The SR-71 was developed in the 1960s as ablack project by Lockheed'sSkunk Works division. American aerospace engineerClarence "Kelly" Johnson was responsible for many of the SR-71's innovative concepts.[2] Its shape was based on theLockheed A-12, a pioneer instealth technology with its reducedradar cross section, but the SR-71 was longer and heavier to carry more fuel and a crew of two intandem cockpits. The SR-71 was revealed to the public in July 1964 and entered service in theUnited States Air Force (USAF) in January 1966.[3]
During missions, the SR-71 operated at high speeds and altitudes (Mach 3.2 at 85,000 ft or 26,000 m), allowing it to evade or outrace threats.[4] If asurface-to-air missile launch wasdetected, the standard evasive action was to accelerate and outpace the missile.[5] Equipment for the plane'saerial reconnaissance missions includedsignals-intelligence sensors,side-looking airborne radar, and a camera.[4] On average, an SR-71 could fly just once per week because of the lengthy preparations needed. A total of 32 aircraft were built; 12 were lost in accidents, none to enemy action.[6][7]
In 1974, the SR-71 set the record for the quickest flight between London and New York at 1 hour, 54 minutes and 56 seconds.[10] In 1976, it became thefastest airbreathing manned aircraft, previously held by its predecessor, the closely relatedLockheed YF-12.[11][12][13] As of 2025[update], the Blackbird still holds all three world records.
In 1989, the USAF retired the SR-71, largely for political reasons,[8] although several were briefly reactivated before their second retirement in 1998.NASA was the final operator of the Blackbird, using it as a research platform, until it was retired again in 1999.[14] Since its retirement, the SR-71's role has been taken up by a combination ofreconnaissance satellites andunmanned aerial vehicles (UAVs). As of 2018, Lockheed Martin was developing a proposed UAV successor, theSR-72, with plans to fly it in 2025.[15]
Lockheed's previous reconnaissance aircraft was the relatively slowU-2, designed for theCentral Intelligence Agency (CIA). In late 1957, the CIA approached the defense contractorLockheed to build an undetectable spy plane. The project, named Archangel, was led byKelly Johnson, head of Lockheed's Skunk Works unit in Burbank, California. The work on project Archangel began in the second quarter of 1958, with aim of flying higher and faster than the U-2. Of 11 successive designs drafted in a span of 10 months, "A-10" was the front-runner, although its shape made it vulnerable to radar detection. After a meeting with the CIA in March 1959, the design was modified to reduce its radar cross-section by 90%. On 11 February 1960, the CIA approved a US$96 million (~$778 million in 2024) contract for Skunk Works to build a dozenA-12 spy planes. Three months later, the May1960 downing ofFrancis Gary Powers's U-2 underscored the need for less vulnerable reconnaissance aircraft.[16]
The A-12 first flew at Groom Lake (Area 51), Nevada, on 25 April 1962. Thirteen were built, plus five more of two variants: three of theYF-12 interceptor prototype and two of theM-21 drone carrier. The aircraft was to be powered by thePratt & Whitney J58 engine, but J58 development was taking longer than scheduled, so it was initially equipped with the lower-thrustPratt & Whitney J75 to enable flight testing to begin. The J58s were retrofitted as they became available, and became the standard engine for all subsequent aircraft in the series (A-12, YF-12, M-21), as well as the SR-71. The A-12 flew missions over Vietnam and North Korea before its retirement in 1968. The program's cancellation was announced on 28 December 1966,[17] due both to budget concerns[18] and because of the forthcoming SR-71, a derivative of the A-12.[19]
The SR-71 designation is a continuation of thepre-1962 bomber series; the last aircraft built using the series was theXB-70 Valkyrie. However, a bomber variant of the Blackbird was briefly given the B-71 designator, which was retained when the type was changed to SR-71.[20]
During the later stages of its testing, the B-70 was proposed for a reconnaissance/strike role, with an "RS-70" designation. When the A-12's performance potential was clearly found to be much greater, the USAF ordered a variant of the A-12 in December 1962,[21] which was originally named R-12 by Lockheed.[N 2] This USAF version was longer and heavier than the original A-12 because it had a longer fuselage to hold more fuel. The R-12 also had a crew of two in tandem cockpits, and reshaped fuselagechines. Reconnaissance equipment includedsignals intelligence sensors, aside-looking airborne radar, and a photo camera.[21] The CIA's A-12 was a better photo-reconnaissance platform than the USAF's R-12: since the A-12 flew higher and faster, and with only a pilot, it had room to carry a better camera[18] and more instruments.[22] The A-12 flewcovert missions while the SR-71 flew overt missions; the latter had USAF markings and pilots carriedGeneva Conventions Identification Cards.[23]
During the1964 campaign, Republican presidential nomineeBarry Goldwater repeatedly criticized PresidentLyndon B. Johnson and his administration for falling behind theSoviet Union in developing new weapons. Johnson decided to counter this criticism by revealing the existence of the YF-12A USAF interceptor, which also served as cover for the still-secret A-12[24] and the USAF reconnaissance model since July 1964. USAF Chief of Staff GeneralCurtis LeMay preferred the SR (Strategic Reconnaissance) designation and wanted the RS-71 to be named SR-71. Before the July speech, 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 story that the president had misread the aircraft's designation.[25][N 3] To conceal the A-12's existence, Johnson referred only to the A-11, while revealing the existence of a high-speed, high-altitude reconnaissance aircraft.[26]
In 1968, Secretary of DefenseRobert McNamara canceled the F-12 interceptor program. The specialized tooling used to manufacture both the YF-12 and the SR-71 was also ordered destroyed.[27] Production of the SR-71 totaled 32 aircraft: 29 SR-71As, two SR-71Bs, and one SR-71C.[28]
The SR-71 was designed for flight at overMach 3 with tandem cockpits for a crew of two: a pilot; and a reconnaissance systems officer who navigated and operated the surveillance systems. It was extremely important for the pilot and RSO to work well together as a crew.[29][30][31] The SR-71 was designed with the smallest radar cross-section that Lockheed could achieve, an early attempt at stealth design.[32] Aircraft were painted black. This color radiated heat from the surface more effectively than the bare metal, reducing the temperature of the skin and thermal stresses on the airframe.[33] The appearance of the painted aircraft gave it the nickname "Blackbird".
Titanium was used for 85% of the structure, with much of the rest beingpolymercomposite materials.[34] To control costs, Lockheed used a more easily worked titanium alloy, which softened at a lower temperature.[N 4] The challenges posed led Lockheed to develop new fabrication methods, which have since been used in the manufacture of other aircraft. Lockheed found that washing welded titanium requiresdistilled water, as the chlorine present in tap water iscorrosive;cadmium-plated tools could not be used, as they also caused corrosion.[38] Metallurgical contamination was another problem; at one point, 80% of the delivered titanium for manufacture was rejected on these grounds.[39][40]
The high temperatures generated in flight required special design and operating techniques. Major sections of the skin of the inboard wings were corrugated, not smooth. Aerodynamicists initially opposed the concept, disparagingly referring to the aircraft as a Mach 3 variant of the 1920s-eraFord Trimotor, which was known for its corrugated aluminum skin. But high heat would have caused a smooth skin to split or curl, whereas the corrugated skin could expand vertically and horizontally and had increased longitudinal strength.
Fuselage panels were manufactured to fit only loosely with the aircraft on the ground. Proper alignment was achieved as the airframe heated up, withthermal expansion of several inches.[41] Because of this, and the lack of a fuel-sealing system that could remain leak-free with the extreme temperature cycles during flight, the aircraft leakedJP-7 fuel on the ground prior to takeoff,[42] annoying ground crews.[23]
The outer windscreen of the cockpit was made of three layers of glass with cooling sections between them.[citation needed] The ANS navigation window was made of solidquartz and wasfused ultrasonically to the titanium frame.[43] The temperature of the exterior of the windscreen could reach 600 °F (320 °C) during a mission.[44]
Detail of SR-71A at theMuseum of Aviation,Robins AFB showing red lined no-step areas. Not shown on this museum exhibit is the additional NO STEP wording on operational aircraft which showed to which side of the line the warning was applicable.
The Blackbird's tires, manufactured byB.F. Goodrich, contained aluminum and were inflated with nitrogen. They cost $2,300 each and generally required replacing within 20 missions. The Blackbird landed at more than 170 knots (200 mph; 310 km/h) and deployed a drag parachute to reduce landing roll and brake and tire wear.[45]
Water vapor is condensed by the low-pressure vortices generated by the chines outboard of each engine inlet.
