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If you still don't think that it's possible to travel downwind faster than the wind, Rick Cavallaro has a deal for you: He'll sell you the Blackbird, the land yacht that currently holds the record for traveling downwind at 2.8 times the speed of the wind, and you can try it yourself.
That's right: The home-built cart that proved that it's possible to travel downwind faster than the wind, a vehicle that settled one of the longest-standing disputes in the physics community, is now for sale on eBay. The price is currently at a little over $1,200, with over 30 bids and five days left.
It's a rare opportunity to own a piece of science history. After all, Newton's apple has long since rotted away, and Franklin's kite and key are lost. The Blackbird may not have the same place in folklore, but it's still pretty important. The question of whether it's possible to travel downwind faster than the wind vexed physicists for ages. Cavallaro, an aerodynamicist, kitesurfer and paraglider, decided that he wouldn't answer the question with numbers on paper. Instead, he'd create a cart and race it in the desert.
Built in 2010 with help from Joby Energy, Google, and San Jose State University, the ultralight cart is made mostly of foam and has a 17-foot-tall propeller. The wheels turn the prop, which provides forward thrust. But the wind itself also acts as an external power source, and a powerful transmission keeps it all in motion.
The Blackbird not only holds the record for traveling downwind faster than the wind, but last year the downwind team modified the cart so it could travel upwind faster than the wind by changing the pitch of the propeller blades and modifying the transmission so the propeller turned the wheels. Once again, it set a record, going 2.01 times the speed of the wind.
The achievement that Cavallaro says he's most proud of isn't any record, but it's that he brought a brain-teaser to life. This year, the American Association of Physics Teachers even used the case of the Blackbird in a test to determine which students get to attend the International Physics Olympiad.
"It did everything we were hoping it would," he wrote in an email to supporters. "I had always hoped it would do what brain-teasers are supposed to do - challenge your gut and make you think out of the box. But it's time to clear it out and make room."
