Thesis (Ph.D. (Physics)) -- University of Limpopo, 2021 / Titanium metal and its alloy components find extensive applications in various industries such as aerospace, medicine and automotive due to its light weight-strength ratio. More importantly, titanium-based components with better surface finishing are required in the titanium manufacturing industries. However, these components suffer from surface roughness and brittleness due to the formation of alpha-case layer. Recently, the etching process has been widely used for metal surface modification, but the etching mechanism and the choice of etchant are not well prescribed. On the other hand, the adsorption of halogen molecules on the metal surface has received much attention due to their technological applications and relevance for material surface processing, corrosion and etching. This is considered as a promising approach towards selecting an effective etchant for the metal surface etching process. In this study, the first-principle approach has been used to study the adsorption behaviour of halogen molecules and ions on Ti (100) and (110) surfaces. Their adsorption mechanism was deduced from the calculated adsorption energy, heats of formation, desorption energy, work function, charge density difference and density of states. In particular, to understand how different etchant can influence the properties of titanium metal surface during etching process. Firstly, the free halogen molecules (HF, HCl, HBr and HI), as well as the clean Ti (100) and (110) surfaces were investigated to deduce the reactivity and surface stability, respectively. It was established that the HF dissociate easily due to its lowest dissociation energy and higher electronegativity, which suggest stronger interaction with the Ti surfaces. The halogen molecules stability trend was found to follow the order of HF>HCl>HBr>HI consistent with the electronegativity strength. Furthermore, it was also found that Ti (110) is the most stable surface displaying the lowest surface energy as compared to Ti (100) surface. v Secondly, the adsorption of halogen molecules on Ti (100) and Ti (110) surfaces was studied to investigate the chemical interaction and their reactivity. The halogens were adsorbed on three possible adsorption sites (Top, Bridge and Hollow) and their reaction is spontaneous. Moreover, the bridge and top sites were found to be the most favourable sites on Ti (100) and Ti (110) surfaces, respectively. Our results showed that all halogen molecules dissociate spontaneously on both Ti surfaces. The findings revealed that the adsorption of halogen molecules on Ti surfaces is energetically favourable suggesting adsorption energy strength order of 𝐸𝑎𝑑𝑠𝐻𝐹>𝐸𝑎𝑑𝑠𝐻𝐶𝑙>𝐸𝑎𝑑𝑠𝐻𝐵𝑟>𝐸𝑎𝑑𝑠𝐻𝐼. This indicates that the adsorption of HF molecule on these surfaces is thermodynamically more stable than HCl, HBr and HI molecules. Also, our results revealed that the adsorption of halogen ions (F-, Cl-, Br- and I-) is more favourable than the adsorption of halogen molecules (HF, HCl, HBr and I) on the bridge site in both Ti surfaces considered. The F ion was found to be the most preferable than Cl, Br, and I ions. In addition, the interaction of halogen ions with Ti surfaces was deduced with regards to electron charge. We found that the amount of electron charge transferred depends on the adsorption energy strength. In particular, it was found that the F atom accepts more electrons than other halogen ions. Moreover, the spherical shape was observed, this suggests that the charge density distribution between Ti atom and halogen exhibit ionic bonding behaviour. We also found that the adsorption of halogen has a stronger effect on the work function of Ti surfaces depending on the halogen ion. The magnitude of the induced work function varies from the halogen ionic order of F>Cl>Br>I. Lastly, in order to describe the dependence of the surface coverage of an adsorbed molecule, F2 and Cl2 molecules were adsorbed on Ti (100) surface at different coverages. We observed the formation of etching products TixFy and TixCly species on the surface. The heats of formation (EHF) and desorption energy of volatile etch products were calculated. Our findings show that the formed volatile molecules (TixFy and TixCly) are energetically favourable (EHF<0), suggesting an vi exothermic process. We also found that the TixFy clusters is more stable with lower heats of formation than the TixCly species. Moreover, the desorption energy of the formed volatile (TiF4) species was found to be lower than TiCl4 indicating that that TiF4 species desorb easily. This demonstrates that F2 is more suitable for surface etching as compared to Cl2. / Council for Scientific and Industrial Research (CSIR) and the Department of Science and Innovation (DSI)

Pilots and other aircrew members are often required to perform tasks involving a substantial amount of mediational or cognitive activity. Generally speaking, workload estimation techniques have not been tested to determine their relative sensitivity and intrusion to mediational piloting tasks. An experiment comparing the sensitivity and intrusion of eight workload estimation techniques was conducted using a mediational loading task in a three-degrees-of-freedom moving-base aircraft simulator. The primary task mediational loading required the pilots to solve a variety of navigational problems while maintaining straight-and-level flight. The presented problems were sorted prior to the experiment into low, medium, and high difficulty problems. The eight techniques included opinion measures (modified Cooper-Harper rating scale and multi-descriptor rating scale), spare mental capacity measures (time estimation and tapping regularity), primary task measures (mediational reaction time and control movements per unit time), and physiological measures (pulse rate variability and pupil dilation). A sensitive technique was defined as a technique which indicated statistical differences of scores across the three mediational load levels. An intrusive technique was defined as a technique which significantly changed the primary task measures compared to the primary task measures obtained in a control condition. One opinion measure (modified Cooper-Harper measure (time (mediational rating scale), one estimation), and one spare mental capacity primary task measure reaction time) demonstrated sensitivity. Mediational reaction time demonstrated sensitivity to all levels of load. The other two showed partial sensitivity to load. One spare mental capacity measure (time estimation) demonstrated intrusion on two primary task measures (mediational reaction time and percent error response). / Ph. D.

