Inventing the Supercritical Wing

Whitcomb was hardly an individual content to rest on his laurels or bask in the glow of previous successes, and after his success with area rul­ing, he wasted no time in moving further into the transonic and super­sonic research regime. In the late 1950s, the introduction of practical subsonic commercial jetliners led many in the aeronautical community to place a new emphasis on what would be considered the next logical step: a Supersonic Transport (SST). John Stack recognized the impor­tance of the SST to the aeronautics program in NASA in 1958. As NASA placed its primary emphasis on space, he and his researchers would work on the next plateau in commercial aviation. Through the Supersonic Transport Research Committee, Stack and his successor, Laurence K. Loftin, Jr., oversaw work on the design of a Supersonic Commercial Air Transport (SCAT). The goal was to create an airliner capable of outper­forming the cruise performance of the Mach 3 North American XB-70 Valkyrie bomber. Whitcomb developed a six-engine arrowlike highly swept wing SST configuration that stood out as possessing the best lift – to-drag (L/D) ratio among the Langley designs called SCAT 4.[194]

Manufacturers’ analyses indicated that Whitcomb’s SCAT 4 exhib­ited the lowest range and highest weight among a group of designs that would generate high operating and fuel costs and was too heavy when compared with subsonic transports. Despite President John F. Kennedy’s June 1963 commitment to the development of "a commercially success­ful supersonic transport superior to that being built in any other country in the world,” Whitcomb saw the writing on the wall and quickly disas­sociated himself from the American supersonic transport program in 1963.[195] Always keeping in mind his priorities based on practicality and what he could do to improve the airplane, Whitcomb said: "I’m going back where I know I can make things pay off.”[196] For Whitcomb, practi­cality outweighed the lure of speed equated with technological progress.

Whitcomb decided to turn his attention back toward improving sub­sonic aircraft, specifically a totally new airfoil shape. Airfoils and wings had been evolving over the course of the 20th century. They reflected the ever-changing knowledge and requirements for increased aircraft perfor­mance and efficiency. They also represented the bright minds that devel­oped them. The thin cambered airfoil of the Wright brothers, the thick airfoils of the Germans in World War I, the industry-standard Clark Y of the 1920s, and the NACA four – and five-digit series airfoils innovated by Eastman Jacobs exemplified advances in and general approaches toward airfoil design and theory.[197]

Despite these advances and others, subsonic aircraft flew at 85-percent efficiency.[198] The problem was that, as subsonic airplanes moved toward their maximum speed of 660 mph, increased drag and instability devel­oped. Air moving over the upper surface of wings reached supersonic speeds, while the rest of the airplane traveled at a slower rate. The plane had to fly at slower speeds at decreased performance and efficiency.[199]

When Whitcomb returned to transonic research in 1964, he specifi­cally wanted to develop an airfoil for commercial aircraft that delayed the onset of high transonic drag near Mach 1 by reducing air friction and turbu-

lence across an aircraft’s major aerodynamic surface, the wing. Whitcomb went intuitively against conventional airfoil design, in which the upper sur­face curved downward on the leading and trailing edges to create lift. He envisioned a smoother flow of air by turning a conventional airfoil upside down. Whitcomb’s airfoil was flat on top with a downward curved rear sec­tion.[200] The shape delayed the formation of shock waves and moved them further toward the rear of the wing to increase total wing efficiency. The rear lower surface formed into deeper, more concave curve to compen­sate for the lift lost along the flattened wing top. The blunt leading edge facilitated better takeoff, landing, and maneuvering performance. Overall, Whitcomb’s airfoil slowed airflow, which lessened drag and buffeting, and improved stability.[201]

With the wing captured in his mind’s eye, Whitcomb turned it into mathematical calculations and transformed his findings into a wind tun­nel model created by his own hands. He spent days at a time in the 8-foot Transonic Pressure Tunnel (TPT), sleeping on a nearby cot when needed, as he took advantage of the 24-hour schedule to confirm his findings.[202]

Just as if he were still in his boyhood laboratory, Whitcomb stated that: "When I’ve got an idea, I’m up in the tunnel. The 8-foot runs on two shifts, so you have to stay with the job 16 hours a day. I didn’t want to drive back and forth just to sleep, so I ended up bringing a cot out here.”[203]

