No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

Controlling the position and attitude of a helicopter hovering in the presence of atmospheric turbulence is a difficult task which demands considerable pilot work-load which becomes even more difficult'when a load is suspended from the helicopter, because the oscillations of the load aggravate the situation. Tasks that require a suspended load to be kept fixed relative to a point in space, while the helicopter remains at hover, are extremely difficult to achieve. Several load-positioning systems exist but provide inadequate solutions to the problem. A brief account of such systems and their limitations is given before describing the automatic hovering control system proposed in this thesis. It causes appropriate motion of the helicopter to achieve the desired stationarity of the load. The techniques of modern control theory were employed to design this optimal controller. Digital simulation was used for testing the response of the resulting optimal system. The mathematical model of two connected rigid bodies moving in space (representing the helicopter and suspended load) is described in detail. Several combinations of cable length-load weight were chosen and in each case the response of the closed-loop system was investigated. It was found that considerable reduction of the oscillations of the load can be achieved when suitable cable arrangements are used. The use of winch control of lateral displacement of the load also improves the lateral response of the entire system. An augmented mathematical model was used which included both the dynamics of the control actuators and the models representing atmospheric turbulence and sensor noise. Since many of the state variables of the system cannot be physically measured, it is obvious that only limited information on the state of the system would be available for processing by such a controller. Therefore two solutions to the problem were considered: (i) the use of a state estimator to provide to the controller the lost feedback information; , and (ii) the use of an output regulator which takes into account the fact that limited feedback information is available. The responses of the closed-loop systems using each of these solutions were investigated and compared. The numerical problems encountered in this design are analysed and some means .of overcoming them are suggested. Finally, the best combination of cable arrangement and controller is described with reference to several important factors such as system simplicity and performance.

A methodology has been developed for predicting aircraft safety and reliability incorporating both C.C.F.s(Common-Cause Failures), and phased missions. Failure behaviour of an aircraft, or its systems due to both independent failures and C.C.F.s are modelled by the Markov process, and simulated using Monte Carlo method with the robust variance reduction techniques. Prediction of safety and reliability is made through discrete-event simulation of aircraft operations. Validation was made by comparing the predicted safety and reliability results of B767 ETOPS aircraft propulsion system, using the developed methodology, to those obtained from the analysis of real operation data. The credibility and the accuracy of the developed methodology are shown through the comparison of results. A case study was conducted for investigating the safety and reliability of the propulsion system of two-, three- and four-engined aircraft using the developed methodology. The case study produced valuable results concerning the safety of ETOPS flight, which were not previously known. These results were able to be used for further trade studies of aircraft design to decide the number of engines, and also for establishing new regulations for ETOPS flights.

Airlines are not able to conduct their businesses in the same way as other global transnational industries. They are inhibited by the foreign ownership restrictions in Air Services Agreements and national laws. Since the United Kingdom and the United States signed the first Bermuda agreement in 1946, the nationality clauses contained in virtually all bilaterals have limited the companies designated to provide services to those airlines owned and managed by nationals of the respective countries. A key reason why foreign ownership rules remain in place is that they protect national airlines. In doing so, they also limit the strategies available to governments whose carriers are in difficulties. The 57 years old bilateral system restricts the development of international air services, adversely affecting airlines and their users- travellers and the tourism and air freight industries. As time goes on, the rapidly changing air transport environment of privatisation, liberalisation and globalisation is forcing airlines to seek structural adjustments in order to survive in the new millennium. Airlines are asking to have more freedom for their strategies, in order to enhance their profitability. Pressures have been growing to ease the ownership rules contained in bilateral agreements to allow airlines greater commercial freedom. As there is no comprehensive research on the topic, this study aims to provide a detailed analysis of the impact of airline ownership rules. It will provide a point of reference for organisations like ICAO and nations to review the ownership issue in the future. This research starts with a review of the historical background, the current limitations in different countries and the pros and cons of ownership rules. It analyses how aviation markets have been influenced to date around the world and how governments and carriers have responded to these influences. It goes on to identify the main benefits and risks of foreign investment, and the motives for foreign investment in the EU and Asia- Pacific. It assesses the prospects for change in ownership rules under multilateral and plurilateral proposals, and develops a strategy for changing the current ownership rules. It concludes by predicting how airlines will react to such changes and makes suggestions for European Airlines in the Asia-Pacific region.

Nitrile rubbers (copolymers of butadiene and acrylonitrile) are widely used throughout the aerospace, automobile, construction and footwear industries. The useful properties of nitrile rubbers include excellent resistance to the action of oils, petroleum fuels and solvents, combined with good heat and abrasion resistance. These properties derive from the polar nature of the cyanide group on the polymer chain and rubbers with high oil resistance contain 40 - 50 mole % acrylonitrile. Unfortunately, at low temperatures the elastomeric properties of such rubbers are poor. One of the objectives of this work was to investigate whether the working temperature range of nitrile rubbers could be extended by chemicalmodification, in particular by grafting poly (tetrahydrofuran) (PTHF) onto the nitrile rubber. PTHF is a low melting, crystalline polymer with a glass transition temperature, Tg, of -84°C, above which it is rubbery. The polymerisation of THF can be initiated by the generation of suitable carbonium ions which attack the ethereal oxygen of the THF molecule forming an oxonium ion. Propagation occurs via this oxonium ion intermediate by a cationic, ring-opening mechanism. This 'living' polymerisation can be terminated by many nucleophilic reagents such as water, methanol, etc. In view of the polymerisation characteristics of THF, it can be grafted to a nitrile rubber backbone by two distinct methods. The first is a 'grafting from' technique, which involves initiation of the THF polymerisation from carbonium ion sites generated on the polymer backbone. In these experiments, described in Chapter 2, the parent rubbers were first functionalised by dihalocarbenation, bromination and allyl bromination, and on reaction with a suitable silver salt cationic centres were generated on the backbone. This method proved to be unsuitable for preparing well-defined graft copolymers of PTHF. The second process, a 'grafting onto' technique, involved a 'coupling' reaction between 'living' PTHF and functional groups previously attached to the nitrile rubber backbone. This method, which was finally chosen to prepare a range of graft copolymers of PTHF, is described in Chapters 3 and 4. One to 3 mole % of the diene residues in the nitrile rubber were first epoxidised then treated with HC1 to open the epoxide rings to yield chlorohydrin groups. The hydroxyl substituents functioned as terminators in a 'coupling' reaction with the 'living' PTHF to form a graft copolymer. Since polymerisation of THF at room temperature is fairly slow the lengths of the grafted chains could be controlled by monitoring the time from initiation to termination. The graft copolymers and precursors were examined by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and for solvent resistance. The DSC results show that grafting with PTHF reduces the Tg of low nitrile rubbers but has little effect on the Tg of high nitrile rubbers. This is believed to be due to a greater degree of phase separation of the PTHF component in the high nitrile rubbers. Consequently, the physical properties of these PTHF-high nitrile rubber grafts are not those of a homogeneous amorphous blend of the two components, TGA of the PTHF graft copolymers suggest that the PTHF graft destabilises the nitrile rubber to heat. However, PTHF is well known to be susceptible to hydroperoxidation and it is likely that thisc effect is attributable to peroxides rather than the PTHF chains per se. An antioxidant should be capable of inhibiting hydroperoxidation. Finally, the solvent resistance of the PTHF graft copolymers, especially from high nitrile rubbers, is lower than that of the original nitrile rubber.