Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / This thesis presents the analysis, design, simulation and practical implementation of a novel control system for a variable stability blended-wing-body unmanned aerial vehicle. The aircraft has a moveable centre of mass that allows it to operate in an aerodynamically optimised minimum drag configuration during cruise flight. The primary purpose of the control system is thus to regain nominal static stability for all centre of mass positions, and then to further regulate motion variables for autonomous way point navigation. A thorough analysis of the parameters affected by the varying centre of mass position leads to the identification of the main control problem. It is shown that a recently published acceleration based control methodology can be used with minor modification to elegantly solve the variable stability control problem. After providing the details of the control system design, the customised avionics used for their practical implementation are presented. The results of extensive hardware in the loop simulations verify the functionality of the controllers. Finally, flight test results illustrate the practical success of the autopilot and clearly show how the control system is capable of controlling the variable stability aircraft at centre of mass locations where a human pilot could not.

Thesis (MScEng (Electrical and Electronic Engineering))--Stellenbosch University, 2005. / The successful development of a conventional flight autopilot for a model aircraft is presented. All aspects of the autopilot design are considered, from modeling to flight tests. A mathematical aircraft model, as a function of the aircraft’s physical parameters alone, is presented. A controller architecture capable of regulating the motion variables required for conventional flight using only low cost, off-the-shelf sensors is developed. The controller design complements the aircraft model development technique used, by reducing the sensitivity of the controller performance to the model accuracy. The avionics and ground station design is presented. The avionics includes a generic Inertial Measurement Unit (IMU). The total avionics cost is only R5000. Results from three days of flight tests demonstrate the autopilot’s success. Its rapid success can largely be attributed to the extensive simulations of the entire autopilot in the two non-linear simulators developed.

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, 2006. / This project developed a low-cost avionics system for a miniature helicopter to be used for research in the field of autonomous flight (UAVs). Previous work was done on a small, electrically powered helicopter with some success, but the overall conclusion was that the vehicle was underpowered. A new vehicle, the Miniature Aircraft X−Cell, was chosen for its ability to lift a larger payload, and previous work done with it by a number of other institutions. An expandable architecture was designed to allow sensors and actuators to be arbitrarily added to the system, based on the CAN standard. A CAN sensor node was developed that could digitize 12 channels at up to 16 bit resolution and do basic filtering of the data. Onboard computing was provided by a PC/104 based computer running Linux, with additional hardware added to interface with the CAN bus and assist with timing. A simulation environment for the helicopter was evaluated and shown to provide a good test bed for the control of the helicopter. Finally, the avionics was used during piloted test-flights to measure data and judge the performance of both the modified helicopter and the electronics itself.

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.

Small units maneuvering on the battlefield have little time to establish data links and interface with the Global Information Grid (GIG) while trying to achieve an objective. The bandwidth and interface requirements necessary to receive live data from current strategic level systems limit the small unit operational user's ability to receive and act upon data and intelligence. Without the ability to interface with current strategic-level UAV assets, these small units are left without a comprehensive operational picture. Mini-UAVs offer the capability for the tactical user, in a variety of missions, to have direct control over the aerial asset without intervention from higher authority. Organic UAV assets can be used to collect data relevant to small units without the need for connecting to intelligence systems. This offers increased mobility and a dedicated collection platform; however, there are still drawbacks to this capability. This thesis examines mini-UAVs, and their integration into the Coalition Operating Area Surveillance and Targeting System (COASTS) network.

Approved for public release; distribution is unlimited / The defense response to a Chemical and Biological attack would be importantly based on predicting the dispersion of a toxic cloud. Considering that an Unmanned Air Vehicle would provide the capability for embedding and positioning inertial and air data sensors geographically as required, real-time wind estimation can be performed for every actual position of the flying device in order to predict the plume moving direction. The efforts in this thesis concentrate on the demonstration and validation of procedures for obtaining Wind Estimation close to real-time and its instantaneous display. The presented work is based on a particular UAV platform available at the NPS Aeronautical Department and it aims to establish a general methodology, which may be used on other flying devices with similar available sensors. An accurate estimation of real wind for a particular combat scenario will enable operational units to have a near real-time decision aid. This final result could be integrated into a Command and Control net, to assist in a focused way the response to a Chemical and Biological attack and to map the source or the region to be affected. / Lieutenant Commander, Chilean Navy

Simple, cheap and reliable echo-based ultrasonic ranging systems such as the Polaroid ranging unit are easily applied to indoor applications. However, to measure the range between an unmanned helicopter and a moving ship deck at sea using ultrasound requires a more robust ranging system, because rushing air and breaking water are known ultrasound noise sources. The work of designing, constructing and testing such a system is described in this dissertation. The compact, UAV ready ultrasound transmitter module provides high power, broadband arbitrary signal generation. The separate field-ready receiver is based on a modern embedded Digital Signal Processor (DSP), providing high speed matched-filter correlation processing. Large time-bandwidth signalling is employed to maximise the signal to noise ratio of the ranging system. Synthesised experiments demonstrate the ability of the correlation processing to reliably recover timing from signals buried in noise. Real world experiments demonstrate decimetre accuracy with two centimetre resolution, ten metre range and 32Hz refresh rate. A maximum boresight range of up to 38m is supported.

Unmanned Aircraft Systems (UAS) represent a significant potential for growth in the aerospace industry. Their use in military operations has increased exponentially in the last decade alone, requiring a corresponding increase in training airspace in the United States. In addition to military usage, UAS have the potential to fulfill a myriad of roles for both the public and private sectors. However, the use of UAS has been limited in the National Airspace System (NAS) to military and public applications and only under fairly restrictive Certificates of Authorization or Waiver (COA). The only way to truly realize the potential of UAS is to fully integrate them into the NAS. The desire to integrate UAS was recently codified into law with the 2012 FAA Modernization Act, mandating integration by specific, fairly short timelines. There are several challenges currently preventing the full integration of UAS that range from technological to procedural areas. However, the one common theme in all of these challenges is Safety. Across the literature on this topic there is no consensus on how safe UAS need to be to achieve integration, whether UAS can currently meet specified safety targets, and if not, what is the best way to achieve the safety goals. The purpose of this effort was to demonstrate a comprehensive framework for analyzing UAS integration efforts using a Target Level of Safety (TLS) approach. Using reliability tools, aircraft encounter models, and data from a wide variety of sources ranging from manned aircraft safety, explosives, falling debris and earthquake damage, the primary outcome of the effort was a better understanding of the risk to second and third party persons as a result of UAS operations in the NAS. This framework and associated models are validated using reliability and casualty data from manned aircraft operations. The framework is then applied to several relevant and specific cases to demonstrate the impact of policy decisions on UAS reliability and allowed operational areas. The supporting research and analysis can serve as a baseline for future integration analysis and decision-making efforts, and was designed to allow stakeholders and decision makers in this field to assess UAS safety, and set minimum system reliability requirements and mitigation system effectiveness standards.