Boeing 2707 supersonic transport
The 2707, Boeing’s contender for a supersonic transport, may seem like ancient history now, but then it was advanced in both concept and technology. Maybe it was too much.
Because the jet race had already been won by the UK with the de Havilland Comet DH.106 and the then designated USSR with the Tupolev Tu-104, the US had no choice if it wanted to turn the tide in the supersonic sector. . especially as the same two countries were preparing to launch such designs of their own, respectively in the form of the Aerospatiale-British Aerospace Concorde and the Tupolev Tu-144 in the early 1960s.
The consensus in this early pure jet period was that supersonic air travel would be the next logical evolution from subsonic.
Several aircraft manufacturers in the United States made submissions to fill this segment. Boeing, for example, considered a Mach 1.8 aircraft, with a capacity for 227 passengers. Lockheed’s concept was more ambitious and radical. He produced a design proposal that incorporated an airfoil-shaped fuselage and a double-composite delta wing projected to reach Mach 3 speeds. However, the capability was not unlike that of Boeing’s aircraft in 218. Designated the NAC-60, North American’s concept closely resembled the military B-70 Valkyrie, itself a supersonic design with canards, a composite sweep delta wing, and four aft-mounted aircraft. motors grouped in pairs. It was also programmed for the Mach 3 realm of speed.
Boeing’s 2707-100, numerically considered the first of the second generation of supersonic airliners after the 707, was finally selected on December 31, 1966. Unlike the aircraft of the United Kingdom and the USSR, from the beginning it was intended to eclipse the limits of traditional aircraft. configuration, structure and speed, offering a longer useful life.
Constructed of titanium to withstand the 500 degree Fahrenheit structural temperatures generated by friction from its anticipated cruising speed of 1,800 mph/Mach 3, it sported a variable geometry hang glider, rotating on screw jacks and titanium bearings to meet extreme needs. speed variations, ranging from low subsonic approach speeds in the extended position to high supersonic cruise speeds in the retracted position. Trailing edge flaps were installed for the first part of the flight.
The tailplane, with separate vertical and horizontal surfaces, was otherwise conventional.
Power was to have been provided by four engines attached to the underside of the General Electric wing.
A full-scale wooden model of the supersonic plane, intended to carry 300 passengers, was built.
Although the 113 optional orders placed by 26 airlines around the world looked promising in June 1967, the ambitious design had exceeded the technological expertise to make it a reality. In addition to the inherent instability it demonstrated during wind tunnel testing, the swing-wing aircraft’s weight was prohibitively excessive, with a 40,000-pound penalty, leaving less available for the fuel needed to provide the range they sought. the aircraft carriers.
Immediate solutions of reduced passenger/payload capacity and/or increased fuel/gross weight proved inadequate.
Supersonic flight, except in limited high-altitude military form, was poorly understood at the time, especially for scheduled and routine commercial operations, and obstacles existed far beyond the design teams’ drawing board. Public reactions, sometimes bordering on hysteria, for example, included protests over the sonic boom, the resulting property damage on the ground, exclusion from ground flights (which reduced the aircraft’s potential market in airlines) , the increase in global temperatures, the melting of the polar ice caps, the destruction of terrestrial and oceanic flora and fauna, and the reduction of the radiological protection of the ozone layer.
Bureaucratically, the program was continually delayed by re-evaluations of the airframe and engine and the award of necessary government funding for the design.
Because the type, as conceived in its initial version, did not offer acceptable payload and range capabilities, a second, the 2707-200, was proposed. Although it featured a stretched fuselage and Tu-144-like canards above and behind the cockpit, it weighed 750,000 pounds, 25 percent heavier than anticipated and larger than that of a 500-passenger 747-100, and thus failed. meet the FAA final design submission deadline.
Even his 23,000-pound weight-loss program put his gross weight 52,000 pounds over target.
While its radical swing-wing feature was technologically feasible, it was unable to deliver the necessary parameters, because Boeing was unable to integrate the pivots, engines, and landing gear into an efficient engineering package.
