A paratrooper model sensitivity analysis for personnel airdrop

Abstract

Personnel airdrop operations are subject to the unsteady flow around aircraft and variations in the paratrooper's exit orientation, body, weight, and balance. This could lead to non-repeatable airdrop operations including the possibilities of the paratrooper colliding with the aircraft or, after parachute deployment, another paratrooper leaving the opposite side. An exit trajectory sensitivity analysis addressing variations in mass distributions, exit velocity, initial position, and initial orientation is, therefore, an essential tool to increase aircrew and soldier safety. The goal of this study is to conduct time accurate simulations of two high-fidelity paratrooper models with different weight and balance data exiting the left- and right-side troop/exit doors of a C-130 after an initial prescribed motion. The aircraft model has an open troop door with fully-opened air deflector and extended flaps flying at 1,000 ft and 130 kn, and without propeller blades. Upon completing an initial prescribed motion, the paratrooper model is permitted to respond to the influence of the aircraft flow field and gravity. Solutions are calculated using HPCMP CREATETM-AV Kestrel software. In these simulations, the initial exit motion, position, and orientation are fixed. Trajectory data are extracted and compared. A normalized parameter of distance to the paratrooper diameter is defined to measure the trajectory translation deviations from a baseline exit case. The results show that trajectory data are more sensitive to the weight and balance data than aerodynamic forces/moments, which are functions of body profiles. For all tested right exits, the maximum deviations measure about three paratrooper body reference diameters, and all follow similar trajectory paths. Cases with small moments of inertia around the z-axis and a small side-force can lead to a negative yaw turn at initial exit times and a possible contact of main canopy container with the aircraft. The results show that left and right exit trajectories are very different mainly due to the asymmetries of paratrooper models. The results of these simulations document and characterize the associated strong moments, and the final states of the trajectories will serve as initial conditions for the subsequent parachute deployment.