Behm Acoustic Sounder for Aircraft
A 1926 National Advisory Committee for Aeronautics technical memorandum, issued by the NACA for aeronautical engineers and researchers, documenting the Behm acoustic sounder for aircraft. The page shows three photographs captioned Fig. 1 through Fig. 3, and a designer could take from them the stark, documentary look of early aviation instrumentation: a close view of a mounted air-sounder on an airplane, a cramped cockpit of sending and receiving apparatus, and a grid of recorded trace strips.
