4.4 Creating Performance Functions

Overview

In this section we will repackage our aircraft performance test data into three callable functions:

Code

We will create three functions:

These functions will each return three values:

• fuel flow [lb/hr]

• true airspeed [KTAS]

• vertical speed [ft/min]

Note the cruise function has no altitude input, because we have fixed this profile to be at 30,000 ft MSL. The cruise function will still return a vertical speed value like the others, but it will be 0. Note also that none of the functions have inputs for atmospheric temperature and pressure; this is a deliberate simplification because we did not vary these parameters in our test cases. 

To create these functions we inspect our flight test plots and then manually create tables to fit the data into lines or curves. We select a handful of point pairs and then perform lookups using:

• .interp from numpy

• RegularGridInterpolator() and CubicSpline() from SciPy

Cruise

Starting with cruise:

Climb

Bonus function: climb distance estimator

We will create one extra function to estimate the climb distance for a given aircraft weight and starting altitude.

The calls produce these results:

Chapter Summary

In this chapter we performed some simple test flights, analyzed data from the flight recordings, and made functions to quickly lookup performance values. In the next chapter we will use these functions to compute a vertical trajectory for the flight plan.