lift and drag mode AWE.

Because the kite is travelling along the tether, tether is essensially stationary, thus no drag. So ultra long tethers could be [more] feasible

There would still be some practical limitations, but maybe a good starting point?

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No crosswind flight and no rope drive spinning around its longitudinal axis? Then that’s not similar I think. If you had your kite spinning around your (main/lifter) line then it would be quite similar.

I’m not drawing a diagram to not limit the reader’s imagination. And whatever I drew would also not match how it would really look under the influence of reality.

Imagine a rope drive fixed between two points, (temporarily or permanently) attach however many lines to the loop and attach to each of those lines at least one kite. The distance between the lines on the loop (in my first idea) would need to be at least the length of the lines so you can use that to somehow reduce the turning radius (and thus speed) of the kite when it is going down. Now spin the rope drive around its longitudinal axis to match the spinning of the kites. The kites going up and down won’t interfere with each other – on paper – because they are on the opposite sides of the (now troposkein shaped, I think) rope drive.

In my mind the most important imaginative leap you need is, how to change the ground station from a black box to something that could work. You could spin the generator along with the rope drive but that’s an inelegant and probably problematic solution.

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Sorry for hijacking your thread. I am describing another Laddermill. After more consideration, I lost faith in my idea quite quickly

I think most ground station issues may be solved by having only one kite. With only a single kite the idea is approaching normal Yoyo design.

An out there option is to completely detach the kites and let them fly back to the rope near ground, then somehow reattach to the tether. Could be possible if you can detect the tether from a distance with high accuracy.


You’d then have to fly your kite upwind for potentially several kilometers. Wouldn’t that be a problem? Catching and reattaching to the tether feels possible.

A hybrid of mine and your idea maybe: instead of 2 fixed pulleys, you now have 4, 2 on the ground k line lengths apart, 2 in the air k line lengths apart, your loop goes around those. Now the kites going up only circle around the line going up. The kites going down are in low drag mode. In the air the fixed points would probably be below each other.

Perhaps the kites going down could go faster than the loop.

I think this fixes many of the issues of my first idea. (black box ground station, excessive troposkein rope drive deformation, kites crashing into each other), but it introduces the need for some kind of swivel at the line attachment to the loop. And now the pulleys and ground station are a new kind of more approachable black boxes.

I think it is not a problem with rigid kites. The glide number in free flight and weight decide how fast they can return and at what «elevation angle». You will have a maximum winspeed but it might be very high, depending mostly on those factors…

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To keep two pulleys apart and airborne will probably necessitate a rigid frame due to the high tether tension? There are many practical reasons that the «return» part of the tether must have a little tension also


@Windy_Skies, you suggested a rope drive (your sketch below) for several methods including laddermill. Indeed rope drives have numerous advantages of which the possibility to connect the fast crosswind flight to the generator, increasing its rpm compared to yo-yo systems for example.

This is a rope drive transmission on the ground. However if this rope drive is airborne, and completed with ropes at the ends, would the resulting system be more or less close to what you envision as “another laddermill concept”? If yes, how is it possible to solve the issue of required “rigid frame” such like @tallakt evokes?

My feeling is that a rope drive would be suitable on the ground to benefit from the “earth as spar” (Dave Santos’ concept), in spite of some possibilities within a laddermill, in spite of the successful @Kitewinder’s device.

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Let’s forget about the airborne part for now to keep it simple. So now you have access to any number of fixed points at any desired altitude for you to attach your various elements to.

The central idea in my first concept is to have the rope drive spin around its longitudinal axis and have the kites spin around the rope drive. The central idea in my second concept is to have the kites spin around the taut side of the rope drive loop.

How would someone design the attachment of the kite tether to the rope drive loop to make it work with the pulleys and to lengthen and shorten the kite tether, what would the ground station look like, and so on.

My comment:

That was an implicit question. I was trying to remember what company/companies had been developing something like that and wondering if anyone here knew.

The rope drive must have a production/return tether distance so large that the production looping not interfere with the return tether.

This is simply solved by flying figure of eights at one side of the production tether.

Kites on the return tether need not loop. They can simply fly/glide.

I still think the major issue with the whole concept is what makes it better than normal yoyo…

You’d need a “smart” kite for that, your kite will not continuously fly at its highest speed, you’d perhaps need a longer (branching) kite tether, the kite will pull the production tether in an off-axis direction from the rope drive, deforming it. That are some of the problems I imagine doing it like that has.

Edit: but the overarching system should look fairly similar whether you do figure of eights or circles so looking at one might give you ideas for the other.

For an indication of how I feel about it.

I put some of the imagined benefits in my first post. Anyone can think of more benefits and drawbacks. We might learn something by brainstorming about the concept that we also might apply to other concepts, or just further our understanding of the world. Do you really need a lifter kite for example, and (if not) could this be a next step for yoyo development?

Let’s simplify further: we have a (loop of) line with either permanent or detachable beads on it that goes around at least one or two fixed points. Perhaps we want some of the beads to slide backwards and forwards (at the fixed points) to for example shorten/lengthen the tether connecting to the kite. Perhaps we want the beads to detach and reattach.

How would you, should you, or could you design the beads and the fixed points? Once you’ve come up with a mechanism that you like you can work on improving it and making it more suitable for your application. Maybe something, perhaps another idea, will come from that.

The idea of permanent or detachable beads reminds me of fixed grip and detachable chairlifts.

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One more interesting concept.
A horizontal ground-based “laddermill” type device has been built and run at a windfarm many years ago, using the ground to separate the end stations. I’ve long-considered using the ground to separate parts of wind energy, including a theory that crosswind separation is key to wind energy in general, and as you know my design work in AWE and wind energy goes back to the 1970’s. Many other designs, going way back in time, have used the ground to separate stations. I believe this includes Payne? This was long before Santos began his internet musings on wind energy, so ascribing “ground-as-spar” to him would be in error.

I think this is a great idea from Dave Santos (@kitefreak). His concept is applicable to a multi-anchored (at least two anchors for an arch) flexible wing, using the ground as spar instead of carrying a heavy rigid part aloft. This is perhaps an essential key to scaling. It is not the same as using the ground only to separate the end stations.

That said the concept you describe looks to be interesting. Do you intend to use rigid sails as blades? Have you a sketch or a link please? Thanks.

Hi Pierre: What idea? What concept? Not sure what you are referring to.

Was on one yesterday. 4 minutes to the top! Will be on them again soon. The (man-made, so far) snow is here at 8000 feet elevation! (overlooking Los Angeles) I love going over jumps! Let the skis take up the impact of landing - it’s all how you let them slap down, and they absorb all the kinetic energy. Nice to do something normal and fun again!

This concept could be: using the ground as a giant beam, allowing a network of flexible kites to scale without limit. Perhaps @kitefreak could provide a better explain or demonstrate it.

Pierre: The general concept seems potentially valid, but not a new idea. How many hundreds of brainstorming configurations have we discussed over the last decade+ that use multiple anchor points on the ground? Most of them? I’m not quite seeing what exactly is new here. Would love to hear more.

If that allows safer and larger networked kites, this is a fine idea.

I think multiple anchors is a better wording than ground based spar. A spar will generally move with the kite, so does that mean that a ground based spar must rotate also?

Multiple anchors - plain, simple, no confusion.

…or am I missing something?