The SR-71 was the second operational aircraft,[46] after theLockheed A-12,[46] designed to be hard to spot onradar. Early studies instealth technology indicated that a shape with flattened, tapering sides would reflect most radar energy away from a beam's place of origin, so Lockheed's engineers addedchines and canted the vertical control surfaces inward. Specialradar-absorbing materials were incorporated intosawtooth-shaped sections of the aircraft's skin.Cesium-based fuel additives were used to somewhat reduce the visibility of exhaust plumes to radar, although exhaust streams remained quite apparent. Ultimately, engineers produced an aircraft with a wing area of about 1,800 sq ft (170 m2) but a radar cross-section (RCS) of around 110 sq ft (10 m2).[47] Johnson later conceded that Soviet radar technology advanced faster than the stealth technology employed against it.[48]
While the SR-71 carriedradar countermeasures to evade interception efforts, its greatest protection was its combination of high altitude and very high speed, which made it invulnerable at the time. Along with its low radar cross-section, these qualities gave a very short time for an enemysurface-to-air missile (SAM) site to acquire and track the aircraft on radar. By the time the SAM site could track the SR-71, it was often too late to launch a SAM, and the SR-71 would be out of range before the SAM could catch up to it. If the SAM site could track the SR-71 and fire a SAM in time, the SAM would expend nearly all of thedelta-v of its boost and sustainer phases just reaching the SR-71's altitude; at this point, out of thrust, it could do little more than follow its ballistic arc. Merely accelerating would typically be enough for an SR-71 to evade a SAM;[5] changes by the pilots in the SR-71's speed, altitude, and heading were also often enough to spoil any radar lock on the plane by SAM sites or enemy fighters.[31] At sustained speeds of more than Mach 3.2, the plane was faster than the Soviet Union's fastest interceptor, theMikoyan-Gurevich MiG-25,[N 5] which also could not reach the SR-71's altitude.[49] No SR-71 was ever shot down.[6]
The SR-71 featured chines, a pair of sharp edges leading aft from either side of the nose along the fuselage. These were not a feature on the early A-3 design; Frank Rodgers, a doctor at the Scientific Engineering Institute, aCIAfront organization, discovered that a cross-section of a sphere had a greatly reduced radar reflection, and adapted a cylindrical-shaped fuselage by stretching out the sides of the fuselage.[50] After the advisory panel provisionally selected Convair's FISH design over the A-3 on the basis of RCS, Lockheed adopted chines for its A-4 through A-6 designs.[51]
Aerodynamicists discovered that the chines generated powerfulvortices and created additionallift, leading to unexpected aerodynamic performance improvements.[52] For example, they allowed a reduction in the wings'angle of incidence, which added stability and reduced drag at high speeds, allowing more weight to be carried, such as fuel. Landing speeds were also reduced, as the chines' vortices created turbulent flow over the wings at highangles of attack, making it harder tostall. The chines also acted likeleading-edge extensions, which increase the agility of fighters such as theF-5,F-16,F/A-18,MiG-29, andSu-27. The addition of chines also allowed the removal of the plannedcanard foreplanes.[N 6][53][54]
The SR-71 used the same powerplant as the A-12 andYF-12. It consists of three main parts: inlet, J58 engine and its nacelle, and ejector nozzle. "Typical for any supersonic powerplant the engine cannot be considered separately from the rest of the powerplant. Rather, it may be regarded as the heat pump in the over-all system of inlet, engine, and nozzle. The net thrust available to propel the aircraft may be to a large extent controlled by the performance of the inlet and nozzle rather than by the physical potentialities of the engine alone."[55] This is illustrated for the Blackbird by the thrust contributions from each component at Mach 3+ with maximum afterburner: inlet 54%, engine 17.6%, ejector nozzle 28.4%.[56]
When stationary and at low speeds the inlet caused a loss in engine thrust. This was due to the flow restriction through the inlet when stationary. Thrust was recovered with ram pressure as flight speed increased (uninstalled thrust 34,000 lb (150 kN), installed at zero airspeed 25,500 lb (113 kN) rising through 30,000 lb (130 kN) at 210 knots, unstick speed).[57]
At supersonic speeds not all the airflow approaching the inlet capture area entered the inlet. At supersonic speeds an intake always adapts to the engine requirements, rather than forcing air into the engine, and the unwanted air flows around the outside of the cowl, causing spillage drag. More than half the air approaching the capture area had to be spilled at low supersonic speeds and the amount reduced as the design speed was approached because the inlet airflow had been designed to match the engine demand at that speed and the chosen design point ambient temperature. At this speed the spike shock touched the cowl lip and there was minimal spillage (with its attendant drag) as shown by Campbell.[58] The inlet and engine matching was also shown by Brown,[59] who emphasized the benefit of increased engine airflow at higher Mach numbers that came with the introduction of the bleed bypass cycle. These two authors show the disparity between inlet and engine for the Blackbird in terms of airflow and it is further explained in more general terms by Oates.[60]
Engine operation was adversely affected when operating behind an unstarted inlet. In this condition the inlet behaved like a subsonic inlet design (known as a pitot type) at high supersonic speeds, with very low airflow to the engine. Fuel was automatically diverted, by the fuel derich system, from the combustor to prevent turbine over-temperature.[61]
All three parts were linked by the secondary airflow. The inlet needed the boundary layers removed from its spike and cowl surfaces. The one with the higher pressure recovery, the cowl shock-trap bleed, was chosen as secondary air[58] to ventilate and cool the outside of the engine. It was assisted from the inlet by the pumping action of the engine exhaust in the ejector nozzle, cushioning the engine exhaust as it expanded over a wide range of pressure ratios which increased with flight speed.[62]
Mach 3.2 in astandard day atmosphere was the design point for the aircraft. However, in practice the SR-71 was more efficient at even faster speeds and colder temperatures. The specific range charts showed for a standard day temperature, and a particular weight, that Mach 3.0 cruise used 38,000 lb/h (17,000 kg/h) of fuel. At Mach 3.15 the fuel flow was 36,000 lb/h (16,000 kg/h). Flying in colder temperatures (known as temperature deviations from the standard day) would also reduce the fuel used, e.g. with a 14 °F (−10 °C) temperature the fuel flow was 35,000 lb/h (16,000 kg/h).[63] During one mission, SR-71 pilotBrian Shul flew faster than usual to avoid multiple interception attempts. It was discovered after the flight that this had reduced the fuel consumption.[64] It is possible to match the powerplant for optimum performance at only one ambient temperature because the airflows for a supersonic inlet and engine vary differently with ambient temperature. For an inlet, the airflow varies inversely with the square root of the temperature, and for the engine, it varies with the direct inverse.[65]
Powerplant
The inlet extends from the spike tip to the four sets of three louvers that vent the spike boundary layer bleed overboard through four spike support struts. The more-forward louvers vent the forward bypass bleed. The engine extends from there to the ejector nozzle blow-in doors (shown open) and the nozzle extends from there to the ejector flaps (shown closed).
Diagrams show operation of the air inlet, flow through the engine (primary air), nacelle flow past the engine (secondary air), and flow into the ejector nozzle (primary, secondary and tertiary air).
This picture of an uninstalled engine being tested illustrates the need for cooling air around the exhaust duct. The engine, when installed as part of the powerplant, has secondary cooling air at 1,200 °F (650 °C) passing over the afterburner duct which is heated internally by combustion up to 3,200 °F (1,750 °C). The heating, followed by the primary nozzle restriction, accelerates the exhaust to sonic speed as it leaves the primary nozzle (shown). The ejector nozzle (not shown) surrounds the primary exhaust with secondary and tertiary air to cushion its expansion in the ejector nozzle.
The engine inlets needed so-called mixed external/internal compression with internal supersonic diffusion since all-external compression used on slower aircraft caused too much drag at Blackbird speeds. Their features included a centerbody or spike, spike boundary-layer bleed slots where normal shock was located, a cowl boundary layer bleed "shock trap" entrance, streamlined bodies known as "mice", forward bypass bleed ports between the "mice", rear bypass ring, louvers on external surface for spike boundary layer overboard, and louvers on external surface for front bypass overboard. Venting this bypass overboard produced high drag: 6,000 lb (27 kN) at cruise with 50% door opening, compared to the total aircraft drag of 14,000 lb (62 kN).[66] Designer David Campbell holds a patent on the inlet's aerodynamic features and functioning,[67] which are explained in the "A-12 Utility Flight Manual"[68] and in a 2014 presentation by Lockheed Technical Fellow Emeritus Tom Anderson.[69]
When an inlet was operating as an efficient supersonic compressor—a status called "started"—supersonic diffusion took place in front of the cowl and internally in a converging passage as far as a terminal shock where the passage area began to increase and subsonic diffusion takes place. An analog control system was designed to hold the terminal shock in position.
