Risking My Life To Settle A Physics Debate

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 sailboat and you're sailing it straight downwind...

• 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 recumbent. 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 downwind, 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 its 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 brainteasers.

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 sails 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 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 propeller. 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 kilometers per hour wind and everywhere else, there would be 10 kilometers 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.

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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.