[RedDevil]

Remember the blue roller that goes faster than the plank moving it?
If you put it upside down it would still go faster than the plank in the opposite direction.

Just like Blackbird would do if you set the gearing of the propeller to move the air faster than the car (instead of slower than the car)
In that case the forces trying to turn the propeller with the wind would be stronger than the force on the wheels trying to move the propeller against the wind. So the propeller starts to turn with the wind, and the gearing forces the wheels to move the car toward the wind.