In this historical photo from the U.S. space agency, Langley installed an experimental low-drag test panel on the wing of a Douglas B-18 airplane in the spring of 1941. The panel was fitted with suction slots and pressure tubes for a free flight investigation of the transition from laminar to turbulent flow in the boundary layer. The pressure at each tube was measured by liquid manometers installed in the fuselage.
The National Advisory Committe on Aeronautics (NACA) was a precursor to NASA. NACA was created by Congress in 1915.
Each weekday, SPACE.com looks back at the history of spaceflight through photos (archive).
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