What type of seal uses a layer of sealant between two fastened overlapping surfaces?

The correct answer is the Fay seal, which is characterized by the application of a layer of sealant between two overlapping surfaces that have been fastened together. This type of seal creates a barrier to fluid and gas, making it effective for maintaining airtight and watertight conditions in various aerospace components.

Fay seals are particularly utilized in the assembly of airplane fuselages and wings where the structural integrity of the joint is critical, and the sealant plays a vital role in protecting the internal surfaces from exposure to environmental factors. The design inherently allows for load distribution between the surfaces while also accommodating any potential thermal expansion or contraction that might occur during operation.

Understanding the specific function and application of Fay seals is essential for aerospace mechanics, as it helps in ensuring the longevity and reliability of aircraft structures.