But in the early years of operation, the analog computers could not always keep up with rapidly changing inputs from the nose boom. If the duct back pressure became too great and the spike was incorrectly positioned, the shock wave become unstable and would shoot quickly forward to a stable position outside the cowl. This "inletunstart" would often extinguish the engine's afterburner. The asymmetrical thrust from the other engine would cause the aircraft to yaw violently.SAS, autopilot, and manual control inputs would attempt to regain controlled flight, but extreme yaw would often reduce airflow in the opposite engine and stimulate "sympathetic stalls". This generated a rapid counter-yawing, often coupled with loud "banging" noises, and a rough ride during which crews' helmets would sometimes strike their cockpit canopies.[70] One response to a single unstart was unstarting both inlets to prevent yawing, then restarting them both.[71] After wind-tunnel testing and computer modeling by NASA Dryden test center,[72] Lockheed installed an electronic control to detect unstart conditions and perform this reset action without pilot intervention.[73]
During troubleshooting of the unstart issue, NASA discovered that the vortices from the nose chines were entering the engine and reducing engine efficiency. To fix this, the agency developed a computer to control the engine bypass doors. Beginning in 1980, the analog inlet control system was replaced by a digital system, Digital Automatic Flight and Inlet Control System (DAFICS),[74] which reduced unstarts.[75]
Inlet
Entry to the inlet. Behind is the outer wing and hinged portion of the nacelle that encloses the engine. The spike is shown in the forward position (for speeds below Mach 1.6). Just discernible behind the cowl lip are spike boundary layer bleed slots where the normal shock is located at higher speeds when the spike has moved rearwards, the cowl bleed "shock trap" ram intake, streamlined bodies ("mice") and, between the mice, the forward bypass door openings[76] that dump unwanted air externally through the front louvers and cause nacelle drag.[77] When the landing gear is down, ambient air flows in reverse through the bypass to supplement the front inlet flow into the engine.
A rear view of the inlet where air enters the engine. Two features were added after flight testing highlighted the need: 1) "mice," visible as streamlined shapes, added to reduce the diffusion rate after pilots noted rumbling; and 2) rear bypass doors added to prevent unstarting the inlet during descents with low engine flow.[78] The ring of doors is at the extreme rear of the inlet as shown by their accompanying rear-turning scoop, extending from 7 o'clock to 5 o'clock, which directs the air through the nacelle to the ejector nozzle.[79] The door actuator[80]
Schlieren flow visualization of shock waves for started and unstarted inlet at Mach 2
The engine was an extensively re-designed version of the J58-P2, an existing supersonic engine which had run 700 development hours in support of proposals to power various aircraft for the US Navy. Only the compressor and turbine aerodynamics were retained. New design requirements for cruise at Mach 3.2 included:
operating with very high ram temperature air entering the compressor, at 800 °F (430 °C)
a continuous turbine temperature capability 450 °F (250 °C) hotter than previous experience (Pratt & Whitney J75)
continuous use of maximum afterburning
the use of new, more expensive, materials and fluids required to withstand unprecedented high temperatures
The engine was an afterburning turbojet for take-off and transonic flight (bleed bypass closed) and a low bypass augmented turbofan for supersonic acceleration (bleed bypass open). It approximated a ramjet during high speed supersonic cruise (with a pressure loss, compressor to exhaust, of 80% which was typical of a ramjet). It was a low bypass turbofan for subsonic loiter (bleed bypass open).[81][82]
Analysis of the J58-P2 supersonic performance[83] showed the high compressor inlet temperature would have caused stalling, choking and blade breakages in the compressor as a result of operating at low corrected speeds on the compressor map. These problems were resolved by Pratt & Whitney engineer Robert Abernethy and are explained in his patent, "Recover Bleed Air Turbojet".[84] His solution was to 1) incorporate six air-bleed tubes, prominent on the outside of the engine, to transfer 20% of the compressor air to the afterburner, and 2) to modify the inlet guide vanes with a 2-position, trailing edge flap. The compressor bleed enabled the compressor to operate more efficiently and with the resulting increase in engine airflow matched the inlet design flow with an installed thrust increase of 47%.[83][85] A continuous turbine temperature of 2,000 °F (1,090 °C) was enabled with air-cooled first stage turbine vane and blades. Continuous operation of maximum afterburning was enabled by passing relatively cool air from the compressor along the inner surface of the duct and nozzle. Ceramic thermal barrier coatings were also used.
The secondary airflow through the nacelle comes from the cowl boundary layer bleed system which is oversized (flows more than boundary layer) to give a high enough pressure recovery to support the ejector pumping action. Additional air comes from the rear bypass doors and, for low speed operation with negligible inlet ram, from suck-in doors by the compressor case.
Engine/nacelle
View of J58 engine shows some features required for flight at Mach 3.2: titanium inlet guide vanes and first stage compressor blades for lighter weight at high ram temperatures, transonic first stage compressor blades and low hub/tip ratio compressor entry, both scaled from the bigger Mach-3 J91 engine compressor, 2-position flaps on the inlet guide vanes and three of the six bypass tubes.
The afterburner was rated for continuous operation at 3,200 °F (1,800 °C) made possible with ceramic coatings (colored white) on duct liner and flame holders[86] and compressor bleed air cooling the duct and nozzle (above Mach 2.1 when the bleed was flowing). The nozzle is fully open, the maximum afterburning position. The main purpose of the variable nozzle area was to control engine operation which it did in conjunction with varying heat release in the afterburner.
The inlet at left was depressed when the engine ran at high power settings with inadequate inlet ram (stationary and low flight speeds). The lower-than-ambient pressure in the inlet brought in extra air through the spike bleed and forward bypass louvers shown on the inlet external surface. Adequate secondary cooling air came in through the suck-in doors (shown open on the hinged nacelle).
The nozzle had to operate efficiently over a wide range of pressure ratios from low, with no inlet ram with a stationary aircraft, to 31 times the external pressure at 80,000 ft (24,000 m). A blow-in door ejector nozzle had been invented by Pratt & Whitney engineer Stuart Hamilton in the late 1950s[87] and described in his patent "Variable Area Exhaust Nozzle".[88] In this description the nozzle is an integral part of the engine (as it was in the contemporary Mach 3 General Electric YJ93.[89] For the Blackbird powerplant the nozzle was more efficient structurally (lighter) by incorporating it as part of the airframe because it carried fin and wing loads through the ejector shroud. The nozzle used secondary air from two sources, the inlet cowl boundary layer and rear bypass from immediately in front of the compressor. It used external flow on the nacelle through the tertiary blow-in doors until ram closed them at Mach 1.5. Only secondary air was used at higher speeds with the blow-in doors closed.
At low flight speeds the engine exhaust pressure at the primary nozzle exit was greater than ambient so tended to over-expand to lower than ambient in the shroud causing impingement shocks. Secondary and blow-in door air surrounding the exhaust cushioned it preventing over-expansion. Inlet ram pressure increased with flight speed and the higher pressure in the exhaust system closed, first the blow-in doors and then started to open the nozzle flaps until they were fully open at Mach 2.4. The final nozzle area did not increase with further increase in flight speed (for complete expansion to ambient and greater internal thrust) because its external diameter, greater than nacelle diameter would cause too much drag.[90]
Ejector-nozzle
Ejector nozzle at the rear of the powerplant. The engine nozzle (left) is the first component in the exhaust system, followed by the secondary and tertiary air flows and ejector nozzle. The tertiary doors are open. There is a fixed convergent/divergent shroud and the ejector nozzle trailing flaps are at their minimum area (closed). These nozzle and door positions correspond with full afterburner up to transonic speed, after which the doors close and flaps start to open. Secondary air from the inlet passes between the engine and nacelle and joins the blow-in door air to control the expansion of the engine exhaust through the shroud and trailing flaps.
A similar viewing angle, unstick speed 210 knots, to the "exploded" view, and with the same operating configuration: afterburner nozzle open, blow-in doors open and trailing flaps closed due to low internal pressure with low speed low inlet ram. Note the dark con-di shroud. Air entering the blow-in doors joins secondary air from the inlet and flows over the fixed shroud surface and trailing flaps while surrounding the exhaust from the engine.
