23 ms·

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

210 points by dutchbrit 5y ago

catchmeifyoucan 5y ago
Actually, knowing it works now. Even internal combustion engines have only a 40% energy efficiency in converting gas to power, the rest is lost as heat. In this case, I'm trying to think how the wind energy is lost, and it seems that some of that might be lost to the static friction in turning the wheels, and also the attached propeller. However, the energy used to turn the propeller is outputted again, as thrust. Since the initial wind was enough to overcome the static friction, any additional power might be causing it to move faster than the wind. I'm no physicist, but this is pretty cool.
- dahart 5y ago
  > Since the initial wind was enough to overcome the static friction I’ve seen this idea in a couple of comments here, but I’m not sure what it means, can you elaborate? Rolling wheels are still under static friction. They don’t become dynamic friction unless the wheels are in a skid. Unless what you’re talking about is the static friction of the oiled axle, but I assume that’s not what you meant?
IgorPartola 5y ago
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, irrelevant, etc. Try it with this passage: > They even brought in several of science's biggest names, including Bill Nye and Neil deGrasse Tyson, to help decide who was right. This part just stands out like a sore thumb.
- pteraspidomorph 5y ago
  Science's Biggest Names! It got a chuckle out of me while reading.
  - dagw 5y ago
    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).
- ben_w 5y ago
  In this case, your BS detector is giving you a false result: https://youtu.be/yCsgoLc_fzI?t=275 https://youtu.be/yCsgoLc_fzI?t=275
  - IgorPartola 5y ago
    Thanks for the data point! I would still argue that BN and NdT are only the biggest names in pop science (as in people who wear “I <3 science” t shirts) and not in science as in academia. But that’s cool that they did weigh in on this subject.
Someone1234 5y ago
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 https://www.youtube.com/watch?v=yCsgoLc_fzI
- Tuna-Fish 5y ago
  The small demonstration that made it click for me is from that video: https://www.youtube.com/watch?v=yCsgoLc_fzI&t=812s https://www.youtube.com/watch?v=yCsgoLc_fzI&t=812s This is exactly what the blackbird does, only with a propeller pushing air in place of the big wheel, and it's a much clearer and simpler demonstration of the same idea, which you can trivially verify.
  - iamgopal 5y ago
    This is simplest and best explanation, no doubt why he got his PhD in physics education.
- gibba999 5y ago
  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.
  - ses1984 5y ago
    Ok I have taken college level mechanics (after physics 1-2) and I have no idea what you’re saying.
    - 5y ago
zamadatix 5y ago
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_vehicle) https://en.m.wikipedia.org/wiki/Blackbird_(wind-powered_vehi...
- IgorPartola 5y ago
  Like the professor in TFA I am also confused: how can the ground be imparting power to the propeller while moving downwind?
  - efxhoy 5y ago
    wind pushes vehicle. wheels spin. wheels drive propeller (via gears). propeller pushes vehicle. I first assumed it was the other way around with wind->propeller->wheels, which it is not.
  - CarVac 5y ago
    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.
    - formerly_proven 5y ago
      Wind does not drive the propeller.
      - CarVac 5y ago
        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.
    - IgorPartola 5y ago
wccrawford 5y ago
I saw the Xyla Foxlin video about this (and her treadmill version) and that was a fun build to watch.
marcodiego 5y ago
This was posted about a week ago: https://news.ycombinator.com/item?id=28010133 https://news.ycombinator.com/item?id=28010133
everly 5y ago
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.
- Strilanc 5y ago
  The professor's reasoning is near the start of the video about the bet [1]. Basically they thought the makers of blackbird were fooling themselves (e.g. measuring slower wind at the bottom of the car vs the top of the propeller, or getting pushed above the average wind speed by gusts then selectively reporting). 1: https://www.youtube.com/watch?v=yCsgoLc_fzI https://www.youtube.com/watch?v=yCsgoLc_fzI
- xaedes 5y ago
  $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!
michaelt 5y ago
> 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 doubt the system would work!
- sopooneo 5y ago
  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.
  - Valgrim 5y ago
    Then what is spinning the wheels?
    - wizzwizz4 5y ago
      The fact it's going forwards.
      - Vvector 5y ago
        And what's making it go forward?
        Retric 5y ago
        The wind.
        wizzwizz4 5y ago
        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.
sopooneo 5y ago
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 https://www.youtube.com/watch?v=q2il8Fagbyk
- dd36 5y ago
  Can it be done with solar sails?
  - goldenkey 5y ago
    Solar sails only absorb enough energy for tiny crafts in space, a frictionless environment. You overestimate photon flux momentum from the sun.
    - Akronymus 5y ago
      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.
      - goldenkey 5y ago
        The mirrors are extremely heavy and solar sails are exclusively used above our atmosphere, in space, where more flux from the sun is received. The flux even at earth orbit is a measly 47e-7 Newtons per square meter. That's 0.00016905632 pounds per square inch. You still stand by what you just stated? It's not feasible to do below clouds, in an environment with constant friction, air or water resistance. The only reason you can do it in space is because that tiny slow acceleration can accumulate over a long period of time. This precludes frictional losses that would normally be incurred within atmospheres.
        Akronymus 5y ago
ColinWright 5y ago
Other discussions: https://news.ycombinator.com/item?id=27695869 https://news.ycombinator.com/item?id=27695869 https://news.ycombinator.com/item?id=27696621 https://news.ycombinator.com/item?id=27696621 https://news.ycombinator.com/item?id=27707791 https://news.ycombinator.com/item?id=27707791 https://news.ycombinator.com/item?id=27987321 https://news.ycombinator.com/item?id=27987321 https://news.ycombinator.com/item?id=28000727 https://news.ycombinator.com/item?id=28000727
database_lost 5y ago
"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...
- dmurray 5y ago
  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.
  - database_lost 5y ago
    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)
    - ehsankia 5y ago
      He did study Physics but his main field is science education, I think it's fair to assume a physics professor would know a bit more. I also think it's a bit of your own preconceived notion at play here assuming that calling someone a "Youtuber" is meant as a negative. This is equivalent to saying "Science communicator vs physics professor", which is a fair portrayal.
      - database_lost 5y ago
        I really don't think being called a Youtuber is meant as negative. I take issue with how the writer chose to present this story. If this was about the intricacies of ad revenue on YouTube for example, great, no need to specify he also has a physics degree. But I'm disappointed to see them paint him as just a guy who "likes to break down funky science" (and made 10k off a physicist) when he is more than that, with relevance to the actual story. For someone who doesn't know his work, he might as well be one of the guys burning snow with lighters a few months ago to prove its fake snow...
choffee 5y ago
Is this similar to sailing? Where the lift generated by wind passing over the curved sail or prop blade produces more lift allowing the boat or car to go faster than the wind speed.
- ehnto 5y ago
