- Find "k" as above
using the Spirit of St. Louis maximum velocity and the takeoff weight
less 20 kg (an arbitrary amount of fuel to attain maximum velocity).
Once you have determined k, write an equation for velocity as a function
of lift (as in our example). V= ( L / 0.038
- Using a function
grapher, graph this equation (default window settings are acceptable).
Do you recognize the graph? It is half of
a parabola opening to the right.
- Now key in the
following RANGE window values: xmin=1000, xmax=2500, xscl=100, ymin=120,
ymax=220, yscl=10, and graph the equation. Because the domain and range
are limited to real Spirit of St. Louis values, the curvature of the
parabola segment is limited.
- Return to the equation
and solve it for lift. L= 0.038 V2.
Graph the equation. Then exchange the x and y values in the RANGE window;
that is, key in: xmin=120, xmax=220, xscl=10, ymin=1000, ymax=2500,
yscl=100, and graph. The parabola segment now opens upwards, instead
of to the side.