The purpose of this thesis is to present a study on motorcycle aerodynamics with particular regard to the performance characteristics of faired and unfaired types in use today for road racing and speed record attempts. To achieve this, a wind tunnel procedure for the testing of scale models was developed with emphasis on the problems involved in obtaining valid data from large model-to-tunnel area blockage ratios, (approximately 15'%). Following a review of the results, which included six aerodynamic force and moment coefficients and their variation with Reynolds number and yaw angle, a programme of drag reduction was pursued which approached the problem from two directions: firstly, by using simple bolt-on devices for conventional fairings, designed so as to obviate the need for major machine modifications and secondly, by a complete redesign of the motorcycle.� The latter involved the use of more efficient aerodynamic shapes and also achieved a reduction in frontal area without compromising rider comfort. The final result was a machine which would provide greatly enhanced racing performance through a drag reduction of approximately 40% and also lend itself to the incorporation of radical primary and secondary safety features, beneficial both an the track and public roads. Preliminary studies into a computational flow simulation as a first stage to the full prediction of fairing pressure distribution are also included. The techniques explored attempted to retain a reasonable accuracy of result without recourse to excessive computer power or complicated calculations. This was achieved successfully with the simple models considered, despite the highly separated nature of the simulated flow.

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Drag measurements for excrescence arrays of square section mounted on a smooth wall and subjected to two adverse pressure gradients in equilibrium are obtained. Differences in drag which arise when the excrescences are uniformly distributed and when tending to isolation are shown. Flow visualization photographs using the surface oil flow technique are presented to illustrate different flow patterns around arrays of varying spacing. A prediction model for the drag of excrescence arrays based on the results obtained was devised. Its range of application could be extended to excrescences of varying shape providing they are sufficiently small to be immersed in the logarithmic part of the boundary layer. Drag results are determined by both a momentum defect and a pressure distribution technique. These results are compared and the difference between them is partially attributed to the change in surface friction between the excrescences and partially to some lack of two-dimensionality in the test procedure. Corrections for the latter effect are made to the data obtained.

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