An SR-71 refueling from aKC-135Q Stratotanker during a flight in 1983.An SR-71 refueling from aKC-10 Extender. KC-10s were added in the mid-1980s as additional tankers.[91]
JP-7 fuel was used. It was difficult to ignite. To start the engines,triethylborane (TEB), whichignites on contact with air, was injected to produce temperatures high enough to ignite the JP-7. The TEB produced a characteristic green flame, which could often be seen during engine ignition.[64] The fuel was used as a heat sink for the rest of the aircraft to cool the pilot and the electronics. An electric starting system was not possible due to the limited capacity of the cooling system, so the chemical ignition system was used.[92]
On a typical mission, the SR-71 took off with a partial fuel load to reduce stress on the brakes and tires during takeoff and also ensure it could successfully take off should one engine fail.[93] Within 20 seconds, the aircraft traveled 4,500 ft (1,400 m), reached 240 mph (390 km/h), and lifted off. It reached 20,000 ft (6,100 m) of altitude in less than two minutes, and the typical 80,000 ft (24,000 m)cruising altitude in another 17 minutes, having used one third of its fuel.[23] It is a common misconception that the planes refueled shortly after takeoff because the fuel tanks, which formed the outer skin of the aircraft, leaked on the ground. It was not possible to prevent leaks when the aircraft skin was cold and the tanks only sealed when the skin warmed as the aircraft speed increased. The ability of the sealant to prevent leaks was compromised by the expansion and contraction of the skin with each flight.[94] However, the amount of fuel that leaked, measured as drops per minute on the ground from specific locations, was not enough to make refueling necessary.[95]
The SR-71 also requiredin-flight refueling to replenish fuel during long-duration missions. Supersonic flights generally lasted no more than 90 minutes before the pilot had to find a tanker.[96]
SpecializedKC-135Q tankers were required to refuel the SR-71. The KC-135Q had a modified high-speed boom, which would allow refueling of the Blackbird at near the tanker's maximum airspeed. The tanker also had special fuel systems for movingJP-4 (for the KC-135Q itself) and JP-7 (for the SR-71) between different tanks.[97] As an aid to the pilot when refueling, the cockpit was fitted with aperipheral vision horizon display. This unusual instrument projected a barely visibleartificial horizon line across the top of the entire instrument panel, which gave the pilotsubliminal cues on aircraft attitude.[98] If a KC-135Q was not available any tanker with JP-4 or JP-5 could be used in an emergency to avoid losing the aircraft, but with a Mach 1.5 speed limit.[93]
On hot days, when approaching the maximum fuel load of 80,285 lb (36,415 kg),[93] the left engine had to be run with minimum afterburner to maintain probe contact.[99]
Before takeoff, a primary alignment brought the ANS's inertial components to a high degree of accuracy. In flight, the ANS, which sat behind the reconnaissance systems officer's (RSO's), position, tracked stars through a circular quartz glass window on the upper fuselage.[64] Its "blue light" sourcestar tracker, which could see stars during both day and night, would continuously track a variety of stars as the aircraft's changing position brought them into view. The system's digital computerephemeris contained data ona list of stars used for celestial navigation: the list first included 56 stars and was later expanded to 61.[101] The ANS could supply altitude and position to flight controls and other systems, including the mission data recorder, automatic navigation to preset destination points, automatic pointing and control of cameras and sensors, and optical or SLR sighting of fixed points loaded into the ANS before takeoff. According to Richard Graham, a former SR-71 pilot, the navigation system was good enough to limit drift to 1,000 ft (300 m) off the direction of travel at Mach 3.[102]
As the SR-71 had a second cockpit behind the pilot for the RSO, it could not carry the A-12's principal sensor, a single large-focal-length optical camera that sat in the "Q-Bay" behind the A-12's single cockpit. Instead, the SR-71's camera systems could be located either in the fuselage chines or the removable nose/chine section. Wide-area imaging was provided by two ofItek'sOperational Objective Cameras, which provided stereo imagery across the width of the flight track, or anItek Optical Bar Camera, which gave continuous horizon-to-horizon coverage. A closer view of the target area was given by theHYCON Technical Objective Camera (TEOC), which could be directed up to 45° left or right of the centerline.[110] Initially, the TEOCs could not match the resolution of the A-12's larger camera, but rapid improvements in both the camera and film improved this performance.[110][111]
SLAR, built byGoodyear Aerospace, could be carried in the removable nose. In later life, the radar was replaced by Loral's AdvancedSynthetic Aperture Radar System (ASARS-1). Both the first SLAR and ASARS-1 were ground-mapping imaging systems, collecting data either in fixed swaths left or right of centerline or from a spot location for higher resolution.[110] ELINT-gathering systems, called the Electro Magnetic Reconnaissance System, built by AIL could be carried in the chine bays to analyze electronic signal fields being passed through, and were programmed to identify items of interest.[110][112]
Over its operational life, the Blackbird carried variouselectronic countermeasures (ECMs), including warning and active electronic systems built by several ECM companies and called Systems A, A2, A2C, B, C, C2, E, G, H, and M. On a given mission, an aircraft carried several of these frequency/purpose payloads to meet the expected threats. Major Jerry Crew, an RSO, toldAir & Space/Smithsonian that he used ajammer to try to confusesurface-to-air missile sites as their crews tracked his airplane, but once his threat-warning receiver told him a missile had been launched, he switched off the jammer to prevent the missile from homing in on its signal.[113] After landing, information from the SLAR, ELINT gathering systems, and the maintenance data recorder were subjected to postflight ground analysis. In the later years of its operational life, a datalink system could send ASARS-1 and ELINT data from about 2,000 nmi (3,700 km) of track coverage to a suitably equipped ground station.[citation needed]
SR-71 pilotBrian Shul in full flight suitThe crew of a NASA Lockheed SR-71 Blackbird standing by the aircraft in their pressurized flight suits, 1991
Flying at 80,000 ft (24,000 m) meant that crews could not use standard masks, which could not provide enough oxygen above 43,000 ft (13,000 m). Specialized protectivepressurized suits were produced for crew members by theDavid Clark Company for the A-12, YF-12, M-21 and SR-71. Furthermore, an emergencyejection at Mach 3.2 would subject crews to temperatures of about 450 °F (230 °C); thus, during a high-altitude ejection scenario, an onboard oxygen supply would keep the suit pressurized during the descent.[114]
The cockpit could be pressurized to an altitude of 10,000 or 26,000 ft (3,000 or 8,000 m) during flight.[115] The cabin needed a heavy-duty cooling system, as cruising at Mach 3.2 would heat the aircraft's external surface well beyond 500 °F (260 °C)[116] and the inside of the windshield to 250 °F (120 °C). An air conditioner used aheat exchanger to dump heat from the cockpit into the fuel prior to combustion.[117] The same air-conditioning system was also used to keep the front (nose) landing gear bay cool, thereby eliminating the need for the special aluminum-impregnated tires similar to those used on the main landing gear.[118]
Blackbird pilots and RSOs were provided with food and drink for the long reconnaissance flights. Water bottles had long straws which crewmembers guided into an opening in the helmet by looking in a mirror. Food was contained in sealed containers similar to toothpaste tubes which delivered food to the crewmember's mouth through the helmet opening.[119][120]
SR-71s first arrived at the 9th SRW's Operating Location (OL-8) atKadena Air Base, Okinawa, Japan on 8 March 1968.[127] These deployments were code-named "Glowing Heat", while the program as a whole was code-named "Senior Crown". Reconnaissance missions over North Vietnam were code-named "Black Shield" and then renamed "Giant Scale" in late 1968.[128] On 21 March 1968, Major (later General)Jerome F. O'Malley and Major Edward D. Payne flew the first operational SR-71sortie in SR-71 serial number 61-7976 from Kadena AFB, Okinawa.[127] 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; Palmdale, California; Kadena Air Base, Okinawa, Japan; andRAF Mildenhall, UK. The aircraft was flown to theNational Museum of the United States Air Force nearDayton, Ohio in March 1990.
