15 / 20
Which statement below is correct regarding the power required for a helicopter flight?
  • A
    Power required to overcome induced drag and profile drag decreases with increasing TAS whereas the power required to overcome parasite drag increases.
  • B
    Power required to overcome induced drag decreases with increasing TAS whereas the power required to overcome parasite drag and profile drag increases.
  • C
    Power required to overcome induced drag increases with increasing TAS whereas the power required to overcome parasite drag and profile drag decreases.
  • D
    Power required to overcome induced drag, parasite drag and profile drag increases with increasing TAS.
Refer to figure.

Parasite drag is the drag generated by the non-lifting components of the helicopter’s fuselage and is significantly affected by the increased speed. So, as speed increases, parasite drag increases as well, thus it is minimum at hover where speed is zero.

In general, it states that the Power required is: Drag x TAS. Thus, the Parasite Power required to overcome the parasite drag is: Parasite drag x TAS. Since, the Parasite drag increases with speed, then the Parasite Power to overcome the parasite drag increases with speed, as well.


Induced drag or lift-dependent drag or lift induced drag is the drag which is created or “induced” as an inevitable consequence of generating lift.

In the hover in still air, the induced airflow increases, decreasing the effective angle of attack, so the lift production required is more and as a result the induced drag becomes greater.

As forward speed increases, the induced airflow decreases, increasing the effective angle of attack, so the lift required to maintain altitude becomes less and as a result the induced drag decreases. Thus, induced drag is at maximum when the airspeed is zero in still air conditions and decreases as forward speed increases.

Similarly, it states that the Induced Power required to overcome the induced drag is: Induced drag x TAS.

Since, the induced drag decreases as forward speed increases, then the Induced Power to overcome the induced drag will also decrease as forward speed increases.

Rotor Profile Drag is the drag created when the rotor is moved through the air, when no lift is being generated and it is made up of the blades form (pressure) and skin friction drag.

Rotor profile drag would at first seem to be independent of forward speed, as the increased drag on the advancing blade would be offset by the reduced drag of the retreating blade. In fact, this effect is proportional not to the blade speed, but to the square of the blade speed. Although, it is almost constant at very low airspeeds, rotor profile drag rises gently as airspeed increases.

Similarly, it states that the rotor profile power required to overcome the rotor profile drag is: Rotor profile drag x TAS.

Also, the Rotor profile drag increases as forward speed increases, then the Rotor profile Power to overcome the rotor profile drag will also increase as forward speed increases.

Your Notes (not visible to others)



This question has appeared on the real examination, you can find the related countries below.