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

<a href="https:&#x2F;&#x2F;archive.is&#x2F;FhZfN" rel="nofollow">https:&#x2F;&#x2F;archive.is&#x2F;FhZfN</a>

<i>&gt; The secret to Blackbird, Cavallaro explained, is that once the wind gets the vehicle going, its wheels start to turn the propeller blades — they&#x27;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.</i><p>That&#x27;s a terrible explanation - no wonder people doubt the system would work!

The most surprising thing here is that someone on Twitter made a bet, lost the bet, and then actually <i>paid</i> said bet.<p>Playing devil&#x27;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].<p>[0] <a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=yCsgoLc_fzI" rel="nofollow">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=yCsgoLc_fzI</a>

&gt; Any sailor worth their salt can tell you that a boat can travel faster than the wind by cutting zigzag patterns; that&#x27;s called tacking.<p>This is a pedantic point, but when you&#x27;re cutting zigzag patterns downwind it&#x27;s called jibing, not tacking.<p>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.

&quot;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.&quot;<p>The &quot;popular YouTuber&quot; is Derek Muller, who studied Engineering Physics and has a PhD in Physics Education Research... It&#x27;s so frustrating to see how the writer tried so hard to make as much as clickbait-y title as possible...

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.<p>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 <i>by</i> the blades.<p>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&#x27;s self sustaining and the vehicle keeps accelerating until all the forces involved reach equilibrium, which is around 2.8x the wind speed.<p>This all works because the blades are geared to the rear wheels in the <i>opposite</i> way everyone is expecting.

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:<p><a href="https:&#x2F;&#x2F;youtu.be&#x2F;VUgajGv4Aok" rel="nofollow">https:&#x2F;&#x2F;youtu.be&#x2F;VUgajGv4Aok</a><p>There&#x27;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.<p>(Xyla&#x27;s channel is a great follow overall btw)

For those that hate the way news articles are written I found the Wikipedia article a much clearer read <a href="https:&#x2F;&#x2F;en.m.wikipedia.org&#x2F;wiki&#x2F;Blackbird_(wind-powered_vehicle)" rel="nofollow">https:&#x2F;&#x2F;en.m.wikipedia.org&#x2F;wiki&#x2F;Blackbird_(wind-powered_vehi...</a>

I think I have an analogy that actually explains how this works.<p>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.<p>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&#x27;re also generating some electric power, sourced from the handrail.<p>Now, instead of grabbing the handrail with your hand, yo hold another electric skateboard, and use the power from your feet&#x27;s skateboard to power that, so you are actually being pulled along the handrail. You&#x27;d be inching along the handrail, going faster than it.

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: &quot;People do the impossible all the time and the guidance they get from everyone around them is that they are INSANE&quot;<p>I think these are the closest we get to moments of &#x27;magic&#x27; in real life.

The treadmill demos made me think of another counterintuitive possibility that I wondered if anyone had pulled off: sailing a boat <i>indirectly</i> up a river in no (bank relative) wind.<p>Turns out, it has been done: <a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=q2il8Fagbyk" rel="nofollow">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=q2il8Fagbyk</a>

I think this explains it conceptually best: <a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=k-trDF8Yldc" rel="nofollow">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=k-trDF8Yldc</a><p>I&#x27;m surprised people have such trouble with this.

Other discussions:<p><a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=27695869" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=27695869</a><p><a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=27696621" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=27696621</a><p><a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=27707791" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=27707791</a><p><a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=27987321" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=27987321</a><p><a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=28000727" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=28000727</a>

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

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.<p><a href="https:&#x2F;&#x2F;mythresults.com&#x2F;blow-your-own-sail" rel="nofollow">https:&#x2F;&#x2F;mythresults.com&#x2F;blow-your-own-sail</a><p>It also reminds me of the Brayton Cycle, and turbofan&#x2F;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.<p>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.

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).<p>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.

<i>Kusenko &quot;conceded on a technicality — that the vehicle moves marginally faster than the wind temporarily,&quot; Cavallaro said. &quot;I offered him another $10,000 bet, because his technicality is entirely wrong, but I know I won&#x27;t be hearing from him.&quot;</i><p>Can anyone explain this line&#x27;s reasoning?

