Tethered-aligned vs crosswind kites in yo-yo mode

Flexible kites are considered for easy comparison. The reel-in phase is assumed to be equivalent in time and energy consumption. The crosswind kites look like winners at first glance. But let’s take a closer look.

An example of tethered-aligned:

Two examples of crosswind kites are mentioned on:

A crosswind kite like that on the two examples above can have a reasonable lift to drag ratio of 4. (L/D)² = 16, leading to 16 times the potential power of a tethered-aligned kite of same area, and only 10.4 by taking account of a cosine³ coefficient of 0.65 with an elevation angle of 30 degrees, perhaps even far less if one takes into account the irregularities during the reel-out production phase (see on this subject the zigzag curves on the documents mentioned above), and the tether drag as tether length increases.

The elevation angle of a tethered-aligned kite is far higher, being about 50 degrees, perhaps more (see some pilot kites). If the wind is strong enough, the loss of elevation angle would be mitigated, as I experimented with my sled. The tether drag is lower than in crosswind mode, so higher altitudes can be reached, leading to more powerful and consistent winds, including low and high level jets. In addition kite trains are particularly suitable, the number of kites compensating the lack of power by area.

So as a first conclusion flexible crosswind kites are better for relatively low altitudes, but are competing with existing wind turbines, while tethered-aligned kites could harness really high altitude winds where there is no competition.

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Pierre I think this heads toward a laddermill, which was apparently just given up on after a lot of hype about how great it was. I’d still like to build one. I’ve been wanting to since the late 1970’s. I do not see any reason it could not work. Well, I’m sure stuff would go wrong, but I think it would be worth a try. Probably take a few iterations (builds) to get one to work, but after that it could be just refining something that at least works.
I thought SuperTurbine was a step beyond laddermill, but I was disappointed nobody ever built a laddrmill. All those interns - sheesh!

Indeed Selsam’s “Auto-Oriented Wind Harnessing Buoyant Aerial Tramway” (towards the end of the long page): then this device was called Laddermill.

And in this classification tethered-aligned include both Chinese umbrella AWES (see above) and Laddermill.

I think it could perhaps be transformed into a Laddermill, the parachutes (umbrellas) deflating naturally in the downhill portion of the loop, being depowered.

Perhaps some other arrangements, comprising a train of Sharp rotor, could be found, as well as “simple” tethered-aligned kite trains and Laddermill-like.

Today I measured the traction of a 1.7 m² sled weighing 0.385 kg, at 6 to 10 m/s wind speed: traction 2 kg to 6 kg. This kite looked to be stable in spite of the low altitude of 5 to 10 m.

Even when holding and releasing 2 m of tether (out of the 10 m), the kite rose a little or a lot depending on the wind speed while he was backing away, whereas when the experiments were performed with a lower wind speed of 3 to 5 m/s, the kite went down when I unwound 0.5 m of tether slowly.

Is this kite suitable for a kite train and in higher scales?

Unlikely to work in a train .
A train requires a line up (often in front of the kite like the morse sleds you showed recently)
Sometimes the line is through the kite from the central bridle point through the top skin.
In this case…
When the lower kites in a train surge in turbulence they can wrap around the tight line going through their center. This deflates and collapses the lower kites.
Kite trains kites tend to need some frame rigidity.

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Sleds have a light longitudinal frame (thin carbon bars), and some soft kites looks to work, like Guangdong parachutes.

A non-starter idea from the beginning.
Drag-based - so I guess AWE people will want to call it lift-based, right?
Back to Windergarten.
One more “press-release breakthrough”.
I remember debunking this years ago.
Sooooo… what’s the latest on this “technology”?

Not more, not less than others.

Scientific publications put all yo-yo systems into “lift” category. Perhaps “pull kite” would be less confusing. As you know the limit is 4/27 instead of 16/27 (Betz limit). So the kite can cover the full area as well as a smaller crosswind kite will cover the same area.

Each approach has its pros and cons, until one actually emerges.

Sometimes we change the record.

It is not so difficult to debunk any AWES as none of them reaches utility-scale market.

22 kW at several hundred meters height, it is not so bad.


