Small components with a big effect

New procedure to improve Shop Replaceable Units

The Boeing 737 series, developed as long ago as the 1960s, and the Airbus A320 range, designed in the 1980s, are the world's most successful commercial airliners. Together, they make up approximately 65 percent of all commercial aircraft in current deployment. Although both ranges have been subject to recurring modifications and improvements over the years, many of the components and items of equipment in use today have a design age of more than 30 years. Similar can also be said of the repairs, which even today are carried out using materials and procedures based on the initial OEM design. The development of new repair procedures therefore offers substantial potential for savings and optimisation in terms of weight, durability and repair costs.

Lufthansa Technik initiated the "AIRtech - Advanced Innovative Repair Technologies" research project in order to exploit this potential in the future. The project is focussed on researching innovative repair technologies and methods to improve SRUs (Shop Replaceable Units) by using modern materials, manufacturing techniques and construction methods. SRUs are faulty components which are removed from equipment and directly replaced with other stock SRU components that have already been repaired. The term "equipment" is used to refer to all components in an aircraft which perform a transformation of signals, materials or energy. This includes refrigeration turbines in the air conditioning as well as starter motors for jet engines and hydraulic systems. Faulty equipment components, such as housing, bearings and shafts, are repaired and refinished in the workshops so as to fulfil the demanding requirements of flight operations.

The research project began by making a detailed selection of eight different components. Amongst the components selected is a mounting for an electric motor that drives a pump in the aircraft hydraulic system. Compared to the OEM mounting, the new motor mounting has improved geometry, is made either of composites or aluminum, is cheaper to produce and repair – thanks to its modular construction – and is 65 percent lighter. After a precise examination of the geometry, the production of several demonstrators can begin. With a fiber-reinforced composite, the finer type and laminate structure can be precisely defined, allowing for appropriate optimization of the geometry. Concluding stress tests can be used to confirm the preliminary calculations.

A further component that is in the focus of the research project is the cooling fan rotor. This component serves to ensure the air supply for the aircraft cabin during surface operations. Until now, it has consisted purely of an aluminum alloy; in the future, a titanium alloy shall be used. As titanium shows greater rigidity than aluminum, a significantly longer product life can be expected for the component. Structural adjustments to the geometry and thickness means that the weight has barely changed compared to the original component, even though the density of titanium, at 4.5 g/cm ³, is significantly higher than that of aluminum (2.7g/cm ³).

Significant weight savings have also been achieved with the vacuum generator, a pump used to create a static pressure difference between the cabin and the waste water container. The new component is produced from plastic using a generative production technique ("3D printing"), with improved geometry and wall thickness. Selective laser sintering is used to locally melt and fuse a plastic powder, creating the new component layer by layer. The component, until now made of an aluminum alloy with substantial production overheads, will in future consist of polyamide plastic. This material is not only 50 percent lighter than aluminum; it is also so economical to produce using this generative technique that in the future, faulty components will not need to be repaired but can be replaced with a new component where needed. Beyond this, the plastic is less subject to chemically induced corrosion.

For customers, the improved durability and weight reduction in components result in reduced fuel consumption and a significant cost reduction for airline operations. Maintenance costs also sink, meaning a further reduction in operating costs. As it has been demonstrated that the replicated components are either the same as or better than the OEM components in terms of geometry, fit, function, rigidity and safety, the aviation authorities can certify them directly. Lufthansa Technik is joined by strong partners in this project: the Hamburg University of Applied Sciences, the Helmholtz-Zentrum Geesthacht and the Plastics Competency Center (Kunststoffkompetenzzentrum) at the Lübeck University of Applied Sciences. The AIRtech research project, launched at the start of 2012 and running until December 2013, is funded by the Department of the Economy, Transport and Innovation of the City of Hamburg.