  Yes, that's where the creator got the idea I believe. He was imagining two sails rotating around a cylinder, which it turns out, is a propeller.
- mumblemumble 5y ago
  Yes. If I remember right, the angle of attack of the propeller blades when this thing is at speed ends up being about the same as that of the sail when the boat's on a beam reach. To extend the analogy further, I think that the wheel-and-chain mechanism ends up functioning analogously to the boat's keel.
omega3 5y ago
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_vehicle) https://en.m.wikipedia.org/wiki/Blackbird_(wind-powered_vehi...
- marcan_42 5y ago
  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.
Jedd 5y ago
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 https://en.wikipedia.org/wiki/Apparent_wind [1] https://en.wikipedia.org/wiki/High-performance_sailing https://en.wikipedia.org/wiki/High-performance_sailing
- aaron695 5y ago
  This is not what they are talking about. It's always step one to get past to understand what's going on here. I don't believe DDWFTTW has been achieved on water.
  - jasonwatkinspdx 5y ago
    You are mistaken. It has been achieved, and the fastest race boats today do it routinely. This is one of the reasons you don't see spinnakers on boats like the America's Cup AC72s, AC50s, F50s, huge open class trimarans, etc. I'm not sure the first boat to achieve it, but it wouldn't be surprising if it was done during the Clipper era. Those boats held 24 hour records from 1860 something all thee way to the 1980s, where modern racing yachts finally eclipsed them.
    - aaron695 5y ago
      I think we just have different definitions. It's about the "Directly" You need a propeller to go Directly Downwind Faster Than The Wind as far as I know. I think on water it has to be very large. I expect there are other ways other than a propeller but haven't seen them. A half way definition (This isn't DDWFTTW to me either), I'd like to know if an America's Cup boat could beat a balloon? So it would be allowed off the 'race track' but it has to come back to meet/beat the balloon at the narrow finish line. So it would cover a much larger distance than the balloon and still beat it to the finish line. Is this possible in practice? The Veritasium video doesn't actually answer this, it kinda goes around it. [edit] If it's symmetrical which it should be, as long as they are going downwind faster than the balloon, they just reverse it at the halfway point and get back inline with the balloon but ahead.
villgax 5y ago
Is there an equivalent for water/hydrofoils maybe?
- foxyv 5y ago
  I think in his original video he described how a tacking boat can go faster than one going straight down wind. As I understand it, that was the inspiration for the propeller. Here is a good site explaining it: https://newt.phys.unsw.edu.au/~jw/sailing.html https://newt.phys.unsw.edu.au/~jw/sailing.html > How can boats sail faster than the wind? Lots of boats can – especially the eighteen footer skiffs on Sydney Harbour. Ask a sailor how, and he'll say "These boats are so fast that they make their own wind", which is actually true. Ask a physicist, and she'll say that it's just a question of vectors and relative velocities.
- xaedes 5y ago
  "The physics of a push-me pull-you boat" http://202.38.64.11/~cxyu/AJP_pushmepullyouboat.pdf http://202.38.64.11/~cxyu/AJP_pushmepullyouboat.pdf
textman 5y ago
large ocean yacht racing boats can go much faster than the wind: https://www.kqed.org/science/8503/how-do-these-boats-sail-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-sail-faster-than-the-wind https://www.straightdope.com/21344013/how-can-racing-yachts-... I think I read somewhere that an ice sailboat did 143 mph.
- paconbork 5y ago
  The difference here is that the vehicle in the article is traveling parallel with the wind
  - theli0nheart 5y ago
    I thought the video below provided a good explanation for why this works. The physics are similar to those of a single sailboat going faster than the wind. Imagine two sailboats on a cylindrical ocean on diagonal tacks, on opposite poles, and rotating around the core with rods connecting them to the core. Now you have a propeller. :) https://www.youtube.com/watch?v=jyQwgBAaBag&t=404s https://www.youtube.com/watch?v=jyQwgBAaBag&t=404s
tpoacher 5y ago
"I offered him another 10,000 bet" is such bullcrap though. For the guys making the vid this is win win due to youtube ads. Kusenko isn't exactly taking a cut from that.
- zamadatix 5y ago
  It's one of the top YouTube channels, they make money off YouTube ads constantly whether or not the professor wants to double down or not. The idea was to point out Kusenko knew it wasn't just a technicality that lost him the original bet even if he didn't want to admit it when conceding.
dahart 5y ago
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 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.
- tootie 5y ago
  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.
  - dahart 5y ago
    That seems too dismissive of the part that’s counter-intuitive, and I think this is legitimately counter-intuitive, which is why physics professors are losing bets. The fan on the boat is blowing air forward from behind the sail, and by it’s very presence on the boat, it applies a force to the boat that is trying to move the boat in reverse. Without the sail, the boat does move in reverse. It’s surprising that one can seemingly recover more force to push the boat forward than was already used to push the boat in reverse. IIRC Myth Busters confirmed the result but didn’t come to a detailed conclusion as to why, which could involve the shape of the hull, directions of the hull & sail relative to the fan direction, or some aerodynamics of the air blocked by the sail. In any case, I think it’s quite different from putting the fan in the water facing backwards to propel forward.
tzs 5y ago
If you believe that sailboats can beat a drifting balloon downwind by zigzagging, then there is a very good explanation in the original Veritasium video that shows that this is essentially the same thing. Here's a link to the section of the video with that explanation [1]. Watch about 2 or 3 minutes starting there and it becomes clear. [1] https://youtu.be/jyQwgBAaBag?t=404 https://youtu.be/jyQwgBAaBag?t=404
rkalla 5y ago
This blew my damn mind 10 years ago when it was first written up in Wired - the way the article was written, the build up to the actual run... all of it was so inspirational and today I still refer to it in my mind whenever I think: "People do the impossible all the time and the guidance they get from everyone around them is that they are INSANE" I think these are the closest we get to moments of 'magic' in real life.
pengaru 5y ago
The propeller is being used a forward motion compensator. At a standstill, the wind just acts on the entire vehicle including the stationary propeller, and sets the whole thing in motion. Without the propeller, going directly downwind would be limited by the speed of the wind acting directly on the vehicle which otherwise lacks any relevant moving parts for the wind to act on. By adding the propeller, driven by the forward motion via the wheels, a part of the vehicle now moves backwards (imagine the cross-section of a propeller blade as it spins, its intersection with the wind travels backwards into the wind) to compensate for the forward movement, giving the wind something to act on even when the vehicle travels faster than the wind.
- cblconfederate 5y ago
  I wonder how one would go about making such machine that would work in zero gravity. Without friction, something else would have to convert part of the wind force to propeller torque. Maybe small turbines could be added that would spin according to apparent wind (forward or backward) and spin the propeller to generate additional lift.
  - pengaru 5y ago
    Fun thought exercise, but are there any practical scenarios where one has wind but no gravity?
    - cblconfederate 5y ago
      solar wind
      - pengaru 5y ago
