Frozen chickens have an unusual role to play when it comes to ensuring the safety of aircraft. They are used to simulate high-speed bird strikes when testing new wing and fuselage designs.
This gives designers useful information about how the aircraft is damaged. A team at the University of Limerick is working on alternatives, based on computer modelling, which can predict how aircraft components will perform before they are built.
The university is involved in two EU-funded projects related to aircraft safety, explained Dr Michael McCarthy of the Mechanical and Aeronautical Engineering Department. He leads a €2.2 million project that involves building computer models for complex bolted aircraft joints and he is also one of five "work-package leaders" on a €5 million project named CRAHVI, Crash-worthiness of Aircraft for High Velocity Impact.
Both projects aim to make aircraft crashes more survivable. As part of this the researchers want to find computer-based methods for simulating how components respond in crashes. "If you can understand how the structures perform, then you can design a safer structure," Dr McCarthy explained.
The first project is called BOJCAS, Bolted Joints in Composite Aircraft Structures and involves 11 partners including Airbus UK, SAAB and EADS Airbus. The team at UL includes Dr Gouri Padhi, Mr Walter Stanley, Mr Vincent Lawlor and Mr Conor McCarthy.
Modern aircraft are made of lightweight but very complex composite materials which bolt together in complicated ways. The UL team is working on software that will model how a joint will perform before it is built.
"What we are most interested in is, if you have a complex part with many bolts, the load may not be distributed evenly between the bolts," Dr McCarthy explained. One or two bolts might come under particular stress because of the joint geometry and the software predicts the ones at greatest risk of failure.
UL compares its computer-model results against experimental work which confirms the model findings. The goal is to produce a software package that can create new models for any joint design.
Similar work is underway at UL as part of the larger CRAHVI project which is led by Airbus UK and has 20 partners including most of Europe's commercial aircraft manufacturers. The work at UL is headed by Dr McCarthy, assisted by Dr Jiarun Xiao, a postdoctoral fellow from the People's Republic of China.
The project addresses the threat to aircraft from relatively high-speed impacts with foreign objects as well as survivable crash landings on different surfaces.
The UL models predict how individual components and component groups perform under various conditions, Dr McCarthy explained.
Aircraft cannot be certified until they have gone through a battery of tests including simulated bird impacts. Lab-based impact simulations are expensive and time consuming however and the models will help lead to the best designs more quickly. "If you can produce modelling techniques which are accurate enough, then you can reduce the number of tests you have to do," Dr McCarthy said.
Modelling complex structures involves breaking a virtual aircraft down into smaller parts - for example the leading edge of a wing - and then producing a model for each part. There is a modelling equation for each structural part and other members in the research group then carry out physical experiments to confirm the model results.