Beating Gravity - Lockheed A-11, A-12, SR-71 and YF-12A Blackbird

Legend has it that the Lockheed Blackbird series had its origins in 1958, when it was realised that the U-2 reconnaissance aircraft could not rely forever on its ceiling of over 70,000 feet (21335 m.) to keep it safe. Another version is that the design began as a long-range interceptor to meet a requirement calling for an altitude capability of at least 106,000 feet (32310 m.).

Whatever the pre-history, after bidding by Boeing, General Dynamics, Lockheed and North American, a development contract was awarded to Lockheed, by the CIA, on 28th August 1959. The next day, initial funding of $4.5 million was approved, to cover development from 1st September 1959 to 1st January 1960. Development would take place under the codename Oxcart.

It would have been an imposing assignment. The Lockheed F-104A, with a ceiling of 60,000 feet and a speed which could briefly reach Mach 2, had just entered service in 1958. Now Lockheed had to design an aircraft which could sustain Mach 3 at much higher altitudes.

By 1960 the development of a trio of Mach 3 aircraft, the A-12, YF-12 and SR-71, was under way. The A-12 flew in 1962, the YF-12 in 1963 and the SR-71 on 22nd December 1964. All development took place at Groom Dry Lake, north of Las Vegas, Nevada.

The A-11 or A-12 was conceived as a replacement for the U-2 in the strategic reconnaissance role. It was a light, single-seat forerunner of the SR-71, and was operated by the CIA until the USAF Blackbird became fully operational in 1968. The YF-12 was a spin-off development, a long-range interceptor never ordered into production.

Lockheed were asked to design a jet aircraft which would be at home for long periods in a domain which had usually only been visited briefly by rocket planes. The new aircraft would have to be capable of handling prolonged exposure to high altitude and high temperatures.

They started from scratch, and designed what has been described as a small supersonic airliner. For the sake of achieving long range, Lockheed emphasised streamlining in cruise mode, at the expense of other characteristics such as turn rate or ground performance.

Low drag at Mach 3 required a delta wing form. Space was needed for a great amount of fuel, and to accommodate this and to keep the centre of gravity forward, the fuselage projected well ahead of the wing. Engines and fuselage were given 'chines' (aerodynamic projecting vanes, merging with the wing) to improve directional stability, and the fuselage was canted up so its chines would serve as a lifting canard.

With the long fuselage and delta wing, a conventional vertical tail surface would have been shielded in take-off and landing, so a pair of vertical surfaces were mounted on the very large engine nacelles. High temperatures by kinetic heating of the aircraft by the surrounding air were predicted with some accuracy. At cruise speed, the leading edges and intakes would be exposed to 800°F (over twice the heat of a soldering iron); most of the wings and fuselage would face 450-500°F (twice as hot as the hottest household oven). Outer skin temperatures around the rear of the engine nacelles would reach 900-1,100°F, with the jetpipes glowing white hot even on minimal afterburner settings whilst cruising.

To cope with these temperatures, more than 90% of the fuselage was designed to be built of titanium alloy. Conventional fuels and lubricants were also unuseable at high temperatures. A fuel known as JP-7 was used, capable of withstanding high temperatures and stored in tanks in the wings and fuselage with no insulation. The fuel is so stable that a match dropped into a pool of it will reputedly extinguish, but it is very toxic.

A cold Blackbird fuselage has many leaks, leading to fuel spillage, and ground crews must be protected from exposure; those leaks close as the skin temperature rises. Lubricant oils designed for this type of aircraft must be pre-heated before take-off. Hydraulic fluids and seals, radomes, wiring, and glazing all presented heat-related problems to be addressed.

Some general heat reduction was achieved by building chordwise corrugations into the wings to accommodate expansion and increase the area available to dissipate heat. The aircraft would also be painted in a highly-emissive dark blue paint (almost black) to emit heat 2.5 times faster than unpainted titanium.

After several setbacks, the first of the Blackbird series was ready for taxiing trials in April 1962 at Groom Dry Lake. With little fuel on board the aircraft, believed to have been known as A-11 (the 'A' possibly from the CIA custom of referring to its aircraft as 'Articles') lifted unexpectedly. It did not handle well, and looked briefly as if its career might be short, but the test pilot landed it again at the far end of the runway. Two days later a scheduled test flight took place. Apart from slight shedding of RAM (Radar Absorbent Material) from the leading edges, all went well. On 30th April, 1962, the aircraft, known as A-12, made its first 'official' flight in front of government representatives.

As many as 18 A-11s (or A-12s) were thought to have been built, serialled from 60-6924 to 60-6941. Three of these were modified to prototypes for the YF-12A (possibly also designated A-12). Two were also adapted to carry a D-21 drone aircraft on a dorsal pylon.

