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What is the effect on the Best Rate of Climb speed and on the Best Angle of Climb speed, when expressed as a TAS, if altitude increases?

  • A

    Both decrease.

  • B

    Best angle of climb increases and best rate of climb decreases.

  • C

    Both increase.

  • D

    Best angle of climb decreases and best rate of climb increases.

Refer to figures.
The Best Rate of Climb speed, VY, is found at the lowest point of the power required curve (Point 1), which is also the minimum power required speed, VMP and the maximum endurance speed, VMAX END.

The Best Angle of Climb speed, VX, is found on the tangent at the power required curve from the power available line at the vertical axis (0 kt) (Point 4).

As altitude increases, the TAS for a given IAS increases. This fact would cause the power required curve just to be stretched out to the right.

But, power required is Drag x TAS, so the increase in TAS also causes the power required curve to move up.

Thus, the combined effect is that the power required stretches up along its tangent from the origin.

As a result, both the tangent at the power required curve from the power available line at the vertical axis (0 kt) and the lowest point of the power required curve, which correspond to VX and VY, move to the right and as TAS both increase.

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