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SR-71 Blackbird

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The  SR-71 (Image of a trainer version. Note the second canopy)
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The USAF SR-71 (Image of a trainer version. Note the second canopy)

The Lockheed SR-71 Type A, 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 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 has ever been shot down.

Contents

History

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 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). The entire trip took only 68 minutes. The SR-71 also holds the record for flying from New York to London, an incredible 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, the fastest commercial aircraft flying as of 2005, averages 7 hours.)

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 Mildenhall, England. The aircraft was flown to the United States Air Force Museum near Dayton, Ohio 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.

Variants

Missing image
MD-21_Blackbird_rearview.jpg
D-21B Drone mounted on MD-21 Blackbird

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 only surviving M-21 is on display, along with a D-21B Drone, at the Museum of Flight in Seattle.

Details

Missing image
SR-71_flight_instruments.triddle.jpg
The flight instrumentation of SR-71 Blackbird

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 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.

The JP-7 jet fuel is interesting in its own right: originally developed for the A-12 Oxcart plane in the late 1950s, it has an extremely high flashpoint to cope with the heat, to the extent that a match dropped in a bucket of JP-7 does not ignite it. The fuel also contains fluorocarbons to increase its lubricity, an oxidising agent to enable it to burn in the engines, and even a caesium compound, A-50, which disguises the exhaust's radar signature. As a result, JP-7 is said to be more expensive than malt Scotch whisky, which gives some idea of how much a single SR-71 mission would have cost.

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

An SR-71 in flight
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An SR-71 in flight

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 aviation buffs 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 in any currently known configuration. Specifically, these groups cite the specific maximum temperature for the compressor inlet of 427C. 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.

There is a smaller group of individuals that believe the SR-71 is already capable of Mach 4 or greater. This is supported primarily by the reconnaissance flights where the mission times and distances travelled could only be accounted for by speeds between Mach 3.6 and 4.1. It is projected by a few that later improved craft might approach speeds 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 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 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.

SR-71 in fiction

The Marvel Comics superhero team the X-Men fly a custom high-performance airplane called the "Blackbird". The name is no coincidence; originally the plane was supposed to be a modified SR-71, but the capacities of the aircraft, including a crew compartment able to hold over six people and VTOL capability, were far removed from the factual aircraft. In recent years the "Blackbird" depicted in the comics is a futuristic new design, unrelated to the SR-71.

The SR-71 is also featured (somewhat unrealistically) in the 1985 movie D.A.R.Y.L..

In the cartoon G.I. Joe, the COBRA Night Raven and the Joe's special force Sky Patrol's Sky Raven look similar to the Blackbird. The Night Raven is the only one with the pilot drone.

An M-21 and D-21 drone were also featured in the game Metal Gear Solid 3: Snake Eater. The D-21 drone used in Metal Gear Solid 3: Snake Eater was modified to accomodate a passenger, that would be dropped in a parachute jump during flight.

Specifications

General characteristics

  • Crew: 2
  • Length: 107 ft 5 in (32.7 m)
  • Wingspan: 55 ft 7 in (16.9 m)
  • Height: 18 ft 6 in (5.6 m)
  • Wing area: 1,800 ft² (170 m²)
  • Empty: 65,000 lb (29,000 kg)
  • Loaded: 170,000 lb (77,000 kg)
  • Maximum takeoff: lb ( kg)
  • Powerplant:Pratt & Whitney J58-1 continuous bleed-afterburning turbojets; 32,500 lbf (145 kN) thrust

Performance

  • Maximum speed: Mach 3.32
  • Maximum speed: 2,193 knots (4,062 km/h)
  • Combat range: 2,900 miles (5,400 km)
  • Ferry range: miles ( km)
  • Service ceiling: 85,000 ft (26,000 m)
  • Rate of climb: ft/min ( m/min)
  • Wing loading: 94 lb/ft² (460 kg/m²)
  • Thrust/weight ratio: 0.382:1

See also

Other photographs

External links

Related content

Related development: A-12 Oxcart - Lockheed YF-12 - Lockheed M-21

Comparable aircraft:

Designation sequence: XB-68/SM-68 - RB-69 - XB-70 - SR-71 - XGAM-72 - XSM-73 - SM-75

Related lists: List of military aircraft of the United States - List of reconnaissance aircraft


Lists of Aircraft | Aircraft manufacturers | Aircraft engines | Aircraft engine manufacturers

Airports | Airlines | Air forces | Aircraft weapons | Missiles | Timeline of aviation

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