Google-Backed Wind-Powered Car Goes Faster Than the Wind

sterlingda writes "A wind-powered car has been clocked in the US traveling downwind 2.85 times faster than the 13.5 mph wind. The definitive research by Rick Cavallaro of FasterThanTheWind.org is being funded by Google and Joby Energy. The run should now settle the DWFTTW (downwind faster than the wind) debate that has been raging for some time on the Internet about whether or not such a feat was possible."

Comments

Re:What debate ?

[Jedi Alec]

If you'd read some of the provided links, you'd have seen that the requirement was for the vehicle to be powered solely by wind, so no gravity involved except in its usual role of keeping the wheels on the ground ;-)

In other news, scientists actually getting their hands dirty turn out to know more about their chosen field than a bunch of people on the interwebz.

Re:Debate?

[prionic6]

http://en.wikipedia.org/wiki/Sailing_faster_than_the_wind

Re:Debate?

[ls671]

Read TFA, parent is correct concerning the wheels :

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.

Re:Debate?

[Pharmboy]

I hate spelling nazis, but since you are suggesting a search, the correct spelling is Ascher H. Shapiro. I only found this out as I was trying to take your advice and search for him.

A million monkeys at a million keyboards...

[jtownatpunk.net]

"The run should now settle the DWFTTW (downwind faster than the wind) debate that has been raging for some time on the Internet about whether or not such a feat was possible."

You're new to the internet, aren't you, son? No amount of reality can end an internet debate.

Re:Very old news.

[waimate]

You are correct, but only for boats sailing across the wind or to windward. Modern yachts cannot sail faster than the wind *downwind*. Indeed, downwind is their slowest point of sailing, which is why many yachts tack downwind rather than sail dead downwind. Sailing boats cannot do what is claimed here. What is claimed here is substantially cool.

The Oracle Trimaran..250% faster than the wind...

[droopus]

The Oracle trimaran that recently won the America's Cup had no problem exceeding wind speed due to aerodynamics, and the insanely cool carbon fiber wing that added to sail volume and power, and allowed them to use a fixed-shape sail - a huge advantage. They had no problem sailing between 16 and 24 knots upwind in 5 to 10 knots of wind—that’s 2.5 times wind speed.

They went even quicker periodically, and had a five knot downwind advantage. The first race report shows that the Oracle trimaran was able to almost constantly fly both outer and center hulls (amazing on a boat this big.,.I sail Hobies and this shit is HARD) and execute some slick pre-race maneuvers (which is how you really win sailing races).

So yes, sailboats have been exceeding wind speed for a while, but not by 250%..until now. When a car does that, I'll be impressed.

Re:Very old news.

[natehoy]

For sailors: By using a propeller rather than a sail, the "sail" this boat is using is simulating a continuous optimal downwind tack (the propeller blades are at a tack angle to the wind)

For cyclists: The wind is being turned into rotational force like the cranks on a bicycle. Since they now have rotational force, they can use gearing to take maximum advantage of that force.

Does that make it clearer?

Re:How it could possibly work

[pthisis]

Physicsforum explained it well at http://www.physicsforums.com/showthread.php?t=274996

The kinetic energy of the net movement of earth and of the atmosphere (in the centre of mass frame) is thermodynamically available and (neglecting friction and relativity) can accerate a sufficiently light mass arbitrarilly fast. Thus, DDWFTTW is obviously not physically impossible (and numerous conceptually-trivial schemes have been suggested).

It is empirically known that yachts or sailing boats can continuously travel diagonally with (as well as against) the wind at speeds (such that even the component of their velocity in the direction of the wind is) significantly faster than the wind.
        In the boat's frame of reference (assuming steady nonaccelerating state, inviscid flow, etc) the sail can be oriented such that any (sufficiently) diagonal headwind (or tailwind) is redirected more into the sternward direction (with the same speed, by conservation of energy), such that the reaction force on the boat (while mostly perpendicular to the keel) has a positive component in the direction of the bow; (neglecting friction) a sailboat can accelerate forward as long as the wind relative to the boat is not arriving directly from the front.
        In the water's frame of reference (assuming the boat is already moving forward) this redirected breeze is always slower than the incoming wind (draw the trig'), losing energy and momentum to the boat (later frictioned to the water), independent of how fast this lets the boat accelerate compared to the windspeed. (Learn More)

The simple idea behind the fan and wheeled trolly contraption is that the belt (which couples their respective axels) performs exactly the role of the sailboat's keel (imagine sailing on a ringworld).
        The belt/gear ratio constrains the propellor-tip to move through space on a fixed helical trajectory of constant diagonalness (the ratio of forward to transverse motion, or pitch to circumference), ensuring that (as long as the atmosphere is moving forward relative to the ground) the propellor tips are never moving directly into the wind and thus (identifying the propellor blade with a yacht's sail) a forward thrust component can be obtained regardless of whether the velocity of the cart itself is less, equal or more than the wind velocity.
        The limiting factors are the aforementioned ratio, the fixed-angle pitch of the propellor-tip's blade-sail, the windspeed (relative to the ground), drag and friction. For any constant windspeed, the ratio and the propellor sail-pitch together determine a maximum cart velocity (downwind relative to the ground) at which forward thrust can be produced (this can be larger than the wind velocity but not infinite) but it is a tradeoff because the ratio simultaneously increases drag, and (with the ratio also fixed) tuning the propellor sail-pitch for higher cart-velocity decreases its efficiency at lower cart velocities.