Lockheed SR-71 Blackbird

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This article is about the supersonic aircraft. For the music band, see SR-71 (band).

Template:Infobox Aircraft 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 "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 have an extremely low radar signature. 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. No SR-71 was ever shot down.

History

Predecessor models

The A-12 Oxcart, designed for the CIA by Kelly Johnson at the Lockheed Skunk Works, was the precursor of the SR-71. Lockheed used the name "Archangel" for this design, but many documents use Johnson's preferred name for the plane, "the Article". As the design evolved, the internal Lockheed designation went from A-1 to A-12 as configuration changes occurred, such as substantial design changes to reduce the radar cross-section. The first flight took place at Groom Lake, NV, on April 25 1962. It was an Oxcart labeled the A-11 configuration since it was equipped with less powerful Pratt & Whitney J75s because development of the Pratt & Whitney J58s intended for the Oxcart was delayed. When the J58s finally arrived at the "Ranch" (Groom Lake's Area 51) and were installed, the Oxcart configuration number was changed to its final A-12 nomenclature (the J58s became the standard power-plant for all subsequent A-12s). Eighteen aircraft were built in three variations, of which three were YF-12As, prototypes of the planned F-12B interceptor version, and two were the M-21 variant (see below).

The Air Force reconnaissance version was originally called the R-12 (see the opening fly page in Paul Crickmoore's book SR-71, Secret Missions Revealed, which contains a copy of the original R-12 labeled plan view drawing of the vehicle). However, during the 1964 presidential campaign, Senator Barry Goldwater continually criticized President Lyndon B. Johnson and his administration for falling behind the Soviet Union in the research and development of new weapon systems. Johnson decided to counter this criticism with the public release of the highly classified A-12 program and later the existence of the reconnaissance version.

Name and designation

The USAF had planned to redesignate the R-12 aircraft as the RS-71 (Reconnaissance-Strike) as the successor to the RS-70 Valkyrie, which had two test Valkyries flying at Edwards AFB, California. However, then USAF Chief of Staff Curtis LeMay preferred the SR designation and wanted the RS-70 to be named SR-70. Before the Blackbird was to be announced by Lyndon B. Johnson on February 29 1964, LeMay lobbied to modify Johnson's speech to read SR-71 instead of RS-71. The media transcript given to the press at the time still had the earlier RS-71 designation in places, creating the myth that the president had misread the plane's designation. [1] [2]

This public disclosure of the program and its designation came as a shock to everyone at Skunk Works and Air Force personnel involved in the program; at this time all of the printed Maintenance Manuals, Flight Crew Handbooks (the source of Paul Crickmoore's page), training vufoils, slides and materials were still labeled "R-12" (The 18 June 1965 Certificate of Completion issued by the Skunkworks to the first Air Force Flight Crews and their Wing Commander are labeled: "R-12 Flight Crew Systems Indoctrination, Course VIII" and signed by Jim Kaiser, Training Supervisor and Clinton P. Street, Manager, Flight Crew Training Department). Following LBJ's speech, the designation change was taken as an order from the Commander-In-Chief, and immediate republishing began of new materials retitled "SR-71" with 29,000 blueprints altered.

First flight and usage

Although the predecessor A-12 first flew in 1962, the first flight of an SR-71 took place on December 22 1964, and the first SR-71 to enter service was delivered to the 4200th (later, 9th) Strategic Reconnaissance Wing at Beale Air Force Base, California, in January 1966.

On March 21, 1968 Major (later General) Jerome F. O'Malley and Major Edward D. Payne flew the first operational SR-71 sortie in SR-71 serial number 64-17976. During its career, this aircraft (976) accumulated 2,981 flying hours and flew 942 total sorties (more than any other SR-71), including 257 operational missions, from Beale AFB, California; Palmdale, California; Kadena Air Base, Okinawa, Japan; and RAF Mildenhall, England. The aircraft was flown to the United States Air Force Museum near Dayton, Ohio in March 1990.

In a seventeen-year period of its its operational history (from July 20, 1972 to April 21, 1989) the SR-71 flew without a loss of any type. Other operational highlights:

  • 3,551 Mission Sorties Flown
  • 17,300 Total Sorties Flown
  • 11,008 Mission Flight Hours
  • 53,490 Total Flight Hours
  • 2,752 hours Mach 3 Time (Missions)
  • 11,675 hours Mach 3 Time (Total)

While deployed in Okinawa, the SR-71s and their aircrew members gained the nickname Habu (as did the A-12s preceding them) after a southeast Asian pit viper which the Okinawans thought the plane resembled.

