More efficient in-flight aircraft testing methods
EU-funded researchers are bringing important in-flight aircraft testing technologies from the lab bench to the production line, for substantial cost, time and safety benefits.
© AIM2 Project
All aircraft and aircraft structural parts have to be certified as flightworthy before they can be used in real operations. Flight testing is a key step in the certification process, but it is also one of the most expensive and time-consuming – and it has a significant impact on the environment, burning fuel and producing polluting emissions.
The EU-funded AIM2 project, coordinated by Fritz Boden of Germany’s DLR, is applying new and more efficient methods for measuring the behaviour of aircraft structures, and it is bringing these methods to the aircraft manufacturing industry where they are needed.
“Classical, physically based measurements, using pressure probes, strain gauges, accelerometers and the like, require a lengthy installation process and often irreversible modifications to the tested structures,” says Boden. “In contrast, the new methods we are applying under AIM2 are non-intrusive, they are optically based.”
Boden explains how researchers are using special camera installations and dot patterns, for example, to record the operation of aircraft propellers during flight tests. Then, with the help of powerful computer tools, researchers can analyse the resulting images to determine the shape and deformation of propeller blades in flight by means of a measurement system called Image Pattern Correlation Technique.
Other AIM2 testing methods involve fibre-optic sensors that can detect changes in pressure, strain and temperature. Infrared imagery is being used to visualise the surface temperature of wings and other flight structures, while laser technologies enable precise determination of air velocity.
AIM2 research represents the logical extension of previous work carried out under research done under its predecessor, the AIM project. AIM2 ends in September 2014.
“AIM demonstrated the feasibility of using optical measurement techniques in wind-tunnel and in-flight testing for certification,” Boden says. “With AIM2, we are continuing to make substantial improvements in the AIM technologies, but we are also taking the next important step, that is bringing these technologies from the lab bench to industry, to enable their more routine use for in-flight measurement and testing.”
Most of these techniques have been demonstrated in a research environment, says Boden, but they are not yet ‘user-friendly’ enough to be useful to technicians working in the real world.
“Therefore we are defining application rules and setup parameters for each technique,” he adds. “And we are preparing tools and software and a special handbook to help teach inexperienced users how to undertake advanced in-flight measurements properly.”
The project’s teaching exercise also included a flight-testing workshop in Poland in September 2013. There, AIM2 partners delivered presentations and demonstrated their techniques on a PW-6 sailplane at the Rzeszów University of Technology.
“The new AIM2 methods enable fast and cost-efficient flight testing and thus save time, money and fuel. The whole process requires less time at the flight test bed compared to conventional methods,” Boden says. “Furthermore, unexpected aircraft behavioural issues can be investigated in-situ, while the aircraft are actually in operation, impacting directly on flight safety.”
Boden says the AIM2 testing techniques can also potentially be used in other sectors, including wind turbine and automobile manufacturing and in the construction of tall buildings.
The new in-flight techniques have been assessed by AIM2’s industrial partners, including small aircraft manufacturers such as Evektor (Czech Republic) and Piaggio (Italy) and Airbus, one of world’s largest aircraft manufacturers based in Europe.