Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

businessinsider.com

Post reply on HN
Print view View original

181–190 of 263 posts

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

#181

Post by jasonwatkinspdx »

Joeri wrote: post #103
foerbert wrote: post #43

Earlier quoted context omitted.

The wind, I think. My current impression is that when it is starting, the whole thing is basically just acting as a big sail. You could lock the propeller and prevent it from spinning and it would still move forward. After that is where I start to get more fuzzy on the matter. On the one hand it makes sense that by using some of the speed from the wind to do other things, you can extract more total energy from the wi…

I may be wrong, but this is how I understand it. The propellers push against the wind. Effectively you’re creating a faster wind by pushing back at it. The energy that drives the propellers still comes indirectly entirely from the wind, but wind across a larger volume behind the propeller so therefore carrying more energy.

You've got it exactly right.

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

#182

Post by jasonwatkinspdx »

cblconfederate wrote: post #143
twobitshifter wrote: post #136

Earlier quoted context omitted.

It’s really not that complicated - wind speed is not the same as energy. The propellor is a device that pushes against the air to move forward, it takes energy from the wind, produces a force, and the force produces momentum in the vehicle. We know that a stationary turbine can continually take power from the wind. When that wind energy is stored in a battery it can power your car much faster than the wind. This just…

Sailboats can run faster than the wind because of lift (which is not involved here), but not when running away from the wind

Propellers are lift devices. The lift vector is parallel to the axis of rotation.

It all works the same downwind, and the crazy fast boats like the AC72s do in fact sail faster than the wind when running away from the wind.

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

#183

Post by haberman »

sopooneo wrote: post #174
haberman wrote: post #156

> 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. This is a pedantic point, but when you're cutting zigzag patterns downwind it's called jibing, not tacking. I guess there are high-performance boats that can go faster than the wind upwind, and that are so fast that they can perform downwind tacking (since apparent wind stays ahead…

But what about once you are going downwind faster than the wind, and thus experience an apparent headwind? I'm not a sailor, but I thought I'd seen people using the term "tacking downwind" to describe that.

You will experience an apparent headwind when sailing on a broad reach faster than the wind, yes. But the jibe involves turning downwind (thus losing lift), as well as bringing the sails across (which will temporarily de-power them). It's been a while since I've been sailing, but I don't think most boats can maintain an apparent headwind through the entire maneuver, even if they are capable of faster-than-wind speed.

Some can, which is why I mentioned downwind tacking for high-performance boats, but I think it takes a pretty fast boat to manage it.

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

#185

Post by Ericson2314 »

jasonwatkinspdx wrote: post #176
haberman wrote: post #156

> 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. This is a pedantic point, but when you're cutting zigzag patterns downwind it's called jibing, not tacking. I guess there are high-performance boats that can go faster than the wind upwind, and that are so fast that they can perform downwind tacking (since apparent wind stays ahead…

State of the art in crazy expensive racing yachts (think America's Cup) is limited by cavitation on the foils to a bit over 50 knots. Ice boats are setting records over 120 knots. If someone figures out a magic foil, that gap may close, which is a thought that blows my mind.

Wow I had no idea, thank you.

I was in a relative's ice boat once. I was pretty wonderfully terrifying -- awesome in all senses.

To do that on water would be quite something!

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

#186

Post by smsm42 »

My first thought about it was that it's awesome. The sad thing is that my second thought about it was that if somehow physics became political, this guy would be banned from Youtube for "physical misinformation" - after disagreeing with a renown expert in the field - and maybe we would never found out about it.

But, apparently, there's a way for people to disagree about science - without any of the sides being evil or stupid - and there's a way to find out who's right. Maybe we could learn something bigger from this?

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

#187

Post by colechristensen »

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.

You’re harvesting the energy from the difference in velocity of the ground and the wind. Sure it is easy to think about that being possible when you’re attached to the ground but it’s perfectly possible when you’re moving too. Regardless of how fast you are moving or in which direction there is always that difference been air and ground.

To go faster than the wind you just have to be a bit clever in how you capture that available energy.

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

#188

Post by slowmovintarget »

jcims wrote: post #159
cfallin wrote: post #151

Earlier quoted context omitted.

The way this clicked for me (it took some thought!) was to see it as a lever, or at least an analogue to one. Imagine a lever with the fulcrum on one end, attached to the ground. Wind pushes on the middle, and the car is at the other end of the lever. So wind exerts more force with less speed, and the car moves forward with more speed but less force. That's basically what the linkage and gear ratio between the wheels…

I think this is a good intuition about it, and Xyla Foxlin goes into this a bit in her video explaining the build for Veritasium's video. https://youtu.be/VUgajGv4Aok?t=432 The essential 'gear' ratio is between forward motion of the vehicle and the propeller pitch (essentially how far the prop would screw through a tub of jello for a given amount of rotation). The vehicle has to move *faster* on the ground than the p…

And one of the Veritasium videos: https://www.youtube.com/watch?v=yCsgoLc_fzI

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

#189

Post by gpderetta »

blueblisters wrote: post #132
mumblemumble wrote: post #50

Earlier quoted context omitted.

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…

Perhaps another way to think about it - tailwind. Aircraft can derive energy from the wind even when they're going faster than the wind-speed. The propeller arrangement is a glider that is being pushed by the wind. The glider is tethered to a cart whose wheels in-turn drives the propeller to become a "powered" glider. Without a tether, the relative speed of the glider with respect to the wind would be zero. With the…

Very good explanation. Thanks. I was thinking of some other contraptions to explain this (to myself mostly), but the glider->powered glider made it click. Even if it might not exactly how this vehicle work, at least it demonstrates a system that can obviously go faster than the wind speed.

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

#190

Post by guy_named_matt »

I feel that the Business Insider title is really misleading and counterproductive; because Derek Muller is not 'a youtuber' -- he's a serious physics educator, with a PhD in physics education research, and with probably the best youtube channel (or any channel, in any medium) in the world for explaining physics content; which has been running for a decade; and with nods from multiple famous physicists IN THIS VERY VIDEO saying that he is the best that there is. So the claim that 'A youtuber bet a physicist and won' just makes it seem that experts are wrong, whereas in reality, this was expert vs. expert. That being said, physics is such that if 'some youtuber' bet a physicist, and was right... physicists would concede.
Post reply on HN