A3XX: engineering a new way to fly

Citation

(2001), "A3XX: engineering a new way to fly", Aircraft Engineering and Aerospace Technology, Vol. 73 No. 1. https://doi.org/10.1108/aeat.2001.12773aaf.004

A3XX: engineering a new way to fly

A3XX: engineering a new way to fly

Keywords: Airbus, Air transport

Airbus believes that, as the flagship of the twenty-first century, the A3XX will not only be the most spacious civil aircraft ever built, but will also be the most advanced – representing a novel technology platform from which all future commercial aircraft programmes will evolve. As the programme enters its final definition phase due for completion by the end of 2001, an array of new technologies for materials, processes, systems, and engines has already been developed, tested and adopted. All technology considered for the A3XX is said to be carefully studied to determine its effects over the lifetime of the aircraft, and is proven to be fully mature and capable of delivering long-term benefits before it is selected. Each selection therefore contributes to attaining or bettering the programme targets, in keeping with the basic design tenets of reliability, low seat-mile cost, passenger comfort and environmental friendliness.

We are informed by Airbus that a number of innovations introduced on the A3XX will ensure considerable weight savings despite the aircraft's prodigious spaciousness, and countless tests run to date show that aerodynamic performance of the aircraft will also be significantly enhanced. The company points out that better aerodynamics and lower airframe weight reduce the demands placed on engines and translate into lower fuel burn, reduced emissions into the atmosphere, and lower operating costs.

An estimated 40 per cent of the aircraft structure and components will be manufactured from the latest generation of carbon composites and advanced metallic materials, which, besides being lighter than traditional materials, claim significant advantages in terms of operational reliability, maintainability and ease of repair. The A3XX is said to be the first aircraft ever to boast a carbon fibre central wingbox – representing a weight-saving of up to one-and-a-half tonnes compared to most advanced aluminium alloys. A monolithic carbon fibre reinforced plastic (CFRP) design has also been adopted for the fin box and rudder, as well as the horizontal stabiliser and elevators. Furthermore, the upper deck floor beams and pressure bulkhead will be made of CFRP, while the wing covers will be constructed from advanced aluminium alloys. The fixed wing loading edge will be manufactured from thermoplastics, and secondary bracketry in the fuselage (serving, for example, to hold the interior trim) is also likely to be made of thermoplastics. Further applications of thermoplastics are reported to be under investigation, such as for the ribs in the fixed leading edges of the vertical and horizontal stabilisers.

The upper fuselage shell of the A3XX will, Airbus informs us, be fashioned from GLARE, a laminate alternating layers of aluminium and glass-fibre reinforced adhesive, which in addition to being some 10 per cent less dense than aluminium – for a weight-saving of around 800kg – has reportedly proven superior in terms of fatigue and damage resistance. Testing is said to have demonstrated that an artificial crack subjected to thousands of flight cycles barely increases in size. The new material is also said to have a high degree of corrosion resistance with the first glass-fibre layer preventing any penetration beyond the superficial aluminium coating. GLARE uses a hot bonded manufacturing process but is repaired in the same way as standard aluminium.

We understand from Airbus that several innovative manufacturing techniques have been selected for use on the A3XX programme, some of which are said to have proved so advantageous that they will go into series production earlier on other aircraft programmes. One example quoted is the technique of laser beam welding which will be used to attach the "stringers" (longitudinal reinforcements) of the lower fuselage shell instead of traditional riveting. This technique not only engenders a potential weight reduction, it is also thought to be much faster than conventional riveting – eight metres of stringers can be laser beam welded per minute. The method includes a built-in automated inspection unit and tests run on the resulting structures to determine damage and fatigue tolerance have reportedly demonstrated that they behave as well as or better than conventional alloy construction. A further major advantage claimed of this technique is that it eliminates fasteners, and thereby the major source of corrosion and fatigue cracks. Laser beam welding will go into series production as early as 2001, for the manufacture of the fuselage lower skin panels on the single-aisle A318, and the technique is likely to be adopted for all newly developed aircraft at Airbus Industrie.

The A3XX's hydraulic system, for the first time ever in civil aviation, will have an increased pressure of 5,000lb per square inch (psi), as opposed to the traditional 3,000lb psi. This increased power is necessary to handle the A3XX's flying controls and the reduction in component size, connections and piping not only lowers the weight of the aircraft by around one tonne but also improves its maintainability. In fact military aircraft already use these high pressure systems and the change is believed to be an evolutionary move which has stood up well to qualification testing. Trials with existing hydraulic fluids and components are reported to have shown that the fluid does not degrade under the higher pressures and no evidence of erosion was found.

In addition to the increased hydraulic pressure, a dual architecture for the flight control system has been implemented, with both hydraulic and electrical energy sources. According to Airbus never before, on civil or military aircraft, have the flight controls been governed by both hydraulic and electrical circuits and this innovation provides valuable and unprecedented redundancy. Indeed, instead of the traditional three hydraulic circuits, the A3XX will offer two hydraulic and two electrical, providing more flexibility in terms of reconfiguration as well as enhanced operational reliability.

The A3XX will, it is thought, benefit from a completely redesigned double spool air generation system which is more efficient in terms of thermodynamic cycles, provides more flexibility between different air generation requirements on the ground and at cruise, takes up less space and offers more redundancy and damage-resistance. Indeed, airliners are generally equipped with two air-conditioning packs, each of which, in a series of thermodynamic cycles, converts high-temperature, low-pressure bleed air (from the compressor stages of the engines) into pressurised cabin air at room temperature. Instead of using four such packs to generate the necessary air, the A3XX will be equipped with two innovative double-packs, in which each unit performs separate functions of the overall cycle. This more robust approach provides valuable systems redundancy as well as greater efficiency overall.

Airbus Industrie signed agreements (MOUs) for the development of the A3XX's engines with Rolls-Royce in October 1996 and with The Engine Alliance (a joint venture between General Electric and Pratt & Whitney) in May 1998. Both engine manufacturers have since made considerable progress in the definition of appropriate engines, in keeping with Airbus Industrie's requirements in terms of performance, reliability, noise reduction and environmental friendliness. Rolls-Royce is developing the Trent 900, a derivative of its successful Trent family which are available on Airbus Industrie's A330/A340 family of aircraft. For its part, The Engine Alliance is developing the GP7200.

While the baseline A3XX's engines all provide 68K/68,000lb of thrust, powerplants will be certificated at 75K/75,000lb of thrust, with growth potential up to 80K/80,000lb, building-in a wide margin of flexibility, allowing for the growth of the A3XX family. In addition, the engines are reported to all offer a reduction in noise levels, NOx emissions and fuel consumption.

According to Airbus Industrie it is thanks to its new generation engines, alongside advanced wing and undercarriage design and technology, that the A3XX not only will comply with current noise limits but also will meet expected future international and local noise limits. As a result, the company believes that the A3XX will be quieter than today's largest airliner.

Airbus Industrie considers that, as far as emissions are concerned, the A3XX will minimise greenhouse gases in the high atmosphere, even though they are not regulated. In the company's opinion, if there were an absolute limit for emissions in high altitudes, more passengers could still be carried with the A3XX. Furthermore they believe that, since more seats per aircraft lead to a reduction of average frequency of the world's aircraft fleet, this together with less fuel consumption per passenger yields a significantly reduced environmental impact in the long term. Airbus is also of the opinion that, due to its larger capacity, the A3XX will make better use of available take-off and landing slots, thus reducing fuel wasted in airborne delays and holding patterns.