Measures of Deformation: Ballooning
When a convertible car is moving on the road its soft-top changes shape due to the aerodynamic pressures acting on the soft-top itself. This has some negative effect on car aesthetics as well as on the acoustic level inside the car, due to the increase in noise leakage through the sealing caused by the soft-top deformation.
Soft-top 'ballooning' can be measured in the wind tunnel by a 'laser-based' measuring device. In this way the soft-top frame can be optimized and fabric can be chosen so as to minimize 'ballooning'.
An example of these 'ballooning' maps is shown in the following figures.