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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

#51

Post by mumblemumble »

jrs235 wrote: post #47
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.

Understandable that it doesn't take much wind for a vehicle well under a pound. But what about one that weighs well over 100 pounds?

The 100 pound vehicle also has a much larger cross section to the wind. And its propeller is further off the ground, so it's getting cleaner wind than the little model version.

I can get a boat that weighs more and has less sail area going on less wind than that. And that thing has to be dragged through the water on top of everything else.

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

#52

Post by Akronymus »

goldenkey wrote: post #31
dd36 wrote: post #23

Earlier quoted context omitted.

Can it be done with solar sails?

Solar sails only absorb enough energy for tiny crafts in space, a frictionless environment. You overestimate photon flux momentum from the sun.

Solar sails indeed only absorb a tiny amount of energy, BUT per given area.

They can theoretically made to be extremely large without much weight relative to the size. Which in turn allows you to accelerate even quite large payloads in a reasonable amount of time.

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

#53

Post by database_lost »

dmurray wrote: post #34
database_lost wrote: post #29

"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…

Having 9.5 million subscribers on a science-based YouTube channel is definitely more notable than having gone to university, or indeed having a PhD. I think the writer picked the correct description here.

I see your point, but the title and first paragraphs try to paint the picture of a "funky science" youtuber betting a UCLA physicist $10k and winning (which for me is very different to the truth: UCLA physicist bets another physicist $10k and loses)

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

#54

Post by Jedd »

Sailing faster than the apparent wind[0] has been going on for a while, especially on v.high performance land and water yachts. [1]

The physics involved still twist my brain, but there's nothing terribly new here.

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

[1] https://en.wikipedia.org/wiki/High-performance_sailing

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

#55

Post by wongarsu »

jrs235 wrote: post #47
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.

Understandable that it doesn't take much wind for a vehicle well under a pound. But what about one that weighs well over 100 pounds?

In the veratasium video [1] you can see it starting just from the wind (first attempt is around 5:20). It works just fine because as you scale up the vehicle you scale up the propeller, so there's plenty of surface for the wind to push against.

1: https://www.youtube.com/watch?v=jyQwgBAaBag

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

#56

Post by chongli »

DebtDeflation wrote: post #17
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…

Yeah, my first inclination is that since the wind is turning the propeller and the propeller is turning the wheels via a gear system, the speed of the vehicle will be determined by the propeller speed, the gear ratio, and the tire diameter (ignoring friction and air resistance for a moment). The gear ratio is the critical component. It's not like the propeller is a simple sail. I could be completely missing something…

No, the wind is not turning the propeller, the wheels are.

The reason the wheels are able to turn the propeller without slowing the vehicle down is that the speed of the wheels over the ground is greater than the speed of the propeller through the air thanks to the tailwind.

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

#57

Post by shagie »

IgorPartola wrote: post #8
zamadatix wrote: post #3

For those that hate the way news articles are written I found the Wikipedia article a much clearer read https://en.m.wikipedia.org/wiki/Blackbird_(wind-powered_vehi...

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

The original Veritasium video https://youtu.be/jyQwgBAaBag

The video of the bet and the further explanations - https://youtu.be/yCsgoLc_fzI -- at 13:28 is an example without aerodynamics.

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

#58

Post by marcan_42 »

omega3 wrote: post #48

I find it extremely counterintuitive, especially this part: In 2012, Blackbird also demonstrated sailing directly upwind with twice the speed of the wind.[0] [0] https://en.m.wikipedia.org/wiki/Blackbird_(wind-powered_vehi...

I posted an explanation for the downwind version above, but here's the gist of why all this is possible:

To extract energy from the wind, you need a reference that is slower than the wind. The ground is one such reference. The vehicle gets access to that reference via the wheels. It can therefore extract power from the wind regardless of where it's going or what it's doing.

So it's like a wind turbine on the ground, connected to a car that has nothing to do with it. Of course the car can go faster than the wind in this situation; the wind speed doesn't matter, only the drag of the car and how big your wind turbine is (how much energy you can get out of it).

This vehicle just makes the whole thing self contained with gearing and counterintuitive rotation of the propeller. It's touching the ground and can use that reference via the wheels, so it can pretend to be a stationary wind turbine on the ground this way. That means it can go downwind, or upwind; doesn't matter. As long as the wind is moving relative to the ground, it can harness that energy.

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

#59

Post by Retric »

jrs235 wrote: post #46
Retric wrote: post #41

Earlier quoted context omitted.

No, it’s light enough for the wind to start pushing it.

Even with 100+ pounds (50+ kg)?

Yes, at the extreme end you can find videos of 3,000+ lb cars flipped by the wind.

It looks quite aerodynamic, but by comparison I can start pushing a 3,000lb car on flat level ground. So this thing probably needs less than 10 pounds of force to start moving.

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

#60

Post by wizzwizz4 »

Retric wrote: post #42
Vvector wrote: post #40

Earlier quoted context omitted.

And what's making it go forward?

The wind.

The propeller pushing backwards on the wind uses up less energy than it gets from the wind blowing it – when it spins backwards to “keep pace with” the wind, that means the wind is faster than it and it can get boosts from the wind.
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