Comparative analysis of different methods to compute ditching loads

Ditching is an emergency condition that ends with a planned “landing” of the aircraft on water. Four main phases may be considered in a ditching event: Approach, Impact, Landing and Floatation. This paper will address the loads aspects of the second phase, an extreme case of fluid-structure coupling where high pressures are developed during the impact of the sliding aircraft with water, which in turn may cause rupture of the structure, jeopardizing the required safe evacuation of crew and passengers.
This problem is gathering significant attention from public and institutions especially after some recent events with large media coverage (like the ditching on the Hudson River, US Airways Flight 1549, 15 January 2009).
Currently there are very few tools available to determine the loads generated during the ditching impact phase. This paper will present (and compare among them) ditching loads methodologies, one experimental and four different numerical simulation approaches:
- Experimentally measured ditching test results obtained in two European funded research projects: SMAES (Smart Aircraft in Emergency Situation, 2011-2014) and SARAH (Increased Safety and robust certification for ditching of aircrafts and helicopters, 2017-2019).
- Synthetic pressures derived analytically by matching SMAES experimental results.
- Smooth Particle Hydrodynamics (SPH) technique embodied in an explicit FEM code
- Computational Fluid Dynamics (CFD).
- Semi-Analytical Water Entry Approach
The main objective of the paper is to compare different alternatives, decide which are currently the most suitable ditching loads methodologies that could be used to simulate this event during aircraft design and certification. The ditching loads have to be obtained as a function of the aircraft classical landing parameters (e.g. horizontal and vertical speed, pitch angle etc). and should be applicable to any aircraft geometry. The paper concludes with the application of these methodologies to a real case of a medium transport aircraft and suggestion for further research in this area.