When flaps are deployed Down, there is a transient effect that causes the airplane to pitch Up momentarily; but once the steady state condition is attained, the airplane may require Up or Down trim depending on the downwash from the wing and the airplane tail configuration; ie, low horizontal, mid horizontal, or T-tail.
A good example is flying the Cessna 150: at 10deg flaps (first detent), the airplane requires Fwd (Down) elevator trim to maintain 75mph; but at 30deg and 40deg(full flaps) the airplane requires almost full Up elevator trim to maintain 75mph.
In most cases, most airplanes require a considerable amount of Up trim on approach and landing.
How do I know? I've spent 25 years flying full size airplanes.
feihu