Lockheed SR-71 BLACKBIRD gallery 1

The beginnings of this aircraft are inextricably linked to those of its predecessor, the CIA Lockheed A-12 spy plane. In December 1962 the USAF requested a larger and heavier reconnaissance variant called the “R-12”. This new aircraft would have more space for fuel, would carry two crew members and would carry cameras, a side-looking airborne radar (SLAR) and signals intelligence sensors. Again, the design would be in charge of Lockheed’s Skunk Works, more specifically in the person of the aerospace engineer Clarence “Kelly” Johnson, responsible for many of the innovative equipment included in the design. However, the new aircraft was named by USAF Chief of Staff General Curtis LeMay as “SR-71” (Strategic Reconnaissance 71).
The new aircraft was designed to fly at Mach 3 and carried two crew in two separate cockpits mounted in tandem. The pilot sat in the front seat and the reconnaissance systems officer (RSO) who was in charge of the surveillance teams and directing navigation on the mission flight path sat in the rear seat. It carried radar countermeasures for self-protection, although its speed and high flight altitude made it almost invulnerable not only to interception, but also to SAM missiles. The above, together with a very low radar signature, made it practically impossible for the air defenses to detect it and launch the missiles in time to shoot it down.
The Blackbird is built almost entirely (93%) in titanium, a very expensive and extremely difficult metal to work at that time, but very resistant to heat. This material was a great challenge for Lockheed, that encountered huge problems handling it and created new manufacturing methods. Titanium was sensitive to cadmium from tools, tap water or metallurgical contamination. They also devised a new titanium alloy, (Beta B-120), that was cheaper and easier to work at lower temperatures. Paradoxically, the scarcity of rutile ore in the US, from which titanium was extracted, meant that most of the rutile ore needed for the SR-71s came from the USSR through covert operations with Third World countries. Some sources leaked to the press that the SR-71 airframe alone cost about 50 million 1963 dollars.
The outer windscreen of the cockpit was built from a series of high-strength glass, quartz and plastic laminates and was bird-impact-proof. In this area the temperature reached 340ºC during flight, one of the highest in the entire aircraft. The SR-71 had a corrugated outer skin that smoothed out in flight under the effect of heat. Temperatures reached 260 ºC in many parts and up to 590 ºC around the engines, but thanks to this coating, the internal structure heated up much more slowly.
The cockpits also needed special attention, such as a high-power ventilation system due to the extreme temperatures reached on the outside of the aircraft as well as on the windshield. A heat exchanger was used to transfer heat from the cockpit to the front (nose) landing gear bay to cool the tires and not have to use the special ones impregnated with aluminum powder. This same heat was also diverted to the fuel to preheat it before consumption.
It can be said that the SR-71 was the first stealth aircraft, not because it was undetectable by radar, but because all the techniques and technology available at the time were used to make its “signature” as small as possible. The design of the fuselage, with flattened shape and its sharp edges (chines), radar-absorbent materials and even certain fuel additives, such as cesium, to reduce the emission of heat detected by the radar, helped a lot that the Blackbird’s radar cross-section (RCS) was only 10m2. The internal structure was made up of reentrant triangles that “captured” the radar waves and reflected them repeatedly, attenuating them to the point that there were no longer any reflected waves.
The Blackbird‘s paint was special and was manufactured to help radiate heat from the aircraft’s skin and to reduce the radar signature by emitting electrical discharges between the millions of iron spheres that made it up. At cruising speed and altitude this paint changed from black to blue due to these discharges. The challenge that Skunk Works faced was not only the aerodynamics of the fuselage or the engines, but also having to create practically a unique range of lubricants, oils, hydraulic fluids, sealants and insulating materials for this aircraft, a work that was little recognized as it turned out to be the Blackbird an aircraft that even today keeps many of its capabilities secret.
The SR-71 was a cantilevered mid/low wing monoplane aircraft of basically delta shape with rounded tips. The wings resisted “normal” temperatures of 260 ºC, reaching in some points up to 427 ºC. The edge between the engines and the fuselage acted as a canard reducing drag, improving directional stability and providing more lift. Above each engine was installed a vertical plane inclined 15º inwards that could rotate up to 20º to the right or left, in unison or independently.
