Originally Posted by BruceZ
Sailers and windsurfers can go faster than the wind, and even sail against the wind. If you've done any waterskiing you know that it is possible to pass the boat. In both cases a component of the force is developed in a direction other than the direction of the wind or boat by turning the sail (tacking) or the skis. Here's a thorough analysis of sailing faster than the wind by Terence Tao:
I've done a lot of sailing myself and know about sailing faster than the wind. The issue is sailing faster than the wind when it comes from directly behind you. At some point, you might match speed with the wind, but then you are effectively becalmed. How then do you go even faster? I can think of ways where the cart follows a curved path or makes use of a fly wheel, etc., but that is not what appears to be happening in the video.
One issue you might want to consider is that in transitioning from lower than wind speed to higher than wind speed, the propeller will want to change its direction of rotation. The only ways I can think of avoiding that are:
- Rotate the propeller assembly along a vertical axis.
- Invert the camber of the propeller.
#1 does not occur in the video. #2 would make the propeller shape inefficient in at least one of the 2 directions of rotation. In either of #1 and #2, you still have the problem of accelerating when your velocity relative to the wind is zero.