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Main rotor blades with plain trailing edge flaps are investigated as a potential means of vibration reduction using a comprehensive rotorcraft analysis. The analysis is modified to incorporate an unsteady aerodynamic model including flap effects. Predicted blade and pitch link loads show adequate correlation with experimental data. An initial open loop study shows that, for a typical articulated four bladed rotor, significant reductions in fixed system 4/rev vertical shears and hub moments are possible with open loop flap deflections at 3/rev and 4lrev. The reductions are most closely associated with changes in the response of the blade third flatwise bending mode and torsional deflections. A reduction in blade torsional stiffness reduced the effectiveness of the flap in reducing vibration.