A cut above

The Boeing 787 has forced Airbus to reinvent its A330 as the A350 long-range twinjet family. And the manufacturer is convinced that the €4 billion it is spending will enable it to create a more than worthy rival

To the uninitiated, the A350 may seem like a knee-jerk reaction from Airbus to tackle the Boeing 787 with a warmed-over A330. The truth, however, is that the European manufacturer has been pushed by the market into spending €4 billion ($5 billion) to re-invent the current benchmark long-haul 250-seater as a demonstrably better aircraft than its predecessor in every measurement.

Not only is Airbus confident it can match Boeing's promises for the all-new 787 with a derivative aircraft, but it is also sizing the larger member of the two-model twinjet family to attack the smaller 777 model – the -200ER – by offering similar capacity and performance for a much lower cost per seat. "We are positioning the 300-seat A350–900 to be a 777-200ER killer, because we are pushing the technology into an area our competitor did not want to go," says A330/A340/A350 programme manager Olivier Andries.

He says Boeing is under pressure from some potential customers – notably Emirates – to make the stretched 787-9 big enough to replace the 777-200ER. So far, the US manufacturer has politely declined requests to create an in-house successor to a design that has been production for only 10 years.

When Airbus began serious studies into an A330-based counter-attack to the 787 last year, it started with a fairly simple derivative that would have retained much commonality with the A330/A340 family. – but the market told Airbus to try harder.

Speaking at the formal unveiling of the A350 last December, however, Airbus chief commercial officer John Leahy revealed that the launch configuration was the third and most advanced iteration since conception in mid-2004. Earlier proposals had fewer changes and less weight reduction, albeit for a lower development cost and earlier entry into service – 2009 against the current 2010.

And since December's commercial launch, the development effort has continued. The A350 underwent "three or four more" revisions until its design freeze in April, as Airbus worked to improve the twinjet's competitiveness against the 787's clean-sheet design.

The effort has also resulted in Airbus being able to offer, for the first time, a twinjet to rival the 777-200ER's capacity and range. The new model has already generated plenty of headlines, not least because the manufacturer is seeking to partly fund the new aircraft using controversial government launch aid.

While the A350 outwardly looks similar to the A330 from which it is derived, the two aircraft will have little in common, says Andries, adding: "What we've kept from the A330 are the pilot type rating, the external shape and rough dimensions; 90% of the part numbers are to change."

Based on the A330-200/300 family, the smaller A350-800's dimensions are identical to those of the -200 while the -900, which was originally based on the A330-300, has recently gained a two-fuselage frame stretch in the rear fuselage to add an extra seat-row. The -800 will be the first to enter service, in July 2010, with the -900 following by the end of the year.

Heaviest Airbus

Both versions have maximum take-off weights of 245t, 12t more than the heaviest A330. Airbus says the A350-800 can carry 253 passengers in a typical three-class layout – 30 more than the 787-8 – and can take them 555km (300nm) further, to a range of 16,300km. The 300-seat -900 carries 35 more passengers than the 787-9, but has a shorter range of 13,900km compared to the Boeing's 14,800km. The -900's range is only 370km less than that of the much heavier, but similarly sized 777-200ER.

"The design of the A350 represents a very significant weight and drag reduction over the A330, which will provide a significant step forward in fuel efficiency," says Andries, who puts the break-even at "about 400-500 aircraft – typical of a long-range aircraft programme". The major new elements of the A350 are:

•  Fuselage structure;
•  wing structure and improved high-speed aerodynamics;
•  engines, nacelles and pylons (the latter titanium) ;
•  landing gear;
•  auxiliary power unit;
• empennage;
•  wider, rearranged cabin with new bins and larger windows;
•  flightdeck functions;
•  systems;
•  crew rest compartment relocated.

Andries says that the 8t weight saving over the A330 is due to 60% of the A350's structure being constructed from advanced materials, compared with 15% on the current models.

