why does my se pitch nose down when i drop my flaperons

Its trying to commit suicide- next time try not to intervene.

Because that's that airplanes do. If you want the aerodynamics of it, it's because the wing's center of lift changes when you drop the flaps. Depending on how it moves and what the wing configuration is, the nose will either lift or drop. If you have a radio that is capable of flaperons, then it's most likely got mixing, so mix in up elevator with the flaps going down.

I agree with the remedy suggested by buildflycrash.

I was always told that when you drop flaps the nose is suppose to pitch up not down an was wondering if there might be somthing wrong in my set up

Like I posted above, it varies with the plane. Trust me on this one, I've been a full scale flight instructor for years, and had to go through a lot of classes on aerodynamics. It all depends on flap design, wing design/location, cg location, and airspeed that you are carrying when you put the flaps out. In general, most planes do pitch nose up, but there are plenty that put the nose down.