The two types
Induced drag is the drag that results directly from generating lift. As the wing deflects air downward to create lift, it also creates a rearward force component — induced drag. It is highest at high angles of attack (low speed) and decreases as speed increases.
Parasitic drag (also called zero-lift drag) comes from the shape and surface of the aircraft pushing through the air. It includes form drag (from the aircraft's frontal profile) and skin friction. Parasitic drag increases with the square of airspeed — double the speed, four times the parasitic drag.
Quick reference
| Direction | Parallel to relative wind, opposing motion |
| Opposing force | Thrust |
| Induced drag | High at low speed / high AoA — decreases with speed |
| Parasitic drag | Low at low speed — increases with V² |
| Total drag minimum | At the speed where induced = parasitic drag (best L/D speed) |
Best L/D speed: Because induced drag falls with speed and parasitic drag rises, total drag has a minimum at one specific airspeed. This is the best lift-to-drag ratio speed — it's also the most aerodynamically efficient cruise speed and, for a glider, the best glide speed.