This propeller craft was built to
settle a physics debate because what its creators claim it can do is so
counterintuitive that it seems to violate the law of conservation of energy. So I've come here to drive it
myself and see if it really works. And is it safe? It feels makeshift.
I'm not gonna lie. I need some wind. Give me a gust. It's a
little unbalanced. Isn't it? Slow it down, Derek! Pull tack, pull tack! This video was sponsored by Kiwico,
more about them at the end of the show. I've come to El Mirage, a dry lakebed, a couple hours from Los Angeles to
race a one of a kind propeller craft. It's called Blackbird. And I'm here with its inventor, Rick - Howdy! And the current owner, Neil. It all started with a brain teaser: Can any wind-powered
vehicle go directly downwind faster than the wind itself? If you've got a sail boat and you're
sailing it straight down, wind. - Yeah. As soon as that sailboat is
going the same speed as the wind, then there is no more wind. That is
correct. You can't push the sailboat. So sailboats can't just go
downwind faster than the wind. Not straight downwind. -Not straight downwind? Not direct downwind. Imagine a boat floating in the water. As the wind picks up, it pushes
the sail, accelerating the boat. The boat gets faster and
faster until its speed exactly matches the
wind. But at this point, the wind can't push the
sail anymore. I mean, if you imagine it from the
frame of reference of the boat, there's no longer any apparent wind. There's no air moving over the boat
because the air and the boat are moving together at the same speed. So a sailboat going directly
downwind can only match the speed of the wind, never exceed
it, even if there's no drag. But the claim is Blackbird can do it. It can go straight downwind faster
than the air that is pushing it. Well the weather forecast is
still holding. Okay, good. We can feel it's at like one now. Yeah. But El Mirage has a reputation of like
when it fills in... Yeah, it happens. It happens. I think we start somewhere
in the middle. All right. Well, let's, let's move over. We're moving to a spot
that will give us a long, straight path downwind with no obstacles. All we need now is for the wind to
pick up and maintain its direction. But we've been out here in the
hot desert for hours and there is still no wind. This is Gene. He runs
the YouTube channel Potato Jet. All the awesome drone shots
in this video are his. So if you like cameras and
gear and amazing drone shots, go check out his channel. This is, this is about a
typical day. How it goes. Derek, I think the wind is
just chosen its direction. I want to move us to the
other side. We'll set up. We'll point downwind over in
this direction. We'll put you in. Let's make it happen!
Yes. I want to do it! Your feet need to go a long way
down. So it'll feel really recumbant. So maybe I need to... Keep going.
Should I get something behind me? Yup! I'm very reclined. Yeah.
Let me see what I can find. It's slightly terrifying to, uh, not be able to push the brake all the way. So you're kind of right
at the limit of size. Yeah. You wouldn't want to be any
smaller. Uh, so steering is I... - Push to go left, -Push to go left. -Pull to go right. -Pull to go right. While steering with my right hand, I have to control the pitch
of the propeller blades. With my left hand. And then in terms of like, when I'm getting to the end or something
where I really want to slow down, the right move is pull back? You're saying the right move is push forward? I'm glad that the two experts here
are disagreeing on what to do in the emergency case of like, I
just want to stop the vehicle. - Feel which is slowing you down
and do that. [nervous laughter] It's just terrifying not to have
a, a blanket rule. Well, uh, this is intense. I have never tried to go faster than
the wind downwind in a vehicle where I'm just supported by this
mesh hammock under my butt. It feels like being in a rolling coffin. It's just been uh shoddily put
together, but I'm excited to try it. And I'm excited to survive. You can look at that
orange string right there. It's showing that the wind is picking
up behind me. This is what I need. On the front of Blackbird, there's a,
telltale, a little piece of string, which shows which way the wind is
blowing. To drive straight downwind. I just need to follow the telltale. So it should be pointing
straight out in front. Now, if I get up to wind speed, the telltale should drop straight down
because effectively I'll be in still air. I'll be moving exactly
the same speed as the wind. All right, good luck Derek!
- Thank you. I hope I survive this. Come on, come on. I need some wind. Give me a gust. Now, if I can actually
go faster than the wind, the telltale should flip around and point
straight at me, indicating that I have an apparent headwind, even though the true wind, standing
on the ground, is coming from behind. We're going straight downwind. What have I got? Six miles an hour. The string is just dangling. You
see the string dangling there? Oh, I just need a gust right here. I just
need a bit of wind. That's all I need. I will, uh, hop on the brakes
here. Man, we were so close. I mean, I saw that string
dangling down. I was like, okay, this is it. Let's keep going. And then unfortunately. At one point it was
dangling and I asked, what speed are we? And he said, we're five or six
miles an hour. And I'm like damn. Cause he's almost exactly wind speed.
