Pushing the boundaries of bearing performance

Jon Lawson

By monitoring super precision bearings with smart sensor technologies, aircraft operators can estimate the useful remaining life of bearings, enabling service intervals to be extended and maintenance costs reduced, says Jon Everett

Bearings for aviation and aerospace applications have to withstand harsh conditions: extreme temperatures, demanding load profiles and high speeds, as well as being lighter (higher power density) and able to fit into increasingly smaller design spaces.

Each bearing is custom engineered and manufactured for a specific aerospace application. These bearings are becoming more specialised in order to cope with greater payloads and more sophisticated aircraft control systems.

Over the years, Barden has supplied bearings for a variety of auxiliary aircraft positions including navigational gyroscopes, air cycle machines, actuators, starter generators, hydraulic pumps and cabin fan bearings.

Predictive maintenance

There is also a trend towards predictive maintenance and how this technique can help to extend the service intervals of aircraft systems and components. This means suppliers such as Barden need to provide bearing solutions that are highly reliable and able to withstand such extreme, harsh environmental conditions.

The future will almost certainly see an increase in the use of combined bearing and smart sensor technologies in order to provide a basis for predictive maintenance.

Although Barden has always pushed the boundaries of bearing performance to their limits, the use of appropriate and reliable sensor technologies may well enable these boundaries to be pushed even further in the future.

The key is to find new ways of ensuring increased reliability of onboard systems without having multiple redundant systems on the aircraft.

Predicting the life of aircraft starter/generator bearings

Barden UK is currently involved in Clean Sky 2, a European research programme that began in March 2016. The aim of this two-year project is to identify the safe lifetime of engine starter/generator bearings for aircraft by applying diagnostics and prognostics.

The ultimate objective is to improve the safety of aircraft and reduce maintenance costs.

Starters/generators are a key part in aircraft engines and operate under exacting conditions, including extreme temperatures, pressures and constant vibration.

Bearings are fundamental to this application. With the current trend of increasing the starter/generators rotation speed for weight reduction, expectations of the bearing performance are increased.

Currently, bearing wear is mitigated mainly by applying preventative maintenance. Implementation of health monitoring on the bearings will lead to a higher availability of the starter-generators, along with optimisation of the maintenance tasks.

Partners on the programme include Barden UK and FAG Aerospace Germany (bearings), Active Space Technologies (sensors) and Cranfield University.

By applying diagnostic and prognostic tools, the partners hope to estimate the safe lifetime for a bearing, as well as accurate and timely fault diagnosis. This will enable operators to plan maintenance more effectively than is currently possible.

At present, the bearing technical specification has been agreed and sensor choice defined. The next steps include developing appropriate system architectures and specific software algorithms for data analysis, diagnosis and the estimation of remaining useful life. In the longer term, a prototype will be constructed and tested at the facilities of FAG Aerospace in Germany.

Satellite applications

Another key growth market for Barden UK is satellites and space applications. Traditionally, building and launching a satellite was a multi-million pound investment, but more recently, the size and cost of a satellite have reduced.

One area Barden UK has been heavily involved in is the reaction wheel of a satellite.

A reaction wheel is a type of flywheel used primarily by spacecraft and satellites for altitude control without using fuel for rockets or other reaction devices. They are particularly useful when the spacecraft must be rotated by very small degrees. They may also reduce the mass fraction needed for fuel.

This is accomplished by equipping the satellite with an electric motor attached to a flywheel which, when its rotation speed is changed, causes the satellite to begin to counter-rotate proportionately through conservation of angular momentum.

The failure of one or more reaction wheels can cause a satellite to lose its ability to maintain position and thus potentially cause a mission failure. Therefore, the reliability of reaction wheel bearings is absolutely critical.

The bearings are custom engineered with high surface finish requirements and visual appearance of the raceways.

The bearings are also assembled in clean room conditions (exceeding flight-critical aerospace applications) using special handling techniques and are supplied to the customer with full data traceability.

Other key growth markets

Outside of aerospace, Barden UK also predicts a growing demand for its products in industrial markets. Industrial robotics, for example, is a market that will require more sophisticated high precision bearings as the robots themselves become more complex and diverse in their movements.

Global presence

Barden and its sister company FAG Aerospace are both situated within the Aerospace Business Unit of their parent company Schaeffler. Both companies work closely together on joint development partnerships with technology leaders in the aviation and aerospace industry. Their customers are world-renowned manufacturers of aircraft, aircraft engines, helicopters, space launchers and satellites.

Jon Everett is Managing Director of The Barden Corporation (UK) Ltd.

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