[MarkV]

Sailboats and land yachts are interesting. On a beam reach you can certainly sail faster than the wind, but essentially perpendicular to the wind vector.

The downwind velocity component can also be greater than windspeed:


downwind_vectors_en_3.png (68.85 kB . 600x542 - viewed 4249 times)

Here the vectors for a section of a propeller blade on the cart that goes directly downwind faster than the wind:


downwind_propeller_vectors.png (75.75 kB . 644x542 - viewed 4175 times)

[MarkV]

I think this contraption can go faster than the wind for a few moments but that would be it.

No, it can go faster than the wind in steady sate, because it cannot use stored energy for propulsion and is able to accelerate while being above windspeed.

Derek Mueller posted the data from the official NALSA record runs here:
https://twitter.com/veritasium/status/1407103269961273355 [nofollow]
More details here:
https://www.nalsa.org/DownWind.html [nofollow]

Video analysis of Derek's own run also shows acceleration while being above windspeed:
https://twitter.com/veritasium/status/1407473631521771522 [nofollow]

[MarkV]

Now, what I'm less sure about is whether you can sail into the wind faster than the wind.

Yes you can, and for upwind travel the rotor acts as a windmill. But in the downwind faster than wind case it's a propeller.This vehicle did both:
- It went 2.8x windspeed directly downwind
- it went 2.1x windpseed directly upwind

[MarkV]

He even shows a clear close-up image of the exposed gear assembly. It shows that the whole system is purely mechanical.

His transparency brings credibility.
The ratio of the gears seems to be 1:1
So the speed multiplier must come from wheels radii vs blades radii, and also blades angle.

The radius of the blades doesn't matter for the speed multiplier. Just the wheel radius, transmission ratio and the pitch of the propeller.

[Bored chemist]

Now, what I'm less sure about is whether you can sail into the wind faster than the wind.

Yes you can, and for upwind travel the rotor acts as a windmill. But in the downwind faster than wind case it's a propeller.This vehicle did both:
- It went 2.8x windspeed directly downwind
- it went 2.1x windpseed directly upwind

Well, I'm glad that's sorted.

[hamdani yusuf (OP)]

Then Coco from the video would be right: It can't work at all. It would slide or lock or break.

In my diagram, one of the conveyors is slippery. Nothing has to break.
What does it take to move in reverse direction?

[MarkV]

Then Coco from the video would be right: It can't work at all. It would slide or lock or break.

In my diagram, one of the conveyors is slippery. Nothing has to break.

Then it will slide.

What does it take to move in reverse direction?

Just turn it upside down.

But if that's not allowed then look at my diagram. The formula for this case is:

V/W = 1 / (1 - r/R)

To make V/W negative, you must have:

r > R

But note that r still touches the upper wheel, while R still touches the ground/lower belt. To make this work requires a double rail / split belt on which the now smaller R parts roll. So turning it upside down is really easier.

[hamdani yusuf (OP)]

What does it take to make it move slower than the wind?

[MarkV]

What does it take to make it move slower than the wind?

For this the advance ratio A must be negative, so you have to get rid of the blue wheel or apply the ruler at the bottom of the blue wheel.

[MarkV]

I can lean out of the basket and put the wheel in contact with the ground so it spins the generator and creates electricity.
I can use that electricity to run a motor and have that drive a propeller and I can use that to move my balloon through the air in any direction I choose.

That wheel on the ground will be a big drag and slow you down considerably.  Since the generator and the motor are not 100% efficient (the propeller is not 100% efficient either) I do not think that you will be able to even make it back up to your speed before you lowered the wheel.

The thrust at the propeller can be higher than the drag at the wheels because the relative velocity of the ground is higher than the relative velocity of the air.

Power = Force x Velocity

[hamdani yusuf (OP)]

What does it take to make it move slower than the wind?

For this the advance ratio A must be negative, so you have to get rid of the blue wheel or apply the ruler at the bottom of the blue wheel.

My analysis shows that to go faster than the wind, the bottom wheels must spin in reverse direction than the top. Halc pointed this out earlier. Even your own formula implies that. It just turns out that spinning in reverse direction  requires less components.

[MarkV]

What does it take to make it move slower than the wind?

For this the advance ratio A must be negative, so you have to get rid of the blue wheel or apply the ruler at the bottom of the blue wheel.

My analysis shows that to go faster than the wind,...

Just to clarify: Above I was answering the question about making it move slower than the wind.

... the bottom wheels must spin in reverse direction than the top.

Well, it depends on which side of the wheel the ruler/belt is interacting with it (see the single spool). But if you stick to:
- top-side for the top wheel
- bottom-side for the bottom wheel
then yes.

The advance ratio A is the ratio of relative velocities, that your gearbox is trying to achieve:

A = air_relative_velocity / ground_relative_velocity

When moving with the air but faster, or against the air, the air_relative_velocity and ground_relative_velocity have the same sign so A > 0. When moving with the air but slower, they have opposite signs so A < 0.

I'm attaching a plot of advance ratio vs. maximal speed. For a gear box with no slippage you can assume the ideal velocity (blue line). With slippage and drag (like the propeller cart) you get something like the red velocity line.To make sense of the diagrams in the table below, you should watch the video on the bottom.


rotor_carts_01.png (209.85 kB . 812x1000 - viewed 4575 times)

[MarkV]

Follow up video:

[Just thinking]

Yes. By capturing the wind in a large area and venturing it that increasing the pressure = higher velocity.

[Eternal Student]

Hi all.

This has been well covered in YouTube Videos,  many of which are cited in this thread.
I think there are now videos and web pages showing people how to print their own working model using a 3D printer.

   Further improvements might include adding a gear box or continuously variable transmission.  Rotate the propeller slower at low road speeds to get the thing started and increase the gear ratio between road wheels and propeller to reach higher speeds.   I wonder if you could get more control and better performance by replacing the mechanical linkage between road wheels and propeller with an electrical linkage instead.   Have dynamos on the road wheels and an electric motor to drive the propeller  etc.
    Also, put more propellers on the vehicle (stacked one above the other on a longer mast but also stacked side-by-side) and more wheels on the road to drive those propellers if you wish.  I suspect the next set of developments will be more about practical and conventional engineering rather than conceptual physics.  It's been interesting watching how the conventional wisdom has been changed and this is one of those times when when something has been discovered that didn't require a million dollars and a particle accelerator.  It's a great example of classical invention and discovery that could almost have been done in someone's garden shed.

[hamdani yusuf (OP)]

In engineering, simplicity is a virtue. Complexities should not be added unnecessarily. "No part is the best part", Elon Musk once said.

[MarkV]

Further improvements ...

Improvements with what goal? I don't think this will ever be used for transport. And if you want to beat their record, you have to prove that you cannot use any stored energy for propulsion. Adding variable or electric transmission will just make it more difficult to get the vehicle qualified.