Lockheed SR-71 Blackbird

The Lockheed SR-71 "Blackbird" was an advanced, long-range, Mach 3+ strategic reconnaissance aircraft.It was developed as a black project from the Lockheed A-12 reconnaissance aircraft in the 1960s by the Lockheed Skunk Works.Clarence "Kelly" Johnson was responsible for many of the design's innovative concepts. During reconnaissance missions the SR-71 operated at high speeds and altitudes to allow it to outrace threats. If a surface-to-air missile launch was detected, the standard evasive action was simply to accelerate and outrun the missile

The SR-71 was designed for Mach 3+ flight. The high temperatures generated during Mach 3 flight required its airframe to be made mostly of titanium. To control costs, Lockheed used a more easily worked alloy of titanium which softened at a lower temperature.

The SR-71 was designed to minimize its radar cross-section, an early attempt at stealth design. Finished aircraft were painted a dark blue, almost black, to increase the emission of internal heat and to act as camouflage against the night sky. The dark color led to the aircraft's call sign "Blackbird".

Air inlets

The air inlets had to be designed to allow for cruising at over Mach 3.2, yet keep air flowing into the engines at the initial subsonic speeds. At the front of each inlet was a sharply-pointed movable cone called a "spike" that was locked in its full forward position on the ground and during subsonic flight. As the aircraft accelerated past Mach 1.6, an internal jackscrew withdrew the spike as much as 26 inches (66 cm) inwards;an analogue air inlet computer, based on pitot-static, pitch, roll, yaw, and angle-of-attack inputs, would determine how much movement was required. By moving, the spike tip would withdraw the shock wave, riding on it closer to the inlet cowling until it just touched slightly inside the cowling lip. In this position shock-wave spillage, causing turbulence over the outer nacelle and wing, was minimized while the spike shock-wave repeatedly reflected between the spike centerbody and the inlet inner cowl sides. In doing so, shock pressures were maintained while slowing the air until a Mach 1 shock wave formed in front of the engine compressor

The backside of this "normal" shock wave was subsonic air for ingestion into the engine compressor. This capture of the Mach 1 shock wave within the inlet was called "Starting the Inlet". Tremendous pressures would be built up inside the inlet and in front of the compressor face. Bleed tubes and bypass doors were designed into the inlet and engine nacelles to handle some of this pressure and to position the final shock to allow the inlet to remain "started". Air that is compressed by the inlet/shockwave interaction is diverted directly into the afterburner to be mixed and burned. This configuration is essentially a ramjet and provides up to 70% of the aircraft's thrust at higher mach numbers.Ben Rich, the Skunkworks designer of the inlets, often referred to the engine compressors as "pumps to keep the inlets alive" and sized the inlets for Mach 3.2 cruise, the aircraft's most efficient speed

Stealth and threat avoidance

The SR-71 was the first operational aircraft designed around a stealthy shape and materials. There were a number of features in the SR-71 that were designed to reduce its radarsignature. The first studies in radar stealth technology seemed to indicate that a shape with flattened, tapering sides would reflect most radar energy away from the radar beams' place of origin. To this end, engineers suggested the addition of chines and an inward canting of the vertical control surfaces. Special radar-absorbing materials were incorporated into sawtooth shaped sections of the aircraft's skin, as well as cesium-based fuel additives to reduce the visibility of exhaust plumes to radar. However, the SR-71 was still easily detected on radar while traveling at speed due to its large high-temperature exhaust stream. The SR-71 had a radar cross section (RCS) of around 10 square meters, much greater than the later Lockheed F-117 Nighthawk, which had an RCS equivalent in size to a ball bearing.

Rich's team showed that the radar return was reduced, Kelly Johnson later conceded that Russian radar technology advanced faster than the "anti-radar" technology employed against it. Although equipped with a suite of electronic countermeasures, the SR-71's greatest protection was its top speed, making it almost invulnerable to the era's weapons technologies. In its service life, no SR-71 was shot down, despite attempts to do so. It flew too fast and too high for surface-to-air missile systems and was faster than the Soviet Union's principal interceptor, the MiG-25. Accelerating would typically be enough to evade a missile fired against an SR-71.

Chines

Head-on view of an A-12 on the deck of the Intrepid Sea-Air-Space Museum.

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; Dr. Frank Rodgers, of the Scientific Engineering Institute (a CIA front company), had 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. 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.When the Blackbird was being designed, no other airplane had featured chines, and Lockheed's engineers had to solve problems related to the differences in stability and balance caused by these unusual surfaces. Chines remain an important design feature of many of the newest stealth UAVs, such as the Dark Star, Bird of Prey, X-45 and X-47, since they allow for tail-less stability as well as for stealth.

Aerodynamicists discovered that the chines generated powerful vortices and created additional lift, leading to unexpected aerodynamic performance improvements. The angle of incidence of the delta wings could then be reduced for greater stability and less drag at high speeds; more weight, such as fuel, could be carried to increase range. Landing speeds were also reduced, since the chines' vortices created turbulent flow over the wings at high angles of attack, making it harder for the wings to stall

General characteristics

• Crew: 2 (Pilot and Reconnaissance Systems Officer)
• Payload: 3,500 lb (1,600 kg) of sensors
• Length: 107 ft 5 in (32.74 m)
• Wingspan: 55 ft 7 in (16.94 m)
• Height: 18 ft 6 in (5.64 m)
• Wing area: 1,800 ft² (170 m²)
• Empty weight: 67,500 lb (30,600 kg)
• Loaded weight: 152,000 lb (69,000 kg)
• Max. takeoff weight: 172,000 lb (78,000 kg)
• Powerplant: 2 × Pratt & Whitney J58-1 continuous-bleed afterburning turbojets, 34,000 lbf (151 kN) each
• Wheel track: 16 ft 8 in (5.08 m)
• Wheelbase: 37 ft 10 in (11.53 m)
• Aspect ratio: 1.7

Performance

• Maximum speed: Mach 3.3 (2,200+ mph, 3,530+ km/h, 1,900+ knots) at 80,000 ft (24,000 m)
• Range: 2,900 nmi (5,400 km)
• Ferry range: 3,200 nmi (5,925 km)
• Service ceiling: 85,000 ft (25,900 m)
• Rate of climb: 11,810 ft/min (60 m/s)
• Wing loading: 84 lb/ft² (410 kg/m²)
• Thrust/weight: 0.44