For configurations where the nacelle may come into contact with the ground, nacelle separation designs are widely used to protect the wing and the fuel tank structure. To meet the requirements of regulation, it is necessary to obtain accurate dynamic loads and ensure that the engine and the nacelle break away from the wing. In a crash event where the impact load generated by the crash is greater than the strength of the fuse pins, for instance, when the aircraft sinking speed exceeds the threshold speed, the fuse pins fail, and the nacelle breaks away from the wing structure. In general, fuse pins are mounted between the pylon and the wing structure. In addition, protection of the fuel tank structure and cabin occupants should be considered in extreme cases, where loads and forces exceed those associated with the abovementioned design conditions. It needs to be combined with a slip angle of up to 20°. Moreover, the landing gear should be fully retracted, and any other combination of landing gear legs should not be extended. Civil aviation regulation Part 25 requires an aircraft to sink at a speed of at least 1.52 m/s (5 fps) and in a maneuverable state to avoid damage to the fuel tank when it crashes on the ground with the maximum landing weight. Therefore, the wing and fuel tank structures should be designed such that they are not damaged during primary and secondary impacts to the airframe. Although most emergency landing events are relatively controllable, the nacelle inevitably comes into contact with the ground. In these aircraft, the distance between the nacelle and the ground is small, especially in the wheel-up landing condition. Wing-mounted engine has emerged as the primary configuration of civil aircraft. The protection of fuel tanks and cabins during takeoff and emergency landing of civil aircraft is a critical topic in aircraft design.
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