Abstract
Main rotor actuator failure leads to catastrophic accidents for single main rotor helicopters. This paper focuses on safe landing trajectories after an actuator is locked in place by the remaining actuators, without introducing other control inputs. A general swashplate geometry is described, and new reconfiguration solutions for the control mixer are presented. The safe landing trajectories are obtained by formulating a nonlinear optimal control problem based on a nonlinear helicopter dynamic model and geometry constraints due to actuator failure. Safe landing trajectory results are shown with various initial forward velocities of all actuator failure cases. The safe initial speed boundaries are also explored by employing speed sweeps.
Highlights
Helicopter control, whether for manned or unmanned helicopters, is primarily done by the control system of the main rotor, consisting of the swashplate, servos, pitch links and pitch horns
Plenty of work has been done on fixed-wing actuator faults or failures [3,4,5,6], most studies on helicopters have been focusing on the partial loss of effectiveness of actuators and actuator control bias [7,8,9,10,11,12]
The general geometry of a single main rotor helicopter swashplate actuator is analyzed, and new configurations of the control mixer are designed for each actuator failure case, without changing the original geometries of the mechanical structure
Summary
Helicopter control, whether for manned or unmanned helicopters, is primarily done by the control system of the main rotor, consisting of the swashplate, servos, pitch links and pitch horns. After one of the actuators gets stuck, the helicopter is controlled by the other two remaining actuators of the swashplate and variation of rotor speed for vertical control. Qi [15] proposes a control system based on a linear-quadratic regulator, and focuses on finding new references by a reference redesign method after one actuator is stuck In their studies, the control inputs consist of rotor speed as well. If the longitudinal speed is changed while retaining the collective pitch, there will be a corresponding response in vertical speed It is mentioned in [13] that the vertical speed can be obtained by flying to a specific forward speed that supports the decent rate, such a phenomenon is only utilized within a small speed range around the speed where the failure takes place.
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