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Twin engined propeller driven commuter aircraft pose particular challenges in their design as well as in their operation. This thesis examines both aspects through computer techniques geared specifically towards such aircraft. A program (GATEP, General Aviation Twin Engine Propeller driven) is developed to assist in the preliminary design phase. It is utilised to compare the characteristics of individual designs, conduct parametric studies around a baseline design, and estimate potential improvements. The mass, aerodynamics, and vital performance items are calculated, with particular attention focused on characteristics critical to this type of aircraft, such as the Balanced Field Length and Second Segment Climb Gradient. Studies are presented showing the applicability of GATEP to a typical commuter design. The operational optimisation of propeller driven commuters is addressed through SCOPE (Short haul Commuter Optimum Profile Evaluation), a program designed to determine optimum flight profiles for the short stage routes along which these aircraft operate. Multivariate Optimisation (M.V.O.) techniques are used to analyse the entire flight. The climb and descent segments are shown to be particularly important, and the methods used are applicable to common flying techniques (without requiring an autopilot). Flight profile optimisation has been previously treated as a mathematical exercise in relation to large jet aircraft. SCOPE uniquely offers a method for studying propeller driven types, and places emphasis on realistic operating techniques including Air Traffic Control constraints.

As long as there is a certain degree of flexibility i.e. relative motion, the contacting surface of a mechanical component will experience fretting damage, in the form of fretting wear and/or fretting fatigue, depending on the loading conditions and performance requirements. In the present investigations, the fretting wear behaviour of aeroengine materials were studied by both experimental (mainly gross slip regime) and finite element approaches involving the various aspects of fretting variables (applied normal load, strokes, wear duration, material hardness, lubrication and etc. ) that affects the material tribosystem. The aeroengine materials are the Super S/CMV and AerMet®l00 ultrahigh strength steel alloys and Inconel 718 nickel-base superalloys. The present works highlights a number of issues important to fretting damage, which involves studying: (1) the effect of nitriding and lubrication on Super S/CMV steel experimentally and wear data validation and prediction by FEM based on a modified Archard's equation; (2) the effect of moderate temperature on the fretting behaviour of Inconel 718 alloy; (3) the different material combinations (Super S/CMV, AerMet®100, and Inconel 718) on fretting wear. The following experimental tools are utilised to investigate the morphological changes of the contacting surfaces during fretting. A simple crossed round-on-flat arrangement was used to determine the coefficients of friction and the wear coefficients applicable to the contact configuration and loading conditions. Surface topography changes were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The presence of various phases and elements were analysed by x-ray diffraction (XRD) and energy dispersive x-ray (EDX). The wear depth and wear width were profiled using a surface profilometer for the wear coefficient calculation. The use of FE simulation was to validate and predict the wear data. The evolution of contact geometry and contact variables, including contact pressure and relative slip were studied. The implications of these predicted results are discussed with respect to fretting fatigue prediction, leading to new insight into the experimentally-observed effects of slip regime on crack initiation.

This research was motivated by the move of aero-engine manufacturers to provide services as well as products. With leasing arrangements such as TotalCare©, the aero-engine manufacturers are responsible for the operation, management and maintenance of their products while airlines pay a contracted rate for their use. As a result, aero-engine manufacturers need to minimise the cost their products incur over their lifecycle to increase profits. It is widely accepted that the greatest scope to reduce costs is in the design stage. Hence, the aim of this thesis is to create tools and methodologies for designers which will allow them to monitor the impact of design decisions on whole life cost. Two different approaches to designing for whole life cost were presented. The Life Cycle Cost (LCC) approach and the comparatively novel Value Driven Design (VDD) approach. It was observed from research literature that models for both LCC and VDD need to be tailored to specific objectives in order to keep the scope of the model manageable. This makes generic LCC or VDD models unfeasible and consequently the reuse of these models is limited. With this in mind, a methodology was developed for creating integrated analyses models which were customisable, modular and transparent so as to facilitate future modification and reuse. It used a commercial software integration package called Isight, and modular analyses modules. Model Based Systems Engineering (MBSE) was also used in the development of the integrated model architecture. Case studies were performed for both LCC and VDD approaches to allow comparison of their respective merits and flaws. Finally several avenues of future work in VDD and MBSE were discussed.

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This thesis explores the prediction of rearwards fan noise propagation within the bypass duct and its radiation into the far feld. Two recently developed models: B-induct and GXMunt, are exploited in application to real engine bypass ducts and their performance is evaluated. These methods are an improvement on current industry standards, allowing realistic duct geometry and flow conditions to be modelled with reasonable computation and time demands. The main focus is on the model b-induct. B-induct predictions for bypass attenuation are integrated into an industry standard whole engine model, and predictions of far-feld noise are obtained for a modern high bypass-ratio engine. These predictions compare more favourably with measured data from full-scale static engine tests than similar predictions made using a standard uni-form rectangular duct model for the bypass attenuations, indicating that b-induct is an improvement over the current model. Initial studies on the effect of duct geometry on noise propagation suggest a noise benefit for a duct with higher curvature when compared to a typical Baseline design. This suggestion is confirmed using measured data from zero-flow rig tests. Predictions for three-dimensional duct geometries are also performed to show the effect of scattering due to bifurcations within the duct. B-induct allows for the specific bypass geometry and liner positions to be taken into account when performing impedance optimisations. A new optimisation procedure is proposed in which b-induct predictions are used within an existing whole aircraft noise prediction model. This procedure is used to select liner impedances for a modern engine bypass duct. B-induct is demonstrated to be a promising new tool within the engine design process, for both analysis of the impact of rear fan noise on whole engine noise, and assessment of potential low noise bypass configurations.