Browsing by Author "Kriel, Steven Cornelius"
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- ItemAutomated aerial refuelling of a large receiver aircraft(Stellenbosch : Stellenbosch University, 2016-03) Kriel, Steven Cornelius; Jones, T.; Engelbrecht, J. A. A.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: Performing aerial refueling of a large receiver is an extremely strenuous task for a pilot. Automating the aerial refueling for a large receiver is thus highly desirable. While significant research has been performed on the autonomous aerial refueling of unmanned and fighter-sized aircraft, the challenges of autonomously refueling a large receiver are largely unknown. This thesis seeks to investigate these challenges. Primarily it seeks to determine whether the long distance between the centre of gravity (CG) and refueling receptacle (RR) has a meaningful impact on controller design. A linear model is derived to describe the movement of the receiver aircraft’s refueling receptacle during aerial refueling. This novel linear model is compared to existing linear aircraft models. Through analysis it is shown that the distance between the CG and the RR must be included in the dynamic model of the receiver. A novel normal controller is designed using a new architecture that takes the relative movement of the CG and the RR into account. An axial controller is derived using an innovative high-drag configuration in order to combat the slow engine response of large aircraft. Optimal control is used to design an RR specific lateral controller. Other challenges relating to the refueling of a large receiver are also investigated. A control strategy for the tanker is developed using existing FBW control inputs and hold modes. The tanker control is designed to be supplied by a pilot and does not require any customisation of flight software. It is expected that tanker downwash will have a significant effect on the receiver. The linear models and non-linear simulation are adapted to include uncertain downwash disturbances. The controllers are customised to control the receiver in various trajectories: approach, toboggan, and racetrack. The linear models are augmented with a linearised model of the Airbus A330 MRTT’s fly-by-wire (FBW) system. The FBW system is slightly adapted to be suited to automatic control. The controllers are redesigned to operate through the FBW. The designed controllers are tested in a non-linear simulation. Simulations are performed in light and medium turbulence, as defined in MIL-STD-1797. Robustness tests are performed with regard to downwash and sensor delays. Through numerous non-linear simulations on two different simulators, it is shown that the control system is capable of performing automated aerial refueling in light and medium turbulence.
- ItemA comparison of control systems for the flight transition of VTOL unmanned aerial vehicles(Stellenbosch : University of Stellenbosch, 2008-03) Kriel, Steven Cornelius; Jones, T.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.This thesis details the development of linear control systems that allow a vertical take-off and landing unmanned aerial vehicle to perform transitions between vertical and horizontal flight. Two mathematical models are derived for the control system design. A large non-linear model, describing all the dynamics of the aircraft, is linearised in order to perform optimal control using linear quadratic regulator theory. Another model is decoupled using time scale separation to form separate rigid body and point mass dynamics. The decoupled model is controlled using classical control techniques. Simulation results are used to judge the relative performance of the two control schemes in several fields including: Trajectory tracking, sensitivity to parameters, computational complexity and ease of use.