New, eco-efficient aircraft will significantly reduce the levels of carbon dioxide and nitrogen oxides emissions into the atmosphere. To achieve these important goals, aircraft designers are exploring new ways to integrate advanced engines and propulsion concepts into aircraft
Many promising concepts, like the contra-rotating open rotor (CROR) engine cannot directly replace the current generation of engines, as they require significant changes to the aircraft’s design like the rearward shift of the engines away from the wing. This, allows for large fan or rotor diameters or multiple fans, which help achieve unprecedented levels of fuel efficiency and emissions reductions with reduced cabin noise and enhanced passenger comfort.
The main safety issue with CROR technology is the high energy release of debris following engine burst or blade-off events. The development of impact shielding against high-energy engine debris is a must for the implementation of CROR propulsion technology in the rear fuselage of future civil regional aircraft.
The EU-funded REDISH project addressed this challenge by investigating innovative shielding solutions. “These aimed to comply with aeronautical structural requirements and standards, namely regarding weight efficiency, which is the main source for fuel efficiency and reduction of emissions,” says project coordinator Dr Cláudio Lopes.
Analysis at laminate and composite levels
Researchers applied a coupled experimental-numerical development approach to a number of possible configurations and developed high-fidelity simulation tools for carrying out virtual testing. This significantly reduced the need for costly physical testing and accelerated the shielding development process.
Project partners conducted analyses at the laminate level, evaluating the capacity of the shielding materials to resist perforation from the impact of metal fragments and frangible carbon fibre composites using flat laminate samples and ranking it as a performance indicator. The next phase at the component level studied the final shielding configuration and also determined the structure’s capacity to resist perforation.
The team also investigated other qualitative indicators at both the laminate and component levels in addition to structural performance. “These included ‘evaluation easiness’ which reflects the availability, ease of application, and accuracy of methods for predicting the structural performance of the different solutions; and ‘implementation easiness’ which reflects the aspects related to implementation, maintenance and costs of materials,” explains Dr Lopes.
Additional benefits
The selection process identified more than 30 solutions for the next evaluation step involving high-fidelity finite element analyses. This resulted in a higher-fidelity ranking of more than 20 evaluated solutions. According to Dr Lopes: “This was then reduced to 14 solutions that were actually manufactured and evaluated in the framework of another Clean Sky 2 project.”
REDISH successfully described the material behaviour at different length scales from ply to laminate to component level. An additional advantage of this bottom-up approach is that changes in the properties of the constituents (fibre, matrices), the fibre architecture or laminate lay-up can be easily incorporated to provide new predictions of the macroscopic behaviour of the composite under impact. Furthermore, “aeronautical-worthy high-energy impact shielding will also provide protection against other type of threat, such as terrorist attacks,” Dr Lopes concludes.