        Is that really practical considering the already high velocity of the particles? If you matched the downwind particle velocity (>100km/s?) it seems unlikely any mechanical motion compensator could move fast enough to make any significant gain to be worthwhile... but I'm no expert, maybe I'm missing something obvious.
1-6 5y ago
I never had a good experience with my Joby GorillaPod. All the plastic cup pieces developed cracks and the friction just wasn't there. The structural contraption holding up the propeller looks shotty as well. I'm pretty sure Joby Energy and Joby Photographic equipment are separate entities but that name Joby doesn't instill any confidence.
gubby 5y ago
I think the key conceptual thing that's difficult to grasp is the propellor's interaction with the wind. Forgetting the speed of the car vs the wind for a moment, the propellor is arranged so it is trying to push air into the wind (i.e. it is propelling the craft). So, whatever force the wind might impart on a simple flat disc of similar radius to the prop, the force the prop actually experiences is higher than that because it is pushing against the wind. For me, this realisation that the prop is pushing against the wind, increasing the overall force, unlocked understanding how this craft is possible.
neonate 5y ago
https://archive.is/FhZfN https://archive.is/FhZfN
JoeAltmaier 5y ago
Any sailboat?
thehappypm 5y ago
I think I have an analogy that actually explains how this works. Imagine one of those people-mover walkways like they have at the airport. Standing next to it on a skateboard, you grab the handrail. Even though the skateboard has energy loss to friction, you go exactly as fast as the handrail. Now imagine you put a little electric generator in the wheels of the skateboard. Now, not only are you moving at the speed of the handrail, you're also generating some electric power, sourced from the handrail. Now, instead of grabbing the handrail with your hand, yo hold another electric skateboard, and use the power from your feet's skateboard to power that, so you are actually being pulled along the handrail. You'd be inching along the handrail, going faster than it.
- rusk 5y ago
  This apparently violates conservation of energy as you’re claiming to take energy from one source, put it through some apparatus (i.e two skateboards) to produce more energy without putting anything additional in. Can you account for this?
  - ladberg 5y ago
    The people-mover has to expend more energy to push you because you're applying a stronger drag force, so energy is conserved.
    - rusk 5y ago
      Okay so in this case the people mover is drawing the additional energy. Additional energy is being provided from somewhere i.e a diesel generator somewhere up stream has had to increase her fuel consumption to maintain the power on the network.
      - tofof 5y ago
        Right. The people mover is analogous to the wind. You can get to move at the windspeed through drag alone, at which point you no longer move relative to the air. The air is being robbed of only the fraction of energy that you're losing to drag (rolling resistance, as there is no air resistance now). This is you riding along with the peoplemover on the skateboard. But then increase the rolling resistance - the generators on skateboard wheels -- but you still, by drag, move at the wind speed, you're just stealing more energy from the wind/peoplemover now. Then you use that energy (simply by a chain linkage) to spin the propeller, blowing air aft. The propeller pushes air backward, changing the speed of the air molecules in the region behind the vehicle from whatever they were moving at, e.g. 10 knots relative to the ground, to 0 relative to the ground. That energy pushes the propeller and with it the vehicle forward, by Newton's 3rd law. This is the second electric skateboard driving forward, in the frame of reference of the peoplemover. So now you're moving faster than wind speed, in the direction of the wind, stealing more power from the airstream (peoplemover) than you could steal by the (original) drag of your craft alone. You got there by increasing your rolling resistance, which won't slow your craft until the rolling resistance exceeds the available force from the wind. In the analogy, this would be equivalent to jamming your brakes so hard against the floor that you stop the peoplemover rail from moving at all. You use the extra energy -- the amount being spent by the wind to counteract your increased rolling resistance -- to push yourself faster forward.
jayd16 5y ago
This is like putting a turbocharger on a sailboat. I love it.
- rusk 5y ago
  A turbo charger increases fuel consumption though. You can’t just consume more wind.
  - ladberg 5y ago
    In this case they are actually "consuming" more wind. A normal sail "consumes" wind by taking moving wind and reducing its speed to 0. This "consumes" wind by taking moving wind and sending it back the other direction, so it creates more thrust per unit wind.
    - rusk 5y ago
      Sounds to me like it improves efficiency rather than consumes more
      - ladberg 5y ago
        Yep, I thought about it a bit more and you're totally right.
      - jayd16 5y ago
        Same could be said for a turbocharger but we just happen to set the fuel mixture dynamically.
        rusk 5y ago
        No, turbo specifically draws more fuel. You’re using an elastic definition of efficieny that I’m not gona jive with as energy supply from wind is constant. EDIT it’s more like gearing.
  - jayd16 5y ago
    Sure you can. Why not? Can't you extract varying amounts of energy from wind resulting in varying wind speed in your wake?
haberman 5y ago
> 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 of the mast), but this is the exception, not the rule.
- jcims 5y ago
  Side note, this is my favorite mode of exhibiting pedantry. Let the conversation flow while still correcting terminology. Thanks for the info.
- sopooneo 5y ago
  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.
  - haberman 5y ago
    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.
    - morei 5y ago
      The F50 sailing class used in SailGP can remain foiling during jibes in winds as light as 8 knots. That is, the boat always sees an apparent headwind during the entire downwind run.
  - 5y ago
jcims 5y ago
Derek from Veritasium asked Xyla Foxlin to build a functional model, and she goes through the trials and tribulations of that in quite a bit of detail in her video here: https://youtu.be/VUgajGv4Aok https://youtu.be/VUgajGv4Aok There's a key aspect discussed in 7:10 relating to the ratio of the propeller pitch to the vehicle forward motion that is necessary for this to work. (Xyla's channel is a great follow overall btw)
- mianos 5y ago
  Although not adding much value to the comment, I concur that her channel is great to watch. She is so enthusiastic she would make even the grumpiest professor smile.
- fho 5y ago
  Xyla channel is definitely worth a look. But she is somewhat rubbing me the wrong way (no pun intented) ... I am not sure if she had a channel before this one, but she basically appears out of nowhere with a perfect brand image: https://www.youtube.com/watch?v=3B9XYJJY6IQ https://www.youtube.com/watch?v=3B9XYJJY6IQ From the get go she is connected into the wider content creation sphere. Appearing in videos from Veritasium, BPS.space, Dolphin Labs, probably some more. She is every nerds wet dream ... smart, creative and good looking with a overly happy attitude. I don't want to talk bad about her ... It's just too perfect for me not to be somewhat suspicious.
jcims 5y ago
The thing I wonder about stuff like this is that a phenomenon we see in one domain will typically transfer to another domain. For example, the 'hydraulic analogy' [1] for electronic circuits is pretty damn good at least on a macroscopic level. I wonder if there are applications of this phenomenon in other types of physical systems (including electronics).
- rusk 5y ago
