Dynamic analysis of a variable mass sled system under variable forces

The sled system is used to test anti-penetration structures, ejection seat, and spacecraft equipment that its technology is owned by a few developed countries. In this research, the dynamic analysis of applied forces on the system has been investigated. The effective forces on the sled include propulsive force, drag force, lift force, and friction force, which are all variable. To obtain the propulsive force according to the functional and geometric specifications of the designed sled, the grain engine design has been carried out to reach 0.85 Mach in a second. After extracting the governing equations for extracting the propulsive force, the changes of the propulsive force during the combustion time were obtained and formulated. At the next step, numerical simulation is used to obtain the lift and drag forces and after validating the numerical solution with experimental research, the values of drag and lift forces at different speeds are extracted and formulated. Next, due to sled mass variations during the combustion step, the friction force between the rail and the slipper is obtained. Finally, the differential equation and dynamic behavior of the system are analyzed. The results show that amount of friction force is negligible in comparison with other forces. Also, the highest pressure is applied to the inner part of the slipper, which can lead to wear and damage of the rail surface at high speeds and lead to the sled deviating from the rail track.