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Why Wind Turbines Have Three Blades (cringely.com)
425 points by rfreytag on May 6, 2016 | hide | past | web | favorite | 189 comments

Three blades is the smallest number that reduces the vibrations due to the blades crossing the support structure. When a blade crosses the support its applied force is reduced because the wind is slower around the support. This reduction in forces creates a yawing torque that can lead to unwanted vibrations. Much of the structural stiffness and bearing requirements are related to these effects. Three blades minimizes the effect because when one blade crosses the support the other two blades are out in a Y shape, shortening the force differential when compared to two blades.

This is spot on and the real reason. Thank for posting this, I was working on a much larger comment but yours is better because it says the same thing in fewer words.

If tower thump were not an issue then a one bladed turbine would be the best possible turbine (cost efficiency wise).

Further down he's even arguing for turbines with 12 blades, it's a ridiculous number and quite inefficient unless you want very high torque at low rpm such as for directly driving a mechanical waterpump.

Jacques, you are too nice, you could have said you have also the practical experience of what is building a windmill[0]. A very nice read for people enjoying both using a computer and their hands building stuff.

[0]: http://jacquesmattheij.com/how-to-build-a-windmill

Is there any particular reason why that piece never uses the phrase "wind turbine"? That's actually what it is, right?

At the risk of stereotyping; because he's Dutch? :)

Because lay-people call them windmills.

You mean a real, practical, one bladed turbine like these guys? http://www.powerhousewind.co.nz/story.htm

Even though 12 blades are less efficient, the article points out that they may have advantages for the bigger system of a whole wind farm, availability of sites, production, transport, control and non-generating time. It's not beyond belief that all those other advantages could counteract the reduced efficiency. You can't really know from intuition unless someone actually studies it.

Another example - commercial aircraft are known to have a relatively inefficient shape, but that's cheaper to produce than the more complex and more aerodynamic alternatives even though they would reduce fuel costs.

It's significant that high-solidity turbines with many blades are in use. As you say, they're quite common in small-scale settings like water pumping.

An article purporting to 'discover' that design would probably be more shocking if it wasn't already in common use for sensible applications.

cool. I thought I had read in an issue of Popular Science or Discover magazine that one blade was theoretically the best but I don't know enough about it to say for sure.

you're probably thinking about a propeller - as in the type on an airplane or boat that puts energy into a fluid.

I'm not an expert but I'm pretty sure there is a big difference from a device trying to pull energy out of the fluid.

A quick google didn't lead me to an authoritative source, but I know I have read many times that a one-bladed propeller is the most efficient.

Oh, I had thought an infinite number of infinitely thin blades got you the closest to Betz's limit?

Wouldn't that just be a disk?

Interesting. Isn't a fish fin (as in the fins on the side etc) essentially a one-bladed propeller?

The three blade approach also offers better outcomes for repair costs (and animal strikes). High-blade, high-solidity designs are more likely to break in extreme weather (even a stopped windmill takes a lot of strain at 70% solidity) and repair is usually necessary after failure of a single blade.

Between that and your points, my impression is that many-blade designs aren't useful beyond small scale generation, which is exactly where they're still in use. There are an awful lot of three-blade advantages that went completely neglected in this piece.

In the 1980s there was a hype of one and two blade designs.

I always found the one blade designs most fascinating and vividly remember a video of the three one blade rotors of the Monopteros 50. Each blade was 56 m long. There was also GROWIAN, a two blade design with 100 m diameter on a 100 m tower.

All of these projects were abandoned and the towers demolished. The three blade design has won for the reasons you stated.

I searched hard for the Monopteros video but there isn't even a good picture which shows all three towers. By-catch: Wikipedia page about unconventional wind turbines [1]

[1] https://en.wikipedia.org/wiki/Unconventional_wind_turbines

Somewhat related, there are a few airplanes with one-bladed propellors, for example:


In this example, it's used purely because of compactness when stowed.

So, this is a redesign. I was told that old Windmills (used for milling) evolved to have an even number of removable blades. This allowed the mill to continue operating, while repairing a damaged blade -- simply remove the opposing blade, during repairs.

This is generally true. Mill or pumping turbines generally have a lot of blades (for higher torque), which obviously increases the risk of blade failure. That can be offset by having designs which aren't decommissioned by blade loss.

Of course, that's much less appealing for commercial installations, where access to the blades is expensive and difficult.

edit: also, even blade counts on big, high-powered turbines tend to get into problems with resonance by being symmetrical.

For a two blade system, could that vibration problem be addressed by extending the support up beyond the nacelle, so that both blades cross slower wind spots at the same time?

No. That changes whether the turbine is pitching up and down on top of the post, but doesn't change the fact that the turbine shaft is pulled out (or pushed into) the turbine with different force at the crossover point. That will create vibration even more in the long-post model you describe.

There's a question then, why are support towers solid? Maybe they should be made more like the Eiffel Tower?

Because a lattice tower has much worse properties when it comes to interacting with the wind. The behavior of the air behind the rotor is as important as getting quality air to flow through the rotor.

Some early windparks used lattice towers, and some of those survive to the present but they are now known to be worse performance wise than tubular towers.

A Shukhov tower [0] has minimal wind loading, due to its hyperboloid sections.

[0] https://en.wikipedia.org/wiki/Shukhov_Tower

That profile is not very well suited to having a windmill on top of it. The problem is that the nacelle is tilted backwards only a few degrees so you need a very slender tower (or you'll have tower strikes in high winds).

The cooling towers of a nuclear plant follow the same principle. The sides are formed from straight structural members angled in opposite directions (doubly ruled), and the gaps are filled with concrete.

The profile of a hyperbolic wind tower may be altered such that the cross section at maximum height minus blade radius is at a minimum. The largely conical profile of the existing Shukhov towers were used for power transmission lines and a radio broadcast antenna.

Check this out: http://www.pbs.org/wgbh/nova/next/tech/proposed-hyperboloid-...

Interesting! You'd think that the major wind power manufacturers would have looked at all possibilities. One major immediate concern is that these look quite ugly and fat compared to the relatively thin and slender supports that the latest generation of turbines uses. I'd love to see a side-by-side comparison of these towers and the various alternatives.


Is one example of lattice towers in production that I know of (but not like the ones you describe and I have never seen those being used for windmills).

As mentioned in Jobs quote near the top of the article, you often find that people tend to do things in a certain way just because that is what has been done before. No one bothers to experiment because the old way has always been good enough.

This is why is is sometimes difficult to avoid premature optimization, because post-maturity optimization tends not to happen, even when it may be warranted. I know of no wind farm anywhere that is used for side-by-side comparisons of wind turbine technologies. It would very likely have to be owned by a university and supported by public funds.

I have never seen a hyperboloid lattice or diagrid structure in person, but they are not entirely unheard of for shapes that do not require a lot of space efficiency in the tower portion, such as for lighthouses, observation decks, water towers, radio towers, etc.:







>No one bothers to experiment because the old way has always been good enough.

If you are a manufacturer though, you have all of the incentives to come up with something more efficient though. Wind turbines aren't controlled by a monopoly are they?

Lattice towers were common in the past, and are still the best weight/material to strength choice. Other considerations have led to the tubular steel tower dominating, though a new generation of enclosed lattice towers is being developed.


Probably to be more durable, because of the closed surface - the Eiffel tower has very high maintenance costs as it has to be steadily re-painted. It would probably not be necessary that much for modern steels, but unlike wind turbines the Eiffel tower also does not stand close to the coast or directly in the sea, where highly corrosive winds blow.

Additionally the enclosed space is useful. Inside the wind tower is a lot of equipment. There is the electronics for converting the power and monitoring the wind tower. There is a lift for ease of access to the nacelle. Current wind towers are 80m tall, next generation wind towers are more than 100m to access more reliable higher strength winds.

I don't think this is a strong driver. GE 1.5 MW turbines only have a relatively small space near the base of the tower that is consumed by power electronics and control systems.

Siemens has largely gone to a system where everything is in the nacelle. This way it makes it easier to completely test and connect the power electronics and control, since more of the work is done at the factory instead of in the field. Labor and equipment is much more expensive in the field than in the factory.

