Nonlinear dynamic behavior of parachute static lines

Static line deployed parachute jumping is the most efficient technique used by the United States Army Airborne Corp to deliver paratroopers to target drop-zones. The static line connects the parachute pack worn by the jumper to the anchor line of the jump aircraft. When the jumper exits the aircraft, slack in the static line is drawn tight as the jumper falls below and to the rear of the aircraft. The resulting tensile force generated in the static line achieves a magnitude of approximately 400 pounds before the parachute pack-closing loop is torn open thereby initiating canopy deployment. In some instances, the jumper becomes entangled in the line and prevents the appropriate tensile force from reaching the pack-closing loop. In most of these cases, the jumper remains entangled and is towed back into the aircraft by a high-speed winch connected to the onboard terminal of the anchor line. On rare occasions, the static line fails and the jumper is required to manually activate the reserve parachute to avoid fatal impact with the ground. Static lines are complex fabric structures that exhibit highly nonlinear behavior while experiencing large deformations. Quasistatic tests were conducted to characterize the behavior of these materials. Drop weight tests simulating actual parachute jumps were also conducted. The forces applied to the test lines were recorded as functions of time. This data is used to determine the force-elongation behavior of the line during the dynamic tests. Results indicate that a significant amount of energy is dissipated during the loading-unloading process. The behavior during the loading phase is similar to that observed during static tests. The unloading phase is significantly different. A mathematical model for the predicting the dynamic response is presented. (C) 2003 Elsevier Science Ltd. All rights reserved.