No description available.

As a consequence of metal fatigue, cracks can develop and grow in operational aircraft. Periodic inspections must be made in order to detect and repair them before they reach a dangerous length. Cracks which grow from holes are a significant problem for aircraft since the wings and fuselage can contain many thousands of fasteners, or rivets. Since it is impractical to remove them all, inspection must be made with them installed. Research into the application of eddy currents to this problem has led to the development of a scanning procedure in which a small coil is moved around the circumference of the fastener while its impedance is repeatedly measured at different positions. This set of data constitutes an image which can be analvsed using pattern recognition techniques to identify the presence of a crack. A self-contained automated instrument has been built on these principles. It incorporates a microprocessor which controls all aspects of the systems operation, including analysis and display of results. Tests show that it can detect the presence of simulated radial cracks as small as 0.2 mm long beneath the heads of fasteners. The natural extension of these ideas leads to the concept of eddy-current imaging in which a 3D picture of a defect is reconstructed from measurements of the surface magnetic field. The feasibility of implementing this, using techniques such as tomography, is discussed.

No description available.

When we consider regional differences in air safety, a call for regional solutions is needed. This research probes the current situation in Taiwan and part of Asia from a regional perspective, aiming to better understand safety management in this region. Data was drawn from an extensive survey involving both airline pilots and aviation authority officers. The research investigated respondents' perceptions in airline safety management, and examined at their opinions about the role of aviation regulatory authorities and language disadvantages when exchanging safety information. The results demonstrated that there were key differences between the Captains and the First Officers surveyed in many aspects of airline safety management. The First Officers were more eager to have a blame-free and information-shared culture in current bureaucratic systems than were the Captains. Most pilots expected airline top management and aviation regulatory authorities to take more information responsibility for circulating safety related messages and information. It is believed that a confidential incident reporting system is one of the most appropriate tools for improving safety. It would be sensitive enough to provide early identification and warning for rooting out underlying causal factors, and allow constant tracking of hazards and evaluation of risks they involve. Hence, the second part of the thesis discusses the feasibility of establishing a national-level confidential incident reporting system in Taiwan from the viewpoints of the airline pilots and the air traffic controllers. The survey showed that there was great expectation for the introduction of a national- level confidential reporting system. However, there was need to undertake a high profile promotional period within the aviation community, followed by a two-year trial period. This would help to motivate potential reporters, eliminate their fear of punitive action, and enable consensus and support to be sought from the airlines. Initially, it is advised to begin with the participant of flight crew and air traffic controllers only. At the end of the trial period, an evaluation of the system achievements was recommended. After two years of successful operation the system might be extended to include maintenance personnel, cabin crews and other relevant parties.

A review of techniques for stability and response investigations is presented and the averaging technique of Beecham- Titchener-Simpson is applied to the lateral equations of. motion for two combat aircraft. The analytic technique predicts oscillation amplitudes and frequencies accurately, for non-linear aerodynamic characteristics with respect to sideslip or roll rate. However, limitations of the method are apparent when non-linearities in roll rate and sideslip are treated simultaneously. Rates of growth to limit cycle oscillations are predicted by the averaging method and two formulations for a local damping factor are compared with simulation results. Results from extensive wind tunnel tests on a High Incidence Research Model (HIRM) are presented along with estimates of dynamic stability derivatives and polynomial fits to the wind tunnel data. The lateral stability and response of the HIRM at high angles of attack, is investigated using the analytic techniques described earlier, as well as simulations. Six degree of freedom eigenvalue results for the HIRM are shown. An investigation into the effects of cross-coupling derivatives and different forms of roll rate data, using non-linear and linearised simulations, concludes the thesis.

A study has been conducted into the design of civil aircraft seats which are forward-facing and use the lap-belt method of restraint. Within these terms of reference, the response of the seat restraint occupant system (SROS) to impact loading has been analysed using physical (dynamic testing) and analytical (computer simulation) modelling techniques. With the increasing use of fibre-reinforced polymer composites in aircraft for weight efficiency, and the consequent appearance of composite seats, attention must be given to the crash performance of these structures. Composite structures are characterised by brittle failure with low impact energy absorption, in comparison to the collapse of metal structures which may exhibit plastic deformation prior to failure. However, using the developing technology of composite sub-structures with high specific energy absorption capability, seat structures have been modified to incorporate composite load-limiting elements. The redesign process involved the compatibility of energy absorber loads with occupant dynamics to minimise injury potential, together with the alleviation of forces in the structural load path to reduce damage and preclude failure of the seat, floor track, and other components. Shortcomings of existing seat designs were assessed, and the dynamics of lap-belted occupants analysed, including secondary head impact with the forward seat structure. The computer' model created was validated against the results of dynamic tests, and then used in a parametric study of occupant dynamics. Conclusions and recommendations include guidlines relating to the future design of both metal and composite seats.

University of Macau / Faculty of Science and Technology / Department of Electromechanical Engineering

No description available.

The effect of sweep on separation bubbles as occurring in the subsonic flows past thin flat plates with rectangular leading edges has been studied experimentally. The distance between separation and reattachment, at high Reynolds number, was about 5.5 times the plate thickness in the flow region undisturbed by end effects. This distance was independent of sweepback for sweep angles up to and including 45<SUP>o</SUP>. The chordwise distribution of a static-pressure coefficient and a coefficient of the intensity of the static-pressure fluctuations, both measured on the surface of the plate and based upon the free-stream velocity component normal to the leading edge, were independent of the sweep angle up to and including 30<SUP>o</SUP> to a first approximation. The spectra of the static-pressure fluctuations, however, displayed some qualitative changes with increasing sweep angle. The distribution of a coefficient of the chordwise skin-friction component, based upon the free-stream velocity component normal to the leading edge, was independent of sweep up to and including 30<SUP>o</SUP> to a crude first approximation. The chordwise velocity profiles non-dimensionalised by the local external chordwise velocity component, were independent of sweep up to and including 45<SUP>o</SUP> in the separation bubble but downstream of reattachment small but persistent changes occurred with increasing sweep angle. Smoke-flow visualisations in the swept and the unswept flow at low Reynolds number displayed the presence of typical vortex loops in the reattachment region, many of which broke up and were partially entrained into the separation bubble.

Thesis (M.B.A.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / 2031-01-01