They kill a lot of birds too -- birds perch on the bars and then fly off only to be stuck by a blade they didn't see.

I know it's not really what you mean, but jacket foundations are fairly common in offshore wind. The emerged part is still always a solid tube.


Random question, why not 1 blade and a counterweight?

One-blade systems do have a counterweight. There are two parts to the vibration problem: One is that the flow field on the lee side of the tower is quite a bit different from the rest of the blade's sweep, so there is a once-per-turn torque pulse in that part of the path. The other is that the air flow field above the height of the nacelle is different from that below the nacelle. Since you are still in the planetary boundary layer, the airspeed varies with height.

by that single explanation, 12 blades would be even better...

it was also explained to that in very cold weather, the three blade design helps prevent any single blade from gathering too much ice from the wind? so if the top one gets a lot of ice its weight will shift it around? i am no engineer, could be nonsense.

Looks like a support structure innovation is needed

This is only partially related to my other long post here, but it should be mentioned. This article appears to be largely about potential to disrupt the wind industry with outside the box thinking. But in the more than a decade I have been working in this industry the single most disruptive change in project performance was targeting low wind speeds rather than high, and accepting that turbines will have to shut down in higher winds.

The main way this is achieved is to take a huge rotor and put it on a small generator. More energy is lost at high winds, but the ramp up from no generation to maximum is much faster. Since most projects spend the majority of their time along that ramp rather than at rated power this results in large gains in annual energy.

This means that some sites once considered to be marginal to end up being good to very good. One area I've been working in saw a more than 25% increase in predicted energy for the same capital cost with the new turbine types.

I just can't leave well enough alone, and did a quick and dirty very high level analysis:

For a low to middling wind site in the US, with a 7.5 m/s average wind speed represented by a Rayleigh distribution:

Using a GE 1.5-77, the most common turbine in use in the US in the late 2000s, I calculate 40.5% gross capacity factor, and estimate net capacity factor of 33.5%.

Using a GE 2.0-116, one of the most energetic turbines on the market for low-wind sites, I calculate a 53.2% gross capacity factor, and estimate a net capacity factor of 44.1% using the same annual loss parameters as before.

For a hypothetical project of equivalent size we get over 30% more energy every year from the same wind by only changing from the old technology to the new, and we build less infrastructure to support it. The new machines are taller, and we probably need the same amount of total land for the project.

Wind power is still largely a greenfield industry. There's no point in putting expensive (and risky) effort into suboptimal sites when so many optimal sites are still unexploited.

Cringely's assumption that new designs aren't being tried because the industry is stupid is almost certainly wrong. More likely, they're still going after the low hanging fruit, and will start optimizing design for suboptimal locations once they've fully exploited the optimal ones. But there's a lot less profit in using more expensive turbines to harvest less wind.

There are a number of companies and people working on potentially innovative ideas, but it's not an easy thing. Serrated trailing edges and vortex generators are easy enough to test (reduced noise from one, increase energy from the other). Others such as shrouded turbines, or multi-segment blades are difficult.

Another thing vendors are doing now is purposefully running generators beyond their design at higher wind speeds (getting 2.2 MW from a 2.0 MW generator, for example), provided that other operating parameters are measured to be within range. This is usually driven by cooling requirements.

Right. It's a diverse industry with the chance to make some very large money over the next few decades and beyond. The engineering efforts are fascinating. So when Cringely rolls his eyes and smirks at those conventional wisdom know-nothings ignoring the genius of his buddy... well, I suppose it's about what I expect from Cringely.

This over-confidence in your ability to change an industry is a good trait IMO. It powers entrepreneurial activity. While his hypothesis might be wrong in full implementation, it's possible there is some partial innovation here that could come out of testing out this idea. It's possible the constraints faced by large wind mills are not the same for smaller ones, for example.

It's easier to dismiss radical thinking than to continually pursue them in the face of pervasive dismissiveness.

Radical improvements aren't generally from minor refinements.

time for this https://en.wikipedia.org/wiki/Evolved_antenna but with fields of turbines as a system

Wind power is still largely a greenfield industry.

It's not. There are a limited number of good onshore wind sites near big loads. California has only four good sites, and they all have big wind farms. There are lots of sites with enough wind northward from the Texas panhandle, but no big loads within a thousand miles.

But your assumption that the industry is already doing the right thing is exactly what the article is speaking out against. Personally I don't know but I do believe there is a lot of value in questioning conventional wisdom.

Further, some empirical data would be nice. A few different configurations in different areas over a year would be a good start.

These may exist but I've not yet seen them.

On the note of "innovation", looking for the term for vertical turbines, I came across this article from 2011:

"Changing Winds: The Evolving Wind Turbine": http://www.powermag.com/changing-winds-the-evolving-wind-tur...

It has (what appears to my untrained eye to be) a quick overview of various designs. To me it seems that vertical turbines makes a lot of sense - if for no other reason than it would seem like most of those designs get you more "turbine" for your build-costs/materials (and less "inert tower").

I'm not in the wind industry and am not a ME, but rather a EE, but why couldn't you build a big vertical-axis wind turbine and then couple that to multiple generators, a big one and a small one, with gearing that lets the windmill drive either one? Then in low winds, you can drive the small generator at its optimal speed range, and then in high winds, you can switch over to the big generator and drive it at its optimal speed range (the small generator is decoupled in this mode).

Obviously, this would be much more costly because of the additional big generator and the complication of the drivetrain. But it'd let you harvest a bunch of energy when it's really windy. And with a vertical-axis mill, not only would this be better for wildlife (lower overall speeds), the generators would be on the ground, not way up in the air, and driven by a shaft from the mill through its tower, so servicing would be easier and the weight and size of the generators and the drivetrain wouldn't be an issue.

I think you've misunderstood the innovation. The innovation in using a generator that is smaller than the blades and tower are capable of supporting isn't in the light-load efficiency of the generator. Its in the lower capital cost of the electrical system.

From a perspective a little closer to the industry, I think the answer is just "costs".

This idea has higher turbine costs (and site profitability already ranges from impressive to deeply marginal), and the extra profit from the high end isn't excellent. Cringely overstates the money lost in high-wind conditions - most shutdowns are for low wind or to avoid damage in storm conditions, which are rather different than smooth, profitable high wind.

Further, it might offer major operating-cost hits even with ground-based generators simply by being a major break with existing systems. Obviously that's surmountable, but it means that the system has to be better for a lot of sites to be worthwhile.

That said, there are definitely vertical mill projects in the works, and I wouldn't be surprised if some of them have switchover generators.

For horizontal axis turbines two speed generators were historically a thing, usually with two sets of windings which were engaged at different speeds.

This works, but is less efficient and mechanically more taxing on the machine than variable speed, variable pitch angle systems.

There is a very easy idea to achieve this, like the way tesla did to its induction motor, just use multiple windings.

* I don't understand his explanation of starting torque. You can jump-start that problem by other means in the alternator. Torque and power should be decoupled anyway by blade pitch.

* There is such a huge difference between a 12m blade and a 60m blade that I don't see how the comparison is at all relevant. We played with smaller turbines for decades before we reached this sort of price efficiency.

* Betz' law explicitly disavows picking a number of blades: "Assumptions: 1. The rotor does not possess a hub and is ideal, with an infinite number of blades which have no drag. Any resulting drag would only lower this idealized value. ..."

* Betz' law is a three-dimensional consequence of convervation laws, not an observation about turbulent blade interactions. "Consider that if all of the energy coming from wind movement through a turbine was extracted as useful energy the wind speed afterwards would drop to zero. If the wind stopped moving at the exit of the turbine, then no more fresh wind could get in - it would be blocked. In order to keep the wind moving through the turbine there has to be some wind movement, however small, on the other side with a wind speed greater than zero. Betz' law shows that as air flows through a certain area, and when it slows from losing energy to extraction from a turbine, it must spread out to a wider area. As a result geometry limits any turbine efficiency to 59.3%."

* We already have a good idea what a moderate redesign of the fundamentals of a wind turbine looks like; It points downwind, it's huge like the existing turbines, and its two blades bend. They just need to solve the tower strike problem. https://www.technologyreview.com/s/401583/wind-power-for-pen... https://www.technologyreview.com/s/528581/two-bladed-wind-tu...

