The Power of Aircraft Engines at Altitude
This is a 1939 NACA-style technical report on aircraft engine performance at altitude, issued by the National Advisory Committee for Aeronautics for aeronautical engineers and test staff. Its pictures are plain line graphs of horsepower, charge pressure and spark plug temperature against altitude, inlet temperature and airspeed, plus a schematic sketch of an altitude test wind tunnel setup; a designer could take from them only the clean grid-and-curve chart style and the sparse labelling conventions.
