The wing of the Airbus A380 static test specimen suffered a structural failure below the ultimate load target during trials in Toulouse earlier this week, but Airbus is confident that it will not need to modify production aircraft.
The airframer has been running load trials on a full scale A380 static test specimen in Toulouse since late 2004 (pictured below). After completing ?limit load? tests (ie the maximum loads likely to experienced by the aircraft during normal service), progressively greater loads have been applied to the specimen towards the required 1.5 times the limit load. Engineers develop finite element models (FEM) to calculate the load requirements.
The failure occurred last Tuesday between 1.45 and 1.5 times the limit load at a point 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.? He adds that the ultimate load trial is an ?extremely severe test during which a wing deflection of 7.4m (24.3ft) was recorded?.
The European Aviation Safety Agency (EASA) says that the maximum loading conditions are defined in the A380 certification basis. ?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. This process is ongoing and will be completed before type certification.? However Garcia says that the failure of the wing below the 1.5 target will require ?essentially no modifications? to production aircraft: ?This static test airframe has the first set of wings built, and we have refined the structural design for subsequent aircraft due to increased weights etc. We will use this calibration of the FEM to prove the adequacy of the structure on production aircraft.? EASA says that it is aware of the structural failure but "cannot make a statement about the specific failure as it has not been officially briefed by Airbus on what the cause was, and the certification process is ongoing ". Garcia says that the FEM calculations had already established that the A380?s wing had ?no margin at ultimate load. We had a weight saving programme and ?played the game? to achieve ultimate load.? However in earlier briefings, Airbus structural engineers had stated that it planned to carry out ?a residual strength and margin research test? in 2006 after completing ultimate load trials. The results gleaned from the static testing will be extrapolated for the future aircraft developments over the next 40 to 50 years says Garcia. ?It is normal to refine and strengthen the structure of new heavier or longer range variants,? he says.
Airbus is approaching the quarter-distance mark in the A380 flight-test programme, having cleared a number of key hurdles, but still faces a daunting 10 months of trials to complete certification and prepare the aircraft for entry into service with Singapore Airlines at the end of 2006.
By the beginning of December the three flying A380s had completed 586 of the expected 2,500 flight hours, and 161 flights, and the fleet is averaging 65-70 flight hours a month.
Initial water ingestion trials at the Istres test centre have been carried out, with the A380 being accelerated to and decelerated from 70kt (130km/h) through a water trough, but these tests will have to be completed once some modifications are incorporated, says vice-president flight tests Fernando Alonso. We had to abort the test as some hydraulic pipes to the brakes were bent, he says.
Het grootste Airbus vliegtuig ooit.
Assembly of the main Engine Alliance flight test aircraft (MSN009) has been completed, and its first flight is scheduled for April. Champion says certification of this version is expected in the first quarter of 2007 to enable deliveries to begin to launch customer Emirates in April 2007.
The successful demonstration of the A380‚??s maximum design speed (Vmd/Mmd) of Mach 0.96 on 1 December marked the completion of the opening of the A380‚??s flight envelope, with flutter testing having been concluded in November. Lelaie says that a Vmd attempt earlier in the flight test programme had to be aborted at Mach 0.93 when we detected a shock wave, but this was rectified by calibration
Airbus A380 flight-test and programme management executives as the ultra-large aircraft is prepared for the critical next stages of the test effort. The flight envelope has been cleared, and the difficult negotiations with customers to reschedule deliveries following the programme slippage have been completed. While there is an aura of quiet confidence in Toulouse that the A380 programme will be able to keep to its revised timetable, the company can barely disguise its anger and surprise over the recent interim recommendations by the International Civil Aviation Organisation (ICAO) to greatly increase separation distances for the aircraft.
Alonso says that MSN004, which joined the flight test programme on 18 October, is dedicated to performance measurements and engine development. It completed the main evaluation of cruise performance on 9 November and there are complementary evaluations continuing until the end of December. Lelaie says there are indications that the A380 could end up cruising slightly faster than its nominal published speed of M0.85
MSN004, which spent a week at the Dubai air show in November wowing the crowds in its Emirates colour scheme, is mid-way through an extensive two-month evaluation of low-speed performance test. Lelaie says the next major task for the flight test team is to fine-tune the fly-by-wire flight control rotation law.
Alonso says that Airbus was quite surprised by the ICAO interim policy letter issued on 10 November, which recommended a dramatic increase in the separation requirements for the A380 from the standard heavy aircraft distances of 4nm, 5nm and 6nm (7km, 9km and 11km) during approach, depending on the size of aircraft following, to 10nm regardless of the category in trail (see graphic). ICAO has also increased the 5nm cruise separation to 15nm for the A380. The ICAO policy is based on a type of computation that has not been validated by flight test measurements we disagree with its recommendation, says Alonso. He adds that there has been no demonstration that the 747 is the limit for the heavy category.
Other ongoing flight test activities include: structural identification; further autoland work; and development of various systems ‚?? fuel, electrics (including testing of ram air turbine performance) and air conditioning (with complete ducting).
Meanwhile, in October, MSN001 was used for four days of noise evaluation tests at Moron air base in Spain, where Airbus verified whether the target for the A380‚??s external noise levels can be achieved with current configuration. The aircraft completed over 100 flyovers to measure approach and take-off noise. Alonso says that final noise tests need to be completed, when fairings for the landing gear designed to further attenuate noise may also be trialed, as they were not ready for the Moron session.
Cold soak trials are set for early in 2006, while the maximum-energy rejected take-off test will be undertaken at Istres, France, and is currently planned for March/April, says Lelaie. The braking system is not yet fully tuned, he adds
Airbus senior vice-president flight test Claude Lelaie says that a total of 43 pilots have now flown the aircraft, including representatives from customers and from European and US aviation authorities. ‚??The first customer airline pilots flew the aircraft after the Dubai air show when we had eleven Emirates pilots ‚?? including three who had never flown an Airbus ‚?? fly two touch‚?? and goes each at Ras Al Khaimah,‚?Ě says Lelaie.