Parasite drag describes the drag caused by the non-lifting components of the helicopter, most notably the fuselage and its components.

Like the Profile drag, the Parasite drag is made up of:

• Skin friction,
• Form drag
• Interference drag

Interference drag is caused when the different local airflows around the helicopter collide into each other causing vortices or turbulent flow.

1. Removed doors increase the interference drag (part of the parasite drag), because the airflows around the helicopter do not pass so smoothly.

2. External mounted equipment (hoist/winch) increases the parasite drag, because the helicopter's frontal profile increases.

3. Extended landing gear will also increase the parasite drag, because both frontal profile increases and the airflow beneath the helicopter does not pass so smoothly.

As a result, a bigger pitch angle to provide the total rotor thrust required and more power is required to overcome the increased parasite drag. For a given total rotor thrust and power available, the power margin (power available - power required) will decrease, thus reducing the helicopter's climb performance and as result the take-off distance must increase to clear any obstacle along the take-off flight path by the regulatory vertical clearance.