Eurofighter Typhoon Goes Ultrasonic

Flying close to the speed of sound in a ground attack role or rocketing to 1500mph ten miles high in air-to-air combat, the Eurofighter Typhoon will take some of the toughest punishment ever handed out to a military aircraft.

Designed to replace the RAF’s ageing Tornado F3s and Jaguars, much of Eurofighter’s strength is due to the use of advanced materials in its construction.

The plane’s airframe is 60% carbon fibre laminate (a composite of carbon fibre laminated with a matrix of thermoplastic resin), a higher percentage than for any comparable machine currently in production, and the use of this strong material ensures lightweight construction as well as enhancing performance.

However, close attention must be paid to the structural integrity of this material, as internal imperfections such as voids, de-laminations, foreign body inclusions or porosity can compromise mechanical strength. To avoid potentially catastrophic failure great care is taken to detect and eliminate any such imperfections before they reach the assembly line.

A major element of this inspection regime is a 2×5 axis ultrasonic scanning rig able to position and simultaneously scan large panels with complex contour geometry. At the heart of this rig is a 3-axis panel component holding system designed and built by Basingstoke based Time & Precision Industries. This system positions components in a range of attitudes to allow a complete raster scan to be made on even the most complex multi-contoured mouldings.

Because ultrasonic energy cannot usually be propagated through air, water is used as a coupling agent. It is therefore critical to ensure accurate relative positioning of the ultrasonic transmission and receiving heads with minimal adjustment time and a high degree of repeatability. To meet these demanding conditions, the entire unit is designed to operate reliably to a high degree of repeatability in a water-drenched environment.

The use of ultrasound in (Non-destructive Testing) NDT applications isn’t new to BAE Systems, but with over 90 different components of all shapes and sizes requiring inspection, and Eurofighter production calling for around 450 panels per month by 2002, a highly adaptable production machine was needed.

The scanning rig is able to scan the entire range of components from air brake shell to the large 4×1.5 metre cockpit side skin. The system incorporates a positioning and holding fixture with a lateral X-axis, fore and aft Y-axis and vertical axes Z1 & Z2. The X-axis is belt driven with a parallel slave follower unit. Drive is via a Parker HLE100 belt drive with a 4 metre travel. All axes are powered by Parker MD3450 IP65 rated brushless servo motors with integral absolute encoders for closed loop feedback, and positioning is via a Parker BDHX75 servo drive unit controlled through an industrial touch-screen PC.

Extensive use of existing off-the-shelf components – like the MiniTec modular construction system – is said to have reduced design time and avoided costly budget over-runs.

Time and Precision Tel: 01256 328428

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