After three decades, is the 747 finally about to be stretched?
In February 1969, the first 747 climbed into a wintry Seattle sky and launched the age of the widebody. Who could have guessed that 35 years later Boeing would be studying the most realistic stretch derivative yet devised, and be laying the groundwork for the sixth major model of the family?
There are indeed growing signs that, thanks directly to the birth of the 7E7 and indirectly to the emergence of the Airbus A380, the vision of a stretched 747 entering service in the 40th anniversary year of its first flight might finally become reality. Discussed virtually from day one, the stretched 747 has remained an unfulfilled pipedream without substance or reason. Now, despite the sceptics, Boeing believes there could be both technical and commercial reasons for a rethink.
So what has changed? Technically, Boeing's drive to develop the 7E7 is producing a growing stockpile of advanced propulsion, systems and structures knowhow that could be "game changers" in the search for new levels of efficiency with a radically revamped 747 design. Commercially, it has identified a small but significant market opportunity for a 450-seater for which the stretched 747 appears ideally suited. The market, estimated at between 300 and 350 aircraft over the next 20 years, is part of a much larger "200-seater gap" which Boeing forecasts could require up to 2,800 aircraft over the same period. The "gap" lies between the Airbus A340-600 and A380-800, and with no chance of Airbus plugging it with a product of its own, Boeing is eager to fill the need with 777-300/300ERs, 747-400ERs and - potentially - the 747 Advanced.
While Airbus naturally downplays firstly the significance and even the true existence of a "200-seater gap" in its portfolio, it does not dispute that its resources are stretched to the limit while it sees the A380 safely into service. Boeing also has its hands full with the 7E7, but sees the possible development of the 747 Advanced as a well-timed, relatively low-risk, low-cost venture to take advantage of this market opportunity. It also provides a new growth path for the 747 family and extends the capacity gap between it and the 777-300/300ER towards the more competitive 15-20% range.
"The Advanced is starting to take shape and it is going down the right path," says product and services marketing director Randy Tinseth, a veteran of previous 747 stretch attempts, including the long-abandoned -600X. "We were getting really close to selling the -600X, but even as we did, the market began shrinking," he adds. The 550-passenger -600X and its smaller sibling, the equally doomed 465-passenger -500X, were meant to bracket the A3XX, but were killed off in January 1997. The axe fell amid ominous signs of airline financial woes in Asia and the USA, tepid market interest, climbing development costs and, finally, Airbus's decision to accelerate what was to become the A380.
The decision also led to Boeing's strategic realignment in favour of long-range twins and the pursuit of market fragmentation, but it did not mean the abandonment of the 747. Continued improvements were made on the production line, and in the product, the results of which culminated in the emergence of the higher-gross weight 747-400ER and the birth of studies into a quieter, longer-range -400XQLR. However, despite its best efforts, the economics of the study derivative were far from compelling by the standards of both Boeing and the airlines, and it was not until the advent of the 7E7 and its "game-changing" powerplants that the picture began to alter.
"The landscape has been changing since we last looked hard at 747 derivatives," says product marketing regional director Brad Till. "We fundamentally see a much smaller market for an aircraft larger than the 747, and we don't see a business case that makes sense for an all-new aircraft. But we think using the 7E7 technology provides a good approach and now that looks like it's got merit. The market certainly is interested in a 400- to 450-seat aircraft, but we've got to make sure it makes sense, and we think this does."
Targets for the 747 Advanced, internally dubbed -400X by product development, are based around improved operating economics, longer range and guaranteed compliance with London's QC2 noise limits. Buoyed by signs of new life in the existing -400/400ER/400F markets, Boeing is also seeing renewed interest in the Advanced. "We don't see it being a 'barn burner' in terms of the orderbook, but we think it will stay strong for a number of reasons," says Till. "A lot of customers are not interested in moving up to the A380, and there are still a lot of people in a 'wait-and-see' mode. The 747 fits into the existing market infrastructure, whereas the A380 is limited. The Advanced fits into the ICAO Code F size category [below the ICAO-established 80 x 80m box within which the A380 fits]."
In the meantime, new details are emerging about the design of the Advanced, which will be put through windtunnel tests in 2005 in the run-up to an expected go-ahead decision in 2006. With timing tied closely to the development of the General Electric GENX and Rolls-Royce Trent 1000 engines for the 7E7, entry into service is expected to be late 2009 or early 2010 - 18 months to two years behind the new twin.
The passenger version will be a stretched variant of the -400ER with a 2.03m-long plug inserted into the constant-section double deck forward Section 42 at fuselage station 740. A second 1.53m plug will be inserted close to the trailing edge at fuselage station 1480, a natural production break between the overwing Section 44 and aft fuselage Section 46 where the aft pressure bulkhead of the body gear wheel well is situated. Total overall length increases to 74.2m compared with 70.6m for the current model. The stretch is optimised for increased seating capacity by adding most of the length in the double-deck section.
