Energy Absorber Design and Analysis for Military Utility Helicopter Troop Seats
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In most of the helicopter platforms, usage of vertical or sideward ejection seats are not preferred since it is not practical considering the existence of the rotating main rotor blades on top and the spinning action caused by the main rotor which could yield uncontrolled behavior during jettisoning. In addition, it is not possible to provide ejection seats for each and every occupant on board. Therefore, to increase the chance of survivability of occupants, helicopter platforms and their components such as landing gear, fuselage and seats shall be designed crashworthy especially in vertical direction. Considering the importance of the seat for crashworthiness assessment, it becomes critical to investigate on seat energy absorption in a comprehensive way. According to regulations or military design standards, helicopter seats shall absorb some fraction of crash energy via plastic deformation mechanisms to save the life of the passengers during a crash. Accordingly, helicopter seats shall be qualified and shall be dynamically tested with the test scenarios provided in the applicable design standard. In this thesis study, a tube-stud type energy absorption system is designed and integrated into a simplified troop seat to verify its performance in dynamic test conditions specified by MIL-S-85510. In order to absorb the crash energy and to decrease the load transferred to the occupants to the acceptable levels, the studs plastically deform the tube and decrease its diameter. The energy absorber concept is analyzed with dynamic explicit workbench of ABAQUS® and then tested in METU Central Lab Mechanical Testing Laboratories. After the correlation of the analyses and the test results, the energy absorber system is integrated into a simplified military troop seat and then analyzed to simulate the crash test scenario. The crash pulse provided in the MIL-S-85510 is applied and the results are evaluated.