Furthermore, this idea that nobody's studying the number-of-blades problem is bogus too. When I worked abroad as a research assistant in the Wind Energy Project Group at the TU Delft (biggest tech university in the Netherlands), one of the researchers showed me a very interesting wind turbine that had a massive, elegantly curved blade on the one side and a big blob on the other. He explained, "We've been doing some simulations on these one-blade designs, even though they look goofy. This blob is just a counterweight, it is very cheap to produce because you don't need any advanced materials to use it. So the question is, if you had three times the budget to spend on just one blade, could you make it so good that it would outclass the three-blade model completely?"

In fact I asked why he wasn't going with 5 or 7 or 9 blades (he explained that even numbers tend to be Bad News) and he explained that the big problem was, as you increase the number of blades, the proportion of the rotor disk that consists of blade gets higher, which means the force on the tower component gets larger -- it goes something like the third power of wind-speed. Every few years or so, hurricane-force winds batter parts of Europe, and therefore there is a massively important design requirement that the wind turbine not completely be obliterated during these violent storms. An airplane with a funky propeller can of course be stored indoors when this happens; a turbine would require maintenance technicians to disassemble each one the day that the high-wind forecast was received.

Googling some of these related issues brings me to the page:


However I cannot say with great certainty whether this is the same person that I heard these things from, or just a peer in the same field with the same general conclusions.

The power is also proportional to the swept area of the rotor disk, which increases by the square of the radius. This means the number of smaller windmills will have to go up by the square of the blade length.

12m blades have an area of 452m^2

60m blades have an area of 11,300m^2

At the same efficiency, you would need 25 times more windmills to generate the same power. Even if Cringely's theory is correct that smaller windmills can be made to be more efficient (doubtful), requiring an order of magnitude more physical hardware (towers, generators, etc.) is going to be a killer cost increase.

Did you factor in the increase in running time? If you can run at almost 90% of the time then you get a 4 fold increase in output as compared to the bigger turbines. So instead of 25 times as many, it's 5 times as many which isn't that bad.

That is going off the assumption that he'll get his optimal running time.

His basic assumption is one I've often seen... that a lot of very smart engineers working in a fast-moving and big money industry all make the exact same design mistake, because they're lazy and stupid and follow conventional wisdom rather than clever new thinking.

Which is sometimes true, but far more often, it's because those engineers know something you don't, because working on this problem is their job.

> They just need to solve the tower strike problem.


The fact that this piece spent a lot of time vaguely implying that the Betz limit can be beaten is a testament to its insincerity. The entire point of that equation is that it applies before any real-world concerns are involved.

There are a few good points here (e.g. per-field profit is a different goal than per-rotor efficiency), but it feels a lot like an out-of-field expert assuming that no one in the field has ever been creative.

> I don't understand his explanation of starting torque

That's because Cringley doesn't, either. The starting torque is entirely provided by the wind, not the grid.

I think what he's talking about (not bothering to re-read) is the power required to magnetize the alternator components in the first place, so the alternator works at all. They use electromagnets rather than permanent magnets, because electromagnets are much cheaper, especially at that size. This is a fixed power requirement, so if the alternator can't generate more than that fixed power need to operate, there's no point in running.

Magnetizing power (and other constant-term losses) are a very small portion of the rated turbine power in a doubly-fed induction generator (DFIG).

Edit (one more thing): At this scale, permanent magnet (PM) machines aren't much more efficient than DFIG machines. It turns out that eddy current losses in the stator back iron remain as a significant term in both machines. But for a DFIG machine, the eddy current losses at light load are reduced by quite a bit relative to the losses produced by a PM machine. Since real-world wind turbines end up operating at partial load for much of their life, the effects basically wash out, or are even a net negative for the PM machine.

As an aside, the use of electromagnets occasionally produces hilarious failures. There have been some rare signaling errors that push a huge amount of power through the alternator and turn windmills into giant fans (at least until they shred themselves).

Tower strike, and less well known but probably equally important to longevity: tower thump.

Thanks for the clear explanation of Betz's law.

This is a classic example of sub-optimization (and even if it's hand-wavey pseudo-science and may be wrong, the general concept is still interesting).

Each individual wind turbine is optimized to be the "most efficient" it can possibly be.

But not in the context of the environment, which requires complex control systems and methods to reduce damage in non-optimal conditions.

And not if you take cost and efficiency of the whole system into account; where four times as many small turbines with less complexity run more often and produce more overall output.

But hey, each wind turbine is "optimal." Interesting.

Most complex systems have this property. Even (especially?) your business.

This kind of thinking contributed to American rocketry being trapped in a local maxima for decades. There are many reasons it became trapped, but one of the primary reasons was that rocket scientists would insist on optimising rocket engines at the expense of every other aspect of the vehicle.

"The logic of rocket equation is brutal and inexorable", the NASA rocket scientists would say. "As the performance of the rocket engine decreases linearly, the propellent requirements increases exponentially. Therefore it is imperative to have the highest-possible performance from your rocket engines. The combustion of liquid hydrogen / oxygen is the highest-efficiency chemical reaction, and therefore liquid hydrogen is the only propellant we will consider using for our engines."

All of this was correct, but also wrong. It was wrong in a whole-systems context, because:

A.) Liquid hydrogen is much lower-density than traditional rocket fuels like Kerosene, requiring far larger and heavier structures to carry the same amount of energy, and larger and heavier engines and plumbing and everything else -- and the structural mass of a rocket matters.

B.) Liquid hydrogen will boil off and leak through anything, requiring massive amounts of insulation (again, adding weight), and far stricter operational protocols around the fueled vehicle.

C.) Liquid hydrogen is so cold that it will embrittle and shatter ordinary metals and requires much more exotic and expensive metallurgy.

and finally, D.) The alternative, kerosene, gives you less efficient engines but also much lighter-weight vehicles -- and sure, per that inexorable logic of the rocket equation, you need to use more fuel for the same amount of payload, but kerosene is cheaper than milk so who fucking cares?

Anyhow, the upshot of this is that US rocket scientists spent literally tens of billions of dollars developing hyper-locally-optimised rocketry schemes, most of which failed outright. For the remainder, for every dollar of kerosene they didn't have to buy, they probably spent upwards of $1000 on exotic aerospace hardware. Finally, they gave up and just bought kerosene-based engines from the Russians.

So then there's Elon Musk. And of course there's a ton of brilliant rocket science in the Falcon, but much of the reason for SpaceX's success is because it doesn't optimise solely on the rocket science. They optimise for cost as a whole, and consider factors like design, manufacturing, operations, reusability, etc. to be relevant to the question of cost.

For example: the Falcon 9 would undoubtedly be more efficient if it had a hydrogen-based upper stage. But doing that would cause it to lose most of its commonality with the lower stage, requiring an entirely new design, manufacturing, and operations workforce. Which would cost several orders of magnitude more than the extra kerosene required to fly a "sub-optimal" rocket. The reason they've already cut the price of launch by about 80% vs. (say) the Space Shuttle is because they optimised the whole system, keeping the unique part count and operational complexity as low as possible.

I still sometimes hear old-school rocket scientists grumble about how the Falcon is a less optimised vehicle than the Shuttle, though. They just don't get it. Never will.

Anyhow, that was a tangent. Fascinating to think that wind turbines might be amenable to a similar class of disruption.

> Anyhow, that was a tangent

It's also untrue, US rocketry kept varied propulsion types throughout its history including both RP1-only and LH2-only as well as mixed stages, HTPB and Aerozine. Your painting of rocket scientists as some sort of confederacy of dunce unable to get a grip on tradeoffs is not only inane it's insulting bullshit.

I started reading Ignition! and it is a hoot. I really get the impression that the rocket fuel scientists fixated, not because of personal issues (though hilarity ensues there), but because the search space is damn large (at least while still discovering how fuels interacted). Or worse, it just takes a damn long time to even properly test. So when you found something promising, you really dug into it.

Yes, it's a fantastic book. Not necessarily a good role model for future work, but it perfectly captures the spirit of rocket science at the time: http://library.sciencemadness.org/library/books/ignition.pdf

Everyone who grew up idolizing rocket scientists should read it. If you have problems with missing pages or broken figures, try a different PDF viewer. The PDF has something odd about it that confuses some in-browser viewers.