The Blackbird‘s tires retracted inward during flight and went into compartments surrounded by fuel to insulate them from the heat. However, they had to be inflated with nitrogen and and those of the rear landing gear were impregnated with aluminum powder. The installation of a braking parachute on the aircraft helped reduce tire wear during landing, but they had to be changed after 20 missions approximately. The parachute was deployed when the aircraft was rolling at about 100 km/h.
One of the fundamental elements that allowed the Blackbird to have a very high cruising speed were the air inlets of the engines built by Hamilton Standard. These elements slowed the speed of the air entering the engine to subsonic speeds. Inside were some mobile cone-shaped devices called “spike” (inlet cone) that moved forward or backward to control the shock wave generated during flight and also the airflow that entered the engines. The position of these elements was vital to avoid too high air pressure inside the engines and that the shock wave did not destroy the engines.
In the beginning the inlet cones were controlled by analog computers that did not act with the required speed and sometimes gave rise to the so-called “inlet unstart”. These variations in airflow could cause afterburner shutdowns leading to dangerous yaws to one side which in turn produced unwanted bangs and jerks and even stalling in the most severe cases. Starting in 1980, the analog computer was replaced by a digital one and Lockheed installed an electronic system that detected these inlet unstarts and reset the engines without pilot intervention.
Blackbird carried two Pratt & Whitney J-58 (JT11D-20B) axial-flow turbojet engines. These engines offered a thrust of 10,419 kg dry and 14,496 kg wet, and had the peculiarity of changing cycles at 3,220 km/h acting as a ramjet. This conversion allowed the engines to fly at this enormous speed while generating only a tenth of their thrust, something totally unique. The engines were designed to have their maximum efficiency at Mach 3.2, but it was found after some missions in which this speed was exceeded, that the engine was even more efficient at higher speeds.
The engine acted like a normal afterburning turbojet during takeoff and acceleration up to Mach 2, but then it used a compressor that injected air and raised the temperature of the afterburner, achieving more power until reaching maximum speed. The maximum speed was limited by the maximum temperature of the air received by the compressor. J-58 engines were guaranteed up to 430 ºC. For the total thrust required, 60% was provided by the air inlets, another 30% by the exhaust, and the remaining 10% by the engines.
The fuel used by the Blackbird is called JP-7 (Jet Propellant 7), which is a low volatility and high flash point fuel specially developed for this aircraft. To start the engines, triethylborane (TEB) had to be injected into the engine chambers to preheat the JP-7 so that it could ignite. This fuel was delivered to the engines at high pressure and at a temperature of around 316 ºC.
In the fuselage and wings were nine large fuel tanks, divided into six groups, with a capacity of about 46,000 liters. The outer walls of these tanks were formed by the aircraft’s own skin. The fuel in the fuselage tanks was the one that was consumed last since it took longer to heat up than that stored in the wings. The fuel tanks had leaks on land due to their design. They were designed so that when the temperature of the aircraft rises during the flight, the expansion of the joints will seal the tanks. Each fuel tank carried an inert nitrogen atmosphere to ensure its pressurization. This nitrogen was injected into the tanks during flight to avoid possible fires due to the extremely high temperatures caused by friction with the air.
The exorbitant consumption of the J-58 engines at high speed made in-flight refueling essential during SR-71 missions. The 46,000 liters of JP-7 did not last more than 90 minutes at maximum speed. A fleet of 56 Boeing KC-135A tanker aircraft were modified to operate on JP-7 fuel. In addition, a high-speed boom and special fuel systems for moving JP-4 and JP-7 between different tanks in the tanker aircraft were installed. These new tankers were designated KC-135Q.
The aircraft had 4 compartments along the fuselage chines in which standard sensor modules could be installed. In the nose, in front of the cockpit, there was a removable chine in order to be able to use different combinations of interchangeable sensors depending on the mission. These systems included long-range panoramic and oblique cameras, side-looking airborne radar (SLAR), a linear infrared, and various ELINT/COMINT antennas and receivers. It also had a tracking camera and an infrared camera that recorded the entire mission, as well as two recorders for ELINT and SLAR systems.
