Did you know that the YF-12 was the forerunner to the famous and terrifying SR-71? According to NASA, "the YF-12 "Blackbird" was an experimental fighter-interceptor version of the Lockheed A-12 reconnaissance aircraft."
A record-breaking aircraft
The aircraft was a record-breaker achieving a speed record of 2,070.101 mph and an altitude record of 80,257.65 feet on May 1, 1965. Three YF-12 would ultimately be developed, but only two would survive.
"Under its research agreement with NASA, the Air Force provided the agency with two YF-12As in 1969. On June 24, 1971, one of the planes experienced an in-flight fuel line failure that led to a fire in the right engine," stated NASA.
The pilots were unable to save the smoking aircraft and chose to eject. They were not injured, but the YF-12A was lost forever. It was, however, replaced by another third YF-12 plane that was slightly different than the previous two.
"The plane was replaced by a "YF-12C." The YF-12C (so-called) differed from the YF-12A in that the A-model had a round nose while the C-model had its chine carried forward to the nose of the airplane (see three-views below). There were other differences in internal and external configuration, but the two aircraft shared common inlet designs, structural concepts, and subsystems," explained NASA.
A research plane
The YF-12 was used by NASA as a research plane mainly due to its ability to sustain a cruise speed greater than Mach 3. The aircraft was fabricated primarily from titanium alloy, which enabled it to withstand skin temperatures of over 500º F.
The space agency used the aircraft to undertake research "in aerodynamics, propulsion, controls, structures, subsystems and other areas such as the physics of the upper atmosphere, noise tests and measurements, and handling qualities."
Those tests were complemented by a series of wind tunnel tests, laboratory experiments, and analyses resulting in over 125 technical reports whose information was later incorporated into the design of other supersonic aircraft.
Perhaps the most significant of the studies undertaken during the YF-12's lifespan was the Cold Wall Experiment. This experiment consisted of exposing a cooled cylinder to the friction and heat of a Mach 3 environment.
"The cylinder, which was hollow, equipped with sensors, and mounted beneath the aircraft, was cooled with liquid nitrogen and insulated from the heat that was generated during flight. When the plane neared Mach 3, a primer cord was used to blow the insulation from the frigid cylinder," explained NASA.
"Temperature, pressures, and friction readings from the cylinder in flight were compared with information developed from theoretical analysis and wind-tunnel simulation. The findings were a major achievement in fluid dynamics research."
Eventually, however, in 1977, the YF-12 program was ordered to be shut down, but NASA found it so useful that it used some of its own residual funding to keep the project going well into 1979. Like all good things, the YF-12 did come to an end and was replaced by a faster version, but its history is undeniable.