  This seems to be highly domain specific though. It’s reading to me like an example of what you can do when you have highly advanced knowledge of a domain to the point where you can do stuff that looks like magic, specifically because it apparently violates generalised principles established across domains.
- jasonwatkinspdx 5y ago
  Acoustics relies on an analogy to electronic circuit components.
noxer 5y ago
Very bad article. Watch the 2 videos instead.
- protomyth 5y ago
  Well, 3 https://youtu.be/VUgajGv4Aok https://youtu.be/VUgajGv4Aok Xyla Foxlin's video has the information about the proper ratio of wheel to propeller to make it all work.
smsm42 5y ago
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?
- tkzed49 5y ago
  > Maybe we could learn something bigger from this? It seems to me that Derek did several things right here: - Choose a topic with which he has relevant experience - Collect experimental data supporting his hypothesis - Fairly address opposing viewpoints, in this case by providing a platform for a dissenting expert to present his evidence Are there examples of similar videos being removed from youtube for misinformation?
guy_named_matt 5y ago
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.
protomyth 5y ago
Kusenko "conceded on a technicality — that the vehicle moves marginally faster than the wind temporarily," Cavallaro said. "I offered him another $10,000 bet, because his technicality is entirely wrong, but I know I won't be hearing from him." Can anyone explain this line's reasoning?
- tofof 5y ago
  Kusenko, who conceded the bet to Veritasium's Muller, only conceded that if you accelerate an object to wind speed and then the wind suddenly dies, your (low-drag) vehicle will continue downrange at a speed greater than the (now zero) speed of the wind on momentum alone. That technicality, however, is a complete misunderstanding of how the vehicle works. The designer of the vehicle, Cavallaro, apparently only built the vehicle to prove the soundness of the physics to doubters, according to the narrative given by the Veritasium video. That designer offered a second $10,000 bet to Kusenko presumably simply excluding the technicality that Kusenko 'lost' to. It would be a simple bet: that the vehicle can accelerate to and sustain a speed faster than any momentary peak wind speed during the race. Since the vehicle can reach 2.8x the wind speed, all it would take is the vehicle doing so while no gusts exceeded, say, 2.5 the average wind speed during the run. The actual explanation, which apparently still escapes Kusenko: If the wind speed is 10 knots from west to east, then this vehicle can accelerate to 10 knots going east by drag (east) alone. At that speed the apparent flow of air (from the reference frame of the vehicle) is zero, and so the drag (east) force on the vehicle is also now zero. At that point, you can rob energy from the wheels (manifesting as increased rolling resistance or west drag) to drive the propeller. This increased rolling resistance doesn't slow the craft, as long as the total rolling resistance is less than the drag force of the wind pushing us forward. We use this energy to rotate a propeller to push air to the west. From the stationary/ground reference frame, the propeller will have the effect of slowing the airflow behind the vehicle from 10 knots relative to ground to 0 knots relative to ground. This energy -- robbed from the air -- pushes the vehicle forward (east) by Newton's third law. The counterintuition is that the energy that pushes the vehicle forward is robbed from the wheels, i.e. from the vehicle itself. It's correct to understand that the acceleration from such a scheme would be (at best) a net zero. The vehicle was already travelling at 10 knots, so the additional energy now being extracted from the wind makes the vehicle travel faster than 10 knots. Assuming the mass of the displaced air roughly equals the mass of the vehicle, this would get the vehicle to a total speed of 20 knots. As far as I understand it, you can then get the sqrt(2)~=1.4 multiplier from the pitch of the blades - the propeller blades do not face 'straight downwind' (perpendicular to the wind) but are angled. I think that this 1.4 * 2 * windspeed is what gives the 2.8 figure mentioned in the article.
mensetmanusman 5y ago
Part of the key to understanding the intuition of this is to recognize wind as a flux field that is an energy source and consider the limits of a sail that has infinite surface area and zero mass, it could slowly accelerate and propel a frictionless wheel close to the speed of light (this would be a fun calculation). Starting from that point, you realize that by shrinking the surface area to human sizes of interest, you can utilize a larger surface area of wind energy to move mass to larger speeds with some limitations based on friction of the wheels and so forth which is a function of gravity and materials available, etc.
gpderetta 5y ago
As noted elsethread, planes can extract energy from slower tail winds. I wonder if a sailplane with a ram air turbine in the front and a propeller on the back can go faster than tail the wind.
ummonk 5y ago
The key thing to understand this is that it isn’t using a turbine blown by the wind, but rather a propeller that blows the air backwards, with the propeller being driven by the wheels connected to the ground.
robbrown451 5y ago
I think this explains it conceptually best: https://www.youtube.com/watch?v=k-trDF8Yldc https://www.youtube.com/watch?v=k-trDF8Yldc I'm surprised people have such trouble with this.
- ummonk 5y ago
  Yeah, this was exactly the mental model I used to simplify it. Nice to see it in action.
  - robbrown451 5y ago
    I bet your mental model didn't have all the stuffies, though.
    - ummonk 5y ago
      Yeah they add a nice touch - might start inserting them in my mental models going forward.
- cblconfederate 5y ago
  in this case though, it's not the ground that provides the motion but the wind. The mental equivalent of this with wind is not straightforward
  - robbrown451 5y ago
    In the video, the ruler is the equivalent to the wind. Admittedly he then shows moving the ground, to further illustrate the concept.
geocrasher 5y ago
The wind pushes the props because they are sails. Moving sails, but sails none the less. But instead of being windmills, they turn as if they were blowing into the wind. Their sheer sail area moves the car forward. The faster the car goes forward, the faster the blades turn. Eventually the blades are churning the air in front of them, creating a cushion of air behind the vehicle. The wind is no longer pushing the blades, it is pushing the cushion of air created by the blades. That air cushion is now part of the vehicle. As the speed increases, the cushion grows in size to the point which it collapses behind the vehicle. At that point, it's self sustaining and the vehicle keeps accelerating until all the forces involved reach equilibrium, which is around 2.8x the wind speed. This all works because the blades are geared to the rear wheels in the opposite way everyone is expecting.
deleted 5y ago
[deleted]
thehappypm 5y ago
I already commented but have another way to think about this. Release the Blackbird from rest. It’s easy to visualize what happens: the wind turns the propellers, which turns the wheels, and the Blackbird rolls forward. While the Blackbird is going slower than the wind, this is a straightforward system. What happens when the Blackbird is going the same speed as the wind? In that case, the wind is no longer pushing the rotor, since there’s no difference in speed. However, the rotor is still spinning! So now it acts like a propellor — pushing against the wind.
rapnie 5y ago
Now that this thread is not really active anymore I'd like to comment that Business Insider is the record holder of the year for Surveillance Capitalism Sites for me, with 24 trackers present in this article (after I disabled all the tracking I could in the popup dialog, no less).

