Veritasium is wrong. Blackbird vehicle explanation.

A wind powered vehicle faster than the wind? Final explanation of this puzzle, intuitive and simple as it should be from the beginning because it's not a rocket science.
"An idea that 99 percent of people declare impossible. Ninety-nine percent of the rest can’t figure out how it’s done." - Can a wind-powered vehicle move exactly with the wind faster than that wind speed?

[killbeas]

One of the correct statements you make is that rolling resistance is approximately a constant. This is true. Then you make a major error in saying this is the only force the cart has to overcome. This is patently false. As the cart picks up speed, the propeller turns faster. Since the only thing driving the propeller is the wheel, the retarding force at the edge of the wheel increases the faster the cart goes. So the prop has to create thrust to overcome an increasing force retarding the carts motion. The only way it does this is that the prop thrust is proportional, but more than, the retarding force of the wheels which is increasing as the cart speeds up. This is due to the constant multiplying force of leverage (the more you put in the more you get out on the other end [not energy but force]) So the cart accelerates until the aerodynamic drag of the cart, the propeller (because it is stirring up air turbulence also) the rolling resistance plus the internal drive train losses equal the thrust force on the cart from the propeller. At this point, all forces and torques are in balance and the cart no longer accelerates. It is at a limit speed well above windspeed.

Note that this leverage is a changeable parameter by the pilot by varying the pitch of the propeller blades and can be a high ratio (lots more force of the prop than the wheels) to a low ratio (very near the same thrust at the prop compared to the retarding force of the wheels [again, very little to do with rolling resistance]).

Cavallaro, Borton, and Derek are all correct that the fundamental principle that makes the cart work is one of leverage. Your error is thinking that rolling resistance is the primary retarding force and it is completely wrong. The tangential force at the wheel to drive the prop is much much larger near limit speed above windspeed, and without the leverage the cart would never work. Once you understand this, you should not retract your video as it is a valuable discussion and it illustrates a misconception that others have fallen into. But you should change the title, and declare that you were the one in error and they were correct.

[eyytee]

Your main error: The orange force F at the wheels, is needed to balance the aerodynamic torque on the propeller. This orange force F:
- Does act as an external backwards force on the vehicle, so it must be included in the force balance that determines acceleration (additionally to rolling resistance).
- It exists right from start, even when the vehicle is not moving yet, if the propeller is already in positive pitch, as was the case for their prototype with fixed pitch. See "BUFC second run" and note how slowly it starts, despite significant wind. That's not due to rolling resistance (which is rather small), but mostly due to the braking force from the propeller torque.

[spqqodd]

Easiest explanation to understand. So basically the energy added to the system at the beginning by the wind pushing the cart is eventually taken back out by drag in the other direction, if my understanding is correct.

[DogDaysofSanford]

Yes, until the cart is moving faster than the tailwind. The built up momentum will propel it forward for a little bit but then the speed will drop off due to no energy being added to the system. Once the speed drops to the speed, or a little bit lower, of the tailwind then the leverage kicks in again and the cycle continues. That's what we see in the video. otherwise it would just accelerate to an infinite speed.

[stoicwam]

The professor was right.

If he was wrong then the vehicle should keep traveling when no wind is present after an initial push.

There should be a chart where at wind speed of 1 mph the cart moves at 2.7 mph, at 2 mph the cart moves at 5.4mph and so on.

But this chart will never be made because it brakes the 1st law of thermal dynamics.

As for the treadmill test is ludacris!if anything it is simulating a head wind. this should be able to chart on a graph as well. What do you think will happen when the treadmill goes at a walking speed? The answer is nothing will happen.

To really test it they should take the most optimal small scale modle that they have created, make a wind tunnel the length of a football field where every bit of air in the tunnel flows exactly the same speed (as close as possible), have multiple readings take place throughout the tunnel to get average wind speed and then set the unit down and see if it can beat the average wind speed th get to then end. But it can't and won't. It would be cheaper to build this than that large unit but they can fudge the numbers with the large unit

how fast should it go at 1mph, 2mph, 3mph. There should be a graph charting this.

Wind tunnel and unit on a track is the best way to test. Keep it small like the treadmill units. Have steady wind speed. But this won't happen because it would ruin the theory.

If it runs faster than the wind @ a wind speed then it should be able to run faster than the wind at 0 mph. Let me explain:

If it's the wheels powering the propeller which pushes the vehicle faster than the wind then after starting the unit with a push the wheels should be able to power the propeller and push it at the same rate as when it has wind.

A vehicle moving at 11 mph with a 10 mph tailwind is moving upwind at 1mph. The wind in perspective to the vehicle is now a head wind. A vehicle traveling 1 mph in no wind has a 1mph head wind. It's the same thing. Get the vehicle started with a push and it should beable to power itself. I don't think I'm missing anything but if I am please explain

just rewatched the blackbird professor bet video. @12:05 the claim is made "the propeller thrust force is greater than the drag on the wheels".

If this statement is true we can expect the unit to produce greater thrust force in a no wind test. Just get the vehicle started with a push and then the propeller will overpower the drag that wheels produce

Im not into all the math equations but just coming from a practical standpoint imo the black bird is a hoax

[infinitelyexplosive]

Get two ice cubes that weigh the same and put them on something flat. Push on both of them at the same time, one at the very edge and one in the middle. They both move forward, but the one you pushed on the edge of also starts spinning. Clearly the force wasn't used up to create the torque, since they both move.

