Comic for Wednesday, 10/16 (Early High Res)

Nah, the net movement of the reaction mass is what matters. Since the air will bounce off the sails and move backwards, there will be a small forward thrust, though not as much as if they simply turned around and blew backwards, because of the inelastic dampening of the sails and the turbulence of reversing the flow at that interface. Assuming, of course, that they blow hard enough to reach those sails. If it were a person the thrust would dissipate before reaching that distance, having pushed off the static air in between, and the nominal thrust would indeed push them backward.