RogerBW's Blog

Pulling Power from the Sky 07 December 2020

2020 documentary, dir. Kate Stirr: IMDb.

The Makani project tried to solve a simple problem: wind turbines are already big and expensive, but there's more wind at higher altitudes. So why not put a wind turbine on a kite rather than on a pole?

That in itself is a decent idea (turbine-generators are heavy, but it looks basically solvable); but every time there was a decision to be made, the engineers took the most complicated option. Let's not just loft a turbine; let's have it circling in the sky, sweeping through a larger area of air. Yes, there will indeed be more power. But this means the thing has no stable gliding state: it will constantly be looping on its tether.

The progress of the project seems to be a catalogue of repeating bad ideas discarded from historical aircraft designs. The initial version of the kite was a flying wing; then later it changed into a tail-sitter, which would transition from a rotor-borne takeoff into a forward gliding mode and back again; and it was intended to land and take off (vertically) from a ground station which would also handle the tether. Oh, and all of this is supposed to happen in all weather conditions without human intervention.

Flying wings are hard; only one (the B-2) has gone into production, and the extent to which it works is distinctly arguable. Converting tail-sitters are hard; nobody has ever got one working without severely compromising its performance in conventional flight, and I don't think one has ever gone into production. VTOL is hard; the aircraft which do it are dedicated to it to the point that that capability becomes their primary virtue. All of these things add weight and complexity. There were plenty of smart engineers involved… but couldn't they have found one with a hobby of aviation history who could tell them why this particular idea didn't work on all previous occasions it had been tried?

To me this seems like a cautionary tale about working to the maximum extent of your capability: if you design something so complicated that you can just barely understand it, then when things fail you don't have enough margin of understanding that you can work out what's going wrong and try to fix it. This documentary makes it feel as though each person was doing that: they are taken entirely by surprise by wind state excursions that didn't happen in their simulations. They design their tether for a constant load plus safety margin and apparently don't account for jerk. (Or long term fatigue from repetitive stress cycles; they didn't ever fly for long enough to gather data on that.) Their kite has protruding fins and they're surprised when the tether gets caught on them. They change the design at full scale without getting a working small model first. They are committed people doing many things well, but there doesn't seem to have been anyone here with an overall picture of the project, just lots of specialists having fun working on their own bits of it.

Of course there's a problem in that the team had to work to artificially short deadlines in order to get the investors to maintain their interest and continue to supply money (e.g. "if we don't manage crosswind flight by the end of the year they'll pull the plug"). The engineers definitely made decisions to fly before they were ready, and that kind of need to produce a flow of short-term results that don't aid the overall project is an intrinsic problem with relying on investors. But the investors kept paying as the system got more complicated, going from an initial fabric kite to a huge eight-motored 600kW-generating carbon-fibre beast merely as the single unit proof of concept – presumably they had nobody working for them who understood the thing either. They kept paying as conventional ground-based wind turbines got better and cheaper, and the only potentially profitable niche the project could find was deep water offshore, adding a new set of environmental challenges. Eventually they stopped paying, but it would be fair to argue that they should have done so rather earlier (obviously that's an easy decision to make in hindsight). There's basically nothing here about relations between the project team and the investors, and it would be fascinating to know what control the latter tried to exert other than by setting deadlines.

One traditional way in which capitalism externalises development costs is by letting the entity that paid them go bankrupt and allowing a new entity to buy its assets and leave the debts – that's how both Iridium and Globalstar got their starts. But nobody seems to have been lining up to buy any of the Makani hardware or patents.

Thanks to the Yorkshire Ranter for pointing me at this documentary. It's freely available on YouTube.


  1. Posted by John Dallman at 09:25pm on 08 December 2020

    I have an impression that lots of people with "a hobby of aviation history" like watching films of things that go zoom and woosh, and a few of them buy books that touch on the engineering problems, read them, and retain the information. My basis for this is that I ask new hires at work if they're interested in aviation history, because the company's background is entangled with that, although we aren't in the industry. About a third of them say they are, but a much smaller proportion have ever /heard/ of the A-12 project, which is the key point.

    One part of the Silicon Valley business model is starting afresh and not steering away from the things that have been hard in the past. This can work with software, because hardware has grown so much, and it can work with computer hardware, because that has had such huge gains in recent history. But it tends to fail for well-developed fields with genuinely hard problems (XKCD example: https://xkcd.com/1831/).

    Elon Musk is fairly good at this model, and he apparently insists on the hard problems being identified and tackled first. This project seems not to have done that.

  2. Posted by RogerBW at 10:04pm on 08 December 2020

    See also cryptocurrency boosters, who look out of their Silicon Valley offices, see that transferring money from one bank account to another takes days, and say "the world needs a better way of doing this". The world has one; it's just not in the USA yet.

    Whether the existence of the Makani team may have exerted any pressure on conventional wind turbine designers to improve things, beyond what they were doing already, is not mentioned in the documentary.

  3. Posted by Owen Smith at 02:02am on 09 December 2020

    When I sell my Qualcomm shares in the US on etrade.com, they take about 2 days from "yeah we'll buy that here's the price" to being "settled" ie. I have the money. It then takes about another 2 days for the wire transfer to get from ETRADE to my USD bank account details at TransferWise. This is all within the USA. When I then login to TransferWise to convert the USD to Sterling and send to my UK Santander bank account they say it takes about 5 seconds. I can't tell if that's true, I've never managed to login to Santander fast enough to verify it.

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