3D Airflow & Induced Drag

081-01-04Pablo Asensio Martínez2026-04-011 min

Wing Tip Vortices

On a finite wing (3D), air flows from the high-pressure area (under the wing) to the low-pressure area (over the wing) around the wing tip.

  • This creates a rotating vortex at each wingtip.
  • Direction: Inwards over the top surface, Outwards under the bottom surface.
  • Result: Downwash behind the wing.

Induced Drag ($D_i$)

The downwash tilts the local relative airflow downwards.

  • The lift vector (perpendicular to airflow) is tilted backwards.
  • The horizontal component of this tilted lift is Induced Drag.
  • Formula: $ D_i \propto \frac{L^2}{\rho V^2 \times AR} $ Or in coefficient form: $ C_{D_i} = \frac{C_L^2}{\pi \cdot AR \cdot e} $

Factors Affecting Induced Drag

  1. Speed: Induced drag is inversely proportional to $V^2$. High at low speed (Take-off/Landing). Low at high speed.
  2. Lift: Proportional to $L^2$. Heavier aircraft = More lift needed = More induced drag.
  3. Aspect Ratio (AR): High AR (long narrow wings like gliders) reduces tip vortices and induced drag.
  4. Winglets: Physical barriers that reduce the flow around the tip, reducing vortex strength and induced drag.

Wake Turbulence

The vortices persist behind the aircraft and constitute Wake Turbulence, which can be hazardous to following aircraft (especially light ones).