Despite initial enthusiasm for the transonic airliner, carriers now want value for money

When Boeing decided last month to terminate Sonic Cruiser, it marked the second time in as many years that the US manufacturer had made a dramatic U-turn in its long-term product development plans.

In 2001, the arrival of the transonic airliner project, amid much fanfare, distracted from Boeing's simultaneous decision to shelve the 747X Stretch programme. Eighteen months on, Sonic Cruiser is dead and Boeing's energies are being deployed on to the conventionally configured Super Efficient Airplane project.

To paraphrase Oscar Wilde: to lose one aircraft project may be regarded as a lose both looks like carelessness. Boeing knows that if its credibility is to survive intact, then Super Efficient must succeed where the 747X Stretch and Sonic Cruiser failed, and become a reality.

Super Efficient is a conventional configuration that started life as a "reference" model against which to judge the promised benefits of the much faster Sonic Cruiser studies. While the Super Efficient option may be a step backward in excitement terms, Boeing expects it to offer the chance of a paradigm shift in low-cost, point-to-point operations for cash-strapped carriers.

That, in essence, is why most people believe the interesting-looking Sonic Cruiser flopped and the rather dull Super Efficient design won. It is costs, not looks, that interest airlines - particularly since 11 September 2001. Until then, there was reason to believe Boeing's Sonic ambitions for a high-speed fragmenter could have taken off.

Sweet spot

The design was close to achieving its goal of being commercially viable with a 20% faster cruise speed, and windtunnel tests confirmed that basic stability and control characteristics were "steady and level" at Mach 0.98, the so-called "sweet spot" in the cruise-drag curve.

Indeed, following the almost messianic zeal with which Boeing announced the Sonic Cruiser in March 2001, many leading carriers were quick to jump on the transonic bandwagon. Within two months, American Airlines' Don Carty and Virgin Atlantic's Sir Richard Branson openly embraced the concept, with Branson saying in May 2001: "I truly believe this aeroplane will change the way the world flies. We expect to order between three and six aircraft." Others remained circumspect but quietly enthusiastic about what they saw as the first realistic attempt to gain affordable speed since Concorde.

Emirates managing director Maurice Flanagan summed up the feelings of many at the time when he said: "It has been a year of anticipated revolutionary change in the industry, with one aircraft manufacturer choosing size and the other now appearing to opt for speed in the forthcoming production cycle. We chose size by being the first airline to order the Airbus A380 superjumbo, but for the future we will keep our options open on speed as we study Boeing's promised Sonic Cruiser and await a likely response from Airbus."

Airbus, not surprisingly, soon revealed brief details of high-speed configuration studies but declared that its development plate was rather full with the A380, A318 and others. Boeing, meanwhile, defended its stance on the timing of the Sonic Cruiser, which critics at the time suggested was more of a blatant show-stealer from the formal launch of the A380 than the unveiling of a realistic project.

First cracks

Even after the airline industry collapsed in September and October 2001, Boeing defended the project to the hilt. Boeing Commercial Airplanes president Alan Mulally said the Sonic Cruiser was the "company's number one development priority", while chairman Phil Condit added: "Nothing we have seen [since 11 September] reduces the commitment we have to it. If anything, what we have seen indicates that point-to-point service is going to be critical."

But the first cracks were starting to show as both Condit and Mulally admitted the possibility of delays to the project. The previously mentioned entry-into-service target of 2006 vanished, and Condit agreed development could "move out a bit".

At this stage in the third quarter of 2001, Boeing preferred to perform internal studies on the "value" of speed, while the airlines were too busy surviving to care. Board approval to offer the Sonic Cruiser was still expected to be sought around December 2002, definition was planned to be completed by the end of 2003, with a formal go-ahead the following year and first flight in December 2006.

New programme offices were set up at the former Bomarc missile buildings in Everett and, by early 2002, talks with some of the airlines had restarted.

Walt Gillette, vice-president and general manager of what was then officially called the Sonic Cruiser programme, was upbeat. "The companies are starting to come back now," he said. "The dialogue has really resumed and we now have serious discussions going on again with up to 15 major airlines." Talks and deals were also under way with suppliers, and a set of "technology partners" had begun working with Boeing on new features.

