What area is a fillet seal primarily used in?

A fillet seal is primarily used in fuel cells due to its unique design and function that effectively accommodates the specific requirements for sealing in this application. In aircraft, fuel cells are critical components that hold and manage fuel, and they must be watertight to prevent leaks.

Fillet seals are advantageous in this context because they create a smooth transition between two surfaces, ensuring a secure and flexible seal that can withstand the fuel's properties and prevent leakage. The geometry of a fillet seal helps in distributing stress along the joint, which is essential in areas that undergo thermal expansion or contraction, as well as movements due to air pressure changes.

While other components, such as ailerons and control surfaces, also require sealing, the type of seals used in those applications is typically different, focusing more on aerodynamic efficiency than on the specific fuel concerns seen in fuel cells. Canopies are mainly concerned with visibility and aerodynamics rather than fluid containment, which further differentiates their sealing requirements from those of fuel cells.