A Sample Feature From Aviation News

America's Finest

Above: Precursor to an anticipated generation of Mach 3 bombers, the Mach 2 B-58 Hustler was expensive, short on range, costly to maintain and outpaced by political and military threats of the early 1960s.

1: Riding the Valkyries - the saga of the XB-70A
Good aircraft are frequently born as a phoenix from the ashes of their precursors. So it was with the biggest, fastest and most powerful bomber ever built - the triple-sonic B-70 Valkyrie. To make it happen, the Pentagon had to kill off what seemed like a good idea at the time - a nuclear-powered bomber whose only claim to the record book is that it was an expensive diversion. In the end, the phoenix itself was made redundant by seeming to fly too far and too fast into the future, but it gave the world a glimpse of what might have been in an age where literally anything seemed possible. Having flown in the SR-71 many years ago, David Baker revisits the fascinating story of its contemporary in speed in the first of a two-part feature.

The story begins on New Year's Day, 1948, on the first birthday of the US Atomic Energy Commission, when an influential report on America's future air power favoured development of a nuclear-powered bomber with almost limitless range and a flight time constrained only by the physical endurance of the crew. However, sitting in the middle, the report's authors were cajoled on the one hand by nuclear physicists who cautioned against over confidence in the face of daunting challenges to practicality and on the other by an impatient 'customer' in the form of Gen Curtis Le May in charge of the newly formed Strategic Air Command (SAC). He wanted it quickly and in large numbers, fearing a technical and numerical lead by the Soviet Union in strategic bombers would overwhelm America's ability to deter Russia from a pre-emptive strike at the United States.
In April 1949, despite little progress, authorisation was given for a development programme to begin. Political tensions were high. In Berlin a humanitarian airlift was underway following a blockade by Soviet troops and very soon the Korean war would erupt prompting the first large scale military operation authorised by the United Nations. Under contract by early 1951, General Electric would build the P-1 nuclear turbojet engine and Convair would develop two X-6 aircraft developed from the B-36 to carry it. By June 1955 the programme reached its peak with a determination to begin flight tests by 1959 but that was not to be. The previous year, in October 1954, SAC had issued a mission requirement for a supersonic B-52 replacement it wanted on the ramp by 1965. Defined by WS-110A, the aircraft was to have the carrying capacity of the B-52 and the speed of the Mach 3 Convair B-58 Hustler, just then going into the metal-cutting phase. For both medium and long-range roles, SAC wanted to go supersonic with its nuclear delivery platforms. Simultaneously, requirement WS-125A was issued for a nuclear powered bomber and Convair and Lockheed received work contracts for that project, electing not even to bid for the less glamorous chemically-powered WS-110A. Before the end of 1956 competing bidders Boeing and North American Aviation (NAA) had produced widely differing designs for the chemical bomber, both involving complex and unproven concepts rejected outright by the US Air Force.

Above: When the B-70 was conceived, the only man to have reached the design cruising speed of the new bomber was Milburn Apt in the Bell X-2, seen here in the cockpit of the aircraft in which he would be killed after losing control decelerating from Mach 3 in September, 1956. (All photos, NASA-DFRC).

Burgeoning roles
Throughout 1957 the competing bidders adapted their designs, responding to upgraded specifications that more clearly defined the bomber's role: a maximum speed of Mach 3.0-3.2 at high altitude (Mach 0.9 at low altitude), a maximum ceiling of 75,000ft (22,860m), range of up to 11,000nm and a gross weight of less than 490,000lb (222,264kg). The original weapons specification (WS-110A) had been made redundant, substituted by WS-110A/L defining two separate projects: a manned bomber and a manned reconnaissance aircraft. With a state of urgency roused by Russia's launch of the first artificial earth satellite, Sputnik 1, on October 4, 1957, and (false) rumours that the Soviet Union was already flying a nuclear-powered aircraft, North American Aviation signed a contract on January 24, 1958, for what would be known henceforth as the B-70. It has been falsely reported (even today) that the A-12 (from which the SR-71 Blackbird evolved) was the product of WS-110L but this is not the case since that was cancelled when NAA got the B-70 contract. The reconnaissance requirement had, in fact, been accommodated by the Corona military spy satellite project that had its origins in 1951 and was approved as WS-117L four years later. It would emerge publicly in December 1958 as the Discoverer programme under the guise of a scientific research project. By this time the B-70 had been named Valkyrie after Odin's hand maidens who hovered over battlefields to carry the spirits of dead heroes to Valhalla.

