Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / This thesis details the development and comparison of two linear control systems that performhover control for a vertical take-off and landing unmanned aerial vehicle. A non-linear mathematical model of the aircraft dynamics is developed. A classical successive loop closure control approach is presented, which applies static gains to the decoupled model around hover. A variable gain approach is presented using optimal control, which linearises the aircraftmodel around its state at fixed time steps. Simulation performance and robustness results are examined for both systems. Different aspects of both controller design processes and results are compared, including navigational performance, robustness and ease of use.

Regime recognition is an important tool used in creation of usage spectra and fatigue loads analysis. While a variety of regime recognition algorithms have been developed and deployed to date, verification and validation (V&V) of such algorithms is still a labor intensive process that is largely subjective. The current V&V process for regime recognition codes involves a comparison of scripted flight test data to regime recognition algorithm outputs. This is problematic because scripted flight test data is expensive to obtain, may not accurately match the maneuver script, and is often used to train the regime recognition algorithms and thus is not appropriate for V&V purposes. In this paper, a simulation-based virtual pilot algorithm is proposed as an alternative to physical testing for generating V&V flight test data. A “virtual pilot” is an algorithm that replicates a human’s piloting and guidance role in simulation by translating high level maneuver instructions into parameterized control laws. Each maneuver regime is associated with a feedback control law, and a control architecture is defined which provides for seamless transitions between maneuvers and allows for execution of an arbitrary maneuver script in simulation. The proposed algorithm does not require training data, iterative learning, or optimization, but rather utilizes a tuned model and feedback control laws defined for each maneuver. As a result, synthetic HUMS data may be generated and used in a highly automated regime recognition V&V process. In this thesis, the virtual pilot algorithm is formulated and the component feedback control laws and maneuver transition schemes are defined. Example synthetic HUMS data is generated using a simulation model of the SH-60B, and virtual pilot fidelity is demonstrated through both conformance to the ADS-33 standards for selected Mission Task Elements and comparison to actual HUMS data.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / 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.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / A real time attitude and heading reference system (AHRS) was successfully implemented for use on an airship. The AHRS was tested on board a small airship (blimp) with real data supplied from the inertial measurement unit and GPS receiver. The inertial measurement unit was built with lower grade sensors, resulting in significant reductions in component cost. To ensure accurate navigation results, the high rate inertial measurements were complemented with low rate GPS velocity and position updates in an extended Kalman filter configuration. A study was made of various Kalman filter configurations, especially the possibility of splitting a big Kalman filter into smaller Kalman filters. It was found that the best trade-off between accuracy and processing power was achieved by having two smaller Kalman filters running in sequence. The first extended Kalman filter estimates the attitude of the airship, while the second extended Kalman filter estimates the velocity and position of the airship. The two smaller Kalman filters were implemented on an onboard computer to provide real time estimates of the attitude, velocity and position of the airship.

Thesis (MScEng (Electrical and Electronic Engineering)--Stellenbosch University, 2008. / This thesis presents the design of a control system for the autonomous precision landing of an unmanned aerial vehicle aided by an infra red camera for precision position measurements. An optimal kinematics state estimator was designed using two Kalman filters. A Monocular vision algorithm that uses markers on the runway was developed to supply accurate position measurements on the final approach of the landing. Inner-loop controllers as proposed by [14] and implemented in [5] are used to reduce the aircraft dynamics to a point mass with steerable acceleration vector. Outer-loop controllers as proposed by [13] were modified and expanded to guide the aircraft on the circuit and final approach. The hardware in the loop simulator that was designed in [6] was expanded for optical measurements and used to verify the system. An infra red camera node was designed and built to supply the optical measurements. The system was installed on a model aircraft and partially tested with practical test flights.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2007. / This thesis relates to the successful development of a flight control system to perform a range of aerobatic manoeuvres autonomously. The project is the first to try to extend the flight control capabilities of the Computer and Control group at the University of Stellenbosch. A simplified mathematical aircraft model is developed which encapsulates the important dy- namic characteristics of the airframe. It is demonstrated how computational fluid dynamics software can be used to calculate the stability and control derivatives of a conventional air- frame. A vehicle independent kinematic state estimator is presented and used to obtain the complete aircraft state vector. The estimator makes use of extended Kalman filter theory to combine a series of low quality sensor measurements in an optimal manner. A model predictive control strategy is then used to regulate the aircraft about arbitrary, time variant trajectories. The controller’s architecture is not in any way specific to the aerobatic manoeuvres demonstrated in this project. The avionics and ground station used for the implementation of the estimator and control algorithms are presented. The development of a hardware in the loop simulator is discussed and used to verify the correct implementation of the respective algorithms. Finally, practical results from two days of flight tests are presented.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / This thesis investigates aggressive all-attitude flight control systems. These are flight controllers capable of controlling an aircraft at any attitude and will enable the autonomous execution of manoeuvres such as high bank angle turns, steep climbs and aerobatic flight manoeuvres. This class of autopilot could be applied to carry out evasive combat manoeuvres or to create more efficient and realistic target drones. A model for the aircraft’s dynamics is developed in such a way that its high bandwidth specific force and moment model is split from its lower bandwidth kinematic model. This split is done at the aircraft’s specific acceleration and roll rate, which enables the design of simple, decoupled, linear attitude independent inner loop controllers to regulate these states. Two outer loop kinematic controllers are then designed to interface with these inner loop controllers to guide the aircraft through predefined reference trajectories. The first method involves the design of a linear quadratic regulator (LQR) based on the successively linearised kinematics, to optimally control the system. The second method involves specific acceleration matching (SAM) and results in a linear guidance controller that makes use of position based trajectories. These position based trajectories allow the aircraft’s velocity magnitude to be regulated independently of the trajectory tracking. To this end, two velocity regulation algorithms were developed. These involved methods of optimal control, implemented using dynamic programming, and energy analysis to regulate the aircraft’s velocity in a predictive manner and thereby providing significantly improved velocity regulation during aggressive aerobatic type manoeuvres. Hardware in the loop simulations and practical flight test data verify the theoretical results of all controllers presented