In 1963, the CIA recruited its first 11 pilots for their new aircraft. By November, Oxcart was declared operational. It would not see an operation until November 1967, by which time four of their ten aircraft had been lost. By now it had flown at Mach 3.56 and at 96,200 feet (29322 m).

In 1963 it was realised the program could not remain secret for ever, and in November, US President Lyndon Johnson was briefed. He directed the preparation of a formal announcement for release in the new year. The existence of the A-11 was revealed by the President on US television on 29th February, 1964. He announced that the USAF posessed a new high-speed, high altitude reconnaissance aircraft capable of speeds of over 2,000 mph (3219 km/h) and altitudes of over 70,000 ft (21335 m.) - the U-2's early ceiling. Only profile photos, revealing little of the aircraft's plan form, were released, of an aircraft showing a buzz number of FX-934. Johnson named it as the A-12.

Whilst work progressed on development of the A-12, a separate project group worked in parallel, modifying the entire fuselage forebody of the aircraft to interceptor standard. Meanwhile, a further spin-off project to develop a bomber version, the RB-12, reached mock-up stage. It was cancelled because it was considered too much of a threat to the North American XB-70A Valkyrie.

The interceptor program on behalf of the USAF resulted in the variant being designated YF-12A according to USAF nomenclature. It would be equipped with Hughes AN/ASG-18 pulse-Doppler radar in the nose, and have the fuselage chines modified to house a small number of AIM-47 air-to-air missiles.

Initial missile launch tests in April 1964 were disappointing, but in March 1965 a YF-12A successfully engaged a Q-2C target drone at 40,000 ft. (12195 m).

On 1st May that year - exactly five years after Powers' U-2 was shot down - a YF-12A serial 60-6936 broke several records - many of them set by Soviet aircraft. These included absolute altitude, absolute straight-line speed and absolute speed on a 1000 km (621 mile) circuit.

Fourteen days later, Lockheed received a contract for a production version of the YF-12A, to be designated F-12B. Hughes also received a contract to further develop the radar. However, Secretary of Defense McNamara opposed the F-12 development, and on three occasions from 1966 to 1968 denied the USAF access to funds appropriated by Congress for its production. After a decision to downgrade Aerospace Defense Command, which therefore rendered the F-12 unnecessary, the YF-12A program was officially closed down on 5 January, 1968.

In June 1969 an agreement between the USAF and NASA allowed the agency access to the stored YF-12A aircraft, and gave them a unique research vehicle. Most of the NASA workload fell to 60-6935. After 145 NASA flights, the last on 31 October, 1979, it was retired to the USAF Museum at Wright-Patterson AFB.

Four A-12 aircraft were selected for possible deployment from Kadena, Okinawa under code name Black Shield in 1965. The first did not leave Area 51 until 22nd May, 1967 for the six-hour flight to Okinawa. Declared operational on May 29th, weather reports indicated conditions were perfect for a camera run over North Vietnam.

On the 31st, 60-6937 climbed to meet a tanker aircraft, then continued to operational altitude. It entered hostile airspace at Mach 3.2 and 80,000 ft (24390 m). It overflew Haiphong, Hanoi and Dien Bien Phu, refuelled, and came back for a pass near the Demilitarized Zone. It returned to Kadena after a 3 hour 40 minute flight, during which several SAMs were fired, all detonating well behind the aircraft which its CIA pilots knew as Cygnus. Its photos revealed 10 high priority targets, and 70 of the 190 known SAM sites.

In 1963, Lockheed undertook a new project, named Tagboard. This was the M-21/D-21 project, conceived in the aftermath of the loss of Gary Powers' U-2 over Russia. Manned overflights of the USSR had, as a result, been banned. The ban led to an increasing drive towards the development of unmanned reconnaissance aircraft.

By June a D-21 had been mated to a mother-ship in Lockheed's Burbank 'Skunk Works'. Two A-12s (60-6940 and 60-6941) were fitted to carry the new equipment. The first flight of the new "mother-daughter" combination took place at Groom Dry Lake on 22nd December, 1964.

The D-21 drone was launched at the command of a control officer sitting in a second bay in the A-12. Possibly, launch could occur with the A-12 making a "fire alarm" incursion, to distract defenses and launch the drone under heavy jamming. It then flew independently according to the program in its INS (internal navigation system), which told it its track, flight profile, camera 'on' and 'off' points, and bank angles. The D-21 would then descend to an ocean pickup point, ejecting the palletised camera to be picked up from its parachute by a HC-130 Hercules equipped with the MARS (Mid-Air Recovery System). The drone itself would be destroyed as it descended by a barometrically-detonated charge.

The earliest tests were successful. However, an operational test off California, on 31 July 1966, using a fully fuelled drone at Mach 3.2, ended in disaster. Although all looked well, the drone engine suffered an "unstart". On release it slammed into the A-12, lifting its nose so the Mach 3.2 airstream tore the forward fuselage from the rest of the aircraft. The crew ejected safely from the tumbling fuselage, but one drowned before rescue.

