UCLA physics professor loses $10k bet about downwind kart

Originally published at: UCLA physics professor loses $10k bet about downwind kart | Boing Boing


I’m amazed that the professor would make this bet nearly 11 years after the Blackbird was officially recognized by the North American Land Sailing Association as traveling more than double the wind speed in July 2010. The physics were discussed extensively at the time and he must have thought that a whole bunch of people were fools. But he certainly paid the price for his hubris.


Now I want to see someone do this with solar wind.


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Ha! At 6:35 there is an email from Bill Nye saying that “I am pretty sure the inventors of the Blackbird are fooling themselves, or us, or both…”


This is going to be plane-on-a-conveyor-belt all over again, right?
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Bill Nye is a very smart guy and great communicator, but nobody is equally competent in all fields of science and physics. I feel like he’s got the image of the stereotypical all-purpose movie scientist that nobody could possibly live up to.


if I had the time and money, I’d try a computer controlled version with a cvt to see how far it can be pushed.

Or maybe a sailboat version? I dunno, it just seems really cool and underexplored.


There are a few fun designs here that look like they work: WIND POWERED SHIPS MARINE RENEWABLE ENERGY RESEARCH ROTARY SAILS


Even a simple sailing boat can go faster than the wind that pushes it (although not against it), This is not underexplored, these are well known facts. Tried, tested, researched, explained. There is no mystery here.


Regardless of whether it goes faster than the wind, they’ve still got a nice tree trimmer there.


That’s why the acronym expands to Directly Down Wind Faster Than The Wind, not at an angle. Which I believe was covered in the video when I saw it weeks ago.


I was almost yelling at the screen at the point where he was explaining how he manually had to adjust the pitch of the propeller. That’s where a simple circuit and actuator would have excelled.

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I’m not familiar with the blackbird sailboat, but a sailboat is a different animal than a windmill.

Second, I am not sure how the windmill is transferring power to the car - mechanically driving the wheels, or generating electricity and running a motor.

But in general as the car approaches wind speed the wind driving the windmill will reduce to zero and stop generating power.

Now if it coasts through that period then the windmill will being pushed through the air - now being driven from the other direction. But it does not seem like it would accelerate here - it would loose force through friction and end up at equilibrium where the windspeed at the windmill is zero.

The whole thing smells like a perpetual motion machine.

I’ll bet you $10,000 dollars it isn’t.


Ah, but you are assuming perpetual motion machines can’t work.

The Blackbird isn’t a sailboat and it very much does not operate like a windmill. But I’ll second @heng in betting you whatever sum you like that it does move faster than the wind that’s pushing it.


Did you watch the video? This is the very opposite of a windmill. The wind does not turn the propellor. The rear wheels do (literally like the pedals on a bicycle turn the rear wheel). The propellor pushes the air back like a fan.


I know people make a lot of analogies as to how this vehicle works, but for me the clearest demonstration in the video is 14 minutes in, where he does the demo with the 2x4 and that simple car thing. It very clearly shows the basic principle that you can take advantage of a relative speed difference between two media (air and ground, or in this case a slowly moving board and the ground) to make a vehicle which is in contact with both media travel faster than that speed difference. If you can accept that, then it’s not much of a leap to accept that it can be done on a larger scale with the propeller even if you don’t understand all the details of how the equations work.


Actually, I think it does both – does it not start out being powered like a windmill, and then changes prop pitch, and converts to driving the propeller from the wheels? Thats what I took away from the video.