The Blackbird wind cart from Thin Air Designs attained a speed 2.86 times faster than the wind while it was being powered only by the wind, continuously, which seems counter intuitive but here is a video to confirm that. The trick to going faster than the wind is the 17ft (5.19m) propeller connected to the wheels. The wheels twist the propeller that gives the force to the lightweight cart that increases the wheel revolutions, thus increasing sharp edge speed. The wind speed was 10knots (18.5kp,11.5mph) and the cart speed levelled out at 28.6knots (53kph, 33mph) during their high speed testing in the desert.

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via: fasterthanthewind