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Old 10-25-2012, 04:40 PM   #31 (permalink)
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Right, but there's a huge difference between "within 10 degrees" and "directly into". What the OP is talking about is leveraging wind resistance and headwind to generate power for a net gain, which is impossible.

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Old 10-25-2012, 04:43 PM   #32 (permalink)
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Quote:
Originally Posted by zapato View Post
Right, but there's a huge difference between "within 10 degrees" and "directly into". What the OP is talking about is leveraging wind resistance and headwind to generate power for a net gain, which is impossible.
Not really. Why would 10 degrees be a theoretical limit if you can rotate your "sail" like a turbine? Check into it.
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Old 10-25-2012, 06:38 PM   #33 (permalink)
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Quote:
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Not really. Why would 10 degrees be a theoretical limit if you can rotate your "sail" like a turbine? Check into it.
A sail is just a cloth wing and a propeller is multiple wings that rotate around a hub, a propeller spining is just like a sale boat tacking in to the wind.
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Old 10-26-2012, 11:26 PM   #34 (permalink)
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Quote:
Originally Posted by zapato View Post
What the OP is talking about is leveraging wind resistance and headwind to generate power for a net gain, which is impossible.
Yes, it's impossible - just as bumblebees can't fly, those silly Wright Brothers will never get that contraption off the ground, and rockets won't work in space because there's nothing for them to push against.

I prefer the alternative hypothesis: that the people claiming these things were impossible just didn't understand the physics :-)
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Old 02-09-2013, 09:31 PM   #35 (permalink)
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I think the point is that if a wind (air velocity over a surface) exists it can be used to propel a vehicle in any direction, most efficient being with the wind.

So wind can be used, converted mechanically is probably most efficient, to push against the surface (ground or water etc.) and propel the vehicle forwards, but if there is no wind relative to that surface then just like sailboats in dead calm air, she aint goin nowhere. No matter how fast you drive airspeed is stationary with respect to the ground and hence you cannot use this percieved wind as a form of perpetual motion.

You could however make a small wind powered model that drives around on your bonnet to amuse you while you drive, but it will probably increase your overall drag too.
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Old 02-09-2013, 09:47 PM   #36 (permalink)
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...look-up the turbosail system used on Cousteau's ship "Alcyone":

Turbosail? | Technology | Cousteau
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Old 02-09-2013, 10:30 PM   #37 (permalink)
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Landsailers at WindPower Sports

Twice the wind speed.

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Old 02-11-2013, 11:05 AM   #38 (permalink)
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Quote:
How can it travel faster than the wind?

The Greenbird can travel faster than the wind thanks to a phenomenon known as ‘apparent wind’.

For example, you are riding your bicycle on a completely calm day with no wind. However, you can feel wind on your face and it feels stronger as you pedal faster. That is because as you move forward, the motion creates its own wind.

Now imagine you are riding your bicycle but there is a strong breeze coming at you from the right. This natural wind is called "true wind".

When you add this side wind to the cycle ride, the wind the rider feels is now somewhere between the true wind (from the side) and the man made wind (from ahead). This resultant wind is know as the ‘apparent wind’ and will have a speed and apparent wind angle, measured from the direction of travel to the apparent wind angle.

The Greenbird is so efficient that it can travel at up to 3 to 5 times the true wind speed on land.



Read more about it here.

The Greenbird - the fastest wind powered vehicle on Earth!

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Last edited by redneck; 02-11-2013 at 11:16 AM..
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Old 02-11-2013, 07:43 PM   #39 (permalink)
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Uh, if I'm not mistaken, these greenbird speeds are achieved by a wing style sail on a beam reach, going across the wind. Not into it. How does this relate to a turbine stuck in the nose of a car?
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Old 02-11-2013, 08:37 PM   #40 (permalink)
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Quote:
ChazInMT
Uh, if I'm not mistaken, these greenbird speeds are achieved by a wing style sail on a beam reach, going across the wind. Not into it. How does this relate to a turbine stuck in the nose of a car?
It was in regards to.

Quote:
Old Mechanic

Landsailers at WindPower Sports

Twice the wind speed.

regards
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We now return you to your regularly scheduled program.




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