Airbus A3XX Makes Extensive Use of Composites
As the flagship of twenty-first century aeronautics, the A3XX will be the most spacious and most advanced civil aircraft ever built, laying the groundwork cornerstone for a unique technology platform from which all future commercial aircraft programs will evolve. As the program enters its final definition phase slated for completion by late 2001, an array of new technologies for materials, processes, systems, and engines have already been developed, tested and adopted. Before being selected, all technology has to be proven fully mature and capable of delivering long-term benefits. A number of innovations introduced on the A3XX will slash weight despite the aircraft's incredible bulk. To date, countless tests show that aerodynamic performance of the aircraft is extensively enhanced. Streamlined aerodynamics and lower airframe weight put less strain on the, entailing lower fuel burn, fewer emissions into the atmosphere, and a drop in operating costs.
An estimated 40 percent of the aircraft's structure and components will be manufactured from the latest generation of carbon composites and advanced metallic materials. Besides being lighter than traditional materials, they are also on the cutting edge of operational reliability, maintainability, and easy repair. This will save up to one and a half tons of weight compared to most advanced aluminum alloys. A monolithic CFRP (carbon fiber reinforced plastic) design has also been adopted for the fin box, rudder, horizontal stabilizer, and elevators. The upper deck floor beams and pressure bulkhead will also be in CFRP while the wing covers will be made from advanced aluminum alloys. The fixed wing leading edge will be in thermoplastics, and secondary mounting brackets in the fuselage (to attach the interior trim, for instance) in thermoplastic composites. Other thermoplastic applications are being studied, with a focus on the ribs in the fixed leading edges of the vertical and horizontal stabilizers.
The upper fuselage shell of the A3XX will be fashioned from GLARE, a laminate alternating layers of aluminum and glass-fiber reinforced adhesive. Not only is it roughly 10 percent lighter than aluminum (a weight saving of approx. 800kg) but it proves to have greater fatigue and damage resistance. The new material also withstands corrosion extremely well, with the first glass-fiber layer preventing any penetration beyond the superficial aluminum coating. Although GLARE uses a hot bonded manufacturing process, it can be repaired as easily as standard aluminum.
Laser Beam Welding
Several innovative manufacturing techniques have been selected for the A3XX program. Some are so advantageous they will go into mass-production for other aircraft programs (predating the A3XX). For instance, laser beam welding will replace standard riveting to attach the stringers (i.e., longitudinal reinforcements) of the lower fuselage shell. Not only does laser beam welding slash weight, it is also much faster than conventional riveting, welding up to eight meters of stringers per minute.
Tests run on the structures to determine damage and fatigue tolerance have shown they behave as well or better than conventional alloy constructions. A further major advantage of laser beam welding is that it does away with fasteners, a major source of corrosion and fatigue cracks. In 2001, laser beam welding will go into mass-production for the manufacture of the fuselage lower skin panels on the single-aisle A318. The technique will probably be used for all newly engineered aircraft at Airbus Industrie.
Hydraulic and Electric Systems for Flight Controls
For the first time ever in civil aviation, the A3XX's hydraulic system will have increased pressure. The increased power is required for handling the A3XX's flight controls. The smaller size of the components, connections, and piping cuts down on aircraft weight by roughly a ton but also improves maintainability. Military aircraft already use these high-pressure systems. Installing them on the A3XX is a move that has passed qualification testing. Trials with existing hydraulic fluids and components have shown that the fluid does not deteriorate under higher pressures, and no evidence of erosion has been found.
In addition to increased hydraulic pressure, a dual architecture was installed for the flight control system, with both hydraulic and electrical energy sources. Never before on civil or military aircraft have the flight controls been governed by both hydraulic and electrical circuits. Instead of the standard three hydraulic circuits, the A3XX will have two hydraulic and two electrical systems, providing more flexibility for re-configuration, and enhanced operational reliability.
The A3XX will also get a completely re-designed double spool air generation system that has more efficient thermo-dynamic cycles; provides more flexibility between different air generation requirements on the ground and at cruise; takes up less space; and provides more redundancy and damage-resistance. Airliners are usually equipped with two air-conditioning packs, each drawing on a series of thermodynamic cycles to convert high-temperature, low-pressure bleed air (from the compressor stages of the engines) into pressurized cabin air at room temperature. Instead of using four packs for air supply, the A3XX will be equipped with two new generation double-packs where each unit performs separate functions of the overall cycle. This more reliable approach provides valuable systems redundancy and greater efficiency, overall.
Quieter than Today’s Jumbo Jets
Airbus Industrie signed memorandums of understanding for A3XX engine development with Rolls Royce in October 1996 and with Engine Alliance (a General Electric and Pratt & Whitney partnership) in May 1998. Since then, both engine manufacturers have made major strides in defining the appropriate engines. They have complied with Airbus Industrie's requirements for performance, reliability, noise reduction, and environmental friendliness. Rolls Royce is engineering the Trent 900, an offshoot of its successful Trent family (found on Airbus Industrie's A330/A340 aircraft range). Engine Alliance is working on the GP7200. The baseline A3XX engines will provide a wide margin of flexibility allowing for the growth of the A3XX family.
Thanks to its new generation engines and advanced wing and undercarriage design and technology, the A3XX will not only comply with current noise limits but will also meet projected international and local noise thresholds. Consequently, the A3XX will be quieter than today's largest jumbo jets. Noise per passenger (an increasingly relevant measure for airlines and airports) generated by an A3XX will be half that of a Boeing 747, meaning the A3XX will fully comply with the new strategy to cut yearly noise levels at airports.
Slashing Greenhouse Gases
The A3XX will slash greenhouse gases in the high atmosphere (although regulations do not yet exist for these emissions) by burning up to 15 percent less fuel per passenger than a Boeing 747. Accordingly, if there were an absolute limit for high-altitude emissions, the A3XX could still carry more passengers. More seats per aircraft leading to a drop in the average flights worldwide combined with less fuel consumption per passenger will substantially abate the long-term environmental impact.
Despite the larger size of the Airbus Industrie’s new plane compared to the Boeing 747, polluting emissions in the landing-take-off cycle will also be at the bottom end of the spectrum compared to the US plane’s emissions. They will be well below both current and expected regulations limiting polluting emissions. Thanks to its greater capacity, the A3XX will make better use of available take-off and landing slots, thus reducing fuel wasted in delays and holding patterns.
Mr Eric Charrier
ADIT - Agence pour la Diffusion de l'Information technologique
33 (0)3 88 21 42 42