I loved the section on mercaptans -- they persisted way longer than they needed to on experiments with some of the worst smelling chemicals anywhere.

> It's also untrue, US rocketry kept varied propulsion types throughout its history including both RP1-only and LH2-only as well as mixed stages, HTPB and Aerozine.

My account was simplified, but the tangent was long enough already. It's true that in the early days of US rocketry (through the 1960s), there were a large variety of propulsion types that were experimented and deployed. The stasis didn't really set in until the 1970s.

Since then, it's also true that solids and hypergolics continued to have a role, both as strap-on boosters (because gravity losses) and in military systems (and their derivatives) where cryogenic liquids aren't advisable. (The military was always more whole-systems and pragmatic about their approach to rocketry.) Finally, it's also true that non-LH2 legacy rockets (and their closely-related derivatives) continued to fly (because switching costs).

However: in civilian rocketry (eg. NASA), as far as new developments were concerned, the picture is as I described. I was peripherally involved in that scene during the 1990s and had many people at NASA and LockMart tell me personally, quite explicitly, that specific impulse was very nearly the sole determinant of rocketry, and that therefore no fuel other than LH2 would ever be considered. Feel free to look at the kind of arguments cited during the fuel-density wars on sci.space.policy if you want a feeling for the kind of vehemence with which this opinion was expressed.

So, yes, I stand by my story. From the mid-1970s through the mid-2000s, US rocketry development was wholly paralysed, due in very large part to these kind of attitudes and overly-narrow optimisations. As evidence, I present the NASP, X33, and SLI, amongst dozens of smaller, equally failed initiatives. Feel free to counter with some examples of successful new rockets (as opposed to derivatives like the Pegasus, Taurus, and Delta III) developed during that period. The only examples you'll be able to find are Delta-IV -- which switched to LH2 at frankly mind-blowing expense, has had an uninspiring career, and is about to be axed -- and the Atlas V -- which gave up and just bought LOX/RP1 engines from Russia, since the US had lost the expertise to develop decent LOX/RP1 engines itself.

I'm not saying that the US civilian aerospace industry was a confederacy of dunces, just that for 30+ years it had the productive output of one. It was certainly well-supplied with smart people, but yes they were absolutely unable to get a grip on tradeoffs, and it showed.

> is not only inane it's insulting bullshit.

You've got a lot of HN Karma, but you haven't yet learned that people here prefer evidence-backed arguments to ad-hominem attacks?

One fun counter-argument to my thesis: the FastTrac engine which was developed in the late 1990s: https://en.wikipedia.org/wiki/Fastrac_(rocket_engine)

At the time, however, I recall hearing endless griping from various corners that NASA had the gall to fund a non-LH2 engine. Internally, this was justified as being nothing more than a cheap and cheerful way to get the X-34 to its flight regime -- definitely not a serious rocket engine, no sir! That was LH2's job! Everyone knew that!

The support of the RP1 rebels within NASA wasn't enough to keep it alive, and the program was cancelled after a few years. Later, it was resurrected as the template for SpaceX's first generation engines. So I personally consider this to be the exception that proves the rule.

>You've got a lot of HN Karma, but you haven't yet learned that people here prefer evidence-backed arguments to ad-hominem attacks?

Your evidence is:

>I was peripherally involved in that scene during the 1990s and had many people at NASA and LockMart tell me personally, quite explicitly, that specific impulse was very nearly the sole determinant of rocketry... Feel free to look at the kind of arguments cited during the fuel-density wars on sci.space.policy if you want a feeling for the kind of vehemence with which this opinion was expressed.

Your entire point is based on bulletin board discussions and anecdotal evidence from being peripherally involved with rocketry in the 90s (which given context, I'm taking to mean "I hung out in space forums and bulletin boards and talked with people who claimed to be rocket engineers.")

I enjoyed reading both of your posts about this (with a grain of salt), but it's a bit silly to call someone out for lack of evidence after writing several hundred words without a single piece of hard evidence supporting it.

> Your entire point is based on bulletin board discussions and anecdotal evidence from being peripherally involved with rocketry in the 90s (which given context, I'm taking to mean "I hung out in space forums and bulletin boards and talked with people who claimed to be rocket engineers.")

Oh for fuck's sake. I don't like arguments from authority, but if you really want one: yes, I hung out on internet space forums in the 90s and am thus aware of their contents. But I also was a member of the Space Access Society and regular attendee of its conferences; an organiser for the National Space Society and regular attendee of its conferences; and an organiser and founding member of the Mars Society and regular attendee of its conferences. In this context, I was personally well-acquainted with folks like Gary Hudson, Robert Zubrin, and Buzz Aldrin, as well as innumerable lesser-known individuals from NASA, Boeing/Lockmart, and the various alt.space renegades. The stories I tell come directly from my contacts with them.

Furthermore, the "evidence" I provided was citations of the NASP[1], the X-33[2], and the SLI[3]. The first two represented NASA's flagship attempts to develop new space-launch systems during 80s and 90s; they failed due to weight growth and integration problems stemming from over-optimisation of the (LH2) propulsion system at the expense of all the rest of the vehicle's systems. By the time of the SLI in 2000, RP1 was starting to find a (small) place at the table again, but the program still failed due to too narrow a focus on propulsion optimisations. I figured that anybody familiar with the space industry (as the person I was replying to seemed to be) should be familiar with these failures and their underlying causes; they are not exactly secrets.

1: https://en.wikipedia.org/wiki/Rockwell_X-30

2: https://en.wikipedia.org/wiki/Lockheed_Martin_X-33

3: https://en.wikipedia.org/wiki/Space_Launch_Initiative

I'm confused now....so you're saying that in the history of US rocket implementations (in actual deployed projects), the optimal design was used every time (and therefore the comment you are replying to is completely incorrect)?

You're confused only because you're trying to pick between a false dichotomy. Nkoren basically stipulated that US rocket scientists were too shortsighted/ignorant/stupid to look past their tiny niche to realize that their hyperoptimization for liquid hydrogen was a net negative. Masklinn asserts that it's not true that they were so hyperfocused on liquid hydrogen that they ignored tradeoffs and alternatives, and that in fact they were flying kerosene rockets the entire time as well.

I'm absolutely certain that Masklinn did not assert that the optimal design was used every time or that NKoren's comment was completely lacking any accurate information. Neither of these assertions needs to be made to dispute the central idea that US rocket scientists are too incompetent to even consider alternative fuels or broader design tradeoffs.

Ah, thank you.

> Anyhow, the upshot of this is that US rocket scientists spent literally tens of billions of dollars developing hyper-locally-optimised rocketry schemes, most of which failed outright. For the remainder, for every dollar of kerosene they didn't have to buy, they probably spent upwards of $1000 on exotic aerospace hardware. Finally, they gave up and just bought kerosene-based engines from the government.

What do you mean by this? The Mercury Atlas launch vehicle used kerosene / LOX in its first stage. The Saturn V used kerosene / LOX in its first stage and LOX / LH2 in subsequent stages.

Also, for the majority of spaceflight, both manned and unmanned, "US rocket scientists" were the government, right? Especially after WWII.

Sorry, I should have been clear that I was talking specifically about the era from roughly the mid-1970s until the mid-2000s. Prior to that, US rocket scientists were wildly innovative and also rather good at trade studies. Subsequent to that there was Elon Musk. In the interim, several decades of rot while stuck in a local maxima.

I wonder how much of that was a set of theoretical blinders (as you say), vs. how much of it was just the practical result of the huge demands of the Space Shuttle program.

The STS famously had all sorts of contradictory goals (some came from outside NASA) that resulted in sub-optimal design tradeoffs--which in turn required the highest-performance engines NASA could get their hands on.

From the outside, looking back, it seems like the Space Shuttle was so (unexpectedly) demanding that it basically took over NASA for 25 years. Maybe there just weren't enough resources to pursue other launch vehicle ideas, even if people there recognized the need.

As the OP has already responded, he's talking about the 70s and onwards until Musk came on the scene.

