Preform for forming complex contour structural assemblies

A preform for forming a lip of a nacelle defining a complex contour having opposite inner and outer mold line surfaces and defining a center extending along an arc, the preform comprising:

• a first skin member defining a desired convex contour of the outer mold line surface of the lip;
• a second skin member defining a desired convex contour of the inner mold line surface of the lip, the second skin member connected to the first skin member to define a first gas chamber between the first and second skin members;
• a cellular core member disposed in the first gas chamber and defining a plurality of cells between the first and second skin members;
• a gas connection in fluid communication with the first chamber and configured to deliver a pressurized fluid to the first chamber for supporting the core member in the first chamber;
• a closeout member connected to the second skin member by a weld joint, the closeout member positioned opposite the first skin member and defining a second gas chamber between the closeout member and the second skin member with the second skin member defining the desired convex contour of the inner mold line surface of the lip;
• and
• a gas connection in fluid communication with the second chamber and configured to deliver a pressurized fluid to the second chamber, concurrent with delivery of the pressurized fluid to the first chamber, to urge the preform away from the closeout member and against a contour surface of a die.