The aerodynamic stability of a Le Mans prototype race car under off-design pitch conditions

Abstract

The current generation of sports racing cars such as those competing under the Le Mans “LM”P and “LM”GTP regulations are particularly sensitive to the pitch of the vehicle. This is a consequence of the low ground clearances that must be adopted to maximise the benefits that can be gained from ground effect and of the very large floor plan area of these cars. To achieve optimum cornering and straight line performance the suspension characteristics are often tuned to the aerodynamic forces in order to reduce the pitch and hence the drag of the vehicle at high speeds whilst retaining relatively high downforce when cornering. A series of accidents at the 1999 Le Mans 24-hour race have highlighted the potential instability of these vehicles which resulted in the catastrophic ‘take-off’ of one of the “LM”GTP cars during the race and others during qualifying and the pre-race ‘warm-up’. The data presented here have been extracted from a detailed experimental study of a typical “LM”GTP car under design and off-design pitch conditions including extreme cases of nose-up pitching moment to assess the onset of instability i.e rotation leading to take-off. Additional data are presented to demonstrate the influence of possible regulation changes upon these parameters.