A blanket assembly for forming a composite charge onto a forming mandrel includes upper and lower heating blankets configured to have a composite charge slidable therebetween during translation along the forming mandrel. The blanket assembly has a pair of wedge elements with tapered sections that are each positionable between the lower heating blanket and the mandrel side surfaces. The wedge element top sides are inclined from the tapered section forward end to the tapered section aft end. The upper heating blanket exerts a blanket forming pressure for progressively forming the composite charge into the cross-sectional shape of the forming mandrel collectively defined by the mandrel side surfaces and wedge element top sides as the composite charge passes over the tapered sections of the blanket assembly. The wedge element top sides maintain the laterally outboard portions of the composite charge in approximately parallel relation to a level tangent to the mandrel top portion.