Bombardier has already thrown its hat into the more-than-100-seats jetliner ring with its C Series design and Embraer is considering its response to perceived market requirements (see box). But industry leaders Airbus and Boeing have been markedly reticent to reveal more of their thinking on the characteristics needed in designs to replace their A320 and 737, respectively, in the 150-passenger class by the end of the next decade.

Airbus studies of a possible new 150-seater are being conducted under the title “new short range” (NSR). According to Christian Scherer, executive vice president and head of strategy and future programs, the European airframer is now considering airline requirements rather than a straight A320-replacement design. “There are [different] segments and we want to provide what the market wants, so we are looking at anything above 100 seats, up to medium-haul capacity of 240 to 250 seats where you run out of single-aisle options,” he explained.

Scherer acknowledged that at 230 to 250 seats, different needs might drive varying wing sizes and propulsion solutions. The first requirement is a fairly short range– 1,800 nm typically driven by larger European customers, while the other is medium-range–more like 4,500- to 5,000-nm transatlantic, U.S. long transcontinental, or U.S.-Hawaii flight sectors.

Airbus has said that a new single-aisle will want U.S. transcontinental range, predicting that the market bulk will remain “where the A320 sits now [with] ‘just a tad’ longer range to be comfortably U.S. diagonal transcontinental range,” Scherer said. The company recently extended A320 range by 200 nm to just short of 3,000 nm.

The European manufacturer has to decide the size and value of the market(s) and whether development of discrete designs by at least two manufacturers is justified. “That’s a question we can’t answer yet,” Scherer said.

Airbus has long believed in the inevitable increase in aircraft average size (confirmed also by Boeing market forecast statistics) and while it studying requirements for aircraft with as few as 100 seats, the company denies it is planning such a small model. “Airbus wants to remain absolutely relevant in analyzing and understanding the market above scope clause,” said Scherer. “That doesn’t mean that we are contemplating 100 seats, because we are not. The bulk of the demand remains solidly single-aisle [and] six-abreast around A320/321 size.”

Given the prospect of emerging competitors in the 100- to 130-/140-seat segment, including Asian designs, Scherer expects “a frenzy and extremely competitive pressure, especially for some new players” as they make their first real ventures as integrators. “We will keep an eye on who is doing what and at what level of technology because their next step will be for them to move up,” he added.

Airbus believes its current single-aisle cross section is quite adequate, but Scherer was at pains to say any new development is a long way from definition or design freeze. Any series of aircraft, he maintained, would have a “normal market distribution,” which he further explained as “A320-size plus a little more [capacity] with comfortable transcontinental range, [retaining] the ideal single-aisle, six-abreast layout.”

Will a new generation use a lot of composite material? Airbus is trying to “move away from philosophy to what is pragmatic business sense,” said Scherer. “The smaller the aircraft the less obvious nonmetallic materials become because there is less volume from which to save weight.”

He said the complexity and cost of carbon-fiber fuselage aerostructures is higher than with alloys, but it becomes less significant for larger, longer-range aircraft. “For short-range aircraft the question is open. A decision today would be [for] metallic,” if only because of problems of damage during ground handling, especially with many turnarounds a day.

But such considerations are currently irrelevant, according to Scherer. “We don’t have to decide today. We have done a lot of research on repairability of carbon-fiber fuselages and the cost effectiveness in production. We have a long way to go before we can mass-produce carbon-fiber fuselages and airlines have a way to go before they can have structurally immune airframes.”

Airbus has focused studies on simplicity and ease of boarding and disembarking, including ideas about simplifying baggage handling and increasing the likelihood of safe delivery. In the future, Scherer predicted, passengers will want more and better service, especially ease of turnaround, quick access to bags, and simplicity in travel. And, in-flight entertainment will be less important on shorter flights.

“The most telling [requirement for future airliners] is probably [performance] relative to today,” continued Scherer. “Most successful programs have established a step ahead in economic efficiency, [and] productivity has to increase. But it must be measurable and substantial.” He added that by this he meant that the future aircraft will have to be at least 20 to 25 percent more economical than the equipment they are set to replace.

Accordingly, Airbus will make significant investments in a few technological developments that it expects to converge in time and quality toward a 20- to 25-percent productivity gain “at the end of the next decade, not earlier,” said Scherer. The company will continue to focus on fuel-burn savings and foresees convergence among emerging air-traffic management (ATM) solutions.

Airbus does not expect to develop a basic low-cost carrier (LCC) variant, despite some operators’ pursuit of every last ounce of weight and every penny of acquisition and operating cost. “There would not be much difference in operating cost between an A320 legacy [carrier] or an A320 LCC,” said Scherer. “We would want to be careful about having any ‘school bus’ [model], [but we] do want modularity of design and to offer a choice.”

