The University of Ghent uses GEN5i from HBM to measure the impact of bird strikes

Bird strikes are being simulated in the laboratory of the Department of Applied Materials Science at the University of Ghent in order to gain insight into the consequences of bird impacts with aircraft. The collisions are set up not only to test materials and parts but also to set technical design constraints for minimising the effects of bird strikes. The testing facilities have been expanded now that the laboratory is going to participate in the European commission’s E-Break project. To assist in the project, the university has acquired an HBM GEN5i data recorder (meanwhile the successor model GEN7i is available), which has been specially developed for data acquisition at extremely high speeds.

“Bird strikes can have fatal consequences for aviation”, says Geert Luyckx, who supervises the laboratory’s contribution to E-Break. “A collision with a bird doesn’t itself necessarily cause a lot of physical damage, but even a slight imbalance in an aero engine can eventually lead to severe damage to and failure of the engine. Investigating the consequences of bird strikes in aviation has been part of extensive test procedures for many years.”

The department has gained a considerable reputation for analysing the consequences of bird strikes. A test facility was built in 1997 in the context of ‘Experimental simulation of birdstrike on airplane parts’ (part of the European BRITE-EURAM II project). Initial simulations were only of strikes by birds weighing 500 grams, but the facilities have been expanded for the new project to handle impacts by birds of 1.8 kilos, equivalent to the weight of a duck. There are also tests with weights of four kilos, equivalent to a goose. Although the aviation industry conducts tests using real birds, the laboratory in Ghent uses blocks of gelatine, which have similar mass and behaviour. The gelatine is cast in a bullet-shaped mould and then shot at the test object. The tests are standardised and are carried out in accordance with the specifications of aircraft manufacturers such as Airbus.

Simulated bird strikes: The entire test is recorded on video.

Test set-up: A number of quantities can be measured during the simulated bird strikes

“The test set-up in the laboratory is quite simple”, explains Frederik Allaeys, who is responsible for performing the tests. “The bullet-shaped bird is loaded into a tube and shot out at a pressure of some 30 to 40 bar, which gives it a speed of 200 to 250 metres a second. At the end of the tube is a metal chamber containing the part to be tested. This could be complete components, fan blades or plates made from new types of material. There is underpressure in the chamber in order to reduce air resistance, and the effects of the pressure wave on the measurement. Before entering the chamber the bird passes through a stripper that removes the sheath from the block of gelatine.”

A number of quantities can be measured during the simulated bird strikes: the bird’s speed and acceleration, the pressure, displacement, vibration and impact of the strike, and possibly the amount of stretch and deformation of the materials. The entire test is recorded on video. Preparing a test takes about a day and the average cost of each one is some 1500 euros. Each test is performed twice to validate the results. It is very important for the progress of a test to be recorded and analysed accurately, which is difficult to do for an event that lasts only about two seconds. To do this the university needed a data acquisition system that could not only collect and process data from multiple measurement channels simultaneously, but could do so at very high speeds. The trigger in such tests is crucially important in starting all recording simultaneously and on time.

GEN5i: high-speed data acquisition

The University of Ghent bought an HBM GEN5i for the project. According to Frederik Allaeys, this data acquisition system was chosen in particular because of its modular structure, which allows cards for different applications to be added easily. The GEN5i is a complete, portable data acquisition system that has been specially developed for high-speed data acquisition with sampling rates of up to 100 megasamples per second. It can be expanded to a maximum of 160 simultaneous measurement channels, and is therefore suitable for complex measuring set-ups. The laboratory in Ghent uses an average of ten to fifteen channels and sampling rates of up to 25 MS/s.

The GEN5i data recorder is a complete computer containing an integral hard disk for storing data. This data can be sent for further analysis via standard interfaces such as WLAN, Gigabit Ethernet or USB. In addition, the standard configuration of the recorder includes various filters, as well as HBM’s Perception software for the processing, analysis and visualisation on the screen of an enormous amount of measurement data. The GEN5i is a transient recorder, which records extremely fast and one-off signals. This type of signal is often characteristic of destructive material tests, fire tests and high voltage. The recorder can be configured and started quickly, thanks to its simple user interface and proprietary software.

HBM GEN5i data recorder, in front of the test preparation.

Bird strike analysis as part of the 'E-Break Project'

The specially configured measurement set-up in the laboratory at the Department of Applied Materials Science will be contributing to the E-Break project, which runs from October 2012 to September 2016 inclusive and is financed by the European Commission. “E-Break has been set up to limit the emissions and noise nuisance caused by aviation”, explains Frederik Allaeys. “Aero engine manufacturers try to optimise the efficiency of their engines in order to minimise the emissions of CO2 and NOX, as well as reducing fuel consumption and maintenance costs.

This has led to the development of high-pressure engines, which are not only as much as 50% smaller but rotate considerably faster and generate much higher temperatures. This affects engine design and the materials used, as the engines have to be extremely sturdy but must not be any heavier. New composite materials and titanium-aluminium alloys have been introduced to accomplish these goals. The technology, materials and components that are crucial for the development of this new type of engine are being tested in the context of E-Break. The bird strikes are only a small part of the project, but will provide essential information for the design and the safety of the new generation of engines and their components.”

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