Lockheed X-7

The Lockheed X-7, nicknamed the Flying Stove Pipe, was an American unmanned test bed of the 1950s for ramjet engines and missile guidance technology. Development began in December 1946 after the United States Air Force asked for an unmanned ramjet test vehicle able to reach at least Mach 3. Lockheed gave it the in-house designation L-171, and the Air Force first called it PTV-A-1 before it became the X-7 in 1951. The vehicle was dropped from a B-29 or B-50 carrier aircraft, accelerated on a rocket booster and then ran on its ramjet, and it was recovered by a multi-stage parachute that left a nose rod to plant it upright in the ground. Steel and nickel alloy construction coped with air friction heating before titanium was widely used. A total of 130 flights were flown from April 1951 to July 1960, and the X-7 became the basis of the later AQM-60 Kingfisher target drone.