The USAF could fly each SR-71 on average once per week because of the extended turnaround required after mission recovery. Very often an aircraft would return with rivets missing, delaminated panels, or other broken parts such as inlets requiring repair or replacement. There were cases of the aircraft not being ready to fly again for a month due to the repairs needed. Rob Vermeland,Lockheed Martin's manager of Advanced Development Program, said in an interview in 2015 that high-tempo operations were not realistic for the SR-71. "If we had one sitting in the hangar here and the crew chief was told there was a mission planned right now, then 19 hours later it would be safely ready to take off."[129]
From the beginning of the Blackbird's reconnaissance missions over North Vietnam and Laos in 1968, the SR-71s averaged approximately onesortie a week for nearly two years. By 1970, the SR-71s were averaging two sorties per week, and by 1972, they were flying nearly one sortie every day. Two SR-71s were lost during these missions, one in 1970 and the second aircraft in 1972, both due to mechanical malfunctions.[130][131] Over the course of its reconnaissance missions during the Vietnam War, the North Vietnamese fired approximately 800 SAMs at SR-71s, none of which managed to score a hit.[132] Pilots did report that missiles launched without radar guidance and no launch detection, had passed as close as 150 yards (140 m) from the aircraft.[133]
While deployed at Okinawa, the SR-71s and their aircrew members gained the nicknameHabu (as did the A-12s preceding them) after apit viper indigenous to Japan, which the Okinawans thought the plane resembled.[1]
Operational highlights for the entire Blackbird family (YF-12, A-12, and SR-71) as of about 1990 included:[31]
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)
Only one crew member, Jim Zwayer, a Lockheed flight-test reconnaissance and navigation systems specialist, was killed in a flight accident.[114] The rest of the crew members ejected safely or evacuated their aircraft on the ground.
An SR-71 was used domestically in 1971 to assist the FBI in their manhunt for the skyjackerD.B. Cooper. The Blackbird was to retrace and photograph the flightpath of the hijacked 727 from Seattle to Reno and attempt to locate any of the items that Cooper was known to have parachuted with from the aircraft.[134] Five flights were attempted but on each occasion no photographs of the flight path were obtained due to low visibility.[135]
European operations were flown from RAF Mildenhall, England, with two weekly routes. One was along theNorwegian west coast and up theKola Peninsula, monitoring several large naval bases belonging to the Soviet Navy'sNorthern Fleet. Over the years, there were several emergency landings in Norway, four in Bodø and two of them in 1981, flying from Beale, in 1985. Rescue parties were sent in to repair the planes before leaving. On one occasion, one complete wing with engine was replaced as the easiest way to get the plane airborne again.[136][137]
The Baltic Express route entered throughDenmark and the narrow corridor between Sweden andEast Germany.
The other route was known as theBaltic Express, which started from Mildenhall and went throughJutland and theDanish straits before going out over theBaltic Sea.[138] At the time, theUSSR controlled the airspace from theDDR to theGulf of Finland, withFinland andSweden pursuing neutrality in the Cold War. This meant thatNATO aircraft entering the Baltic Sea had to fly through a narrow corridor of international airspace betweenScania andWestern Pomerania, which was monitored by both theSwedish andSoviet Air Forces. Starting a counter-clockwise 30-minute loop, the Blackbirds would thenreconnoiter along the Soviet Union's coastal border, before slowing down to Mach 2.54 to make a left turn south ofÅland, and then follow the Swedish coast back towards Denmark. If the SR-71s attempted the turn at Mach 3, they could end up violating Swedish airspace, and the Swedes woulddirectViggens to intercept the offending aircraft.[138][139]
The combination of a monitored entry point and a fixed route allowed the Swedes and the Soviets a chance toscramble interceptors.[138] Swedish radar stations would observe the15th Air Army dispatchSu-15s fromLatvia, andMiG-21s andMiG-23s fromEstonia, although only the Sukhois would have even a slim chance of successfully intercepting the American aircraft.[139] The greater Soviet threat came from the MiG-25sstationed atFinow-Eberswalde in the DDR. The Swedes noted that the Soviets usually would send a singleMiG-25 "Foxbat" from Finow to intercept the SR-71 on their way back out of the Baltic Sea. With the Blackbird flying at 72,000 ft (22 km), the Foxbat would regularly close to an altitude of 62,000 ft (19 km), precisely 1.9 mi (3 km) behind the SR-71, before disengaging. The Swedes interpreted this regularity as a sign that the MiG-25 had successfully simulated a shoot-down.[138][139][140]
The Swedes themselves would typically assert their neutrality by dispatching Saab 37 Viggens fromÄngelholm,Norrköping orRonneby. Limited by a top speed of Mach 2.1 and aservice ceiling of 59,000 ft (18 km), the Viggen pilots would line up for a frontal attack, and rely on theirstate-of-the-artavionics to climb at the right time and attain amissile lock on the SR-71.[138][139] Precise timing and target illumination would be maintained with target location data supplied to the Viggen'sfire-control computer fromground-based radars,[141] with the most common site for thelock-on being the thin stretch of international airspace betweenÖland andGotland.[142][143][144] Out of 322 recorded Baltic Express sorties between 1977 and 1988, the Swedish Air Force claims that they succeeded in attaining missile lock on the SR-71 in 51 of them.[138][145] However, with a combined closing speed of Mach 5, the Swedes were reliant on the Blackbird not changing course.[138][139]
On 29 June 1987, an SR-71[N 7] was on a mission around the Baltic Sea to spy on Soviet postings when one of the engines exploded. The aircraft, which was at 66,000 ft (20 km) altitude, quickly lost altitude and turned 180° to the left and turned over Gotland to search for the Swedish coast. Thus, Swedish airspace was violated, whereupon two unarmed[146] Saab JA 37 Viggens on an exercise at the height ofVästervik were ordered there. The mission was to do an incident preparedness check and identify an aircraft of high interest. It was found that the plane was in obvious distress and a decision was made that the Swedish Air Force would escort the plane out of the Baltic Sea. A second round of armed JA-37s from Ängelholm replaced the first pair and completed the escort to Danish airspace.[138][139][147] The event had been classified for over 30 years, and when the report was unsealed, data from theNSA showed that multiple MiG-25s with the order to shoot down the SR-71 or force it to land, had started right after the engine failure. A MiG-25 had locked a missile on the damaged SR-71, but as the aircraft was under escort, no missiles were fired. On 28 November 2018, the four Swedish pilots involved were awarded medals from the USAF.[147]
The two most widely proposed reasons for the SR-71's retirement in 1989, offered by the Air Force to Congress, were that the plane was too expensive to build and maintain, and had been rendered redundant by other evolving reconnaissance methods, such as unmanned vehicles (UAVs) and satellites. Another view held by officers and legislators is that the SR-71 was terminated due toPentagon politics.[citation needed]
In 1996, a former 1st-SRS and 9th-SRW commander, Graham, presented a strongly supported opinion that the SR-71 provided some intelligence capabilities that none of its alternatives could provide in the 1990s, when the SR-71 was retired.[148] Opinion remained divided as to how crucial, or disposable, those unique advantages properly were.
Graham noted that in the 1970s and early 1980s, to be selected into the SR-71 program, a pilot or navigator (RSO) had to be a top-quality USAF officer, so SR-71 squadron and wing commanders often pursued career advancement with promotion into higher positions within the USAF and the Pentagon. These generals were adept at communicating the value of the SR-71 to a USAF command staff and a Congress who often lacked a basic understanding of how the SR-71 worked and what it did. However, by the mid-1980s, these "SR-71 generals" all had retired, and a new generation of USAF generals had come to believe that the SR-71 had become redundant, and wanted to pursue newer, top secret programs like the newB-2 Spiritstrategic bomber program.[31] Graham said that the last-mentioned one was only a sales pitch, not a fact, at the time in the 1990s.
