Jim Smart
September 11, 2006

Huff & Puff Cousins - Jet Engines & Turbochargers
Suck, squeeze, blow! It's all about getting air molecules into motion in the fastest, most furious way possible to make power. Jet engines and turbochargers do the same basic thing. Each takes in and rams huge amounts of air into combustion chambers to make the most of a compressed and ignited fuel charge. Jet engines, in their most basic form, draw air into compressors (suck), ram it into combustors (squeeze), which blows hot gasses under pressure across whirling turbine blades (blow), that are tied to a shaft connected to compressor blades. The turbine blades maintain continuous combustion as long as we keep combustors supplied with atomized fuel.

The more fuel fed to the combustors, the greater combustion rages, which makes more and more thrust at the exhaust pipe. Revving jet engines is known in aviation as "spooling" because jet engine compressors are shaped like sewing spools. When power is applied, you are "spooling" the engine.

In the very beginning of jet travel, jet engines were crude, loud, obnoxious, smoky powerplants that didn't make much power. As the '60s unfolded, the noisy, smoky turbojet gave way to the turbofan (also called a fan jet), which enabled jet engines to make even more thrust by adding a high-thrust fan stage ahead of the compressors. The fan stage looked more like a windmill on steroids. In the late '60s, with the advent of jumbo jets, fans were bigger, becoming a whopping 85 percent of a jet engine's thrust.

To give you some idea of the difference turbofans made in jet propulsion, the Pratt & Whitney JT3C turbojet, which powered the Boeing 707 and Douglas DC-8 jetliners, made around 14,000 pounds of thrust during takeoff. It took four of them to get one of these babies off the ground.

When the Boeing 747 was introduced in 1969, it was a quantum leap in size, powered by four large Pratt & Whitney JT9D turbofans producing approximately 40,000 pounds each of takeoff-rated thrust. Like the 707 and DC-8 that launched the jet age 10 years earlier, there were four engines. This was considered a lot of thrust at the time thanks to a large, 8-foot-diameter fan.

When Boeing introduced the super-long-range 777-300 series twin-jet in the '90s, it also introduced the new General Electric GE90-115B monster mash turbofan-127,000 pounds of thrust on takeoff, the most powerful jet engine ever made. Similar engines from Rolls Royce power the Airbus A380 super jumbo jet.

Despite the great strides in jet power over the past half century, the "suck-squeeze-blow" principle remains the same, and it's shared with the humble turbocharger. Regardless of application, turbochargers use hot exhaust gas to drive the power-enhancing compressor, which force-air feeds waiting combustion chambers hell-bent to make power.