Addressing aircraft hazards through cutting-edge simulation
While advances in safety technology have made aviation one of the safest forms of transport, researchers are constantly striving to make testing ever more rigorous. An EU-funded project has successfully developed a cost-effective simulation for extreme icing conditions, which should benefit both industry and passengers.
Air travel is statistically one of the safest modes of transport today. This is partly because so much research has been devoted to addressing the risks of flying. Under certain weather conditions, ice forming on aircraft wings and engines, for example, can present a serious danger to air travel, which is why the aircraft industry has to carry out thorough testing before being awarded flight certification.
The main icing hazard for aircraft icing is represented by water droplet clouds, since ice crystals do not easily stick on to aircraft surfaces while water droplet clouds can be subjected to crystallisation on these surfaces. This can lead to the formation of ice on vital parts of the aircraft.
Unfortunately, flight tests in icing conditions are difficult and costly, while extreme icing conditions – such as when super-cooled large droplets (SLDs) form – are even harder to address. SLDs are water droplets characterised by a larger diameter that can accumulate on aircraft components, increasing flight hazard.
Accumulated ice can distort wing shape, potentially affecting the lift required to keep the plane in the air. A four-year EU-funded project has found a cost-effective means of rigorously testing aircraft for this threat.
Improved icing simulation
EU researchers felt that current research and testing techniques could be improved, if validation tests can be carried out as part of the certification process in wind tunnels. To be acceptable, this method would have to demonstrate that it was completely reliable and trustworthy. Furthermore, existing wind-tunnel techniques and numerical simulation tools would need to be significantly expanded to cover the more extreme SLD conditions.
“Aviation authorities require that aircraft have to be designed to fly safely in icing conditions,” explains project coordinator Guiseppe Mingione. “Recent aircraft incidents and studies have demonstrated that the icing certification envelope defined in the certification requirements should be extended to include SLD conditions. The objective of the EXTICE project was to improve the capability to simulate icing SLD so that their effect can be better taken into account in aircraft design.”
Launched in 2008, EXTICE has succeeded in improving such simulations, which will significantly help the development of safer aircraft and reduce development costs. The project compared ice accretion obtained in icing wind-tunnel testing to icing accumulated on a specific test article installed on an aircraft flying in icing conditions. The comparison was performed by using the same numerical code for the simulation of icing wind-tunnel tests and for in-flight icing.
A critical review of the results was then performed. The positive outcome achieved from the project means that it will soon be possible to reduce the number of flight tests by using more simulations during aircraft design and development.
“Each company – and each country – has a reduced budget for research activity these days,” points out Mingione. “European co-operation allows us to not only put together different competencies and expertise, but to also perform activities that would not be possible by a single company. It would not have been possible to perform this project without European Commission co-funding. EXTICE will bring benefits to the aviation industries, while all passengers will also benefit from the design of safer aircraft.”