Pain spells gain for the aeroplane

Engineers at BAE Systems have come up with a cunning way of cutting down on down-time whilst aircraft are taken out of service for safety checks

Researchers at BAE Systems’ Sowerby Research Centre near Bristol are taking their lead from mother nature and developing a technology which will enable aircraft to `feel’ pain and alert engineers to structural faults.

Large passenger jets are regularly taken out of service for safety checks, and while essential, this expensive, time-consuming process often merely shows that everything’s fine. Thus, a perfectly safe aircraft has been sat in a hangar while it could have been up in the air earning money.

BAE Systems’ solution to this, demonstrated at the Royal Society’s recent New Frontiers in Science exhibition, is a smart technology which uses an embedded network of sensors to diagnose the structure’s health and automatically identify exactly what work, if any, needs to be done.

BAE’s engineers are currently looking at incorporating two different kinds of sensor into this system.

Optical fibre sensors have been demonstrated as an ideal way of monitoring the stresses and strains on, for example, the wing of a plane. Ideal for embedding into composite materials, optical fibres are typically only 0.125mm in diameter, and therefore much more compact than traditional electrical devices like strain gauges.

These optical fibres are sensitised at pre-selected locations by imprinting a localised pattern, called a Bragg grating, in the core of the fibre. This invisible grating has the property of reflecting only a narrow range of wavelengths. Then, when the fibres are bent or twisted, as they would be during flight, the wavelength of the light they are transmitting is modulated according to the strain on the wing. This information can then be converted into readable data and used to tell the ground support crew what needs to be done.

While the cost of the optical fibre technology is currently high, Peter Foote of BAE’s advanced research lab expects things to change. `Thanks to the telecomms boom the cost of optical fibre is set to plummet.’ He also expects many other industries to embrace the technology and lower the cost further.

A further problem with composite structures is that rather than producing an obvious dent, impact can cause what is known as `barely visible’ impact damage. This undermines the structural integrity of an aircraft, but has always been particularly hard to find. The researchers’ solution has been to come up with a system of sensors that actually `listens’ for damage.

When a structure is damaged and under changing strain, the damaged regions generate faint pulses of sound. A carefully positioned array of piezo-electric sensors, all acting like tiny microphones, and all receiving the sound at different times, can be used to pinpoint the exact location of the damage using a signal processing triangulation technique.

Foote believes that it will be between 5 and 10 years before the technology begins appearing on production aircraft.

BAE Systems Tel: 01509 228491; Fax: 01509 211516

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