Airbus quietly works on A320 successor

AVIATION WEEK

Airbus Refines A30X Design
Feb 8, 2009
By Robert Wall
Airbus has been quietly testing models of a potential A320 replacement, even though a formal program launch is years away.

The wind-tunnel efforts signal that, behind the scenes, Airbus is busy advancing the configuration for what it internally calls the A30X. The work parallels engine makers’ activities: They are now stepping up efforts to validate the technologies required to power the next-generation short-haul products for both Airbus and Boeing.

Airbus is exploring novel aircraft configurations in a wind-tunnel facility, says a company official. Because the A30X concepts differ markedly from traditional Airbus designs, extensive evaluations have to be performed, he adds.

Last year, Boeing reset its 737 Replacement Study work, essentially saying that it was not satisfied with where its efforts were going and wanted to start over.

Airbus has been evaluating new configurations through both internal research and the European Union-funded Nacre (New Aircraft Concepts Research) project. Through Nacre, Airbus assessed forward-swept wings, rear-mounted turbofan and open-rotor engines, and vertical tailplanes. So far, the company has been reluctant to say what research holds the most promise. The €30-million ($38.4 million) program will end this spring.

The A30X has undergone several rounds of low-speed wind-tunnel tests using a subscale model. The trials have focused on airflow at landing, with speeds not exceeding Mach 0.2. Despite much work on computer-aided design, the tunnel tests are still seen as a cheaper way to gain needed airflow and loads data, the Airbus official says. Running computer models at different attitudes is costly; whereas in a wind tunnel, the model can simply be rotated and the impact measured, he adds.

Airbus’s interest in unusual aircraft configurations could signal that open-rotor engines are now attracting serious attention. They cannot be wing-mounted as traditional turbofans and are often shown by Airbus positioned on the empennage to shield the ground from powerplant noise.

Company officials have been consistently vague about when the A30X may come to market, partly to avoid hurting sales of the A320 family. However, John Leahy, chief operating officer for customers, recently said the new aircraft would not be available before 2020.

The timing uncertainty is a headache for engine manufacturers, which are trying to decide what technologies they can expect to mature in time for the new aircraft. But this is not stopping them from pushing ahead with various research and development activities.

CFM International, for example, will run its LeapX core around midyear. It will also be running tests of a full-scale resin-transfer-molding composite fan. LeapX is the CFM56 follow-on that the General Electric/Snecma joint ventureis designing, in part, with an eye on the next-generation single-aisle aircraft. The companies also are studying open-rotor designs.

One big question in the engine realm will be whether Pratt & Whitney and Rolls-Royce can agree on a way to maintain their International Aero Engines partnership, which now offers the V2500 for the A320 family. But Rolls and Pratt have very different ideas about the future engine, and so far there has been little indication that a consensus will be possible.

Pratt is betting heavily on its geared turbofan and last year started work on the Advanced GTF that would power the future Boeing or Airbus aircraft. The goal is to assess technologies and demonstrate them in 2012-13, says Bob Saia, Pratt’s vice president for next generation products. To boost efficiency, the company wants to further advance its gear system from a 3:1 ratio to more than 4:1, says Saia, allowing the fan to run slower and thereby improving performance. The bypass ratio for that engine hasn’t been set, but should surpass 12:1, while the engine pressure ratio should top 50:1, he adds.

Some of the Advanced GTF technologies could also be used to update new builds of the first-generation GTFs. Enhancements being explored include active combustor controls, advanced and lightweight materials, and advanced aerodynamics for the fan and compression system, as well as intelligent prognostic health management.

A 40,000-lb.-thrust-class GTF should be able to handle the likely size requirement for which Boeing and Airbus are striving, according to Saia. Airframers have indicated that aircraft size could range up to 250 seats. What remains unclear is whether a single engine or aircraft type will emerge to cover the short- to medium-haul sector.

Although novel aircraft configurations are largely associated with open rotors, Saia says the GTF could also be used for unorthodox aircraft designs, including forward-swept wings – which Airbus has been considering to improve laminar flow. One issue that Pratt will be assessing as it evaluates recent flight-test data (see p. 46) is how its critical fan-drive gear system would be affected by fuselage mounting or other installation options.

In the meantime, Rolls has been reluctant to narrow its design options, preferring to continue working on a two-shaft RB282 derivative configuration, a three-shaft RB285 and an open-rotor concept.

The open rotor should deliver around 15% improved specific fuel consumption over standard engines at a speed of roughly Mach 0.8. Rolls is pursuing a two-spool core with counterrotating propellers. Scale-model tests also have shown that one of the big concerns about open rotors – noise – can be overcome.

Trials in the Netherlands and U.K. suggest that an open-rotor-powered design can be made quieter than current-generation aircraft, says a Rolls official. The open-rotor configuration should be ready for service in 2018.

Rolls engineers hope to draw on a variety of research efforts to advance underlying technologies. While the European Clean Sky program focuses heavily on open rotors, other projects – including the U.K.-funded Environmentally Friendly Engine (using a Trent 1000) – focus on upgrading more traditional designs. The EFE demonstrator is now being built at Rolls-Royce’s Bristol, England, facility, and it is slated to start running this year. Lessons from the program, including the lean-burn combustor, could still be fed into the TrentXWB, the latest Rolls engine being developed for the Airbus A350XWB, says the Rolls-Royce official.

For the engine manufacturers, a major variable is that they don’t know exactly when Airbus and Boeing aim to launch a new aircraft. Moreover, says one engine official, what will trigger the two airframers into action is hard to gauge – whether it be economic realities or new certification standards. New demands on noise or other environmental performance could serve as a catalyst.