The Wing Planform
A wing's planform — its shape viewed from above — determines most of its aerodynamic character. Aspect ratio controls induced drag, sweep governs transonic behavior, and taper ratio affects the spanwise lift distribution. Every aircraft represents a specific compromise among these parameters, optimized for its mission. A long-range airliner needs high AR and moderate sweep; a dogfighter needs low AR and high sweep for agility.
Aspect Ratio and Induced Drag
Induced drag is the penalty for generating lift in a finite wing. Air leaks around the wingtip from high pressure below to low pressure above, creating trailing vortices. Higher aspect ratio wings have less tip leakage relative to their span, producing weaker vortices and less induced drag. The relationship is direct: doubling AR approximately halves the induced drag coefficient for the same lift. This is why albatrosses and sailplanes share the same slender wing shape.
Sweep: Cheating the Sound Barrier
When an aircraft approaches Mach 1, shock waves form on the wing and drag increases dramatically. Wing sweep reduces the effective Mach number felt by the wing cross-section — if the wing is swept 30°, the perpendicular flow component is only cos(30°) ≈ 0.87 times the flight speed. This allows higher cruise speeds before drag divergence. The Boeing 707 (1958) was the first successful swept-wing airliner, establishing the template for all modern jets.
Taper and Lift Distribution
An elliptical lift distribution minimizes induced drag — Ludwig Prandtl proved this in 1920. While an elliptical wing planform achieves this naturally (like the Spitfire), it is expensive to manufacture. A trapezoidal wing with a taper ratio near 0.4 closely approximates the elliptical distribution at far lower cost. Modern wings fine-tune the distribution with twist (washout), varying airfoil sections along the span, and carefully positioned winglets.