Master of Science

This thesis describes the development of a nonlinear flight dynamics model for a small, fixed-wing unmanned aerial vehicle (UAV). Models developed for UAVs can be used for many applications including risk analysis, controls system design and flight simulators. Several challenges exist for system identification of small, low-cost aircraft including an increased sensitivity to atmospheric disturbances and decreased data quality from a cost-appropriate instrumentation system. These challenges result in difficulties in development of the model structure and parameter estimation. The small size may also limit the scope of flight test experiments and the consequent information content of the data from which the model is developed. Methods are presented to improve the accuracy of system identification which include data selection, data conditioning, incorporation of information from computational aerodynamics and synthesis of information from different flight test maneuvers. The final parameter estimation and uncertainty analysis was developed from the time domain formulation of the output-error method using the fully nonlinear aircraft equations of motion and a nonlinear aerodynamic model structure. The methods discussed increased the accuracy of parameter estimates and lowered the uncertainty in estimates compared to standard procedures for parameter estimation from flight test data. The significant contributions of this thesis are a detailed explanation of the entire system identification process tailored to the needs of a small UAV and incorporation of unique procedures to enhance identification results. This work may be used as a guide and list of recommendations for future system identification efforts of small, low-cost, minimally instrumented, fixed-wing UAVs. / MS / This thesis describes identification of a series of equations to model the flight motion of a small unmanned airplane. Model development for small unmanned aerial vehicles (UAVs) is a challenging process because they are significantly affected by small amounts of wind and they usually contain inexpensive, lower quality sensors. This results in lower quality data measured from flying a small UAV, which is subsequently used in the process to develop a model for the aircraft. In this work, techniques are discussed to improve estimation of model parameters and increase confidence in the validity of the final model. The significant contributions of this thesis are a comprehensive explanation of the model development process specific to a small UAV and implementation of unique procedures to enhance the resulting model. This work as a whole may be used as a guide and list of recommendations for future model development efforts of small, low-cost, unmanned aircraft.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2004. 220 leaves single printed pages ,preliminary pages i-xiv and numberd pages 1-188.Includes bibliography.list of figures and used a Hp Scanjet 8250 Scanner to pdf format (OCR), / ENGLISH ABSTRACT: This thesis describes the process followed to determine the short-term control and stability derivatives of an ASK-13 glider (ZS-GHB). The short-term control and stability derivatives are obtained by parameter estimation done using data recorded in flight. The algorithm used is the MMLE3 implementation of a maximum likelihood estimator. To collect the flight data sensors were installed in the ZS-GHB. Sensors measuring the control surface deflections, translation acceleration, angular rates and the dynamic and static pressure are needed to provide enough data for the estimation. To estimate accurate derivatives specific manoeuvres were flown by the pilot, to ensure that all the modes of the glider were stimulated. The results reveal that the control and stability derivatives estimated from the flight data are not very accurate but are still suitable to be used in simulating the glider's motion. / AFRIKAANSE OPSOMMING: Hierdie tesis beskryf die proses wat gebruik is om die kort periode beheer en stabiliteit afgeleides van 'n ASK-13 sweeftuig vas te stel. Die kort periode beheer en stabiliteit afgeleides is verkry deur parameter afskatting op data wat gedurend vlugte van die sweeftuig opgeneem is. Die algoritme wat gebruik is om die parameters af te skat is die MMLE3 voorstelling van 'n maksimale moontlikheid afskatter. Om vlug data te versamel sensore moes in die sweeftuig geinstalleer word. Die sensore meet beheer oppervlak hoeke, versnellings, hoeksnellhede en die dinamies en statiese lugdruk om te verseker dat daar genoeg data is vir die afskatting. Om die afgeskatte parameters akkuraad te kry moet die loods spesefieke manoeuvres vlieg om seker te maak dat al die moduse van die sweeftuig is gestimuleer. Die resultate wat gelewer is 'n stel kort periode beheer en stabiliteit afgeleides wat nie akkuraad is nie, maar wat weI goed genoeg is or ie bewegings van die sweeftuig te simuleer.

