What does a monocoque fuselage primarily rely on for its strength?

A monocoque fuselage primarily relies on the skin or covering for its strength, which is a key characteristic of this design approach. In a monocoque structure, the external skin bears the loads and helps to maintain the shape of the fuselage. This construction method eliminates the need for an internal framework, making the fuselage lightweight yet strong and capable of withstanding aerodynamic stresses. The continuous surface of the skin distributes the loads across the entire structure, enhancing structural integrity and efficiency.

The other options do not accurately represent the main characteristic of a monocoque design. While internal frame structures might provide additional support in other types of fuselage designs, they are not a defining feature of a monocoque fuselage. Engine support is crucial for the overall aircraft structure but is not specific to the monocoque's strength characteristics. Wing connections, while important for the aircraft's stability and overall performance, do not contribute to the inherent strength of the monocoque fuselage itself. Thus, the focus on the skin or covering as the primary strength element is what makes the monocoque design unique and effective.