A400M flight tests approach finishing stages, but two milestones remain to be met in 2011
Despite being nearly three years behind schedule, the military airlifter test program is progressing through its final year amid a surprisingly calm atmosphere.
Test personnel recognize there is still ample time for hiccups to occur, but the head of flight-test operations at, Fernando Alonso, says, “we are in pretty good shape,” even if “we are still prone to find things” as the trials unfold. The program has logged 2,500 flight-test hours, with 3,700 hr. expected for the entire campaign.
That is not to say that the A400M development is running to the revised program schedule. Developers may miss two key 2011 targets: garnering the A400M's type certification and flying the fifth test aircraft. Both events could slide into 2012, though Alonso argues that “what is really important is the entry into service,” and that remains likely to occur late next year.
Contractual issues also remain a concern. For instance, France has expressed displeasure at the initial in-service support offering put forward by industry.
But developers are largely satisfied that no major engineering hurdles are staring them in the face at the moment, especially now that two of the main technical problems the program encountered this year—both linked to the TP400D turboprop engine—have been addressed. Fixes are being implemented.
One problem manifested itself in June, when a flight-test aircraft suffered an inflight engine shutdown because of a component failure. Analysis found that the fatigue crack in the gear-tooth fillet radius was caused by resonance in the idler gear at cruise propeller speed, says Simon Henley, president of the Europrop International engine consortium.
The idler gear has been redesigned to shift the frequency at which the resonance occurs and thereby avoid the material fatigue. In addition to making the adjustment for new engines, the component will be replaced on current powerplants. Engineers also have developed an algorithm to help identify early signs of failure to prevent an inflight shutdown.
The other issue is linked to the high-pressure compressor, which prompted the removal of three engines owing to problems that occurred on the ground.
Henley says blade fatigue was found to have been caused by wake separation from an upstream variable inlet guide vane, compounded by an acoustic resonance. The problem arose only in a tight speed range, he notes.
A double fix has been developed: One adjusts the full-authority digital engine control to ensure the compressor does not run at the speed at which the problem occurs; the second involves a redesign of the variable inlet guide vane to eliminate the wake separation.
Overall, engine performance is ahead of specification, with current TP400Ds already beating by 1% the specific fuel-consumption target for the entry-into-service standard powerplants, says Martin Maltby,program technical director. Assembly of the engines for the first customer aircraft, MSN007 for the French air force, is scheduled to start by year-end, with delivery to Military by the second quarter of next year.
In the flight-test program as a whole, much of the focus in recent months has been on completing certification work. Alonso says the work is on track, but he will not project when it will be finished.
One reason Airbus is finding it difficult to predict when the type certification will be achieved is related to weather conditions. For instance, only 40% of the anti-icing campaign has been completed, largely because of benign weather in Europe in the last couple of months. With winter approaching, however, much of the work could be completed soon in only four flights.
Airbus Military has redesigned the wing deicing system after flight trials identified buffet problems in an earlier setup. Now it will deice the No. 1 leading edge (LE1) slat, the third leading edge (LE3) slat and part of the fourth (LE4). The previous plan called for LE3, LE4 and LE5 to be deiced.
Otherwise, Alonso says, 100% of the performance trials and 70% of the work linked to flight controls and handling qualities are completed.
As with the deicing tests, crosswind trials have been hampered by lack of suitable conditions. But Ed Strongman, chief test pilot for Airbus Military, notes that in tests with takeoffs at 25 kt. crosswind gusting to 37 kt. and landings at 26 kt. gusting to 34 kt., the engines performed without problem.
Moreover, certification authorities have just validated the minimum control ground velocity (VMCG) with an engine failure on takeoff for the airlifter, achieving a speed of 88.9 kt. and beating the 90-kt. target, says Strongman. The figure is particularly critical for the short runway performance of the airlifter.
To meet VMCG requirements with its powerful TP400D turboprops, Airbus Military has devised a system where the opposite engine automatically spools back up to 25% of thrust depending on the speed at which the failure occurs. That assures the aircraft remains within the allowed 10-meter (33-ft.) variance from centerline.
Also completed last month were trials at the French flight-test center at Istres in which the A400M passed through a water bath to ensure the spray from the wheels is not ingested by the engine to cause a flameout. The A400M passed that test, although Airbus identified a small design problem when the water wake penetrated a cavity associated with a main landing gear door and caused some damage. That component will now have to be redesigned.
High-energy rejected takeoff and passenger and crew evacuation trials have been completed, too.
Flight-testing has demonstrated that the A400M can forego the active noise suppression system for the cabin, which developers expected to include. Lower noise in the cabin means saving more than 200 kg (440 lb.) by eliminating the need for the active system.
The pending 2011 milestone in addition to achieving type certification, first flight of MSN006, is on hold. Alonso notes that the aircraft is basically ready to fly, with engines in hand, but the focus for MSN006 will be on function and reliability testing next year. That entails a 300-hr. flight-test program in which the aircraft has to demonstrate it is ready for service. The question now is whether to fly the aircraft soon and upgrade it later in preparation for the endurance trial or wait for some final configuration elements to be ready, install them and then begin trials in the proper standard.
A number of activities are on the agenda for next year, though Strongman says not all the work needs to be completed for entry into service, so some could be deferred if the schedule gets tight. Those agenda items are:
•A renewed focus on validating military elements of the airlifter, including flare and chaff ejection, performance of the defensive aids sensors, and closer scrutiny of the communications suite and mission management system. Strongman notes that some risk-reduction activities have already been undertaken, including dry air-to-air refueling contact and flying with night-vision goggles and military loads.
•Climate envelope expansion, with hot-and-high performance likely to be tested in La Paz, Bolivia, in the spring. Those trials were planned for this year but delayed by a self-imposed flight-test restriction because of TP400D issues. Further cold-weather tests are also planned, this time using MSN006, which has the most production-representative cabin.
•Air drop of paratroopers and gravity loads.
•Validating ground loading and unloading using different cargos.
•Actual air-to-air refueling to build on the 15 dry contacts already completed. Airbus Military identified some adjustments it wants for the flight control laws in refueling to optimize handling. First refueling trials with helicopters are also coming into focus, as well as using the A400M as a tanker with its refueling pods.
•Flights from unprepared runways— those made of grass, dirt and gravel.
But even if there again appears to be some schedule margin, the pressure is still on to bring testing to a close. With Europe's spending in decline, the Middle East is seen as a hot growth market, though the A400M will be absent from this week's Dubai air show. Asked if the aircraft will participate, Alonso says “forget it. We have put a veto on air show flying this year. The priority is certification.”