The days up to and including the Apollo missions were the US's glory days; all the great innovation in rocketry was happening then, and it culminated in the Saturn V, which was a big success (esp. considering the level of overall technology back then, and what they were trying to do). And, as you pointed out, it used kerosene. It still remains (I'm pretty sure) the largest and heaviest-lift launch vehicle in all of human history. We still haven't surpassed it, and it was designed in the 1960s.

What have we done since the Apollo program was canceled early? Nothing as notable. A bunch of really expensive launches to LEO with an overpriced space-going pickup truck basically. And a bunch of small launches (satellites, probes, etc.) using rockets that were designed way back then for launching nuclear weapons. We're still highly dependent on rocket engines built by Russia. The whole Space Shuttle idea itself was stupid: the costs and complexity were huge because of the idiotic requirement of being able to retrieve military satellites from orbit and bring them back intact and in secret. If it weren't for that, they never would have come up with such an absurd design, and would have just stuck with much cheaper capsules like the Soyuz and the upcoming manned vehicles by the US.

> What have we done since the Apollo program was canceled early? Nothing as notable.

ISS? Hubble? Various Mars rovers?

Sure they aren't as notable as putting humans on the freaking moon, but that's also a pretty impossibly high bar to match. The only thing that would best it is humans on Mars.

> We're still highly dependent on rocket engines built by Russia.

That's not entirely true. The Soyuz-U does have by far the most launches of any system at 771, true. But the still successful Atlas II (63 launches and also the most reliable system to date) used all Rocketdyne engines. The newer Atlas V does use a Russian engine for the first stage but Rocketdyne for the second.

The Delta IV is also all Rocketdyne. It's also entirely LH2/LOX and yet weighs less than the Falcon 9.

>ISS? Hubble? Various Mars rovers?

As I said before, nothing as notable.

>Sure they aren't as notable as putting humans on the freaking moon

And it seems you agree with me!!

>but that's also a pretty impossibly high bar to match. The only thing that would best it is humans on Mars.

Wrong, there's plenty of things that would best Apollo. A serious space station (like the rotating one in 2001) perhaps at a Lagrangian point, a Moon base, Moon or asteroid mining operations, orbital construction of a longer-range spacecraft, creation of nuclear spacecraft engines, etc. Basically all the stuff we dreamed about back in the Apollo days and then never bothered to do and just forgot about.

>What have we done since the Apollo program was canceled early? Nothing as notable.

Their robotic missions have been hugely successful.

Consider just the number of them: Viking, Voyager, Galileo, Deep Space, Cassini, New Horizons, Dawn, Kepler, and Juno. That's not even counting our many Mars probes. It's pretty impressive to launch a new interplanetary probe that frequently, and every one of them accomplished its mission.

We have now sent probes to every planet in the Solar System, two dwarf planets, asteroids, and comets. If we are still in an era where crewed interplanetary travel is impractical, we're making the most of it with these uncrewed missions.

And how many of those probes required entirely new rocket technology, instead of being launched on top of a system designed decades ago to launch ICBMs?

Probes are nice for science, but they really don't inspire people the way manned flights, space stations, etc. do. Nor do they require nearly as many resources; they comparatively cheap and simple. The resources poured into Apollo were enormous, and the technologies derived were hugely significant. What technologies were derived from New Horizons? Probably none. I'm not saying it shouldn't have been launched; it was absolutely a worthy project. But it just doesn't compare to Apollo in any way. So as I said before: "nothing as notable".

> The reason they've already cut the price of launch by about 80% vs. (say) the Space Shuttle is because they optimised the whole system

No, it's because their system is much less capable and benefits from having a starting point of 50 years of accumulated knowledge.

Take Musk & the Space-X team and plop them in 1980 and you would not get the same Falcon 9 that exists today. You wouldn't get anything close.

Comparing the space shuttle to the Falcon is idiotic, anyway. The shuttle had capabilities that no other launch system has had or will have anytime soon (for better or worse).

They also cut the cost of launch heavily when compared to ULA ... and ULA also benefits from all the advantages you describe.

https://en.wikipedia.org/wiki/Hydrogen_embrittlement is caused by hydrogen diffusing through the metal, not by cold. Cold actually slows the diffusion.

Howto colonize the moon, build CN tower size rail gun and rail gun the parts to build another rail gun CN tower on the moon

you know what would be funny if they make a CN tower size rail gun and rail gun materials to the moon to build the same thing LOL

did scientists rule out rail guns ?

Yeah, another example that comes to mind is Combined Heat and Power (CHP) plants, where the efficiency of power generation is actually lower, but the heat that's normally wasted is made useful.

Erm, I don't know if I trust Cringely when it comes to this sort of thing. He sold a reality show to PBS, "Plane Crazy (1998)"[1] with the promise he could design and build a small plane in 30 days that was unlike any other that had ever been built.[2]

His engineer just flat out refused to produce any plans for this design. He tried to make something like his plane happen anyway, going without sleep for weeks, and had a meltdown on camera. The show eventually had to be about him giving up on his cherished design and building a throwback to biplanes, with a family of artisans who are experienced in building them.

I had the feeling that Cringely was trying to channel Steve Jobs and it didn't work out. (Note: Jobs drives other people to do impossible missions without sleep, not himself, and doesn't display his work until it's ready, giving the appearance of effortless superiority).

Anyway as for this wind farm idea, the evidence of his friend's alternative propeller design is interesting. But let's also note that that this friend chose not to pursue wind farms, maybe for a reason.

[1] http://www.pbs.org/cringely/pulpit/1998/pulpit_19980724_0005...

[2] EDIT: I am not an aviation person, and my memory of this is poor, but from Googling I see apparently he wanted to make it out of unusual materials, have foldable wings, and put the engine behind the pilot. I have a memory of his design requiring the pilot to straddle the drive train to a front-mounted propeller. I don't know how problematic that is, but I remember it as being presented as a major problem.

EDIT 2: To be honest I feel a bit bad now about this being a top-voted comment, as Cringely learned a lesson on camera that many startup people learn behind closed doors – confidence is great, but trying to innovate in too many directions at once will kill you. Maybe that means that he is more cautious now, so perhaps he's really sure this thing will work. On the other hand, it was the first thing I thought of, that maybe he doesn't have a great track record with aviation iconoclasm.

I had the feeling that Cringely was trying to channel Steve Jobs and it didn't work out.

Tries to channel Steve Jobs and it doesn't work out. This is something like common Silicon Valley misstep #2.

> His engineer just flat out refused to produce any plans for this design Do you know why? I'm thinking maybe it's because it was dangerous for the pilot?

Sorry, I'm relying on my memory of a show I saw like 20 years ago. I know nothing special about aviation. But I just found a contemporary thread about it here from other homebuilt aviation enthusiasts.


The P-39 was a successful WWII fighter plane with a mid-engine:


Russian pilots loved it. British and American pilots, not so much.

Yeah, that is true. Mainly because the deletion of its supercharger for production, but also relevant to the topic here, pilots didn't love having that drive shaft between their feet.

Still a functional design though, with certain advantages.

Who the hell was responsible for all the supercharger deletions? If this was done by a bureaucrat, then this is a prime example of tremendous damage done by bureaucrats to their own side in wartime. P-38. P-39. I'm sure there are other craft that were effectively nerfed.

I don't think that history is well understood, and there are a lot of urban legends around it, I think. It may have been a political/bureaucratic thing. It may be that Bell needed to stop fiddling around with design and start manufacturing airplanes before they went bankrupt. It may be that we wanted a second-tier fighter to give to some of our less friendly allies, that we could beat if we had to. It may be that Bell just couldn't get it to work right. Another story that I have heard is that they were fearful of losing the supercharger hi-tech to enemy hands. I don't know which, or to what degree any of those stories are true.

The juiced up v2, the P-63 King Cobra had a proper supercharger system. It was more capable at high altitude - though the USAAF felt that the P-51 was better.

After the war, the remaining few P-63s (and P-39s that could be retrofitted with better engines) dominated air racing. Flying very fast at low altitude and turning on a dime (that mid-engine) generally out flew the P-51s. But since most of them were sent to the Soviets and elsewhere, and our own leftovers were simply scrapped or used for gunnery drones, there are very few left. I have never seen one in person.

