Reference:  Abbott, Richard. Analysis and Design of Composite and Metallic Flight Vehicle Structures 3 Edition, 2019

A truss is a rigid framework made up of members, such as beams, struts, and bars to resist deformation by applied loads. The truss-framed fuselage is generally covered with fabric or molded composite panels.

The truss-type fuselage frame is usually constructed of 4130 steel tubing welded together in such a manner that all members of the truss can carry both tension and compression loads, reference Figure 22.12.1‑1. In some aircraft, principally the light, single engine models, truss fuselage frames may be constructed of aluminum alloy and may be riveted or bolted into one piece, with cross-bracing achieved by using solid rods or tubes.