ON SEPTEMBER 16, 2013, THE CS100, the newest jet in Bombardier’s cutting-edge CSeries of aircraft, took its first test flight. It was a game-changing moment: the CS100 is part of a new aerodynamic revolution—an ultra-efficient airplane designed to cut airline operating costs and one of the first to use super-lightweight composite materials. To ensure that the CS100 was sufficiently lightweight and aerodynamic, it underwent more than 4500 hours of wind tunnel tests—tests that resulted in subtle design changes that improved its performance, reducing fuel consumption and CO₂ emissions each by 20% compared to existing passenger jets.

The CSeries is a spectacular advance from the 1903 maiden voyage of the Wright Flyer, the first successful powered airplane flight, in Kitty Hawk, North Carolina. Yet the Bombardier engineers—and all aeronautic engineers—owe an enormous debt to the Wright Flyer’s inventors, Wilbur and Orville Wright. What made the Wrights truly visionary was their wind tunnel, an apparatus that let them experiment with many different designs for wings and control surfaces. Doing experiments with a miniature airplane inside a wind tunnel the size of a shipping crate gave the Wright Brothers the knowledge that would make heavier-than-air flight possible.

Some 110 years later, Bombardier tested the design of its CSeries aircraft using more than 20 sophisticated miniature scale models inside state-of-the-art wind tunnel facilities in six countries. It also augmented its wind tunnel testing with leading-edge computational fluid dynamics testing, made possible through the use of supercomputers that are 100 000 times faster than the computers in use when the aircraft currently serving this market were designed. Thus, while a miniature airplane—whether inside a packing crate, an ultramodern wind tunnel, or a complex simulation scenario—is not the same thing as an actual aircraft in flight, it is clearly a very useful model of a flying plane—a simplified representation of the real thing that can be used to answer crucial questions, such as how much lift a given wing shape will generate at a given airspeed.

Needless to say, testing an airplane design in a wind tunnel or with computer simulations is cheaper and safer than building a full-scale version and hoping it will fly. Likewise, models play a crucial role in almost all scientific research—economics very much included.

In fact, you could say that economic theory consists mainly of a collection of models, a series of simplified representations of economic reality that allow us to understand a variety of economic issues. In this chapter, we’ll look at two economic models that are crucially important in their own right and also illustrate why such models are so useful. We’ll conclude with a look at how economists actually use models in their work.