A dissertation submitted to the Faculty of Engineering and the Built Environment, School of Mechanical, Industrial and Aeronautical Engineering, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science in Engineering. Johannesburg, May 2016 / The present work describes the practical implementation of systems identification techniques to the development of a linear aerodynamic model for a small low-cost UAV equipped with a basic navigational and inertial measurement systems. The assessment of the applicability of the techniques were based on determining whether adequate aerodynamic models could be developed to aid in the reduction of wind tunnel testing when characterising new UAVs. The identification process consisted of postulating a model structure, flight test manoeuvre design, data reconstruction, aerodynamic parameter estimation, and model validation. The estimators that were used for the post-flight identification were the output error maximum likelihood method and an iterated extended Kalman filter with a global smoother. SIDPAC and FVSysID systems identification toolboxes were utilised and modified where appropriate. The instrumentation system on board the UAV consisted of three-axis accelerometers and gyroscopes, a three-axis vector magnetometer and GPS tracking while data was logged at 25 Hz. The angle of attack and angle of sideslip were not measured directly and were estimated using tailored data reconstruction methods. Adequate time domain lateral model correlation with flight data was achieved for the cruise flight condition. Adequacy was assessed against Theil’s inequality coefficients and Theil’s covariance. It was found that the simplified estimation algorithms based on the linearized equations of motion yielded the most promising model matches. Due to the high correlation between the pitch damping derivatives, the longitudinal analysis did not yield valid model parameter estimates. Even though the accuracy of the resulting models was below initial expectations, the detailed data compatibility analysis provided valuable insight into estimator limitations, instrumentation requirements and test procedures for systems identification on low-cost UAVs. / MT2016

Inflatable-wing Unmanned Aerial Vehicles (UAVs) have the ability to be packed in a fraction of their deployed volume. This makes them ideal for many deployable UAV designs, but inflatable wings can be flexible and don’t have conventional control surfaces. This thesis will investigate the use of wing warping as a means of autonomous control for inflatable wings. Due to complexities associated with manufacturing inflatable structures a new method of rapid prototyping deformable wings is used in place of inflatables to decrease cost and design-cycle time. A UAV testbed was developed and integrated with the warping wings and flown in a series of flight tests. The warping wing flew both under manual control and autopilot stabilization.

A new hybrid micro vehicle, called the Hopping Rotochute, was developed to robustly explore environments with rough terrain while minimizing energy consumption over extended periods of time. Unlike traditional robots, the Hopping Rotochute maneuvers through complex terrain by hopping over or through impeding obstacles. A small coaxial rotor system provides the necessary lift while a movable internal mass controls the direction of travel. In addition, the low mass center and egg-like shaped body creates a means to passively reorient the vehicle to an upright attitude when in ground contact while protecting the rotating components. The design, fabrication, and testing of a radio-controlled Hopping Rotochute prototype as well as an analytical study of the flight performance are documented. The aerodynamic, mechanical, and electrical design of the prototype is outlined which were driven by the operational requirements assigned to the vehicle. The aerodynamic characteristics of the rotor system as well as the damping characteristics of the foam base are given based on experimental results using a rotor test stand and a drop test stand respectively. Experimental flight testing results using the prototype are outlined which demonstrate that all design and operational requirements are satisfied. A dynamic model associated with the Hopping Rotochute is then developed including a soft contact model which estimates the forces and moments on the vehicle during ground contact. A comparison between the vehicle's motion measured using a motion capture system and the simulation results are presented to determine the validity of the experimentally-tuned dynamic model. Using this validated simulation model, key parameters such as system weight, rotor speed profile, internal mass weight and location, as well as battery capacity are varied to explore the flight performance characteristics. The sensitivity of the hopping rotochute to atmospheric winds is also investigated as well as the ability of the device to perform trajectory shaping.

