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09/03/2011
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In a combined effort to keep the world's oldest flying jet aircraft working, 1940s engineering and 2011 welding expertise have joined forces at manufacturing, engineering, materials and joining specialist TWI.
 A thin sheet stainless steel shroud surrounding the jet pipe of a North American Aviation F-86A Sabre jet fighter was in need of some specialist attention when it was delivered to TWI. The purpose of the shroud is to deflect any leaking exhaust gases away from the internal structure during the brief period, between start up, and the engine reaching running temperature, when previously weeping seals around the jet expand and become leakproof.
Although within limits, several small cracks and tears were in need of attention during the Sabre's annual maintenance if the aircraft was to achieve its Permit to Fly. Because there is no direct civilian equivalent, such historic ex-military aircraft fly under this permit system rather than the Civil Aviation Authority's certificate of airworthiness.
"It's very tricky to weld materials like this but we're lucky here at Duxford," said Roger King of the Aircraft Restoration Company. "TWI's experts are almost on our doorstep. Its arc welding department had exactly the skills we required and offered to help us out."
Using TIG welding, and an appropriate consumable for the aged material, TWI was able to arrest and repair cracks in the wafer thin material.
"It's not a structural part," clarifies King. "It is a heat deflector.
Had it made a structural contribution a more rigorous and detailed procedure would have been demanded. New parts no longer exist for this aircraft so the only alternative to repair would be to remanufacture from scratch."
The cracked state of the shroud has been attributed to strain and thermally related fatigue. During its 64 year life the component would have endured many thousands of heating and cooling cycles. "The Americans are very good at mass production," says King. "The part was probably rolled and formed in mass production back in the forties. Nowadays a replacement would have to be hand beaten."
The Sabre is best known for its service in the Korean War where it was pitted against the Soviet MiG-15.
The Golden Apple Trust, which owns the Sabre believe it to be the oldest airworthy jet powered aircraft in the world - its first flight was in March 1949.
The Sabre is expected to be back on view at its Duxford base by April 2011 and will be flown at many British and near European air shows this summer.
Image courtesy of gadgetophilia.com
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Author
Chris Shaw
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