North American X-15
In a list filled with superlative and record-breaking aircraft, many would argue the X-15 beats them all. The plane is basically a rocket with a cockpit, as it could achieve beyond-hypersonic (Mach 5, more than five times the speed of sound) speeds and had to be dropped out of a plane before landing on its own. Conceived in the 1950s and flown in the 1960s, the X-15 was built to test the boundaries of flight; its record height in flight was set at just over 350,000 feet (67 miles) above the ground. The X-15 advanced NASA’s (and just before that, NACA’s) understanding of how to build aircraft to deal with different pressures and temperatures as the plane moved at record-breaking speeds and glided down after its rocket stopped giving it thrust. The aircraft is evidence that a wacky design can be practical, too.
