Stealth and Lockheed's Blackbird

Was the Blackbird really a first-generation stealth aircraft? Or was it just a high-speed camera (pun intended 😀 )?

The answer is a little of both. To understand the nature of the Blackbird’s stealth design, one first has to consider the time period. What passes for advanced stealth technology today, in the 21st Century, is far different from what passed for stealth technology in the 1950’s. So in that respect, the Blackbird is not a stealth design by today’s standards, which are set by the F/A-22 and B-2A. But that still isn’t entirely accurate. That’s like saying the F-4 wasn’t an advanced fighter design because it doesn’t live up to current standards and compare to, say, an Su-27M FLANKER-E.

So, by the standards that existed in the 1950’s and 1960’s, the Blackbird was the most advanced, stealthiest thing in the sky. This is why it is regarded as being a first-generation stealth aircraft. It laid the groundwork for the technological advances Lockheed would make in the 1970’s with the HAVE BLUE and SENIOR PROM programs. The same thing applies to fighter aircraft, this is why aircraft like the F/A-22 are classified as fifth-generation fighters.

Let’s examine the background of the Blackbird. Not many people realize it, but the program to develop the CIA’s A-12 Blackbird, project OXCART, actually began in 1958, two years before Francis Gary Powers’ infamous shootdown over the USSR. The CIA was well aware that new technology was being developed in the field of air defence in the Soviet Union, namely more advanced SAM systems and higher performance interceptor aircraft. Ergo, it was decided that the next-generation reconnaissance aircraft would have to have new technology designed to defeat these systems. The end result? It was determined that the right mix of technology for the new aircraft would include high performance, advanced ECM systems, and low observable technology.

In this case, the low observable technology was aimed primarily at defeating radar systems. No IR-guided SAM in the world would ever have the performance needed to defeat the Blackbird as it turned out anyway, and the MiG-25P was still unknown (although the Soviets certainly knew of the OXCART at an early stage, it was the aircraft the MiG-25P was designed to defeat).

Both Lockheed and Convair responded with aircraft designs under project GUSTO. Lockheed’s infamous advanced design bureau, nicknamed the Skunk Works, proposed both the subsonic G2A and the Mach 3 capable ARCHANGEL. The G2A was rejected, as it was intended to be a low observable aircraft but test results showed that it would be detectable by existing Soviet radar systems. Convair responded with a parasite aircraft known as FISH, which would be launched from a modified B-58 bomber and use ramjet power to reach a speed of Mach 4. Both proposals were initially rejected by the GUSTO committee in July of 1959, causing both companies to submit refined designs in the late summer of the same year. Lockheed responded with the A-12, the twelfth design study under the ARCHANGEL program. The A-12 was a low-Radar Cross Section (RCS) Mach 3 aircraft, developed from the A-11 design that had been rejected by the committee in 1959 due to its high RCS. Convair’s resubmission consisted of the KINGFISH design, a Mach 3.2 low-RCS aircraft now intended to take off and land conventionally. On August 28, 1959, Lockheed was announced as the winner. Both aircraft had similar performance characteristics, but Lockheed’s design was chosen due to its lower projected costs. Lockheed’s aircraft program was given the codename OXCART, a moniker allegedly chosen to hide the aircraft’s amazing speed.

