Refer to figure.
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
Some parasite drag is produced in the hover by the rotor downwash striking the fuselage, but the effect is small and, thus, ignored. So, the parasite drag is only considered as a function of the forward speed of the helicopter.
As forward speed increases, the parasite drag increases too. More specifically, the parasite drag increases with the square of the speed and quickly becomes very significant, unlike rotor profile drag which increases only slightly with forward airspeed.
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