SR-71 Blackbird

The Lockheed SR-71 "Blackbird" is a retired long-range, high-altitude strategic reconnaissance aircraft developed as a black project by Lockheed's Skunk Works for the United States Air Force (USAF). Derived from the CIA's single-seat A-12, it was lengthened to carry more fuel and a two-man crew, revealed publicly in July 1964 and entered service in January 1966. It cruised at Mach 3.2 at 26,000 m (85,000 ft); of 32 built, 12 were lost in accidents and none to enemy action. On 28 July 1976 it set world records for speed over a straight course and for altitude in horizontal flight, both still standing as of 2026. The USAF retired it in 1989, reactivated three airframes from 1995 and retired it for good in 1998; NASA flew the last two until 1999.

Development

In late 1957 the CIA asked Lockheed for a successor to the U-2 that would fly higher and faster, and Project Archangel began in 1958 under the head of the Skunk Works in Burbank, California. After a 1959 redesign cut the radar cross-section by 90 percent, the agency signed a US$96 million contract for 12 A-12s on 11 February 1960; the A-12 first flew at Groom Lake, Nevada, on 25 April 1962, and 13 were built. The USAF ordered its own derivative, which Lockheed called the R-12, signing for six aircraft on 28 December 1962. It had a longer fuselage for more fuel, tandem cockpits for a pilot and a reconnaissance systems officer (RSO), reshaped chines and a payload of signals-intelligence sensors, side-looking radar and cameras. Unlike the covert A-12, it flew overtly in USAF markings and never crossed the Warsaw Pact or China.

President Johnson revealed the aircraft on 25 July 1964 as the "SR-71", the designation the Chief of Staff had lobbied for in place of RS-71. The prototype first flew at Palmdale, California, on 22 December 1964. The A-12 was cancelled in 1966 and the shared tooling destroyed in 1968. Production totalled 32 aircraft: 29 SR-71As, two SR-71B trainers and one SR-71C.

Design

The SR-71 was shaped for the smallest radar cross-section Lockheed could achieve, an early stealth attempt: flattened chines along the fuselage, vertical fins canted inward, radar-absorbing material in sawtooth skin sections and a caesium fuel additive to dull the exhaust plume's radar return. The result was a wing area of about 170 m² (1,800 sq ft) with a radar cross-section of around 10 m² (110 sq ft). Titanium made up 85 percent of the structure, much of the rest polymer composites; Lockheed had to develop new fabrication methods and at one point rejected 80 percent of the titanium delivered. Fuselage panels fitted loosely on the ground, aligning only as the airframe expanded by several inches in flight, which is why the aircraft leaked JP-7 before take-off, and the skin was painted black to radiate heat. The aircraft is 32.74 m (107 ft 5 in) long with a 16.94 m (55 ft 7 in) span, and weighs 30,617 kg (67,500 lb) empty and 78,018 kg (172,000 lb) at maximum take-off.

Above Mach 3 the inlet produced 54 percent of the thrust, the ejector nozzle 28.4 and the engine itself 17.6. Each Pratt & Whitney J58 (JT11D-20) was rated at 110 kN (25,000 lbf) dry and up to 151 kN (34,000 lbf) in afterburner; six external bleed tubes passed 20 percent of compressor air to the afterburner, matching engine airflow to the inlet and raising installed thrust by 47 percent; in high-speed cruise the engine approximated a ramjet. Inlet "unstarts", which killed the afterburner and yawed the aircraft violently, were reduced by the Digital Automatic Flight and Inlet Control System (DAFICS) from 1980. JP-7 doubled as a heat sink and was so hard to ignite that triethylborane was injected to start the engines; refuelling came from dedicated KC-135Q tankers. Maximum speed was 3,540 km/h (1,910 kn), Mach 3.3, at 24,000 m (80,000 ft), with a service ceiling of 26,000 m (85,000 ft).

A Nortronics astro-inertial navigation system tracked stars by day and night, holding drift to about 300 m (1,000 ft) at Mach 3. The 1,588 kg (3,500 lb) sensor fit included Itek Operational Objective Cameras or an Optical Bar Camera for horizon-to-horizon coverage, a HYCON Technical Objective Camera steerable 45 degrees off track, a Goodyear side-looking radar later replaced by Loral's ASARS-1 synthetic-aperture radar, and an AIL electronic-intelligence suite.

Operational History

The first aircraft reached the 4200th (later 9th) Strategic Reconnaissance Wing at Beale AFB, California, in January 1966. Operating Location 8 at Kadena Air Base, Okinawa, received its first SR-71A on 8 March 1968, and 61-7976 flew the first operational sortie over Vietnam on 21 March 1968. Missions over North Vietnam and Laos ran at about one a week for two years and nearly daily by 1972; two aircraft were lost there to mechanical failures, in 1970 and 1972, while some 800 North Vietnamese SAMs were fired without a hit. Later missions covered North Korea, Cuba, Nicaragua, Libya and the nuclear installations of Israel and South Africa.

Detachment 4 began operations from RAF Mildenhall on 20 April 1976, flying two routes: north along the Norwegian coast to the Kola Peninsula to watch the Soviet Northern Fleet, and the "Baltic Express" along the Soviet coast, turning south of Åland at Mach 2.54 to stay out of Swedish airspace. The Swedish Air Force claims its JA 37 Viggens achieved missile lock in 51 of 322 recorded Baltic Express sorties between 1977 and 1988. On 29 June 1987 an engine explosion at 20,000 m (66,000 ft) forced 61-7964 to descend and turn into Swedish airspace, where Viggens escorted it to Denmark while MiG-25s were launched against it.

On 28 July 1976, 61-7962 set the altitude-in-horizontal-flight record of 25,929 m (85,069 ft) and 61-7958 the absolute speed record of 3,529.6 km/h (2,193.2 mph), about Mach 3.3. On 1 September 1974 an SR-71 flew New York to London in 1 hour 54 minutes 56.4 seconds. The USAF ended the programme on 22 November 1989 after the last missions in October, citing cost (US$85,000 an hour) and the lack of a real-time data link. Congress voted US$100 million on 28 September 1994 to reactivate three aircraft, and Detachment 2 of the 9th Reconnaissance Wing flew them from Edwards AFB from 28 June 1995 with a near-real-time ASARS-1 data link. After the President's October 1997 line-item veto of the programme's US$39 million and the Supreme Court's June 1998 ruling striking down the line-item veto, the USAF permanently retired the type in September 1998. NASA's Dryden Flight Research Center flew two Blackbirds for research until the last SR-71 flight, by 61-7980 (NASA 844), on 9 October 1999.

Variants

• SR-71A: Main production variant, 29 built, flown by the 9th SRW from Beale, Kadena and Mildenhall and later by NASA.
• SR-71B: Two-seat trainer with a raised second cockpit for the instructor; two built, one (61-7956) later serving NASA as 831.
• SR-71C: Single hybrid trainer assembled from the rear fuselage of the first YF-12A and the forward fuselage of an SR-71 static-test article; nicknamed "The Bastard".