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Drag Forces Experienced by Two, Full-Scale Vehicles at Close Spacing

Patrick Hong, Bogdan Marcu, Fred Browand,
Aaron Tucker, University of Southern California

EXECUTIVE SUMMARY:The present study aims to document the drag reduction for a two-vehicle platoon by operating two full-scale Ford Windstar vans in tandem on a desert lakebed. Drag forces are measured with the aid of a special tow bar force measuring system designed and manufactured at USC. The testing procedure consists of a smooth acceleration, followed by a smooth deceleration of the platoon. Data collected during acceleration allows the calculation of the drag force on the trail-vehicle, while data collected during deceleration is used to calculate the drag on the lead vehicle. Results of the full-scale tests show that the drag behaviors for the two vans are in general agreement with the earlier conclusions drawn from the wind tunnel tests--namely, both vans experience substantial drag savings at spacings of a fraction of a car length.

INTRODUCTION: One of the new, state-of-the-art technologies to be employed within the Automated Highway System concept is the organization of freeway traffic into platoons of close-following vehicles. Close-following is achieved by utilizing computer control to automatically maintain a close spacing between the members of the platoon. As presently conceived, each vehicle is equipped with automatic throttle, brake and steering, as well as a means for determining accurate headway position and for communicating with other vehicles within the platoon. Earlier wind tunnel studies at USC have predicted that substantial drag savings can be achieved through close-following. For example, members of a 7-8 vehicle platoon are predicted to have an average drag approximately 1/2 the drag value experienced by each vehicle in isolation. Furthermore, all vehicles in the platoon participate in the drag savings. Lower values of drag translate directly to improvements in fuel economy and to a reduction in emissions.

Full Report: UCB-ITS-PRR-98-5 (306K PDF File)

Related Research:

UCB-ITS-PRR-95-35 (4.2MB PDF File)
"The Aerodynamic Performance of Platoons: Final Report", Michael Zabat, Nick Stabile, Stefano Frascaroli, Frederick Browand.

UCB-ITS-PRR-98-04 (6.3MB PDF File)
"The Aerodynamic Forces on Misaligned Platoons", Bogdan Marcu, Fred Browand.

UCB-ITS-PRR-98-06 (244K PDF File)
"The Influence of Close-Following Upon Cooling Module Air Flow","Fred Browand, Bogdan Marcu, Christian Sharpe.

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