The D-21s were modified to correct the inlet problem blamed for the failure, but were only launched operationally from B-52s of 4200th Test Wing for missions over China. Some 19 D-21s were ultimately returned to Davis-Montham AFB, most remaining there for some years. They were officially retired in 1976.

The SR-71 began with a 1962 study contract to identify and define various mission options for the A-12 platform, among them a reconnaissance-strike role. Two different mock-ups, referred to as R-12 and RS-12, were built. On 18th February 1963 Lockheed received authorsation to build six aircraft, which would be based on the R-12 and known as SR-71 by the USAF.

The RS-12, and later the B-12/B-71 strike version proposals, failed to gain a production contract. Despite the design's capabilities, the lobbying power of the XB-70 and FB-111 supporters was blamed.

President Johnson publically announced the existence of the aircraft on 24th July, 1964. According to some reports, he accidentally referred to it as the SR-71, which those accounts suggest should have been RS-71, to follow Lockheed's RS-70 Mach 3 project. In any event, the SR-71 differed in appearance from the A-12 in having a more elliptical nose plan. A second crew person, the reconnaissance systems officer, sat in a bay behind the pilot. Bay sensors differed from those in earlier aircraft, and the nose section was interchangeable, to allow for various mission requirements.

Among improvements to the SR-71 camera system was a heightened resolution, believed capable of discerning to 1¾-1½ inch (4.4-3.8 cm) from operational altitudes.

The first SR-71, 64-17950, made its maiden flight on 22nd December, 1964, at Palmdale. Development progressed; and in November and December 1965, two SR-71B twin-position pilot trainers completed their first flights. The first of these was delivered in February 1966 to Beale AFB.

A spacing 'wedge' was added aft of the cockpit area after an SR-71 lost control on 23rd January, 1966 and disintegrated, killing one crewman. The wedge moved the centre of lift forward and gave the aircraft a distinctive nose-down tilt.

The first overseas deployment of the SR-71 Blackbird was to Kadena, Okinawa in March 1968, and the first operational mission was flown late in March over Khe Sanh, Vietnam. The mission was an outstanding success, revealing positions which had gone undetected by other recon types. The crew were each awarded the Distinguished Flying Cross, and strikes over the next few days ultimately led to the relief of Khe Sanh on 7th April.

The SR-71 (named Habu by the Okinawans after a local poisonous viper) continued to fly missions over Vietnam, Korea, China, Iran and around the Soviet Pacific Fleet bases, Kamchatka and the Soviet Far East. Despite official distaste for the name, Habu stuck, and aircraft returning from missions had snakes painted on the fuselage beneath the cockpit to record their tally.

The SR-71s of 9 RW continued to set records. On 26th April 1971 Lt. Col. Estes covered 15,000 miles (24140 km) in approximately 10.5 hours, at Mach 3 except when refuelling, earning the USAF's Mackay Trophy. On 1 September 1974, Maj. Sullivan, in Blackbird serial 64-1792 flew from New York to London (3,490 mls / 5616 km) in 1 hour 56 minutes. A week later the aircraft set a new record of 3 hours 47 minutes from London to Los Angeles (5,645 mls / 9084 km) to arrive in L.A., using local times, about four hours before taking off from London.

Several more records were established in 1976, including a new record around a 1,000 km course of 2,092.294 mph (3367.13 km/h) on 27th July; and a straight-line horizontal flight record the following day of 2,193.17 mph (3529.47 km/h) at 85,069 ft (25929 m).

The SR-71 continued in service through the 1980s. Small detachments, typically of 1-2 aircraft, operated regularly from Kadena and from Mildenhall, England. The SR-71 made a comeback from a short retirement in January 1997, and continued working into the late 1990s. Its home unit is the 12th AF's 9 RW (Reconnaissance Wing), at Beale AFB, California. The SR-71s are based with 9 RW Det 2 at Edwards AFB, Cal.

NASA YF-12A Images YF-12 images below are from the NASA Dryden Flight Research Center at Edwards, California Open YF-12 gallery on NASA website
NASA YF-12A Movies (requires Quicktime - download) NASA Dryden Flight Research Center website: SR-71A/YF-12 takeoff and flight YF-12A low level test flight NASA SR-71 Movies SR-71 takeoff and flight SR-71 flyover SR-71 takeoff from Edwards Air Force Base SR-71 in-flight refueling SR-71 LASRE refueling from a KC-135 SR-71 LASRE in flight over the Mojave Desert SR-71B Blackbird pilot trainer aircraft

Related links:

More about the YF-12A Blackbird from the Smithsonian Air & Space magazine website.
AVIATION EXPLORER :: LOCKHEED SR-71 FACTS