What is the primary purpose of a swept wing in aircraft design?

The primary purpose of a swept wing is to prevent the aircraft from reaching Mach Critical, or MCRIT. As an aircraft approaches the speed of sound, shock waves begin to form on the wings, which can lead to increased drag and a loss of lift. Swept wings are designed in such a way that they effectively delay the onset of these shock waves by reducing the effective angle of attack as the aircraft approaches high speeds. This design allows for higher cruising speeds and improves overall aerodynamic efficiency, particularly in transonic and supersonic flight regimes.

While enhancing fuel efficiency is a beneficial outcome of using swept wings, the principal mechanism at play is the ability to manage airflow and delays in shock wave formation. Additionally, while swept wings can contribute to overall structural weight savings in some designs, that is not their primary design intent.