A forced oscillation radial seal is described for regenerative air preheaters which contain rotatable radial plates having upper and lower edges. The forced oscillation seal includes a base with a first portion attached to a lateral face of the plates adjacent the upper and lower edges, and a second free portion, with a pivot system having an axis attached to the second free portion, and a rigid sealing sheet with a first free portion, second portion, and central portion, the sealing sheet attached at its central portion to the pivot system. The forced oscillation seal includes a counterweight attached to the sealing sheet so the sealing sheet reassumes a vertical position after forming a seal with a sealing surface, and a plurality of springs in contact with the sealing sheet and base along the axis of the pivot system, which cooperate with the counterweights to force the seal to oscillate.