[subductionzone]

You started to go wrong when you said that the orange tangential force would not affect the velocity of the cart.

[coolaun]

Hallo Piotr, I have a question for you: if you take a simple cart, give it a push to get it rolling, and then turn on a dynamo that takes power from the wheels to turn on a light, does the dynamo slow down the cart?

[sergiyisakov]

I think you're missing propeller resistance in your equation or at least include it in rolling resistance. Rolling resistance is a resistance of wheels without propeller. But if we add a propeller then we need to apply more force to the wheel to create thrust. And "generated" thrust force will not exceed the force applied to propeller, so the only driving force here is the wind. I guess the whole trick of this experiment was using inertia to temporarily accelerate the cart.

[justinberg]

I commented on the original video. The speed of the wind is not a true measurement of its power. Air has mass, and therefore has kinetic energy when moving. Hypothetically, if we substituted the wind, and instead use the impact of a train moving at say 50 mph vs a toy car moving 50 mph the train would make the propellers spin much faster than the toy car. You can't just measure energy by speed alone. Propellers are also designed to catch air to create thrust. The car is NOT...ALSO, Imagine if the car being used was very aerodynamic, and the wheels were virtually frictionless.

[yup]

The vehicle initially accelerates due to the tailwind pushing on all surfaces of the vehicle.

It is important to note the propeller is initially stalled! Once the wheels can turn the propeller fast enough it will unstall and only then start to produce thrust.

The vehicle is able to exceed the wind because the tailwind reduces airflow through the propeller enabling it to produce maximum thrust (static thrust) for far longer.

I hope this helps :)

[johnborton]

Of course the tangential force impacts the velocity of the cart. It must be overcome by a force in the opposite direction or cart doesn't move.

Wow.

[FlyNAA]

Say you put a round garbage can lid down on an ice rink, and push tangentially on the edge. You really think the center will not move?

[unleashthecomposerinyou]

The vehicle works by harnessing the tail wind even beyond the tail wind speed. In other words utilizes the tail wind to the maximum. The key to this puzzle is that the vehicle is moving against the ground and has to power the props whereas the props is working against the relative wind which is less than ground speed (ie speed relative to an observer on ground frame). The propeller static thrust is larger than when in a headwind. This difference in force (thrust - wheel resistance) > 0. This accelerates the vehicle. The cart speed reaches the terminal speed when the energy input from tailwind is spent on drag of vehicle, propeller losses, drive train etc.

[rodfreess]

Stanislaw, Tadeusz and Wojciech went to the Polish American convention in Chicago. They checked into the hotel but there was only one room available, due to the huge attendance, so they decided to share a room. The room was $30 so they each paid $10. But then the clerk realized he hadn't given them the special convention rate of $25, so he sent $5 with the bellboy to return to them. The bellboy figured there was no way he could divide $5 evenly, so he kept $2 and gave each of them $1.

So, if they each paid $9, times three people equals $27 and the bellboy kept $2, equaling $29 dollars, where did the other dollar go?

I understand your explanation well enough, the concept you are trying to convey is helpful. Maybe the problem is your english is good enough to be taken as perfect, but your accent confuses americans as more intelligent and technical than you intend? no offense intended.

Like the joke, we have a simple explanation that is very confusing only if you let it confuse you. The simple explanation that I haven't seen yet is simply adding up the distance traveled as you would for a simple diagram of forces. That is, the car will approach the wind speed with a flat square sail, and the propeller will push the car a certain speed, and those speeds/distances will ADD together to make the car travel faster/further than the wind. And that's my guess where the other dollar went. Not a technical accounting, just an explanation for how it's possible.

[joakimquensel]

I agree the wheel size explanation was not making sense. However, wheel size/gearing matters because propeller speed must be high enough for the propeller wing to be efficient. It needs to generate higher thrust force than the propellers wings drag force. This is what makes it possible for the car to go faster than wind speed, part of the thrust force translate into kinetics energy of the vehicle moving forward, another part goes to overcome the propeller drag force (turning the wheels) and the rest of energy goes to various friction losses and vehicle aerodynamic drag. Which means car will accelerate as long as the thrust energy from the propeller is larger than the rest of these energies.

And the reason it does not break the laws of physics is that the vehicle uses the energy of the wind that slows down as it is passing the propeller when it comes to thrust force vs drag force of the propeller wing.

[Notsokyle]

Im a pilot and I only know about left turning tendencies 💀

[tarng]

I have limited education in physics and math but I do have an opinion on your video. Please make more videos in english. Your english is great, your accent is nice and your explainations are such that a layman can understand your point. I love the graphics you used too. They were to the point and there was no more or less than necessary. Great job.

[ChrisBreederveld]

Here are some links to the video's he's talking about:

When looking back on the videos and all the math involved I find it very brazen of the author of this video to state "his arguments are wrong" based on one very specific use of the leaver analogy.
There are many point that check out mathematically in Veritasium's video and I would dare to say all of them. It's just that the argument of the leaver seems to confuse this author.

Also I believe the statement about the rolling resistance is false; rolling resistance is constant over distance, but not over time.
All forces in this video are time dependent which means that the rolling resistance should also be, so this means that force should not be constant.

Disclaimer: I'm not all that versed in all the math going on, but I do believe there are certain things not addressed in this video, like a clear explanation of why Veritasium was wrong (which is the title of the video).

[tritonum]

I knew something was missing from his explanation. Thanks!!!