Tandem Air Propellers
A 1937 NASA technical report on tandem air propellers, with a schematic section of a propeller dynamometer. The record is thin, so the drawing itself is the main evidence. The single figure shows a cutaway of a motor-and-gear housing with field and armature labelled, a shaft running to two propeller discs marked P1 and P2, and a gear train. A designer could take from it a clean, labelled engineering diagram style with straight leader lines and lettered call-outs.
