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Modeling and control of a heavy-lift helicopter consisting of large and small tilting rotors

In this study, we have proposed an unconventional UAV design. We aimed heavy lifting in an efficient way, without using complicated swashplate mechanism. Helicopter consist of two large propellers to carry the main payload, two small propellers to stabilize the roll attitude, and two servo motors to control the yaw axis. Large propellers will be more efficient than the small propellers owing to their greater disk area. For this reason, main lifting will be achieved by two large propellers. Conventional quadcopters have "PNPN" (P: Clockwise, N: Counterclockwise) propeller arrangement. However, the system we proposed has "PPNN" propeller arrangement to compensate the reaction torques of equally sized propeller pairs which are placed at opposite sides. However, quadcopters with "PPNN" propeller arrangement loses controllability upon hovering. Therefore, controllability is satisfied by adding servo motors to small propellers for tilting. We have derived the nonlinear dynamic equations, linearized the system around the equilibrium point and performed controllability analysis. An autopilot and controller is designed and, the system is simulated with realistic parameters. System performance is shown to be satisfactory.