The Closing of the Aviation Frontier

A tiny white airplane soared upward under rocket power, its vapor trail bright against the blue-black sky. It was September 1956, and Capt. Iven Kincheloe was taking the experimental X-2 to a record altitude of 126,000 feet—some seven miles higher than the previous record.

Later that month Kincheloe’s fellow test pilot Capt. Milburn Apt, flying that same X-2, set out to break the speed record and become the first man to fly above Mach 3—three times the speed of sound. He did it, reaching Mach 3.2, or nearly 2,100 miles per hour, but he did not survive the flight. His plane went out of control in a high-speed turn, and Apt ejected but was unable to deploy his main chute. With the pilot gone, the X-2 righted itself and glided on its own to a landing that Apt could have survived had he stayed with his craft.

Those were the risks that such men faced as they pushed at the frontiers of flight. In 1956 those frontiers were receding at a pace never seen before. Only three years earlier the test pilots Scott Crossfield and Chuck Yeager had topped Mach 2 for the first time; now Mel Apt had gone beyond Mach 3. Similarly dramatic increases were occurring with the hottest Air Force fighters too. In 1953 the new F-100 had stirred excitement by becoming the first jet to break the sound barrier in level flight. But in 1956 the even newer F-104 was in production, and it would exceed Mach 2 every time a pilot opened the throttle. During those three years the speed of record-setting fighters and experimental planes ratcheted upward by a full Mach.

There was every reason to expect this pace to continue. In June 1956 the Air Force awarded a contract for the experimental X-15, which was to fly above Mach 6 and reach altitudes as high as 250,000 feet. Republic Aviation was pursuing a particularly far-reaching fighter project, the F-103; that plane’s design called for a top speed of Mach 3.7, and its engine already was being tested. The first supersonic bomber, the B-58, flew in 1956. And even in commercial aviation the jet was sweeping all before it, with both the Boeing 707 and Douglas DC-8 airliners under way as major projects. In time, it appeared, fighters, bombers, and airliners might all follow the experimental planes toward higher and higher Machs.

But it did not happen. When Captain Apt touched Mach 3.2, he already was exceeding what would emerge as the limit of practical flight. His record would indeed be matched and broken—by SR-71 reconnaissance planes, which would fly routinely at that speed, and by the X-15, which would set a new record at Mach 6.7, or 4,520 mph. But such aircraft would amount to special-purpose speedsters; in no way would they mark a path that aviation in general was going to follow.

The limit of military aviation, for most practical purposes, would prove to lie around Mach 2.5. Practical civil aviation would not even exceed the sound barrier. The arrival of these limitations, the closing of the aviation frontier, came during the 1960s. In particular, between 1959 and 1971 three separate projects marked the highest levels for the speeds of aircraft, as leaders in aviation tried to bring bombers, fighters, and airliners into the realm of Mach 3. All three projects were cut back or else abandoned, and there are no serious efforts to renew them or to undertake anything like them. With the demise of these projects—the B-70 bomber in 1959, the YF-12A interceptor after 1965, and the Boeing supersonic transport in 1971—a half-century of advances in aircraft speeds and altitudes came to an end.

The first of these aircraft was the B-70, a supersonic heavy bomber of intercontinental range. In the mid-1950s the very existence of intercontinental bombers was only a few years old. The first such craft, the six-engine B-36, had entered flight test in 1946. It was clumsy and slow, but for a number of years it was the only bomber with enough range to reach the Soviet Union from bases on American soil.

During the mid-fifties the Air Force began to acquire a proper fleet. These were B-52s, eight-engine subsonic jets with swept-back wings and speeds exceeding 500 mph. With midair refueling they could reach any target in the Soviet empire. Still, amid aviation’s rapid pace of advance, such aircraft were likely to become obsolete all too soon. During 1954 and 1955 Air Force officials took the first major steps toward planning for the B-52’s replacement. The new bomber was to be in active service “in the general time period of 1965 to 1975,” before giving way to a yet more advanced design.

The technology of the day did not appear to permit the building of true supersonic long-range bombers, able to exceed the speed of sound all the way to Moscow and back. Instead, the Air Force expected that the new aircraft would cruise subsonically over most of their flights, to save fuel. Then, near the targets, they would accelerate to supersonic speed, maintaining this speed during a reach of 1,000 nautical miles before returning to subsonic cruise for the long flight home.

