Joining structural members using foam

A method of forming an aircraft component, the method comprising:

• providing an aircraft skin member selected from a rotor blade, a fuselage, a tail-boom, an empennage, a horizontal stabilizer, a control surface, a wing, or an internal-to-external fuselage transition for an aircraft;
• bonding a first end of a honeycomb structure to a surface of the aircraft skin member, the honeycomb structure comprising a plurality of connected cells, each cell comprising a plurality of surfaces, wherein adjacent cells share a common vertical surface;
• spraying foam in a fluid state on a second end of the honeycomb structure, the second end opposite the first end;
• and
• curing the foam on the second end of the honeycomb structure from the fluid state to a solid state to bond the foam in the solid state to the aircraft skin member.