The Road Not Taken

In Uncategorized on January 3, 2013 by hillermuseum

Delta SST
The Quest for the Supersonic Transport

For some three quarters of a century, the development of powered flight was characterized by the relentless pursuit of speed. Wilbur and Orville Wright had to meet a speed goal to sell their Flyer to the United States Army in 1908. Glenn Curtiss became the toast of Europe by besting the legendary Louis Bleriot in a speed race on French soil at the world’s first air meet in 1909. In the First World War airplanes that we today would call fighters were instead known as “pursuit” planes to emphasize their ability to overtake slower aircraft in flight.

The time between the wars saw the awesome international engineering spectacle of the Schneider Trophy races, in which leading aircraft designers around the world competed for the glory of racing the world’s fastest aircraft. Between 1913 and 1931 the winning speed at the Schneider race rose from 46 to 340 miles per hour, reflecting the rapid evolution of both airframes and powerplants.

The fortunes of civil aviation also rose as airplane speeds reached ever higher plateaus. In the mid 1920s the Ford Trimotor was the epitome of airline travel, offering pedestrian transportation at a cruising speed of scarcely 80 knots—hardly faster than a train. By the mid 1930s air travel had more than doubled its pace, with the revolutionary Douglas DC-3 flying reliably at 180 knots. A decade later, DC-3s were joined in postwar skies by propeller-driven aircraft such as the Lockheed Constellation, which could fly nonstop across the country at nearly 300 knots.

By the end of World War II, propeller-driven aircraft had approached the ragged edge of performance, especially in large aircraft. The enormous wartime Boeing B-29 was powered by four huge Wright engines, each churning out nearly 200 times the power of the humble motor Charlie Taylor first built for the Wright Brothers in 1903—yet the aircraft’s engines had little margin for error, and failures were common. The post-war Constellation airliner had four engines of even greater power, but inflight shutdowns were so common that the craft was known to pilots and mechanics as the “world’s best tri-motor”. Fortunately, an entirely new propulsion technology had arrived, promising safer, more reliable, and even faster flight—the jet engine.

In July 1949, the world’s first jet-powered airliner took to the skies over Hertfordshire, England. The de Havilland DH 106 Comet represented an enormous leap in capability, not just for a nation that had seen the kite-like Vickers Vimy lumbering on in service scarcely a decade earlier, but for the entire world. Powered by four turbojet engines embedded in its wing roots, the Comet reprised the Vimy’s role linking Great Britain to the far-flung nations that sprang from her pre-war empire. The Comet’s cruising speed of 400 knots was faster than any propeller-powered transport. Ten years later the American Boeing 707 and Douglas DC-8 jetliners ruled the skies, crossing continents and oceans alike at eye-watering speeds exceeding 500 knots.

Much as the propeller-driven giants of the 1940s pushed up against the limits of engineering, the sleek jetliners of the 1960s quickly reached an aerodynamic limit—the speed of sound. Sound travels at roughly 770 miles per hour—some 650 knots—at sea level. The actual speed varies with both temperature and especially altitude, and hence high aircraft speeds are often described not in knots or miles per hour, but instead by their Mach number—the aircraft’s speed divided by the speed of sound where the aircraft is flying. The 707 and DC-8 regularly flew at eight tenths the speed of sound, or Mach 0.8. Faster flight would enter the transonic regime, with drag increasing exponentially and airflow changing dramatically as the speeding airframe met a shock composed of its own sound waves.

The first rocket-propelled research airplane achieved supersonic flight in 1947, and by 1960 the United States Air Force’s airline-sized Convair B-58 regularly flew at Mach 2.0. To many aircraft designers and airline executives, development of a supersonic jetliner clearly appeared to be the next step in an unending quest for speed.

Great Britain’s British Aircraft Corporation—a conglomerate of British aircraft makers that ultimately formed the core of today’s BAE—sought to regain an edge in aircraft design by leapfrogging to supersonic transports. Daunted by the expected development cost, the British government insisted on pursuing the project with an international partner. Despite some effort to engage the United States in this project, only France and its own national planemaker, Sud Aviation—today part of EADS, the parent organization of Airbus—wished to proceed. A treaty committing both France and Great Britain to construction of a supersonic airliner was signed in 1962. The airplane known as Concorde took its name from this agreement.

Taking to the sky for the first time in 1969, Concorde was indeed a technological marvel. Designed specifically for supersonic flight, Concorde’s design was unlike any previous airliner. Its small delta-shaped wing, long, tapered fuselage, drooping nose and lack of a horizontal stabilizer were utterly distinctive. Able to cruise over three hours at a speed just above Mach 2, Concorde had no competitor when it entered airline service with British Airways and Air France in 1976.

A few years earlier, however, Concorde’s shape was not quite so unique, and competition appeared to be at hand. The Soviet Union also initiated development of a supersonic jetliner in the 1960s, and the resulting Tupolev Tu-144 first few several months before Concorde. Although superficially similar to Concorde, the Tu-144 employed different engineering solutions to many of the challenges of supersonic flight. The Soviet airliner suffered through a difficult development period, including a catastrophic accident at the Paris Air Show in 1973. Although placed in limited passenger service for a brief period in the 1970s, the Tu-144’s range and reliability did not compare to the Anglo-French Concorde and it was relegated to mail flights and high speed research from the early 1980s.

