Probing the details

Probing the details
Published: 26 November 2017 - 5:40 a.m.

Over 114 years, aircraft structures of wood and cloth have been replaced with complex alloys and composites, and internal combustion engines with highly efficient gas turbines. One area which remains as important as ever, however, is safety and the significance of maintenance and testing in ensuring the continued success of flight.

The requirement for testing of critical structural components of both commercial and military aircraft has increased significantly. Regular inspections of hundreds of critical areas on each aircraft, as well as careful attention to quality assurance in the manufacturing process are essential to maintaining the aerospace industry’s outstanding safety record.

Aircraft manufacturers and operators use a variety of non-destructive testing (NDT) methods and other inspection technologies in these examinations, with different methods being best suited for specific tasks in different areas, and these are recommended accordingly in the corresponding manufacturer’s test procedures and service bulletins.

Aircraft which were once maintained retrospectively, are now designed with inspection in mind. Access ports are introduced into the design at engineering stage, meaning that areas hard to reach can be inspected with the use of specialist equipment with little or no need for disassembly, helping to remove the element of human error, increasing the ability to maintain a high level of safety; leading to lower down time and maximum operational capabilities for both airlines and military organisations alike.

In the last decade the requirement for advanced Remote Visual Inspection (RVI) in the aerospace industry has rapidly evolved. RVI extends the reach of the human eye into small, enclosed spaces that otherwise cannot be seen, using a combination of CCD, LED and video-capturing technologies.

A slim and highly flexible viewing device is inserted into the area of interest through a small opening and guided by the operator with a joystick, providing a bright, clear image for the operator to view.

By far the most common application of RVI within the aerospace industry is in the inspection of gas turbine jet engines, predominantly for inspection of turbine blades, compressor blades, combustion chamber liners, fuel nozzles, and other engine components for potential problems including combustion deposits, erosion, surface cracking, and foreign object impact damage, as well as for inspection of inaccessible areas of airframe for visible corrosion and cracking.

A gas turbine is subjected to extremely high temperatures– at take off, the RB211-524 used to power a 747-300 reaches temperatures in excess of 1,400°C at 430psi. At these temperatures, there is the potential for parts of the engine after the combustion section where ignition takes place, to melt instantly, if it were not for the clever design of the components which make up this turbine section.

Each component is covered in a special plasma based ‘thermal barrier coating’ and hundreds of small holes are designed into the components–specifically nozzle guide vanes and turbine blades–allowing a cushion of comparatively cooler air to pass over the components thus protecting them from this possibility.

Of course, the potential for these cooling holes to become blocked can lead to portions of these turbine blades to become damaged, and the aerospace industry has a number of guidelines in place to confirm how large a defect can be before it becomes adverse to safety. As such, during routine inspection, these defects (if any) are monitored using RVI techniques and measured to determine if the aircraft can be deemed airworthy again.

Gas turbines present a challenging environment in which to work with a videoscope or video borescope, with some areas being highly reflective, such as turbine blades and burner assemblies; and some areas extremely dark, such as the combustion chamber, nozzle guide vanes and areas of the turbine. Capturing a sharp and clear image in these areas is equally difficult. Certain advances in RVI technology have helped improve workflow, providing inspectors and operators with an easier platform to obtain the best possible images.

With the launch of Olympus’s IPLEX RX early this year, this issue of different requirements for both bright and dark areas was solved overnight, meaning that inspectors could move from dark matte sections within an aircraft, to inspect highly reflective components with no requirement for change.

With the launch of IPLEX RX, Olympus unveiled a new processing technology named PulsarPIC. PulsarPIC worked with the CCD sensor, the processor and the new, high powered illumination system to automatically adjust physical light output, CCD exposure time and electronic gain. In darker areas, more light is released along with more gain and a longer exposure time, and in brighter, more reflective areas, less light is used, a lower exposure is used and less gain is required. This intelligent adaptation allows for much more efficient defect inspection delivering high quality high resolution results every time.

In May this year, the IPLEX RX received an important update and Olympus launched a new version of the highly acclaimed 3D Stereo Measurement Technology, allowing an inspector to quickly and simply calculate the depth, length, area, perimeter and perpendicular distance, all from the touch of a joy stick.

The inclusion of proprietary SPOT Ranging technology provides the inspector with a simple traffic light display giving a clear indication of when the scope is positioned correctly in order to obtain an accurate measurement and a new feature was added, allowing an inspector to navigate more easily to a target with single screen viewing, without the requirement to operate in the binocular view associated with stereo measurement of the past.

This update has been extremely well received industry wide and changes the way in which inspection can be carried out to this high level. Where historically, large equipment was required weighing in excess of 20kg in certain circumstances, the IPLEX RX provides this full functionality, with the industries highest resolution images in an extremely portable package weighing in at less than 2.7kg.

It takes working with large players within the aerospace industry, in commercial, private and defence sectors, for companies such as Olympus to gain a more intrinsic understanding of the requirements within the sector. As technology evolves, and more efficient and functional equipment becomes available, our instruments will be able to contribute to the quality of products and add to the safety of infrastructure of their customers on a global level.

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