210 points by dutchbrit 5y ago

Actually, knowing it works now. Even internal combustion engines have only a 40% energy efficiency in converting gas to power, the rest is lost as heat. In this case, I'm trying to think how the wind energy is lost, and it seems that some of that might be lost to the static friction in turning the wheels, and also the attached propeller. However, the energy used to turn the propeller is outputted again, as thrust. Since the initial wind was enough to overcome the static friction, any additional power might be causing it to move faster than the wind. I'm no physicist, but this is pretty cool.

dahart 5y ago
> Since the initial wind was enough to overcome the static friction I’ve seen this idea in a couple of comments here, but I’m not sure what it means, can you elaborate? Rolling wheels are still under static friction. They don’t become dynamic friction unless the wheels are in a skid. Unless what you’re talking about is the static friction of the oiled axle, but I assume that’s not what you meant?

IgorPartola 5y ago

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, irrelevant, etc. Try it with this passage: > They even brought in several of science's biggest names, including Bill Nye and Neil deGrasse Tyson, to help decide who was right. This part just stands out like a sore thumb.

pteraspidomorph 5y ago
Science's Biggest Names! It got a chuckle out of me while reading.
- dagw 5y ago
  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).
ben_w 5y ago
In this case, your BS detector is giving you a false result: https://youtu.be/yCsgoLc_fzI?t=275 https://youtu.be/yCsgoLc_fzI?t=275
- IgorPartola 5y ago
  Thanks for the data point! I would still argue that BN and NdT are only the biggest names in pop science (as in people who wear “I <3 science” t shirts) and not in science as in academia. But that’s cool that they did weigh in on this subject.

Someone1234 5y ago

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 https://www.youtube.com/watch?v=yCsgoLc_fzI

Tuna-Fish 5y ago
The small demonstration that made it click for me is from that video: https://www.youtube.com/watch?v=yCsgoLc_fzI&t=812s https://www.youtube.com/watch?v=yCsgoLc_fzI&t=812s This is exactly what the blackbird does, only with a propeller pushing air in place of the big wheel, and it's a much clearer and simpler demonstration of the same idea, which you can trivially verify.
- iamgopal 5y ago
  This is simplest and best explanation, no doubt why he got his PhD in physics education.
gibba999 5y ago
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.
- ses1984 5y ago
  Ok I have taken college level mechanics (after physics 1-2) and I have no idea what you’re saying.
  - 5y ago

zamadatix 5y ago

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_vehicle) https://en.m.wikipedia.org/wiki/Blackbird_(wind-powered_vehi...

IgorPartola 5y ago
Like the professor in TFA I am also confused: how can the ground be imparting power to the propeller while moving downwind?
- efxhoy 5y ago
  wind pushes vehicle. wheels spin. wheels drive propeller (via gears). propeller pushes vehicle. I first assumed it was the other way around with wind->propeller->wheels, which it is not.
- CarVac 5y ago
  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.
  - formerly_proven 5y ago
    Wind does not drive the propeller.
    - CarVac 5y ago
      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.
  - IgorPartola 5y ago

wccrawford 5y ago

I saw the Xyla Foxlin video about this (and her treadmill version) and that was a fun build to watch.

marcodiego 5y ago

This was posted about a week ago: https://news.ycombinator.com/item?id=28010133 https://news.ycombinator.com/item?id=28010133

everly 5y ago

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.

Strilanc 5y ago
The professor's reasoning is near the start of the video about the bet [1]. Basically they thought the makers of blackbird were fooling themselves (e.g. measuring slower wind at the bottom of the car vs the top of the propeller, or getting pushed above the average wind speed by gusts then selectively reporting). 1: https://www.youtube.com/watch?v=yCsgoLc_fzI https://www.youtube.com/watch?v=yCsgoLc_fzI
xaedes 5y ago
$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!

michaelt 5y ago

> 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 doubt the system would work!

sopooneo 5y ago
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.
- Valgrim 5y ago
  Then what is spinning the wheels?
  - wizzwizz4 5y ago
    The fact it's going forwards.
    - Vvector 5y ago
      And what's making it go forward?
      - Retric 5y ago
        The wind.
        wizzwizz4 5y ago
        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.

sopooneo 5y ago

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 https://www.youtube.com/watch?v=q2il8Fagbyk

dd36 5y ago
Can it be done with solar sails?
- goldenkey 5y ago
  Solar sails only absorb enough energy for tiny crafts in space, a frictionless environment. You overestimate photon flux momentum from the sun.
  - Akronymus 5y ago
    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.
    - goldenkey 5y ago
      The mirrors are extremely heavy and solar sails are exclusively used above our atmosphere, in space, where more flux from the sun is received. The flux even at earth orbit is a measly 47e-7 Newtons per square meter. That's 0.00016905632 pounds per square inch. You still stand by what you just stated? It's not feasible to do below clouds, in an environment with constant friction, air or water resistance. The only reason you can do it in space is because that tiny slow acceleration can accumulate over a long period of time. This precludes frictional losses that would normally be incurred within atmospheres.
      - Akronymus 5y ago

ColinWright 5y ago

Other discussions: https://news.ycombinator.com/item?id=27695869 https://news.ycombinator.com/item?id=27695869 https://news.ycombinator.com/item?id=27696621 https://news.ycombinator.com/item?id=27696621 https://news.ycombinator.com/item?id=27707791 https://news.ycombinator.com/item?id=27707791 https://news.ycombinator.com/item?id=27987321 https://news.ycombinator.com/item?id=27987321 https://news.ycombinator.com/item?id=28000727 https://news.ycombinator.com/item?id=28000727

database_lost 5y ago

"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...

dmurray 5y ago
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.
- database_lost 5y ago
  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)
  - ehsankia 5y ago
    He did study Physics but his main field is science education, I think it's fair to assume a physics professor would know a bit more. I also think it's a bit of your own preconceived notion at play here assuming that calling someone a "Youtuber" is meant as a negative. This is equivalent to saying "Science communicator vs physics professor", which is a fair portrayal.
    - database_lost 5y ago
      I really don't think being called a Youtuber is meant as negative. I take issue with how the writer chose to present this story. If this was about the intricacies of ad revenue on YouTube for example, great, no need to specify he also has a physics degree. But I'm disappointed to see them paint him as just a guy who "likes to break down funky science" (and made 10k off a physicist) when he is more than that, with relevance to the actual story. For someone who doesn't know his work, he might as well be one of the guys burning snow with lighters a few months ago to prove its fake snow...

choffee 5y ago

Is this similar to sailing? Where the lift generated by wind passing over the curved sail or prop blade produces more lift allowing the boat or car to go faster than the wind speed.

ehnto 5y ago
Yes, that's where the creator got the idea I believe. He was imagining two sails rotating around a cylinder, which it turns out, is a propeller.
mumblemumble 5y ago
Yes. If I remember right, the angle of attack of the propeller blades when this thing is at speed ends up being about the same as that of the sail when the boat's on a beam reach. To extend the analogy further, I think that the wheel-and-chain mechanism ends up functioning analogously to the boat's keel.

omega3 5y ago

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_vehicle) https://en.m.wikipedia.org/wiki/Blackbird_(wind-powered_vehi...

marcan_42 5y ago
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.

