Graphite (carbon) composites are selected for aircraft structures primarily when which property is most important?

• A. Used when weight reduction is the main goal
• B. Used when cost is a priority
• C. Used when stiffness is the prime requirement
• D. Used when electrical conductivity is required

Answer: (C)

Graphite carbon fiber composites are chosen for aircraft structures primarily for their exceptional stiffness-to-weight ratio. In flight, keeping deflection under load and controlling aeroelastic behavior are crucial, and stiffness directly affects shape retention, flutter margins, and load path efficiency. Carbon fibers offer a very high modulus, so when they are embedded in a lightweight matrix and laid up in directions that suit the load, you get a structure that is very stiff without adding much weight. This stiffness can be tailored to meet specific structural requirements, which is why these materials are favored for primary structures where rigidity is key. While weight reduction is a benefit of using composites, and cost and conductivity are considerations, they are not the primary driver like stiffness is.