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Comparison studies have been conducted on a 1:16th scale model and a full scale tractor trailer of a variety of sealed aft cavity devices as a means to develop or enhance commercial drag reduction technology for class 8 vehicles. Various base cavity geometries with pressure taps were created for the scale model. The studies confirmed that length has an important effect on performance. The interaction of the boat-tailed aft cavity with other drag reduction devices, specifically side skirts, was investigated with results showing no discernable drag performance interaction between them. Overall, the experiments show that a boat-tailed aft cavity can reduce the drag up to 13%. Full-scale tests of a commercially derived product based on these scale tests were also completed using SAE Type II testing procedures. Full-scale tests indicated a fuel savings of over 6.5%.

A series of over-the-road tests have been conducted to evaluate and optimize sealed aft cavity geometries for drag reduction on tractor trailers. Several test trucks and methods were used to conduct road tests at various sites in northern New York. The results obtained on back to back repeat runs indicated a potential savings of 0.6 mpg for an optimized four-sided configuration. The sealed aft cavity geometry that provided the best performance was found to have a 15 degree inset on the side and top panels and a 7 degree inset on the bottom panel. Recommendations for conducting similar tests and how to avoid problems are also presented.