# Introduction to Modeling Engine Thrust

Introduce readers to the physics behind thrust available and thrust required.

The first example that you will use to show off Python’s functionality is graphing thrust required and thrust available for an Airbus A321 at sea level, 10,000 feet, and 35,000 feet (often stylized as FL350 for Flight Level 350, meaning 35,000 feet). This example allows you to demonstrate the plotting capabilities of Matplotlib, the graphing library, and Python’s ability to accept functional programming inputs like writing equations and iterating over `lists`

. Explaining the relationship between thrust available, the thrust required, and drag is beyond the scope of this course; however, you will make use of the fact that thrust required equals drag at the steady, level, unaccelerated cruise condition to calculate thrust required by calculating drag. You will also assume that thrust available at different altitude scales with the ratio of the density of air, so sea level thrust is the nominal thrust of both engines, and thrust output at 35,000 feet is the sea level thrust times the ratio of the density of air at 35,000 feet over the density of air at sea level. As an equation:

$\text{Thrust}_{\text{FL350}} = \text{Thrust}_{\text{SL}} * \frac{\rho_{\text{FL350}}}{\rho_{\text{SL}}}$

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