The USAF may have seen the SR-71 as a bargaining chip to ensure the survival of other priorities. Also, the SR-71 program's "product", which was operational and strategic intelligence, was not seen by these generals as being very valuable to the USAF. The primary consumers of this intelligence were the CIA, NSA, and DIA. A general misunderstanding of the nature of aerial reconnaissance and a lack of knowledge about the SR-71 in particular (due to its secretive development and operations) was used by detractors to discredit the aircraft, with the assurance given that a replacement was under development.[31]Dick Cheney told the Senate Appropriations Committee that the SR-71 cost $85,000 per hour to operate.[149] Opponents estimated the aircraft's support cost at $400 to $700 million per year, though the cost was actually closer to $300 million.[31]
The SR-71, while much more capable than the Lockheed U-2 in terms of range, speed, and survivability, suffered the lack of adata link, which the U-2 had been upgraded to carry. This meant that much of the SR-71's imagery and radar data could not be used in real time, but had to wait until the aircraft returned to base. This lack of immediate real-time capability was used as one of the justifications to close down the program. The counterargument was that the longer the SR-71 was not upgraded as aggressively as it ought to have been, the more people could say that it was obsolescent, which was in their interest as champions of other programs (a self-fulfilling bias). Attempts to add a datalink to the SR-71 were stymied early on by the same factions in the Pentagon and Congress who were already set on the program's demise, even in the early 1980s. These same factions also forced expensive sensor upgrades to the SR-71, which did little to increase its mission capabilities, but could be used as justification for complaining about the cost of the program.[31]
In 1988, Congress was convinced to allocate $160,000 to keep six SR-71s and a trainer model in flyable storage that could become flightworthy within 60 days. However, the USAF refused to spend the money.[150] While the SR-71 survived attempts to retire it in 1988, partly due to the unmatched ability to provide high-quality coverage of theKola Peninsula for theUS Navy,[151][152] the decision to retire the SR-71 from active duty came in 1989, with the last missions flown in October that year.[153] Four months after the plane's retirement, GeneralNorman Schwarzkopf Jr., was told that the expedited reconnaissance, which the SR-71 could have provided, was unavailable duringOperation Desert Storm.[154]
The SR-71 program's main operational capabilities came to a close at the end of fiscal year 1989 (October 1989). The 1st Strategic Reconnaissance Squadron (1 SRS) kept its pilots and aircraft operational and active, and flew some operational reconnaissance missions through the end of 1989 and into 1990, due to uncertainty over the timing of the final termination of funding for the program. The squadron finally closed in mid-1990, and the aircraft were distributed to static display locations, with a number kept in reserve storage.[31]
From the operator's perspective, what I need is something that will not give me just a spot in time but will give me a track of what is happening. When we are trying to find out if theSerbs are taking arms, moving tanks or artillery intoBosnia, we can get a picture of them stacked up on the Serbian side of the bridge. We do not know whether they then went on to move across that bridge. We need the [data] that a tactical, an SR-71, a U-2, or an unmanned vehicle of some sort, will give us, in addition to, not in replacement of, the ability of the satellites to go around and check not only that spot but a lot of other spots around the world for us. It is the integration of strategic and tactical.
— Response from AdmiralRichard C. Macke to the Senate Committee on Armed Services.[155]
SR-71A (2) and SR-71B trainer (center), Edwards Air Force Base, California, 1992
Due to unease over political situations in the Middle East andNorth Korea, the US Congress re-examined the SR-71 beginning in 1993.[154] Rear AdmiralThomas F. Hall addressed the question of why the SR-71 was retired, saying it was under "the belief that, given the time delay associated with mounting a mission, conducting a reconnaissance, retrieving the data, processing it, and getting it out to a field commander, that you had a problem in timelines that was not going to meet the tactical requirements on the modern battlefield. And the determination was that if one could take advantage of technology and develop a system that could get that data back real time... that would be able to meet the unique requirements of the tactical commander." Hall also stated they were "looking at alternative means of doing [the job of the SR-71]."[155]
Macke told the committee that they were "flying U-2s,RC-135s, [and] other strategic and tactical assets" to collect information in some areas.[155] SenatorRobert Byrd and other senators complained that the "better than" successor to the SR-71 had yet to be developed at the cost of the "good enough" serviceable aircraft. They maintained that, in a time of constrained military budgets, designing, building, and testing an aircraft with the same capabilities as the SR-71 would be impossible.[31]
Congress's disappointment with the lack of a suitable replacement for the Blackbird was cited concerning whether to continue funding imaging sensors on the U-2. Congressional conferees stated the "experience with the SR-71 serves as a reminder of the pitfalls of failing to keep existing systems up-to-date and capable in the hope of acquiring other capabilities."[31] It was agreed to add $100 million to the budget to return three SR-71s to service, but it was emphasized that this "would not prejudice support for long-enduranceUAVs" such as theGlobal Hawk. The funding was later cut to $72.5 million.[31] The Skunk Works was able to return the aircraft to service under budget at $72 million.[156]
Retired USAF Colonel Jay Murphy was made the Program Manager for Lockheed's reactivation plans. Retired USAF Colonels Don Emmons and Barry MacKean were put under government contract to remake the plane's logistic and support structure. Still-active USAF pilots and Reconnaissance Systems Officers (RSOs) who had worked with the aircraft were asked to volunteer to fly the reactivated planes. The aircraft was under the command and control of the9th Reconnaissance Wing at Beale Air Force Base and flew out of a renovated hangar atEdwards Air Force Base. Modifications were made to provide a data-link with "near real-time" transmission of the Advanced Synthetic Aperture Radar's imagery to sites on the ground.[31]
The reactivation met much resistance: the USAF had not budgeted for the aircraft, and UAV developers worried that their programs would suffer if money was shifted to support the SR-71s. Also, with the allocation requiring yearly reaffirmation by Congress, long-term planning for the SR-71 was difficult.[31] In 1996, the USAF claimed that specific funding had not been authorized, and moved to ground the program. Congress reauthorized the funds, but, in October 1997, PresidentBill Clinton attempted to use theline-item veto to cancel the $39 million (~$70.6 million in 2024) allocated for the SR-71. In June 1998, theUS Supreme Court ruled that theline-item veto was unconstitutional. All this left the SR-71's status uncertain until September 1998, when the USAF called for the funds to be redistributed; the USAF permanently retired it in 1998.
28 December 1962: Lockheed signs contract to build six SR-71 aircraft
25 July 1964: President Johnson makes public announcement of SR-71
29 October 1964: SR-71 prototype (AF Ser. No. 61-7950) delivered toAir Force Plant 42 at Palmdale, California
7 December 1964:Beale AFB, California, announced as base for SR-71
22 December 1964: First flight of the SR-71, with Lockheed test pilot Robert J "Bob" Gilliland at Palmdale, California[158]
21 July 1967: Jim Watkins and Dave Dempster fly first international sortie in SR-71A, AF Ser. No. 61-7972, when the Astro-Inertial Navigation System (ANS) fails on a training mission and they accidentally fly into Mexican airspace
5 February 1968: Lockheed ordered to destroy A-12, YF-12, and SR-71 tooling
8 March 1968: First SR-71A (AF Ser. No. 61-7978) arrives atKadena AB, Okinawa to replace A-12s
21 March 1968: First SR-71 (AF Ser. No. 61-7976) operational mission flown from Kadena AB over Vietnam
29 May 1968: CMSgt Bill Gornik begins the tie-cutting tradition of Habu crews' neckties
3 December 1975: First flight of SR-71A (AF Ser. No. 61-7959) in "big tail" configuration
20 April 1976: TDY operations started atRAF Mildenhall, United Kingdom with SR-71A, AF Ser. No. 61-7972
27–28 July 1976: SR-71A sets speed and altitude records (altitude in horizontal flight: 85,068.997 ft (25,929.030 m) and speed over a straight course: 2,193.167 miles per hour (3,529.560 km/h))
August 1980:Honeywell starts conversion of AFICS to DAFICS
15 January 1982: SR-71B, AF Ser. No. 61-7956, flies its 1,000th sortie
29 June 1987: 61-7964 flying a reconnaissance mission over the Baltic Express when its experienced an engine failure, causing it to drop into Swedish airspace. SwedishViggens were sent to intercept an SR-71 for violating Swedish airspace. They assessed the emergency situation and rendered support to the aircraft by defending it from potential Soviet threats. The Swedish interceptors escorted the Blackbird until it reached Danish airspace where it was safely recovered. The incident was declassified in 2018 and the four Swedish air force pilots received U.S. Air Medals over 31 years after the incident.[159]
21 April 1989: SR-71, AF Ser. No. 61-7974, is lost due to an engine explosion after taking off from Kadena AB, the last Blackbird to be lost.[6][7]
22 November 1989: USAF SR-71 program officially terminated
6 March 1990: Last SR-71 flight under Senior Crown program, setting four speed records en route to the Smithsonian Institution
20 March 1990: SR-71A #61-7964 (17964) last flight. Delivered toOffutt AFB for permanent display. On display at theStrategic Air and Space Museum in Ashland, Nebraska.
