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A 1:10-scale wind tunnel development program was undertaken by the National Research Council of Canada and Airshield Inc. in 1994 to develop trailer side skirts that would reduce the aerodynamic drag of single and tandem trailers. Additionally, a second wind tunnel program was performed by the NRC to evaluate the fuel-saving performance of boat-tail panels when used in conjunction with the skirt-equipped single and tandem trailers. Side skirts on tandem, 8.2-m-long trailers (all model dimensions converted to full scale) were found to reduce the wind-averaged drag coefficient at 105 km/h (65 mi/h) by 0.0758. The front pair of skirts alone produced 75% of the total drag reduction from both sets of skirts and the rear pair alone produced 40% of that from both pairs. The sum of the drag reductions from front and rear skirts separately was 115% of that when both sets were fitted, suggesting an interaction between both.

During the late 1970's and early 1980's considerable effort was expended in the improvement of truck aerodynamics to reduce fuel consumption. This first-generation effort focused on aerodynamic drag reduction obtained from add-on aerodynamic aids to the cab or the trailer, from improved cab shaping and from body/trailer front-end edge rounding. Rising fuel prices have renewed interest in further aerodynamic improvements. This paper will review past developments and show that several unused concepts offer potential as second-generation, add-on, fuel-saving technology. It will raise the issue of finding successful means for bringing them profitably into service, which will require concerted action by the trucking industry, manufacturers and government.

The National Research Council of Canada (NRC) is commencing a new round of aerodynamic development of heavy trucks in partnership with Natural Resources Canada (NRCan), the Canadian Trucking Alliance (CTA) and the US Department of Energy (DOE). The program is meant to take second-generation, add-on technology from the wind tunnel to the fleet. The purpose is to reduce fuel consumption and greenhouse gas emissions. The benefit is that the fuel reductions pay the operators to improve their vehicle emissions. 1:10-scale model tests in the NRC 2m × 3m wind tunnel, followed by full-scale tests on a Navistar 9200 Day Cab with 40-foot trailer in the NRC 9m × 9m wind tunnel, were employed to develop the add-on devices of interest. The results demonstrated significant fuel savings from a combination of longer cab extenders, trailer skirts and trailer boat-tails that reduced fuel consumption as much as the contemporary aerodynamic cab packages.

Wind tunnel measurements on a rectangular vehicle-like shape and on two detailed, scale-model trucks have been employed to define the front and rear edge geometries that minimize aerodynamic drag. Optimum configurations are identified with sufficient detail for commercial vehicle design purposes. Comparisons of the model-scale measurements with limited measurements on a full-scale straight truck in a large wind tunnel support the interpretation of these test results.