Drag

Drag is the aerodynamic force acting opposite to the aircraft direction of motion through the air. Drag must be overcome by thrust from the engines for the aircraft to maintain or increase speed.

Types of drag:

• Parasite drag: Caused by the aircraft shape and skin friction — increases with speed squared
• Induced drag: A byproduct of lift generation — decreases with speed
• Wave drag: Caused by shock waves at transonic/supersonic speeds

At a specific speed, total drag is minimized — this is the speed for maximum range (best L/D ratio). Aircraft designers use streamlining, winglets, and laminar flow technology to reduce drag.