32 SR-71 airframes were built, 29 as SR-71As for operational missions and 2 as SR-71B trainers. The 32nd airframe was fabricated in 1969 as a hybrid trainer designated the SR-71C by mating the back half of an YF-12 wrecked in a 1966 landing accident with a fully functional SR-71 forward section of a static test specimen. Of all SR-71s, 12 (including one trainer) were lost in flight (or ground) accidents. Only one crew member, Jim Zwayer, a Lockheed flight test reconnaissance and navigation systems specialist, was killed from a flight accident. The rest of the crew members ejected safely or evacuated their aircraft on the ground.

The United States Air Force retired its fleet of SR-71s on January 26 1990, allegedly because of a decreasing defense budget and high costs of operation. The reconnaissance aspect of the SR-71 could be performed cheaper, and often better by reconnaissance satellites and drones. It was a great plane, but eventually there was nothing it could do, that could not be done better by other devices, and it was very expensive to operate. Also, parts were no longer being manufactured for the aircraft, so other airframes had to be cannibalized in order to keep the fleet airworthy. The USAF returned the SR-71 to the active Air Force inventory in 1995 and began flying operational missions in January 1997. The planes were permanently retired in 1998.

Variants

D-21B Drone mounted on M/D-21 Blackbird

One notable variant of the basic A-12 design was the M-21. This was a A-12 platform modified by replacing the single seat aircraft's Q bay (which carried its main camera) with a second cockpit for a launch control officer. The M-21 was used to carry and launch the D-21 drone, an unmanned, faster and higher flying reconnaissance device. This variant was known as the M/D-21 when mated to the drone for operations. The D-21 drone was completely autonomous; having been launched it would overfly the target, travel to a rendezvous point and eject its data package. The package would be recovered in midair by a C-130 Hercules and the drone would self destruct.

The program to develop this system was canceled in 1966 after a drone collided with the mother ship at launch, destroying the M-21 and killing the Launch Control Officer. Three successful test flights had been conducted under a different flight regime; the fourth test was in level flight, considered an operational likelihood. The shock wave of the M-21 retarded the flight of the drone, which crashed into the tailplane. The crew survived the mid-air collision but the LCO drowned when he landed in the ocean and his flight suit filled with water.

The only surviving M-21 is on display, along with a D-21B Drone, at the Museum of Flight in Seattle, Washington. The D-21 was adapted to be carried on wings of the B-52 bomber.

Records

The SR-71 remained the world's fastest and highest-flying operational manned aircraft throughout its career. From an altitude of 80,000 ft (24 km) it could survey 100,000 miles2·h-1 (72 km2·s-1) of the Earth's surface. On July 28, 1976, an SR-71 broke the world record for its class: an absolute speed record of 2,193.167 mph (3,529.56 km·h-1), and a US "absolute altitude record" of 85,068.997 feet (25,929 m). The Soviet MiG-25 'Foxbat' high-altitude interceptor broke the record, reaching an altitude of 37,650 m on August 31 1977 (MIG-25). Several planes exceeded this altitude in zoom climbs but not in sustained flight. When the SR-71 was retired in 1990, one was flown from its birthplace at United States Air Force Plant 42 in Palmdale to go on exhibit at what is now the Smithsonian Institute's Steven F. Udvar-Hazy Center (an annex of the National Air & Space Museum) in Chantilly, Virginia, setting a coast-to-coast speed record at an average 2,124 mph (3,418 km·h-1). The entire trip took 64 minutes.[3] The SR-71 also holds the record for flying from New York to London: 1 hour 54 minutes and 56.4 seconds, set on September 1 1974. (For comparison, commercial Concorde flights took around 3 hours 20 minutes, and the Boeing 747 averages 7 hours.)

Design and operational details

The flight instrumentation of SR-71 Blackbird

The airframe was made of titanium obtained from the USSR during the height of the Cold War. Lockheed used all possible guises to prevent the Soviet government from knowing what the titanium was to be used for. In order to keep the costs under control, they used a more easily worked alloy of titanium which softened at a lower temperature. Finished aircraft were painted a dark blue (almost black) to increase the emission of internal heat (the fuel was used as a heat sink for avionics cooling) and to act as camouflage against the sky.

When the Soviets developed the high speed (Mach 2.83) MiG-25, they chose nickel steel for the airframe. The methods they employed to shape titanium at the time produced a brittle sheet of metal during the forming process and the sheets tended to crack and shatter when being forced into shape.

