Numerical Study for the Optimal Flap Chord Length of a Two-element Airfoil

In designing a two-element wing for a racecar, consisting of a main element and a flap, one parameter to be chosen is the ratio of the flap chord length to the main element chord length. To find the optimal flap chord length, CFD simulations were performed in 2D using the FX63-137 airfoil for both the main element and the flap. Some important findings are that the flap chord length should be 40 to 70% of the main element chord length, that the maximum downforce occurs at the flap angle of about 50°, and that the flap chord length and angle should be smaller as long as the desired downforce is obtained in order to reduce the drag. These findings will help design better two-element wings.