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As long as an aeroplane is in a steady climb:
  • A
    VX is always less than VY.
  • B
    VX is always greater than VY.
  • C
    VX may be greater or less than VY depending on altitude.
  • D
    VY is always greater than VMO.

Refer to figures.

Best Angle of Climb Speed (VX) is found at the maximum excess of Thrust - in other words, where the gap between the Thrust available and Thrust Required "Drag" curves is the greatest.

  • For a Jet - VX is the same IAS as VMD
  • For a Prop - VX is slower than VMD (close to VMP)
Best Rate of Climb Speed (VY) is found at the greatest excess of Power over Power Required.
  • For a Jet - VY corresponds to 1.32 VMD
  • For a Prop - VY is the same IAS as VMD
During a climb, VX is normally always less than VY. However, as altitude increases the power required curve moves up and to the right, since the power available decreases and the power required increases. As a result, the value of VX increases until the absolute ceiling where these speeds meet at the same value VX = VY. The correct option should state that VX is always lower or equal to VY, but this option is not available.

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