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Refer to figure.
Which of the following diagrams correctly shows the change in the position of the power required curve with altitude, given that H2 is at a greater altitude than H1?
• A
Diagram a
• B
Diagram b
• C
Diagram c
• D
Diagram d

Refer to figure.
Propeller aircraft cannot measure thrust output, only power (Power = Thrust x Velocity). This means that it is often useful to change thrust required (drag) graphs into power required graphs, by multiplying by speed (TAS) again. The curve looks the same, but if you get to compare them, the power required curve is steeper and a little to the left.

This is where it can get a little complicated, as drag graphs are often created with IAS on the X-axis, for easy usage at all altitudes, but Power = Thrust x True Airspeed. This means that for the same thrust required (drag), an increase in altitude causes a higher TAS and therefore a higher power required.

There we have it then; for increased altitude, the power required curve will look almost the same, but for each point on the curve (which is a certain IAS), the TAS will be higher (so the curve moves to the right) and therefore the power required will also be higher (so the graph moves upwards). The graph therefore moves upwards and rightwards, away from the origin, so figure (d) is correct.

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