Science Fair Project Encyclopedia
|Length||107.42 ft||32.74 m|
|Wingspan||55.58 ft||16.94 m|
|Height||18.5 ft||5.64 m|
|Wing area||1,800 ft²||167.2 m²|
|Empty||65,000 lb||29,484 kg|
|Loaded||170,000 lb||77,112 kg|
|Engines||Two Pratt & Whitney J58-1 (JT11D-20B) continuous-bleed afterburning turbojets|
|Power||32,500 lbf||145 kN|
|Maximum speed||2,193 mph||3,532 km/h|
|Combat range||2,982 mi||4,800 km|
|Service ceiling||85,000 ft||25,908 m|
The Lockheed SR-71, unofficially known as the Blackbird, is a long-range, advanced, strategic reconnaissance aircraft developed from the Lockheed YF-12A and A-12 aircraft by Lockheed's Skunk works, which was also responsible for the U-2 and many other advanced aircraft. In particular, the legendary "Kelly" Johnson was largely responsible for many of the concepts behind the aircraft. The SR-71 was one of the first aircraft to be shaped to have an extremely low radar signature.
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. The United States Air Force retired its fleet of SR-71s on January 26, 1990, because of a decreasing defense budget and high costs of operation. 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.
Throughout its career, the SR-71 remained the world's fastest and highest-flying operational aircraft. From an altitude of 80,000 ft (24 km) it could survey 100,000 miles²/h (72 km²/s) of the Earth's surface. On July 28, 1976, an SR-71 set two world records for its class: an absolute speed record of 2,193.167 mph (3,529.56 km/h) and an absolute altitude record of 85,068.997 feet (25,929 m). 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 the Smithsonian Institute's National Air & Space Museum in Washington, D.C., setting a coast-to-coast speed record at an average 2,124 mph (3,418 km/h). The entire trip took only 68 minutes.
The aircraft flew so fast and so high that if the pilot detected that a surface-to-air missile had been launched, the standard process of evasive action was, simply, "accelerate". No SR-71 aircraft are known to have been shot down.
On March 21, 1968 Major (later General) Jerome F. O'Malley and Major Edward D. Payne made the first operational SR-71 sortie. During its career, this aircraft 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 (Base) Mildenhall, England. The aircraft was flown to the United States Air Force Museum in March 1990. In Okinawa, the A-12s (and later the SR-71s) gained their nickname Habu after a southeast Asian pit viper which the locals thought the plane resembled.
Thirty-two planes were built. Of these, 12 were lost in flight accidents but all crews ejected safely, except in the case of one M-21 crash (see below).
The originally planned USAF designation for the aircraft was B-71, then RS-71, following on from the planned RS-70, a reconnaissance version of the XB-70. However Curtis LeMay preferred the SR designation and wanted the RS-70 to be named SR-70. When the Blackbird was to be announced by Lyndon B. Johnson on February 29, 1964, Johnson's speech was modified by LeMay to read SR-71 instead of RS-71. The media transcript given to the press at the time still had the incorrect RS-71 designation in places, creating the myth that the president had misread the plane's designation.
The A-12 was the original aircraft, also known as Article 11 or A-11 by Lockheed/CIA. 18 were built, of which 3 were converted into YF-12A's, Prototypes of the planned F-12 interceptor version.
The most notable variant of the basic SR-71 design was the M-21. This was a SR-71 platform modified to carry and launch the D-21 drone, an unpiloted, faster and higher flying reconnaissance device.
Confusingly, this variant was known as the M-21 when the drone was absent, and the MD-21 when it was attached to the plane. 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 crashed into the mother ship shortly after being launched, destroying the M-21 and killing the Launch Control Officer.
The airframe was made of titanium obtained from the USSR during the height of the Cold war. The builder 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. They painted the aircraft dark blue (almost black) to dissipate heat and to act as camouflage against the sky.
