A fluid turbine apparatus includes a fixed structure and a rotating structure supported by the fixed structure. The rotating structure includes a central shaft, and at least two wings connected to the central shaft. Each of the wings includes a wing frame, at least one door and a respective at least one door stopper. Each of the doors pivots relative to the respective wing frame between closed and open positions. In use, the door located at one side of the central shaft facing a flow of fluid is in the closed position with fluid force transferred to the door, while the door located at the opposite side of the shaft is in the open position with fluid passing through the respective wing frame. The fluid force creates a torque that rotates the central shaft. Apparatuses can extract power from wind or water current.