The plane was designed to have a very small 'radar cross-section' — the SR-71 was an early stealth design. However, the radar signature aspects of the SR-71 design did not take into account the extremely hot engine exhaust, and it turns out that this exhaust can reflect radar. Ironically, the SR-71 was one of the largest targets on the FAA (Federal Aviation Administration) long range radars, which were able to track the plane at several hundred miles.

The red stripes found on some SR-71s are there to prevent maintenance workers from damaging the skin of the aircraft: as in this image. The curved skin near the center of the fuselage is thin and delicate. There is no support underneath with exception of the structural ribs, which are spaced several feet apart.

Air inlets

A critical design feature to allow Mach 3.0+ cruising speeds, yet provide subsonic air flow into the turbojet engines were the air inlets. At the front of each inlet was a sharp, pointed moveable cone called a "spike" that was locked in the full forward position on the ground or when in subsonic flight. During acceleration to high speed cruise, the spike would unlock at Mach 1.6 and then begin a mechanical (internal jack screw powered) travel to the rear up to a maximum of 26 inches (66 cm). The original air inlet computer was an analog design which, based on pitot-static, pitch, roll, yaw, angle-of-attack inputs, would determine how much movement was required. By moving, the spike tip would withdraw the shockwave riding on it into the inlet body where reflections of the shockwave from the inlet cowl to the spike and back to the cowl would cause a loss of energy and slow it down until a Mach 1.0 shockwave was formed, the backside of which was subsonic air for ingestion into the engine compressor. This capture of the shockwave within the inlet was called "Starting the Inlet". Tremendous pressures would be built up inside the inlet and in front of the compressor face. Bleed holes and bypass doors were designed into the inlet and engine nacelles to handle some of this pressure and allow the inlet to remain "started". So significant was this inlet pressure build-up (pushing against the inlet structure) that at Mach 3.2 cruise, it was estimated that 58% of the available thrust was being provided by the inlet, 17% by the compressor and the remaining 25% by the afterburner. Ben Rich, the Lockheed Skunkworks designer of the inlets, often referred to the engine compressors as "pumps to keep the inlets alive" and sized the inlets for Mach 3.2 cruise (where the aircraft was at its most efficient design point).[1] (Presumably he was being somewhat facetious, as inlets don't use propellant and thus don't create net thrust, otherwise the SR-71 would have been built with more inlets... in fact the compressor and afterburner make up for the inlet compressors aerodynamic losses and add further thrust.)

In the early years of the Blackbird programs, the analog air inlet computers would not always keep up with rapidly changing flight environmental inputs. If internal pressures became too great (and the spike incorrectly positioned), the shockwave would suddenly blow out the front of the inlet, called an "Inlet Unstart". Immediately, the air flow through the engine compressor would cease, thrust dropped and exhaust gas temperatures would begin to rise. Due to the tremendous thrust of the remaining engine pushing the aircraft asymmetrically along with the sudden deceleration caused by losing 50% of available power, an unstart would cause the aircraft to yaw violently to one side. SAS, autopilot, and manual control inputs would fight the yawing, but often the off angle extreme would reduce airflow in the opposite engine and cause it to begin "sympathetic stalls". The result would be rapid counter yawing, often loud "banging" noises and a rough ride. Pilots and RSOs occasionally experienced their pressure suit helmets banging on their cockpit canopies until the initial unstart motions subsided.

One of the standard counters to an inlet unstart was for the pilot to reach out and unstart both inlets; this drove both spikes out, stopped the yawing conditions and allowed the pilot to restart each inlet. Once restarted, with normal engine combustion, the crew would return to acceleration and climb to the planned cruise altitude.

Eventually, a digital air inlet computer replaced the original analog one. Lockheed engineers developed control software for the engine inlets that would recapture the lost shockwave and re-light the engine before the pilot was even aware an unstart had occurred. The SR-71 machinists were responsible for the hundreds of precision adjustments of the forward air by-pass doors within the inlets. This helped control the shock wave, prevent unstarts, and increase performance.