Whitcomb and researcher Larry L. Clark published their wind tunnel findings in "An Airfoil Shape for Efficient Flight at Supercritical Mach Numbers,” which summarized much of the early work at Langley. Their investigation compared a supercritical airfoil with a NASA airfoil. They concluded that the former developed more abrupt drag rise than the latter.[204] Whitcomb presented those initial findings at an aircraft aerody­namics conference held at Langley in May 1966.[205] He called his new inno­vation a "supercritical wing” by combining "super” (meaning "beyond”) with "critical” Mach number, which is the speed supersonic flow revealed itself above the wing. Unlike a conventional wing, where a strong shock wave and boundary layer separation occurred in the transonic regime, a supercritical wing had both a weaker shock wave and less developed boundary layer separation. Whitcomb’s tests revealed that a supercriti­cal wing with 35-degree sweep produced 5 percent less drag, improved stability, and encountered less buffeting than a conventional wing at speeds up to Mach 0.90.[206]

Langley Director of Aeronautics Laurence K. Loftin believed that Whitcomb’s new supercritical airfoil would reduce transonic drag and result in improved fuel economy. He also knew that wind tunnel data alone would not convince aircraft manufacturers to adopt the new airfoil. Loftin first endorsed the independent analyses of Whitcomb’s idea at the Courant Institute at New York University, which proved the viability of the concept. More importantly, NASA had to prove the value of the new technology to industry by actually building, installing, and flying the wing on an aircraft.[207]

Just as if he were still in his boyhood laboratory, Whitcomb stated that: "When I’ve got an idea, I’m up in the tunnel. The 8-foot runs on two shifts, so you have to stay with the job 16 hours a day. I didn’t want to drive back and forth just to sleep, so I ended up bringing a cot out here.”[208]

Whitcomb and researcher Larry L. Clark published their wind tunnel findings in "An Airfoil Shape for Efficient Flight at Supercritical Mach Numbers,” which summarized much of the early work at Langley. Their investigation compared a supercritical airfoil with a NASA airfoil. They concluded that the former developed more abrupt drag rise than the latter.[209] Whitcomb presented those initial findings at an aircraft aerody­namics conference held at Langley in May 1966.[210] He called his new inno­vation a "supercritical wing” by combining "super” (meaning "beyond”) with "critical” Mach number, which is the speed supersonic flow revealed itself above the wing. Unlike a conventional wing, where a strong shock wave and boundary layer separation occurred in the transonic regime, a supercritical wing had both a weaker shock wave and less developed boundary layer separation. Whitcomb’s tests revealed that a supercriti­cal wing with 35-degree sweep produced 5 percent less drag, improved stability, and encountered less buffeting than a conventional wing at speeds up to Mach 0.90.[211]

Langley Director of Aeronautics Laurence K. Loftin believed that Whitcomb’s new supercritical airfoil would reduce transonic drag and result in improved fuel economy. He also knew that wind tunnel data alone would not convince aircraft manufacturers to adopt the new airfoil. Loftin first endorsed the independent analyses of Whitcomb’s idea at the Courant Institute at New York University, which proved the viability of the concept. More importantly, NASA had to prove the value of the new technology to industry by actually building, installing, and flying the wing on an aircraft.[212]

The major players met in March 1967 to discuss turning Whitcomb’s concept into a reality. The practicalities of manufacturing, flight char­acteristics, structural integrity, and safety required a flight research program. The group selected the Navy Chance Vought F-8A fighter as the flight platform. The F-8A possessed specific attributes that made it ideal for the program. While not an airliner, the F-8A had an easily removable modular wing readymade for replacement, fuselage-mounted landing gear that did not interfere with the wing, engine thrust capable of opera­tion in the transonic regime, and lower operating costs than a multi-engine airliner. Langley contracted Vought to design a supercritical wing for the F-8 and collaborated with Whitcomb during wind tunnel testing begin­ning during the summer of 1967. Unfortunately for the program, NASA Headquarters suspended all ongoing contracts in January 1968 and Vought withdrew from the program.[213]