SR-71 Blackbird, Lockheed


SR-71 Blackbird Photo by Mark Schenk.

The SR-71 is a famous Mach 3+ spy plane. This is the fastest aircraft ever known to be in service with an air force. The large, delta-winged SR-71 gets is performance from the unusual J-58 engines, that act like ramjets at high altitude and speed. It was related to the the YF-12 fighter and its precessor, the A-12 CIA-operated spy aircraft. Recently, the a number of SR-71s was put back in service from a premature retirement.

The Lockheed SR-71, unofficially known as the Blackbird and by its crews as the Habu, was an advanced, long-range, Mach 3 strategic reconnaissance aircraft developed from the Lockheed YF-12A and A-12 aircraft by the Lockheed Skunk Works (also responsible for the U-2. It flew from 1964-1998. The legendary Clarence "Kelly" Johnson, in particular, was the man behind many of the design's advanced concepts. The SR-71 was one of the first aircraft to be shaped to reduce radar signature. However, the aircraft was not stealthy and still had a fairly large radar cross-signature, and was visible on ATC radar for hundreds of miles, even when not using its transponder. This fact is further corroborated by the fact that missiles were fired at them quite often after they were detected on radar. The aircraft flew so fast and so high that if the pilot detected a surface-to-air missile launch, the standard evasive action was simply to accelerate. Twelve aircraft are known to have been lost, all through non-combat causes.

Type: SR-71A
Task: reconaissance
Year: 1966
Crew: 2
Wing Span: 16.94 m
Wing area: 170 m²
Wing loading: 460 kg/m²
Wing Aspect ratio: 1.7
Length: 32.74 m
Height: 5.64 m
Engines: 2 * 14740 kg P&W J-58 continuous-bleed afterburning turbojets
Empty weight: 30600 kg
Max.Weight: 77111 kg
Thrust/weight: 0.382
Max. Speed: Mach 3.3+ or 3530 km/h at 24000 m
Ceiling: 26000 m
Rate of climb: 60 m/s
Max. Range: 4800 km
Armament: none


SR-71 BLACKBIRD

The SR-71 Blackbird strategic reconnaissance aircraft was developed by the Advanced Developments Projects Division at Lockheed Martin's Skunk Works. It is the world's fastest and highest flying aircraft to reach full-scale development and production. SR-71 aircraft are assigned to the 9th Reconnaissance Wing at Beale Air Force Base and operate from Edwards Air Force Base, California.

The SR-71 entered service in 1968 and was retired in 1990, but in 1994 the US Congress directed that the SR-71 should be re-instated to operational readiness and deployed to meet the need for a broad area coverage reconnaissance platform. The aircraft were brought out of retirement and two aircraft were mission ready by the third quarter of 1995.

NASA has two SR-71 aircraft, one SR-71A and one SR-71B trainer aircraft for aeronautical research. The aircraft are based at the Dryden Flight Research Centre at Edwards, California. The characteristics of the aircraft and its flight are used in the development of new supersonic and hypersonic aircraft and propulsion systems.

SR-71 has a crew of two, pilot and reconnaissance officer. The aircraft is unarmed but is equipped with an electronic countermeasures (ECM) system.

DESIGN

The airframe structure is mainly of titanium and titanium alloys capable of withstanding the heat generated by sustained supersonic flight. The aircraft's control surfaces are: the all-moving nearly vertical tail surfaces above each engine nacelle; the ailerons forming the trailing edge on the outer wings, which provide control in roll; and the elevators on the trailing edges between the engine exhausts, which govern the pitch of the aircraft.

SENSORS

The aircraft, which can survey 100,000 square miles per hour, is equipped with a suite of intelligence sensors, including the Lockheed Martin ASARS-1 Advanced Synthetic Aperture Radar, which provides all weather day and night intelligence data. ASARS-1 is installed in the nose of the aircraft.