The shape of the vehicle is designed so that the plane had a very small 'radar cross-section' — the SR-71 was an early stealth design. In addition, the geometry of the airframe is such that the engine inlets are inline with the shockwave from the nose of the aircraft. This compressed the air in a similar way to a ramjet and permitted higher performance. Indeed, at top speed more than 80% of the thrust was due to the ramjet effect. However, for this effect to operate successfully it also necessitated moveable inlet cones; incorrect positioning tended to make the engines 'unstart', a curious euphemism for when the engine's combustion is essentially blown out like a candle. 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 violently yaw to one side. This caused at least one pilot to crack his crash helmet on the cockpit canopy, although no aircraft were known lost to this event. Lockheed engineers eventually developed control software for the engine inlets that would recapture the lost shockwave and relight 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.
Due to the great temperature changes in flight, the fuselage panels were supposedly essentially loose. Proper alignment was only achieved when the airframe warmed up, due to the air resistance at high speeds, and the airframe then expanded several inches. Because of this, and the lack of a fuel sealing system that could handle the extreme temperatures, the aircraft would leak its specially formulated 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 airplane landed no one could approach it for some time as its canopy was still hotter than 300 degrees Celsius. Asbestos (non-fiberous) was also used, such as in non-ceramic automotive brakes, due to its high heat tolerance.
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.
The skin of the SR-71 is 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 is allowed to expand vertically as well as horizontally without overstressing, which also increases longitudinal strength. Despite the fact that it worked, aerodynamicists were aghast at the concept and accused the design engineers of trying to make a 1920's era Ford Trimotor, known for its corrugated aluminum skin, go Mach 3.
The J-58 engines used in the Blackbird are the only military engines ever designed to operate continuously on afterburner, and actually become more efficient as the aircraft goes faster. Each J-58 engine could produce 32,500 lbf (145 kN) of static thrust. Conventional jet engines cannot operate continuously on afterburner and lose efficiency as they go faster.
The Blackbird's engines started up with the assistance of an external "start cart", a cart containing two Buick V-8 engines which was rolled out onto the runway underneath the aircraft. The two Buick engines powered a single, vertical driveshaft connected to a single J-58 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.
Myth and lore
The plane has developed a small cult following, given its design, specifications, and the aura of secrecy that surrounds it. Some conspiracy theorists have speculated that the true operational capabilities of the SR-71 and the associated A-12 have never been revealed. Most individuals speculate that given a confluence of structural and aerodynamic tolerances that the plane could fly at a maximum of Mach 3.3 for extended periods, and could not exceed Mach 3.44 without resulting in complete failure. Specifically, these groups cite the specific temperature for the compressor inlet of 427 °F (220 °C), where this temperature is exceeded at Mach 3.3, and thus, the nose temperature of the plane's titanium skin becomes such that the glass of the cockpit melts. The speed of Mach 3.44 is cited as the speed at which the engine design fails, noting a position of permanent "unstart".
There is a smaller group of indviduals, mostly based on what could be considered unsubstantiated accountings and theories involving the plane, which hold based on that information that the SR-71 was modified to approach flight values of Mach 5. This is supported primarily by the reports of the reconnaissance missions which the plane undertook, where the seeming mission times could only be accounted for by speeds between Mach 3.6 and 4.1. Deriving this as fact for early SR-71s, it is projected by these groups that the latter improved vehicles could approach values of Mach 4.5, and be competitive with the X-15 under specific flight conditions.
It should be noted that the SR-71's Pratt & Whitney J58 engines never exceeded testbench values above Mach 3.6 in known and 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 which is immediately flyable, it may never be known what the true design tolerances of the aircraft were, or if these tolerances were ever approached in flight. This fact in and of itself has considerably magnified the seemingly mythical nature that surrounds this aircraft for these particular groups.
SR-71 in fiction
The superhero team the X-Men are depicted using a modified SR-71 but the capacities of the aircraft including a crew compartment able to hold over six people is far removed from the factual aircraft.
- SR-71 Online
- The heart of the SR-71 : the J-58 engine
- The Online Blackbird Museum
- Crash site of SR-71 #953 - Crashed on December 19, 1969
- Blackbirds.net page on the A-12 family
List of military aircraft of the United States - List of reconnaissance aircraft
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