I don't think you can use a Y harnes with flaperons. Ailerons, yes, but to add flaps, you need additional control to operate the servo's in the same direction. This is needed for flaps because of where the linkage is.. they are either both inside or outside, not one inside and one outside as necessary for the surfaces to move in the opposite direction for ailerons.

The ailerons servos are mounted so that both have the control arms facing either away from the fuselage or both facing the fuselage. The rotation for both servos are in the same direction (as can only happen with a Y harness or by programming separate channels for dual channel operation). This moves one servo arm forward while it moves the other rearward. Flaps.. both have to move in the same direction.

If you do go with flaperons, and use two separate channels, then remember that when you use the flaps, you remove some control authority from the ailerons because the down aileron will already be down from the flaps, and it can only go so far.

It's best to have two separate pairs of surfaces, one pair dedicated to flaps (inboard pair) and the other pair for ailerons (outboard pair) and then program a separate channel for the flaps. You CAN use a Y connector for both if you wish in this arragement.

CGr.