I feel that the Business Insider title is really misleading and counterproductive; because Derek Muller is not &#x27;a youtuber&#x27; -- he&#x27;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 &#x27;A youtuber bet a physicist and won&#x27; just makes it seem that experts are wrong, whereas in reality, this was expert vs. expert. That being said, physics is such that if &#x27;some youtuber&#x27; bet a physicist, and was right... physicists would concede.

large ocean yacht racing boats can go much faster than the wind: <a href="https:&#x2F;&#x2F;www.kqed.org&#x2F;science&#x2F;8503&#x2F;how-do-these-boats-sail-faster-than-the-wind" rel="nofollow">https:&#x2F;&#x2F;www.kqed.org&#x2F;science&#x2F;8503&#x2F;how-do-these-boats-sail-fa...</a><p>Also this: &quot;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&quot; from: <a href="https:&#x2F;&#x2F;www.straightdope.com&#x2F;21344013&#x2F;how-can-racing-yachts-sail-faster-than-the-wind" rel="nofollow">https:&#x2F;&#x2F;www.straightdope.com&#x2F;21344013&#x2F;how-can-racing-yachts-...</a><p>I think I read somewhere that an ice sailboat did 143 mph.

The propeller is being used a forward motion compensator.<p>At a standstill, the wind just acts on the entire vehicle including the stationary propeller, and sets the whole thing in motion.<p>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.<p>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.

I already commented but have another way to think about this.<p>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.<p>While the Blackbird is going slower than the wind, this is a straightforward system.<p>What happens when the Blackbird is going the same speed as the wind?<p>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.

I think the key conceptual thing that&#x27;s difficult to grasp is the propellor&#x27;s interaction with the wind.<p>Forgetting the speed of the car vs the wind for a moment, the propellor is arranged so it is trying to push air <i>into</i> 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.<p>For me, this realisation that the prop is pushing against the wind, increasing the overall force, unlocked understanding how this craft is possible.

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.<p>In this case, I&#x27;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&#x27;m no physicist, but this is pretty cool.

My first thought about it was that it&#x27;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 &quot;physical misinformation&quot; - after disagreeing with a renown expert in the field - and maybe we would never found out about it.<p>But, apparently, there&#x27;s a way for people to disagree about science - without any of the sides being evil or stupid - and there&#x27;s a way to find out who&#x27;s right. Maybe we could learn something bigger from this?

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.<p>Odd that the professor was so keen on betting in that case.

Sailing faster than the apparent wind[0] has been going on for a while, especially on v.high performance land and water yachts. [1]<p>The physics involved still twist my brain, but there&#x27;s nothing terribly new here.<p>[0] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Apparent_wind" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Apparent_wind</a><p>[1] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;High-performance_sailing" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;High-performance_sailing</a>

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&#x27;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.<p>[1] <a href="https:&#x2F;&#x2F;youtu.be&#x2F;jyQwgBAaBag?t=404" rel="nofollow">https:&#x2F;&#x2F;youtu.be&#x2F;jyQwgBAaBag?t=404</a>

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 &#x27;hydraulic analogy&#x27; [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).

I find it extremely counterintuitive, especially this part:<p>In 2012, Blackbird also demonstrated sailing directly upwind with twice the speed of the wind.[0]<p>[0] <a href="https:&#x2F;&#x2F;en.m.wikipedia.org&#x2F;wiki&#x2F;Blackbird_(wind-powered_vehicle)" rel="nofollow">https:&#x2F;&#x2F;en.m.wikipedia.org&#x2F;wiki&#x2F;Blackbird_(wind-powered_vehi...</a>

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.

As noted elsethread, planes can extract energy from slower tail winds.<p>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.

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.

Is there an equivalent for water&#x2F;hydrofoils maybe?

I never had a good experience with my Joby GorillaPod. All the plastic cup pieces developed cracks and the friction just wasn&#x27;t there. The structural contraption holding up the propeller looks shotty as well. I&#x27;m pretty sure Joby Energy and Joby Photographic equipment are separate entities but that name Joby doesn&#x27;t instill any confidence.

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

This was posted about a week ago: <a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=28010133" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=28010133</a>

Very bad article. Watch the 2 videos instead.

Now that this thread is not really active anymore I&#x27;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).

Any sailboat?

&quot;I offered him another 10,000 bet&quot; is such bullcrap though.<p>For the guys making the vid this is win win due to youtube ads. Kusenko isn&#x27;t exactly taking a cut from that.

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:<p>&gt; They even brought in several of science&#x27;s biggest names, including Bill Nye and Neil deGrasse Tyson, to help decide who was right.<p>This part just stands out like a sore thumb.