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A wind-powered vehicle that can travel twice as fast as the wind itself

businessinsider.com

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Re: A wind-powered vehicle that can travel twice as fast as the wind itself

#21

Post by formerly_proven »

CarVac wrote: post #15
IgorPartola wrote: post #8

Earlier quoted context omitted.

Like the professor in TFA I am also confused: how can the ground be imparting power to the propeller while moving downwind?

The wind pushes the propeller, the gearing of the wheels to the propeller cause the overall vehicle to advance faster than the blades on the propeller (as seen by the wind). It's an overdrive—the wind pushes the vehicle faster than the wind itself, but the vehicle gets less net propulsion force when you sum up the tractive force and the wind force.

Wind does not drive the propeller.

Re: A wind-powered vehicle that can travel twice as fast as the wind itself

#22

Post by IgorPartola »

CarVac wrote: post #15
IgorPartola wrote: post #8

Earlier quoted context omitted.

Like the professor in TFA I am also confused: how can the ground be imparting power to the propeller while moving downwind?

The wind pushes the propeller, the gearing of the wheels to the propeller cause the overall vehicle to advance faster than the blades on the propeller (as seen by the wind). It's an overdrive—the wind pushes the vehicle faster than the wind itself, but the vehicle gets less net propulsion force when you sum up the tractive force and the wind force.

> Downwind, when the vehicle is traveling faster than the windspeed, the ground is the fastest-moving medium relative to the vehicle, so the wheels harvest the power and impart it to the rotor, which propels the vehicle.

So the wind pushes the vehicle faster than wind speed to start with? How?

Re: A wind-powered vehicle that can travel twice as fast as the wind itself

#23

Post by dd36 »

sopooneo wrote: post #14

The treadmill demos made me think of another counterintuitive possibility that I wondered if anyone had pulled off: sailing a boat indirectly up a river in no (bank relative) wind. Turns out, it has been done: https://www.youtube.com/watch?v=q2il8Fagbyk

Can it be done with solar sails?

Re: A wind-powered vehicle that can travel twice as fast as the wind itself

#24

Post by CarVac »

formerly_proven wrote: post #21
CarVac wrote: post #15

Earlier quoted context omitted.

The wind pushes the propeller, the gearing of the wheels to the propeller cause the overall vehicle to advance faster than the blades on the propeller (as seen by the wind). It's an overdrive—the wind pushes the vehicle faster than the wind itself, but the vehicle gets less net propulsion force when you sum up the tractive force and the wind force.

Wind does not drive the propeller.

I did not say that. I wrote "Wind pushes the propeller."

The vehicle is basically extracting energy from the difference in velocity between the ground and the air.

The wind pushes the propeller forward, the ground pushes the wheels backwards.

Re: A wind-powered vehicle that can travel twice as fast as the wind itself

#25

Post by dagw »

pteraspidomorph wrote: post #7
IgorPartola wrote: post #5

This is slightly off topic but I have been using this trick lately to try to determine which part of a news article is likely to be BS: read the article in the movie announcer voice (you know the one: “in a world gone mad, one man…”). Whatever headlines or parts of the article sound boring are likely to be legit and whatever parts sound like they would fit in an action movie are likely overblown, underreseaeched, irr…

Science's Biggest Names! It got a chuckle out of me while reading.

I mean they're not entirely wrong in the sense that if you asked a bunch of Americans to name some currently active 'scientists' then those names would almost certainly be at the top of list (I'd guess that those two plus Anthony Fauci would make up the top 3).

Re: A wind-powered vehicle that can travel twice as fast as the wind itself

#26

Post by gibba999 »

Someone1234 wrote: post #2

The most surprising thing here is that someone on Twitter made a bet, lost the bet, and then actually paid said bet. Playing devil's advocate here a little: The whole machine is very counter-intuitive, and I can see how I myself may disbelieve it if not for the irrefutable demonstration(s)[0]. [0] https://www.youtube.com/watch?v=yCsgoLc_fzI

It's not at all counterintuitive. It's just poorly explained.

Energy is 1/2mv^2, and momentum (related to force) is mv. Anytime you have different speeds, you can arbitrage.

If I am pushing against still air, I can generate nearly-infinite force for arbitrarily little energy.

That's why you use wings instead of pointing jet engines downwards. You push a lot of air by a little bit (lots of mv, not a lot of 1/2mv^2, since v is small).

If I am going an epsilon faster than the wind, with very little energy, I can push hard on the air.

Re: A wind-powered vehicle that can travel twice as fast as the wind itself

#27

Post by CarVac »

IgorPartola wrote: post #22
CarVac wrote: post #15

Earlier quoted context omitted.

The wind pushes the propeller, the gearing of the wheels to the propeller cause the overall vehicle to advance faster than the blades on the propeller (as seen by the wind). It's an overdrive—the wind pushes the vehicle faster than the wind itself, but the vehicle gets less net propulsion force when you sum up the tractive force and the wind force.

> Downwind, when the vehicle is traveling faster than the windspeed, the ground is the fastest-moving medium relative to the vehicle, so the wheels harvest the power and impart it to the rotor, which propels the vehicle. So the wind pushes the vehicle faster than wind speed to start with? How?

The angle of attack of the propeller blades and the gearing relative to the wheels cause the blades to be seen by the wind as moving upwind relative to the ground.

Alternatively, think of it as merely harvesting energy from the velocity difference between the ground and the air. It's connected to the ground by wheels, and to the air by a big prop.

It doesn't matter how fast the vehicle itself is moving as long as the gearing is right.

Ultimately, the top speed is limited to when the friction the vehicle encounters from drivetrain losses and aero drag exceeds the power it can extract from the wind/ground speed difference.

Re: A wind-powered vehicle that can travel twice as fast as the wind itself

#28

Post by Valgrim »

sopooneo wrote: post #16
michaelt wrote: post #13

> The secret to Blackbird, Cavallaro explained, is that once the wind gets the vehicle going, its wheels start to turn the propeller blades — they're connected to the blades by a chain. As the vehicle speeds up, its wheels turn the propeller faster and faster. The propeller blades, in turn, act as a fan, pushing more air behind the land yacht and thrusting it forward. That's a terrible explanation - no wonder people…

You're right that it falls far short, but it corrects one of the fundamental misunderstandings many people have about the vehicle: the wind does not spin the propeller, the wheels do.

Then what is spinning the wheels?

Re: A wind-powered vehicle that can travel twice as fast as the wind itself

#29

Post by database_lost »

"A popular YouTuber filmed himself driving a wind-powered vehicle downwind faster than the wind itself. [...] Muller, the creator of the Veritasium YouTube channel, likes to break down funky science concepts for his 9.5 million subscribers."

The "popular YouTuber" is Derek Muller, who studied Engineering Physics and has a PhD in Physics Education Research... It's so frustrating to see how the writer tried so hard to make as much as clickbait-y title as possible...

Re: A wind-powered vehicle that can travel twice as fast as the wind itself

#30

Post by wizzwizz4 »

Valgrim wrote: post #28
sopooneo wrote: post #16

Earlier quoted context omitted.

You're right that it falls far short, but it corrects one of the fundamental misunderstandings many people have about the vehicle: the wind does not spin the propeller, the wheels do.

Then what is spinning the wheels?

The fact it's going forwards.
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