The Upside-Down Wing

Aeronautical Engineer Richard Whitcomb literally changed the shape of modern aviation when he designed the "Coke bottle" fuselage -- a narrow-waisted plane body that helps high-speed jets to slip through the sound barrier into supersonic flight. Now, 18 years later, Whitcomb has done it again. He has de veloped a radically new wing that will allow subsonic jets to fly faster, more smoothly and more efficiently.

In today's jetliners, if a pilot allows his speed to reach 85% of the speed of sound, a bell rings and a light flash es to caution him to go no faster. There is good reason for the warning. Beyond that limit, the big ships generate turbulence that causes a drastic loss in efficiency and sometimes dangerous buf feting. Thus, although the sonic barrier is around 660 m.p.h. at the normal jet cruising altitude of 35,000 ft., commercial jets are held down to a speed of about 560 m.p.h.

Ample Incentive. Both the airlines and the military have long been anxious to fly faster in their subsonic jets. So there was ample incentive four years ago for Whitcomb and a team of NASA engineers at the Langley Research Center in Virginia to turn from the investigation of supersonic wing design to the problem of subsonic turbulence.

The source of the trouble was the upper surface of the conventional wing, which has a convex curve to provide lift.* When the plane reaches about 80% of the speed of sound, however, the velocity of the air flowing over the upper side of the wing reaches the sonic barrier. A shock wave forms about half way back from the wing's leading edge, disturbing the airflow and increasing drag--the resistance of air to the plane's passage.

In his efforts to reduce turbulence, Whitcomb finally hit upon the design for what NASA now calls the "supercritical wing." To reduce the peak airflow speed and move the shock wave farther back on the wing, he drastically flattened the curvature of the upper wing surface. To compensate for the loss of lift that resulted, he increased the curvature near the wing's trailing edge and put a concave contour on the underside. "Some people think that I merely turned the wing upside down," Whitcomb says.

Reduced Drag. Wind-tunnel data revealed that when the airflow reached sonic and supersonic velocities along the redesigned upper surface, only a modest shock wave was generated near the trailing edge of the wing. There was negligible turbulence. Although the changes did not affect lift, drag was reduced by as much as 20%.

Elated by the results, NASA has ordered the construction of a flight-test version of Whitcomb's wing. At Edwards Air Force Base in California, the wing will be mounted on a modified F-8 jet-fighter and will undergo test flights in the summer of 1970. If the performance measured in Langley's wind tunnel is duplicated in flight, a new generation of more efficient subsonic jets may soon be cruising major U.S. air routes at speeds as high as 645 m.p.h.

* In flight, air is forced to flow more quickly over the curved topside than past the flat undersurface. Air pressure above the wing is thereby reduced, and the wing develops lift.

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