Hi Guys
For my 1/2 penny worth
Down flaps increase the undercamber of the airfoil therefore increase lift by causing an greater differential in pressure above and below the airfoil section this would not work at high speed as the laminar flow would be upset at anything above the new airfoil sections correct laminar flow vector, this also moves the Center of Pressure closer to the Center of Gravity and thence makes it easier to stall i.e. c of p gets behind the c of g breakaway of the airflow and stall. The opposite effect by raising the flaps/ailerons up, this effectivly puts washout into the section making it harder to reach an angle of attack that would allow the c of p to get behind the c of g and cause a stall, up flap would effectivly dump lift and allow a much steaper approuch without stalling, ensure you have enough elevator authority, down flap makes the aircraft more prone to float on and on and on and on but does decrease the landing speed, but only up to a point where the stall is violent, don't forgett here we are flying small scale airfoil sections in full size air Renolds numbers be damed.

Mike