Uncommanded Trim Tab

My RV 12 has just over 35 hours flown
Everything was working fine but on the last few flights I've been having trouble stabilizing the plane.After takeoff and with the plane in level suddenly it assumes a strong nose down.Using the trim up I can stabilize the plane but the same happen again other times. Can someone help me?

You need to sort out what is happening before you fly the aircraft again. Are you getting uncommanded trim or is there another control system issue you are correcting with trim? I would want a complete inspection of the entire pitch control system. I know nothing about the RV12 but you don?t want to be flying a aircraft with uncommanded pitch excursions.

Benedito

I had more hours than your plane but I had uncommanded trim changes that turned out to be wire chafing behind the instrument panel. I could not get the uncommanded movement to happen in the hangar.
The wires from the switches (specifically the trim switch wires) were routed across the top of the main control box and plugged into that box. Where the wires crossed other plugs and the finger screws that tighten down other plugs that have a rough surface to help with tightening. This rough surface was wearing through the side of a wire, the trim down wire, and would short or activate, the trim down once it touched the finger screw. This would only happen when the planes engine was running because it needed the vibration for the wire to contact the metal finger screw.
Once I found it I reprotected the trim wire, put a plastic tube over the finger screw (and others I felt could cause the same problem), and everything was working normal again.
I would check the wires from the trim motor in back to make sure none of those are shorting out, and then behind the panel from the switches. Happy hunting.

Thanks Patric. Next weekend I will remove the panel cover and start to search demaged wires.