A critical assessment of the usefulness of small scale wind tunnel data in optimizing the design of heavy duty cab-over-engine tractor/trailer combinations is presented. The correct selection of cab leading edge radii has long been recognized as a dramatic means of reducing aerodynamic drag and hence fuel consumption. However, the validity of extrapolating small scale wind tunnel designs into full size vehicles has been a source of continuing controversy. Results of literature search and original wind tunnel studies lead to the conclusion that carefully conducted one-tenth scale wind tunnel investigations can be used to select accurate and somewhat conservative full-scale designs.
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