Variable Thrust Vector Device The basic components of a Variable Thrust Vector Device (VTVD) are as follows: a solid tie rod with a warp attached to the front lug  and the bridles to the rear lug a strong main frame which is free to rotate around  the tie rod a top spinning rotor assembly a bottom spinning rotor assembly  a protective shroud around the rotors to prevent damage during normal operations drives, sensors and electronics to provide the VTVD  with a level of autonomous operation as well as  under remote control over a data link Operating principle of the VTVD In operation each spinning rotor would be independently controlled and the force it generated would be proportional  to its speed of rotation. The two equations that apply to the VTVD are: Magnitude of the resultant force vector: FR = Ft + Fb Magnitude of the rotating torque: Tr = Fb * a - Ft * a (where Ft is the force generated by the top rotor, Fb is the force generated by the bottom rotor and a is the distance from the center of the VTVD to the point on the rotor at which the force acts). This simulation video below illustrates the basic effects of changing the speeds of the rotors on the movements of the VTVD Below is a more detailed step-by-step explanation of the VTVD operation To move the trawl to a new position (i.e. downwards): Compute new position thrust vector and optimum travel vector. Increase speed of top rotor and/or reduce speed of bottom rotor. Due to the difference in the thrusts of the rotors, a torque is developed, which heels the device outwards. Increase speed of bottom rotor and/or reduce speed of top rotor. This will stop rotation of the device at the heel  angle determined by the travel vector. The horizontal component of this vector = spread force required. The vertical component = force required to move the trawl downwards at preset speed. Increase speed of bottom rotor and/or reduce speed of top rotor. This will rotate the device to the heel angle  determined by the new position force vector. Equalise speeds of rotors, adjust to match magnitude of new force vector. Monitor the depth, spread and force vector. Adjust force vector, if necessary, to maintain the set trawl parameters.
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