The North American X-15 is a strong contender for the title of “Everyone’s Favorite X-plane.” Conceived in the 1952-1954 period
Because of the large fuel consumption of its rocket engine, the X-15 was air launched from a B-52 aircraft at about 45,000 feet and speeds upward of 500 mph. Depending on the mission, the rocket engine provided thrust for the first 80 to 120 seconds of flight. The remainder of the normal 8- to 12-minute flight was without power and ended in a 200-mph glide landing.
For “altitude” missions, the X-15 climbed steeply until it exhausted its propellants, then arced upward, unpowered. X-15 reached its peak altitude – 354,200 feet (almost 67 miles) above the Earth’s surface – on 22 August 1963, with NASA pilot Joseph Walker in the cockpit.
Indeed, the X-15 design was so much like that of a space vehicle, with a long and slender aircraft featuring a pointed nose cone. It was a missile-shaped vehicle with an unusual wedge-shaped vertical tail, thin stubby wings, and unique side fairings that extended along the side of the fuselage.
The initial 24 powered flights used two Reaction Motors XLR11 liquid-propellant rocket engines, enhanced to provide a total of 16,000 pounds of thrust as compared to the 6,000 pounds that a single XLR11 provided in 1947 to make the Bell X-1 the first aircraft to fly faster than the speed of sound. The XLR11 used ethyl alcohol and liquid oxygen. Due to the intense heat generated at high-speed, high-altitude flying, the X-15’s body construction consisted of a nickel-chrome alloy covering known as “Inconel X”.
By November 1960, Reaction Motors was able to deliver the XLR99 rocket engine, generating 57,000 pounds of thrust. The remaining 175 flights of the X-15 used XLR99 engines, in a single engine configuration.
The X-15 is the fastest aircraft ever made. After initial test flights in 1959, X-15s became the first aircraft to reach Mach 4, 5, and 6, and to operate well above 30,500 meters. On October 3, 1967, pilot William J. “Pete” Knight flew the X-15 on its fastest flight reaching 7,273 km/h. Among the 12 pilots who flew the X-15 were future Apollo 11 commander Neil Armstrong and Space Shuttle astronaut Joe Engle.
- Crew: One
- Length: 50 ft 9 in (15.47 m)
- Wingspan: 22 ft 4 in (6.81 m)
- Height: 13 ft 3 in (4.04 m)
- Wing area: 200 sq ft (19 m2)
- Empty weight: 14,600 lb (6,622 kg)
- Gross weight: 34,000 lb (15,422 kg)
- Powerplant: 1 × Reaction Motors XLR99-RM-2 liquid-fuelled rocket engine, 70,400 lbf (313 kN) thrust
- Maximum speed: 4,520 mph (7,270 km/h, 3,930 kn)
- Range: 280 mi (450 km, 240 nmi)
- Service ceiling: 354,330 ft (108,000 m)
- Rate of climb: 60,000 ft/min (300 m/s)
- Thrust/weight: 2.07