A group known within Boeing as the "big seven" formed the first phase of what the US airframe maker hoped would form a global network of partners. These included Alenia of Italy, Hawker de Havilland of Australia, the three main Japanese aerospace companies - Fuji, Kawasaki and Mitsubishi Heavy Industries - plus Vought Aircraft Industries and Boeing's Wichita division. The initial focus was on advanced structures technology, the first goal being a 60-70% composite structure by weight.

By the middle of the year, Boeing had added GKN Aerospace Services, Stork Fokker Aerostructures and Fischer Advanced Composite Components to its aerostructures technology team. It also refined its basic Sonic Cruiser concept into three main configurations. The first was the by-now familiar baseline canard-configured aircraft with a large aft wing and clear supersonic development potential. Made mostly from advanced composites, its design features included a trimmable canard with elevators, forward retracting main gear, 6:1 bypass ratio engines, elevator/ailerons on the trailing edge between the nacelles, an all-electric environmental control system (ECS), electric flight control system (FCS), integrated vehicle health management (IVHM) and simple hinged leading and trailing edge flaps.

The second and third designs both featured mid-wing configurations and conventional empennage, offering better compatibility with ground infrastructure such as airport jetways. However, they suffered performance penalties because of the area-ruling required to compensate for the aft tail configuration. The engines of the faster mid-wing design were mounted on the wing trailing edge. The slower mid-wing design was more profoundly area-ruled with higher-fineness ratio engine nacelles mounted on pylons on the wing leading edge.

While all three Sonic configurations firmed up, the same advanced structures and systems technologies were applied to the ever-evolving Super Efficient Airplane. Dating to the pre-Sonic product development studies of 1999 and before, this was a single-model product aimed at bridging the coming gap between the 737-800/900 and 777-200.

Designed loosely as the basis for a family to fulfil the needs of both 757 and 767 operators, it had assumed the project name Yellowstone alongside similar projects named after US national parks. Others included Project Glacier, which became Sonic Cruiser, and another was thought to be Project Yosemite, a future new large aircraft concept.

Firmly established as the "reference" baseline model, initial projections promised that the Super Efficient would consume around 10% less fuel than the Sonic Cruiser and 17-20% less per passenger than a 767-300. It now commanded new respect from the airlines, which began to see its dramatic cost benefits as a lifeline to survival.

Reluctantly admitting to this new surge of interest in a reference model, Boeing began to see advisory group airlines such as British Airways advocating efficiency over speed. In the run-up to the 2002 Farnborough air show, it became clear the hoped-for airline recovery was not going to materialise as soon as hoped - a fate likely to be shared by the Sonic Cruiser.

At the show in July, Gillette said the company was "just not sure" of the chances of getting board approval by the end of the year, while Condit, with an eerie echo of the months leading up to the 1996 cancellation of the 747-500X/ 600X, said the possibility of launching was still "pretty good, but not 100%".

Mulally gave perhaps the biggest clue of the coming change when he said: "There have been intense discussions with airlines about the value of speed. We don't know the answer yet. If it turns out that we can't value the time saving, then we will see what the next development should be."

By October, Boeing knew the Sonic Cruiser was not the preferred option after a meeting with its airline group at which, crucially, no operator gave a high "rating" to the aircraft's Mach 0.96-0.98 cruise speed. Bowing to the inevitable, Boeing changed gear and Mulally began a global trip to discuss the decision, and the Super Efficient Airplane alternative, with airlines and suppliers.

Shortened hybrid

Resembling a shortened hybrid between a 777-200 and 767-400, the first firm details of Super Efficient were revealed by Flight International in November (Flight International, 12-18 November). Configured with a circular fuselage cross-section with room for LD3 containers, very high 10:1 bypass ratio engines, raked tips, inboard retracting main gear and simplified wing trailing edges, the aircraft has a 56.7m (186ft 2in) span and a length of 59m.

The aircraft will encompass other systems and materials technologies considered for the Sonic Cruiser, possibly including titanium-graphite structures and composite skin stringers. It will be "more electric" with hybrid FCS, electric engine start, ice protection and environmental control. It will also have advanced flight controls, a common systems architecture and IVHM.

The final decision came in mid-December, but by then the industry was prepared. As with Concorde three decades before, the harsh realities of economics had killed off the fast aircraft concept in favour of low-cost efficiency.

Source: Flight International