Aerodynamicist Rick Cavallaro settled an argument two years ago when his wind-powered Blackbird vehicle clipped along at 2.86 times the speed of the wind going downwind. Last week, after making a few modifications, the New Jerusalem airport in Tracy, Calif. was the scene for another record when the Blackbird hit a top speed 2.1 times faster than the wind speed when headed upwind.
Writing in his blog, Cavallaro says "At 2.1X windspeed directly upwind, Blackbird nearly tripled the standing record of 0.75X wind speed. But to be fair, the existing record was held by one of the vehicles in the Aeolus race which imposes a number of significant constraints on the vehicle design that I don’t have."
To get the Blackbird to go upwind, Cavallaro had to replace the prop with turbine blades and reverse the transmission. He also changed the gearing. The turbine blades drive the wheels. To prevent the resulting torque roll from flipping the small cart, Cavallaro made the rear asymmetrical with the left side longer than the right.
Several news outlets covered Cavallaro's latest run, but you can read about it first hand in his own words here: https://fasterthanthewind.wordpress.com/2012/06/06/background-and-history/