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Aerodynamic testing of heavy commercial vehicles is of increasing interest as demands for dramatically improved fuel economy take hold. Various challenges which compromise the fidelity of wind tunnel simulations must be overcome in order for the full potential of sophisticated aerodynamic treatments to be realized; three are addressed herein. First, a limited number of wind tunnels are available for testing of this class of vehicle at large scales. The authors suggest that facilities developed for large or full-scale testing of race cars may be an important resource. Second, ground simulation in wind tunnels has led to the development of Moving Ground Plane (MGP, aka Rolling Road (RR)) systems of various types. Questions arise as to the behavior of MGP/RR systems with vehicles at large yaw angles. It can actually be deduced that complete simulation of crosswind conditions on an open road in a wind tunnel may be impractical.

The issue of ground simulation in wind tunnels has led to the development of Moving Ground Plane (MGP, aka rolling road) systems of various types. Motorsports aerodynamics has perhaps been the primary application to date, where the range of vehicle yaw angles tends to be quite limited. In fact, since yaw angles are typically developed as result of vehicle slip in cornering, or asymmetric set-up in the case of stock cars, they are limited to a few degrees. Further, since in both cases the vehicle centerline typically rotates with respect to the relative velocity vector (i.e. simulating vehicle slip in cornering), it seems clear that yawing the vehicle in the wind tunnel above a fixed (non-rotated) MGP is a valid simulation option. In the case of vehicles operating in strong crosswind conditions, for example commercial vehicles (heavy trucks) on interstate highways, the situation is more complex.

This paper reviews the development of a new test capability for race cars at the Langley Full-Scale Tunnel. The existing external force balance of the Langley Full-Scale Tunnel, designed for use with full-scale aircraft, was reconfigured for automobile testing. Details of structural modifications relevant to supporting cars and force measurements are shown. A specialized automobile force balance, measuring vehicle drag and individual wheel downforce, was then designed, constructed and calibrated. The design was governed by simplicity and low cost and was tailored to the stock car racing community. The balance became fully operational in early 1998. The overall layout of the automobile balance and comparisons to reference data from another full-scale wind tunnel is presented.