By weight, 37% of the aircraft will be made from carbonfibre-reinforced plastic (CFRP), increasing to 46% if landing gear is excluded: the centre wing-box and a large part of the wing; the vertical fin and horizontal tailplane; and the aft fuselage (section 19/19A). CFRP will also be used for the fuselage keel beam, window frames and belly fairing. The window frames alone net a 100kg (220lb) saving.

The remaining 23% of new materials are represented by third-generation aluminium-lithium alloys, which will make up a "significant part of fuselage", says Andries, generating about 700kg in weight saving. Here, Airbus has taken a different approach from Boeing with the 787, which adopted an all-carbonfibre fuselage after running a competition among suppliers of carbonfibre and advanced alloys.

"Airbus did a fairly extensive study on the cost/benefit trade-off of CFRP against aluminium-lithium," says A350 chief engineer Dougie Hunter. "But, as we want to use existing tooling and production techniques from the A330/A340, the cost-benefit trade-off does not look so good for us. We would need completely new tooling for the composite fuselage, and the repairability of CFRP fuselage panels would be a concern to our customers. So it just doesn't trade to adopt a composite fuselage at this point."

As a result, aluminium-lithium is being used for the fuselage skin panels and floor structure, where it will give better corrosion resistance than the current aluminium-copper alloy structure. Compared with 2000-series alloys, which have been employed in aircraft construction over the last 25 years, "aluminium-lithium provides equivalent strength for around 5-6% less density", Hunter says. He adds that, although the price of aluminium-lithium is declining, it is "not quite down to where aluminium is yet – but it's getting close".

Although dimensionally similar to the A330 wing, the A350 wing is almost entirely composite, allowing Airbus to save around 2.5t compared with using aluminium alloys. CFRP (the M21 carbonfibre epoxy pre-preg adopted for the A380) is used for the front, centre and rear and inner-rear spars, as well as the upper and lower skin panels. The wing ribs remain metallic, as currently proposed, although a move to CFRP is being evaluated. The centre and outer wing boxes are fabricated from CFRP.

Fluid dynamics

Aerodynamic revisions to the wing from use of the latest computational fluid-dynamics tools will yield a 1% reduction in cruise drag. These new tools have also been used to optimise the inner and outer wing sections, the belly fairing, flap fairing and winglet design. Another change is to replace the A330's inboard slat with a more efficient "droop nose" device, borrowed from the A380. "This provides a 3% drag improvement for take-off and landing – the equivalent of around 2t in take-off weight from a limiting airfield," Hunter explains.

Andries concedes that, at Mach 0.82, the A350's cruise speed will be the same as the existing A330/A340's. However, the "speed flexibility" of the new aircraft has been improved to enable it to fly at Mach 0.83 with minimal drag impact: "This is slightly less than the 787's Mach 0.85, but represents something like 15-20min on the typical transpacific flight. Some airlines may consider this important, some will not," he says.

One of the keys to the A350's performance gain on current designs is the adoption of new-generation engines originally conceived for the 787. "These offer 15% lower fuel consumption than the current engines," says Andries. "We have an agreement with General Electric for the GEnx, which will be the engine offered at entry into service." This powerplant will be available with thrust ratings between 63,000lb and 75,000lb (280kN and 334kN). Airbus is in talks with Rolls-Royce about offering a Trent 1000-based engine as a second option after service entry.

There is a big difference in the philosophy between Boeing and Airbus on their new twins' air conditioning, Airbus deciding to retain the conventional engine bleed-air driven system, while its rival adopts a bleedless system. "You have to condition the cabin and, if you don't use bleed from an engine, then you do it through taking external air with electrical power," Hunter explains. "You still have to get that power from somewhere and, at an engine level, it all relates to the same specific fuel consumption."

Airbus is aiming for a "significant step" in maintenance cost reductions, and is targeting the powerplant as one area to achieve this. Andries says it has secured a way to optimise engine maintenance costs by offering lower thrust ratings as "the cost is a matter of thrust".

The overall target is to reduce maintenance costs by 15% and "we are very confident we can achieve this", says Andries. He adds that, based on current Airbus estimates, the A350-800 will have 3% lower maintenance costs per flight hour than the 787-8.

