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A wind powered car that goes faster then the wind.

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Nik

Sun Jun 06 2010, 02:37PM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

First off the article is here

It all sounded fine and dandy until I got to this paragraph

Cavallaro explained the car is able to move faster than the wind because the propeller is not turned by the wind. The wind pushes the vehicle forward, and once moving the wheels turn the propeller. The propeller spins in the opposite direction to that expected, pushing the wind backwards, which in turn pushes the car forwards, turning the wheels, and thus turning the propeller faster still.

That sounds suspiciously like a self powered car to me. Maybe they mucked up the description when they wrote the article but I think the original premise might be the problem. Once the car is moving at the speed of the wind there is no longer a force to push it along, that means there is no longer a source of power to turn the wheels which turn the fan. By their description it sounds like it should keep accelerating until some part of it fails because it is spinning too fast.

Thoughts?

*edit* By they way they tell it shouldn't it take off and gain speed if there is no wind but you gave it a push?

Pinky's Brain

Sun Jun 06 2010, 03:39PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

All you need to extract energy from the wind is something to push against which is moving at a different speed (the ground, water, whatever). What speed the car is moving at itself is ultimately irrelevant, simply because it can push against the ground it can extract energy from the wind.

Hell, propeller driven vehicles can go straight up wind too ... the limit on speed is friction losses, wind resistances etc.

If there is no wind (relative to the ground) you can give the car a push, but it won't help.

MinorityCarrier

Sun Jun 06 2010, 03:53PM

Registered Member #2123 Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312

Bunk.

Pinky's Brain

Sun Jun 06 2010, 04:29PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

Just consider a car with a wind turbine on it driving with an electric motor, moving (in any direction) and occasionally stopping to run the turbine for electricity (letting it free wheel while moving).

What are the fundamental limits on it's average speed?

Here ... a page with much better thought experiments :

Dr. Slack

Sun Jun 06 2010, 06:09PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Consider a racing yatch. The could run "down" the wind, but that means their speed could never exceed the wind speed. Instead they tack at an angle to go faster than the wind. I was surprised when I first came across this, but what the boat is doing is extracting power from the *difference* in the *water speed vector* acting on the keel, and the *wind speed vector* acting on the sail.

To see niavely how an object can travel faster than either force pushing it, squeeze a lemon pip between thumb and fore-forefinger. It pops out, along the inclined plane of each digit.

Similarly, the racing yatch is squeezed between the pressure on the aerofoil-shaped keel from the water and the sail from the wind, when they are in a suitable direction.

It's quite possible that the guy's car is bunkum and he's trying a FE scam, and it's certain that his description isn't worth the paper it's written on, BUT a car that moves faster than the wind is not impossible, in fact they can be seen in any video of land-yatching. If you consider the turbine as a complicated way of getting a large aerodynamic surface into the wind, and the gearbox/wheels combo as a complicated way of using the ground reaction, then they could work together to make the car break the wind barrier.

Bjørn

Sun Jun 06 2010, 07:08PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Once the car is moving at the speed of the wind there is no longer a force to push it along

If we have wind blowing at an angled blade like this --> \ and the blade is moving in the direction of the wind at the same velocity, then we have no force on the blade. If we now rotate the blade (downwards in the diagram) at the same time and look at a point following the surface of the blade it will at the right RPM appear to stand still relative to the ground and the wind can transfer energy to the blade.

So you can look at the blade as a sail that moves at a 90 degree angle to the wind. Since it works for boats I think it should work with a propeller too. The twist here is that the 90 degree turn is done mechanically and I have no idea if the losses would be larger than the gains.

Renesis

Sun Jun 06 2010, 08:03PM

Registered Member #2028 Joined: Mon Mar 16 2009, 08:13PM
Location: Norway
Posts: 319

These ice yachts can travel <100km/h even in moderate winds, and i believe dr. slack has already explained how.

As for the magic car, meh, it could probably do as bjÃ¸rn suggests and replicate the effect of a sail, but the system losses would make it far inferiour to a simple sail anyway. And as for mr. Cavallaro's explanation, if it was true then the car would continue accelerating infinitely until the car escapes the earths gravity and dissapears into the endlessness.

If his calculations are correct, when that baby hits eighty-eight miles per hour... you're gonna see some serious shit.

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