Slightly relevant, here's a really weird wind turbine designed by a computer: http://m.youtube.com/watch?v=YZUNRmwoijw

The note on the video is quite funny:

Note: I have since discovered I used the wrong viscosity for air on this experiment, so the results aren't valid for use on the earth. (Maybe Jupiter.)

Ah, well. It's still interesting. The design of the turbine is really crazy and not what I would have expected in any environment. So I suspect if he corrected the parameters, it would still come up with a crazy and clever design for Earth use, that humans wouldn't think of.

While I missed that, I'd have to agree that note is quite amusing. Oops, wrong planet.

That was an interesting video, but it was restricted to a 2D simulation on a vertical-axis turbine with exactly 3 blades.

A more intricate genetic algorithm that runs a 3D wind model and accounts for the cost of manufacture would almost certainly produce some more novel solutions that completely demolish our preconceived notions of what turbines should look like, just like the "jellyfish" cross-section. But it would also probably not effectively scale beyond the model size. Genetic algorithms almost always exploit any previously hidden little flaws you may have in your model simulator, such as the rounding error on floating point numbers at the limit of their precision, or even the way in which you represent airflows. They evolve to maximize performance in the modeling environment, so if your model is not perfect, the solution does not always translate to reality.

As such, you always have to test the evolved solutions in the real world before you can say they are better than the designed solution.

Oh yes, this is just some guys weekend project with a simulator. If I wanted to make the optimal wind turbine, I'd add some random noise in the simulator to account for imperfection in the simulation, and do lots of real world tests. Also I'd allow the GA to change more than just a radial shape. But all that adds difficulty and expense.

In fact I've thought about what the optimal way to do real world experiments is. Assuming you want to minimize them as much as possible, if making real prototypes is expensive.

I think you could use machine learning on the results of real world experiments to invent a model. It would predict how well each design would do. Then you could optimize the design to the machine learned model. Which of course won't be very accurate. But then it will give you a new test to do in the real world, which will give you data to make it even more accurate.

You would likely need to do one of every N iterations as a real-world test, and significantly increase the reward for winning a real-world test over a simulated-world test, such that the winners and close runners-up of the real-world tests effectively earn immunity from complete elimination until after the next real-world test round.

Additive volume-printer or subtractive CNC machinery would almost be required to make the physical test models.

Other commenters are focusing on the validity of the sim as a scorer, but there's some other issues here.

Doesn't it seem to converge a little aggressively?

How do you feel about the potential bottlenecking pressures of a breeding pool of size... six?

The parameters of the genetic algorithm are so overwhelmingly ready put things permanently askew from random variations in early stages of the trial sequence that I'm not sure the sim really has a significant impact on the result at all. The author even seems to be aware of this, when he admits running it again does not generate similar results, and starting with a single piece of bias in the initial sample causes that result to dominate.

Genetic algorithms aren't something that can be thrown at a problem with zero attention to the parameters. Sorry, no algorithm is that magical.

All optimization algorithms tend to get stuck in local optima. It's great to try to tune the parameters through experimentation, but he only had enough compute time to run the full GA once or twice.

Generally I think it's best to use a small population, or even just hillclimbing. But with the smaller population it should run and converge much, much faster. Then you can run it multiple times, and take the best result.

I have to wonder if there are some imperfections in the simulation which cause it to evolve toward a blade that's optimal for the sim, but not as good in real life.

He talks about 20 minute tests, and then later uses a 12 hour test and gets a significantly different power number. I wonder how differently the evolution might proceed if he just had more power to run the full tests on each generation.

That was really fascinating -- thank you!

I'm not saying he is wrong, but he makes some bold claims without giving any proof.

Some examples:

> Twelve blades is a nice number.

Why twelve? Why not 50, it's a nice number as well.

> Lipps turbines can operate in faster winds [...] turbines could be allowed to run 24/7 in any wind with no computer

So even in the strongest winds turbines with 40 feet blades do not need to be stopped?

> using permanent magnet generators instead of alternators, but those are more expensive > Use permanent magnet generators leading to [...] even lower cost.

Which is it now?

> what matters isn’t power efficiency per turbine so much as power production per acre of wind farm.

Isn't it rather electricity production efficiency in terms of invested capital?

I get the feeling that the best answer to the question is that empirical testing (perhaps by simulation) points out that three is the optimal number of blades.

This leads me to the question: is it possible to determine a good rotor design by using optimization techniques such as simulated annealing or genetic programming? Or are the simulations too costly?

I can help with this a bit.

The simulations are quite difficult - flow simulation is well-established, but it's a big step from that wind farms. You need to simulate many turbines interacting at a specific site, under a variety of conditions. That's not the problem with modeling single turbines, though.

Rotor design is hard to simulate productively for the same reason that Cringely's analysis is flawed: many of the biggest factors are unrelated to everyday running.

- Even blade counts create resonance patterns that stress your tower.

- High solidity designs suffer more stress in storms (even while stopped), so they break more

- Noise interferes with putting rotors near houses or over pastures

- Storage is difficult and consistency is valuable, so expanding the operating range up to high winds is less useful than expanding it down to low winds

And so on. If you model pure efficiency, the sims are pretty easy. If you model real value, you either can't do it, or you get a search space so jagged that finding maxima is hopeless.

Looks like a fine opportunity to ask - whatever happened to vertical axis wind turbines?

They sounded like they had a bunch of advantages, not least a much higher tolerance for extreme wind conditions, less stress on long (suspended) blades, possibly less gearing issues in translating motion back to the ground - but presumably they had / still have distinct disadvantages?

Even sexier (and less field-tested) than vertical turbines are windbelts.


> Prototypes of the device are claimed to be 10 - 30 times more efficient than small wind turbines. One prototype has powered two LEDs, a radio, and a clock (separately) using wind generated from a household fan. The cost of the materials was well under US$10. $2–$5 for 40 mW is a cost of $50–$125 per watt.

I think the reason plainly is that they are not competitive, perhaps because their advantages aren't important enough disadvantages for horizontal axis turbines.

Wikipedia has a short section:


I think people tend to forget that the big wind turbine manufacturers today started out small, experimenting with various designs before they settled on the three-bladed model. At the moment there's a lot of accumulated research and infrastructure present that allows them to erect giant 3-6-8 MW turbines that can take the hammering of the weather for > 20 years. Competing against this is really, really hard, you really have to a big advantage in your favor and perhaps also decades of research and development.

Scaling issues, I think - they need to be supported at the top as well, and they're dependent on how much weight and wind force the bearings can take.


We all love the story about the clever little guy who thinks outside of the box taking down the big giant corporation who does things the way they have always been done. Cringely trys to tell this as such a story, or could be, or could have been. But there is really no evidence backing it, just his desire to tell a good story.

One graph is worth thousand words.

Rotor power coefficient vs. tip-speed ratio.


You have a computer with servos and winches fly parafoil kites to generate power from wind. This is definitely the theoretically optimal answer. It's also very low capital intensity.


Lots of omitted details there. A kite can pull its tether from one location to another location of lower potential energy, but how does it get back to the higher-energy location? If we're talking about a circular train on a circular track, half of the kites must continually have either a lower-drag configuration or a lower-wind altitude. That's plausible, but that's a lot of additional mechanisms, plus a lot of "cancelled-out" wind traction, plus a lot of friction as the train rolls around the track. Will there be power left over for electricity generation? Probably, but it isn't clear that it will be worth all the trouble. If a reasonable prototype exists, it should have been in the video.

In the 1970s and 1980s there was much more variety in wind turbine design. There were two bladed machines, multi-blade ducted turbines, Darrieus rotors, and other exotic technologies. Outputs were in the 50KW range. Pacheco Pass in Northern California had examples of most of those. Some didn't work too well. Loss of blade accidents were common in the early days, with blades thrown considerable distances.

The three-bladed machines won out commercially. Machine size went up because output vs cost decreases with size, at least up to 1-2 MW. Lots of little machines were a pain to install and maintain.

Wind generators used to be AC generators synchronous to the grid. But with higher power semiconductors available, putting a big AC-DC-AC converter on the output to sync it to the grid is becoming popular.[1][2] This allows generating some power during low-wind conditions, and provides much more adaptability to wind gusts. When the wind speed changes, the blade pitch is adjusted to compensate, but on big turbines, this takes tens of seconds. Being able to adjust electrically in milliseconds avoids power grid transients.

