Makani Archives

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Makani have done something incredible.
Makani have done many incredible things.
Recently, Makani published a record of their development and the lessons learned.

In their words…

The Energy Kite Collection: sharing Makani’s lessons

In 2020 Makani’s journey as a company came to an end. To share the lessons and insights the Makani team gained from their 13 year journey developing an entirely new kind of wind energy technology, the team created The Energy Kite Collection, a portfolio of resources including a technical report, Makani’s entire avionics, flight controls and simulation code repositories, flight logs for every crosswind flight of the M600 prototype, technical videos, a new simulation tool called KiteFAST created with the National Renewable Energy Laboratory, and a non-assertion pledge for the free use of Makani’s worldwide patent portfolio.

The Energy Kite technical report consists of three parts:

Part I
provides an overview of best practices and lessons from Makani’s most advanced energy kite (the M600) and offers suggestions on how to complete a next generation energy kite system.

Part II
is a collection of technical artifacts that outline the design of the energy kite system, Makani’s understanding of the physics of tethered flight, and includes a user guide for the flight logs available online.

Part III
includes reports on flight tests and illustrates Makani’s progress toward long-term permitting and type certification for airborne wind turbines.

We think these materials will be especially interesting to airborne wind developers and researchers, aerospace experts, engineering students, and people who are curious to learn about novel flight vehicles. A full copy of the report and multimedia assets are also available on Internet Archive.

My crass invitiation to viewing some of this resource originally read as follows… I’ve since re-written this first post on theis thread…
Who would like to watch Makani Videos for the rest of the evening?

Here’s a teaser
movies

20180410 RPX-09 - Mid-Air Break Up of Makani M600 During Crosswind Flight [Excerpt]

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https://archive.org/details/makani-power

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Jaw on the floor

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@Rodread provided me a very interesting video containing the power curves I was waiting. I put below a similar but shorter video which contains useful data. It is a big file so opening it takes a long time. Opening it in a new tab makes reading easier.

For what I understand the beginning of the video shows the take-off phase, then the kite in operation from 16:00. The wind speed aloft (first circle in the left) was about 8-10 m/s. The kite speed was between about 38 and 56 m/s. The power generation was negative about half of the time (kite slowdowning), and between 0 and -500 kW, the positive power generation (kite accelerating) having the same values. So there was roughly no generation in average.

An older video (below) represents Wing4e Energy Kite Prototype. It produced between 4 and 8 kW (wind speed about 10-11 m/s). Small flygen AWES seem to work better, undergoing a lesser weight penalty.

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The archive is testament to an amazing body of work on a grand quest.
It was hard work, well executed with some tough constraints.
There are a lot of engineering lessons to be taken on such as
airframes resonance
Using slip-rings
The difficulty of mode changing a wing in multiple regimes
Nicely done @Makani folks
AWES projects all round will benefit from this.

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The big lesson may be the impracticability of the large, rigid and heavy kites, at least by flying in circular figures.

An underestimated problem may be the significant kinetic energy as the kite descends, preventing it from ascending. Thus a wing like M600 weighing a ton and flying downwards at 50 m/s produces 1,250,000 Joule, added to gravity. And its speed upwards is lesser, so its kinetic energy is also lesser.

Perhaps kinetic energy issue during flying downwards phase can be mitigated by flattening the trajectories, using flat figure-eights kiteKRAFT fly-gen kite flew figure-eights.

I think we should stick to sharing observations for now, rather than this turning into another architecture discussion.

I’ll share one: At the end of the full Karmøy flight/crash video, the kite stops flying, but none of the crew seem to be stating whats wrong as they go. So I believe maybe they did not know why they crashed the moment it happens.

So… suggesting software related quite likely.

About power curves - one reason any AWE player would be reluctant to share such videos is that someone will blatantly make assumptions without enough info. For instance, there are many reasons why Makani would perform flights at negative net energy. To know about the power curve, we need detailed info about wind conditions and the details of the flight, software and hardware.

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I quite disagree, although the observation of the videos provides useful information to take into account. The negative power (more red than green in the generation column) is related in several videos mentioning wind speed, mentioning wing speed and its variations during the loop, mentioning the two modes of flight, take-off and generation, and some other parameters, lead to the need to another architecture, or at least another plan of flight, not to mention the in-flight crash. The comparison above between M600 and Wing4e is talking: the smaller Wing4e works better. It is not an affair of software but a matter of wing loading.

Concerning the crash, I have not information enough to know the cause, so I would leave aside the assumptions expressed, which are nothing more than assumptions.

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Just felt for them. Seeing that crash was gutting. I swore too.
Most of the flying was autonomous. Looks like (speculating) there was an override option which might (speculation) have been attempted in the last few seconds. It looked like a similar problem as was encountered in earlier tests where they didn’t have the roll authority in pitched up parked on the tether mode… This equated to spinning round against the tether (more of a yaw)
I think the call was that test was being stopped due to rising wave intensity.
Test went so well until that point.

Loved how shocked everyone was at the drift ~50m of the buoy earlier in the test.

Later in the same post:

Sharing or not sharing, that is the question. I modestly think that I am one of “any AWE player” and I am not “reluctant to share such videos” for the reasons I explained above I resume here: the power curves speak for themselves. Indeed Makani has taken care to indicate the maximum number of readable parameters in real time. And Makani itself is also another and big one from “any AWE player” being not “reluctant to share such videos”, even on YouTube.

