I like the answers from @Lightlyseared and @funkdaddy. I think they’ve nailed it. But I don’t see how the craft can go much more than 1x faster than the wind, at least “dead downwind”. What happens as the speed of the thing over the ground starts to match the wind speed is the sensation of being “pushed” by the wind gets less and less. As soon as you actually match the windspeed, then it feels (to the driver) as if there is zero ‘apparent’ wind; he’d feel a calm around him. And as soon as he travels faster than the wind, then he’d have an apparent wind… in his face. It would seem to him as if he is traveling upwind, straight into the wind.
As he travels faster than the wind at his back, then it feels as if he’s headed into a stronger and stronger headwind. And it’s going to ‘feel’ that way to the propeller blade, too. So my first question is: How does the blade continue to turn in the same direction as it did when the wind was from behind… and ‘felt’ that way?
I don’t think that we’re seeing enough from the video or learning enough from the text to understand the mechanism well enough as the thing matches and then exceeds the speed of the wind. I do agree that the videos seem to show a vehicle with the wind behind it (telltales streaming forward) and then later show a vehicle appearing to head into an apparent wind (telltales streaming aft), and I’m sure that the reason it can happen is because of the turbine effect, with the large propeller blade turning small wheels. I just don’t see how it can be “so much” effective downwind.
I’d have to know a lot more than I do about the thing.
Sailors know that a boat’s fastest point of sail is almost never “downwind”, but reaching across the wind, perpendicular to the direction of the wind. And it’s possible for some craft, such as the sail-powered wheeled vehicles shown, iceboats and hydrofoils to travel faster than the wind… across the wind. This is definitely a different animal.
Very interesting. Thanks for the introduction.