Box Structures for Carrying Loads and Methods of Making the Same

An air vehicle having a bonded box structure for carrying load, the air vehicle comprising:

• an airfoil frame having a first tip and a second tip;
• and,
• a bonded box structure attached to the airfoil frame, the bonded box structure comprising:
• upper and lower composite integrated sandwich panels continuous from the first tip to the second tip of the airfoil frame, the integrated sandwich panels having facesheets sandwiching one or more core portions and adjacent dense packs oriented in an axial direction;
• and,
• a plurality of spars, each spar comprising a web and web attachments and having a spar length in the axial direction, the plurality of spars being connected to the integrated sandwich panels with the web attachments located at the dense packs,
• wherein the facesheets are configured to carry primarily torsion and pressure loads in shear and no significant axial loads, and wherein the dense packs are configured to carry all significant box bending in axial tension and compression loads.

A method of making a bonded box structure for an air vehicle, the method comprising the steps of:

• forming a pair of integrated sandwich panels, each panel formed by:
• fabricating a composite skin by sandwiching a core portion between at least two composite facesheets, each composite facesheet formed by laying up a facesheet composite ply layup substantially comprised of bias oriented plies with, and designing the facesheet composite ply layup to enable the composite skin to provide continuous torsion, shear, and pressure load paths;
• and,
• joining a plurality of dense packs to the composite skin, each dense pack formed by laying up a dense pack composite ply layup comprised of a substantially orthogonal, unidirectional composite tape laminate, and designing the dense pack composite ply layup to enable the dense packs to provide continuous bending and axial load paths;
• and,
• bonding a plurality of spars and stabilizing ribs between the pair of integrated sandwich panels to form a bonded box structure for an air vehicle, the bonded box structure having a unitary configuration.