Flying at an altitude of 24,000 meters, the SR-71 was capable of covering 260,000 km2 in one hour and was therefore equipped with sophisticated high-resolution cameras. For specific areas or objectives, the HYCON Technical Objective Camera (TEOC) was used, which could move 45º to the right or left of the centerline. To photograph large areas, a pair of Itek’s Operational Objective Cameras were used to show images of the entire flight path. And there was a third type of camera which was the Itek Optical Bar Camera, which covered the horizon-to-horizon sector.
Side-looking airborne radar (SLAR) was built by Goodyear Aerospace and was a ground-mapping imaging system that collected data in fixed swaths to the left or right of centerline or from a point location for higher resolution. This equipment was replaced later by a Loral’s Advanced Synthetic Aperture Radar System (ASARS-1). The Blackbird also had an Electro Magnetic Reconnaissance System from the AIL firm with which it captured and analyzed electronic signals (ELINT). This system used to be installed in the chine bays.
The SR-71 did not carry any type of weapons, although for its defense it had several electronic warning and countermeasures (ECM) equipment. These devices were simply designated as “Systems A, A2, A2C, B, C, C2, E, G, H, and M”. In any case the Blackbird could evade missile attacks simply by accelerating or slightly changing course, since at such high speeds, the slightest change meant great distances. Flying at Mach 3.2 the Blackbird covered 1,500 meters in one second! While it was in service no fighter was able to intercept it, because the MiG-25 Foxbat could get close, but it could not climb to the necessary altitude.
One of the most amazing systems of the SR-71 was known as “astro-inertial guidance system (ANS)”. This system created by Northrop for the SM-62 Snark and AGM-48 Skybolt missiles was adapted for the Blackbird, allowing extremely precise automatic navigation. This system used a digital computer to which a list of stars used for celestial navigation was entered. At first the list included 56 stars, which later increased to 61.
The ANS was aligned before takeoff and allowed navigation both day and night thanks to its “blue light” source star tracker. The system was installed behind the RSO’s station and tracked the stars through a circular quartz window. This system could control all the parameters of the mission such as navigation, positioning, control of sensors, cameras and SLAR radar. This equipment was so precise that it did not tolerate deviations of more than 300 meters at maximum speed.
On December 22, 1964, the SR-71 took flight for the first time. At the controls of it was Lockheed test pilot Robert J “Bob” Gilliland. Later, a total of 32 Blackbirds were delivered to the USAF, 29 of the A variant, 2 of the B variant and 1 of the C variant. The basic variant SR-71A was the one that carried out the real missions, the SR-71B was the training variant and differed by having a twin staggered cockpit for two pilots. The SR-71C variant (on the image) was a training variant consisting of the forward fuselage of an SR-71 used for static testing plus the rear fuselage of the first YF-12A. During its career, 12 aircraft were lost in accidents, resulting in the death of one pilot.
On January 1, 1966, the 4200 Strategic Reconnaissance Wing, based at Beale AFB, California, was activated as the SR-71 training unit. A few days later the first SR-71A arrived, followed by two SR-71Bs. This wing was deactivated on June 22, 1966 just three days before the 9th Strategic Reconnaissance Wing based at Beale AFB, California, was activated as the only operational unit of the Blackbirds. This wing would frame its aircraft in the 1st and 99th Strategic Reconnaissance Squadrons. Normally, only 10 Blackbirds are kept operational at the same time. The reason was that all the aircrafts had the same flight hours and the same wear.
On March 21, 1968, the SR-71 flew its first real mission, departing from Kadena Air Base, Okinawa, Japan, where it had been deployed two weeks earlier. Deployments of this type were called “Glowing Heat” and were part of the “Senior Crown” program. This program consisted of carrying out reconnaissance flights over North Vietnam. These flights were codenamed “Black Shield” and later “Giant Scale” sorties.

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