In September of 1959 the CIA issued Lockheed a $4.5 million contract to proceed with RCS studies, finalizing of engineering designs, and structural tests. Although Lockheed’s A-12 design had been selected by the GUSTO committee, there were still concerns about the aircraft’s vulnerability to Soviet radar systems. Radar detects an airborne target by transmitting radio energy and tracking the reflections of this energy from the target. Sharp corners, right angles, and large flat panels are typically the best radar reflectors, and should be avoided as much as possible when designing a low-RCS, or “stealthy,” aircraft. Skunk Works’ engineers theorized that a continuously curving surface would present the fewest number of the aforementioned undesirable traits. To incorporate their theory into the A-12 design, wing extensions called chines were added to the side of the aircraft’s fuselage. The chines were blended into the fuselage and contained saw tooth panels constructed of Radar Absorbent Material (RAM), helping to further reduce the A-12’s RCS. The last measure taken by designers to reduce the A-12’s radar return was to cant the vertical tails inboard by 15 degrees, reducing another of the undesirable right angle joints on the aircraft. Finally, the Skunk Works had achieved its goal of a genuine high speed, low RCS aircraft. Subsequently, on January 26, 1960 the CIA authorized the construction of 12 OXCARTs. In reality, the merging of a high-speed airframe with low-RCS characteristics proved to be a sound concept. As most early warning systems were (and still are) based on radar systems, a low-RCS aircraft would offer reduced detection time and therefore reduced reaction time to the enemy. Consequently, a high-speed aircraft further compounds the enemy’s reaction time. Most SAM systems have a minimum engagement range, and a target approaching the SAM site with a high closure rate means the system must either be highly automated or able to detect the target at a long enough distance to ensure destruction. Low-RCS means a shorter detection distance. Coupled with the fact that most 1960’s-vintage SAM systems were not exactly highly advanced in terms of electronic capabilities, the high-speed, low-RCS OXCART offered a very survivable platform, one that would be exploited for different uses as the program progressed. As an interesting side note, the concept of merging a high-speed flight profile with a low-RCS airframe seemed logical to quite a few people despite the obvious problem with such an aircraft: the heat signature would have been horrendous. No one realized that an aircraft with such a large IR signature would be just as detectable as any other aircraft! Fortunately, as only very short-range SAM systems were equipped with IR-homing systems, and IR detection systems would not reach maturity until the 1970s, this would not be a serious problem. This is, however, one reason often given as to why the assumed successor to the OXCART and SR-71 family, the mythical hypersonic Aurora aircraft, is not a practical concept.

Designing an aircraft for high-speed flight had proved no easy task, and constructing one would prove to be equally difficult. In order to ensure the structural integrity of an aircraft traveling at sustained speeds of Mach 3, or over 2000 miles per hour, special materials would have to be used in the construction of the OXCART. In certain aspects of its flight regime, the A-12’s skin would reach temperatures exceeding 1000 degrees Fahrenheit. Traditional materials used in aircraft construction, such as aluminum, only maintain structural integrity to sustained speeds of around Mach 2.5. The airframe of a Mach 3 aircraft, even though it travels approximately 500-600 mph faster, still manages to reach much higher temperatures than an aircraft traveling in the Mach 2-2.5 realm. The solution for the Skunk Works’ engineers was to construct the A-12 primarily out of titanium, an exotic material that was light enough to be used all over the airframe, but also had the necessary thermal tolerances required of Mach 3 flight. Ironically, the bulk of the world’s supply of titanium resided outside U.S. borders-in the Soviet Union. The CIA was able to covertly acquire the necessary quantities of titanium needed to construct its fleet of reconnaissance aircraft, the methods involved remaining undisclosed to this day, aircraft intended to then gather intelligence on the very country that supplied the materials used in their construction.

Under project Black Shield, the OXCART was to be used as a reconnaissance aircraft; not over the Soviet Union as originally intended, but over Vietnam. The U-2 was over-flying Vietnam as early as 1965, to cover U.S. troop deployments, but the lesson of May 1st, 1960 was still fresh in the CIA’s mind: the U-2 was vulnerable to SAM systems. The S-75 that brought down Francis Gary Powers was in service in growing numbers throughout Vietnam, and no one in the CIA wanted a repeat incident. The OXCART would therefore be used to map all of the known SAM sites in North Vietnam, operating with relative impunity out of Kadena AB, Okinawa. Only on one single mission, flown on December 16th, 1967, was the A-12 detected by a SAM engagement radar. Lockheed had obviously succeeded in delivering a survivable reconnaissance platform.

More to follow later.