Yep. Five or six miles an hour. Just not enough to get you -
right - past there. I needed just like that extra few. Miles an hour. 8's kinda the absolute
minimum, 10 is pretty healthy. Yeah. Yeah. Well, I can't wait. Now you might be wondering how it's even
theoretically possible for this vehicle to go faster than the wind
will. Well sailboats can do it. As long as they're traveling at some
angle to the wind. In this case, the sail acts like a wing air flows
faster over the outer curved surface than the inner side, which generates lift a
force perpendicular to the apparent wind. A component of this lift force
is in the forward direction. So maximum speed is reached when this
forward force is equal to all the drag forces on the boat, pushing it backwards. Some boats can go three
or four times wind speed. Somebody had asked the question. If
a sailboat is tacking down, wind, can it do a VMG velocity made good
directly downwind? Can it beat - if I, if I release a balloon in the air, can the sailboat tack its way down and
beat the balloon to its destination? And I didn't know the answer. It turns out that sailing
at some angle to the wind, a sailboat can go enough faster that
it's resulting velocity directly downwind is faster than the wind
itself. In other words, it can beat a balloon that
is just drifting on the wind. I love brainteasers. I just
love doing brainteaser. So I thought this is really close to a
good brain teaser, but it's right now. It's just a question though. If we make it go straight downwind and
then people were definitely going to say no. If the earth were a cylinder, instead of a sphere, I can have a
sailboat on a continuous downwind tack. The wind is going along the
earth, this cylindrical earth. And the sailboat is just
spiraling its way down. - Hmm. If I put two sailboats, one on
either side, they can both do this... Well. That's a prop. Effectively their sales make a propeller, a propeller that is traveling down
this earth faster than the wind itself. It was, I posted on two
forums that I was on. Right. And I thought people are initially going
to go, no, never work. And then I say, okay, here's how it works. And they
go oh, [bleep] you got us. Boy, I couldn't have possibly been more wrong. This is, obviously, stupid.
Wind isn't some kind of magic. We all want to believe
in perpetual motion, but I just don't see the logic
of this argument as yet. Okay. This is clearly fake. Anyone with
a clue should see the problem here. Once you reach wind speed,
what powers it past that? I am not a stupid person,
but I cannot understand. Ultimately we said, okay, if we build a little model of one and put
it on a treadmill that just puts it to bed. Right. And it worked really well. Now you,
you're holding it back with this spork? otherwise it'll climb right
up the top of the treadmill. Yeah I'm keeping it from coming forward, But people on the internet just wouldn't
believe him. They thought it was fake. And even physics professors were arguing
that the treadmill wasn't a good analog of the real world. And I'm like literally
day one, physics is inertial frames, right? It doesn't matter if you're
moving or the air is moving. The others were saying there's
magnets, there's wires. And you go there's fans out of view.
So then we do one showing, you know, - no fans - the curtains aren't
moving and stuff. And finally he says, we got to build the real thing. Okay. We are cooking. I see we're going seven, seven
miles an hour, eight miles an hour. Come on. You got it. Come on. Uh oh. I'm very sad about this propeller. So I'm guessing this means the
chain has come off. How did it feel? It was a lot of fun. I could feel us
picking up speed. I could see it spinning. I could see that we got up to like
eight miles an hour, nine miles an hour. And I was like, oh, we're
just going to do it. You know? And then all of a sudden I
still felt like I was going, but I noticed that the prop wasn't
spinning, and I thought, oh, that's a terrible sign. So, uh, yeah.
Then we had to stop and fix the, fix the chain. When in doubt use a bigger wrench. So here's the thing about this
vehicle. It's not what it looks like. What you imagine. I bet is that when
the wind blows on that propeller, it spins the way the wind is pushing
it. And that drives the wheels. But that's actually not how this works. The way it works is the
wind pushes it from behind. And just because it's a bluff body, it's just an object
sitting out in the desert. It starts to roll forwards a little bit. Now that causes the wheels to turn
and they're geared to the propeller in such a way that they turn it opposite
the direction the wind is pushing it. So rather than this propeller
operating like a windmill, it spins like a fan pushing air backwards. And that's what drives the craft forwards. So like one of those crazy things
you never think you're going to do, be out in a dry bed with some crazy
propeller vehicle that some physics professors believe break the laws
of science. Yeah. That's cool. Derek, ready to rock.? If you
think so, I'm ready. All right. We're hoping we can
catch one of these puffs. The wind is strong and
the prop is turning, but something is definitely wrong.