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: In this project, system identification is done on the Modular Unmanned Aerial Vehicle (UAV). This is necessary to perform fault detection and isolation, which is part of the Fault Tolerant Control research project at Stellenbosch University. The equations necessary to do system identification are developed. Various methods for system identification is discussed and the regression methods are implemented. It is shown how to accommodate a sudden change in aircraft parameters due to a fault. Smoothed numerical differentiation is performed in order to acquire data necessary to implement the regression methods. Practical issues regarding system identification are discussed and methods for addressing these issues are introduced. These issues include data collinearity and identification in a closed loop. The regression methods are implemented on a simple roll model of the Modular UAV in order to highlight the various difficulties with system identification. Different methods for accommodating a fault are illustrated. System identification is also done on a full nonlinear model of the Modular UAV. All the parameters converges quickly to accurate values, with the exception of Cl R , CnP and Cn A . The reason for this is discussed. The importance of these parameters in order to do Fault Tolerant Control is also discussed. An S-function that implements the recursive least squares algorithm for parameter estimation is developed. This block accommodates for the methods of applying the forgetting factor and covariance resetting. This block can be used as a stepping stone for future work in system identification and fault detection and isolation. / AFRIKAANSE OPSOMMING: In hierdie projek word stelsel identifikasie gedoen op die Modulêre Onbemande Vliegtuig. Dit is nodig om foutopsporing en isolasie te doen wat ’n deel uitmaak van fout verdraagsame beheer. Die vergelykings wat nodig is om stelsel identifikasie te doen is ontwikkel. Verskeie metodes om stelsel identifikasie te doen word bespreek en die regressie metodes is uitgevoer. Daar word gewys hoe om voorsiening te maak vir ’n skielike verandering in die vliegtuig parameters as gevolg van ’n fout. Reëlmatige numeriese differensiasie is gedoen om data te verkry wat nodig is vir die uitvoering van die regressie metodes. Praktiese kwessies aangaande stelsel identifikasie word bespreek en metodes om hierdie kwessies aan te spreek word gegee. Hierdie kwessies sluit interafhanklikheid van data en identifikasie in ’n geslote lus in. Die regressie metodes word toegepas op ’n eenvoudige rol model van die Modulêre Onbemande Vliegtuig om die verskeie kwessies aangaande stelsel identifikasie uit te wys. Verskeie metodes vir die hantering vir ’n fout word ook illustreer. Stelsel identifikasie word ook op die volle nie-lineêre model van die Modulêre Onbemande Vliegtuig gedoen. Al die parameters konvergeer vinnig na akkurate waardes, met die uitsondering van Cl R , CnP and Cn A . Die belangrikheid van hierdie parameters vir fout verdraagsame beheer word ook bespreek. ’n S-funksie blok vir die rekursiewe kleinste-kwadraat algoritme is ontwikkel. Hierdie blok voorsien vir die metodes om die vergeetfaktor en kovariansie herstelling te implementeer. Hierdie blok kan gebruik word vir toekomstige werk in stelsel identifikasie en foutopsporing en isolasie.

The development of large lightweight airframes has resulted in what used to be high frequency structural dynamics entering the low frequency range associated with an aircraft’s rigid body dynamics. This has led to the potential of adverse interactions between the aeroelastic effects and flight control, especially unwanted when incidents involving failures or extreme atmospheric disturbances occur. Moreover, the pilot’s response in such circumstances may not be reproducible in simulators and unique to the incident. The research described in this thesis describes the development of a pilot model suitable for the investigation of the effects of aeroelasticity on manual control and the study of the resulting airframe loads. After a review of the state-ofthe- art in pilot modelling an experimental approach involving desktop based pilot-in-the-loop simulation was adopted together with an optimal control based control-theoretic pilot model. The experiments allowed the investigation of manual control with a nonlinear flight control system and the derivation of parameter bounds for single-input-single-output pilot models. It was found that pilots could introduce variations of around 15 dB at the resonant frequency of the open loop pilot-vehicle-system. Sensory models suitable for the simulation of spatial disorientation effects were developed together with biomechanical models necessary to capture biodynamic feedthrough effects. A detailed derivation and method for the application of the modified optimal control pilot model, used to generate pilot control action, has also been shown in the contexts of pilot-model-in-the-loop simulations of scenarios involving an aileron failure and a gust encounter. It was found that manual control action particularly exacerbated horizontal tailplane internal loads relative to the limit loads envelope. Although comparisons with digital flight data recordings of an actual gust encounter showed a satisfactory reproduction and highlighted the adverse affects of fuselage flexibility on manual control, it also pointed towards the need for more incident data to validate such simulations.

This thesis describes an all-in-one flight control system (FCS) that was designed for unmanned aerial vehicles (UAVs). The project focuses on the embedded hardware aspect of a stand-alone system with low-cost and reliability in mind.