A cruise ship for the skies

Paris, France-Except for the Concorde, one could argue that the last big change in the airliner business was in 1969 when the Boeing 747 entered service. There have been successive, but minor, improvements since to engines, aerodynamics, capacity, and performance but evolution has generally been the rule in airliner technology for thirty years. Now, there is the promise of a step function in capacity with the introduction of the Airbus Industrie A3XXa double deck design that could lead to aircraft with a thousand seats.

At the Air Show here in June, Airbus Industrie revealed further details of its A3XX design, claimed to be the world's first twin aisle, twin deck aircraft. With 40% more space available than on today's largest aircraft, a high level of passenger comfort can be offered. The cargo deck is also full height, permitting it to be used for passenger utilities such as toilets, if required.

Concept layouts show a spacious entrance area with wide staircases leading to the upper cabin, reminiscent of those on a cruise liner. These allow distinct passenger flows and Airbus claims that turn round times on an A3XX would be similar to that on a Boeing 747.

This comparison is typical of the overall approach to design of the new airplane. The B-747-400 now provides the airline industry with a benchmark against which performance of similar large machines is measured. According to Vincent Cassigneul, responsible for A3XX at Aerospatial Matra, "Airbus aims to reduce direct operating costs (DOC) to at least 15% below those of the B-747-400 by a combination of improved techniques and the productivity gains of increased capacity and range".

The first version, A3XX-100, will have a capacity of 555 passengers with a range of 14,200 km (7,650 nautical miles). With this range any destination in the world, apart from Australia, could be reached from London or Paris. Tokyo would be within reach of every airport except those in South America or Southern Africa. A series 200 would have the same range but with 656 seats or 950 seats in a full economy configuration. Extended range aircraft would offer an extra 2,000 km. Combi and freight versions may also be built.

During 1998, Airbus Industrie and airline specialists in a wide range of disciplines met to ensure the aircraft would meet the requirements of operators as regards maintenance, systems, cabin design, ground handling, cockpit design and engines. "The essential configuration elements were frozen in January 1999," says Cassigneul.

"It is Airbus Industrie's intention for 40% of the value of the program to be taken by risk-sharing partners," explains David Velupillai of Airbus Industries. Agreements have already been signed with nine subcontractors, mainly involved in airframe manufacture, with others due to follow.

Design features. Rolls Royce made an early commitment to develop the Trent 900 engine for the aircraft. Specifications include a swept fan, second generation aerodynamics in the low-pressure and high-pressure compressors, and a counter-rotating HP spool. Later an agreement was made with the Engine Alliance (a joint venture formed by GE Aircraft Engines and Pratt & Whitney) to develop the GP7200 engine for the A3XX. As a four-engined design, each engine will have less thrust than those of current two-engine designs and will be some dB quieter.

Wind tunnel tests have been performed as part of a comprehensive wake vortex study and to measure aerodynamic drag. A free flying 1:35 scale model has been used to measure far-field dynamics of the vortices. The aim is to ensure that take off and landing separation between aircraft shall be no worse than that currently in place for the B747-400.

Drag coefficients may be improved by the use of riblets, embodied in a plastic coating on flying surfaces. These have been tested in airline service on A340 aircraft with promising results.

The Constant Speed Drive (CSD) has been a feature of commercial aircraft electrical systems for decades, delivering constant frequency from a variable speed engine. It is complex and expensive equipment. A simpler, variable frequency power system is used on military and smaller aircraft. Airbus is studying the compatibility of such a system with existing electrical loads on the aircraft. Variable frequency generators are smaller and deliver greater output at lower temperatures.

The A3XX landing gear has been configured in the simplest possible way. Oleo length has been reduced with a consequent saving of 1.8 tons of weight. By integrating the undercarriage into the aircraft structure, sufficient cargo space has been created to carry two standard LD3 containers.

Compatible systems. From a ground operations point of view, the A3XX will be accommodated within the infrastructure of modern international airports. The airframe will fit within a virtual 80m square "box" defined by the International Civil Aviation Organization (ICAO) and Airports Council International recommendations. It will be able to maneuver on existing runways and taxiways and be serviced by present-day ground support equipment.

Flight operations will also be simplified with great attention paid to the findings from the Human Machine Interface workshops. These events have been run to gain input from airline pilots. Larger display screens are among the new features planned for the cockpit. There will be tail fin- and belly-mounted cameras to assist in taxiing, enhanced airport navigation aids, and better rest facilities for the crew.

The flight deck layout will continue the philosophy of commonality with other Airbus aircraft. This assists Cross Crew Qualification and minimizes type conversion times, particularly relevant for airlines flying mixed fleets. The tradition of fly-by-wire will be continued.

Discussions with national air certification agencies have covered safety and in particular emergency evacuation. Airbus believes standard evacuation times can be achieved with the 16 exits that are available (four each side for each deck). "With sufficient independent escape chutes that do not interfere with each other on deployment or in use, the target times can be met," says Velupillai.

A3XX sales activity will commence at the end of 1999 to gain customer commitments during the following 12 months. Engineering definition of the aircraft will be finalized at the end of 2001. The first flight is targeted for 2003 with the aircraft entering airline service the following year.

