Conservation of Energy Method for On-Road Aerodynamic Drag Investigation

A significant reduction of the aerodynamic drag can be achieved by the refinement of the vehicle underside. But the investigation of the aerodynamic effectiveness of underfloor panels in wind tunnels turns out to be a challenging task. For this reason on-road methods like coastdown analysis are frequently employed. Most of these advanced coastdown methods determine the coefficients of the total drag by fitting a mathematical model to the measured velocity data. This requires separate time consuming tests in the laboratory to measure the wheel and transmission losses.

The objective of the presented work was the development of an analysis method, which enables a simpler and more practicable on-road determination of aerodynamic improvements. In this method the rolling resistance can be factored out by employing the conservation of energy as basic approach for the investigation of air drag differences. The only required instrumentation is a dynamic air speed indicator and an intelligent memory device to enable a velocity-time and airspeed-time history. No separate test in the laboratory or time consuming preconditioning of the vehicle is necessary.