Why is there a need for swept wings in aircraft design?

Swept wings are primarily employed in aircraft design to manage aerodynamic performance at higher speeds, particularly as the aircraft approaches the critical Mach number (MCRIT). When an aircraft flies at subsonic speeds, the flow of air over its wings is largely uniform. However, as it approaches transonic speeds, shockwaves begin to form on the wings, which can lead to a substantial increase in drag.

By sweeping the wings back, the effective airfoil shape is altered. This design reduces the wing's thickness-to-chord ratio and delays the onset of the shockwaves, allowing the aircraft to operate efficiently at higher speeds. Consequently, swept wings enable aircraft to achieve their optimal performance and stability as they operate close to or at the critical Mach number, resulting in better fuel efficiency and overall aerodynamics in the transonic flight range.

While factors like noise pollution, weight reduction, and cabin size are important considerations in aircraft design, they are not the primary reasons behind the use of swept-wing configurations. The need to enhance speed characteristics and improve performance in the critical flight regimes is the fundamental reason for incorporating swept wings in modern aircraft engineering.