October 2004 
Volume 03, Issue 6 
Historical Perspective

What might have been


Aerospace companies frequently have been engaged in competitive fly-offs-head-to-head comparisons-to determine whose aircraft is best. All too often, the winners in these competitions were only marginally better (if at all) than the losers. Also passed over were other highly innovative aircraft and spacecraft designs made in response to requests for proposals or submitted as unsolicited proposals.

Here, Boeing Frontiers takes a quick look back at history-to see what might have been with some of these designs. The images shown depict what these aircraft might have looked like, had they gone into production.


A conceptual operational NAA F-107D Ultra SabreAs the North American Aviation YF-107 came into being, the U.S. Department of Defense decided to pit it against the Republic F-105B as a nuclear-capable Mach 2 fighter/bomber for the U.S. Air Force. In August 1954, NAA was awarded a contract for nine YF-107 flight-test vehicles and one static test airframe. However, this number was reduced to three in January 1957.

The YF-107 achieved Mach 1.03 on its first flight in September 1956 and hit Mach 2 in November of that year. To accommodate the XMA-12 integrated fire control system (eventually used on the F-105) the 107's unique intake was located above and behind the flight deck.

In early 1957, zoom climb tests reached an altitude of 69,000 feet (21,000 meters), achieved with a pull-up at Mach 2.1, and climbing vertically above Mach 1. However, there would be no publicity for the YF-107's feat, since the Lockheed F-104 was concurrently performing speed and zoom climb flights in official pursuit of new records. Despite this, by early 1957 the strong performance of the YF-107 seemed to position it for a production order.

The F-105 incorporated an internal bomb bay, aimed at better positioning it to win budget monies in the then-ongoing Tactical Air Command fighter versus Strategic Air Command bomber rivalry. NAA, too, designed a semirecessed area in the 107's lower fuselage that fit a wide variety of external stores. Ironically, once in service the F-105's bomb bay would mainly carry fuel.

The Air Force terminated the NAA F-107 contract in March 1957, but the three prototypes continued test flying under the auspices of the National Advisory Committee for Aeronautics (now NASA) until August 1959.


A conceptual NAA M-70 as an X-15B carrier aircraftThe legendary XB-70 cruised at greater than Mach 3 at 75,000 feet (22,800 meters)-powerful performance for the 1960s. The dream began on Dec. 23, 1956, with a $360 million development contract award to NAA to begin work on three prototypes. Powered by six General Electric YJ93-GE-3 engines, the bomber rode on its own shockwave, an acclaimed aerodynamic advance. However, as former NAA President Lee Atwood said more than three decades later, "compression lift was definitely a factor, but overplayed by so-called experts. It was the variable geometry inlet design that provided Mach 3+ cruise." This meant that at the time, NAA had achieved remarkable progress in the propulsion area.

Yet in April 1961, Secretary of Defense Robert McNamara ordered that the three prototypes would be used for research only, and that the XB-70 would not be carried forward as a full-scale weapon system. And despite promises before Congress that three airframes would be built, plans for a third XB-70 were eliminated.

The production B-70, among other features, would have been equipped for quick scramble and conducted air-to-air refueling as routinely as the B-47 and B-52. Although McNamara criticized the XB-70 for not being compatible with the Skybolt and Hound Dog air-to-ground missiles, this generation of missiles had been designed for the subsonic B-52.

After the downing of Gary Powers' Lockheed U-2 over Russia on May 1, 1960, there was an immediate shift in U.S. strategy to develop low-level penetrators. This strategic redirection also played against the high-flying XB-70. Yet during the '60s, '70s and '80s, the Mach 3+ SR-71 survived hundreds of surface-to-air missile launches without a single hit.

The XB-70 program continued with two flight vehicles. Pentagon budget cuts forced changes to the flight deck and crew number, as well as the elimination of a full-up weapons systems, that severely limited NAA's original test plans. When XB-70 AV-2 was lost in a midair accident on June 8, 1966, the program was in trouble. The remaining aircraft flew 22 research missions for NASA before retiring on Feb. 4, 1969.


Boeing X-20 Dyna-SoarA manned reusable space plane operating in the late 1960s would have been a tremendous boon to both the U.S. military's access to space and NASA's space exploration efforts.

In late 1959, Boeing was given the go-ahead to develop a manned reusable space plane, called Dyna-Soar (Dynamic Soaring). Designated X-20, the vehicle was to be placed into orbit by a newly developed Titan III booster. Constructed of several new, exotic alloys, the blunt-wing, delta-shaped vehicle would have a length of 35 feet (10.6 meters) and a span of 20 feet (6.1 meters). It would weigh about 10,000 pounds (4,500 kilograms).

Dyna-Soar's first orbital flight was tentatively scheduled for early 1965, but it didn't happen. Despite a cadre of astronauts in training and an excellent government review of the program and inspection of the full-scale engineering mockup, the U.S. military canceled the Dyna-Soar program in December 1963. The rationale: Dyna-Soar had no viable military mission and was too expensive for a research vehicle.

The partially completed X-20 prototype and the mockup were scrapped, as well as initial tooling set up for a production line for 10 space planes. It would be another 18 years before a first-generation space plane would be flying: the Space Shuttle, which first flew in April 1981.


Boeing SST (Model 2700-200) variable-sweep wing versionIn late 1966, the FAA selected Boeing to be the prime contractor for the first U.S. SST. After initially considering, then shifting away from, a variable-sweep wing design, a full-scale engineering mockup of the (50-degree-sweep) fixed-delta-wing Model 2707-300 was unveiled in June 1970. With a capacity of more than 300 passengers and a speed of Mach 2.7 (1,800 mph or 2,900 kilometers per hour) at 65,000 feet (19,700 meters), the Boeing SST would have been faster and have carried more passengers than the British/French Concorde SST. That passenger load would have helped airlines achieve a more favorable balance sheet.

Throughout Boeing, 4,800 people were working on the program, and by June 1970, orders for 122 SSTs from 26 airlines had been secured. Along with a team of suppliers located in most of the 50 states, seven major aviation subcontractors were involved, including General Electric, which was selected to produce the 60,000 lb.-thrust engines. These were new, clean-burning engines that would propel the SST from New York to Paris in just two hours and 40 minutes.

Unfortunately, Congressional concerns about SST program expense and environmental effects resulted in its cancellation on March 24, 1971. Had the program been allowed to continue, substantial progress might have been made toward solving many of the problems facing supersonic passenger flight today.



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