Airbus to cite structural analysis and production line improvements to ensure certification after “rupture”
Following the failure of an A380 wing during ultimate-load tests last week, Airbus must convince authorities that the A380’s structure complies with certification requirements through analysis of structural calculations combined with data on the improvements introduced on production A380s.
The wing of the A380 static test specimen suffered a “rupture” below the ultimate-load target during trials in Toulouse, but Airbus is confident that it will not need to modify production aircraft.
After completing limit-load tests (the maximum loads likely to be encountered during normal service) on the A380 static test airframe, progressively greater loads are applied up to 150% of limit-load, which is defined as ultimate load. Engineers develop finite element models (FEM) to calculate the load requirements.
“The rupture occurred when we were stepping between 1.45 and 1.5 times the limit load, between the inboard and outboard engines,” says Airbus executive vice president engineering Alain Garcia. “This is within 3% of the 1.5 target, which shows the accuracy of the FEM.”
While this type of failure has precedents, experts say the aim in such tests is to reach the ultimate-load target, without failing, before testing to destruction. Garcia says the trial was an “extremely severe test during which a wing deflection of 7.4m [24.3ft] was recorded” and that the A380 wing was designed to have “no margin” at ultimate load. “We had a weight-saving programme and ‘played the game’ to achieve ultimate load,” he says.
The European Aviation Safety Agency (EASA) says the maximum loading conditions defined for the A380 certification state: “The aircraft structure is analysed and tested to demonstrate that the structure can withstand the maximum loads, including a factor of safety of 1.5.”
Garcia says: “We will use this calibration of the FEM to prove the adequacy of the structure on production aircraft,” adding that “essentially no modifications” will be required for production aircraft: “We have refined the structural design for subsequent aircraft due to increased weights, etc.”
Jonathan Howes, technical director of UK-based certification consultants AeroDAC and, until recently, leading structures certification specialist for the A380 at the UK Civil Aviation Authority, says the rupture “was so close to the ultimate target that it is almost certain to allow approval to be given without the need for a re-test, but this will be subject to a negotiation between Airbus and EASA”.MAX KINGSLEY-JONES / LONDON
Blog:Read Flight international's commercial aviation editor Max Kingsley-Jones explain how Airbus broke the story of how it broke the wing.