Wing root and tip chord, respectively t w Wing plate thickness kn Numbers of vortex elements on wing in y direction kmm The total number of vortices on both the wing and wake l Wing span m w Wing mass per unit length M s Store mass t Time P Dimensionless aerodynamic pressure q,q State-space vector of structural deformation F a Generalized aerodynamic force vector J Jacobian matrix J 1 , J 2 , J 3 Store aerodynamic parameters U f Dimensionless flutter speed (U f /lw 02) U ∞ Free stream airspeed ρ ∞ Density of air λ Wing taper ratio (c t /c r) Λ Sweep angle of wing AR Aspect ratio of wing Γ Vortex strength x s , y s , z s Position of center of gravity of store x p The distance from the nose to pivot point of store c b Chord of slender bodȳ x s Dimensionless center of gravity of store in x Abstract The present paper aims to investigate flutter phenomenon for cropped delta wing with an external store using numerical and experimental methods in a subsonic and incompressible flight regime. Wing structure is modeled based on von Kármán plate theory. The unsteady vortex lattice method is applied to wing aerodynamic model and a slender-body theory is used for store aerodynamic model. The experimental tests have been conducted in an incompressible subsonic wind tunnel. The comparison indicates a satisfactory agreement between the experimental results and the theoretical analyses. Moreover, the effects of different parameters such as wing thickness, wing aspect ratio, spanwise store position, store mass, the aerodynamics of the store, underwing clearance and store center of gravity on both flutter speed and instability boundary of the wing are studied both analytically and experimentally. Also, the system behaviors and the oscillation amplitude are examined experimentally for post-flutter where time history simulation and phase portrait are obtained for various velocities. The FFT analysis of time history measured data shows that beside the dominant harmonic frequency, both superharmonic and subharmonic frequencies are clearly identifiable. The results obtained from experimental bifurcation diagram indicate the presence of hysteresis loop regions corresponding to the stable LCOs.