Lockheed CL-400 Suntan

High Quality Content by WIKIPEDIA articles! Suntan was the code-name of a prototype reconnaissance aircraft program, with the goal of creating a much faster and higher-altitude successor to the U-2, enabled by the use of liquid hydrogen (LH2) as fuel. From 1956-1958, the United States Air Force funded a highly secretive program of research and development on the aircraft (the CL-400, designed at the Lockheed Skunk Works) and engine design, and made significant investments in large-scale LH2 production. In addition to Lockheed, Pratt and Whitney played a major part. Program successes included the concept design of a Mach 2.5 aircraft capable of flying at 30,000 meters, and successful conversion of an existing turbojet engine to run on liquid hydrogen, as well as 25+ hours of testing on a customized LH2 engine design.