Just look at that propelorl. It' a little unbalanced, isn't
it? Pull the pitch! Good. So what's the game plan? If you feel excessive vibration. I think
we got to pull the trigger on it. Yeah. And I want to go right out and say: I
don't think I would drive it in this wind. I will, if you would
like me to. I mean, I will, I will given the opportunity,
but I'm more than hap... I didn't come here to drive. So
you drive it. If you want to do it. If you were going to decide
about getting in like it there a. Is there a point where you
say that's too much? Um, for today and the way
things are? 15 ish. Okay. So 15ish is what we were measuring like
earlier. What are you seeing now? Ehh... That feels like. 15 To me. Yeah. I've been out there for several hours
and first it was just waiting to go. And now it's like, it's broken
and now I was like, we can go, but it might shake itself apart.
And the wind is on the high end. This is sketchy for sure. Oh God. Did We get that on camera?
Did you? I did, Oh no! Uh, what's happening is they're getting
pretty uncomfortable with what they saw in terms of the shake, the wobble. And they're worried that it's gonna
like break in half the whole structural component and the whole propeller is
going to come down on whoever's driving. So they're a little bit, um,
reticent to let me keep driving. So the guy who basically built it, he's going to risk himself
in the driver's seat. And then if it's not shaking itself apart,
then maybe I get another shot after. So that's a, that's the word right now. In Rick's run, it didn't
seem to shake very much. So they think it's safe
for me to jump in. You don't think this wind is much more than. I do. I really do. But it means that you will have
nearly a guaranteed success, but you just got to manage your limit. How much faster than the wind do you
think you need to go? Yeah. -You doing it? Man, It feels like just the
stakes keep getting higher. Like they didn't want me to run
it before 'cause it was too windy. But like now it's windier, but they're
comfortable with me piloting it. So I don't know what to say.
This is frightening, but
also I came here for this. I want to do it. Put me in coach. If this thing doesn't fall
apart, maybe I'll be able. To go faster than the wind this time. I'm getting in that vehicle
and I'm headed that way as fast as I can. The sun is setting and we're going for it. This is the last chance for me to
go faster than the wind downwind. This is the one guys. Back, a little left so that I can make
a straight shot down at the windsock. It looks like we're coming
up on wind speed here. Blackbird is getting faster and faster. I'm just willing it to
go past the wind speed. Come on, come on, come on.
Speed up, speed up with me. Come on, yeah. Wooooo!
Yeah.... And there you have it. The telltale is pointing straight back
at me showing an apparent headwind while the windsock shows the true wind
is in the opposite direction. I'm going faster than the wind. Slow it
down
Derek.
Pull
tack,
pull
tack!
Oooh,
that
was... God damn that got my heart rate up.
Sacred the [beep] out of us Derek. -Did that look scary? Cause
it didn't feel too bad. So how does it actually work? Well, I worked on this video for weeks without
really understanding how it works. So I want to share with you
the way that I understand it. So if this vehicle is moving
at the speed of the wind well, then there's no relative
air motion over the cart. So how can it keep accelerating? If this were like a windmill that required
air to flow over it in order to turn well, then it wouldn't accelerate
anymore, but that's not how this operates. This propeller operates as a fan, which
means if you imagine this still air, the propeller can come down and
hit some of these air molecules, pushing them backwards
and therefore get thrust. It's like having a fan on your cart.
So of course even in still air, having a fan on the cart
will blow you forwards. But that brings up this idea of it feels
like we're getting energy from nowhere. Where's the energy to power the fan coming
from? If it's coming from the wheels, why doesn't that slow us down more
than the fan manages to blow us back. And the answer to that is that you're
moving at a different speed over the ground. than you're moving through the
air because you have that tailwind. So the way I like to
imagine it is like this: there's air everywhere going 10
kilometers per hour down that way. Now, even if we're going
10 kilometers per hour, we can still push air backwards. And so if you were to look at a profile
of the air in a stationary reference point, you would see that the wind
behind the propeller would be moving more slowly downwind than all the other wind. That's because this propeller has
taken some of the energy out of that wind and converted it into the
kinetic energy of this cart. So behind the propeller, there would
be, say, eight kilometer per hour, wind and everywhere else, there
would be 10 kilometer per hour wind. So the energy from this wind behind
the propeller has gone into the cart into accelerating it forwards. So it is moving forward
faster than the wind. Even when this is moving
forward, faster than wind speed, the propeller can still
push the air backwards, slowing down that tailwind and
taking some of that wind's energy, converting it into the kinetic
energy of this vehicle. Now the people who made Blackbird
managed to get a record, they got up to 2.8 times the wind speed. So it is obvious to me from all of the
demonstrations and from riding in the vehicle myself, that this
is physically possible. There is a way to drive a vehicle that
goes downwind faster than the wind. But I know it is so counterintuitive
that I expect a lot of pushback in the comments. My only request
is please be civil. Hey, this video was sponsored by Kiwico
a company that makes awesome hands-on projects for kids. Now the big idea is that while playing
and having fun kids learn about STEAM concepts, that is science, technology,
engineering, art, and math. When I pull out a crate, my kids
jump at chance to make it with me. And what's really handy is that all the
materials you need come right in the box. And that means no running out to
the store. You just open it up and go. Now in this one, we learned about
aerodynamics like lift and drag. And in addition to the project, there's a magazine with
lots of additional content. Now I think this is the best way to learn, by doing something
yourself and having fun. This is how education
really should be. Now. Kiwico has eight subscription
lines targeted at different
age groups all the way down to newborns. So if you want to try
it out, go to Kiwico.com/veritasium50 and you'll get 50% off your
first month of any crate. Now I will put that link
down in the description. So I want to thank Kiwico for sponsoring
Veritasium and I want to thank you for watching. Stop it? You
can push the button now.
