Guide vanes in the 19 foot Pressure Wind Tunnel at Langley Aeronautical Laboratory, National Advisory Committee for Aeronautics, form an ellipse 33 feet high and 47 feet wide. The 23 vanes force the air to turn corners smoothly as it rushes through the giant passages. If vanes were omitted, the air would pile up in dense masses along the outside curves, like water rounding a bend in a fast brook. Turbulent eddies would interfere with the wind tunnel tests, which require a steady flow of fast, smooth air.