An Angle of Attack Correction Scheme for the Design of Low Aspect Ratio Wings With Endplates

Low aspect ratio wings are used extensively on open-wheeled race cars to generate aerodynamic downforce. Consequently, a great deal of effort is invested in obtaining wing profiles that provide high values of lift coefficient. If the wings are designed using 2-D methods, then it is necessary to take into account the change in operating angle of a typical airfoil section that occurs when it operates in the downwash generated by the wing. Accounting for this change during the design phase will ensure that the airfoil sections are optimized for their intended operating conditions. The addition of endplates to the wing serves to counteract the magnitude of the change in operating angle by effectively producing an increase in wing aspect ratio.

During the design process at UIUC, an empirical method was used to provide an estimate of the effective aspect ratio of the wing and endplate combination. However, owing to concerns about the dependence of the formula on the chord of the endplate beyond the chord of the wing, it was decided to attempt to develop a new effective aspect ratio relation. Using CFD, a study was carried out to investigate the aerodynamic changes that occurred when a low aspect ratio wing was used in conjunction with endplates of varying height and varying chord. The angle of attack of the wing was also changed in the study. The aerodynamic changes were then used to deduce changes in the effective aspect ratio.

The resulting data showed that the effective aspect ratio was highly dependent on an increase in the height of the endplate and slightly dependent on changes in the wing angle of attack. There was no significant dependence on the chord of the endplate beyond the chord of the wing. These results were then used to develop a formula linking the aspect ratio of the wing to the effective aspect ratio of the wing/endplate combination