High-Fidelity Simulations of Flight Dynamics and Trajectory of a Parachute-Payload System Leaving the C-17 Aircraft

This paper considers the flight dynamics and trajectory analysis of a parachute-payload system leaving the C-17 aircraft at different deck angles. The C-17 aircraft considered has an open cargo door, extended flaps and with four turbo-fan engines operating at 2,000ft (Above Ground Level, AGL) and an air speed of 150 knots. Payloads include simplified CONNEX containers with either 15.8ft or 20ft lengths, 9ft wide and 5.3ft high. Mass and moments of inertia for these payloads are given. A ring-slot chute with 20\% geometric porosity is considered to extract the payload at zero deck angle. Specifically, this study uses the CREATE-AV Kestrel simulation software to model the chute-payload system. The extraction and suspension lines are modelled using a Catenary capability in Kestrel. The extraction line is connected to the CONNEX and chute confluence points. The chute and payload will undergo responding-body motions to study the flight dynamics of chutes and payload and to determine the trajectory. Trajectory data will be compared with a payload (no chute and cables) leaving the aircraft at positive deck angles. An adaptive mesh refinement technique is used to better capture the engine exhaust flow and the wake behind C-17, chute and payloads. Friction and ejector forces are estimated for payloads to match the exit velocity and time measured during flight testing. Results show that simulation of extracted payloads follow expected trends seen in the flight test. Payload aerodynamic forces inside the cargo bay has small effect on the payload dynamics until it clear the ramp. Larger exit velocities lead to smaller rotation rates. All payloads rotate clock-wise once they leave the ramp. Chute extractions lead to much larger exit velocities and shorter exit time. Payload-chute acceleration corresponds to predicted drag of the chute in previous studies.