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Manufacturing the Eurofighter 'Typhoon' cockpit canopy
Manufacturing the Eurofighter "Typhoon" cockpit canopy
Keywords: Aerospace Composite Technologies, Manufacturing, Cockpit, Windshields
Aerospace Composite Technologies Ltd, a GKN Westland Aerospace company, has created a dedicated manufacturing cell based on a flow process design to ensure the efficient production of the Eurofighter Typhoon windshields and cockpit canopies. Aerospace Composite Technologies Ltd (ACT) has expanded its existing transparency capability through a £1.5 million investment on state-of-the-art handling, machining, product inspection and test equipment, which has helped ACT achieve exceptional levels of accuracy and repeatability during manufacture.
The processes involved in producing a defect free cockpit canopy are delicate and complex and the Eurofighter canopy design is one of the most demanding in the military aircraft industry. It is one of the largest single piece canopies in production measuring 2.6 metres for the single seat and 2.7 metres long for the twin seat variant. It also marks a watershed in transparency design in that it has to absorb significantly higher aerodynamic loads, making it play a greater structural role.
The process starts with billets of modified as-cast acrylic measuring approx. 2m square x 50mm thick. The billets are first placed in an oven and subjected to a heat cycle. Once the billet has the correct temperature profile it is placed immediately on to a bi-axial stretching machine. The material is then clamped around its edges and stretched to a finished size of approximately 3m. The process modifies the material's properties to make it more resilient.
Both sides of the acrylic sheet are then ground and polished to obtain an accurate optical finish. The sheet is then inspected for any optical distortion and internal material inclusions (voids, fibres, etc.). The sheets are then prepared for forming, a proprietary process developed by ACT. The prepared sheet is then formed into the three-dimensional shape of the Eurofighter canopy, using specialised tooling developed by ACT.
Following an initial edge profile the canopy is inspected for optical clarity using the "optical collimator". The equipment uses a number of lasers projected through the canopy on to photo-optic cells, these cells measure the canopies' optical properties for both monocular and binocular deviation typically over 800,000 recorded points across the critical optical zones of the front windshield and rear canopies. The optical collimator was installed last year at a cost of £0.3 million and performs this process in hours instead of days using previous conventional methods.
The canopy's next destination is the new »0.5 million five-axis, twin table CNC machine, which performs detailed machining and edge profiling operations. On completion the canopy is moved to a co-ordinate measuring machine (CMM) to inspect the machined hole locations and correct edge profile/tongue thickness, ultimately qualifying the products inter-change ability.
From here the canopy enters the polishing bay where it is polished and given a pre-coating clean.
It then enters the clean room for the crucial stages, in which ACT's proprietary low observable coating system is applied. To maintain an ultra clean, dust free environment ACT has created a clean room within the clean room, housing a coating vacuum chamber, and other facilities crucial to maintain the canopies' high optical performance.
Once coated, the canopy undergoes final inspection and is prepared for shipment.