Boeing 2707
The Boeing 2707 was an American supersonic passenger airliner project during the 1960s. After winning a competition for a government-funded contract to build an American supersonic airliner, Boeing began development at its facilities in Seattle, Washington. The design emerged as a large aircraft with seating for 250 to 300 passengers and cruise speeds of approximately Mach 3. It was intended to be much larger and faster than competing supersonic transport designs such as the Concorde.
The SST was the topic of considerable concern within and outside the aviation industry. From the start, the airline industry noted that the economics of the design were questionable, concerns that were only partially addressed during development. Outside the field, the entire SST concept was the subject of considerable negative press, centered on the issue of sonic booms and effects on the ozone layer.
A key design feature of the 2707 was its use of a swing-wing configuration. During development, the required weight and size of this mechanism continued to grow, forcing the team to switch to a conventional delta wing. Rising costs, environmental concerns, noise, and the lack of a clear market led to its cancellation in 1971 before two prototypes were completed.
Development
Early studies
began small-scale SST studies in 1952. In 1958, it established a permanent SST research group, which was spending $1 million a year by 1960. It proposed a variety of alternative designs, all under the name Model 733. Most of the designs featured a large delta wing, but in 1959 another design was offered as an offshoot of Boeing's efforts in the swing-wing TFX program. In 1960, Boeing ran an internal competition for a 150 seat transatlantic SST design, and the swing-wing version won.Shortly after taking office, President John F. Kennedy tasked the Federal Aviation Administration with preparing a report on "national aviation goals for the period between now and 1970". The study was prompted in the wake of several accidents, which led to the belief that the industry was becoming moribund. Two projects were started, Project Beacon on new navigational systems and air traffic control, and Project Horizon on advanced civil aviation developments.
Only one month later the FAA's new director, Najeeb Halaby, produced the Commission on National Aviation Goals, better known as Project Horizon. Among other suggestions, the report was used as a platform to promote the SST. Halaby argued that a failure to enter this market would be a "stunning setback". The report was met with skepticism by most others. Kennedy had put Lyndon Johnson on the SST file, and he turned to Robert McNamara for guidance. McNamara was highly skeptical of the SST project and savaged Halaby's predictions; he was also afraid the project might be turned over to the DoD and was careful to press for further studies.
The basic concept behind the SST was that its fast flight would allow them to fly more trips than a subsonic aircraft, leading to higher utilization. However, it did this at the cost of greatly increased fuel use. If fuel costs were to change dramatically, SSTs would not be competitive. These problems were well understood within the industry; the IATA released a set of "design imperatives" for an SST that were essentially impossible to meet—the release was a warning to promoters of the SST within the industry.
Concorde
By mid-1962, it was becoming clear in the US that tentative talks earlier that year between the British Aircraft Corporation and Sud Aviation on a merger of their SST projects were more serious than originally thought. In November 1962, still to the surprise of many, the Concorde project was announced. In spite of marginal economics, nationalistic and political arguments had led to wide support for the project, especially from Charles de Gaulle. This set off something of a wave of panic in the US, as it was widely believed that almost all future commercial aircraft would be supersonic, and it looked like the Europeans would start off with a huge lead. As if this were not enough, it soon became known that the Soviets were also working on a similar design.Three days after the Concorde announcement, Halaby wrote a letter to Kennedy suggesting that if they did not immediately start their own SST effort, the US would lose 50,000 jobs, $4 billion in income, and $3 billion in capital as local carriers turned to foreign suppliers. A report from the Supersonic Transport Advisory Group followed, noting that the European team was in the lead in basic development, and suggested competing by developing a more advanced design with better economics. At the time, more advanced generally meant higher speed. The baseline design in the report called for an aircraft with Mach 3 performance with range in order to serve the domestic market. They felt that there was no way to build a transatlantic design with that performance in time to catch the Concorde's introduction, abandoning the trans-Atlantic market to the Europeans.
In spite of vocal opponents, questions about the technical requirements, and extremely negative reports about its economic viability, the SST project gathered strong backing from industry and the FAA. Johnson sent a report to the president asking for $100 million in funding for FY 1964. This might have been delayed, but in May, Pan Am announced they had placed 6 options on the Concorde. Juan Trippe leaked the information earlier that month, stating that the airline would not ignore the SST market, and would buy from Europe if need be. Pan Am's interest in Concorde angered Kennedy, who called his administration to get Pan Am to redirect its potential funding back to the US SST program.
Kennedy introduced the National Supersonic Transport program on June 5, 1963, in a speech at the US Air Force Academy.