Jedd 5y ago

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

aaron695 5y ago
This is not what they are talking about. It's always step one to get past to understand what's going on here. I don't believe DDWFTTW has been achieved on water.
- jasonwatkinspdx 5y ago
  You are mistaken. It has been achieved, and the fastest race boats today do it routinely. This is one of the reasons you don't see spinnakers on boats like the America's Cup AC72s, AC50s, F50s, huge open class trimarans, etc. I'm not sure the first boat to achieve it, but it wouldn't be surprising if it was done during the Clipper era. Those boats held 24 hour records from 1860 something all thee way to the 1980s, where modern racing yachts finally eclipsed them.
  - aaron695 5y ago
    I think we just have different definitions. It's about the "Directly" You need a propeller to go Directly Downwind Faster Than The Wind as far as I know. I think on water it has to be very large. I expect there are other ways other than a propeller but haven't seen them. A half way definition (This isn't DDWFTTW to me either), I'd like to know if an America's Cup boat could beat a balloon? So it would be allowed off the 'race track' but it has to come back to meet/beat the balloon at the narrow finish line. So it would cover a much larger distance than the balloon and still beat it to the finish line. Is this possible in practice? The Veritasium video doesn't actually answer this, it kinda goes around it. [edit] If it's symmetrical which it should be, as long as they are going downwind faster than the balloon, they just reverse it at the halfway point and get back inline with the balloon but ahead.

villgax 5y ago

Is there an equivalent for water/hydrofoils maybe?

foxyv 5y ago
I think in his original video he described how a tacking boat can go faster than one going straight down wind. As I understand it, that was the inspiration for the propeller. Here is a good site explaining it: https://newt.phys.unsw.edu.au/~jw/sailing.html https://newt.phys.unsw.edu.au/~jw/sailing.html > How can boats sail faster than the wind? Lots of boats can – especially the eighteen footer skiffs on Sydney Harbour. Ask a sailor how, and he'll say "These boats are so fast that they make their own wind", which is actually true. Ask a physicist, and she'll say that it's just a question of vectors and relative velocities.
xaedes 5y ago
"The physics of a push-me pull-you boat" http://202.38.64.11/~cxyu/AJP_pushmepullyouboat.pdf http://202.38.64.11/~cxyu/AJP_pushmepullyouboat.pdf

textman 5y ago

large ocean yacht racing boats can go much faster than the wind: https://www.kqed.org/science/8503/how-do-these-boats-sail-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-sail-faster-than-the-wind https://www.straightdope.com/21344013/how-can-racing-yachts-... I think I read somewhere that an ice sailboat did 143 mph.

paconbork 5y ago
The difference here is that the vehicle in the article is traveling parallel with the wind
- theli0nheart 5y ago
  I thought the video below provided a good explanation for why this works. The physics are similar to those of a single sailboat going faster than the wind. Imagine two sailboats on a cylindrical ocean on diagonal tacks, on opposite poles, and rotating around the core with rods connecting them to the core. Now you have a propeller. :) https://www.youtube.com/watch?v=jyQwgBAaBag&t=404s https://www.youtube.com/watch?v=jyQwgBAaBag&t=404s

tpoacher 5y ago

"I offered him another 10,000 bet" is such bullcrap though. For the guys making the vid this is win win due to youtube ads. Kusenko isn't exactly taking a cut from that.

zamadatix 5y ago
It's one of the top YouTube channels, they make money off YouTube ads constantly whether or not the professor wants to double down or not. The idea was to point out Kusenko knew it wasn't just a technicality that lost him the original bet even if he didn't want to admit it when conceding.

dahart 5y ago

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 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.

tootie 5y ago
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.
- dahart 5y ago
  That seems too dismissive of the part that’s counter-intuitive, and I think this is legitimately counter-intuitive, which is why physics professors are losing bets. The fan on the boat is blowing air forward from behind the sail, and by it’s very presence on the boat, it applies a force to the boat that is trying to move the boat in reverse. Without the sail, the boat does move in reverse. It’s surprising that one can seemingly recover more force to push the boat forward than was already used to push the boat in reverse. IIRC Myth Busters confirmed the result but didn’t come to a detailed conclusion as to why, which could involve the shape of the hull, directions of the hull & sail relative to the fan direction, or some aerodynamics of the air blocked by the sail. In any case, I think it’s quite different from putting the fan in the water facing backwards to propel forward.

tzs 5y ago

If you believe that sailboats can beat a drifting balloon downwind by zigzagging, then there is a very good explanation in the original Veritasium video that shows that this is essentially the same thing. Here's a link to the section of the video with that explanation [1]. Watch about 2 or 3 minutes starting there and it becomes clear. [1] https://youtu.be/jyQwgBAaBag?t=404 https://youtu.be/jyQwgBAaBag?t=404

rkalla 5y ago

This blew my damn mind 10 years ago when it was first written up in Wired - the way the article was written, the build up to the actual run... all of it was so inspirational and today I still refer to it in my mind whenever I think: "People do the impossible all the time and the guidance they get from everyone around them is that they are INSANE" I think these are the closest we get to moments of 'magic' in real life.

pengaru 5y ago

The propeller is being used a forward motion compensator. At a standstill, the wind just acts on the entire vehicle including the stationary propeller, and sets the whole thing in motion. Without the propeller, going directly downwind would be limited by the speed of the wind acting directly on the vehicle which otherwise lacks any relevant moving parts for the wind to act on. By adding the propeller, driven by the forward motion via the wheels, a part of the vehicle now moves backwards (imagine the cross-section of a propeller blade as it spins, its intersection with the wind travels backwards into the wind) to compensate for the forward movement, giving the wind something to act on even when the vehicle travels faster than the wind.

cblconfederate 5y ago
I wonder how one would go about making such machine that would work in zero gravity. Without friction, something else would have to convert part of the wind force to propeller torque. Maybe small turbines could be added that would spin according to apparent wind (forward or backward) and spin the propeller to generate additional lift.
- pengaru 5y ago
  Fun thought exercise, but are there any practical scenarios where one has wind but no gravity?
  - cblconfederate 5y ago
    solar wind
    - pengaru 5y ago
      Is that really practical considering the already high velocity of the particles? If you matched the downwind particle velocity (>100km/s?) it seems unlikely any mechanical motion compensator could move fast enough to make any significant gain to be worthwhile... but I'm no expert, maybe I'm missing something obvious.

