FAA Private Pilot Helicopter (PRH)Helicopter Aerodynamics and SystemsEasy
A flight instructor explains that the total drag acting on a rotating main rotor blade in forward flight consists of profile drag, induced drag, and parasite drag. Which of these is caused by the blade's own airfoil shape and surface friction, and exists even when the blade produces no lift?
- AParasite drag
- BInterference drag
- CInduced drag
- DProfile drag
Show answer & explanationAnswer & explanation
Correct answer: D. Profile drag
Profile drag results from the friction of air passing over the rotor blade's surface and its basic airfoil shape; it exists regardless of the lift being produced. Induced drag is a byproduct of lift generation, while parasite drag comes from non-lifting components moving through the air.
Why the other options are wrong
- A. Parasite drag is associated with non-lifting parts of the aircraft (fuselage, mast, etc.), not the blade's airfoil surface friction.
- B. Interference drag results from airflow disruption where components meet, not a primary rotor drag category taught in this context.
- C. Induced drag is a direct byproduct of producing lift, not present without lift.
Profile Drag
The drag created by the friction of air passing over the rotor blade's surface and its basic airfoil shape, present even when the blade generates no lift.
- One of three main types of rotor drag: profile, induced, and parasite
- Exists independent of lift production
- Increases somewhat with airspeed due to higher airflow velocity
- Distinct from induced drag (lift-related) and parasite drag (non-lifting components)
Memory trick: Profile drag is the blade's 'skin friction tax'—paid even with zero lift.