What is the purpose of longerons in a semi-monocoque fuselage?

Longerons play a critical structural role in a semi-monocoque fuselage. They are longitudinal members that run the length of the aircraft and are designed primarily to resist bending loads. This resistance is essential because the fuselage must maintain its shape and integrity under various loads encountered during flight, such as aerodynamic forces and gravitational forces during maneuvers.

In a semi-monocoque design, the skin is reinforced by various structural elements, among which the longerons are fundamental. They work in conjunction with other components like bulkheads and stringers to distribute loads evenly across the structure. This synergy allows the fuselage to achieve strength without excessively increasing weight, thereby ensuring optimal performance and safety.

The other choices highlight benefits that are not central to the primary function of longerons. While reducing drag and enhancing aesthetic design may be important considerations in aircraft design, they do not directly relate to the structural integrity and load distribution functions that longerons provide. Hence, option C accurately captures the essential purpose of longerons in maintaining the strength and rigidity of a semi-monocoque fuselage.