Fuselage

Due to the great temperature changes in flight, the fuselage panels did not fit perfectly on the ground and were essentially loose. Proper alignment was only achieved when the airframe warmed up due to the air resistance at high speeds, causing the airframe to expand several inches. Because of this, and the lack of a fuel sealing system that could handle the extreme temperatures, the aircraft would leak its JP-7 jet fuel onto the runway before it took off. The aircraft would quickly make a short sprint, meant to warm up the airframe, and was then air-to-air refueled before departing on its mission. Cooling was carried out by cycling fuel behind the titanium surfaces at the front of the wings (chines). Nonetheless, once the plane landed no one could approach it for some time as its canopy was still hotter than 300 degrees Celsius. Non-fibrous asbestos was also used, as in non-ceramic automotive brakes, due to its high heat tolerance.[1]

Stealth

There were a number of features in the SR-71 that were designed to reduce its radar signature. The first studies in radar stealth seemed to indicate that a shape with flattened, tapering sides would reflect most radar away from the place where the radar beams originated. To this end the radar engineers suggested adding chines (see below) to the design and canting the vertical control surfaces inward. The plane also used special radar absorbing materials which were incoporated into sawtooth shaped sections of the skin of the aircraft, as well as fuel additives to reduce the exhaust plumes visibility on radar. The overall effectiveness of these designs is still debated, but since the aircraft did not include other elements of today's stealth technologies, it was still easy to track by radar (and had a huge infrared signature when cruising at Mach 3+).

Chines

The chines themselves were an interesting and unique feature. The Blackbird was originally not going to have chines - it would have looked a little like an enlarged F-104 - but the radar engineers convinced the aerodynamicists to try adding them to a few wind-tunnel models during the design process. They discovered that the chines generated powerful vortices around themselves, generating much additional lift near the front of the aircraft. The angle of incidence of the delta wings could then be reduced, allowing for greater stability and less high-speed drag, and more weight (fuel) could be carried, allowing for greater range. Landing speeds were also reduced, since these powerful vortices created turbulent flow over the wings at high angles of attack, making it harder for the wings to stall. (The Blackbird can, consequently, make high-G turns to the point where the engine air inlets stop working properly and the engines flame out). The chines act like the leading edge extensions which are used to increase the agility of many modern fighters such as the F-5, F-16, F/A-18, MiG-29 and Su-27. Once these advantages were observed during wind-tunnel tests of Blackbird models, the use of canard foreplanes was no longer needed. (Many early design models of what became the Blackbird featured canards.) Chines are still an important part of the design of many of the newest stealth UAVs, such as the RQ-3 Dark Star, Bird of Prey, X-45, and X-47, since they allow for tail-less stability as well as for stealth.

Jet fuel

An SR-71B trainer, shortly after refueling.

Originally developed for the A-12 Oxcart plane in the late 1950s, the JP-7 jet fuel had a relatively high flash point (60 C) to cope with the heat. The fuel also contained fluorocarbons to increase its lubricity, an oxidising agent to enable it to burn in the engines, and even a cesium compound, A-50, which disguised the exhaust's radar signature. As a result, JP-7 was claimed to be more expensive than single malt Scotch whisky, which contributed to the $24-27,000/hr cost of operating the SR-71. For comparison, a U-2 costs only 1/3 as much. On the other hand, a U-2 travels at only 1/4 the speed, can not carry as much reconnaissance equipment, and is much more vulnerable to interception.

Titanium skin

Studies of the aircraft's titanium skin revealed the metal was actually growing stronger over time due to the intense heating caused by aerodynamic friction, a process similar to annealing.

Major portions of the upper and lower inboard wing skin of the SR-71 were actually corrugated, not smooth. The thermal expansion stresses of a smooth skin would have resulted in the aircraft skin splitting or curling. By making the surface corrugated, the skin was allowed to expand vertically as well as horizontally without overstressing, which also increased longitudinal strength. Despite the fact that it worked, aerodynamicists were against the concept and accused the design engineers of trying to make a 1920s era Ford Trimotor, known for its corrugated aluminum skin, go Mach 3.[1]

Engines

Development began using a coal slurry powerplant, but Johnson determined that the coal particles damaged engine components. He then began researching a liquid hydrogen powerplant, but the tanks required to store cryogenic hydrogen did not suit the Blackbird's form factor.[1]

The focus then became somewhat more conventional, though the Pratt & Whitney J58 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 J58 was also unique in that it was a hybrid jet engine: effectively a turbojet engine inside a ramjet engine. Air was initially compressed (and thus also heated) by the shock cones, passed through 4 compressor stages and then was split: some of the air entered the compressor fans ("core-flow" air), while the rest of the air went straight to the afterburner (via bypass tubes). The air in the compressor fans 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 by the turbine (and thus being cooled somewhat), the core-flow air went through the afterburner and met the bypass air.

