Two cases of combined cycle engines（case 1:turbine engine/ramjet/dual mode scramjet

case 2:turbine engine/ejector ramjet/dual mode scramjet）were comparatively studied by using aircraft/engine performance integrated analysis method. Constraint analysis and mission analysis were conducted based on a given mission of the hypersonic vehicle capable of Mach number of 65 cruise. The optimal thrust loading and wing loading satisfying the constraint were obtained

and the corresponding takeoff gross mass and sealevel takeoff thrust were further obtained. Results indicated that under the condition of completing the mission of hypersonic vehicle

case 1 had a comparable takeoff mass with case 2. The takeoff mass of case 1 was 26% lower than case 2

and the takeoff thrust of case 1 was 103% higher than case 2. Considering the stateoftheart of turbine engines

two 129kNthrust turbine engines and two 119kNthrust turbine engines were used for case1 and case 2

respectively. In addition

the takeoff mass increased shapely with the cruise distance. The takeoff masses will be about 85t for both cases when the cruise distance is 4000km.