Study On Air-Tightness Test Method Under Complicated Environment

Manned airship was born in 150 years ago, it became reactive in aviation field since 1980s after the depression of more than half a century. Airship has many merits include low manufacturing and operating costs, small noise pollution, aloft long time staying, wide coverage compared with the conventional aircraft and helicopters. It is a very ideal aerial platform and has been paid more attention by many major countries. Airbag is the main structure of the airship and balloon helium leakage has a great influence to the airship flight height, maximum payload and flight safety. Due to the factors of airbag skin material, airbag producing and airbag stress, it’s inevitable for helium leakage. The detection of helium leakage is crucial for airship flight safety and a deep study in airbag leakage detection should be carried on.Gas pressure method or flow rate method is used for the detection of large volume airtight structure in traditional gas pressure method with high accuracy requirements of sensors. To explore the gasbag air leakage detection under pressure conditions, temperature load and wind load, this paper presents a leakage prediction approach based on balloon surface strain and applies it to solve the leakage measurement problem of high volume low pressure sealed structure when precision of pressure sensor is restricted. A helium leak prediction model of spherical balloon is built based on the relationship between pressure, volume and surface strain. Consider with balloon skin material mechanical performance, a finite element analysis of the relationship between balloon surface strain and pressure is produced and the strain values from theoretical prediction and finite element calculation are compared to verify the accuracy of the prediction model. The influence of temperature change on the leakage of helium gas leak is predicted by using the proposed model. Analysis of pressure changes caused by leakage and the quantitative theoretical analysis of skin internal stress and surface strain is established according to the stress and strain of bus and ring direction with double ellipsoid balloon as an example, under internal pressure. Verification of the theoretical model is proceeded by the results comparison from the theoretical model and finite element model and the most suitable position of airbag pressure change measurement is gotten by using its skin surface strain. For airbag leakage in different pressure conditions and wind load, a finite element calculation is conducted and the most suitable position of airbag pressure change measurement is gotten by using its skin surface strain. The method of leakage measurement based on surface strain as proposed in this paper has some guidance for the leakage measurement and design of airship.