DDWFTTW - Directly Downwind Faster Than The Wind

I'm sorry but at this point I assume you are deliberately not reading what I am writing. I specifically said that I was talking about a different setup to illustrate a point.

I agree that we should be clear with our terminology. The fan is unambiguously a fan and not a turbine. Nobody is confused on this point.

 

It will never go faster than the wind. Write the equation and you will see there is an asymptote at the speed of the wind. The mechanical, friction and other losses will prevent the cart from reaching that speed. If the cart were to at some time exceed that speed, the equation would show a piece function. The only way for that to happen is to have an input of energy into the system. The energy the wheels transfer to the propeller through gearing is internal to the system, therefore the speed will approach the limit (speed of wind) from the left (on the graph) but never reach it. This is all explained in basic thermodynamics and calculus 1.

 

I am reading and explaining to you that it is fundamentally wrong. Further, if the "fan" is never a turbine, the energy input from the wind would never happen as you claim. Also, a "fan" is a device to move air and create turbulence and not particularly good at generating thrust.

 

Do you disagree that a cart with an electrically powered fan would go faster in a tailwind than in still air?

 

No, I disagree that the wind is pushing a stream of air.

 

But clearly the tailwind is transferring energy to the cart, which is allowing it to go faster.

 

Faster than what? Not faster than wind speed. Wind speed is the limit at which no energy in flowing from the environment to the system.

 

Faster than it was going in still air.

And yes faster than the windspeed, after all it has an electrically powered fan on it!

Or are you suggesting that an electrically fan driven cart will not accelerate as the tailwind increases (from zero wind) until the tailwind is greater than the forward speed of the cart?

 

Sorry, if we consider an electrically powered propeller cart, it will accelerate to the maximum speed allowed by its design and construction. It could be faster than air speed over ground (wind).

 

Have you actually written equations which asymptote? If so please post those equations here.

 

Gonzo, you clearly didn't check the videos, you make repeated blanket statements to diss valid arguments instead of going through them in detail. It really does look like you are trolling but I don't think you are. Using electricity was clearly just a way to illustrate the power collected from wheel and spent on propeller. Nobody is suggesting a battery powered cart or similar nonsense. But of course it doesn't make one ounce of difference whether the power is transferred via gears or via wire.

The cart did 2.8x wind speed and there are videos of the cart having streamers changing direction when the vehicle passes wind speed (well outside of the airflow of the propeller). This thread was revived when veritasium did an episode of the cart. Again it fueled similar disputes as over 10 years ago. Lots of people who are smarter than me 1st relied on their intuition and superior knowledge but had to eat humble pie.

You really would do well to try to understand it instead of just claiming it breaks rules of thermodynamics or insinuating that people fail in calculus.

I am out of here. Your loss gonzo if you don't bother understanding it. Luckily the phenomenon doesn't depend on you agreeing with it

 

Okay, but do you agree that the speed of such a cart will be higher in a tailwind than in still air, if everything else stays the same?

 

Yes, within limits. All mechanical systems have limits.

 

I agree that they all have limits!

If we agree that "the speed of such a cart [electrically fan driven] will be higher in a tailwind than in still air, if everything else stays the same" even a little bit, then there must be some mechanism that allows the tailwind to transfer energy to the [electrically fan driven] cart, yes?

 

No. The airflow on the propeller generates thrust. The frame of reference is either the air or the propeller. The velocity of air over ground is not important to calculate thrust.