H. Climent, G. Pastor, J.T. Viana, L. Benítez, A. Iafrati
DOI Number: N/A
Conference number: IFASD-2015-139
Ditching is a planned aircraft event that ends with controlled emergency landing in water. Four main phases may be considered in a ditching event: — Approach: Characterized by aircraft/environment conditions before impact. — Impact: Structural response during the impact (fluid-structure interaction). — Landing: Subsequent motion of the aircraft until stoppage. — Floatation: evacuation of passengers and crew. This paper addresses some aspects of the second phase, an extreme case of fluid-structure coupling were high pressures may develop during the impact of the aircraft with water, which in turn may cause rupture of the structure, jeopardizing the required safe evacuation of crew and passengers. At Airbus DS Military Transport Aircraft Aeroelasticity and Structural Dynamics department ditching has been a topic of continuous research for more than 12 years [1-5]. This interest is also shared by universities, research laboratories and industrial partners that have gathered together in the consortium of the European funded research project SMAES (SMart Aircraft in Emergency Situations). SMAES has devoted part of its activities to perform experimental ditching tests at the CNR-INSEAN, Rome. Data obtained from these tests can be used both, directly or indirectly to validate numerical tools / analytical theories for solving the fluidstructure behaviour during ditching. The paper will briefly describe the tests set up and execution. The tests consist on impact of panels against water at a similar horizontal speed to the expected in a real aircraft ditching event. Panels are geometrically and structurally representative of inner fuselage skins. 64 runs were performed covering a wide variety of parameters: — Quasi-rigid and flexible panels with different stiffness. — Flat panels, positive and negative curvature panels. — Metal and composite. — Pitch angles and horizontal speeds. Test measurements include accelerations, strains, pressures, forces and speeds. The bulky part of the paper is focused on an elaborated analysis of the test results showing the main trends with the different parameters. Several analytical tendencies and correlations will be presented as well as the physical interpretation of these trends. Part of this information (especially time histories of pressures distributions) can be used directly in ditching analysis. In addition, all this material will be of significant help for any researcher developing numerical tools or addressing background theories that could be contrasted against these test results. From the structural dynamics standpoint, one of the most relevant parameters is the structural flexibility: it affects the local pressures distribution and in turn strains and loads. The alleviating effect of flexibility is one of the most important outcomes of the ditching test campaign and it has critical relevance for aircraft ditching certification. Concluding remarks highlight how these results constitute a significant step forward in the understanding of the complex fluid-structure phenomena that takes place during a ditching. The paper will end with suggestions for further work in this area.