A trying youth

The mid-1950s were crucial to the development of a new generation of weapon systems, manned and unmanned. In 1954 the National, Advisory Committee for Aeronautics (NACA) defined requirements for a Mach 7 hypersonic research aircraft also capable of achieving altitudes in excess of 50 miles and known as the X-15. In the following year it awarded North American Aviation Inc., a contract to build three airframes using rocket propulsion developed by Reaction Motors. In 1956 the US Air Force, working primarily with Bell Aircraft Co, developed the concept of a manned boost-glide vehicle launched by ballistic missile for reconnaissance and strike missions with a range of 5,500nm and a speed of 18,000mph. By 1957 this had evolved into the unfortunately named

Dyna-Soar (for dynamic soaring) and in 1958 Boeing and Martin were awarded development contracts. Eventually outgrowing ambitious promises for a manned orbiting space-plane, and being re-designated X-20, it was cancelled in 1963 as cheaper Mercury (and later Gemini) ballistic spacecraft developed by NASA were doing the same job. The Atlas and Titan rockets that launched Mercury and Gemini had been started in 1954 and 1955 and were in launch trials from 1957 proving their worth.

So it was that the B-70 programme for a Mach 3 bomber had exciting competition for funds, yet for all its ambitious specification was considered, at the time, within the capabilities of a burgeoning aeronautical research programme with not even the skies as a limit to performance. In fact, it was about this time that Lockheed forged ahead with the first A-12, which originated as a successor to the U-2 and would be developed into the YF-12A and the SR-71. It was considered to have greater survivability than the subsonic precursor. Nevertheless, this would become the first aircraft to have sustained cruise above Mach 3 and gave rise to over-confident and unrealistic expectations that this flight regime - at altitudes in excess of 60,000ft (18,288m) - was the new 'high ground' of future military air operations. It even led to a new supersonic interceptor, successor to the proposed Mach 4 Republic XF-103 that began life as an idea in 1948 powered by a (dual-cycle) turbo-ramjet but abandoned in 1957 as too much too soon.

Fears that large numbers of Soviet bombers could overwhelm air defence fighters such as the (Mach 1) F-102 Delta Dagger and the (Mach 2) F-106 Delta Dart resulted in a renewed call for a Mach 3 interceptor with a range of at least 1,000 miles to protect the continental United States. NAA successfully argued an economic case based on commonality when competing for the development contract based on a scale-down B-70 but utilising similar technologies and design features, thus saving costs. In June 1957 the USAF awarded NAA a development contract for the F-108 long-range interceptor with a maximum speed of 1,721kts at 72,800ft (22,190m) to fulfil the WS-202A requirement for 480 aircraft of this type. In strict order of development, the F-108 programme was just ahead of the

B-70 but the technical definition of the latter was sufficiently well advanced to allow some sharing of systems with the former.
North American was in its golden heyday of peacetime expansion into the brave new age not only of supersonic combat but of high-end research, having already received the contract to build the hypersonic X-15 and now only a couple of years away from successfully bidding on NASA's Apollo spacecraft. There seemed no limit to speed and altitude and the technical environment into which the B-70 programme was born was not, in fact, as far ahead of its day as the Valkyrie appears in retrospect.

Above: While working at NACA's Ames Aeronautical Laboratory, Alfred Eggers made a crucial discovery concerning shock waves and compression lift that would provide North American Aviation with the theory to design a Mach 3 bomber with great range.

For the rest of this feature please see the June 2006 issue.