Aircraft engine maintenance: it’s a bug’s life

With sensors and motion control now able to exist in miniature, is it time to use the advantages of digital tools to change the way that aeroplane engines are maintained?

The first thing to acknowledge is that anyone running a fleet of aircraft wants them in the air, not in a hangar being maintained. This forms the basis of Rolls-Royce’s IntelligentEngine programme, which aims to use the developments in hardware and digital technology to fuse product and service together. The result, ultimately, should be an engine that safely spends most of its time in the air.

While static sensors have played an increasingly important role in monitoring engines and therefore optimising maintenance schedules, the tools in the IntelligentEngine programme are considerably more dynamic. Not only can they seek out the problems, they can – in their various animated forms – fix them, too.

It should be stated that the ideas described here are at various stages of development. Dr James Kell, Rolls-Royce on-wing technology specialist, says: “While some of these technologies, such as the Swarm robots, are still a long way from becoming an everyday reality, others, such as the remote bore-blending robot, are already being tested and will begin to be introduced over the next few years. We have a great network of partners who support our work in this field and this is an area with the potential to revolutionise how we think about engine maintenance.” 

Closest to adoption is a bore-blending robot that can be remotely controlled by specialist engineers at a central operations centre. The problem it is designed to resolve is the in-situ repair of compressor blades inside jet engines. These are subject to large volumes of air flow and can sometimes incur edge damage, which can be dangerous if left untreated. Repairing the blade in-situ is by far the most cost-effective approach.

However, in-situ inspection and repair of jet engines are inherently difficult due to restricted access to internal components. Usually, the mechanic uses bore tools to manually enter the engine via an inspection port that is typically 9mm in diameter.  It is dark inside the engine, so orienting and manoeuvring the tools is very challenging.  

‘Robotics is an area with the potential to revolutionise how we think about engine maintenance.’

The robot, developed by the Rolls-Royce-led team with the University of Nottingham, has been dubbed ‘Reiner’. It comprises a combination of rotary, prismatic and flexible joints, and was designed to replicate the degree of freedom of hand-held tools to repair a compressor blade in a matter of minutes rather than days. 

At the end of the collaborative project, which was part-funded by Innovate UK and the Aerospace Technology Institute, the prototype was demonstrated on an engine in a Rolls-Royce facility, a world first for this type of repair task. The probe is based around an off-the-shelf dental motor, so it can carry interchangeable tools, meaning the robot could eventually be used to perform a greater range of tasks for other sectors too.

“There is a substantial financial incentive for in-situ repair of industrial assets such as jet engines,” explains Dragos Axinte, professor of manufacturing engineering at the University of Nottingham. “However, the need for highly trained mechanics to travel to the location of a repair often results in inconveniently long downtimes.  

“The emergence of robots capable of replicating human interventions on industrial equipment can be coupled with remote-control strategies to reduce the response time from several days to a few hours. As well as with any Rolls-Royce engine, our robots could one day be used in other industries such as oil, gas and nuclear.” 

Another bio-inspired element in the programme is ‘Flare’, in which a pair of flexible ‘snake’ robots will travel through an engine, like an endoscope, then collaborate to carry out patch repairs to damaged thermal barrier coatings. This project is still under lab testing. 

‘Inspect’ is a network of ‘periscope’ optical sensors permanently embedded within the engine, enabling it to inspect itself to spot and report any maintenance requirements, which they report back to the operations centre. These pencil-sized robots are thermally protected from the extreme heat generated within an engine and the visual data they create would be used alongside the millions of data points already generated by today’s engines as part of their engine health monitoring systems.  

Probably the most engaging of the set, although furthest from practical application, is ‘Swarm’ – miniature bots, around 10mm in diameter, that would be deposited in the centre of an engine via a ‘snake’ robot. They would then perform a visual inspection of hard-to-reach areas by crawling through the engine. These robots would carry small cameras that provide a live video-feed back to the operator, allowing them to complete a rapid visual inspection of the engine without having to remove it from the aircraft. The University of Nottingham is currently applying for research funding with Harvard University to bring the concept to life.

Harvard has expertise in miniaturising robots, but it is not down to the 10mm unit yet. Sebastian de Rivaz, a research fellow at the university’s Wyss Institute, describes the state of the art robot: “Our robot has four legs and is bio-inspired; we took inspiration from the cockroach to develop this over the past eight years. It weighs 1.5g and it’s about 4.5cm long. We want to develop manufacturing segments that allow us to build the robots at smaller and smaller scale, so what we’ve been focusing on are the manufacturing techniques.  

“This is not a finished product right now; it’s still undergoing research. But we’re hoping to not only scale this down so that we can put it in the end of endoscopes but also start mounting cameras on them, increase the number of sensors so that we have this kind of intelligent behaviour of the swarm of robots.”

Such technologies could revolutionise engine maintenance. No longer will teams of specialists need to be flown round the world to repair engines. Local staff will insert devices that feed information to and are controlled from a single site, repairs effectively being carried out remotely.

Savings in time and money would be considerable, but more importantly it would ensure maximum availability for keeping those aircraft engines in the air.