Design and Fabrication of Test Rig to Determine Helium Permeability through Fabric

The fabric of an envelope of Lighter-Than-Air (LTA) systems experiences permeation of LTA gas (usually Helium or Hydrogen) over a period of time. The permeation occurs due to intermolecular spaces in the structure of the fabric, e.g., PVC, PVC coated Nylon, Metalized polymer. This paper describes the design of a test rig to determine the permeability of Helium gas through the fabric. This rig consists of an upper and lower chamber arranged to hold a fabric specimen in between them. A pressurized Helium gas cylinder is connected to the lower chamber through a pressure regulator. A heater is also attached to the lower chamber and a temperature sensor is used to measure the temperature of the test specimen. A Helium leak detector is coupled to the upper chamber to detect the amount of Helium permeated over a period of time. The key objective of this study is to develop and test a robust and reliable permeability tester for characterizing the envelope material.