Design competition
Requests for proposals were sent out to airframe manufacturers Boeing, Lockheed, and North American for the airframes; and Curtiss-Wright, General Electric and Pratt & Whitney for engines. The FAA estimated that there would be a market for 500 SSTs by 1990. Despite not having a selected design, orders from air carriers started flowing in immediately. Preliminary designs were submitted to the FAA on January 15, 1964.Boeing's entry was essentially identical to the swing-wing Model 733 studied in 1960; it was known officially as the Model, but also referred to both as the 1966 Model and the Model 2707. The latter name became the best known in public, while Boeing continued to use 733 model numbers internally. The design resembled the future B-1 Lancer bomber, with the exception that the four engines were mounted in individual nacelles instead of the paired pods used on the Lancer. The blended wing root spanned almost all of cabin area, and this early version had a much more stubby look than the models that would ultimately evolve. The wing featured extensive high-lift devices on both the leading and trailing edges, minimizing the thrust required, and thus noise created, during climb out. The proposal also included optional fuselage stretches that increased capacity from the normal 150 seats to 227.
Lockheed's entry, designated CL-823, was essentially an enlarged Concorde. Like the Concorde, it featured a long and skinny fuselage, engines under the wing, and a compound delta planform. The only major design difference was the use of individual pods for the engines, rather than pairs. The CL-823 lacked any form of high-lift devices on the wings, relying on engine power and long runways for liftoff, ensuring a huge noise footprint. The CL-823 was the largest of the first-round entries, with typical seating for 218.
The North American NAC-60 was essentially a scaled-up B-70 with a less tapered fuselage and new compound-delta wing. The design retained the high-mounted canard above the cockpit area, and the box-like engine area under the fuselage. The use of high-lift devices on the leading edge of the wing lowered the landing angles to the point where the "drooping nose" was not required, and a more conventional rounded design was used. Compared to the other designs, the rounded nose profile and more cylindrical cross-section gave the NAC-60 a decidedly more conventional look than the other entries. This also meant it would fly slower, at Mach 2.65.
A "downselect" of the proposed models resulted in the NAC-60 and Curtiss-Wright efforts being dropped from the program, with both Boeing and Lockheed asked to offer SST models meeting the more demanding FAA requirements and able to use either of the remaining engine designs from GE or P&W. In November, another design review was held, and by this time Boeing had scaled up the original design into a 250-seat model, the Model 733-290. Due to concerns about jet blast, the four engines were moved to a position underneath an enlarged tailplane. When the wings were in their swept-back position, they merged with the tailplane to produce a delta-wing planform.
Both companies were now asked for considerably more detailed proposals, to be presented for final selection in 1966. When this occurred, Boeing's design was now the 300-seat Model 733-390. Both the Boeing and Lockheed L-2000 designs were presented in September 1966 along with full-scale mock-ups. After a lengthy review the Boeing design was announced as the winner on January 1, 1967. The design would be powered by the General Electric GE4/J5 engines. Lockheed's L-2000 was judged simpler to produce and less risky, but its performance was slightly lower and its noise levels slightly higher.
Refining the design
The 733-390 would have been an advanced aircraft even if it had been only subsonic. It was one of the earliest wide-body aircraft designs, with 2-3-2 row seating arrangement at its widest section in a fuselage that was considerably wider than aircraft then in service. The SST mock-up included both overhead storage for smaller items with restraining nets, as well as large drop-in bins between sections of the aircraft. In the main 247-seat tourist-class cabin, the entertainment system consisted of retractable televisions placed between every sixth row in the overhead storage. In the 30-seat first-class area, every pair of seats included smaller televisions in a console between the seats. Windows were only due to the high altitudes the aircraft flew at maximizing the pressure on them, but the internal pane was to give an illusion of size.Boeing predicted that if the go-ahead were given, construction of the SST prototypes would begin in early 1967 and the first flight could be made in early 1970. Production aircraft could start being built in early 1969, with the flight testing in late 1972 and certification by mid-1974.
A major change in the design came when Boeing added canards behind the nose—which added weight. Boeing also faced insurmountable weight problems due to the swing-wing mechanism, a titanium pivot section having been fabricated with a weight of and measuring long and thick, and the design could not achieve sufficient range. Flexing of the fuselage threatened to make control difficult. In October 1968, the company was finally forced to abandon the variable geometry wing. The Boeing team fell back on a tailed delta fixed wing. The new design was also smaller, seating 234, and known as the Model 2707-300. Work began on a full-sized mock-up and two prototypes in September 1969, now two years behind schedule.
A promotional film claimed that airlines would soon pay back the federal investment in the project, and it was projected that SSTs would dominate the skies with subsonic jumbo jets being only a passing intermediate fad.
By October 1969, there were delivery positions reserved for 122 Boeing SSTs by 26 airlines, including Alitalia, Canadian Pacific Airlines, Delta Air Lines, Iberia, KLM, Northwest Airlines, and World Airways.