In the United States, plans had been laid for supersonic civilian transports as early as the 1950s. As Concorde began to take shape in Europe, FAA Administrator Najeeb Halaby became a leading proponent of high speed airliners and ultimately prevailed upon President Kennedy to announce a national program to develop one in 1963. Boeing, Lockheed and North American Aviation all submitted proposals to build a supersonic transport, with Boeing ultimately being awarded a development contract at the end of 1966. Boeing’s original design was intended to travel at Mach 3 carrying over 200 passengers, compared to Concorde’s Mach 2 performance with no more than 100 passengers aboard. To reduce noise and fuel consumption during takeoff and landing, the original Boeing design would have used variable-geometry wings able to swing forward to permit low-speed takeoffs and landings, but also sweep rearwards for supersonic flight. Boeing used a number of internal designations for its SST (supersonic transport) project, but the public most identified it as the Boeing 2707.

As the design matured, the Boeing SST evolved into a simpler aircraft. The variable-geometry wings were abandoned in favor of a delta shape similar to Concorde’s. A full scale mockup was built at Boeing’s Seattle facilities in 1969, and construction of the first two prototypes began.

During the protracted development of the SST in America, public opposition began to rise due to a wide range of diverse issues. A number of environmental concerns were aired, particularly in regards to overland supersonic flight. Supersonic flight creates a shock wave felt and heard on Earth’s surface in the form of a sonic boom. Tests of large supersonic airplanes such as the enormous North American XB-70 over populated areas in the mid-1960s resulted in numerous complaints and damage claims for cracked windows and porcelain fixtures. Financial concerns regarding the high cost incurred by the United States in funding SST development rose as delays mounted, and potential airline customers became deeply skeptical that any supersonic transport would be economical to operate. The high speed of an SST would enable it to make more flights each day, but at the cost of burning enormously more fuel per flight compared to a subsonic airplane. When SST development began in earnest in the early 1960s the cost of jet fuel was a negligible operating expense for the airlines, but by 1970 prices had risen and supersonic flight became less economically compelling. Both houses of the US Congress voted to terminate funding of the supersonic transport in 1971.

The economic and environmental issues that ended the American SST project were in some ways more relevant to Concorde, which carried fewer passengers and had a larger noise footprint than the planned Boeing 2707. However, the treaty agreement signed by France and Great Britain in 1962 contained no provision for cancellation, and Concorde’s development continued. Although Concorde at one point held orders from many airlines for over 70 airplanes, nearly all orders were cancelled after fuel prices spiked dramatically in 1973. Only the national airlines of the two treaty nations ever operated Concorde with their own flight crews, and only 20 were built. After a long service history, both British Airways and Air France retired Concorde from service in 2003.

2003 was a watershed year in aviation, for it marked the first time since Orville Wright winged over the sands of Kitty Hawk one century earlier that the maximum speed of civil air transport decreased. The speed of the fastest commercial jetliner dropped from Mach 2.0 with Concorde to Mach 0.85 on the Boeing 747. Fuel efficiency has supplanted speed as the paramount concern after safety in commercial aviation. Today, Boeing and Airbus battle with each other to design and built new jets that are more fuel efficient than their competitor, not faster.

The legacy of supersonic flight resides at airports and air museums around the world. Three Concorde aircraft are displayed in the United States, and surviving examples of the Tupolev Tu-144 are found in Germany and through the former Soviet Union.

Neither Boeing 2707 prototype was completed before the program was cancelled in 1971. The only artifact to survive was the full-scale mockup, which was exhibited in Florida through the mid-1980s. The forward section of the SST mockup’s fuselage was acquired by the Hiller Aviation Museum during its foundational period and placed on display in San Carlos in 1998.

Next year, the Hiller Aviation Museum will bid adieu to this unique piece of aviation history. The SST will be removed from the Museum’s Gallery in mid-January to make way for new exhibits, and in mid-2013 it will be transferred to the Museum of Flight in Seattle, Washington, adjacent to William Boeing’s original aircraft factory. On Saturday, January 5th, the Museum will open the doors of the SST to the public one final time as part of its Open Cockpit Day event. Many changes are in store for the Hiller Aviation Museum in 2013, but we hope that you will join us for this final opportunity to experience the Boeing SST and hear an echo of the day when speed was king.

Kenneth Owen. Concorde and the Americans, 1997.
National Research Council. U.S. Supersonic Commercial Aircraft, 1997.


2 Responses to “The Road Not Taken”

  1. As a commercial aviation enthusiast, the Boeing 2707-300 had been a constant inspiration to my aviation illustration.
    The Hiller Museum should be commended for their fine stewardship of such an important statement in commercial airliner design. Had they not refurbished it, the remaining forward fuselage section may have fallen thriugh the cracks of history. It’s a shame the rest of the mock-up was left to disintegrate in outside storage, but at least we will all be able to visit what is left of such a beautiful concept. The first Boeing SST 2707, (-100 swinging), mock-up was not saved after the Congress cancelled any further drveloent aid on 1971.

    • Hi Herb,
      Just saw your post. thanks for your interest and although we hated to see the SST leave we know it is going home and the Museum of Flight will make a great exhibit for this historic aircraft!
      Hiller Aviation Museum

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