1-6 5y ago

I never had a good experience with my Joby GorillaPod. All the plastic cup pieces developed cracks and the friction just wasn't there. The structural contraption holding up the propeller looks shotty as well. I'm pretty sure Joby Energy and Joby Photographic equipment are separate entities but that name Joby doesn't instill any confidence.

gubby 5y ago

I think the key conceptual thing that's difficult to grasp is the propellor's interaction with the wind. Forgetting the speed of the car vs the wind for a moment, the propellor is arranged so it is trying to push air into the wind (i.e. it is propelling the craft). So, whatever force the wind might impart on a simple flat disc of similar radius to the prop, the force the prop actually experiences is higher than that because it is pushing against the wind. For me, this realisation that the prop is pushing against the wind, increasing the overall force, unlocked understanding how this craft is possible.

neonate 5y ago

https://archive.is/FhZfN https://archive.is/FhZfN

JoeAltmaier 5y ago

Any sailboat?

thehappypm 5y ago

I think I have an analogy that actually explains how this works. Imagine one of those people-mover walkways like they have at the airport. Standing next to it on a skateboard, you grab the handrail. Even though the skateboard has energy loss to friction, you go exactly as fast as the handrail. Now imagine you put a little electric generator in the wheels of the skateboard. Now, not only are you moving at the speed of the handrail, you're also generating some electric power, sourced from the handrail. Now, instead of grabbing the handrail with your hand, yo hold another electric skateboard, and use the power from your feet's skateboard to power that, so you are actually being pulled along the handrail. You'd be inching along the handrail, going faster than it.

rusk 5y ago
This apparently violates conservation of energy as you’re claiming to take energy from one source, put it through some apparatus (i.e two skateboards) to produce more energy without putting anything additional in. Can you account for this?
- ladberg 5y ago
  The people-mover has to expend more energy to push you because you're applying a stronger drag force, so energy is conserved.
  - rusk 5y ago
    Okay so in this case the people mover is drawing the additional energy. Additional energy is being provided from somewhere i.e a diesel generator somewhere up stream has had to increase her fuel consumption to maintain the power on the network.
    - tofof 5y ago
      Right. The people mover is analogous to the wind. You can get to move at the windspeed through drag alone, at which point you no longer move relative to the air. The air is being robbed of only the fraction of energy that you're losing to drag (rolling resistance, as there is no air resistance now). This is you riding along with the peoplemover on the skateboard. But then increase the rolling resistance - the generators on skateboard wheels -- but you still, by drag, move at the wind speed, you're just stealing more energy from the wind/peoplemover now. Then you use that energy (simply by a chain linkage) to spin the propeller, blowing air aft. The propeller pushes air backward, changing the speed of the air molecules in the region behind the vehicle from whatever they were moving at, e.g. 10 knots relative to the ground, to 0 relative to the ground. That energy pushes the propeller and with it the vehicle forward, by Newton's 3rd law. This is the second electric skateboard driving forward, in the frame of reference of the peoplemover. So now you're moving faster than wind speed, in the direction of the wind, stealing more power from the airstream (peoplemover) than you could steal by the (original) drag of your craft alone. You got there by increasing your rolling resistance, which won't slow your craft until the rolling resistance exceeds the available force from the wind. In the analogy, this would be equivalent to jamming your brakes so hard against the floor that you stop the peoplemover rail from moving at all. You use the extra energy -- the amount being spent by the wind to counteract your increased rolling resistance -- to push yourself faster forward.

jayd16 5y ago

This is like putting a turbocharger on a sailboat. I love it.

rusk 5y ago
A turbo charger increases fuel consumption though. You can’t just consume more wind.
- ladberg 5y ago
  In this case they are actually "consuming" more wind. A normal sail "consumes" wind by taking moving wind and reducing its speed to 0. This "consumes" wind by taking moving wind and sending it back the other direction, so it creates more thrust per unit wind.
  - rusk 5y ago
    Sounds to me like it improves efficiency rather than consumes more
    - ladberg 5y ago
      Yep, I thought about it a bit more and you're totally right.
    - jayd16 5y ago
      Same could be said for a turbocharger but we just happen to set the fuel mixture dynamically.
      - rusk 5y ago
        No, turbo specifically draws more fuel. You’re using an elastic definition of efficieny that I’m not gona jive with as energy supply from wind is constant. EDIT it’s more like gearing.
- jayd16 5y ago
  Sure you can. Why not? Can't you extract varying amounts of energy from wind resulting in varying wind speed in your wake?

haberman 5y ago

> 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 of the mast), but this is the exception, not the rule.

jcims 5y ago
Side note, this is my favorite mode of exhibiting pedantry. Let the conversation flow while still correcting terminology. Thanks for the info.
sopooneo 5y ago
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.
- haberman 5y ago
  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.
  - morei 5y ago
    The F50 sailing class used in SailGP can remain foiling during jibes in winds as light as 8 knots. That is, the boat always sees an apparent headwind during the entire downwind run.
- 5y ago

jcims 5y ago

Derek from Veritasium asked Xyla Foxlin to build a functional model, and she goes through the trials and tribulations of that in quite a bit of detail in her video here: https://youtu.be/VUgajGv4Aok https://youtu.be/VUgajGv4Aok There's a key aspect discussed in 7:10 relating to the ratio of the propeller pitch to the vehicle forward motion that is necessary for this to work. (Xyla's channel is a great follow overall btw)

mianos 5y ago
Although not adding much value to the comment, I concur that her channel is great to watch. She is so enthusiastic she would make even the grumpiest professor smile.
fho 5y ago
Xyla channel is definitely worth a look. But she is somewhat rubbing me the wrong way (no pun intented) ... I am not sure if she had a channel before this one, but she basically appears out of nowhere with a perfect brand image: https://www.youtube.com/watch?v=3B9XYJJY6IQ https://www.youtube.com/watch?v=3B9XYJJY6IQ From the get go she is connected into the wider content creation sphere. Appearing in videos from Veritasium, BPS.space, Dolphin Labs, probably some more. She is every nerds wet dream ... smart, creative and good looking with a overly happy attitude. I don't want to talk bad about her ... It's just too perfect for me not to be somewhat suspicious.

jcims 5y ago

The thing I wonder about stuff like this is that a phenomenon we see in one domain will typically transfer to another domain. For example, the 'hydraulic analogy' [1] for electronic circuits is pretty damn good at least on a macroscopic level. I wonder if there are applications of this phenomenon in other types of physical systems (including electronics).

