Mad Genius - Wind powered vehicle travels 2.8x speed of the wind

[Slide Panda]

Details in the link. Short version is that someone has built a wind powered cart that can travel faster than, um, the wind

http://blog.makezine.com/archive/2010/11/downwind_faster_than_the_wind_black.html

[mitt]

I am surprised so many people thought it was a hoax.  It is not hard to understand how it could be done.  They are just amplifying the wind speed to rotary speed through mechanical ratios.

mitt

[orangelion03]

Effin brilliant.

[He Man]

i bet those same people think that 7800rpm on ur tach means ur wheel is spinning 7800 times a minute.

[Speeddog]

Put me in the skeptic camp. 

[krolik]

But does the plane take off?

[Grampa]

Is Randall driving it?

[Veloce-Fino]

i bet those same people think that 7800rpm on ur tach means ur wheel is spinning 7800 times a minute.

wait it doesn't?  hrm..

[SacDuc]

Once you are traveling faster than the wind isn't the wind force then coming from the opposite direction?

Which is to stay is if you are traveling a constant speed that is the same as the speed of the wind you wouldn't feel the wind.

So unless that thing is storing power and must spend time at sub-wind speed speeds, I call bullshit.
Sac

[lethe]

change pitch of the blades to have the oncoming wind of it's forward motion power it once it exceeds tailwind?
friction losses would negate something I'd thing though otherwise it's a perpetual motion machine 

[mitt]

the more I think about it now I am skeptical too - maybe there is something else going on there like maybe they vehicle is at a slight angle to the wind or something.

mitt

[Speeddog]

It could tack going downwind, and net velocity (velocity made good to sailboat folks) could be greater than windspeed.
Maybe 50% more than windspeed....

Directly downwind at 2.8X windspeed, no way.

[derby]

i'm still waiting on one of you engineering types to build a cart to test your theories like these guys:

Downwind Faster than the Wind (DWFTTW) Myth Challenge

[aguacate]

It's like a piston.  How does a force acting on a piece of metal moving up and down translate into forward motion?  It's the |magnitude| of the speed differential between the fan and the wind that is what drives the cart.

Really it's the magnitude of the speed differential between the ground and the wind.  The cart acts as a rectifying bridge, in electrical terms, between ground and wind, and the potential energy difference is fed back into a force that is acting in the same direction (or opposite depending on your point of view) that the phenomenon is occurring.  It is a feed back loop that stabilizes once the usable power resulting from channeling the potential energy difference between ground and wind equals to the resisting friction forces, which act against the feedback power.  The feedback loop is initially unstable since the resulting forces cause the cart to accelerate, which motion in turn changes the equations for the feedback power being generated, causing the cart to accelerate differently, causing the feedback power to shift, etc.

[aguacate]

Now build shit tons of these and let's put all wind on Earth to a stop!