In and above the tropopause, aircraft efficiency changes with height. What is the trend?

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Prepare for the Endeavor Air Indoctrination Training Test. Study with flashcards and multiple-choice questions, each offering hints and explanations. Get ready for your exam!

Multiple Choice

In and above the tropopause, aircraft efficiency changes with height. What is the trend?

Explanation:
The main idea is that efficiency in the upper atmosphere trends downward as you go higher beyond the tropopause. As altitude increases into the stratosphere, air becomes extremely thin. This thinning reduces lift for a given speed and lowers the mass flow through the engines, so keeping level flight and achieving the same range costs more fuel per mile. While drag continues to fall with altitude, it doesn’t decrease enough to offset the penalties from thinner air and engine performance, especially above the tropopause. That combination makes overall efficiency decrease with height in and above the tropopause.

The main idea is that efficiency in the upper atmosphere trends downward as you go higher beyond the tropopause. As altitude increases into the stratosphere, air becomes extremely thin. This thinning reduces lift for a given speed and lowers the mass flow through the engines, so keeping level flight and achieving the same range costs more fuel per mile. While drag continues to fall with altitude, it doesn’t decrease enough to offset the penalties from thinner air and engine performance, especially above the tropopause. That combination makes overall efficiency decrease with height in and above the tropopause.

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