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Downwind faster than the wind... #212563
06/04/10 05:21 AM
06/04/10 05:21 AM
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Tony_F18 Offline OP
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Tony_F18  Offline OP
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http://www.wired.com/autopia/2010/06/downwind-faster-than-the-wind
Quote
Rick Cavallaro and his friends have built a wind-powered vehicle that travels downwind faster than the wind, solving a riddle that can start fights.

The unusual wind-powered car hit a top speed 2.86 times faster than the wind during one recent run...



-- Have You Seen This? --
Re: Downwind faster than the wind... [Re: Tony_F18] #212566
06/04/10 05:48 AM
06/04/10 05:48 AM
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North-West Europe
Wouter Offline
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Don't all landyachts/iceyachts do that ?

Wouter


Wouter Hijink
Formula 16 NED 243 (one-off; homebuild)
The Netherlands
Re: Downwind faster than the wind... [Re: Wouter] #212570
06/04/10 06:17 AM
06/04/10 06:17 AM
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Tony_F18 Offline OP
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Yes, but with a landyacht to go DDW you would have to built up apparent wind first.
As I understand it this things starts riding downwind from the start.

Re: Downwind faster than the wind... [Re: Tony_F18] #212574
06/04/10 06:53 AM
06/04/10 06:53 AM
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Posts: 12,310
South Carolina
Jake Offline
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Originally Posted by Tony_F18
Yes, but with a landyacht to go DDW you would have to built up apparent wind first.
As I understand it this things starts riding downwind from the start.


Landyachts and this thing do share some features - but I agree that this device is a little different. It points straight downwind and can go faster than the wind. I think a landyacht would still need to maintain some angle (or maybe not?) crazy

A couple of years ago we discussed this at great length here on the forum - the concept of this vehicle is pretty difficult to wrap your head around...but it works. As they pointed out in the article, we have a hard time with this concept because we have direct experience that if we are, for instance, on a bicycle riding downwind at the same speed as the wind - we feel no breeze. Our minds figure this means that there is no power to be had and that there would be a physical wall to traveling faster than the wind. However, these devices don't use the wind to turn the propeller. The propeller always turns against the wind. Initially, the wind drag over the stationary prop starts the vehicle moving forward. As the wheels start moving over the ground, a gearbox transfers that wheel power to start turning the prop (remember that the prop is turning against the wind). As the vehicle builds speed, the prop turns faster and pushes against the wind harder. At this point, the breeze coming off the prop is faster than the wind so it's literally "pushing" itself off the available wind. Because of this, it does not see a dead zone when the vehicle matches the wind speed - the propeller is pushing against the wind which develops a forward force on the car - the vehicle continues to accelerate, the wheels, gearbox, and propeller turn faster. There IS a limited amount of power available that's directly relative to the wind speed and the drag efficiency of the vehicle but it's not limited TO the windspeed - it's limited to the drag of the wheels/bearings/gearbox/propeller/etc. When the drag the vehicle is experiencing is equal to the amount of energy it's available to harness from the wind, it holds a steady speed...in this case, almost 40 mph.


Jake Kohl
Re: Downwind faster than the wind... [Re: Jake] #212575
06/04/10 07:19 AM
06/04/10 07:19 AM

A
andrewscott
Unregistered
andrewscott
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A



voodoo! witch craft! burn it!
actually its very cool. but your gonna have a hell of a time at mcd's drive through window


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