Enhanced aircraft safety in case of lubricant failure
Imagine you’re aboard a plane, enjoying the view through the window. Suddenly, an engine stops working. Should you panic? Well, it depends on the reliability of the airplane’s journal bearings. If they fail to keep the aircraft fan rotating, it will inexorably result in huge drag on one side of the aircraft, and a potential crash. Preventing these fans from stopping is the ultimate objective of the AOrbit project. More concretely, the team led by Professor Seamus Garvey – Professor of Dynamics at the University of Nottingham and Director of the Gas Turbine and Transmissions Research Centre della Rolls-Royce University Technology Centre – aims to enable highly durable surfaces on highly-loaded journal bearings. Such technology would allow the journal bearings to keep operating for several hours even after a failure in lubricant supply. “This value of several hours is important. It is enough for an aircraft to get to a safe place once a fault has been detected,” Prof. Garvey explains. To get there, the team’s first and most challenging task lay in developing a testrig for journal bearings. “We didn’t have to design the actual coatings but rather to produce a testrig that can cater for coatings of many different types. We have made extensive use of external design contractors to develop the rig, all this while ensuring that where work is devolved, responsibility for checking that work also is. The engineering is relatively straightforward – but it’s a lot of work,” Prof. Garvey says. The team is currently still in the stages of rig commissioning due to several delays, but they have already learned much about how to configure it. As soon as it is up and running, they intend to start comparing different bearing surface coating types to support the development of suitable bearing systems. The ambition is clear: allowing for high-performance, high-reliability and low-weight speed reduction gearboxes for the ultra-high bypass ratio aero-engines of the future. Solving the ‘several hours durability’ issue is critical to aero-engines which rely on a gearbox to transform rotational speed for a propulsor. “This matters for the geared turbo-fan engines, geared propeller drives and open-rotor machines. But that’s not all. It will also matter for many ‘electrical drives’,” Prof. Garvey adds. There are two schools of thought in the field of electrical drives: the use of direct drive, and the use of geared drive. The latter – which will be highly reliant on highly-loaded journal bearings if the planet gears of an epicyclic gearbox are to turn relative to their respective axes – seems to be on track to take over the market. AOrbit research is expected to play a key role in their success. Although the project is still in its early stages, the team is already planning to build a more versatile bearing characterisation testrig. This new rig will be used to assess the durability and dynamic stiffness of bearings under various loading conditions.
AOrbit, journal bearings, lubricant, engine failure, testrig, aircraft