I don't know what `OP' is either but a wing section with the same curve top and bottom is a symmetric (non-cambered) section. your tailplane section is probably just something somebody drew, a `Clarke Y' section is a specific cambered section which is not actually flat bottomed. Flying with up trim means you are reflexing the tailplane section, and lowering the effective camber so that it produces less, or maybe `negative' (downward) lift. If you wish to fly with neutral trim you will have to raise the leading edge of the tailplane. How much will depend on the balance point of the airplane, airspeed and the area of the stabiliser, ie, you will have to experiment. Full size pilots have an elevator trim wheel to adjust the tailplane lift for various stages of flight, model pilots usually don't have this control, but we use our elevator trim function as a coarse control of A/c speed.
Evan WB#12.