The firms of Boeing and North American Aviation soon won contracts to prepare preliminary designs. Both design groups proceeded by a brute-force approach, envisaging extremely heavy aircraft crammed full of fuel to achieve intercontinental range. To add still more fuel, they would rely on the droppable wing-tip tanks that were then a standard feature of jet fighters. These teardrop-shaped containers would ride on the ends of the fighter’s wings and be jettisoned at the onset of combat.

In the bomber designs these tanks proved to be virtual airplanes in their own right. They included substantial extensions of the main wings, with each wing extension and attached tank having the size and weight of a medium bomber. A fully fueled aircraft with these wing tips attached would weigh as much as 750,000 pounds, or 50 percent more than a B-52. When presented with these designs, the Air Force general Curtis LeMay, head of the bomber forces, rejected them out of hand. “Back to the drawing boards,” he barked. “These aren’t airplanes; they’re three-ship formations.”

Why was it not possible to design an attractive supersonic bomber? The reason was that beyond the speed of sound, the proposed designs would produce far too much drag. In a long-range aircraft it would be vital to have as much lift as possible for the least amount of drag: a high lift-to-drag ratio, or L/D. Supersonic craft had a powerful source of drag that did not exist at subsonic speeds: shock waves, violent disturbances in the air that would be heard on the ground as sonic booms. Shock waves resemble the V-shaped bow wave produced by a ship, and just as this bow wave steals power and energy from the ship’s engines, so shock waves carry away energy and cut deeply into a plane’s fuel economy.

To overcome this problem would demand nothing less than the discovery of a new physical principle in aerodynamics. Alfred Eggers, an aerodynamicist with the National Advisory Committee for Aeronautics (NACA), was the one who found it. In a classified paper published in 1956, he and Clarence Syvertson proposed that shock waves could actually contribute to an airplane’s lift, thus raising the L/D. To do this, the plane should have a triangle-shaped delta wing. Down the length of the wing, on the underside of the aircraft, a protruding box housing the engines would generate a shock wave that would wrap around the underside of the wing and fuselage. Within this region the shock would cause an increase in the pressure of the air flowing past the plane. This increased pressure, acting over the entire underside, would give the additional lift.

The redesign of the bomber, using this principle, went forward at North American Aviation under particularly tight security. The designers at Boeing, by contrast, distrusted the new principle. After carrying out experiments in wind tunnels, they decided to improve their design using less revolutionary aerodynamic approaches. This conservatism proved costly. Boeing had invented the long-range heavy bomber with its Flying Fortress in the mid-1930s and had gone on to build most of its successors. But two days before Christmas of 1957, the Air Force gave a handsome present to North American—and a coal in the stocking to Boeing. North American had won the competition to build the new bombber, which was soon named the B-70.

Hugh Dryden, the director of NACA, was quick to credit his own organization’s research. Testifying at congressional hearings early in 1958, he stated: “About a year ago, a strange and wonderful thing happened. It was as if the pieces of a jigsaw puzzle began falling into place. Almost simultaneously, research programs that had been underway at the NACA labs in Virginia, California, and Ohio began to pay off. The result … was that the companies and the Air Force suddenly realized it would not be much harder to design a long range bomber that could fly its whole mission supersonic than to design one that would fly subsonic most of the way, and only a small fraction of the flight supersonic. Not only that, but the top speed of the prospective bomber was raised to mach 3, about 2,000 miles per hour.”

At the same time, the age of missiles was advancing, with the prospect that high-speed rockets might replace both fighters and bombers. As the missile programs grew in size, the Air Force’s budget failed to grow commensurately, and a host of advanced aircraft projects fell under a squeeze.

The first round of cancellations came in August 1957, terminating a major fighter project and a long-running effort to develop a pilotless Mach 3 bomber. Two years later three additional projects felt the ax—including the B-70. The White House ordered the Air Force to drop plans to build a fleet of 62 such bombers and to build instead only a prototype, to serve for flight testing.

Maurice Stans, President Eisenhower’s budget director and a powerful advocate of missile programs, was the leading force behind this decision. He drew strong opposition both from the Air Force and in Congress, but 1960 provided a dramatic demonstration of the power of missiles against aircraft when a Soviet rocket brought down a U-2 spy plane. The U-2 could fly at 70,000 feet, the same altitude as the B-70, and this altitude evidently had offered no protection.