Altitude excursions particular to high speed aircraft are investigated in this thesis. An aerodynamic database of the XB-70 is created and a longitudinal linear model is constructed for a high speed cruise flight condition. An examination of the unpiloted aircraft dynamics revealed that the excursions were not due to a poorly handling aircraft. Thus, it is theorized that the excursions are due to pilot vehicle interactions. A classical control method developed a loop closure scheme suitable for acceptable control of the aircraft. The results showed that a pilot should close an inner loop with negative attitude feedback and an outer loop with positive flight path feedback. A modern control method analysis using an optimal control pilot model confirmed the preceding conclusions. Based on these results, the cockpit pitch attitude display resolution should be less than 1° so that the pilot will be able to perform the loop closures necessary for constant altitude flight. / Master of Science

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. 1978. E.A.A.--Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERONAUTICS. / Bibliography: leaves 130-133. / by C.W. Acree, Jr. / E.A.A.

Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. / Includes bibliographical references. / by Arye R. Ephrath. / Ph.D.

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In South Africa, the issue of lack of black pilot skills is a most talked about topic in commercial airlines. Airlines need to find the right set of skills and attitude to operate safely and successfully. Airline safety remains a topic of discussion, therefore airlines need ensure robustness of their selection processes. There are many requirements that a person has to meet before s/he can be offered a first officer job at an airline. The majority of the pilots in South Africa are white males. The study aimed to determine if there are statistically significant differences in cognitive ability test results between Black and White applicants for pilot positions with a South Africa airline. The test battery included a verbal reasoning test, numerical reasoning test, visual thinking, abstract reasoning test, spatial reasoning test, short term memory test, monitoring ability test, hand-eye coordination, sense of orientation test, reactivity test, and a multi-tasking test. The data were extracted with permission from a database maintained on behalf of the airline by an online test provider and subjected to a statistical analysis using measures of central tendency, and spread, in order to report on the significance of the differences between the groups. There is strong evidence that the White group performed better than the Black group on the majority of the tests. It is recommended that further research is done in order to determine the causes of these differences. A comparative study of results on other airlines’ recruitment selection tests and an exploratory study of the impact of socio-economic factors, education quality and language on cognitive ability tests are recommended.

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Since human errors are one of the major causes of flight accidents, the design and operation of the modern aircraft system deals with them seriously. Particularly, the pilot workload on aviation causes human errors. Whenever new procedures are introduced and operated, the aircraft capabilities have been checked in every aspect. However, there has been little study on the impact of the new procedures such as LDLP, SCDA, SATS, and Steep Angle approach on the pilot performance, workload, and stress. In this study, different methods have been tried to understand the relationship between new procedures and the pilots in terms of performance, workload, and stress. The flight factors (e.g. flight experience, gliding angle, and approach area) were examined by the pilot performance, workload, and stress at the "Final Approach to L/D" phase using the single engine Cessna 172R type flight simulator. Five students and five instructor pilots from Embry-Riddle Aeronautical University in Dayton Beach, Florida, participated and they flew under four different simulation tasks of gliding angle and approach area. Their Heart Rate Variability (HRV) and NASA-Task Load Index (TLX) were measured to determine their stress level and subjective workload, respectively. In addition, Landing Performance (LP) data (e.g. landing distance, landing speed) and Above Glide Path Tracking Performance (AGPTP) data were also collected to evaluate pilot performance. As a result, the type of approach area showed a significant effect on pilot performance, workload, and stress determined by ANOVA (HRV, TLX, LP, AGPTP: all are p < .05). Flying over "Populated" area (e.g. a large city) resulted in lower pilot performance and higher pilot workload and stress than that over "Non-Populated" area (e.g. a grass field). Similarly, the levels of a gliding angle showed the statistical difference on the performance, workload, and stress (HRV, TLX, and LP: all are p < .05). During the flight with 4.5 degree, the pilots showed lower performance with higher workload and stress. However, the levels of the flight experience did not have any influence on the performance, workload, and stress levels (AGPTP, LP, TLX, HRV: all are p > .05). In conclusion, flying in Populated area and flying with a 4.5 degree gliding angle increases the workload and stress level of the pilots. In addition, when the pilots were flying over Populated area at Final Approach to L/D phase, they showed lower performance on tracking the glide path. Based on the results, stresses and workload can have a significant impact on flight performance. Therefore, in order to reduce the workload and stress that can cause human errors, it is highly recommended to carefully examine the impact of new flight procedures on pilot workload and stress before they are implemented.