Forced to abandon this variable geometry airfoil concept, he produced a third version, the 2707-300. With an overall length of 268.8 feet, it incorporated the standard supersonic fixed-wing hang glider planform used by Concorde and the Tu-144, with a wingspan of 141.8 feet and an area of 8,497 square feet. The horizontal and vertical tailplane, with a height of 50.1 feet, remained conventional.
However, powered by four 60,000-pound-thrust General Electric GE4/J5P turbojets, it offered twice the capacity and a third the speed of its UK and USSR competitors, and was intended to carry 234 passengers 5,000 miles at a time. Speeds from 1,890 mph to 60,000 – Standing service ceilings. The prototype’s gross weight of 640,000 pounds was expected to rise to 710,000 pounds in production aircraft.
The simplicity, coupled with a reduction in size and the elimination of the weight and aerodynamic obstacles of the variable geometry airfoil, resulted in lower production and unit costs, which, in turn, Boeing believed would have attracted higher sales. . That figure was then imagined to be as high as 500.
In October 1968, or five months before the Concorde first flew, the final 2707-300 was chosen as the US supersonic transport design, and construction of its prototype began in September of the following year, making it on the third commercial aircraft of its class to enter the market. But I never would.
Continuously subjected to a design and development program that was, at times, even more turbulent than that of the Concorde, it struggled to survive.
The obstacles, as befits commercial supersonic technology of the early 1960s, were numerous and insurmountable, including rising research and production costs, rising gross weights, declining ranges and payloads, rising costs per seat-mile, excessive fuel consumption and engine noise, the need for higher-than-subsonic fares, and the fear that first-class passengers would switch to higher-speed transportation, leaving subsonics without the performance they depended on for profitability.
With limited route application the type could only be economically viable at high load factors on very long range routes.
Innovative technology, it had become increasingly apparent, could not support the supersonic concept on a commercial level. However, blinded at times by the need to recapture the title lost during the subsonic run and that “pride goes before the fall” dynamic necessitated by the desire to regain national prestige, the program stood tall with the continued, albeit hurdle-ridden, federal funding.
Needless to say, part of this dynamism was the airlines’ interest in the product, but, as with the Concorde, this began to wane as they were already struggling financially with orders for wide-body 747s.
Doubts from the public, government, and aircraft manufacturers regarding the ability of the 2707-300 to economically achieve its previously claimed noise, payload, and range design goals meant that declining confidence coincided with declining enthusiasm. for the concept.
Presidential support for a supersonic transportation program fluctuated widely. Rising development costs brought about by rising technological hurdles and the need for additional government funding have only resulted in growing opposition. Because Tupolev seemed unable to solve its own problems with the Tu-144 and Concorde’s fuel consumption resulted in initial sales of only ten aircraft to Air France and British Airways (too small a number to pose a competitive threat), the continuing funding 2707-300 could no longer be justified.
On March 18, 1971, therefore, the Chamber voted against, which was echoed several days later by the Senate. Although supporters attempted to restart the program by redirecting the $85.3 million due for completion toward further development, and although the House itself voted for this action on May 12, the Senate rejected it five days later.
Fifteen percent of the first 2707-300 fuselage had been cut by this time and a lengthened 296-foot version was later envisioned, to accommodate 321 passengers.
The three US, UK, and USSR programs had been plagued by unprecedented opposition to new technology that many believed would have been detrimental to the atmosphere, the Earth’s environment, and humanity. Due to its tremendous technological leap, explosive development costs, and intractable engineering difficulties, it never became the expected reality in the US, and after a few route test flights, the Tupolev Tu-144 itself was withdrawn from the air force. service in the USSR.
That only one of those supersonic planes, the Concorde, ever entered the scheduled sector, that it accounted for only a handful of sales to the carriers whose governments they represented, and that the exorbitant fuel costs required to maintain their speed indicate that while that a commercial aircraft design was then technologically feasible, that it was not economically possible.
