Some Noise Requirements for Large Subsonic Wind-Tunnels

From Concluding Remarks: Broadly speaking, model-noise measurement requirements tend to increase somewhat the relative size of tunnel demanded, as compared with aerodynamic requirements. However, a large subsonic tunnel provided primarily for V/STOL aerodynamic testing could certainly permit reliable tests of forward-speed effects on broadband noise as well as on discrete-frequency noise; provided the tunnel incorporated a quiet drive, some acoustic treatment of the tunnel circuit and test-section, and a steady low-turbulence airstream at entry to the test-section even with models in operation. Thus, a new (or modified.) tunnel with test-section size of at least the order of the NASA Ames 40ft x 80ft could accommodate not only noise testing on models with representative noise generators, but also on some full-scale rotors, fan-engine units and aircraft component in probably smaller sizes than tolerated hitherto for aerodynamic testing.