The new Kennedy administration thus lost little time, once in office, in confirming its predecessor’s decision against the B-70. Kennedy’s Defense Secretary, Robert McNamara, recommended anew that the B-70 project go forward only as a prototype for flight testing. In March 1961 Kennedy issued a statement asserting that America’s forthcoming missile capability “makes unnecessary and economically unjustifiable the development of the B-70 as a full weapons system at this time.” With that, the first major push to propel aviation to Mach 3 came to an end.

By then, however, an even more far-reaching effort was at hand. It came from the “Skunk Works,” the advanced-design shop at Lockheed Aircraft. The Skunk Works’ director, Clarence (“Kelly”) Johnson, had already made himself a legend by building a host of pathbreaking craft. America’s first jet fighter, the P-80; the F-104, which flew at Mach 2 and was called “the missile with a man in it”; and the supersecret U-2 of the Central Intelligence Agency all had come from Johnson’s group. The new project would take form as the SR-71 reconnaissance aircraft, the fastest and highest-flying airplane ever to see operational use. Its performance records remain classified to this day, but announced numbers include speeds above Mach 3.2 and cruising altitudes of at least 85,000 feet.

James Eastham, a test pilot who was among the first to fly this new craft, recalls seeing it for the first time in 1962: “I was in a state of shock. Who could imagine such a machine! Kelly reached down into his desk, pulled out a photo—and I just stared at it. I couldn’t believe what I was seeing.” It was more than a hundred feet long and far slenderer than most aircraft, with an immense engine pod, wider than the fuselage itself, mounted in each wing. Yet it introduced no major aerodynamic innovations, and in some respects design was quite conservative. Its engine installation, for instance, was of a type whose basic principles had been understood around 1950.

What made the SR-71 unique was the unusual degree of care and effort needed to make it work. At its high flight speeds, aerodynamic heating would produce temperatures exceeding 600 degrees Fahrenheit, far too hot for aluminum. The B-70 had faced the same problem and had been built with stainless steel. Kelly Johnson wanted to use titanium, much lighter than steel, in the SR-71. Titanium, however, proved to be particularly demanding.

Early samples of titanium alloy were so brittle that they would break if they fell off a desk. They also were extremely hard and difficult to machine. The Lockheed machinists’ drill bits, which cut through aluminum like butter, could make only seventeen holes in titanium before wearing out. On the other hand, titanium was so extraordinarily sensitive to contaminants that the ink from some common marking pens would etch a hole in the metal in only a few hours. Bolt heads broke off when heated. Spot-welded panels assembled in the winter held together well, but panels produced in the summer tended to fall apart.

The problem of the bolts was traced to cadmium, applied as a thin rustproofing layer on workers’ torque wrenches. The cadmium was reacting with the titanium bolt heads, sapping their strength. The spot-welded panels were weak because they had been washed with municipal tap water, which was heavily chlorinated in the summer months. Johnson’s managers got rid of the cadmium-plated wrenches and switched to chlorine-free distilled water for cleaning the panels. The problems disappeared.

When the SR-71 began to fly, a particularly severe obstacle emerged in the functioning of the engine inlets, which fed high-speed incoming air into the turbojets. These inlets proved prone to “unstarts,” in which the flow of air would break down, causing a massive loss of thrust. “An unstart had your full and undivided attention,” recalls Eastham. “The aircraft would yaw violently. Then you were very preoccupied with getting the inlet started again. The speed fell off; you began to lose altitude.” He would follow a procedure to restore normal thrust and then put the engine back on automatic control, “which many times would unstart it again. And when you unstarted on one side, sometimes the other side would also unstart. Then you really had to give it a good massage.” Eventually this problem was largely solved with the installation of a fast-reacting control system to adjust the inlets.

Air Force officials were powerfully impressed with the new airplane. Working with their Lockheed counterparts, they actively supported a plan to build an interceptor version of the SR-71, to be known as the YF-12A in its prototype stage and as the F-12B in a production version. Gen. Herbert Thatcher, head of the Air Defense Command, expected that a fleet of ninety-three such fighter aircraft could protect the entire United States against attack from Soviet bombers. As an initial step Lockheed built three YF-12A craft and proceeded with their flight tests, beginning in 1963.

The results were spectacular. In 1966 the aircraft reached an altitude of 80,259 feet and a speed of 2,070 mph, the latter a world record. More significant, further tests showed that the YF-12A could do useful work at such heights and speeds when pilots used on-board radar to fire missiles at drone bombers in flight at varying altitudes. In one such test, with the plane cruising more than 15 miles up at Mach 3.2, the pilot launched his air-to-air missile and brought down an unmanned B-47 from 120 miles away.

