Folding wing aeroelastic experimental models have been designed and tested in the Duke wind tunnel. The folding wing structure is also modeled theoretically using linear plate theory and divided into three components: the fuselage, the inboard wing, and the outboard wing. A component modal analysis is used to derive the full structural equations of motion for the combined system. A three-dimensional time domain vortex lattice aerodynamic model is used in conjunction with the structural model to investigate the stability of the linear aeroelastic system. The effects of the inboard and outboard torsional stiffness at the attachment points between the components and also the folding angle at the interface lines are discussed. The theoretical and experimental results provide new insights into the folding wing aircraft dynamic behavior and a deeper understanding of aeroelastic stability and its potential impact on a folding wing design.