Does anyone else read that mW as milli Watts?
Not MW Mega Watts

OK so is this 22 kW continuous output? Or is it a brief 22 kW peak?
Do we see it on a meter, or just take their word for it?
Does it include the entire cycle, or just the power part of the cycle?
What is the duration of their operating time on any given day?
I have to tell you, a string of parachutes was about where my head was at for wind energy at age 8 or 9. That was when we were making our own kites.
Still, as you say, nobody knows for sure where this could go.
Wait, maybe this would work well for “disaster recovery”!

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On the video at 1:31, during some seconds of display: 15 to 22 kW.

Thank You Pierre, OK I did see the numbers on the screen.
Well yes, that is a lot of power. Just add a few more parachutes and you can “power X number of houses”. Sure, why not? Parachutes. I’m sure they can pull.

Here are a few points I noticed about this video:

  1. I originally thought the outdoor spooling head was a statue of a lion.
  2. We only saw a very brief glance at the power readout numbers. Assuming we saw a momentary peak, like maybe when they first open the parachute or something. Or maybe the peak power used to reel it back in.
  3. The size of the equipment in the power room seemed way too large for that amount of power. I would think it might take 10 or 20 kW just to get all that heavy shafting etc. turning.
  4. I did not perceive a good, full, working cycle in the sky.
  5. It looked to me like some of it was in fast motion, seemed to be “pumping in and out” but not because the parachutes were changing shape. Seemed very erratic.
  6. It seemed hit/or/miss as to having anything that looked even watchable to show what would look like satisfactory operation, to my eyes at least.
  7. In a strong wind it is going to have trouble staying elevated.
  8. I wonder what their budget is: Large building with a special hole in the window for the tether to go through, all that heavy equipment, all those wind tunnel fans, giant spools of rope - sheesh! They BETTER make some power.
    something tells me they aren’t running one right now.
    Just a hunch.
    Not that we haven’t seen this movie a few times now though, eh fellows?
    I mean, looks like a pretty simple setup.
    They apparently have a huge budget.
    It all “looks” quite do-able.
    So why do you think one isn’t operating anywhere in the world today?
    I’ll bet it;s because it sucks.
    Something that wasn’t in the video.
    If they had anything working well, I’m pretty sure they could have made a much better video of it working.
    Oh well, at least they gave it a try!

Hi Doug: it is the same for the other AWES.

And here is something to think about:
How is it so easy to assume there is none running anywhere today?
Right out of the blue, with no actual information?
Or why would we assume it?
Well 2 reasons occur to me:

  1. We keep hearing all this fluff and yet we don;t see anything in regular operation still;
  2. If a system were in regular operation, we would assume we would be hearing about it.
    (Of course if it were secret, nobody would know about it.)
    But still, it would not stay secret for long - it would have to get out there and be seen, especially with wind energy. And of course the developers would want to get it out there fairly quickly so it could become widely successful.

Oh well, it’s not just with AWE.
It’s 99% of the “press-release breakthroughs” of all kinds we keep seeing everywhere, every day. Magazines need something to write about. People want to get excited about stuff. Only a small percentage of all this “great news” ever pans out . So that doesn’t mean give up, just that some healthy skepticism is warranted in most cases.

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Some experiments today, with a wind speed of about 5 m/s:

  • elevation angle 45-50° for the bear parachute kite (1 m diameter, a toy bear as ballast, 6 slots of which 2 towards the middle and 4 towards the trailing edge which also includes a small additional ballast);

  • elevation angle 60-65° for the parasled.

For a tethered-aligned train of kites, a high elevation angle can be more suitable to reach really high altitudes, but in all configurations, the power/kite area is low, too low.

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The problem with AWES is to deal with two contradictory issues: average lift going with higher elevation angle, energy generation going with a lower elevation angle.

A higher elevation angle with a crosswind kite would be possible with (far) more loss by cosine³ by increasing the elevation angle, say 40-50 degrees instead of usual 30-35 degrees. The lower power by kite area could be compensated by the higher potential of superimposition of dancing (Kitewarms style) or rotating kites, because of a lesser vertical occupation by unity.

Unless in the configuration mentioned just above when crosswind kites sacrifice power to gain average lift.