Secretary of Defense Robert McNamara was much less impressed. He had established the powerful Office of Systems Analysis (OSA) within the Pentagon to study America’s defense requirements and assess proposed weapons. On the basis of OSA recommendations, McNamara judged that the Soviet threat would not require the F-12B. He took the position that other interceptor designs, offering lower speeds and altitudes but also costing less, could serve the nation’s needs.

This led to a three-year conflict between McNamara and Congress, which backed the F-12B and repeatedly appropriated funds to support its production. In the mid-1960s there was not yet an Impoundment Control Act, requiring White House officials to spend appropriated funds, so McNamara simply impounded the money, refusing to spend it.

Late in 1966, with this conflict still unresolved, McNamara took an unheard-of step. He proposed that tooling for the SR-71 be broken up and sold for scrap. Ben Rich, who succeeded Johnson as head of Skunk Works, was shocked: “When an aircraft still has value—when there’s nothing like it—you want to hold on to the tooling.” Johnson, backed by supporters in Congress, fought against this vigorously. He argued that “this tooling is very largely common to the F-12B and, if a decision to destroy it is made, the possibility of ever having a truly advanced interceptor or bomber, based on the SR-71, will be gone forever.”

“We fought it for three years, trying to hide the tools,” Rich recalls. “But we were not successful.” The tooling was government-owned and had been paid for under Pentagon contracts; thus McNamara was within his rights to order its destruction. There was no escape. By early 1970 Johnson was reporting to his Air Force superiors that “the large jigs have now been cut up and we are finishing the cleanup.” The resulting scrap metal was sold for seven and a half cents a pound.

As the F-12B was slowly dying during those years, one last attempt still was under way to carry aviation into the realm of Mach 3. This was the effort to build a supersonic commercial airliner, the SST. President Kennedy had launched the program in 1963, as part of a policy of vastly expanding existing government agencies that dealt with technology. Just as NACA, an aviation research group, had grown into the powerful NASA, which had responsibility for landing astronauts on the moon, so the Federal Aviation Administration (FAA), expanding beyond its traditional concern with airline safety, was to manage the development of a new airliner—the SST.

By the mid-1960s the technology of supersonic flight offered few surprises. The main challenge was simply to ensure airline-like levels of safety, reliability, and low cost. The passengers in an SST, after all, would not be test pilots like Jim Eastham but businessmen, grandmothers, and little sisters. The FAA held a design competition in 1966, with Boeing and Lockheed vying for the chance to build the government-funded prototypes. Boeing won—only to find, a year and a half later, that its design was wrong. Engineering changes of a sort normal in aircraft development had hiked its weight and cut its range to unacceptable levels. The Boeing designers went back to the drawing board and emerged with a new configuration. It bore a remarkable resemblance to the Lockheed design that had lost in the competition.

Meanwhile, the plane’s financial arrangements raised eyebrows. The plan called for the FAA to put up $1.3 billion to carry the program through the construction and testing of two prototypes. The SST would then go into production, and Boeing would pay the government a royalty on each one sold. The $1.3 billion thus was “not a subsidy, it’s a loan,” said William Magruder, the program manager. “By the time the 300th airplane is sold, all of the Government’s investment will be returned to the U.S. Treasury, and when we sell 500 airplanes, there will be a billion dollars in profit to the Government.”

Sen. William Proxmire took the lead in challenging this arrangement. He argued that Uncle Sam was not a venture capitalist and that if such a loan appeared so profitable, then Boeing should tap banks instead. In the words of his fellow senator Gaylord Nelson, “It is doubtful that many of these planes will be purchased.… it is seriously doubted … that the SST can be profitably operated.… If there is sufficient demand to support such a plane, it should stand on its own and be built without subsidy.”

Proxmire and Nelson pressed such arguments throughout the 1960s, but to little avail. As late as 1969 the SST appropriation soared through the Senate on a vote of 58 to 22. But during 1969 two powerful new issues emerged, backed by strong constituencies whose leaders enjoyed major support within the media. These were the demand for “new priorities” and the rapid rise of widespread concern for the environment.

“New priorities” was a battle cry of liberal Democrats who wanted money from NASA and the SST project to be diverted into new initiatives: mass transit, public housing, expanded spending on antipoverty programs. The Nixon administration in time responded strongly to such demands, but Nixon wanted the SST as well.

