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When flying for endurance, then the minimum drag speed is not used. This is because the power required is…
  • A
    Not directly related to fuel flow.
  • B
    Directly related to fuel mass.
  • C
    Related to fuel density.
  • D
    Related to fuel flow.
Refer to figure.
The power required curve can be described as a fuel flow curve. Where the power required is high, fuel flow is high:
  • At the bottom of the curve (Point 1), the power required is at a minimum and fuel flow will be at a minimum as well. The corresponding TAS is the minimum power required speed, VMP, which is also the maximum endurance speed, VMAXEND and best RoC speed, VY.
  • At the intersection between the power available and power required curves (Point 2), where the power margin is zero, since no further power is availbale to accelerate the helicopter in level flight, the VMAX is found. It is the highest sustainable speed (subject to VNE) while flying straight and level.
  • At the tangent of the origin to the power required curve (Point 3), or in other words, to the tangent of the fuel flow curve, the maximum range speed, VMR, is found, which is also the minimum angle of descent speed and the minimum drag speed, VMD, (Best Rotor thrust / Rotor drad ratio).
  • On the power required curve, at the tangent from the power available line at the vertical axis (0 kt) (Point 4), the best angle of climb speed, VX, is found. It is the speed which gives the steepest climb angle to clear obstructions.

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