Continued development of an integrated easy5/ACESII-ATB model for ejection seat simulation

This paper presents continued development and validation of an integrated ejection/crewmember model, specifically the modeling of aerodynamic effects and the crewmember/seat separation process. In a previous study, an ejection seat model, EASY5/ACESII (Engineering Analysis SYstem/Advanced Concept Ejection Seat), was coupled with a crewmember model, the ATB (Articulated Total Body) model. In this study, newly developed algorithms were incorporated into the integrated model to simulate the aerodynamics and seat/crewmember separation. Wind tunnel data from the ejection seat module are used to obtain total aerodynamic forces on the seat/crewmember combination. The crewmember module then uses an analytical method, based on air pressure and the exposed surface area, to calculate the aerodynamic forces and torques applied to the crewmember's individual body segments. These body forces and torques are then subtracted from the total forces and torques to obtain the force components applied directly to the seat in the ejection seat module. Once the man/seat separation signal is initiated, the aerodynamic forces and torques are applied only to the crewmember. Dynamic interaction between the seat and crewmember during the very short period of their separation is complex and critically important. In this study, the harness release and crewmember/seat separation process algorithms were designed and implemented. When the release signal of the harness restraint is generated in the ejection seat module, it is transferred to the crewmember module. The harness belt in the crewmember module is then cut off. Meanwhile, the recovery parachute force from the ejection seat module is sent to the crewmember module. The combined forces due to gravity, recovery parachute, and aerodynamics separate the ejection seat and crewmember. Simulations of F-16/ACESII sled tests were carried out to validate the newly developed features in the integrated model. Simulation results are reported and compared with results of ejection seat sled tests. The validation shows that the model successfully predicts the major features of the ejection seat motion and the crewmember biodynamic responses.