The pole in the center of the VAT generates a turbulent wake that the blades pass through once every rotation. This wake shakes the blade and causes extra stre

The pole in the center of the VAT generates a turbulent wake that the blades pass through once every rotation. This wake shakes the blade and causes extra stress. The blades themselves make a wake also, though not as much as the pole. The horizontal turbines put the pole behind the blades. The pole does make a bow wave, but it is not as bad as the VAT wake. The pole/blade interaction is not as severe.