Airbus is extending the maintenance intervals on the A330 and expects this to be reflected on the A350 by the time it enters service. By then, the A350's interval for intermediate checks at entry into service will be six years (compared with five currently on the A330), which will eventually increase to seven. Similarly, the heavy checks – currently every 10 years – will extend to 12, later increasing to 14.

Flightdeck features

Although the A350's flightdeck will be based on that of the A330, to retain the existing aircraft's type rating, it will incorporate a number of features developed for the A380 and the technology will be "at a level at least identical to our competitor", says Andries. New elements include expanded displays incorporating vertical flightpath information, and the on-board information terminal which provides the functions of an electronic flight bag.

Andries reveals that the redesigned cabin is a significant element of the programme, saying: "We have decided to make a quantum jump in passenger comfort." He adds that Airbus will offer cabin humidity levels of 15-20% and a typical cabin altitude of 6,000ft until the late stages of long-haul flights, when higher flight levels are usual practice.

Internally, the cabin will gain 7.6cm (3in) in overall width at head, shoulder and foot level, due to local fuselage frame cutbacks and resculptured walls. Cabin windows will be 8% larger than those of the A330/A340 family, while bigger overhead bins will hold at least one typical roller bag per passenger in economy, and at least two in business. There will also be improved head clearance for passengers, and economy-class seats will be wider than the current standard at 18in (45cm) – the same as in the A380.

Both A350 models have gained seat capacity through rearrangement of the passenger cabin, partly thanks to changes to the aft fuselage, which has been redesigned as part of the switch to a CFRP structure, and reshaped to reduce drag. Due to the tailplane's trim actuator being repositioned, the A350's rear bulkhead has been relocated further back, and reduced in size.

The revamp allows for the entry module for the bulk cargo hold crew rest compartment to be moved aft out of the main cabin, providing more space for revenue seats. At the forward end of the cabin, Airbus has relocated the flightcrew rest from its position on the main deck, aft of the cockpit, to the avionics bay below, creating room for eight more seats.

"We have relocated in-flight entertainment system electronics from this area to the back end of the aircraft," adds Andries. All the changes enable the A350-800 to accommodate 253 passengers in a typical three-class layout, increasing to 300 on the -900, making both aircraft around 10% bigger than their 787 competitors.

"We took a strategic decision to position the aircraft 10% above the respective 787s in terms of seat capacity," says Andries. "North American customers generally prefer smaller aircraft, while Asian, Middle Eastern and European customers favour bigger aircraft. If the airline is very confident that it will be able to fill those seats, then those 26 additional seats have enormous value. The equation is simple: one seat equals $1 million in revenue," he says.

Efficiency

Andries adds that, due to the greater size of the A350 and the weight reduction, the operating weight empty per seat is better: "To an airline looking at the aircraft's efficiency on a per-seat basis, this is a significant driver of cash operating cost. We will offer an aircraft with the same seat capacity as the 777-200ER and the same range as our current A340-300 and the 777-200ER with 20% less weight per seat. We will have unbeatable cash cost per seat advantage of 16.5% over the -200ER."

With such dramatic savings promised, the arrival of the A350 could adversely affect part of the existing Airbus product line. But Andries is quick to point out: "We do not see the A350 as a substitute for the current A330. That model will be more positioned to the regional market. It is then more a question of pricing policy."

Efforts are under way to expand the performance of the new family. Airbus is known to be studying weight increases of up to 25t, which would enable the manufacturer to close the range-capability gap between its products and the 787-9 and 777-200ER. It could also provide the basis for a stretch, if the market demands.

So Airbus has defined its new, long-range twin, and is now awaiting approval to make the industrial launch, which is expected at the Paris air show, when the manufacturer looks set to announce a stream of launch orders. "We expect to have a significant launch base by then," says Andries. Shortly afterwards, the manufacturer hopes to hear if its applications for launch aid have been successful – but that is another story.

Note *2004 delivery conditions

MAX KINGSLEY-JONES/TOULOUSE

Source: Flight International