As high speeds, the initial shock-cone compression made the core air start out hotter, before being further heated by the compressor and in combustion, therefore less fuel had to be added to the combustion chamber in order not to melt the turbine blades immediately downstream. 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 dangerously high temperatures, and little fuel could be added in the combustion chamber. This means the whole compressor-combustor-turbine set-up in the core of the engine provided little power, and the Blackbird flew predominantly on afterburners, largely using the compression from the shock cones: the engines became ramjets. 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).[1]

At lower speeds both the turbojet (engine core) and the ramjet (with the afterburners running without any bypass air) work, but at higher speeds the turbojet largely shuts down and just sits in the way of the air flowing through the ramjet.

Originally, the Blackbird's engines started up with the assistance of an external "start cart", a cart containing two Buick Wildcat V8 engines which was 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.

Sensors

In addition to optical camera equipment, sensors which could be carried aboard the SR-71 included an Advanced Synthetic Aperture Radar System (ASARS-1) manufactured by Goodyear Aerospace. ASARS-1 was a high-resolution reconnaissance system with long-range radar mapping capabilities. [4]

Myth and lore

The plane developed a small cult following, given its design, specifications, and the aura of secrecy that surrounded it. Some conspiracy theorists speculated that the true operational capabilities of the SR-71 and the associated A-12 were never revealed. Most aviation buffs speculate that given a confluence of structural and aerodynamic tolerances, the plane could fly at a maximum of Mach 3.3 for extended periods, and could not exceed Mach 3.44 in any currently known configuration. Specifically, these groups cite the specific maximum temperature for the compressor inlet of 427 °C (800 °F). This temperature is quickly surpassed at speeds greater than Mach 3.3. Mach 3.44 is given as the speed at which the engine enters a state of "unstart". Some speculate that the former condition can be alleviated by superior compressor design and composition, while the latter might be solved with improved shock cones. It is known that the J58 engines were most efficient at around M3, and this was the Blackbird's typical cruising speed.

The SR-71's Pratt & Whitney J58 engines never exceeded testbench values above Mach 3.6 in unclassified tests. Given the history of the plane, the advanced and classified nature of much of its original design, and most importantly, the simple fact that no SR-71 exists in a form that is immediately airworthy, it may never be known what the true design tolerances of the aircraft were, or if these tolerances were ever approached in flight. This unverifiability undoubtedly contributes to the myths and fallacies surrounding the SR-71.

The SR-71 was the first operational aircraft designed around a stealthy shape and materials. The most visible marks of its low radar cross section (RCS) are its inwardly-canted vertical stabilizers and the fuselage chines. Comparably, a plane of the SR-71's size should generate a radar image the size of a flying barn, but its actual return is more like that of a single door. Though with a much smaller RCS than expected for a plane of its size, it was still easily detected, because the exhaust stream would return its own radar signature. Furthermore, this is no comparison to the later F-117 whose RCS is on the order of a small ball bearing.

Specifications (SR-71A)

Orthographically projected diagram of the SR-71A Blackbird.
Orthographically projected diagram of the SR-71A Blackbird.

General characteristics

  • Crew: 1 or 2
  • Wheel track: 16 ft 8 in (5.08 m)
  • Wheel base: 37 ft 10 in (11.53 m)
  • Aspect ratio: 1.7 Performance

    SR-71 aircraft on display

    Places to see a Blackbird on display include:

    See also External links below

    Other images

    Popular culture

    • The SR-71 also featured in a Belgian-French comic book series "Buck Danny", where the hero, Buck Danny, finds a secret test base for the prototype of the SR-71/A-12, and eventually is greeted by fellow test pilots on this highly secret base. Because of the period when this comic book appeared, not all the information now known was available.
    • In Manga Science (漫画科学 manga kagaku), a science teaching comic short series, volume 2, an SR-71 was used to demostrate the heat generated in high speed flight. When one of the characters opens the hatch at Mach 2 trying to escape, she fails because of the high temperatures on the surface of the plane. There are small words printed next to her: "The hatch should not be opened in Mach 2".
    • The Tom Clancy novel The Cardinal of the Kremlin mentions the SR-71 as a test tracking target for an experimental anti-ballistic missile defense system (SDI, or less formally, "Star Wars").
    • The SR-71 is stolen and flown by Daryl in the 1985 film D.A.R.Y.L. in order to escape a military institution.

    References

    1. ^ a b c d e Johnson, C. L. (1985), Kelly: More Than My Share of it All. Smithsonian Books. ISBN 0874744911. Cite error: The named reference "johnson_bio" was defined multiple times with different content (see the help page).

    External links

    Related content

    Related development

    Aircraft of comparable role, configuration, and era

    Related lists

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