The Common Data Link (CDL), operating at 274 Mbs, can be used to download the data gathered by the ASARS to a ground station. The CDL operates over a 300 nautical mile line of sight. If the aircraft is out of range of a ground station, ASARS data can be stored on the DCR recorder installed in the aircraft. The stored data can be processed when the aircraft has landed or can be transmitted via the downlink when the aircraft is next in range of a ground station.

According to the particular mission requirement, a panoramic Optical Bar Camera can be installed in the nose of the aircraft instead of the ASARS radar. The Litton Itek Optical Bar Camera is a wide angle system using high resolution wet film.

The point and shoot framing camera installed on the port and starboard side of the aircraft is the Boeing Technical Objective Camera (TEOC) which uses wet film. A 25 megapixel electro-optic sensor backplane, integrated into the TEOC, has been demonstrated in flight trials. The SR-71 can carry two wet film TEOCs, two electro-optical TEOCs or one of each.

The NASA SR-71 aircraft being used as high speed high altitude testbeds are fitted with sensors for aeronautical research. The SR-71 has been used as a camera platform for NASA's Jet Propulsion Laboratory. An upward looking ultraviolet camera is installed in the nosebay. A downward looking camera is used to study rocket engine exhaust signatures, volcano plumes and the spectrum of the earth's atmosphere.

ENGINES

The Pratt & Whitney J58-1 engines used in the Blackbird were the only military engines ever designed to operate continuously on afterburner, and actually became more efficient as the aircraft went faster. Each J58 engine could produce 32,500 lbf (145 kN) of static thrust. Conventional jet engines cannot operate continuously on afterburner and lose efficiency as airspeed increases. The aircraft can achieve a speed over Mach 3.2, more than 2200 miles per hour, and altitudes more than 85,000 feet.

The J58 was unique in that it was a hybrid jet engine: a turbojet engine inside a ramjet engine. At lower speeds both the turbojet (engine core) and the ramjet (with the afterburners running without any bypass air) both work, but at higher speeds the turbojet throttled back and just sat in the middle with the air bypassed around it.

Air was initially compressed (and thus also heated) by the shock cones, passed through 4 compressor stages and then was split by moveable vanes: some of the air entered the compressor fans ("core-flow" air), while the rest of the air went straight to the afterburner (via 6 bypass tubes). The air travelling on through the turbojet was further compressed (and thus further heated), and then fuel was added to it in the combustion chamber -- it then reached the maximum temperature anywhere in the Blackbird, just under the temperature where the turbine blades would start to soften. After passing through the turbine (and thus being cooled somewhat), the core-flow air went through the afterburner and met with any bypass air.

At around Mach 3, the increased heating from the shock cone compression, plus the heating from the compressor fans, were already enough to get the core air to high temperatures, and little fuel could be added in the combustion chamber without the turbine blades melting. This meant the whole compressor-combustor-turbine set-up in the core of the engine provided less power, and the Blackbird flew predominantly on air bypassed straight to the afterburners: forming a large ramjet effect. No other aircraft does this. (This shows how the temperature tolerance of the turbine blades in a jet engine determine how much fuel can be burned, and thus to a great extent determine how much thrust a jet engine can provide).

Performance at low speeds was anemic. Even passing the speed of sound required the aircraft to dive. The reason was that the size of the turbojets were traded to reduce weight but to still allow the SR-71 to reach speeds where the ramjet effect became prominent and efficient; and then the plane became alive and rapidly acceleated to mach 3.0. The efficiency was then good due to high compression and low drag through the engine and this permitted large distances to be covered at high speed.

Originally, the Blackbird's engines started up with the assistance of an external "start cart", a cart containing two Buick Wildcat V8 engines which were rolled out onto the runway underneath the aircraft. The two Buick engines powered a single, vertical driveshaft connected to a single J58 engine. Once one engine was started, the cart was wheeled over to the other side of the aircraft to start the other engine. The operation was deafening. In later years, the J58s were started with a conventional start cart.

The aircraft carries 12,200 gallons (84,000 pounds) of fuel. The unrefuelled range is more than 2000 miles. An in-flight refueling receptacle is located on the centreline top of the fuselage.



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