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Thursday, March 24, 2011

Faster Than The Wind

In my opinion, One Man's Quest to Outrace Wind is a great article. It's well written, tells a great story with plenty of suspense, and is educational.

The core topic is "DDWFTTW", which stands for "Directly DownWind, Faster Than The Wind" and refers to a vehicle or vessel powered only by the wind. Until recently, it had always been thought to be impossible to build a wind-powered vehicle that could go faster than the wind while going directly down wind. That's because once the platform reaches the same speed as the wind, it seems like there would not be any wind forces acting on it, so how could it go faster if it's powered only by the wind?

Someone figured out how to do it and proposed his concept on the Internet.

And he was promptly ridiculed and called an idiot by almost everyone including physics professors.

He built a small prototype that proved the concept.

And he was promptly ridiculed and called a fraud and an idiot by almost everyone including physics professors.

He and a very small group of supporters managed to raise $15,000 to build a full size version that could carry a person. They demonstrated it to the Land Sailing Association where it clearly went directly down wind much faster than the wind.

Finally, most people believed him!

What's interesting to me is that the approach is very, very clever, but it's not really that complex, yet a lot of people just refuse to believe it, even after it's been clearly demonstrated.

No one is so blind as those who refuse to see.

14 comments:

Susan's Husband said...

Interesting, but I don't think I would have been skeptical. To me, the counter-intuitive point is that you can have any purely wind powered object with a downwind vector velocity greater than the wind velocity. But everyone agrees that's possible with a sailboat. I would think that all the arguments against Blackbird would apply just as well to that situation.

Bret said...

I first saw the article via a mailing list that I'm on with a group of old college fraternity brothers, several of which are physics professors. I found the approach very clearly explained and I wasn't skeptical at all either.

The physics professors, on the other hand, were quick to declare it a hoax or otherwise dismiss it as impossible. I had to explain it to them and overcome their objections which is absurd, since I'm only a software guy. It might be a case where too much knowledge was an impediment to their ability to absorb information. Or maybe overconfidence in that they felt they could take a quick look and make a pronouncement on it without having to read the explanation and think it through.

Susan's Husband said...

Yes, I understand the approach. It's the starting point I find counter-intuitive.

So you have a plane where the wind blows at speed V in the +x direction. Then you have a sailboat S which sails at some angle θ between 0 a d π/2 to the x-axis. Its velocity is (a,b).

The base claim is that you can have a > V. Isn't that weird? I can see the arguments against the guy's machine, but I don't see how you can't apply the exact same arguments to this situation. Why is the y component significant? Do those professors think there's some function of θ that limits a, forcing a ≤ V as θ → 0? Wouldn't S see a wind blowing in the -x direction once a > V?

I accept that yes, you can have a > V, it's clearly well documented. But you might ask the professors why the y-axis component matters. That's what I don't understand for the counter argument.

Susan's Husband said...

I did the smart thing and ask She Who Is Perfect In All Ways and she explained that I just need to think of a > V as tacking in to the wind. After that, everything was clear, including how Blackbird works. The rotating and angled props let it tack in to the wind even when going directly in to the wind. If that's true, you should be able to get it to go upwind (although it might require an initial push).

Bret said...

Yes. The only "magic" is that a sail boat can tack its way upwind (i.e. the velocity (a,b) can have a < 0), after which everything else follows.

I learned to sail long before I learned about wings, sails, and lift so it really was magic to me for a long time. Heck, it still seems like magic!

Rick said...

>> It might be a case where too much knowledge was an impediment to their ability to absorb information.

Or as they say - the greatest impediment to learning anything is already knowing everything.

>> If that's true, you should be able to get it to go upwind (although it might require an initial push).

We're just about to start building a turbine to replace the prop. Then it will go directly upwind - faster than the wind. And it won't even need an initial push.

Bret said...

Hey Rick,

Does anybody sell a toy version (either assembled or kit) of the down wind device that would run on a treadmill? I could probably design one, but I don't have the time.

Rick said...

>> Does anybody sell a toy version (either assembled or kit) of the down wind device that would run on a treadmill?

I made a set of 3 build-videos for the simple treadmill cart. You can find it on YouTube if you search Spork33. It gives all the part numbers, suppliers, etc. And a pretty detailed description on how to build it.

Make magazine is running an article on the build this month I believe. They threatened to offer a kit, but I don't know if that's gone anywhere.

Howard said...

Rick:

Way cool and well done!

Or as they say - the greatest impediment to learning anything is already knowing everything.

Oh yes, nothing like being gobsmacked as a
reminder of the importance of keeping an open mind.

Bret:

Is this another internet moment? (see last comment of that post...)

Rick and his efforts are another example that refute the conventional wisdom about science. There is a fair interpretation of the historical record that claims the thought experiments and hands-on tinkering of innovators has contributed more to science than the other way around. ( as discussed here and here)

Howard said...

correction

that last link in the prior comment is here

erp said...

There is a fair interpretation of the historical record that claims the thought experiments and hands-on tinkering of innovators has contributed more to science than the other way around.

Which is why the current method of federal funding of research is so counterproductive. The people who get the grants are the good grant writers, not the innovative geniuses.

Bret said...

Howard,

It's always cool when people stop by to comment on posts written about them.

I can certainly believe the interpretation that hands-on, market driven innovation is more effective, but as I've posted in the past, there may be a place for both private and government funded research, though I could be wrong.

Hey Skipper said...

I was all like "no way, doood" until I came to this para:

And the balloon-versus-sailboat thought experiment he came up with took him to another planet: a cylindrical planet entirely covered by water, with a constant wind blowing down its length. Call it Planet 50-Gallon Barrel and visualize a balloon racing a sailboat from one end to the other.

Then suddenly the room got real bright as the light went on over my head.

IMHO, the source of genius is seeing from a slightly different angle what everyone else has long since taken for granted.

Bret said...

I liked the cylindrical planet idea because it relates a sail to a propeller.

Given that one guessed that DDWFTTW is possible (since boats tacking can beat the balloon), clearly standard sail rigging wouldn't do it. The other choice that might jump to mind would be some sort of system involving a propeller.