Objectives & Challenges

The problem

Aircrafts and helicopters often travel above open waters and thus have to prove a safe water landing under emergency conditions. This is particularly true for fixed-wing aircrafts certification, but also for helicopters as they are strongly used to support marine tasks (e.g. serving offshore wind-parks, supporting S&R actions etc.). The specific challenge for the design of airborne vehicles is to minimize the risk of injury to persons on board during the whole water landing and to give chance for safe evacuation of the occupants. Accordingly, the motion of the aircraft/helicopter along with the forces acting on the structure is studied for controlled water impact during the design phase of an aircraft. Additionally, the subsequent floatation and the evacuation process have to be considered.

With respect to large transport aircraft these requirements are expressed in the certification specification of the European Aviation Safety Agency (EASA) (2008) and the Federal Aviation Administration (FAA) (1990) under paragraph “25.801 Ditching”. Lights and Heavy Helicopters are also subject to international regulations, especially: Certification Specification (CS) under EASA authority and Federal Aviation Regulations (FAR) under FAA authority. The parts common in both regulations: §563 and §801 establish the requirements, which have to be respected to ensure the safety of the occupants. These parts focus on the structural provision and the general ditching behavior of the vehicle. The topic is thus of utmost relevance for aircraft and helicopter manufacturers, which have to prove that the structural integrity is maintained and the experienced damage does not harm the floatation capabilities to ensure a safe evacuation.

In conclusion, a pressing need for more advanced studies to support the development of next-generation, generalized simulation-based ditching-analysis practices is acknowledged by all stakeholders. The substantial public interest in safety increases the importance of the results expected to be produced by the SARAH project which involves representatives from authorities, major OEMs and technology providers.

      Overview

The Challenge

The considered situation has close links with crash simulation, but also distinctive features. Examples of distinctive aspects refer to hydrodynamic slamming loads on airborne vehicles and complex hydromechanics – partially at very large forward speeds – as well as the close interaction of multi-phase fluid dynamics (comprising air, water, and vapor phases) with mechanics of elastic and deformable structures. Design for ditching involves more than the analysis of loads and a subsequent strengthening of frame sections. It often requires major campaigns for the identification of favorable approach/flight-path conditions together with an adjustment of handling the vehicle during approach in line with the pilots flying capabilities to minimize the remaining kinetic energy of the vehicle to be transferred into the water. As regards ditching analysis, the severe scale effects inherent to the physics of the hydrodynamic load mechanisms impede the use of experimental strategies for the verification of full aircraft configurations. In addition to these challenges, helicopter specific fluid-structure aspects related to the helicopters Emergency Floatation Systems have to be captured. Moreover, the progressive use of new lightweight designs prohibits transferring experience made with conventional designs during certification or at least is a challenge involving additional studies.

      Overview

The Objectives

…increase the safety of aircrafts and helicopters in ditching / floatation situations…

SARAH focuses on improving the understanding of the underlying phenomena with regard to ditching. In order to achieve this SARAH will tackle the following objectives:

  • improve aircraft/ helicopter certification tools in order to deliver accurate loads to safely design aircrafts/ helicopters and deliver input on how ditching needs to be simulated in order to obtain robust, safe and accurate loading information.​​Within this field of work SARAH will concentrate on delivering simulation means. By taking into account elasticity effects in a two way coupling the complex interaction between structural deformation and vehicle loads can be properly regarded. Environmental effects (ground effect, waves) are also addressed by improving the simulation methods. Work performed here will enable to perform future A/C and H/C certification completely based on simulations without the need for similarity assumptions based on tests.
  • derive a robust way to safely design new configurations (for which no engineering experience is available) with regards to ditching
    • What kind of tools do we need?
    • What kind of design is necessary?
  • use methods obtained to analyse and optimise approach, landing and impact phases to supporting the pilot in water-landing scenarios

      Overview

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 724139.

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