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Historic aircraft restoration

 
Published on 17 January 2012
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The magnesium Spitfire canopy hoop (a) under repair at TWI
The magnesium Spitfire canopy hoop under repair at TWI

The Aircraft Restoration Company and TWI, joined forces in a combined effort to restore a second world war Spitfire with a damaged canopy frame.

Now owned by Rolls Royce, the aircraft is the subject of a major re-fit at ARC's headquarters at the Imperial War Museum at Duxford. The manufacturer was Supermarine Aviation and it was built in 1944 at Castle Bromwich, after which it served one year of active service.

The component needing TWI's expertise was a badly cracked hoop-shaped magnesium casting designed to support the cockpit glass. It was repaired using a welding process which had not been invented when the aircraft was manufactured, namely alternating current tungsten inert gas using an AZ92 magnesium 2.4mm diameter electrode consumable.

Unlike most of the marque this Spitfire was unarmed and featured a pressurised cabin and an appropriately modified rear bulkhead because it was designed specifically for photo reconnaissance above 40000 feet.

The aircraft's construction is largely aluminium, steel and rubber. Titanium was in its infancy in 1940s aviation manufacture and is absent from the Spitfire's design. This example, a Mk XIX, is powered by a Rolls Royce Griffon, a 36 litre V12 engine, bigger than its 27 litre cousin, the Merlin.

The Spitfire is one of the very early aircraft to embrace stressed skin design and is of largely riveted construction. Welding is limited to minor parts with little or no structural role.

 

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The magnesium Spitfire canopy hoop being positioned for installation at ARC
The magnesium Spitfire canopy hoop being positioned for installation at ARC

The cockpit is not structurally enhanced to accommodate pressurisation. There is also a hole in the aircraft belly where a very large format camera would have been installed. Some Spitfires also had side pointing cameras. Sometimes the aircraft would be flown at very low level through sensitive enemy installations and pictures would be taken horizontally or while banking. The Spitfire also features one of the earliest engineered applications of composites, namely Tufnol, a cotton matrix with a phenolic resin binder which makes a very stiff material.

For further information read about TWI services to the Aerospace industry or contact us.

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