Optimization of a single slotted flap with dropped hinge is performed with the objective of increasing the payload of a propeller driven 4-seater general aviation aircraft. Within the optimization loop, two-dimensional aerodynamic characteristics are evaluated using the MSES code, while three-dimensional aerodynamic characteristics and weight are estimated with semi-empirical methods. Genetic and pattern search algorithms are used to minimize the objective function. It is found that the payload can be increased by up to 40% if the stall speed is kept constant. Cruise drag due to flap support fairings increases the fuel burn for 3% on a range of 1000 nm. A method of using the maximum displacement thickness on the flap trailing edge in order to detect separation during optimization is proposed and found to be reliable.@en