Force Generation Unlike conventional trawls, the ATS does not make use of fixed aerofoil-shaped doors, towed at an angle of attack to generate the spreading force. Instead it makes use of a number of spinning rotors or “Magnus Effect” devices. When a spinning rotor is placed in a moving stream, a force is generated at right angles to the direction of flow and  at right angles to the axis of the rotor. This is known as the "Magnus Effect". The direction of the force is determined by the  direction of rotation of the rotor. The size of the  force is dependant on the ratio between the speed of flow of the stream and the tangential speed of  the rotor. Coefficients of lift greater than 11 are obtainable. A lift/drag ratio of 5/1 is typical for a coefficient of lift of 8. When compared to a conventional "aerofoil" device, for the same lift force, the projected area of the  rotor is smaller and the drag force is less. Besides the above, one of the main reasons for  selecting this particular technology for the ATS is  that the lift force is easily and fully controllable  with a fast response time. However this feature  does come at a cost - power is required to drive the rotor. Force generation is but one aspect of the system, the others being able to direct this force in a specific direction and being able to change this direction as required. For this a minimum of two rotors is required and, in the case of this  version of the ATS, one rotor is placed on top of the other to form a Variable Thrust Vector Device (VTVD). For a more mathematical description of Vectors and Thrust Vectoring click here 
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