DDWFTTW - Directly Downwind Faster Than The Wind

The telltales do not change direction, they only hang limp for a moment.

 

What does the airstream of the fan push on?

 

I might have to reconsider my earlier take that you are not trolling. It acts exactly as predicted. Starts with strong back wind (true and apparent wind for the cart). As speed picks up apparent wind slows down up to the point of total calm when it is traveling at wind speed. With further acceleration the apparent wind becomes headwind indicating that cart is going faster than the wind.

 

The sign don't matter an iota here. This is why people like to use the generator and electric motor analogies - to isolate the dilemma outside of mechanical arrangements. But it is all moot.




The propeller in my example of 6m/s in 5m/s wind acts in an airflow coming from the front of the cart. Just like a boat or an airplane would when generating thrust. P=FV is 100% valid here.

It really boils down to this:
Wheels (cart) interact with medium traveling by fast. Propeller (cart) interacts with medium traveling by slowly. You can leverage force from the former to create a larger force in the latter.

Its is logical. It works. It has been proven to work, with small treadmill carts, on paper and in practice with a wind powered Blackbird cart in a sanctioned record run with skeptical land sailing people present.

One can choose to write blanket statements and insinuate others' ignorance with replies like "This is all explained in basic thermodynamics and calculus 1", "This violates the Laws of Thermodynamics." or " there are losses which result in a maximum steady velocity lesser than that of the wind" and demand formulas and calculations - which has been done several times - and provide none themselves.
One can choose to do that. Or try to understand why and how it does work.
To me creating the original prop/boat-on-cylinder video was a heureka moment also from perspective of understanding sailing. It also helps understand how land yachts can make distance good - ie. reach downwind marker faster than the wind. Btw this is also something many claim is impossible despite it being common occurrence with clear margin.

I will still post the veritasium video that goes deeper into the explantions than their 1st one. I am hesitant to do so because I am bit annoyed that they never credited me for the original boat on cylinder video which they re-created.

 

Is the reaction force from accelerating the air.

 

Kerosene,

Great video!
Mark Drela (a member here) even makes an appearance!
Perhaps you should make Gonzo a $10 000 bet.

BB

 

That video is truly fantastic. And you have to respect the physics prof. An old dog that can learn new tricks isn't actually old.

 

Yet again, no. If I were the only one you keep misinterpreting, then it might be that I fail to express myself clearly. But others also tell you that you misinterpret them, so maybe you should start wondering whether you have opinions strong enough that you interpret everything to fit.

From your response to Wil Gilmore:

1) Drag does not just disappear if you let the propeller spin.
2) Have you compared the pitch of the propeller to the direction of rotation? In the video I watched, the propeller would have to either spin the other way round or reverse its pitch in order to work as a wind turbine. It spins slowly enough for much of the video that you can see both direction of rotation and pitch.

kerosene explained why there is no violation of conservation of energy, and I think earlier, tlouth7. I can provide references to articles in Catalyst. Would you read them?

Also, I invite you to explain what is wrong with the claim that a windmill vehicle going directly upwind, and a wheel or water-powered, propeller-driven vehicle going directly downwind faster than the wind are equivalent, and differ only by frame of reference. That is incompatible with your views. Only one of them can be right. So if I am wrong about the frame of reference argument, how am I wrong?

 

Folks, I observe that anyone who has the capacity to learn something new, already has. Those who have not, will not, for reasons of their own. Further effort is only good money after bad.

 

Actually, I find this discussion exceedingly interesting because it is forcing me to consider the problem from ever expanding and changing perspectives, just to try and come up with some new way of explaining myself so that I couldn't be misunderstood.

I have been reviewing in my head, the AC video with the Amazon River scenario and considering explanations for ice boats sailing at 80 knots in 20 knots of wind. There is more to it than simply being squeezed between the forces of lateral resistance and wind direction.

 

Indeed. In the propeller cart system, there is no need for lateral resistance, other than steering.

 

Accelerating the air. Yes, the fan pushes the air and accelerates it from a relatively slow speed, to a relatively fast speed by pushing against the air. It applies the third law of motion to gain motion.

But, isn't that relatively slow speed different with a tail wind? The initial movement of the air relative to the ground puts energy into the system. No matter what the cart does, that energy is always there because the cart is always in the ground/air system.

The air moving across the ground doesn't cease to add to the system just because the cart moves with the air. When the cart is standing still (relative to the ground), air is moving past the cart with energy that can be tapped. When the cart is moving with the air (zero apparent wind), the ground is moving past the cart with energy that can be tapped. The energy is the same in either case. It will always be there.

The trick is to tap that energy from one part of the system, the movement of the cart across the ground, and apply it against the other part of the system, the air. This is how a cart, with a fan run by its wheels pushing back against the air, moves faster than a free wheeling cart just being pushed by the air.

-Will

 

Hello Guys!
The subject of this vehicle has been bothering me for some time, so I analyzed the forces affecting it from the beginning to the end of the experiment. Let me know what you think.

 

I appreciate your presentation but I do not think it is correct.

Your tangential argument is incorrect. The argument that the wheels torque wouldn't try to slow down the vehicle is wrong. Ever been to a car that uses brakes? This is exactly analogous to that. Or one of those old fashioned dynamos on bicycles.

The wheels DO try to slow down the vehicle but there is excess force for propulsion as the relative speed is much less than the relative speed of the propeller in the air.

This also explains why the vehicles doesn't accelerate forever. The _ratio_ of the speed differences gets smaller and smaller with additional speed (ie. it can be considered that the leverage is reducing towards 1)