Jet engine
Reaction engine discharging heated gas to produce thrust.
A jet engine is a reaction engine that creates thrust by shooting out a fast-moving jet of heated gas, typically air. While this broad category can include rockets and water jets, the term usually refers to air-breathing internal combustion engines like turbojets, turbofans, ramjets, pulse jets, or scramjets. These engines generally have a rotating compressor driven by a turbine, with leftover energy producing thrust through a nozzle—a process called the Brayton thermodynamic cycle. Jet aircraft use them for long-distance travel. Early jets used turbojets, which were inefficient at subsonic speeds. Most modern subsonic jets use high-bypass turbofans, which offer higher speed and better fuel efficiency than piston and propeller engines over long distances. A few high-speed engines, like ramjets and scramjets, rely on the vehicle's forward speed to compress air instead of a mechanical compressor.
The thrust of a typical jetliner engine grew from 5,000 lbf in the 1950s to 115,000 lbf in the 1990s. Reliability improved from 40 in-flight shutdowns per 100,000 engine flight hours to fewer than 1 per 100,000 by the late 1990s. This, along with much lower fuel consumption, allowed twin-engined airliners to fly nonstop across the Atlantic by the turn of the century—a trip that earlier would have required multiple fuel stops and three or more engines.
Before World War II, engineers recognized that propeller-driven engines were nearing their limits because propeller efficiency dropped as blade tips approached the speed of sound. To go faster, a different propulsion method was needed, leading to the gas turbine engine. The gas turbine itself wasn't new: John Barber patented a stationary turbine in England in 1791. The first self-sustaining gas turbine was built in 1903 by Norwegian engineer Ægidius Elling, but such engines weren't manufactured due to problems with safety, reliability, weight, and sustained operation.
The first patent for a gas turbine to power an aircraft was filed in 1921 by Maxime Guillaume. His design was an axial-flow turbojet, but it was never built because compressors weren't advanced enough. In 1926, Alan Arnold Griffith published "An Aerodynamic Theory of Turbine Design," leading to experimental work at the RAE. In 1928, RAF cadet Frank Whittle submitted his turbojet ideas to his superiors, developing them further in 1929. He filed his first
- field
- Aerospace engineering, propulsion
- known_for
- Generating thrust via fast-moving jet of heated gas; powering jet aircraft, cruise missiles, and unmanned aerial vehicles
- first operational jet aircraft
- Heinkel He 178 (1939)
- first jet engine in service
- Jumo 004 (1944)
- thrust range (1950s–1990s)
- 5,000 lbf (22 kN) to 115,000 lbf (510 kN)
- reliability improvement
- 40 in-flight shutdowns per 100,000 engine flight hours (1950s) to less than 1 per 100,000 (late 1990s)
Lore & Background
Before World War II, engineers recognized that propeller-driven engines were approaching performance limits due to declining propeller efficiency as blade tips neared the speed of sound. This motivated development of the gas turbine engine, the most common form of jet engine. The key was a gas turbine extracting power to drive the compressor. The first patent for a stationary turbine was granted to John Barber in England in 1791, and the first self-sustaining gas turbine was built in 1903 by Norwegian engineer Ægidius Elling. However, such engines did not reach manufacture due to issues of safety, reliability, weight, and sustained operation.
In 1928, RAF College Cranwell cadet Frank Whittle submitted his ideas for a turbojet, patenting a design in 1930 that included a two-stage axial compressor feeding a single-sided centrifugal compressor. In Germany, Hans von Ohain began work on a similar design in 1935, initially unaware of Whittle's work. Von Ohain's first device was experimental and ran only under external power, but he demonstrated the concept. Heinkel supported von Ohain, leading to the HeS 3 engine that powered the He 178, the world's first jet plane, on August 27, 1939. Meanwhile, Austrian Anselm Franz of Junkers introduced the axial-flow compressor in the Jumo 004 engine, which entered mass production in 1944 and powered the Messerschmitt Me 262, the world's first jet-fighter aircraft.
In Britain, the Gloster E28/39 first flew on May 15, 1941, and the Gloster Meteor entered service in July 1944, powered by Whittle's turbojet engines. The Me 262 and Meteor entered service within three months of each other in 1944. After the war, German jet aircraft and engines were studied by the victorious allies, contributing to early Soviet and US jet fighters. By the 1950s, jet engines were almost universal in combat aircraft, and by the 1960s, all large civilian aircraft were jet powered.
Reader's Guide
The jet engine revolutionized aviation by enabling speeds and altitudes unattainable with piston and propeller engines. Its development was driven by the need to overcome propeller efficiency limits as aircraft approached the speed of sound. The key innovation was the gas turbine, which extracts power from the engine to drive the compressor, operating on the Brayton thermodynamic cycle. Early turbojet engines were relatively inefficient for subsonic flight, but by the 1970s, high-bypass turbofan engines achieved fuel efficiency comparable to the best piston and propeller engines. The thrust of a typical jetliner engine increased from 5,000 lbf in the 1950s to 115,000 lbf in the 1990s, while reliability improved from 40 in-flight shutdowns per 100,000 engine flight hours to less than 1 per 100,000. This, combined with greatly decreased fuel consumption, permitted routine transatlantic flight by twin-engined airliners by the turn of the century. Jet engines now power not only aircraft but also cruise missiles, unmanned aerial vehicles, and, in modified form, industrial gas turbines for power generation, marine propulsion, and other applications. The legacy of the axial-flow engine is seen in the fact that practically all jet engines on fixed-wing aircraft have had some inspiration from this design.
Did You Know?
- The first patent for using a gas turbine to power an aircraft was filed in 1921 by Maxime Guillaume, but his axial-flow turbojet was never constructed.
- The Heinkel He 178, powered by Hans von Ohain's HeS 3 engine, was the world's first jet plane, flying on August 27, 1939.
- The Jumo 004 engine, introduced by Anselm Franz, was the first jet engine to enter service, powering the Messerschmitt Me 262 in 1944.
- By the late 1990s, jet engine reliability improved to less than 1 in-flight shutdown per 100,000 engine flight hours, down from 40 in the 1950s.
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