Gravitational waves detection is a challenging scientific objective, faced by scientist in the last 100 years, when Einstein theorized their existence. Despite multiple attempts, it was only in 2016 that the first observation of a gravitational wave was officially announced. The observation, worth a Nobel Prize, was made possible thanks to a worldwide collaboration of three large ground-based detectors. When detecting gravitational waves from ground, the noisy environment limits the frequency bandwidth of the measurement. Thus, the type of cosmic events that are observable is also limited. For this reason, scientists are developing the first gravitational waves detector based in space, which is a much quieter environment, especially in the sub-Hertz bandwidth. The space-based detector is named laser interferometer space antenna (LISA) and its launch is planned for 2034. Due to the extreme complexity of the mission, involving several new technologies, a demonstrator of LISA was launched and operated between 2015 and 2017. The demonstrator mission, called LISA Pathfinder (LPF), had the objective to show the feasibility of the gravitational waves observation directly from space, by characterizing the noise affecting the relative acceleration of two free falling bodies in the milli-Hertz bandwidth. The mission was a success, proving the expected noise level is well below the minimum requirement. The free-falling bodies of LPF, called test masses (TMs), were hosted inside dedicated electrode housings (EH), located approximately 30 cm apart inside the spacecraft. When free falling, each TM stays approximately in the center of the EH, thus having milli-meter wide gaps within the housing walls. Due to the presence of such large gaps, the TMs were mechanically constrained by dedicated mechanisms (named CVM and GPRM) in order to avoid damaging the payload during the launch phase and were released into free fall once the spacecraft was in orbit. Prior to the start of the science phase, the injection procedure of the TMs into free-fall was started. Such a procedure brought each TM from being mechanically constrained to a state where it was electro-statically controlled in the center of the EH. Surprisingly, the mechanical separation of the release mechanism from the TM caused unexpected residual velocities, which were not controllable by the electrostatic control force responsible for capturing the TM once released. Therefore, both the TMs collided with either the surrounding housing walls or the release mechanism end effectors. It was possible to start the science phase by manually controlling the release mechanism adopting non-nominal injection strategies, which should not be applicable in LISA, due to the larger time lag. So, since any release mechanism malfunctioning may preclude the initialization of LISA science phase, the GPRM was extensively tested at the end of LPF, by means of a dedicated campaign of releases, involving several modifications to the nominal injection procedure. The data of the extended campaign are analyzed in this work and the main conclusion is that no optimal automated release strategy is found for the GPRM flight model as-built configuration that works reliably for both the TMs producing a nominal injection procedure. The analysis of the in-flight data is difficult since the gravitational referencesensor of LPF is not designed for such type of analysis. In particular, the low sampling frequency (i.e., 10 Hz) constitutes a limiting factor when detecting instantaneous events such as collisions of the TM. Despite the difficulties of extracting useful information on the TM residual velocity from the in-flight data, it is found that the main cause of the uncontrollable state of the released TM is the collision of the TM with the plunger, i.e., one of the end-effectors of the GPRM. It is shown that the impact is caused by the oscillation of the plunger or by the elastic relaxation of the initial preload force that holds the TM. At the end of the analysis, some improvements to the design of the release mechanism are brie y discussed, aimed at maximizing the probability of performing a successful injection procedure for the six TMs that will be used as sensing bodies in the LISA experiment.

No description available.

Approved for public release, distribution is unlimited / This thesis is concerned with the operational benefit of the Integrated Mechanical Diagnostics Health and Usage Management Systems (IMD HUMS) rotor track and balance (RTB) functionality. The questions addressed are whether there is a savings in flight hours expended on functional check flights (FCF's) when compared to present practices, if there will there be a reduction in directed maintenance man-hours (DMMH) spent on maintenance related to the rotor system, and the impact on Operational Availability. Experiments were conducted using a discrete event simulation model of squadron flight operations and organizational level maintenance. The simulation is generic and can be used in the analysis of other helicopters. Input parameters governing the distributions of maintenance action inter-arrival times were estimated from Naval Aviation Logistics Data Analysis (NALDA) databases and squadron experiences on such systems. The analysis suggests that flight hours spent in FCF are dependent upon vibration growth rate, an unknown quantity, and the maintenance policy for rotor smoothing. Directed maintenance man-hours decrease with increasing numbers of IMD HUMS configured aircraft and further gains are achieved with a maintenance policy suited to a continuous monitoring system. / Captain, United States Marine Corps

Aircraft system identification has been widely used to this day in applications like control law design, building simulators or extending flight envelopes. It can also be utilized for determining flight-mechanical characteristics in the preliminary design phase of a flight vehicle. In this thesis, three common time-domain methods were implemented in MATLAB for determining the aerodynamic derivatives of a subscale aircraft. For parameter estimation, the equation-error method is quick, robust and can provide good parameter estimates on its own. The output-error method is computationally intensive but keeps account of the aircraft's evolution in time, being more suitable for fine-tuning predictive models. A new model structure is identified using multivariate orthogonal functions with a predicted squared error stopping criteria. This method is based on linear regression (equation-error). The code written is flexible and can also be used for other aircraft and with other aerodynamic models. Simulations are compared with experimental data from a previous flight test campaign for validation. In the future, this tool may help taking decisions in conceptual design after a prototype is tested.