Stratospheric airship has great advantages, such as long-endurance, large coverage area, low-cost and so on, these advantages make airship be an ideal stratospheric platform and become highly valued. Airship envelope is a large inflatable membrane structure. As a key component, the envelope features flexible and large displacement. There is strong coupling between envelope structure and the ambient air when airship operating in the high altitude sky. The coupling characteristics have great impact on the aerodynamic and structural performance of airship. Aiming at the aeroelastic characteristics of the envelope structure, a fluid-structure coupled computational method is presented basing on a finite element program. As an example, the envelope structure of airship is computed and the S-A turbulent model is used. The envelope drag coefficient under different attack angle is computed. The contrast between experimental results coming from reference paper and numerical results highlight the correctness of this method. With the developed computational approach, the NPL envelope is also analyzed. The changes of length to diameter ratio, max cross section location and Reynolds number are studied and the aeroelastic characteristics of flexible envelope are analyzed. These results can give some valuable information for precise forecast of the overall airship performance
