A government test pilot flew a supersonic research aircraft at more than Mach 2, twice the speed of sound, in a historic feat that helped aviation engineers and designers understand high-speed flight and the aerodynamics of angled-wing aircraft.
The World War II era brought significant advances in aviation engine technology, including the development of both jet and rocket engines. Germany deployed the ME-262 jet-powered fighter and the ME-163 rocket-powered interceptor, which flew faster than propeller-driven aircraft. Little was known, however, about the aerodynamics of high-speed flight.
The D-558-II Skyrocket.
By the mid-1940’s, the U.S. government began to explore transonic flight, the flight regime from just below to just above the speed of sound. Breaking the sound barrier in 1947 was the Bell X-1, operated jointly by the U.S. Army Air Forces,
A breakthrough in aviation design and engineering knowledge came from analyses of German data on swept-wing aerodynamics, data that was obtained by the United States in the last years of World War II. Data showed that orienting an aircraft’s wing at an angle that was “swept back” from its fuselage—and therefore making it a swept-wing aircraft—could improve high-speed performance. Adding to the U.S. government’s knowledge was the theoretical aerodynamic calculations on the swept-wing concept by aerodynamics specialist R. T. Jones at NACA. The initial plan for the D-558 program was for the Douglas Aircraft Company
The straight-wing D-558-I
The phase two aircraft, called the Skyrocket, was designed by a team led by Edward H. Heinemann, an engineer who designed combat aircraft during World War II. The team’s objective was to extend the achievements of the Skystreak and expand the range of aeronautical knowledge about high-speed flight, the aerodynamic behavior of various wing shapes, and the procedures required to fly controllably at speeds from about Mach 0.8 to about Mach 1.5.
The Skyrocket was similar in shape to the D-558-I, but the Skyrocket had a long, pointed nose to improve its performance at high speed (it was 45 feet long, compared with the Skystreak at 35.5 feet). The Skyrocket was designed to permit installation of two different engines: a three-thousand-pound-thrust Westinghouse J-34 turbojet engine or a rocket motor. Reaction Motors would build the LR-8-RM5 four-chamber rocket motor, which developed six thousand pounds of thrust, for flight at speeds greater than could be achieved using the jet engine.
Three Skyrockets were built. Douglas Aircraft test pilot John F. Martin
Like most experimental aircraft, the Skyrocket exhibited some unexpected flight characteristics. It had a tendency to roll back and forth during the landing approach. Test pilot Robert Champine
Nonetheless, the swept-wing Skyrocket quickly surpassed the speed and altitude records set by the X-1. By 1951 the Skyrocket reached a speed of Mach 1.88 and an altitude of 83,000 feet. The Navy completed its testing and turned the aircraft over to NACA in September.
NACA engineers added nozzle extensions to the rocket engine to prevent the exhaust gas from interacting with the rudder at supersonic speeds. This modification also increased the rocket’s thrust by 6.5 percent in high-speed flight. Knowing of this increased thrust, NACA’s project engineer Herman O. Ankenbruck developed a flight plan that could propel the Skyrocket to a speed exceeding Mach 2. Also, the NACA team knew the Air Force had been planning the same experiment with its X-1A, an improved version of the X-1.
Ankenbruck’s plan required a perfect performance from the pilot and the aircraft, and it took advantage of cold weather to push the Skyrocket past Mach 2. The NACA crew carefully waxed the Skyrocket’s fuselage to reduce drag. Because alcohol (which fueled the rocket engine) is denser at lower temperature, the team chilled the alcohol so more could be added to the Skyrocket’s fuel tank.
Early on the morning of November 20, 1953, the Skyrocket was carried by the P2B bomber to an altitude of 32,000 feet, as high as the P2B could lift it. After dropping clear of the bomber, NACA test pilot A. Scott Crossfield ignited the Skyrocket’s engine and pointed its nose skyward. Employing Ankenbruck’s flight plan, Crossfield climbed to 72,000 feet, then began a shallow dive. The Skyrocket reached a speed of 1,291 miles per hour, Mach 2.005, just as the fuel ran out. “It was very close, but it was all the airplane had in it,” Crossfield said later. Crossfield became the first pilot to reach Mach 2, the fastest the Skyrocket would ever fly. Crossfield became “the fastest man alive,” but for only three weeks. Chuck Yeager
Crossfield and other NACA pilots continued to fly the Skyrockets for about another year, and then the aircraft were retired. The NACA test flights studied the pressure distribution, structural loads, and heating of the aircraft in a program designed to advance the understanding of high-speed aerodynamics.
The three Douglas Skyrocket research aircraft made a total of 333 flights, setting many speed and altitude records. The Skyrockets were packed with instruments to monitor the forces on the jets’ wings and tails and to determine the lift, drag, and buffeting characteristics of a swept-wing plane at transonic and supersonic speeds. These measurements were critical to the design of future swept-wing aircraft, particularly the supersonic fighters that would be the staple of the U.S. military. Skyrocket flights also determined the effects of external devices, including bombs and fuel drop-tanks, on the flight characteristics of aircraft in the transonic region.
The Skyrocket was critical in helping to determine other flight characteristics of swept-wing aircraft, including measuring the coupling of yaw, or side-to-side motion, and measuring pitch, the up-and-down motion of a plane’s nose. These tests helped to solve the “pitch-up problem” in swept-wing aircraft. The Skyrocket flights also solved the problem of how aircraft stability is affected by rocket-exhaust plumes (plume effects were new phenomena for aircraft designers). The Skyrocket was instrumental as well in the better design of the X-15, which military pilots would use to fly to the edge of space in the 1960’s.
-
Crossfield, Albert Scott, and Clay Blair. Always Another Dawn: The Story of a Rocket Test Pilot. Cleveland, Ohio: World, 1960. Crossfield’s personal account of his experiences as a test pilot for the Skyrocket, the X-15, and other high-speed research aircraft during the 1950’s and 1960’s. -
Hallion, Richard P., and Michael H. Gorn. On the Frontier: Experimental Flight at NASA Dryden. Washington, D.C.: Smithsonian Institution Press, 2003. A 554-page history of the research aircraft operated by NACA and NASA. Contains detailed accounts of record-setting aircraft and flights, from those of the X-1 through the X-15, including Crossfield’s Mach 2 flight. -
Libis, Scott. Skystreak, Skyrocket, and Stiletto: Douglas High-Speed X-Planes. North Branch, Minn.: Specialty Press, 2005. A complete account of the Douglas experimental research aircraft. This well-illustrated, 184-page book includes details of the first Mach 2 aircraft and its flight.
Turbojet Engine Is Used in the First Jet Plane
German V-1 and V-2 Weapons Are Deployed
Yeager Breaks the Sound Barrier
First Nuclear-Powered U.S. Submarine Is Launched
Dyna-Soar Space Plane Is Developed
X-15 Rocket Aircraft Program
McDonnell and Douglas Aircraft Companies Merge
Congress Acts to Control Noise Pollution
First Jumbo Jet Is Delivered to Airlines