by 14-inch wind tunnel branch. This was the first hypersonic tunnel at Ames, capable of speeds varying from Mach 2.7 to 6.3. His early research on asymmetric nozzle contours of variable Mach number proved critical to the design of new hypersonic wind tunnels for NACA. He developed a new aerodynamic theory of second-order shock expansion that was used to predict the stability of slender vehicles flying at hypersonic speeds, including missiles and rockets like the Polaris and Aerobee. The American Institute of Aeronautics and Astronautics (AIAA) Lawrence Sperry Award in 1957 recognized the value of Sy’s early work on hypersonic flows.
As a successor to that tunnel, Sy and Alfred Eggers designed the 3.5-foot hypersonic wind tunnel, capable of tests between Mach 5 and 14. The tunnel was a blow-down one, with air heated through a pebble bed heater to prevent liquefaction. Sy became chief of that branch in 1959, as the tunnel became the center of heat transfer studies for reentry vehicles, including the Apollo capsule. The aerothermodynamics database for detailed Space Shuttle design was later compiled in this tunnel, and more than a quarter of all wind tunnel testing done for the Space Shuttle was done there. With his colleagues in this tunnel, Sy did early sketches of some vehicles that the National Aeronautics and Space Administration (NASA) still hopes to build, such as hypersonic skip gliders, direct-to-orbit spacecraft, and hypersonic transports. Sy and Eggers did work underlying the design of the XB-70 Valkyrie, an experimental bomber capable of Mach 3, as well as the M2 lifting bodies, the research precursors to the Space Shuttle orbiter. His work on the M2 was recognized with a 1964 NASA Inventions and Contributions Award. With Eggers he also wrote an influential chapter on hypersonic flow for the Handbook of Engineering Mechanics (New York: McGraw-Hill, 1962).
In 1963 he established and led the Mission Analysis Division, an elite think tank located at Ames but organizationally part of the NASA Headquarters Office of Advanced Research and Technology. Sy’s group defined future aircraft and space missions for NASA as well as the long-term research needed to achieve those goals. There he continued refining concepts