25 July 1991: SR-71B, AF Ser. No. 61-7956/NASA No. 831 officially delivered to NASA Dryden Flight Research Center atEdwards AFB, California
October 1991: NASA engineerMarta Bohn-Meyer becomes the first female SR-71 crew member
28 September 1994: Congress votes to allocate $100 million for reactivation of three SR-71s
28 June 1995: First reactivated SR-71 returns to USAF as Detachment 2
9 October 1999: The last flight of the SR-71 (AF Serial No. 61-7980/NASA 844)
View from the cockpit at 83,000 feet (25,000 m) over the Atlantic Ocean[160]
The SR-71 was the world's fastest and highest-flying air-breathing operational manned aircraft throughout its career and it still holds that record. On 28 July 1976, SR-71 serial number 61-7962, piloted by then Captain Robert Helt, broke the world record: an "absolute altitude record" of 85,069 feet (25,929 m).[13][161][162][163] Several aircraft have exceeded this altitude inzoom climbs, but not in sustained flight.[13] That same day SR-71 serial number 61-7958 set anabsolute speed record of 1,905.81 knots (2,193.2 mph; 3,529.6 km/h), approximately Mach 3.3.[13][163][164] SR-71 pilotBrian Shul states in his bookThe Untouchables that he flew in excess of Mach 3.5 (4,290 km/h; 2,660 mph) on15 April 1986 over Libya to evade a missile.[125]
The SR-71 also holds the "speed over a recognized course" record for flying from New York to London—distance 3,461.53 miles (5,570.79 km), 1,806.964 miles per hour (2,908.027 km/h), and an elapsed time of 1 hour 54 minutes and 56.4 seconds—set on 1 September 1974, while flown by USAF pilot James V. Sullivan and Noel F. Widdifield, reconnaissance systems officer (RSO).[165] This equates to an average speed of about Mach 2.72, including deceleration for in-flight refueling. Peak speeds during this flight were likely closer to the declassified top speed of over Mach 3.2. For comparison, the best commercialConcorde flight time was 2 hours 52 minutes and theBoeing 747 averages 6 hours 15 minutes.
On 26 April 1971, 61–7968, flown by majors Thomas B. Estes and Dewain C. Vick, flew over 15,000 miles (24,000 km) in 10 hours and 30 minutes. This flight was awarded the 1971Mackay Trophy for the "most meritorious flight of the year" and the 1972Harmon Trophy for "most outstanding international achievement in the art/science of aeronautics".[166]
Pilot Lt. Col. Ed Yeilding and RSO Lt. Col. Joe Vida on 6 March 1990, the last SR-71 Senior Crown flight
When the SR-71 was retired in 1990, one Blackbird was flown from its birthplace at USAFPlant 42 inPalmdale, California, to go on exhibit at what is now theSmithsonian Institution'sSteven F. Udvar-Hazy Center inChantilly, Virginia. On 6 March 1990, Lt. Col. Raymond E. Yeilding and Lt. Col. Joseph T. Vida piloted SR-71 S/N 61-7972 on its final Senior Crown flight and set four new speed records in the process:
Los Angeles, California, to Washington, D.C., distance 2,299.7 mi (3,701.0 km), average speed 2,144.8 mph (3,451.7 km/h), and an elapsed time of 64 minutes 20 seconds.[165][167]
West Coast toEast Coast, distance 2,404 mi (3,869 km), average speed 2,124.5 mph (3,419.1 km/h), and an elapsed time of 67 minutes 54 seconds.
Kansas City, Missouri, to Washington, D.C., distance 942 mi (1,516 km), average speed 2,176 mph (3,502 km/h), and an elapsed time of 25 minutes 59 seconds.
St. Louis, Missouri, to Cincinnati, Ohio, distance 311.4 mi (501.1 km), average speed 2,189.9 mph (3,524.3 km/h), and an elapsed time of 8 minutes 32 seconds.
These four speed records were accepted by theNational Aeronautic Association (NAA), the recognized body for aviation records in the United States.[168] Additionally,Air & Space/Smithsonian reported that the USAF clocked the SR-71 at one point in its flight reaching 2,242.48 miles per hour (3,608.92 km/h).[169] After the Los Angeles–Washington flight, on 6 March 1990, SenatorJohn Glenn addressed theUnited States Senate, chastising theDepartment of Defense for not using the SR-71 to its full potential:
Mr. President, the termination of the SR-71 was a grave mistake and could place our nation at a serious disadvantage in the event of a future crisis. Yesterday's historic transcontinental flight was a sad memorial to our short-sighted policy in strategic aerial reconnaissance.[31]
Speculation existed regarding a replacement for the SR-71, including a rumored aircraft codenamedAurora. The limitations ofreconnaissance satellites, which take up to 24 hours to arrive in the proper orbit to photograph a particular target, make them slower to respond to demand than reconnaissance planes. The fly-over orbit of spy satellites may also be predicted and can allow assets to be hidden when the satellite passes, a drawback not shared by aircraft. Thus, there are doubts that the US has abandoned the concept of spy planes to complement reconnaissance satellites.[170]Unmanned aerial vehicles (UAVs) are also used for aerial reconnaissance in the 21st century, being able to overfly hostile territory without putting human pilots at risk, as well as being smaller and harder to detect than manned aircraft.
On 1 November 2013, media outlets reported that Skunk Works has been working on an unmanned reconnaissance airplane it has namedSR-72, which would fly twice as fast as the SR-71, at Mach 6.[171][172] However, the USAF is officially pursuing theNorthrop Grumman RQ-180 UAV to assume the SR-71's strategic ISR role.[173]
SR-71C was a hybrid trainer[175] aircraft composed of the rear fuselage of the first YF-12A (S/N 60-6934) and the forward fuselage from an SR-71 static test unit. The YF-12 had been wrecked in a 1966 landing accident. It has been reported that this Blackbird was seemingly not quite straight and had a yaw at supersonic speeds.[176] However, this was caused by a mis-aligned pitot tube reporting a 4° yaw that was not actually present. It was soon corrected and then flew normally.[175][177] It was nicknamed "The Bastard".[178][179]
(Forward Operating Locations at Eielson AFB, Alaska; Griffis AFB, New York; Seymour-Johnson AFB, North Carolina; Diego Garcia and Bodo, Norway 1973–1990)
Twelve SR-71s were lost and one pilot died in accidents during the aircraft's service career.[6][7] Eleven of these accidents happened between 1966 and 1972.
List of SR-71 Blackbirds
AF serial number
Model
Location or fate
61-7950
SR-71A
Lost, 10 January 1967, in fire caused by failed braking test. Aircraft departed runway and burned.[184]
Lost, 21 April 1989 after compressor failure caused catastrophic left engine failure. Remains of aircraft recovered then on 24 December 1989 buried at sea in theMariana Trench.[206]
Lost, 10 October 1968. Aborted takeoff after wheel assembly failure. Cockpit section survived and located at theSeattle Museum of Flight.[209]
61-7978
SR-71A
Nicknamed "Rapid Rabbit" and wearing aPlayboy bunny image as tail art.[210] (wearing a "black bunny" logo on its tail). Lost, 20 July 1972 after departure from runway.[6][184]
Some secondary references use incorrect 64-series aircraft serial numbers (e.g. SR-71C 64-17981)[214]
After completion of all USAF and NASA SR-71 operations at Edwards AFB, the SR-71 Flight Simulator was moved in July 2006 to theFrontiers of Flight Museum atLove Field Airport in Dallas, Texas.[215]
^While titanium ores are cheap and abundant, converting those ores into metallic titanium is laborious and expensive. Soviet production of metallic titanium was several times US production, so the CIA – without Soviet knowledge – used dummy intermediary firms to obtain Soviet-produced metallic titanium for US military use.[35][36][37]
^TheFoxbats could sustain speeds of Mach 2.83, but they also had an emergency option to reach Mach 3.2 – after which the engines would have to be repaired or replaced.[49]
^Cefaratt; Gill (2002).Lockheed: The People Behind the Story. Turner Publishing Company. pp. 78, 158.ISBN978-1-56311-847-0.
^"Lockheed B-71 (SR-71)". National Museum of the United States Air Force. 29 October 2009. Archived fromthe original on 4 October 2013. Retrieved2 October 2013.
^Brown, William. "J58/SR-71 Propulsion Integration, attachment to CIA-RDP90B001170R000100050008-1, Fig. 3 'Inlet and engine airflow match'".
^"Aerothermodynamics of Aircraft Gas Turbine Engines", Oates, Air Force Aero Propulsion Laboratory, Figure 13.1.17 'Elements of Inlet Airflow Supply Determination', (a) and (b).
