What is the primary function of integral fuel tanks?

Integral fuel tanks are designed to be leak-proof containers that hold fuel within the structure of the aircraft itself, typically formed by the wings and fuselage. This design utilizes the existing space in the aircraft to store fuel, which not only saves weight and enhances fuel efficiency but also contributes to the overall strength and integrity of the airframe. By creating a sealed environment for the fuel, integral tanks help prevent leaks and maintain safety, ensuring that the fuel is contained securely while the aircraft is in operation.

The other choices, while they may pertain to various aspects of aircraft design, do not capture the essential purpose of integral fuel tanks. They do not primarily serve as weight for stability or for storing luggage, nor do they significantly enhance aerodynamics. Instead, their core function revolves around effectively containing fuel, which is critical for aircraft operation and safety.