Environmental awareness was an especially hot issue during 1969 and 1970. A sickeningly messy oil spill at Santa Barbara, California, early in 1969 had provided a rallying point. Thereafter such groups as the Sierra Club and Friends of the Earth went from strength to strength, winning powerful support both in the media and in Congress. Led by David Brower of Friends of the Earth, along with William Shurcliff of the Citizens League Against the Sonic Boom, these groups soon joined forces to oppose the SST.

Their work was made easier by the incautiousness of SST advocates, who had been slow to appreciate the strong public dismay at the sonic booms these aircraft would produce. One Boeing spokesman had described the boom favorably, as “a twentieth-century sound.” C. R. Smith, chairman of American Airlines, pointed with understatement to “an unusual public-relations problem”: An SST, “taking off from New York at midnight and proceeding to Los Angeles or San Francisco, would wake up ten million people en route.”

As their opposition hardened, environmentalists added new charges. SST engines would be so loud as to contribute substantially to noise pollution. The turbojets would release noxious gases into the stratosphere and disrupt the fragile ozone layer, which protects life against dangerous solar ultraviolet rays. Paul Conrad, a Los Angeles Times cartoonist, caught the spirit neatly when he portrayed the engines as garbage cans spewing rubbish.

The issue was closely fought. SST advocates enjoyed the help of administration support, professional lobbyists from the aerospace industry, and the endorsement of labor unions worried about members’ jobs. But when the key vote came in the House of Representatives in March 1971, the SST went down to defeat, 215 to 204. With it went the last hope that aviation would routinely operate near Mach 3.

Across more than a decade, then, with these three projects—B-70, YF-12A, and SST—aviation leaders had seen the curtain ring down on fifty years of advances in aircraft speeds and altitudes. Nor have these decisions been reversed, down to the present day. After the U-2 incident in 1960, Air Force officials saw the future of bombers not in B-70-like speedsters but in aircraft that could penetrate Soviet defenses by flying long distances at treetop level. Ironically, the B-52, which had been expected to serve only for a few years, proved well suited to this task; it remains in service even today. The only other new bombers, the F-111 and B-1B, also emphasize such low-level flying, and they represent reasonably conventional designs that have set no records.

The design of fighter aircraft has also turned away from YF-12A-like performance during the past quarter-century. The emphasis has been on agility, the use of advanced electronics, and the ability to fly repeated sorties with heavy loads of weapons. Indeed, so successful have these efforts been that six F-16 fighter-bombers are now said to do the work of a hundred Flying Fortresses of World War II. However, here too there has been a retreat from the highest speeds. Such aircraft generally stay below Mach 2.5.

In the commercial realm an SST now appears farther away than it was in 1970. Twenty years ago, in addition to the American effort, similar projects were under way in both Western Europe and the Soviet Union. The European work brought forth the Mach 2 Concorde, of which an aging handful remain in service, and that is all. A few research efforts remain active, and now and then one reads of proposals such as the Mach 5 “Orient Express,” which might someday fly from New York to Tokyo in two hours. What stands in the way, however, is the high cost of fuel. There is an irony here, for in 1970 neither supporters nor opponents of the SST realized that this issue would prove so potent. They had no reason to; the price of oil had stayed steady since 1947, and no one expected it to rise so swiftly. Yet the oil crises of the 1970s lay right around the corner.

Since 1970 aviation has not stood still. Stealth technology has offered an important source of innovation as designers have sought to make bombers and fighters less visible to enemy radar and other sensors. Airliners have seen major improvements in both quietness and fuel economy. Yet such advances are very different from those of the 1950s, when test pilots were competing to punch holes in the sky. Aviation matured during the 1960s, reaching its definitive form, and the subsequent changes have largely been those that arise in applying new technology to a mature industry. The civil and military aircraft of that decade are essentially those of today and probably will resemble closely those of tomorrow.

The supporters of the B-70, YF-12A, and SST hoped their aircraft would render obsolete such predecessors as the B-52, the Mach 2.5 fighters of the 1960s, and subsonic commercial jetliners. When these three projects failed to win needed support, it was clear that these “predecessors” would remain in service for many years, pointing to a future of modest improvements rather than one of sweeping change. That is why the controversies over the B-70, YF-12A, and SST are worth remembering, and why an epoch of aviation history died with them.