Abstract: For sealing the gap between the fuselage and a swing-wing of a swing-wing aircraft there is provided an elongated, inflated, flexible bag mounted in a recess of the fuselage, all the longitudinal walls of the bag being of flexible material and including a flexible base-wall affixed by a frame along its two longitudinal edges to the aircraft structure, the bag further having a multiplicity of internal, substantially parallel, closely-spaced, flexible, transverse, flanged diaphragms attached by the flanges along their sides to corresponding longitudinal walls of the bag, the flexible diaphragms, at the inflation pressure employed, being rendered substantially inextensible by reinforcing webs in directions such that the transverse cross-sectional dimensions and shape of the inflated bag are constrained by the diaphragms to conform to the dimensions and shape of the diaphragms, and the diaphragms being apertured to permit inflation of the bag from one end.