CAATS – Automotive Wind Tunnel Statistical Process Control

This paper presents the application of statistical process control (SPC) methods to Windshear, a 180-mph motorsports and automotive wind tunnel equipped with a wide-belt rolling road system. The SPC approach captures the complete variability of the facility and offers useful process performance metrics that are based on a sound statistical framework. Traditional control charts are explored, emphasizing the uniqueness of variability experienced in wind tunnels which includes significant, unexplained short-term and long-term variation compared to typical manufacturing processes. This unique variation is elegantly captured by the three-way control chart, which is applied to estimate the complete process reproducibility with different levels of repeatability of vehicle drag coefficient. The sensitivity of three-way control charts is explored including the evaluation of an alternate group assignment within the same dataset. A practical example is provided evaluating secondary boundary layer fan performance after a failure event to demonstrate the effectiveness of three-way control charts in establishing and maintaining a rigorous automotive wind tunnel maintenance program. SPC charts and their resultant analysis are a function of the test matrix that generates them. The development of a rigorous SPC test matrix is discussed including an example provided by Windshear. This paper is part of a global effort to Commonize Automotive Aerodynamic Testing Standards (CAATS) launched by the Subsonic Aerodynamic Testing Association (SATA).