A. Pérez de la Serna, S. Parra Adán, E. Gómez Viñas, H. Climent Máñez

DOI Number: N/A

Conference number: IFASD-2017-153

Landing is one of the most critical phases in the aircraft operation, as most of the accidents occur during this manoeuvre. National Transportation Safety Bureau (NTSB) statistics show that more than 40% of aircraft accidents occur during landing manoeuvres, and most of them use to imply a substantial damage for the aircraft and/or the crew/passengers. During landing, the vertical velocity of an airplane is quickly reduced to zero when the wheels strike the ground. This process is accomplished by a transfer of energy from kinetic energy of the sinking airplane to internal energy in the shock absorption system, where it is dissipated. The vertical velocity of the airplane is brought to zero within a fraction of a second, and hence the forces applied to the structure through shock strut change from zero to a maximum also in a fraction of a second. This rapid change in velocity, or equally in application of force, excites the lower vibration modes of the structure. Therefore, the structural dynamic characteristics of the structure must be taken into account. Nevertheless, flight test have proved that the assessment of the severity of a landing impact needs to be based not only on sink rate, but also in lift/weight ratio at landing (load factor). According to this fact, there are two scenarios that can make landing manoeuvre particularly critical and severe: — Hard landing: event in which an aircraft has a controlled landing with a large sink rate — Rebound landing: event in which the aircraft touches the ground normally, but goes back to the air for 2-3 seconds and then falls again over the ground. This second impact uses to happen with the spoilers deployed and so, with an important decrease of wing lift, making load factor during the second impact around 0.5-0.7g. This paper presents the continuation of the works performed at Airbus DS Military Transport Aircraft Aeroelasticity and Structural Dynamics department in the last years [1-4]. It will show the methodology to calculate both hard landing and rebound landing, and how these simulations are compared with Flight Test data. It will also prove that sink rate is not the unique relevant parameter in order to assess landing severity.

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In Categories: 1. IFASD 2017, 1.Events, Dynamic loads
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