^A-12 Utility Flight Manual, 15 September 1965, changed 15 June 1968, Fuel Derich System.
^Quote from Reg Blackwell, SR-71 pilot, interviewed for "Battle Stations" episode "SR-71 Blackbird Stealth Plane", first aired on History Channel 15 December 2002.
^SR 71 Flight (Report). Federal Bureau of Investigation. 6 December 1971. p. 340.Beale Air Force Base, California, had offered, free of charge to the Bureau, use of an SR-71 aircraft to photograph terrain over which the hijacked airplane had flown on its trip to Reno
^SR 71 Flight (Report). Federal Bureau of Investigation. 6 December 1971. p. 340.photographic over-flights using SR-71 aircraft were conducted on five separate occasions with no photographs obtained due to limited visibility from very high altitude.
^abcdefghiBonafede, Håkon (10 May 2018)."På skuddhold av SR-71 Blackbird" [At weapons range of the SR-71].Vi Menn (in Norwegian Bokmål). Norway. Archived fromthe original on 10 May 2018. Retrieved12 May 2018 – vianb:Side3.To vanlige "melkeruter" ble fløyet ukentlig [...] Den andre som ble kalt for "Baltic Express" dekket marinebasene og militærinstallasjonene til DDR og de baltiske landene. På grunn av det trange farvannet, bød ruten på utfordringer med å holde seg utenfor territorialgrensene, og flygerne fulgte nesten alltid den samme identiske ruten. [...] SR-71 kom alltid inn over radiofyret "Codan" 80 km sør for København på kurs rett østover. [Two common "milk runs" were flown weekly [...] The second, which was called [the] "Baltic Express" covered the Navy bases and military installations of the DDR and the Baltic countries. Because of the cramped waters, the route presented challenges as to keeping outside the territorial borders, and the pilots almost always followed the same identical route. [...] SR-71 always came in over the radio beacon "Codan" 80 km south of Copenhagen[,] heading east.]
^abcdefLeone, Dario (9 January 2018)."VIGGEN Vs BLACKBIRD: HOW SWEDISH AIR FORCE JA-37 FIGHTER PILOTS WERE ABLE TO ACHIEVE RADAR LOCK ON THE LEGENDARY SR-71 MACH 3 SPY PLANE".The Aviation Geek Club.Archived from the original on 10 January 2019. Retrieved9 October 2023.Almost every time the SR-71 was about to leave the Baltic, a lone MiG-25 Foxbat belonging to the 787th IAP at Finow-Eberwalde in [East Germany] was scrambled. […] Arriving at its exit point, the "Baltic Express" was flying at about 22km and the lone MiG would reach about 19km in a left turn before rolling out and always completing its stern attack 3km behind its target. We were always impressed by this precision; it was always 22km and 3 km behind the SR-71. [this would seem to suggest that these were the parameters necessary for its weapons system to effect a successful intercept if the order to fire was ever given.]
^Simha, Rakesh Krishnan (3 September 2012)."Foxhound vs Blackbird: How the MiGs reclaimed the skies".Russia Beyond the Headlines.Rossiyskaya Gazeta.Archived from the original on 9 August 2019. Retrieved30 May 2015.Swedish air defense [...] radar screens [...] could see the much older but faster MiG-25 screaming in towards the Blackbird. Shortly after the MiG-31s had harried the SR-71 in the Arctic area, a lone MiG-25 Foxbat stationed at Finow-Eberswalde in the former GDR would intercept it over the Baltic. The Swedes observed the SR-71 would always fly at 72,000 ft and the MiG-25 would reach 63,000 ft before completing its stern attack 2.9 km behind the Blackbird. "We were always impressed by this precision, it was always 63,000 ft and 2.9 km behind the SR-71," a retired Swedish Air Force flight controller told Crickmore.
^"TV: Kärnvapensäkra bunkern styrde flygplanen" [TV: Aircraft controlled from nuclear weapon secured bunker].Kundservice (in Swedish). Sweden. 2 May 2017. Archived fromthe original on 2 May 2017. Retrieved7 October 2017.Look at time 5:57.
^abFratini, Korey (29 November 2018)."AF.mil: Swedish pilots presented with US Air Medal". Stockholm:US Air Force.Archived from the original on 8 May 2023. Retrieved7 May 2023.The U.S. was flying regular SR-71 aircraft reconnaissance missions in international waters over the Baltic Sea known as "Baltic Express" missions. But on June 29, 1987, during one of those missions, an SR-71 piloted by retired Lt. Cols. Duane Noll and Tom Veltri, experienced an inflight emergency. [...] presented the Air Medals to Swedish air force Col. Lars-Eric Blad, Maj. Roger Moller, Maj. Krister Sjoberg and Lt. Bo Ignell.
^Marshall, Elliot, The Blackbird's Wake, Air & Space, October/November 1990, p. 31.
^Siuru, William D. and John D. Busick.Future Flight: The Next Generation of Aircraft Technology. Blue Ridge Summit, Pennsylvania: TAB Books, 1994.ISBN0-8306-7415-2.
Graham, Richard H. (2008).Flying The SR-71 – In The Cockpit On A Secret Operational Mission. Minneapolis, Minnesota: Zenith Press.ISBN978-0-7603-3239-9.
Graham, Richard H. (2013).SR-71: The Complete Illustrated History of the Blackbird, The World's Highest, Fastest Plane. MBI Publishing Company.ISBN978-0760343272.
Merlin, Peter W. (July 2005). "The Truth is Out There... SR-71 Serials and Designations".Air Enthusiast.118. Stamford, UK: Key Publishing:2–6.ISSN0143-5450.
Suhler, Paul A.From RAINBOW to GUSTO: Stealth and the Design of the Lockheed Blackbird (Library of Flight Series). Reston, Virginia: American Institute of Aeronautics and Astronautics (AIAA), 2009.ISBN978-1-60086-712-5.
Darwall, Bjarne.Luftens Dirigenter (Air Conductors) (in Swedish). Nässjö, Sweden: Air Historic Research AB, 2004.ISBN91-973892-6-9.
Goodall, James and Jay Miller. "Lockheed's SR-71 'Blackbird' Family A-12, F-12, M-21, D-21, SR-71". Hinckley, UK: AeroFax-Midland Publishing, 2002.ISBN1-85780-138-5.
Grant, R.G.Flight: 100 Years of Aviation. New York: DK Publishing, 2007.ISBN978-0-7566-1902-2.
Hobson, Chris.Vietnam Air Losses, USAF, USN, USMC, Fixed-Wing Aircraft Losses in Southeast Asia 1961–1973. North Branch, Minnesota: Specialty Press, 2001.ISBN1-85780-115-6.
![Entry to the inlet. Behind is the outer wing and hinged portion of the nacelle that encloses the engine. The spike is shown in the forward position (for speeds below Mach 1.6). Just discernible behind the cowl lip are spike boundary layer bleed slots where the normal shock is located at higher speeds when the spike has moved rearwards, the cowl bleed "shock trap" ram intake, streamlined bodies ("mice") and, between the mice, the forward bypass door openings[76] that dump unwanted air externally through the front louvers and cause nacelle drag.[77] When the landing gear is down, ambient air flows in reverse through the bypass to supplement the front inlet flow into the engine.](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aLockheed_SR-71A_Blackbird_at_Evergreen_Aviation_%2526_Space_Museum_(6586637283).jpg)
![A rear view of the inlet where air enters the engine. Two features were added after flight testing highlighted the need: 1) "mice," visible as streamlined shapes, added to reduce the diffusion rate after pilots noted rumbling; and 2) rear bypass doors added to prevent unstarting the inlet during descents with low engine flow.[78] The ring of doors is at the extreme rear of the inlet as shown by their accompanying rear-turning scoop, extending from 7 o'clock to 5 o'clock, which directs the air through the nacelle to the ejector nozzle.[79] The door actuator[80]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aLockheed_SR-71A_Blackbird_at_Evergreen_Aviation_%2526_Space_Museum_(6586640345)_(2).jpg)
![The afterburner was rated for continuous operation at 3,200 °F (1,800 °C) made possible with ceramic coatings (colored white) on duct liner and flame holders[86] and compressor bleed air cooling the duct and nozzle (above Mach 2.1 when the bleed was flowing). The nozzle is fully open, the maximum afterburning position. The main purpose of the variable nozzle area was to control engine operation which it did in conjunction with varying heat release in the afterburner.](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aPratt_%2526_Whitney_J58_18.jpg)
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