This was actually a question on the 2013 USA Physics Olympiad. If anybody's interested, I wrote a detailed solution that quantitatively explains how it works.
This was perplexing till they revealed there was a link to the wheels.
somebody correct me if I'm wrong, but the way I understand it, the "energy" comes not from the wind, or from the land, but from the land and wind moving at different speeds. For me it's more intuitive if we use the wind's frame of reference, and imagine that the wind is still and the land is moving backwards, just like in the treadmill demo at 9:30. In this case, as the land moves backwards, it turns the wheels and turns the propeller into a "fan" pushing backwards, (as Derek explains at 19:00), which pushes the vehicle forwards.
So what I'm getting out of this is that this wouldn't work if the wind were still relative to the ground. They're taking advantage of an energy gradient between the air and the ground. That's why it works on the treadmill, because the ground is moving at a different speed than the air. In that case I think this could work in water too, or really any two flowing mediums you can connect with a mechanism, even two moving masses of air. You could make a boat with some kind of turbine on the bottom to drive a propeller in the air. I wonder if it would be more or less effective to do it in water?
Here is a way to think about it: There are 2 ways in which energy from the wind is transferred to the vehicle
With only the first transfer of energy, the vehicle will only achieve a speed less than the speed of the wind, since the force is due to the drag, which decreases as the delta between the wind and the vehicle speed decreases. (A negative feedback loop)
With the second transfer of energy, from the lift generated by the prop, the force increases when the prop speed increases. So as the vehicle goes faster, the energy transferred from the wind to the vehicle increases. (A positive feedback loop)
Edit: See replies for a better explanation, this does actually seem to work.
Assume the vehicle starts out at airspeed, there is no wind from its perspective. We turn on the prop which we assume has no inertia or friction so all the effort we put in goes into pushing air backwards.
Whatever force we exert to push air backwards will push us forwards (Newton). Since we use our speed to drive the prop, the wheels will apply a backwards force equal to the force pushing back the air.
The force pushing the vehicle forwards and backwards are the same, there is no acceleration.
I actually thought this might work: The difference in velocity of ground and air is present independently of the velocity of the vehicle, this is a form of "order" (in reference to entropy). If I were to wait a long time, the wind would disappear and there would be an equilibrium where the air is not moving relative to the ground (assuming no outside influences). An increase of entropy (loss of usable energy if I understand correctly) must have happened.
I do not see a reason why this usable energy could not be accessed independently of whether I am moving or not, there should be some way of doing it. I just don't see how that contraption could work. It would be very inspiring because I thought there was no way to innovate with something so simple in an area so thoroughly explored.
Criticisms towards the video:
The string used to measure the apparent wind-speed is right in front of a giant fan, why not attach it to the car and show a drone shot of both vehicles moving at the same speed simultaneously?
The sailboat analogy sounded really brilliant at first but I do not think that you are going to be able to go in the downwind direction faster than the wind just because you are at an angle, you may beat a sailboat sailing straight downwind but you are not beating the wind (I feel like the guy misunderstood this). The sailboat does not even have a way to use the difference in air- and ground speed which is the only reason that contraption could have worked.
Even if the guy did misunderstand, coming up with the analogy was quite brilliant and I appreciate that people are trying to make videos like that.
PS: I don't actually know what I am talking about too well so please correct me, I am really interested in whether this actually works or not.
Also: The force pushing back the air is dependent on the velocity relative to ground, but that changes nothing, this should work at all velocities, right?
Is this not the same as an auto gyro rig on a boat like this?
If this works, what causes it to stop working? In other words, why doesn't the vehicle continue to accelerate indefinitely?
I feel like this is the airplane treadmill problem all over again