rusk 5y ago
This seems to be highly domain specific though. It’s reading to me like an example of what you can do when you have highly advanced knowledge of a domain to the point where you can do stuff that looks like magic, specifically because it apparently violates generalised principles established across domains.
jasonwatkinspdx 5y ago
Acoustics relies on an analogy to electronic circuit components.

noxer 5y ago

Very bad article. Watch the 2 videos instead.

protomyth 5y ago
Well, 3 https://youtu.be/VUgajGv4Aok https://youtu.be/VUgajGv4Aok Xyla Foxlin's video has the information about the proper ratio of wheel to propeller to make it all work.

smsm42 5y ago

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?

tkzed49 5y ago
> Maybe we could learn something bigger from this? It seems to me that Derek did several things right here: - Choose a topic with which he has relevant experience - Collect experimental data supporting his hypothesis - Fairly address opposing viewpoints, in this case by providing a platform for a dissenting expert to present his evidence Are there examples of similar videos being removed from youtube for misinformation?

guy_named_matt 5y ago

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.

protomyth 5y ago

Kusenko "conceded on a technicality — that the vehicle moves marginally faster than the wind temporarily," Cavallaro said. "I offered him another $10,000 bet, because his technicality is entirely wrong, but I know I won't be hearing from him." Can anyone explain this line's reasoning?

tofof 5y ago
Kusenko, who conceded the bet to Veritasium's Muller, only conceded that if you accelerate an object to wind speed and then the wind suddenly dies, your (low-drag) vehicle will continue downrange at a speed greater than the (now zero) speed of the wind on momentum alone. That technicality, however, is a complete misunderstanding of how the vehicle works. The designer of the vehicle, Cavallaro, apparently only built the vehicle to prove the soundness of the physics to doubters, according to the narrative given by the Veritasium video. That designer offered a second $10,000 bet to Kusenko presumably simply excluding the technicality that Kusenko 'lost' to. It would be a simple bet: that the vehicle can accelerate to and sustain a speed faster than any momentary peak wind speed during the race. Since the vehicle can reach 2.8x the wind speed, all it would take is the vehicle doing so while no gusts exceeded, say, 2.5 the average wind speed during the run. The actual explanation, which apparently still escapes Kusenko: If the wind speed is 10 knots from west to east, then this vehicle can accelerate to 10 knots going east by drag (east) alone. At that speed the apparent flow of air (from the reference frame of the vehicle) is zero, and so the drag (east) force on the vehicle is also now zero. At that point, you can rob energy from the wheels (manifesting as increased rolling resistance or west drag) to drive the propeller. This increased rolling resistance doesn't slow the craft, as long as the total rolling resistance is less than the drag force of the wind pushing us forward. We use this energy to rotate a propeller to push air to the west. From the stationary/ground reference frame, the propeller will have the effect of slowing the airflow behind the vehicle from 10 knots relative to ground to 0 knots relative to ground. This energy -- robbed from the air -- pushes the vehicle forward (east) by Newton's third law. The counterintuition is that the energy that pushes the vehicle forward is robbed from the wheels, i.e. from the vehicle itself. It's correct to understand that the acceleration from such a scheme would be (at best) a net zero. The vehicle was already travelling at 10 knots, so the additional energy now being extracted from the wind makes the vehicle travel faster than 10 knots. Assuming the mass of the displaced air roughly equals the mass of the vehicle, this would get the vehicle to a total speed of 20 knots. As far as I understand it, you can then get the sqrt(2)~=1.4 multiplier from the pitch of the blades - the propeller blades do not face 'straight downwind' (perpendicular to the wind) but are angled. I think that this 1.4 * 2 * windspeed is what gives the 2.8 figure mentioned in the article.

mensetmanusman 5y ago

Part of the key to understanding the intuition of this is to recognize wind as a flux field that is an energy source and consider the limits of a sail that has infinite surface area and zero mass, it could slowly accelerate and propel a frictionless wheel close to the speed of light (this would be a fun calculation). Starting from that point, you realize that by shrinking the surface area to human sizes of interest, you can utilize a larger surface area of wind energy to move mass to larger speeds with some limitations based on friction of the wheels and so forth which is a function of gravity and materials available, etc.

gpderetta 5y ago

As noted elsethread, planes can extract energy from slower tail winds. I wonder if a sailplane with a ram air turbine in the front and a propeller on the back can go faster than tail the wind.

ummonk 5y ago

The key thing to understand this is that it isn’t using a turbine blown by the wind, but rather a propeller that blows the air backwards, with the propeller being driven by the wheels connected to the ground.

robbrown451 5y ago

I think this explains it conceptually best: https://www.youtube.com/watch?v=k-trDF8Yldc https://www.youtube.com/watch?v=k-trDF8Yldc I'm surprised people have such trouble with this.

ummonk 5y ago
Yeah, this was exactly the mental model I used to simplify it. Nice to see it in action.
- robbrown451 5y ago
  I bet your mental model didn't have all the stuffies, though.
  - ummonk 5y ago
    Yeah they add a nice touch - might start inserting them in my mental models going forward.
cblconfederate 5y ago
in this case though, it's not the ground that provides the motion but the wind. The mental equivalent of this with wind is not straightforward
- robbrown451 5y ago
  In the video, the ruler is the equivalent to the wind. Admittedly he then shows moving the ground, to further illustrate the concept.

geocrasher 5y ago

The wind pushes the props because they are sails. Moving sails, but sails none the less. But instead of being windmills, they turn as if they were blowing into the wind. Their sheer sail area moves the car forward. The faster the car goes forward, the faster the blades turn. Eventually the blades are churning the air in front of them, creating a cushion of air behind the vehicle. The wind is no longer pushing the blades, it is pushing the cushion of air created by the blades. That air cushion is now part of the vehicle. As the speed increases, the cushion grows in size to the point which it collapses behind the vehicle. At that point, it's self sustaining and the vehicle keeps accelerating until all the forces involved reach equilibrium, which is around 2.8x the wind speed. This all works because the blades are geared to the rear wheels in the opposite way everyone is expecting.

deleted 5y ago

[deleted]

thehappypm 5y ago

I already commented but have another way to think about this. Release the Blackbird from rest. It’s easy to visualize what happens: the wind turns the propellers, which turns the wheels, and the Blackbird rolls forward. While the Blackbird is going slower than the wind, this is a straightforward system. What happens when the Blackbird is going the same speed as the wind? In that case, the wind is no longer pushing the rotor, since there’s no difference in speed. However, the rotor is still spinning! So now it acts like a propellor — pushing against the wind.

rapnie 5y ago

Now that this thread is not really active anymore I'd like to comment that Business Insider is the record holder of the year for Surveillance Capitalism Sites for me, with 24 trackers present in this article (after I disabled all the tracking I could in the popup dialog, no less).