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Down wind faster than the wind

I used to sail so I understand how a yacht can go faster than the wind. It's a matter of using the centre board as leverage. Then it's just like squeezing out a pip. It's also how you can sail into the wind.

Which makes me wonder. Should the vehicle be able to move into the wind? It shouldn't be any different to ddfttw?
 
a_unique_person said:
I used to sail so I understand how a yacht can go faster than the wind. It's a matter of using the centre board as leverage. Then it's just like squeezing out a pip. It's also how you can sail into the wind.

Which makes me wonder. Should the vehicle be able to move into the wind? It shouldn't be any different to ddfttw?
Click to expand...

Into the wind is easy .. just mount the propeller as a wind harvesting device, and use the energy from it to power the wheels.
Note that that is not how DWFTTW vehicle works though.

But DWFTTW is basically the same as the sailing with side wind. You are not harvesting wind alone .. you are harvesting speed difference between ground (sea) and wind. So with side wind you can go several times faster than the wind.
Down the wind it's similar. If you go down the wind at the speed of the wind .. you indeed cannot harvest any energy from the wind alone. But at that moment, ground is moving toward you at the speed of the wind. So that's where DWFTTW gets the energy. It's just a lever.
 
Howe does it work?

First, the propeller works like a sail on a boat with the wind pushes against
the propeller accelerating the kart forward. As the kart approaches wind speed
the force delivered by the wind decreases steadily until it reaches wind speed
at which point the force goes to zero. Going faster than the wind causes the
propeller to push against the wind resulting in a force slowing down the cart.

Secondly, the motion of the kart drives the wheels providing power via
the transmission that turns the propeller whose motion pushes against air
accelerating the kart forward. This positive feedback continues until the thrust
of the propeller equals the drag of the propeller at which point the air passing
through the propeller stops moving relative to ground.

picture.php


Essentially, the forward motion of the air gets converted into forward motion
of the kart. But, the kart will never stop all forward motion of the air because
various forms of mechanical losses, like friction, will slow down the kart before
it can reach that velocity.

Engineering students will probably start building karts with carbon fiber
and electric motors and racing them in competitions to see which college
can build the fastest one.
 
Ok.

So the prop is a reactive sail that is powered by the wheels of the cart. All other sails are passive but this one actually pushes against the wind.
The wheels geared to the prop are doing the work of the centreboard of a yacht.
 
Steve001 said:
Posted two days ago by the Veritasium YT channel. A full size real world proof.
https://youtu.be/jyQwgBAaBag
Click to expand...
After following this saga from the beginning, I think the explanation given in this video is probably the most understandable. The energy to propel the cart past wind speed has to come from somewhere, it comes from the air traveling behind the cart. In the explanation this air is slowed down, by the propeller, from 10 mph(relative to the ground) to 8 mph. You would think that this same amount of energy would be removed from the wheels by the resistance of the propeller, but somehow the situation is asymmetrical, I'm not sure why.
 
IT'S ALIVE, IT'S ALIVE!!! after 12 years!!! Talk about reincarnation.

Here's my "proof of concept" turntable contribution from back in the day (turn your sound off. Turntable powered by noisy old drill) - https://youtu.be/QTF5kw51H60

Here's a couple of guys that have copied it more recently . . .

https://www.youtube.com/watch?v=SmlRMfc6bNk

Nice that this guy gives me credit - https://www.youtube.com/watch?v=-O3ZqklSndM


Was never happy with the fact that the prop isn't actually going DDW.


The (virtual) wind moves the cart forward.
The moving cart turns the wheel.
The turning wheel spins the prop that thrusts against the wind.
The prop thrusts against (virtual) still air when the cart reaches the speed of the (virtual) wind.
The thrust moves the cart forward faster than the (virtual) wind.
 
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a_unique_person said:
I still don't see how it can go 2.8 times the speed of the wind. Any speed faster than the speed of the wind has to be a marginal increase.
Click to expand...

Why ? If you can accept ship can go 3 times faster with side wind, why not down the wind ? The source of the energy is the same .. difference of speed between air and the surface. It's just harder to harvest the energy when going down the wind. Simple sail and keel won't do. You need wheels and propeller. But both cases are similar in principle and theoretical maximum speed.
 
I have a question then. With no wind why couldn't you just tow the thing 10 MPH with the wheels driving the propeller. Then release the tow, and have the thing drive itself? Relative wind speed would be similar. But I don't see that working. So I am still thinking this thing has something wrong.
 
a_unique_person said:
I used to sail so I understand how a yacht can go faster than the wind. It's a matter of using the centre board as leverage. Then it's just like squeezing out a pip. It's also how you can sail into the wind.

Which makes me wonder. Should the vehicle be able to move into the wind? It shouldn't be any different to ddfttw?
Click to expand...

See the Veritasium video i posted in this thread. Proof of concept with an explanation.
 
Dr.Sid said:
Why ? If you can accept ship can go 3 times faster with side wind, why not down the wind ? The source of the energy is the same .. difference of speed between air and the surface. It's just harder to harvest the energy when going down the wind. Simple sail and keel won't do. You need wheels and propeller. But both cases are similar in principle and theoretical maximum speed.
Click to expand...

If it is tacking (to some extent sideways to the wind) I can see that. But all the videos and explanation of this that I have seen have them going directly downwind, which buggers the mind more than a ship taking party sideways to the wind does.

I mean, I accept that it works, but it is pretty profoundly counter-intuitive to me because the thing ends up going faster than the air around it, even as it gets its motive energy from the movement of that air.
 
Red Baron Farms said:
I have a question then. With no wind why couldn't you just tow the thing 10 MPH with the wheels driving the propeller. Then release the tow, and have the thing drive itself? Relative wind speed would be similar. But I don't see that working. So I am still thinking this thing has something wrong.
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When you released the tow, going 10 MPH, the craft would have a 10 MPH headwind.
 
Marcus said:
When you released the tow, going 10 MPH, the craft would have a 10 MPH headwind.
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Exactly and if it was in a 10 mile an hour wind, and went 20 mph, it would also have a 10 MPH headwind, and ground speed would seem to cause even more friction at 20 mph than 10 mph. The source said it could go 2x the speed of the wind.

Something seems wrong here to me:boggled:.Maybe I am just not fully getting it?
 
Red Baron Farms said:
Exactly and if it was in a 10 mile an hour wind, and went 20 mph, it would also have a 10 MPH headwind, and ground speed would seem to cause even more friction at 20 mph than 10 mph. The source said it could go 2x the speed of the wind.

Something seems wrong here to me:boggled:.Maybe I am just not fully getting it?
Click to expand...
Since it clearly and obviously works, I'm gonna say yeah. Again, Derek explains it pretty well in the video.
 
Isn't the key not the wind by itself, but the difference between the ground and the wind? The cart is exploiting that difference to derive power to move the cart forward. No difference between ground and wind, the card doesn't move.
 
arthwollipot said:
Since it clearly and obviously works, I'm gonna say yeah. Again, Derek explains it pretty well in the video.
Click to expand...
He does explain it very well. The energy to drive the cart past wind speed comes from the air behind the cart, which is slowed down by the propeller, which is driven by the wheels. The only part I am not clear on is why an equal amount of energy is not removed from from the wheels by the resistance of the prop.


The difference between this incarnation of the thread and the previous one is that we have solid evidence that DWFTTW works, so that any claim that it can't work falls flat.
 
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