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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

#81

Post by paconbork »

textman wrote: post #77

large ocean yacht racing boats can go much faster than the wind: https://www.kqed.org/science/8503/how-do-these-boats-sail-fa... Also this: "According to the World Ice Racing Circuit, ice boats can sail four to five times wind speed. In March 2009 a land sailboat reached 126 miles per hour on a dry lake bed in the Mojave Desert" from: https://www.straightdope.com/21344013/how-can-racing-yachts-... I think I read some…

The difference here is that the vehicle in the article is traveling parallel with the wind

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

#82

Post by otherme123 »

marcodiego wrote: post #61
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…

I really would like a simple explanation of how that is possible. AIUI, when speed is stable, the wheels turning provide power to the propeller. But if the propeller pushes the car, which in turn makes the wheels turn faster making the car faster than the wind itself, what makes it different from perpetual motion machines? I would love a diagram showing how the power flows in this system.

I felt this in a sail boat: when the boat is moving below wind speed, the wind pushes the sail and the boat. At some point, wind and boat equal speeds, so it feels like theres no wind at all except the sail is full.

Some well built boats can generate pull (instead of push) in the sail, as if it was a plane wing. The air passing on the convex (forward) side travels faster than the air on the concave, making the pressure lower on the forward side and pulling the boat, and you feel again the wind but against your face (as if you were running forward). It's a bit counterintuitive, because what your eyes see is the sail pushing the boat. So it's not perpetual motion, because the wind needs to keep blowing or the boat slows again. What slows the boat is the friction boat-vs-water.

In the case of the car above, the wind needs to reach the point of wind speed == car speed, and beyond that the wheels keeps rotating the "sails", and thus keeping the pull. If the wind stops, the car can keep going for some time, but as the speed of the wind through the sails is lower, the pull is also lower and at some point it stops. But in this case, the friction is wheels-vs-ground, much lower than the boat-vs-water above, so the car can keep going (same what happens with a bike when you stop pedaling in a flat surface, the bike can keep going for long, and even a faint pedaling or tail winds keep the thing going). This car is a clever construction to keep the wind at high speeds through the blades.

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

#83

Post by dahart »

slowhand09 wrote: post #66
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…

Its actually the correct explanation tho. This article sucked by the way. It said "Any sailor worth their salt can tell you that a boat can travel faster than the wind by cutting zigzag patterns; that's called tacking." Any sailor worth their salt knows that is not true at all. This practically destroys any credibility on this topic by this author.

> Any sailor worth their salt knows that is not true at all.

You sure? Take a gander at this article https://en.wikipedia.org/wiki/High-performance_sailing

You’re right in the sense that tacking is not the word for sailing faster than wind, but it is true that sailors can tack faster than the apparent wind, and that professional sailors know that. The “apparent” part is an important part of the discussion that the quote didn’t include or clarify, but would be implicitly understood by the saltiest of them.

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

#84

Post by xaedes »

everly wrote: post #12

The article (and wiki page linked in another comment) seem to indicate that this vehicle design already proved it can go faster than the wind over 10 years ago. Odd that the professor was so keen on betting in that case.

$10.000 got donated and a lot of publicity created. I think it is just good marketing. Dunno if it is worth 10k but it got on HN a few times, so it undoubtedly works. And the topic itself is super interesting!

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

#85

Post by [deleted] »

raisedbyninjas wrote: post #74
mumblemumble wrote: post #44

Earlier quoted context omitted.

Any wind that's strong enough to overcome static friction would do the trick, and I can't see why 10mph wouldn't be enough. The small models that you can build at home (sorry, can't find the plans anymore; this was 10 years ago now) do not require a push to get started.

The fan blades are an airfoil, which have a minimum speed to create the lifting effect.

[deleted]

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

#86

Post by [deleted] »

mumblemumble wrote: post #50
Valgrim wrote: post #28

Earlier quoted context omitted.

Then what is spinning the wheels?

Asking what is spinning what is maybe framing it in a way that impedes understanding. A quick summary of the basic forces involved are: The wind pushes the propeller, the propeller pushes the wheels, the wheels push the ground, the ground pushes the wheels, the wheels push the propeller, and the propeller pushes the wind. Or perhaps it's better to say that everything is dynamically interacting with everything else. I…

[deleted]

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

#88

Post by dahart »

Muller’s bet reminded me of the Mysthbusters episode where they put a fan in a boat that blows on it’s own sail and moves the boat forward, which I’m pretty sure I thought wasn’t possible before it aired.

https://mythresults.com/blow-your-own-sail

It also reminds me of the Brayton Cycle, and turbofan/turbojet engines where the output thrust of the blades is applied to subsequent blades that turns the shaft, causing the first fan to spin even faster.

To me this feels similar to blowing on your own sails, and to Veritasium’s Blackbird that blows air against the wind to go faster than the wind. These all feel counterintuitive, but they work.

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

#89

Post by IgorPartola »

LeifCarrotson wrote: post #62
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 wheel friction and gearing allows the vehicle to tie the effective velocity of the sail (actually a propeller) to the velocity of the ground. Energy can be extracted from the interface between the ground at one velocity and the air moving at another velocity. A sail tied to the ground and extending into this wind will exert a force according to the drag equation: Force = 1/2 x drag coefficient x density x area x…

In your static example how does the turbine get back to the front of the vehicle? Does the force of the wind push it there? If so, if the wind is blowing at 10 knots but the base of the vehicle is moving at 20 then as far as the turbine is concerned it is actually being pushed backwards, no? Or is the idea that when you lift the anchor the vehicle slows to below wind speed while the turbine gets pushed?

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

#90

Post by tootie »

dahart wrote: post #88

Muller’s bet reminded me of the Mysthbusters episode where they put a fan in a boat that blows on it’s own sail and moves the boat forward, which I’m pretty sure I thought wasn’t possible before it aired. https://mythresults.com/blow-your-own-sail It also reminds me of the Brayton Cycle, and turbofan/turbojet engines where the output thrust of the blades is applied to subsequent blades that turns the shaft, causing t…

Whether it's an electric fan or your own lungs, it's pulling energy from storage (a battery or your own chemical energy storage) and converting it to kinetic energy. It's no different than if you put the fan or your face in the water facing backwards to propel the ship.
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