NASA Center developed YF-12 supersonic engine research

Supersonic flight became a reality in October 1947 when the Bell X-1 rocket plane broke the sound barrier. NASA's Lewis Research Center (now, NASA Glenn) in Cleveland, which has served as the agency's head of aeropropulsion since its founding in the 1940s., It later helped NASA develop the technology needed to make long supersonic flights possible.

Military aircraft capable of reaching supersonic speeds followed the Bell X-1. In the 1960s, Lockheed's family of Blackbirds (the original A-12, the YF-12 interceptor and the SR-71 reconnaissance vehicle) became the world's first aircraft capable of sustained supersonic speed. However, it has been difficult to extend this capability to large transport aircraft, due to the lack of data collected on propulsion systems during long supersonic flights.

To address issues not identified during design-phase testing of these aircraft and to improve critical technology, Supersonic mixed-compression inlet, as part of a joint NASA/Air Force effort in 1969 the Army loaned two retired YF-12s to the Triton Flight Research Center (today NASA Armstrong). They planned to compare data from YF-12 flights with data collected in wind tunnels at NASA's Ames, Langley and Lewis research centers.

Researchers at Lewis have studied supersonic inlets in wind tunnels since the early 1950s and are in the midst of a comprehensive evaluation of supersonic nozzles and inlets using the F-106 Delta Dart. In this new effort, Lewis was responsible for testing the full-size YF-12 inlet in the center's 10×10 supersonic wind tunnel and analyzing the 32,500-pound thrust Pratt & Whitney J58 engine at the Propulsion Systems Laboratory (PSL).

Although mixed-compression inlets were highly efficient, allowing them to operate as turbojets at subsonic speeds and as ramjets at high Mach numbers, their design made the engines prone to frequent „non-starting” flow disturbances. Unstarts produced instant drag that could stall the engine or cause the aircraft to rapidly roll or yaw. In November 1971, Lewis researchers tested an actual portal from a defunct SR-71 installed at 10×10.

Over the next year, the researchers collected aerodynamic data at different levels in the wind tunnel. They also tested a new gate control system patented by Lewis engineers Bobby Saunders and Glenn Mitchell. This is the first time the system has been tested on full-scale hardware.

The researchers also studied the relationships between the airframe, inlet, engine and control system during normal flight conditions and when experiencing realistic flow disturbances.

In the summer of 1973, a full-scale J-58 engine became the first hardware tested at Lewis. The new PSL is the second highest chamber. For the next year, the researchers captured data under normal conditions and used mesh inlet screens to simulate airflow distortions in aircraft.

The PSL tests measure engine emissions as part of a larger effort to determine the high-altitude emission levels of potential supersonic transports.

The YF-12 program was terminated in 1979 as the agency's aeronautical priorities changed, a year of ground testing in NASA's wind tunnels had already been completed and the YF-12s had completed nearly 300 research flights. The project expanded to include the development of high-temperature instrumentation, airframe pressure and flow mapping, heat loads, and an inlet control system.

NASA engineers have demonstrated that small-scale models can be successfully used to design full-scale supersonic inlets, while flight data have been used to better understand the effect of tunnel interference on submodels and data. Perhaps most importantly, the program at Lewis led to a digital control system that improved the supersonic inlet's response to flow disturbances, virtually eliminating engine restarts.

Many of the program's concepts were integrated into the design of the SR-71 in the early 1980s, and contributed to NASA's continued efforts to achieve supersonic transport aircraft for decades.

Additional Resources:

NASA Facts: Lockheed YF-12

Mach 3+ NASA/USAF YF-12 Flight Research, 1969-1979 Peter Merlin

NASA Facts: SR-71 Blackbird