Turbofan commuter aircraft project design studies
Designing successful commercial aircraft is a difficult business; the stakes are high and the risks numerous. Researchers in the past have developed methods that assist the designers in reducing these risks. In recent years such methods have benefited from improvements in computer technology. The work described in this thesis extends these methods to the design of commuter aircraft. These aircraft are more sensitive to operational requirements than other types due in part to their high zero-fuel mass ratio. It is essential that, for such aircraft, the best information possible is available to the designers. The identification of the optimum aircraft configuration and mission characteristics constitutes a vital part of this knowledge. A review of literature, involving both modem computer-based and traditional search methods, has shown continuing interest in aircraft project design methods from the earliest times to the latest conference. The work presented in this thesis is seen to compliment this interest in computer methods and to apply these techniques to the relatively neglected area of commuter aircraft design. A survey of commuter operation and aircraft types revealed the often conflicting requirements and regulations which govern the design process in this area. Detailed statistical analysis on a collection of commuter aircraft showed no consistent data patterns, but did indicate the bouyant state of the market. Earlier research work on the design of twin-engined turbo-prop aircraft had provided some experience in the design of short-haul aircraft. The new work improves these methods and applies them to larger and faster turbo-fan commuter aircraft. Since the turbo-prop work, the optimiser developed at RAE (Farnborough) has been rewritten to work more efficiently and allow larger problems to be tackled. This new optimiser s linked to a new synthesis routine which simulates turbo-fan aircraft design. The synthesis program was calibrated against industrial design calculations and shown to give acceptably accuracte predictions. The resulting design program is fully described and computer listings are presented. To illustrate the use of the optimisation methods in the devleopment of a new aircraft, a series of industrially related design studies is presented. These studies range from the selection of the initial baseline configuration, through various parameters sensitivity investigations, to the evaluation of aircraft and engine stretch options. To demonstrate more general types of design study, a series of optimisations in which the engine size is variable was conducted. This provides the designer with a knowledge of the absolute (optimum) design surface and allows him to judge the 'penalties' inherent in his chosen configuration.