Blackbird cart runs with wind only twice as fast

Jul 12, 2012 by Nancy Owano report
Photograph of the land yacht Blackbird. Image: Stephen Morris

(Phys.org) -- This month’s news-making word in wind-powered vehicle experiments is “upwind.” Blackbird, a wind powered cart, has shown it can travel upwind at more than twice the speed of circulating air. Rick Cavallaro, an aerodynamicist focused on designing record-setting vehicles that challenge wind speed, first made news two years ago when his Blackbird vehicle raced downwind at 2.86 times the speed of the wind. This time, after modifying his cart, he and his Blackbird team went out to the New Jerusalem airport in Tracy, California, where the vehicle achieved a top speed 2.01 times faster than the wind speed when headed upwind.

Overall, the key modifications that made a downwind Blackbird ready to take on an upwind run included the substitution of the propeller with a turbine that rotates in the opposite direction and transmits power to the wheels.

“After a very long sabbatical, we're finally building some momentum on making our downwind cart go directly upwind faster than the wind,” Cavallaro had reported in the early days of his upwind project.

“We'll use the same vehicle,” he said, but the propeller will come off and will be replaced by a turbine. “The turbine will look very much like the propeller, only hopefully nicer, and with the opposite twist and camber.” He explained that the wind would turn the turbine and that would turn the wheels, “sending us upwind faster than the wind, steady-state. The turbine will also turn the opposite direction from the prop so we can again take advantage of the long left axle to keep us from overturning the Blackbird at speed.”

Cavallaro also had to work out a way to prevent the turbine’s torque from flipping the vehicle over. As a solution, he designed one of its axles as longer than the other, and the Blackbird’s chain drive was reconfigured to fit the asymmetrical axle setup.

The principle behind the upwind-configured Blackbird is similar to that of sailing. Blackbird’s version of two large sails are its blades, spinning around a common axis, moving forward as the cart sails into the wind and cross-wind as the blades turn around the axis.

He said the combination of upwind and cross- motion is identical to that of a sail on a boat on an upwind tack. The sailboat makes use of its keel to constrain the motion of the sail in the correct direction, and in Blackbird’s case, the transmission and wheels perform the same function.

Cavallaro holds the title of Sportvision Chief Scientist and he holds 25 patents in computer enhancement of live sporting events. He received a B.S. in Aerospace Engineering from Georgia Tech and M.S.in Dynamics and Controls from UCLA and worked in aerospace for several years.

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User comments : 8

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Deathclock
1.8 / 5 (5) Jul 12, 2012
This will obviously never be practical, but things learned in the process may be...
plaasjaapie
2 / 5 (4) Jul 12, 2012
First saw this tried about forty years ago. Nice to see it again. :-)
tadchem
not rated yet Jul 13, 2012
This appears in principle to be an aerodynamic equivalent of the hydraulic ram. The key difference is that the hydraulic head required to operate a ram pump is far more reliable and constant than the wind required to operate this contraption.
ziploc
not rated yet Jul 14, 2012
This differs from a hydraulic ram in that it operates in steady-state. No use is made of stored energy or momentum. In one configuration it can go directly downwind at about 3X wind speed - continuously, and in the other configuration it can go directly upwind at about 2X wind speed - continuously.
pmrobes
not rated yet Jul 15, 2012
I have often wondered if a metamaterial could be developed for directing wind around a car such that the wind would "push" the car in whatever direction needed. I have heard of metamaterials that can turn on and off their properties, so why not a metamaterial that can turn on and off its direction of impact.

I don't know much about the physics of this, so please be kind in any opposing responses.
antialias_physorg
not rated yet Jul 15, 2012
I have often wondered if a metamaterial could be developed for directing wind around a car such that the wind would "push" the car in whatever direction needed.

Then stop wondering and start looking up the term 'conservation of momentum'

But you might look up a technology known as a 'sail'.
pmrobes
not rated yet Jul 15, 2012
I don't see why this would violate conversvation of momentum. You might have to lose some of the energy in the redirection process, but I don't see why all would be lost. Metamaterials that allow for the material not to appear are still redirecting it from its 'natural path'

Also the point of using a metamaterial for this would be to integrate it into the body of the vehicle and not have some obtrusive object added to it. This then could be practical for 'real' cars for conserving fuel.
SatanLover
not rated yet Jul 15, 2012
The concept they use is actually a lot like spacetime manipulation for "propulsion".

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