The push for permanent magnet motors in wind turbines is more about converting to direct drive and getting rid of the gearbox. Wind turbine gearboxes are a huge pain, wearing badly for reasons that were only understood in the last few years.

[1] http://www.theswitch.com/wind-power/ [2] http://new.abb.com/motors-generators/generators/generators-f...

Pacheco Pass or Altamont Pass?

Right, Altamont Pass. The Veg-E-Matic for birds - a long, narrow valley filled with row after row of medium-sized wind turbines.

Indeed it is.

Relevant Low-Tech Magazine entries on wind-power, and small windmills:

Urban windmills harm the environment [0]

> A small windmill on your roof or in the garden is an attractive idea. Unfortunately, micro wind turbines deliver hardly enough energy to power a light bulb. Their financial payback time is much longer than their life expectancy and in urban areas they will not even deliver as much energy as was needed to produce them. Sad, but true.

Small windmills put to the test [1]

> A real-world test performed by the Dutch province of Zeeland (a very windy place) confirms our earlier analysis that small windmills are a fundamentally flawed technology

(Note that the picture shows that almost all windmills tested had three blades)

Wind powered factories: history (and future) of industrial windmills [2]

> In the 1930s and 1940s, decades after steam engines had made wind power obsolete, Dutch researchers obstinately kept improving the – already very sophisticated – traditional windmill. The results were spectacular, and there is no doubt that today an army of ecogeeks could improve them even further. Would it make sense to revive the industrial windmill and again convert kinetic energy directly into mechanical energy?

Unlike this story, which certainly sounds interesting but shares no real data to back it up, Kris de Decker thoroughly digs through sources to write articles backed up by available data as best as possible.

[0] http://www.lowtechmagazine.com/2008/09/urban-windmills.html

[1] http://www.lowtechmagazine.com/2009/04/small-windmills-test-...

[2] http://www.lowtechmagazine.com/2009/10/history-of-industrial...

As a kid I always found it interesting that (some?) Spitfire had 4 blade propellors and the main adversary, the [Edit] Bf109 had 3 [1] and wondered, shouldn't there be an optimum?

[1] Not sure both changed the number of blades during WWII.

You mean Bf109 I think. The P-51 started 3 and then moved to 4. Ditto P-47. FW-190 and F6F stayed at 3 whole time afaik. Tempest started with 4. So it varied. But there is a trend of the early (1939) designs to have 3 and the late (1944) designs to have 4. I guess available power from the engine plays a big role, as engines got more powerful they started fitting 4 blades. Using the extra power on 3 blades would require longer blades (which is problematic), spinning them faster (again, problematic as tips reach sound barrier) or increasing the pitch (I guess there are aerodynamic limits for that).

This is a really cool write-up. Another thing that might be of interest was the performance of the aircraft. There's a guy in Texas with 6 non-flying 109s, a couple P-51s, and some other stuff for sale as a lot. He's a former stunt pilot, flew in the movie 'Battle of Britain' and several others.

In his words, the 109 handled much better at the limit than the P-51. The P-51 could dive and go very fast, but with poor control. In his opinion the 109 was the superior aircraft.

Not sure if it relates at all to the prop discussion, but maybe in the grand scheme of engineering? Those warbirds are fascinating pieces of hardware to me.

Thanks, how emberrassing, yes Bf109.

"I guess available power from the engine plays a big role, as engines got more powerful they started fitting 4 blades."

Good one.

Interestingly the prototype Bf109 had two blades.

I wonder if it was a carry over from the first world war when guns fired through the propeller, so the more blades the more chance of shooting it off? (There were systems which regulated when the gun would fire to prevent this happening)

Small turbines do exist. One was installed on This Old House recently: http://www.thisoldhouse.com/toh/tv/ask-toh/video/0,,20961006... (jump to about 15:00)

But, it does have three blades.

I like the idea of wind turbines, but in practice I think PV is the way to go (long term). I realize that for now it's a blend of technologies, but PV doesn't kill millions of birds and bats. I grant you, it's better than burning coal, but still we can do better eventually.

House cats kill 1,000 times more birds than wind turbines. Even cell towers kill more. It's nonissue.

They won't kill the same kind of birds, though. For example, there's a new rule raising the number of bald eagles which can be killed by wind turbines to 4,200 per year. I'm guessing that house cats kill few bald eagles.

It may still be a nonissue, of course, but the comparison with cats doesn't tell the whole story.

Fair point, I was just responding to the idea that wind turbines would kill all the birds, which isn't realistic. As a percentage of the bird population, it's negligible.

I don't see any reason why bald eagles would be more likely to be killed by turbines than other species of birds. If only 0.01% of birds are killed by turbines, then they would only kill 1 bald eagle a year out of thousands.

Regardless, this is more of a reason to invent solutions for repelling birds from turbines. Maybe we could come up with noises or lights that repel them. Or drones, or a water cannon robot. But I'm not certain it's even an issue.

The current rule is something like 1,200/year. There are about 143,000 bald eagles in the US. The 4,200 number is set at a level which they think the species can sustain. I don't know why bald eagles would be more likely to be killed by turbines, but apparently they are:


"Not all bird species are equally vulnerable to wind turbines. Eagles appear to be particularly susceptible."

Not all birds fly the same way, in the same regions, at the same altitudes. Balds eagles tend to soar and hunt in places we like to put wind turbines. Small birds tend to move smaller distances, often in about 100m around a water source.


Wind turbines kill <this type of bird> is highly location specific; so again, saying wind turbines kill lots of bald eagles is also not telling the whole story.

And eagles may kill smaller birds, so the net might be positive? More sub-optimization.

...Eagles aren't generally bird hunters. Bald eagles for instance, eat mostly fish.

It's a nice thought though, just kill off the big birds, and watch the benefits "trickle down" to the little birds. /s

You're going to have to provide documentation of this.

Of what? The new rule allowing for 4,200 to be killed each year is a simple Google away. The conjecture that house cats don't kill many eagles is just common sense, and if that's what you're referring to then I assume you're just making a joke.

House cats should be just that, house cats. Their environmental impact is detrimental. Plus, all of the neighbor cats shit in my raised bed gardens and piss me off.


It's not so bad. We've killed most the native predators, so cats are the only thing keeping populations under control. And like most predators, they generally target sick and weak prey. And the cats are just trying to help fertilize your garden!

> And the cats are just trying to help fertilize your garden!

Yes, that wonderful, fertile cat shit full of Toxoplasma and other parasites. What a great addition to my garden! Not to mention that wonderful feeling and smell when your sink your hands into cat shit while prepping a garden bed.

Your other point, in regards to keeping populations under control, is way off the mark. http://www.nature.com/ncomms/journal/v4/n1/full/ncomms2380.h...

Keep your cats indoors, people! They're great pals to have, but inside.

That study doesn't necessarily contradict anything I said. I agree that cats are now the largest predator species of birds, but we've killed most the other predators. It also credits unowned cats as doing more than half of the predation, so keeping owned cats indoors wouldn't fix it.

Per capita, or overall?


As of 2012, the estimate is something like 225 thousand wind turbines around the world. The best estimates I could find for domestic cat populations is between 200-600 MILLION.

I have no idea why per capita estimates are relevant at all in this context. Wind turbines are vastly larger than cats and serve an entirely different purpose.

The point is birds are not going to go extinct even if we increase the number of turbines ten fold. It wouldn't even make a dent in the bird death rate, which cats are only a small part of.

Hm. Birds multiply by X every year in the spring. Yet each fall we have about the same number of birds as last year. Brutal fact: the fate of almost all birds is to be eaten. If not by cats, then other creatures that live in the cat niche too. Remember domestic cats are a tiny fraction of the world population.

Which world population?

Domestic cats surely dominate all other cats in population.

I didn't realize that to be concerned about something, their extinction had to be on the line. Then again if that is your standard, I can see why you keep talking about birds, instead of bats.

If it's not extinction, what's the issue? We accept that millions of birds die every year. They have to or the population would explode. Everything from cell towers to glass windows kills ridiculous amounts of birds, and no one cares. Why are wind turbines, which don't even make a dent in that, somehow special?

