The Impossible Sailing Machine

[Bob in a quantum-state-of-faith]

They said it couldn't be done:  create a sailing machine that can go directly downwind faster than the actual wind pushing on it's sails...

... but, as it turns out, with some clever application of leverage (in the form of gearing) you can:

http://www.skepticblog.org/2012/10/18/the-impossible-sailing-machine/

The scientific explanation is below the video-- it's leverage.   Archimedes would've been proud.

[Aggie]

For short bursts, it would seem. It doesn't sound like it can continue to outpace the wind indefinitely, just pull forward through it. Presumably the wheels and airflow through the 'sail' would get back to equilibrium fairly quickly. It's an amazing contraption.

[Griffin NoName]

Is it just co-incidence it looks like a wind farm?

[Bob in a quantum-state-of-faith]

For short bursts, it would seem. It doesn't sound like it can continue to outpace the wind indefinitely, just pull forward through it. Presumably the wheels and airflow through the 'sail' would get back to equilibrium fairly quickly. It's an amazing contraption.

That is not the case, as it turns out-- according to the bit, it moves faster than the wind, because it's constantly pushing the air back into the prevailing wind.

This combination of leverage lets the whole thing move faster than the overall wind (but slower than a chunk of wind surrounding the prop itself).

It seems like perpetual motion, but it isn't--- it's leverage.

Is it just co-incidence it looks like a wind farm?

[Aggie]

For short bursts, it would seem. It doesn't sound like it can continue to outpace the wind indefinitely, just pull forward through it. Presumably the wheels and airflow through the 'sail' would get back to equilibrium fairly quickly. It's an amazing contraption.

That is not the case, as it turns out-- according to the bit, it moves faster than the wind, because it's constantly pushing the air back into the prevailing wind.

This combination of leverage lets the whole thing move faster than the overall wind (but slower than a chunk of wind surrounding the prop itself).

It seems like perpetual motion, but it isn't--- it's leverage.

I did catch the part about the pilots looking for gusts in order to move faster...  so that makes sense.

I might be muddled about what part is driving what...  if the wind (via the prop as a 'sail') drives the wheels, the wheels drive the prop, but the prop is providing energy to spin the wheels faster... hmm.

I assume this needs to be on a land-based device, as I suspect the wheel is much more efficient than a water-propeller, and friction is much lower.

[Bluenose]

Call me a total sceptic, but I don't believe it.  I would be looking for batteries and electric motors in that rather heavy looking base.  The explanations given do not add up IMHO, it sounds like the sort of explanations used for so-called perpetual motion machines.

[Bob in a quantum-state-of-faith]

Call me a total sceptic, but I don't believe it.  I would be looking for batteries and electric motors in that rather heavy looking base.  The explanations given do not add up IMHO, it sounds like the sort of explanations used for so-called perpetual motion machines.

Keep in mind there is a lot of wind involved-- the size of the prop is big, don't forget.

Also, an airfoil generates lift as it moves through the air-- and a prop is an airfoil for sure.

The total energy budget here, is rather a large one, and the prop blades are not moving directly with the wind's linear velocity either, but across it.  Moreover, the props do not intersect the whole wind-volume that they circle through either-- they are only a tiny percentage of the whole volume of air moving forward.

If you think hard about an automobile's braking system (not power brakes here), the entire energy-budget to stop the 2-ton vehicle is contained within a single human leg!  The leg travels through six to ten inches, whereas the pads only travel a millimeter or so to press the brake's surface.  But still-- the power of a single human leg is able to stop a 2 ton car from 80mph to zero... because of leverage.

The leverage of the pedal travel of 6 to 10 inches is reduced (and multiplied as a result) to millimeters of travel.

So, too:  speed of the wind is leveraged to higher speed of the vehicle moving within it, by the multiplying effect of the propeller blades traveling across the same moving wind-- there is a lot more wind than there is vehicle too.

[Bluenose]

Yes but if it actually works, then you would not need any wind at all, just give it a shove and it would accellerate.  I am no stranger to aerodynamics, I just don't see how the air flow can result in a direct down wind motion greater than the wind speed.

[Sibling Zono (anon1mat0)]

I see it if the wind and the propeller are perpendicular to the motion of the vehicle, the energy of the propeller could hypothetically make the vehicle move faster than the actual wind if you get enough volume and a large (and light) enough propeller. Counterintuitively I can imagine the contraption working with the vehicle moving against the wind if the rest of the vehicle has a very low drag compared to the system, but I have trouble imagining it moving faster than the actual wind. Lastly, it would never work with the wind in the same direction of the vehicle.

Or I'm not really understanding what's going on?

[Bluenose]

Indeed, and some modern sailing vessels can and do move faster than the wind when moving across the wind or even somewhat into wind.  It's the direct downwind thing I don't buy.  The explanations sound like magic pudding to me

[Bob in a quantum-state-of-faith]

Yes but if it actually works, then you would not need any wind at all, just give it a shove and it would accellerate.  I am no stranger to aerodynamics, I just don't see how the air flow can result in a direct down wind motion greater than the wind speed.

No wind at all would have a zero energy budget-- and you'd get nowhere.   Try not to think of the wind as a single thing-- it isn't, it's dynamic with additional mass/energy entering into the "box" all the time.   (the box being the localized area where the car and the propeller/sail are at any given moment)

The angled propeller is no different than an angled sail in a more conventional sailboat, sailing across the wind (which, if the ratios are right, can exceed the input windspeed).

The rotating, angled prop permits the sail (in this case, a moving prop blade) to move across the prevailing wind, not with it.