What characteristic should flexible lines exhibit to function properly?

Flexible lines are designed to function optimally when they are not stretched tightly. This characteristic is essential for several reasons. Firstly, if a flexible line is overly stretched, it can lose its ability to absorb shock and vibrations, which is crucial in many applications, particularly in aviation and mechanical systems. A relaxed line can better accommodate movements and changes in tension without breaking or becoming damaged, ensuring a smooth operation and reducing the risk of failure.

Additionally, maintaining some slack in the line can help to prevent excessive wear and tear, allowing for an extended lifespan of the material. Proper tension management also aids in maintaining alignment and functionality throughout the system where the line is employed.

The other characteristics listed relate to specific material properties or lengths that may be applicable under certain conditions, but they are not the primary concern for the proper functioning of flexible lines. For example, twisting the lines may affect their performance negatively, while the material composition and length are secondary considerations that depend on the specific application. Therefore, the emphasis on not stretching the flexible lines tightly is most critical for their effectiveness and longevity.