Novel Propeller propulsion, going faster downwind than the wind

[jbinbi]

Mods, not sure what forum to put this in, so please move if not correct...

I came across this video showing a propeller driven car being able to go faster downwind than the wind. If you watch the video he explains how it is done, not sure it would apply directly to a boat as air dynamics are different than wind and ground dynamics.

I have degrees in Physics and Engineering, and I would have taken this bet as well.

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

A Physics Prof Bet Me $10,000 I'm Wrong
A UCLA Physics Professor bet me $10,000 that my video about going downwind faster than the wind was wrong. This video is sponsored by Brilliant. The first 200 people to sign up via https://brilliant.org/veritasium get 20% off a yearly subscription. For more information about the Veritasium Science Communication Contest check out

[skipperpete]

That is AWESOME!!!

[edsailing]

Mind-blowing - as I understand it, it opens up the possibility sailing dead up wind, but don't ask me for a technical explanation!

[tkeithlu]

A sailboat down wind would be comparable to the car with the propeller stationary - pushed by the wind, offering drag, and not going as fast as the wind. A sailboat comparable to the engine-driven car would have its engine running, an additional source of energy, and might exceed wind speed, at which point the sail would collapse totally spoiling your day.

The sail is not the analog of the car propeller, the boat's propeller is.

[Chotu]

Originally Posted by edsailing

Mind-blowing - as I understand it, it opens up the possibility sailing dead up wind, but don't ask me for a technical explanation!

Except you would need some paddle wheels on the side of the boat. Something has to act as the wheels do in this video.

I don’t think the boat propeller is optimized to transfer the energy from the water passing by to the wind turbine.

In any case, it seems also like the drag of a boat is significantly higher than this car out in the desert at high speeds. Somebody should play around with this though. Just for fun.

[jbinbi]

Originally Posted by Chotu

Except you would need some paddle wheels on the side of the boat. Something has to act as the wheels do in this video.

I don’t think the boat propeller is optimized to transfer the energy from the water passing by to the wind turbine.

In any case, it seems also like the drag of a boat is significantly higher than this car out in the desert at high speeds. Somebody should play around with this though. Just for fun.

Yes. This. I am not talking about a sailboat. I am talking about a boat, that has a propulsion system like this, a mast with a propeller (wind turbine), and say water wheels, or something to propel the boat thru the water.

As mentioned above, if your true boat speed is equal to the wind speed from DDW, on a sailboat that is zero apparent wind, so that can't ever work.

[zstine]

Originally Posted by jbinbi

Yes. This. I am not talking about a sailboat. I am talking about a boat, that has a propulsion system like this, a mast with a propeller (wind turbine), and say water wheels, or something to propel the boat thru the water.

As mentioned above, if your true boat speed is equal to the wind speed from DDW, on a sailboat that is zero apparent wind, so that can't ever work.

First, the windmill powered boat has been done. It can sail directly upwind.



Secondly, If you think zero apparent wind means your windmill boat can't go faster downwind, then you don't understand the physics of the car in the video. you don't need apparent wind if the boats underwater propeller is driving the wind propeller and creating thrust as the car does.... Obviously, the drag through the water is going to make this impossible (maybe not for a foiling boat?) But your "zero apparent wind" comment is false. It's just a force balance issue with drag.

[zstine]

https://www.youtube.com/watch?v=IzGCYaJbf0A

[jbinbi]

My zero apparent wind comment is not false, I wrote in regards for a sailboat, not the wind turbine. A boat with a sail is separate case from what this experiment is.

I would be interested in seeing more details on the turbine boat if you have any links, etc. Is this the same as the car experiment, I am assuming the turbine is driving some props? Thanks.

[ArmyDaveNY]

Here is a video by the same person. This has more detail on why and how it works. It should also be noted that a professor who bet him $10,000 U.S. that he was wrong changed his mind, admitted that it worked, and paid the $10,000.

https://www.youtube.com/watch?v=yCsgoLc_fzI&t=7s

[zstine]

Originally Posted by jbinbi

My zero apparent wind comment is not false, I wrote in regards for a sailboat, not the wind turbine. A boat with a sail is separate case from what this experiment is.

I would be interested in seeing more details on the turbine boat if you have any links, etc. Is this the same as the car experiment, I am assuming the turbine is driving some props? Thanks.

sorry, yes I agree that a standard-sail sailboat cannot sail DDW faster than the wind.


The wind turbine boat is called Revelation II. The wind turbine powers a 6 blade propeller. I don't know much more about it. try google

[chasfgr]

Done it been there - usually confusion between True Wind Speed and Apparent Wind speed.
If you're going downwind, your true wind = water speed + apparent wind.
Happens quite frequently fly in a spinnaker in light winds.

[waterman46]

The limit on downwind speed has zero to do with force vs. drag. It has everything to do with apparent wind. No, a wind powered boat, car or whatever cannot go faster than true wind when facing dead downwind, even if drag is completely eliminated. Think how ridiculous that would be. The apparent wind would then be coming from the bow or front of the vehicle, thereby slowing it down again to exactly the speed of the wind. Apparent wind is why a balloon, which has zero drag, only travels exactly the speed and direction of the wind, but no faster or slower. Zero apparent wind means no force on the wind turbine, thus no thrust.

If you ever sailed a fast boat with a spinnaker you'd understand it without explanation.

The video about a bet concerning downwind speed shows several examples of real life situations, some showing upwind motion but none to prove moving downwind faster than the true wind, other than temporarily when the true windspeed drops. Several tricky devices are used. The little wheels under the beam are moving because of external force applied from motion of the beam over the floor. The little devices on the treadmill are actually taking power from the motion of the wheels on the treadmill then transferring it to the air propeller, which is operating in still air as a thrust device, just the opposite of a power generating device.

The graph shows a car where they do 27mph in a true 10mph "tailwind". If this was true windspeed, it is clearly impossible, for the car would be experiencing a 15mph headwind, which would force the propeller the wrong way, slowing the car back to true windspeed (zero apparent wind). Why was there no apparent wind direction and speed device installed on the car itself?

The final statement that tells you that all this is pure BS is "with sufficiently low energy loss, any speed is possible". Really? Then why don't airplanes use this method for power - no engines would be needed! Simply put props fore and aft on the plane connected by a straight shaft.



As for all the complicated math, it is full of bad assumptions (like the one that when the propeller is "driving the vehicle forward" at greater than true windspeed, a negative force on the propeller is the same direction as positive force).


I'd guess the whole thing about the bet was just a joke on the unthinking.

[ArmyDaveNY]

Originally Posted by waterman46

The final statement that tells you that all this is pure BS is "with sufficiently low energy loss, any speed is possible".
I'd guess the whole thing about the bet was just a joke on the unthinking.

I must respectfully disagree with you regarding most of your comments. First, I agree the treadmill experiment wasn't applicable to the postulation. However, the second video addressed each of your concerns, and it should be noted that the physics professor, after reviewing the information presented, changed his mind and agreed that it was possible and that they did demonstrate it.

I am not a physics or engineering professor, but it the science guys in the video changed their mind and validated the information presented, so who am I to disagree? It seems probable and it definitely didn't not come across as a hoax.

[TrentePieds]

When I wuz a lad, way, WAAAAY before telly, let alone "social media" and YouTube, you often heard it said "It was in the paper - it MUST be true!"

Plus ça change, plus c'est pareil

TP