Structure and air permeability of polyamide and polyester parachute fabrics

Parachute fabrics are unique textile structures with special properties, including resistance to repeated dynamic forces, low dynamic friction, and suitable air permeability. These fabrics are commonly composed of PA 6,6 (nylon type) multifilament yarns. They are highly resistant to high-frequency cyclic deformation, lightweight, and compact. Their partial disadvantage is moisture absorption, which can limit the use and storage of parachutes in unsuitable climatic conditions. One possibility for reducing sensitivity to the presence of atmospheric moisture is the use of parachute fabrics made from PET multifilament yarns, which surpass polyamide fabrics in several properties. The aim of this work is to derive a comprehensive geometrical model of parachute fabrics, including their flattening during final calendering, and to compare the air permeability of Ortex parachute fabrics made from multifilament PA 66 and PET yarns, manufactured by Sky Paragliders, Czechia. The geometry and porosity of parachute fabrics are derived from a morphological model of an ideal honeycomb structure of multifilament and flattening of individual filaments into the shape of a Kemp cross-section. Air permeability prediction models based on the well-known linear (Darcy equation) and quadratic (Ergun equation) functions are compared. It is found that the simple linear function (Darcy equation) is suitable, especially for predicting the relationship between air pressure drop and air permeability of parachute fabrics.