The baseline aircraft, with a maximum take-off weight (MTOW) of 422,000kg (930,000lb), will seat up to 450 and have a 14,800km (8,000nm ) range. It will also have a modernised 777-style flightdeck, and be "wired" or e-enabled from the production line for the Connexion by Boeing system. The stretch provides room for two extra belly pallets and additional space in the upper crown area for innovative "sky suites" that include bunks, meeting rooms, rest areas or galley cart stowage.
Although the suites would weigh between 2,270kg and 3,630kg depending on selected layout, Boeing says concepts being explored with the airlines include selling economy-class seats at premium prices to passengers who, after take-off and before landing, would walk up to the suites via a new stairway located by door No 4 for the rest of the flight. Suite designs are under study, with 1m-, 1.5m- and 2m-wide bunks being evaluated. The new design also includes a modernised No 2 door entry with a sweeping, wider stairway to the upper deck and a lofted open space running from the main deck up to the ceiling of the hump. Three additional transparencies would be added to the upper deck belt on the starboard side, with three "skylight" windows directly overhead creating the impression of a "triple decker".
"We have amazed ourselves at what we've been able to do with the space," says interior configuration lead Richard Johnson, adding that changes were made by redistributing environmental control system ducting and other systems to the outer edges of the upper crown. "The main changes were relocating the flight controls from the centreline to the outside." The alterations create a 1.88m-tall stand-up space in the crown, reducing to 1.82m under the frames. Plasma screens are being considered to provide artificial skies and day-like light levels. Although the additional structure adds weight, Johnson says extra rigidity allows some large, weighty legacy parts to be removed. These include a transverse truss known as the "life raft" beam, built to support a large life raft before the invention of inflatable escape slides.
Boeing is sharpening up its marketing claims for the inevitable war with Airbus over the relative performance of the A380 versus the 747 Advanced. Against a datum set by a GE CF6-80-powered 747-400, Boeing predicts the A380-800 block fuel per seat over an 11,000km leg will be about 1% lower, whereas the 747 Advanced, it claims, will be as much as 15% lower thanks to new levels of efficiency in materials, aerodynamics and engine technology. Trip costs for the Advanced will be 2% higher than for the -400, but up to 6% lower in terms of seat kilometre costs over a 5,550km flight. Compared with a A380 configured with 542 seats over the same stage length, however, Boeing believes seat kilometre costs will be 3% lower for the 450-seater Advanced, and trip costs could be up to 19% lower.
The freighter variant is a -400ERF stretched in the same constant cross-section fuselage area at fuselage station 1480, as well as forward at station 1000 where a 3.56m-long plug will be inserted aft of the upper deck hump fairing. Because the upper deck on the freighter is the original short hump of the -100/200 series, this means the plug is inserted further aft relative to the fuselage extension on the passenger derivative. Overall length increase is about 5.1m, making the proposed Advanced freighter the longest variant at 75.8m, providing space for four more main deck pallets and two more lower deck containers and pallets. As the aircraft cross-section takes 2.9m-tall pallets throughout its length, whereas the A380 is configured to carry 2.44m- and 2.08m-sized containers on the main and upper deck respectively, Boeing claims the 747 Advanced will have a design density of 158.6kg/m3 versus 126.6kg/m3 for the A380F. Over 5,550km flights, it believes the Advanced freighter will have 12.4% lower tonne-km costs than the current -400F, and up to 14.6% lower tonne-km costs than the A380F.
All other changes are basically common to both and include modified, bleed-air-generating 7E7 engines mounted on "close-coupled" pylon attachments. "This will give them a larger ground clearance than the A380," says 747/767/777 product development chief Kourosh Hadi. The nacelles will also feature noise-reduction treatments such as chevrons, adds Hadi. Till says modifying the engines for bleed "looks feasible. We've talked to GE and R-R and it's do-able." The wingspan is extended with 777-300ER-style raked tips to 68.6m compared with 64.4m on the current aircraft. The wing will have the trailing-edge wedge drag-reduction feature as well as simpler, double-slotted flaps. In construction, the wing and some parts of the fuselage structure will use newer, lightweight aluminium materials, some developed to compete with composites on the 7E7. An additional 6,440 litres (1,700 USgal) of fuel is stored in the horizontal stabiliser by extending the tank space outboard by several ribs, and by adding tankage forward of the front spar.
Overall, it appears that thanks to the ironic historical intersection of the A380 and the 7E7, there could be at least one more chapter to come in the epic tale of the 747.
GUY NORRIS / LOS ANGELES
Source: Flight International