The link below on YouTube can help to share more easily. The other technical videos are also now available on YouTube.

Another link, leading also to Paula Echeverri’s article:

WOW
https://storage.googleapis.com/x-prod.appspot.com/files/Makani Non-Assertion Pledge.pdf
That’s tech nobility

As for
The Energy Kite technical report consists of three parts:

Part I
provides an overview of best practices and lessons from Makani’s most advanced energy kite (the M600) and offers suggestions on how to complete a next generation energy kite system.
WOW

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Some quote from Paula Echeverri’s article on
https://blog.x.company/sharing-makani-with-the-world-the-energy-kite-collection-ea49398df78c :

Although this is the end for Makani, by open sourcing our work and story we hope to create tailwinds for the next generation of scientists, inventors and moonshot takers to tackle the near-impossible.

And from the Part I , page 13:

1.3 Shortcomings of the M600
The M600 was shown to have several shortcomings. Among these were:
● The novel, untested airfoil design made rosy assumptions about the CL,max that could be
reliably achieved in flight, along with overly optimistic CD
targets.
● As a result, the system L/D (i.e. including parasitic tether drag) was insufficient to
produce the assumed “glide speed”
● The sizing of the wing, combined with lower than expected lift and higher than expected
drag resulted in low power performance
● The roll-stiffening effect of a very tall bridle
rendered the ailerons unable to exert
sufficient roll authority to fly small loops, which are important to power production
● The potential energy swings resulting from large loops forced us into large speed
variations. At low winds, we’re often flying much faster than optimum at the bottom of
the path, and at high winds, we must fly much slower than optimum at the top of the
path to prevent overspeeding at the bottom.
● The resulting large differences in airspeed disallowed the rotors from operating at peak
extraction capability through much of the loop

I note some similarity between:

● The potential energy swings resulting from large loops forced us into large speed
variations. At low winds, we’re often flying much faster than optimum at the bottom of
the path, and at high winds, we must fly much slower than optimum at the top of the
path to prevent overspeeding at the bottom.

And what I wrote above before knowing Makani’s analysis:

It is clear that shortcomings and negative power curves on the videos of M600 (unlike the smaller Wing4e) can be revealed at the end of this project.

All this information is a real treasure and marks the end of a first AWE stage (if not the end of AWE) and the study of new architectures and new flight plans.

There is so much info here.

Figure 4​: Comparison of the Oktoberkite (orange) to the M600 (gray). The Oktoberkite has approximately the same span, but about 60% more chord, hence 60% more wing area, than the M600. This allows it to meet its performance target of 600kW at 11 m/s of wind.

The intro post to this topic needed changed.

Continuing the discussion from Makani Archives:

Page 232 of Part I (thanks to @Rodread to indicate me the curve in the figure 3 with the text below) :

Figure 3: Power curves for the M600, showing the large gap between original design intent and
the realized system. Data shown is a subset of flight test data to isolate a single configuration.
Note that our modeling tools accurately predict the performance deficiency of the M600.

That confirms my observations about power curves of videos on some previous posts like this one or this or this another.

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Hello Pierre:
I completely agree with your assessment regarding the lost opportunity for harvesting electrical power while the heavy aircraft laboriously struggles to fly uphill with every rotation. It goes back to what I’ve been saying for well over a decade now, regarding most AWE efforts: these people don’t know what they’re doing. I don’t care how many fans they had accumulated, how many flattering articles were published repeating their public relations statements, how many “highly-talented” engineers and programmers they hired, a thousand flies can all be wrong, when the basic concept has such blatant holes in it. I would go on to explain more, but at some point I’d rather let people figure it out for themselves. Whether they ever will or not, I don’t know. Maybe I’ll get around to explaining it someday, but it basically goes back to not understanding, or maybe just not sufficiently appreciating, possibly just ignoring, how existing technology works, sufficiently to retain certain overwhelming advantages, gained over thousands of years of wind energy development. Where did they go wrong? If you don’t see it, I’m not gonna mention it. Ignore what was already known 1000 years ago, and you get what you get.

Hi Doug,
Indeed the high speed of the wing accentuates its kinetic energy (wing mass X wing speed² / 2), and this roughly two times more while going downwards than upwards due to gravity, the wing speed² doubling. Downward momentum + gravity is like a “double penalty”. I think Makani more or less mentioned this issue by using “potential energy” expression.

I saw the Makani movie just now and it is clear that they were far from a fine tuned AWE unit. We will never know, but I only know that what was shown was a lower limit to performance that could only be improved upon. Sure complexity and large mass is a big deal. Mass could be alleviated by using three simultaneous kites in a triangle (not solving lower wind range though). Complexity - well I dont know. But it seems they were pretty close to something, and that something could be made to work. But at a cost that did not make the effort worthwhile… I say this opens up the door for anyone who can figure out how to do this cheaper and with smaller mass…

As an interesting takeaway, they made a carbon fiber tether. This could increase the strength to diameter ratio. I leave the details to anyone mechanically inclined. Anyways, their test failed.

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The effect this sudden release of Makani data and media is interesting.
OK the film is inspiring but myopic. This is the documentary of 1 engineering company not of the field of AWE Science and engineering (unlike the AWE documentary by Chase Honaker)
The list of employed jobs at the end tells a large part of the story too.
The work was massively impressive but deserves generalisation across AWES.
With the claimed intent of work … The results should probably have been shared more frequently in smaller just as fabulous bite size releases.
Suggested edit… here is the film documentary