Lockheed SR-71 Blackbird

The Lockheed SR-71 Blackbird holds the absolute world speed record for an air-breathing aircraft: Mach 3.3 (3,529 km/h), set on July 28, 1976. Designed under absolute secrecy by Lockheed’s Skunk Works division under Kelly Johnson, the SR-71 was a strategic reconnaissance aircraft so fast that its standard defensive tactic against surface-to-air missiles was to simply outrun them. Throughout its 24-year operational career (1966–1990, with a brief return 1994–1998), no SR-71 was ever shot down by a hostile missile.

Building an aircraft to cruise at Mach 3.2 required solving engineering problems that had no precedent. At that speed, aerodynamic friction heats the airframe to over 320°C — too hot for the aluminium used in virtually all other aircraft. The SR-71 was therefore built primarily of titanium, which accounted for 93% of the airframe by weight. This created a new problem: the Cold War US had very limited domestic titanium supplies and had to acquire the metal, often through intermediaries, from the Soviet Union — the same country the SR-71 was designed to spy upon.

The aircraft’s fuel, JP-7, was a specially formulated kerosene so stable it could not be ignited by a match at sea level. It was also used as a heat sink, circulating through the airframe to absorb aerodynamic heat before being burned in the engines. On each mission, the SR-71 burned approximately 130,000 litres of fuel and required air-to-air refuelling shortly after takeoff — the aircraft’s fuel tanks leaked on the ground because the titanium panels were designed with gaps that sealed only when the airframe expanded to operating temperature in flight.