Getting Radical?
So should the world expect a radical aircraft configuration to emerge in 10 years? “There’ll be no flying saucers or blended wings for the NSR [aircraft],” insisted Scherer. Airbus is studying a rear-mounted open-rotor engine configuration because “on paper that technology can give at least a further 10-percent fuel saving.” Ground clearance considerations mean open-rotor engines cannot be wing-mounted, explained Scherer. “Rear-mounting poses a technical challenge we have not yet mastered,” he added.

Scherer reported that the geared turbofan engine test-flown on an Airbus A340 test bed represents a very different configuration. Airbus is considering this new technology as a fallback technology should open-rotor not work out.

For its part, Boeing has conducted a 737-replacement study (737RS) over several years, although a discrete group working on that study has been absorbed into broader future-project considerations. After the U.S. manufacturer spoke to “quite a number” of airlines to understand requirements, it was clear that operators had a very high expectation regarding fuel efficiency, operating cost, environmental performance (especially noise and carbon emissions), and cabin standards, according to Boeing Commercial Airplanes director of integrated product strategy Jeff VerWey.

“First and foremost, customer focus is on fuel efficiency, [and you need to] think in terms of 20-percent [improvement] in fuel burn, then a minimum double-digit improvement in direct operating cost, remembering fuel is about half your cash operating cost,” said VerWey. At least 10-percent gains in airframe and engine maintenance costs also will be required, something that told Boeing “how good the current 737 is, and how difficult it will be to replace,” he said.

A major issue is the passenger loads to be carried, particularly the capacity of the smallest variant, said the official, who oversees the planning of product, engine and feature strategies (including propulsion, flight deck and passenger cabin systems). While there is some interest in a 120-passenger model, VerWey told AIN that prospective customers considering environmental factors, fuel price, and infrastructure constraints see the advantage of larger aircraft. The 737 started life offering 66 to 99 seats but over the past 45 years has grown to accommodate as many passengers as did the Model 707.

“The big question is whether there is a 100-seat market. It is not concrete yet,” said VerWey, who added that Boeing is studying requirements ranging from 90 to 220 seats. “Think of a 737[-type] family. The vast interest is in the [168- to 189-passenger] 737-800,” he said. The manufacturer is unsure whether markets for 200-plus seats are medium- or long-haul range.

Having established–at the second attempt–a fuselage cross section for the 707 that was retained for thousands of 727, 737 and 757 variants, Boeing sees an “emerging” view of the required dimensions on a future narrowbody. Since customers want fuel efficiency and under-floor space for standard cargo containers, but passengers seek more comfort–“both of which compromise fuel performance”–Boeing is keen to show the cost of trading one for the other. “Operators have not yet converged on an answer,” VerWey said.

If the capacity of a new aircraft is little different from that of the 737, are range requirements also similar? “It’s about right. Some operators say they do not use all the range available, [so] could the aircraft be more efficient with less fuel range built in? We are looking at the required wing area or lower thrust–factors that [have to] be balanced,” he said.

On the questions of materials, Boeing has been improving its understanding of composites through the new 787. VerWey suggested a new aircraft could be up to 50 percent nonmetallic, although the perceived contribution of such materials on the 787 will not read across directly. “Composites scale up more easily than they scale down,” he said.

VerWey confirmed that the U.S. manufacturer has studied whether there is a case for a basic LCC variant of any new narrowbody, but pointed out that such operators have worked with different business models. He said that selection of seats without tilt mechanism or with more plastic and less fabric was part of the buyer-furnished equipment that did not contribute to the manufacturer’s price.

Having ventured into the future with its Sonic Cruiser artist’s impressions of a possible novel future-airliner configuration, Boeing sees a next-generation narrowbody being very much more likely to follow convention. VerWey said a major consideration will be available engines and their mounting on the airframe.

Options to be considered have included underwing mounting, high-wing layouts and rear-mounted engines. “We have no tendency to jump one way; we are working to understand the implications of alternative solutions,” he said.

While VerWey conceded that Boeing has carried out wind-tunnel tests using models, he said this was for computational fluid dynamics studies. “It is certainly not to try to integrate entire airplanes,” he explained.

The Boeing executive maintained that “bold steps” with the 787, including composites, very-efficient engines, more-electric systems and enhanced passenger experience place Boeing “in a good position, but a next-generation aircraft has to be even better.” Future composites certainly will be important, along with systems, which must take less volume since there is less room. Boeing’s work with engine suppliers has confirmed that timing for a new aircraft is “more toward the latter half of the next decade.”

So, what is driving development? VerWey cites several factors. “Operators are interested in fuel efficiency [and] long-term solutions, [which] means examining all alternatives,” he said. “There is incentive for airlines to standardize because they don’t want to jump from platform to platform.”

Regulation also is a consideration, including noise standards and emissions trading systems, as well as infrastructure. “The availability of new technology will be a final factor driving the timing of a new narrowbody airliner,” concluded VerWey.