Rick Cavallaro and his friends have built a wind-powered vehicle that travels directly downwind faster than the...
Rick Cavallaro and his friends have built a wind-powered vehicle that travels directly downwind faster than the wind, solving a riddle that can start fights.

On May 17, 2010, the wind-powered car went directly downwind 2.86x faster than the wind (with a wind speed of 13.5 mph) in a test run.

On July 2, 2010 they established an official world record by going directly downwind at 2.8x faster then the wind (with wind speed 10 mph).

Their best speed ratio was 3.5x the wind speed. Their fastest downwind run to date was ~54 mph.

On July 16, 2012  with a slightly modified version of the same Blackbird that set the downwind record in 2010, they were able to achieve a recorded and verified run directly UP the wind at 2.01x times the speed of the wind (10 mph wind) and on a separate run achieved a record speed of 22.9 mph, again directly INTO the wind.

Note that if you put such a cart on a treadmill, it'll move forward. This is how it looks like in wind frame of reference.

I'll leave it as an exercise to the reader to convince themselves that it violates no conservation laws (easy), no dynamic laws (slightly harder), and no thermodynamic laws (hardest).

Note that regular sailboats regularly move indirectly downwind faster then wind, while jibing (галс, http://en.wikipedia.org/wiki/Jibe#Use). That means they would overtake a balloon, being blown downwind. 

During the 2009 land speed record, Richard Jenkins in the sand yacht Greenbird was proceeding at 126.2mph, about 3x the speed of the wind on a course ~120 degrees off the true wind. Thus, its speed made good downwind was about 1.5x the speed of the wind.

During a training run for 2010 America's Cup the catamaran Alinghi 5, covered 20 nmi to windward and back in 2.5 hours in 8–9-kt winds, so its average velocity made good was 16 kt, about 1.9x wind speed. This is consistent with the yacht being able to sail at about 15 deg off the apparent wind. Indeed, the catamaran sails so fast downwind that it is always sailing upwind with respect to the apparent wind.

During the first race of the 2010 America's Cup, the winning yacht USA 17 sailed 20 nmi to windward in 1.5 hours, in winds of 5–10 kt. Thus its velocity made good upwind was about 1.8x windspeed, consistent with being able to sail about 13 degrees off the apparent wind when sailing upwind. She sailed 20 nmi downwind in 1.05 hours, so her velocity made good downwind was about 2.5x windspeed, consistent with being able to sail about 14 degrees off the apparent wind when sailing downwind. During the second race, she reached the windward mark in 1 hour, in 7-8 kt wind, so her velocity made good was about 13.2 kt, ~1.65x wind speed.

http://www.wired.com/autopia/2010/06/downwind-faster-than-the-wind/
http://www.nalsa.org/DownWind.html
http://www.fasterthanthewind.org/
http://en.wikipedia.org/wiki/Sailing_faster_than_the_wind#Sailing_dead_downwind_faster_than_the_wind
http://en.wikipedia.org/wiki/Blackbird_(land_yacht)
http://www.wired.com/autopia/2010/06/downwind-faster-than-the-wind/

Labels: Oleg Zabluda

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