I have not been able to find satisfactory methods on design of slotted flaps, or flaps in general. Most of the answers are about eyeballing or experience. Can you guide me on what could be good starting points.
The images below are what I have design using internet advice, I would like your comments on it.
EDIT: Some information about the design considerations, The airfoil is S2091 with a chord of 40cm and a wingspan of 3.2 metres operating between 0.3 to 1.3 million Reynolds number. Its meant for a UAV that weighs around 35kgs. Without flaps the landing speed is around 18 m/s (65kmph) which I want to lower with use of slotted flaps.
So far I am using thumb rules like having flap roughly the shape of an airfoil and their relative position to trailing edge of airfoils as a given percentage of chord length. But hit and trial doesn't feel like an optimal approach to designing and I seek to understand how others approach this problem. I can design the mechanisms and structures myself, I need help with the aerodynamic design.