Which of the following diagrams correctly shows the change in the position of the power required curve with altitude, given that H

_{2}is at a greater altitude than H

_{1}?

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 (__. The graph therefore moves

**so the graph moves upwards**)**upwards and rightwards**, away from the origin, so figure (d) is correct.

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