Longitudinal Control Via Distributed Propulsion and Elevator Deflection

Open Access
Author:
Gill, Charlotte Salome
Area of Honors:
Aerospace Engineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Jacob Willem Langelaan, Thesis Supervisor
  • Philip John Morris, Honors Advisor
  • George A Lesieutre, Faculty Reader
Keywords:
  • Differential Thrust
  • Propulsion
  • Longitudinal Control
  • Aircraft Dynamics
  • Stability and Control
  • Simulation
Abstract:
An aircraft can be controlled without the use of control surfaces by applying differential thrust across multiple motors. Trimming the aircraft without elevator has the potential to reduce the trim drag during cruise, which would improve the aircraft’s flight efficiency. Differential thrust was analyzed for a SB-XC (a 14 foot wingspan RC aircraft) at trim conditions by modeling the aircraft using linearized longitudinal equations of motion. Longitudinal flight control is examined using a combination of differential thrust to trim the aircraft and elevator deflection for disturbance rejection. The configuration of the motors for longitudinal control is analyzed by varying the static margin and Cm0 of the aircraft to compute the necessary moments from the thrust force for the aircraft to trim across a wide range of flight conditions. Longitudinal control is implemented using successive loop closure: elevator controls pitch angle and pitch angle is used to control airspeed. The total thrust controls the climb rate, so trim is achieved by calculating the difference in thrust that results in zero pitching moment at the desired flight condition. A flight speed controller and rate of climb controller were designed using the root locus method to optimize the aircraft response. From this model it was found that it is possible to use differential thrust to trim an aircraft at different commanded speeds and rates of climb while using the elevator to correct for small disturbances.