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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 from 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 testsænamely, both vans experience substantial drag savings at spacings of a fraction of a car length.

The purpose of this report is to experimentally determine the air flow through the cooling module (air-conditioning condenser plus engine radiator) of a Ford Windstar minivan when the van is operated at a fraction of a vehicle length behind a lead van. Pressures and temperatures are measured across the cooling module while the vans are in operation, and a standard calibration relates the pressure drop to the flow velocity through the cooling module. The Windstars are connected in tandem and driven on a test track at spacings of 0.22, 0.28, 0.38, 0.62, 0.88, and 1.0, expressed as fractions of the Wind-star length. For the purposes of the test, an override switch is installed to allow the close-following van to be operated either with both cooling fans remaining on or with both fans disabled. Air flow is expressed either as a volume flow, in cubic meters per second, or as the fraction of the flow for a van operating in isolation at the same forward speed.

The results reported are from tests on July 6-8, 1999, on a limited-access 12km section of I -15 in San Diego. The tests involved 2, 3 and 4-car platoons operated and maintained by PATH personnel under the auspices of CALTRANS and utilized Buick LeSabre sedans under fully automatic longitudinal and lateral control. Multiple sensor data was acquired, including the fuel injector pulse width. We demonstrate that the fuel injector pulse width, in combination with engine RPM and forward speed, can be used to determine accurate estimates of instantaneous fuel consumption. The repeatability for total fuel consumed over a 2.4 km portion of the test path is ±1% based upon multiple single car runs over the three day period, with the major portion of the uncertainty arising from changing wind conditions. Fuel savings for individual vehicles vary from 0-10% depending upon number of vehicles, vehicle spacing, and vehicle position within the platoon.

Drag measurements are made on each of the members of 2, 3 & 4-vehicle platoons. One-eighth scale vehicle models are used in a wind tunnel equipped with a suction surface ground plane for boundary layer control. Strong interaction between vehicles takes place for spacings less than one vehicle length, leading to drag values substantially lower than for an isolated vehicle. All vehicles in the platoon experience lower drag. The average drag coefficient for a 4-vehicle platoon at a nominal spacing of 0.2 vehicle lengths is just 56 percent of the drag of the vehicle in isolation. It is also concluded that little additional benefit is achieved by forming platoons longer than 6-7 vehicles. Finally, the 2-vehicle platoons are operated in different orientations-front-to-front, back-to-back and reversed-to provide an estimate for drag reduction sensitivity to vehicle shape.

Axial force, side force and yawing moment are measured on each member of a three-vehicle platoon subject to crosswind conditions. The longitudinal spacing between vehicles is varied from 0 to 0.72 vehicle lengths in a large set of combinations covering both symmetric and non-symmetric configurations. Crosswind is simulated by yawing the platoon ten degrees with respect to the axis of the wind tunnel. Axial forces are significantly smaller for close-following. At a spacing of 0.1 vehicle lengths, the average axial force coefficient at yaw is diminished to about 61% of the value for a single vehicle at yaw. The air stream is redirected by the presence of the platoon so as to diminish side forces and yawing moments on trailing vehicles.