Enter Robert T. Jones

"R. T.” Jones was a brilliant, flight-obsessed, and largely self-taught fluid dynamicist, having dropped out of the University of Missouri to join a flying circus, then working as a designer for Nicholas-Beazley, a small Missouri aircraft company. When the Great Depression collapsed the firm, his father used political connections as Chairman of the local Democratic Party to secure Jones a job running elevators in the U. S. Capitol. In his spare time and evenings, he studied mathematics and aerodynamics with Albert Zahm, the aeronautics Chair at the Library of Congress, and with Max Munk at Catholic University. Despite his lack of a formal engineering degree, through the efforts of Representative David Lewis (a homespun Maryland progressive with a strong interest in self-improvement who had taken math instruction from the young elevator operator), Jones received a temporary appointment as a "sci­entific aide” to the NACA. There, he quickly proved such a gifted and insightful researcher that he soon secured a coveted permanent posi­tion at Langley, consorting with the likes of John Stack, Eastman Jacobs, and Theodore Theodorsen.[17]

As he considered Griswold’s "glomb,” Jones recognized that its extremely low aspect ratio shape (that is, a shape having a very long

wing root in relation to its total wingspan) could not be adequately ana­lyzed using conventional Prandtl-rooted "lifting line” theory. Instead, Jones drew on the work of his mentor Munk, using papers that Munk had written on the flow of air around inclined airship hulls and swept wings, and one by the Guggenheim Aeronautical Laboratory’s Hsue-shen Tsien, a von Karman associate at the California Institute of Technology (Caltech), on airflow around inclined bodies of revolution. He analyzed it using linear equations governing two-dimensional incompressible flow, con­sidering his results of little practical value, recalling three decades later, "I thought, well, this is so crude, nobody would be interested. So I just hid it in my desk.”[18]

But it sparked his curiosity, and in January 1945, by which time he was busy thinking about nonlinear compressible flows, he had a rev­elation: the equations he had developed months earlier for the glomb analysis could be applied to a low aspect triangular wing operating in supersonic flow, one whose wing-leading edges were so sharply swept as to place them within the shock cone formed around the vehicle and hence operating in subsonic flow. In these conditions, the wing was essentially "fooled” into behaving as if it were operating at a much lower Mach number. As Jones recalled, "It finally dawned on me that the slen­der wing theory would hold for compressible flow and even at supersonic speed if it were near the center of the Mach cone. So, I immediately got the paper out and I added the compressible flow parts to it, which was really the important part, and then I wondered well, why is it that this slender wing doesn’t have an effect on compressibility? Then I realized that it was because the obliquity of the edge and that this is the sim­ple sweep theory and would work in spite of the compressibility effect. So, I wrote a paper which incorporated the slender wing theory and also sweep theory.”[19] Jones then moved from considering a slender triangular delta [Д] to the sharply sweptback wing [л], the reverse of

Germany, where the high-speed swept wing had preceded, not followed, the delta.[20]

Jones’s delta and swept wing utilized, for their time, very thin airfoil sec­tions, ones typical of supersonic aircraft to come. In contrast, German swept and delta wing developer Alexander Lippisch had employed much thicker sections that proved unsuitable for transonic flight. His tailless rocket – propelled swept wing Me 163 Komet ("Comet”) interceptor, for example, essentially became uncontrollable at speeds slightly above Mach 0.82 thanks to stability changes induced by shock wave formation on its relatively thick wing. His design for a rocket-boosted, ramjet-powered delta fighter, the P 13, had such thick wing and tail sections—the pilot actually sat within the leading edge of the vertical fin—that it could never have achieved its desired transonic performance. As discussed subsequently, postwar NACA tests of a captured glider configuration of this design, the DFS DM-1, confirmed that transonic delta wings should be far thinner, with sharper leading edges. As a consequence, NACA researchers rejected the Lippisch approach, and, though some of them tried extrapolations of his designs (but with lower thickness-chord ratios and sharper leading edges), the NACA (and industry as well) adapted instead the thin slender delta, a la Jones.[21]