Airbus Industrie is owned by four leading European aerospace companies DaimlerChrysler Aerospace of Germany with 42.1% (after acquiring Spain's CASA along with its share), Aerospatiale of France with a 37.9% share, and British Aerospace with 20%. The partners have dual roles as shareholders and industrial participants: carrying out the design and manufacture of the aircraft under the co-ordination and management of Airbus Industrie. Here are some of the partners' design responsibilities:

COMPUTER AIDED DESIGN

The Airbus partners have integrated project teams (design, production, purchasing, and support) in their aircraft programs including the A3XX. The development program is underway using the Airbus Concurrent Engineering (ACE) process, which has been used to great effect on the A340 series. It uses three-dimensional rendering of the aircraft to verify structures, systems, and equipment. This is believed to be the first large scale industrial application of a shared CADD S.5 CAD/CAM method. The CAD PDM system is supplied by Parametric Technology Corp. together with dVISE visualization software from Division Ltd. Engineers can simulate the passenger cabin and crew environment, ground handling, and maintenance techniques. Instead of the time and cost of building a physical mock up of the aircraft, an electronic version can be seen and manipulated on a computer screen. Integration of CAD and visualization ensures that design changes are immediately reflected in the simulation. "Our key users will be able to visualize and interact with a virtual mock up as it develops under the PDM," explains Steve Tothill of British Aerospace. "We can conduct daily project design reviews and verify that the products are right."

"The commonality of the CAD/CAM system with the earlier aircraft designs will enable accelerated design of the A3XX," explains Jean-Claude Bernodat of Aerospatiale Matra. Electronic networking of all participants in the project18 companies in different countries also radically improves efficiency of the design process.

MATERIALS

Airbus has been using composites on the stabilizers of its aircraft for some time. The A340-500 and -600 will go a step further than this by using composites on the rear pressure bulkhead and keel beam. This part is 16m long, weighs 1.6 tons, and is the first use of carbon fibre in such a major structural element of an airframe. The A3XX will utilize these developments and add to them. Most probably the outer wing will be made in carbon fiber which will achieve a 20% savings in weight.

Investigation of new materials for structures is underway, and Airbus Industrie partners are heavily involved in the development of new processes that will provide a stronger, lighter weight airframe. GKN Westland, for example, produces large composite structures like under-carriage fairings and control surfaces in composite. "We can also offer resin transfer molding (RTM) which may be suitable for A3XX," explains Tony Roden. "This has previously been labor intensive but cost improvement has been made with machines that can knit a shape together from CAD software while resin is being impregnated into the form."

"Primary carbon fiber has been robust in service," says David Velupillai of Airbus, "But different formats of sandwich construction have been tried to optimize performance." Detailed examination is being made of glass laminated reinforced epoxy (GLARE) and carbon fiber reinforced plastics (CFRP). In evaluating new materials, Airbus is not only concerned with cost and weight but availability, how readily they can be introduced in the manufacturing process, how safely they mix with other materials, and their maintainability through the aircraft's life. Daimler-Chrysler Aerospace has already started development work on wing and fuselage components made from CFRP.

AVIONICS

"The avionics will constitute a major system to be integrated by Airbus with a central computer rather than separate processors," thinks Kenneth Estelle of Smiths Industries which is working with Sextant Avionique on a flight management system (FMS). Airbus is still soliciting various approaches to technology but inclines towards an Ethernet architecture that can offer data transfer rates of 100 Mbytes/sec, many times higher than present systems. The concept is called Avionics Full Duplex Switched (AFDX) Ethernet and will use slightly different protocols from commercial Ethernet. The processor is likely to be commercially available unit, not a special design.

The "interactive cockpit" is pushing avionics technology to new limits. "Today level 1 security for commercial aircraft is 1 in 10^-9 but this level is likely to be higher in the A3XX," says Estelle.

The FMS will be one area where accuracy contributes to better DOC. It allows an aircraft to take advantage of routes equipped with air traffic management facilities. Flying a more accurate course can make a difference of some percent to fuel used, for example.

HYDRAULIC SYSTEMS

Commercial aircraft hydraulic systems have been standardized on 3,000 psi (207 bar) since the DC4 Skymaster in 1942. Most high-performance military aircraft have 4,000 psi (276 bar) and this was the pressure selected for Concorde. A few military aircraft such as the French Rafale have moved to a 5,000 psi (345 bar) system and the same is being considered for the A3XX. Increased pressure means a smaller system: narrower gauge conduit, smaller actuators, and less fluid volume so smaller reservoirs. Overall there could be a weight saving, of 1.5 tons.

Yet if conventional axial piston pumps are used these would have to be bigger and better, according to Wolfgang Jung of Parker Aerospace, division of Parker Hannifin Corp. Depending on system design, there may be 4 or 8 pumps, electric or engine driven.

Further tests will be necessary to determine whether Skydrol®the standard, fire-resistant hydraulic fluid used today-will work in a higher-pressure system.

Electro-hydraulic actuator (EHA) technology is being studied. EHA would provide an autonomous emergency back up instead of tripling the conventional hydraulic system. It would save some weight by reducing the level of redundancy in the existing system a development not favored by all.

AIRPORT STRUCTURE

The basic A3XX will have a maximum take off weight of (MTOW) of 540 tons. Consideration of the effects on pavement is being validated by a series of tests to measure real loads exerted by four- and six-wheel bogies. Another element of this research is to test different pavement structures to destruction by fatigue through simulated heavy aircraft use. In each test area strain gauges that measure cumulative stress are installed.

Airbus has initiated its own Pavement Experimental Program but, in addition, other agencies are also interested. The recent ceremonial opening of the National Airport Pavement Test Facility (NAPTF) in New Jersey, U.S., marked the start of a new era in airport pavement design. This is predicated on the expectation of large capacity aircraft such as A3XX-entering service early in the 21st century.

Airbus is studying the feasibility of boarding and deplaning passengers direct to the upper deck. This would speed up turn around but would require new types of airport passenger piers.