Composites are widely used for the constructions of various components of aircraft due to its appreciable properties than its counterpart conventional metals. This research work focuses on  stress analysis of flaps (high lift device) used in the high rage aircrafts. NACA AG09 and SC20610 airfoils are used for developing such flaps. Two different flaps(plain flap and slotted flap) are chosen for this analysis. The loads acting on these flaps during flight conditions are determined using ANSYS-CFD software and the structural analysis are done by using NASTRAN and PATRON software. For structural analysis two different materials, Basalt Fibre Reinforced plastic(BFRP) composite and Glass Fibre Reinforced plastic(GFRP) composites are used. The stress at various layers of the BFRP flap is higher than that of GFRP flap