Reshaping the Delta: Deriving Conical Camber

Having preceded the explication of the swept wing in Jones’s original research, the roots of the delta’s redesign now lay, somewhat ironically, in his expanding upon the slender swept wing research he had first begun at Langley. After the war, Jones had left Virginia’s Tidewater region for the equally pleasant Bay area environment of Sunnyvale, CA, and there had continued his swept wing studies. By 1947, he had evolved a sharply swept symmetrical airfoil planform he considered suitable for a supersonic jet transport. Such a planform, with the leading edges of the wings within the shock cone formed around the vehicle and thus in a region of subsonic flow, could perhaps have a lift-to-drag (L/D) ratio as high as 10, though at the price of much higher landing speeds.[98] Tests of a small model in the Ames 1-foot by 3-foot supersonic tun­nel and a larger one in the Ames 40-foot by 80-foot tunnel encouraged Jones and inspired fellow Ames researchers Charles F. Hall and John C. Heitmeyer to build upon his work. Hall and Heitmeyer considered the behavior of the combined wing-body, with the wing twisted and
given camber (curvature) to evenly distribute the flight loads, deriv­ing a sharply swept and tapered wing configuration that demonstrated an L/D of 8.9 during tunnel tests to Mach 1.53.[99] In the refinement of its planform, it called to mind the shape (though, of course, not the airfoil section) of Whitcomb’s later supercritical transonic transport wing conceptualizations.[100]

Hall and Heitmeyer next broadened their research to examine slen­der deltas likewise featuring aerodynamic twist and camber. In 2 years, 1951-1952, they coauthored a dozen reports, culminating in the issu­ance of a seminal study by Hall in the spring of 1953 that summarized the lift, drag, pitching moment, and load distribution data on a variety of thin delta wings of varying aspect ratios operating from Mach 0.25 (touchdown velocity) to Mach 1.9. Out of this came the concept of lead­ing edge "conical camber”: twisting and rounding the leading edge of a delta wing to minimize performance-robbing drag generated by the wing’s own lifting force. The modified delta had minimal camber at the wing root and maximum camber at the tip, the lineal development of the camber along the leading edge effectively representing the surface of a steadily expanding cone nestled under the leading edge of the wing.[101]

Hall’s conical camber, like Whitcomb’s area rule, came just in time to save the F-102 program. Both were necessary to make it a success: Whitcomb’s area rule to get it through the sound barrier, and Hall’s to give it acceptable transonic and supersonic flying qualities. If over­shadowed by Whitcomb’s achievement—which resulted in the young Langley aerodynamicist receiving the Robert J. Collier Trophy, American aviation’s most prestigious award, in 1954—Hall’s conical camber con­cept was nevertheless a critical one. Comparative flight-testing of the YF-102 at the NACA High-Speed Flight Station at Edwards from late
1954 to mid-1955 with and without conical camber indicated that con­ical camber gave it lower drag and increased its maximum lift-to-drag ratio by approximately 20 percent over a test Mach number range of 0.6 to 1.17, at altitudes of 25,000, 40,000, and 50,000 feet. Transonic sta­bility of the cambered versus symmetrical YF-102 more than doubled, and "no severe pitch-up tendencies were exhibited, except when accel­erating or decelerating through the trim-change region.”[102]

With the advent of conical camber, the age of the practical transonic – supersonic delta wing had arrived. By mid-decade, the F-102’s aero­dynamic deficiencies had been cured, and it was well on its way to ser­vice use.[103] Convair designers were refining the delta planform to generate the F-102’s successor, the superlative F-106, and a four-engine Mach 2+ bomber, the delta wing B-58 Hustler. Overseas, Britain’s Fairey Company had under test a delta of its own, the F. D.2, which would shortly estab­lish an international speed record, while, in France, Dassault engineers were conceptualizing a design that would spawn the Mirage family and be responsible, in 1967, for one of the most remarkable aerial victories of all time. Jones’s supersonic delta vision from over a decade previously had become reality, thanks in part to Whitcomb’s interference studies (which Jones himself would expand at Ames) and Hall’s conceptualiza­tion of conical camber.