Semi-monocoque is the most popular type of structure used in aircraft nowadays, composed of a long tube shape with a large number of longitudinal reinforcements (stringers) and circumferential reinforcements (frames) which carry all stresses .
Source: wiktionary
The semi-monocoque construction provided higher strength with less weight, the aerodynamic shape required less horsepower to pull (improving gas mileage) and it provided smoother towing.
Source: wiktionary
Incredibly strong, and capable of supporting the weight of several people, the cardboard laminates operate as semi-monocoques with an intermediary plywood armature.
Source: wiktionary