The experimental characterization of the torsional and transverse stiffnesses of a braided parachute suspension line

GPS-guided parachutes are used by the military to deliver supplies to personnel in the field. During descent, the suspension lines can vibrate as a result of vortex shedding and oscillating aerodynamic forces. In addition to challenging the targeting accuracy, these vibrations can generate sound that can compromise silent entry operations. The availability of a fundamental understanding of the relationship between braid architecture and associated vibrations would provide insight on how changes in the design of suspension lines could mitigate these vibrations. In the current research, the torsional and transverse stiffnesses of a braided parachute suspension line are characterized as a function of the state of tension. The torsional behavior is investigated using static and dynamic torsion tests, and the transverse behavior is studied using a pluck test. The torsional and transverse stiffnesses are found to increase with increasing tension on the suspension line. The effective transverse stiffness is found to correlate to that which can be derived from the vibrating string under tension equation. These stiffness properties can be used as inputs for fluid-structure-interaction (FSI) models to develop a calibrated FSI simulation to investigate the role that the mechanical behavior of the suspension line plays in its flow-induced vibrational response.