How Does a Jet Engine Work?

Q: You once wrote that your job as an air travel columnist isn’t to burden readers with technical jargon or bore them with specifications about airplanes. “To travelers,” you said, “a discussion of GPS satellites or how a jet engine works is guaranteed to be uninteresting.” Well, if you don’t mind my asking, how does a jet engine work?

In retrospect, I suppose there’s nothing terribly tiresome about this question, and perhaps I owe it to readers to address such a core topic.

Essentially, air is blown out the back faster than it’s drawn in the front, pushing the plane forward. The most powerful motors made by Rolls-Royce, General Electric and Pratt & Whitney generate in excess of 100,000 pounds of thrust.

Picture the engine’s anatomy as an assembly of geared, rotating discs — compressors and turbines — like a series of back-to-back fans. Air is pulled in and directed through the compressors. It’s squeezed tightly, mixed with vaporized kerosene, and ignited. The combusted gases then come roaring out the back. Before they’re expelled, however, a series of rotating turbines absorbs some of the energy. The turbines spin the compressors and the large fan at the front of the nacelle. Older engines derived almost all of their thrust directly from the hot exploding gases. On modern ones that big forward fan does much of the work, and you can think of a jet as a kind of ducted fan, spun by a core of turbines and compressors.

Besides providing thrust, the engines are tapped to supply the electrical, hydraulic, pressurization and deicing systems. Hence the term “powerplant.”

A turboprop engine is, at heart, a jet. In this case for better efficiency at lower altitudes and along shorter distances, the compressors and turbines drive a propeller rather than generate thrust directly. Loosely put, a turboprop is a jet-powered propeller. Hence the name jet-prop, sometimes used in lieu. There are no pistons in a turboprop engine, and the prefix shouldn’t elicit confusion with turbocharging in the style of an automobile. Turboprops are safer and more reliable than pistons, and offer a more advantageous power-to-weight ratio. They’re also expensive, which is why most private planes don’t have them.

This article is part of a collection that originally appeared on Salon.com. Patrick Smith, 38, is an erstwhile airline pilot, retired punk rocker and air travel columnist. His book, Ask the Pilot (Riverhead) was voted “Best Travel Book of 2004″ by Amazon.com. Patrick has traveled to more than 55 countries and always asks for a window seat. He lives near Boston.

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