I don't see why the numbers would be significantly different on bat death rates than bird death rates.

PV can kill or destroy habitat of other creatures, though this is probably almost entirely avoided in certain circumstances (rooftop installations, for one) where the damage has already been done.

Everything we do, does that. Fortunately the places we put PV tend not to be virgin forests or other places we haven't already destroyed for our benefit.

Wind turbines aren't built in virgin forests either. They're generally in farmland, which is pretty well ecologically destroyed already.

In California they seem to go just about anywhere. Sure not virgin forest, but maybe native savannah?


I never claimed that they were, and bats and birds are prevalent in farmland.

There is a lot of bad information here, and it appears there are others in these who are also better informed than the author. Let me just hit up a couple of points that are fundamentally wrong, though.

- "Conventional wisdom says wind farms should have their turbines placed in such a way that they don’t interfere with each other, the fear being that placing one turbine too closely in the shadow of another will reduce the efficiency of the showed turbine." True, and this is why we have wake models based to predict the losses from other turbines and optimize placement.

- "The rule of thumb, then, is that turbines be placed no closer than seven diameters apart. Keep that number in mind." Not true. You may find that a 7x7 array is relatively common in offshore applications, but a typical onshore application is more likely to be between 2-4 diameters apart in a row, with rows 7-13 diameters apart front to back.

- "Oh, and turbines are placed seven diameters apart. That’s it, no CFD." Wrong. But CFD is generally computationally complex, so we usually use models with reduced fluid dynamics equations to make it possible to iterate quickly. See previous comment about wake models.

- "In some cases wind farm automation can cost as much as the turbines, themselves." I'd like to see these magical cases. A typical 2 MW turbine costs $2 million to purchase, and about $3-3.5 million total as part of an overall project of 50 turbines. SCADA is a minor fraction of this, as is operations.

- "Shorter blades are stronger than longer blades, so the Lipps turbines can operate in faster winds." This is a non-issue. There are very few sites in the world that require even the highest wind speed turbine designs; most of the world is less windy, and the majority of sites benefit from using turbines designed for lower winds.

- "Use permanent magnet generators and the turbines could be allowed to run 24/7 in any wind with no computer control required at all, leading to more production at even lower cost." Computer control of turbines is a non-issue, and the cost is minimal relative to the raw materials cost of the machines.

- "This is because they use alternators that consumer electrical power to energize their windings so there is no point in turning-on the alternator (energizing those windings) until there’s enough wind to generate a net positive amount of electricity." This is only a little bit correct, and mostly not. Wind turbines by design generally need to be connected to the grid to run, but winding energization is not why they don't start generating until there is enough wind. Turbines are generally on all the time, and typically consume anywhere from 10 to 50 kW at idle. And I don't know why he's using the term "alternators" to describe the turbine generators. The most common generator type is a doubly-fed induction generator, but squirrel cage induction generators, permanent magnet generators, and synchronous generators are often used. Usually turbines are connected to the grid through power converters which allow them to run at various speeds while remaining electrically synchronized with the grid.

- "Remember the diameters are smaller so instead of hundreds of turbines we’re talking about thousands of turbines for the same wind farm. Imagine a field of mature dandelions." This is actually a problem. When you can get 100 MW with a 50% capacity factor by building 50 machines in one township in Nebraska, why would you want to build 1,000 machines instead? How is that less complex?

- "Try breaking into the industrial wind power business without at least $1 billion in capital. It can’t be done. The incumbent companies like it that way, too." Manufacturing is capital intensive. News at 11.

- "Lipps wind farms could be closer to cities and therefore have lower transmission losses, further increasing power output." Wind farm placement is about where the wind resource is. It's an economic decision.

- "The result of all this not starting and then stopping is that throughout the year an average workload of 23 percent is reached by inland wind farms, 28 percent for coastal farms and 43 for off-shore." I have to assume his "average workload" here (a term I've never heard in the industry) is equivalent to capacity factor, which is the ratio of actual energy produced to the maximum possible. Most new projects in the windy areas of the US have predicted capacity factors of greater than 40 percent. High wind losses are typically very low, and online time is typically very high.

- "China will build the heck out of those smaller blades." China is also building the heck out of the larger blades. China has more wind capacity installed than any other nation.

- "And no insane cows, either. Cattle can’t be pastured under wind farms because the motion of the turbine blades and especially their sound drives cows crazy." Tell that to these cows https://www.flickr.com/photos/ashcreekphoto/7793429362 (did he even do an image search before posting that? I've built wind projects on cattle ranches.)

Why does this post use such an old, crappy US wind map? Why not the newer DOE wind maps available at http://apps2.eere.energy.gov/wind/windexchange/wind_maps.asp

I'm sure I could go on, but this is just a fundamentally misinformed article. It's trying to make an aerodynamic argument (which I am not qualified to judge) using a mess of bad or incorrect information.

Came here to point out that I live next to a dairy farm smack dab in the middle of about (100) 1.5MW turbines. Cows aren't particularly intelligent animals to begin with, but they certainly don't suffer from fainting spells just because they graze under a huge turbine.

Other (industrialish) things cows don't mind: - Tractors - Feed grinders - Silage conveyors - Automatic Milkers - Being lifted to a horizontal position to have their hooves trimmed. - Having their eggs artificially inseminated.

I was unsure about the credibility of Cringely on the topic of turbine blade count right up until I read this statement. Then I was sure about his credibility.

Thanks for the detailed, informed post!

The 2016 tag is not really necessary; this was published today.

"why... very often the turbines aren’t turning at all?" Someone told me that demand varies and it's easier to shut down a windmill than a nuclear reactor.

More blades and closer spacing between windmills optimizes power / land area. But what matters is power / capital cost.

He tried to touch on that - making the blades shorter but in greater quantity will drive efficiencies of scale in manufacturing and shipping. And smaller turbines lead to cheaper towers. Hard to know if he's right without crunching actual numbers though.

With land area being one factor that goes into capital cost.

I'm interested in the results when Cringely builds his farm. For example support costs from thousands instead of hundreds of turbines. How many on one pole are best. Also building costs over time e.g. when costs go down due to robots planting poles etc. which favors farms with more poles above those with fewer poles.

I don't know much about wind turbines and the behaviour of moving volumes of air with regard to airfoils but there's one point I picked off of the article.

If I were to put my money either in the most advanced big-farm wind high-tech or in something that is decentralized, mass-produced, and well-abused by all kinds of groups of people, it would be the latter.

The article mentions that one billion is not enough to enter the game. That surely excludes a lot of the smartest and brightest people who might come up with new innovations and the billion-scale investments also seek conservative returns, further culling new ideas.

This comment on the post is pure gold!

Fascinating! It’s not about asking questions, it’s about asking the right questions! The first framing question is efficiency from blade to outlet, but it’s really about effciency from capital markets to factory floor to farm to outlet.

That should become a mantra. It's about efficiency from capital markets to revenue per customer.

I would have guessed that it's a trade-off between efficiency and mimizing public outrage in densely populated areas (yes, outside the US that can be an issue). Three blades, when the turbine is not working, block less from the view than a large number of blades (which converge towards giant white surfaces).

Here's a much better Wind Resource Map than the one in the article: http://www.tindallcorp.com/site/user/images/USA_Wind_Map_for...

http://apps2.eere.energy.gov/wind/windexchange/wind_maps.asp has this map plus state by state maps available for download as relatively high resolution PDFs.

The more worrying part of this is that you need 1H capital to even try to get into this business if all you do is build the monsters. So that means few competitors (or even one) which makes monopolist behavior and unimaginative thinking likely.

It seems Steve Jobs was inspired by Socrates: https://en.m.wikipedia.org/wiki/Socratic_method

In some parts of the world they use 2 blades so they can lay down the system when the wind is too high (think tornado/hurricane season)

The less number of blades - the higher efficiency, should be an odd number to avoid standing wave and symmetric too. Thus 3.

Why can't the blades be staggered so they don't follow in each other's wake?

this is one of the best articles i have read recently. I too am a big fan of always asking why and trying to buck the trend of "thats just the way it is".

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