For plane-spotters around the world, the long-awaited entry into service of the Airbus A350 XWB earlier this year was an historic moment in the making. The twin-engine, wide-body jet, painted in the distinctive livery of launch customer Qatar Airways, marked a new era of civil aviation, representing the culmination of a decade of collaboration between engineers at plants in the UK, Germany, France and Spain.
So far, the plane has been a runaway success. Airbus has 780 orders on its books already, with major airlines such as British Airways, Lufthansa, Cathay Pacific and Etihad set to start taking delivery of the A350 XWB over the coming months.
It's the technology on the A350 XWB that most excites aviation enthusiasts around the world, most notably its extensive use of carbon fibre. Composites are applied extensively, across 53% of the fuselage and wings, being used for structures that on previous civil aircraft programmes would have been made from aluminium.
Construction of the fuselage sections is made by assembling four-skin panel sections – two lateral side panels, one at the crown, and another for the belly – onto carbon fibre frames. In contrast to other composite aircraft, this construction technique has allowed for a tailoring of composite layup thickness to each panel, based on calculations of local fuselage stresses and loads. The use of composites is dovetailed with the application of titanium and advanced aluminium-alloys which help to diminish the requirement for corrosion-related maintenance checks on the aircraft. Indeed, Airbus says that overall fatigue and corrosion maintenance tasks on the A350 are reduced by 60% when compared to similar sized aircraft using conventional materials.
Wing matters
The plane also looks distinctive, thanks to an advanced wing design which was optimised through extensive use of computational fluid dynamics and wind tunnel testing for a fast cruise speed of Mach 0.85. Improved aerodynamic efficiency acts to reduce journey times and extends the aircraft’s range. Most noticeable is the exaggerated wingtip fence device – the arrow-shaped surfaces attached to the tip of the wing – which has been designed to enhance the overall efficiency, saving fuel by reducing drag while lowering noise emissions by improving take-off performance.
All three A350 XWB aircraft in the family share the same wing planform – a 64.7m wingspan, a total area of 442 sq. metres, and high swept leading edge. In addition the internal wing structure will be scaled to meet the requirements of each aircraft variant.
The distinctive A350 XWB wing
Innovative concepts applied to the A350 wing’s high-lift devices will reduce noise and drag while also improving the aircraft’s low-speed performance. One of these innovations is the stream-wise deployment of trailing-edge flaps. On a traditional swept-wing jetliner, the outboard flaps extend at an angle to the airflow. For the A350, flap deployment is along the direction of flight – resulting in better lift efficiency and improved low-speed performance, while reducing noise.
Other A350 XWB wing enhancements include the adoption of a drop-hinge mechanism to improve the flap’s deployment kinetics, along with the introduction of a downwards movement for the upper wing spoilers to fill the gaps that occur when flaps are extended.
In addition, the A350 XWB’s flight computer performs in-flight trimming of the inboard and outboard flaps, creating a variable camber wing that adapts to different flight conditions.
Innovation inside
The A350 XWB’s onboard systems have been optimised for two primary criteria: robustness for ensured reliability and operability; and simplicity for reduced maintenance time and cost.
Solid-state power control technology eliminates the need for individual circuit breakers in the cockpit, cabin and electronics bay – providing a more modern method of power control management throughout the aircraft. The application of variable frequency generators, which were first introduced with the A380 super-jumbo, provides more power with less weight and lower maintenance costs, along with increased reliability and time-between-removals.
Another A380-proven concept is the use of two hydraulic circuits, instead of three on other jetliners, with redundancy provided by a dual-channel electro-hydraulic backup system. In addition, the A350’s hydraulics will be operated at the higher pressure level of 5,000 psi., which also is used on the A380. This increased operating pressure reduces the size of pipes, actuators and other system components while also facilitating the overall access – leading to improved reliability and maintainability, as well as reducing weight and increasing cost savings.
As a “connected” aircraft, Airbus says the A350 XWB is able to send data to the ground during flight – improving communications between jetliner and ground crews, and facilitating efficient “in-advance” maintenance operations that support better air traffic management.
Propulsion properties
In terms of propulsion, the A350 XWB will be powered by Rolls-Royce Trent engines which have been specifically developed for the programme. The engines have a take-off rating of between 74,200 lbf (330 kN) to 97,000 lbf (430 kN), depending on aircraft configuration. It's a three-shaft turbofan design, with a high bypass ration of 9.3, which has high levels of commonality with Rolls-Royce existing family of Trent civil engines.
Starting at the front of the Trent XWB, the engine features an ultra-efficient swept fan with a diameter of 300cm. Rolls-Royce says the wide-chord fan blades are the lightest and strongest in the world, having been tested to withstand a multiple birdstrike. The swept fan design has been employed to give quieter operation and optimum core engine protection. An optimised bearing load management system reduces sealing air requirements, says Rolls-Royce.
The Trent XWB was developed specifically for the A350
Advanced compressor aerodynamics deliver a module weight saving of 15% through the use of blisk technology, while single skin combustion casing reduces engine weight and simplifies engine maintenance. Efforts have also been made to improve the efficiency of the 2 stage IP turbine to deliver greater thrust. The HP turbine rotor, which consists of 68 blades and rotates at 12,000 rpm, generates centrifugal loads of up to 10 tons on each blade. The HP turbine produce more than 50,000 horsepower, which amounts to 800 horsepower per blade.
Combustion temperatures exceed the melting point of the combustion chamber material. Advanced cooling sees air used together with ceramic coatings to enable the material to exist in these extreme conditions.
First deliveries
None of this technology will amount to much unless the A350 XWB meets the expectations of customers, both in terms of reliability and ease of maintenance for the operators, and comfort for passengers.
It's early days on that score, with the launch carrier – Qatar Airways – taking delivery of its first aircraft in January of this year, serving routes between Doha and Frankfurt. Qatar Airways has configured its A350s to hold 283 seats, including 36 full-flat-bed business class seats and 247 in coach.
Next up it's Vietnam Airlines, Finnair and Cathay Pacific, as Airbus gets into a drumbeat of production. Only time will tell if the A350 XWB will become a legend of the skies.
The first A350 XWB was delivered to Qatar Airways in January