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General Electric J47 Jet Engine
These B-47 planes use jet engines to provide thrust and to move them forward. Photo from the collection of Mark Natola.
..the first engine with axial flow approved for non-military use. Axial flow is airflow straight through a cylinder.


First test flight: 1948
Engine weight: 1,100 kg (2,500 pounds)
Thrust: 22,000 newtons (5,000 pounds of force)
Maximum altitude: 15 km (50,000 feet)

The J47 engine was first conceived in March 1946. Since that time many variations of the J47, including many technical innovations, have been designed and produced. In all, GE built over 30,000 J47 engines. It has applications in many types of aircraft, including bombers, reconnaissance, interceptors, and fighter planes.

The J-47 turbojet displayed at the Science Center has an afterburner to increase engine power at takeoff and during altitude acceleration. It also has an anti-icing feature, a more efficient compressor for increased airflow, and a high-altitude starting system.

Jet Engine Function
The main purpose of a jet engine is to shoot air quickly out through the back of the engine, which pushes the plane forward. Just like air rushing out of a balloon makes the balloon fly around, hot gas shooting out the back of an engine thrusts the plane ahead. Jet engines work like piston engines in that they have four steps - intake, compression, combustion and exhaust. The four steps take place in one continuous flow rather than in back and forth actions. Air is sucked in at the intake and is compressed by a compressor turbine or fan. This dense air is then mixed with fuel, which is burned, causing the gases to expand very quickly. The hot burning mixture increases speed rapidly and flows past a series of turbines, causing them to rotate at high speed. The turbines are mounted on the same shaft as the compressor, which provides its rotation. Then the exhaust gases are emitted past a cone, where Newton's Third Law of Motion takes over. On the diagram below, you can see the four steps air goes through as it passes through the jet engine. Definitions for each of the steps are included below the diagram.

Intake sucks air into the engine.
Compression squeezes the air. Row after row of spinning blades force air through and compress it, raising the air pressure. The wing-shaped blades get closer and closer together deeper into the engine.
Combustion heats up the air. In the combustion chamber, pressurized air mixes with jet fuel. A flame heats the mix, and it expands very quickly.
Exhaust shoots the heated air out the back of the engine. Fast-expanding hot gases from the combustion chamber shoot out the exhaust nozzle. Pushing the fast-expanding hot gases from the combustion chamber out the back moves the engine forward.

Jet engines provide great power with light weight, simplicity and reliability. However, they are expensive to build and use a lot more fuel than piston engines of similar power. They are more efficient than piston engines at high altitudes, where airplanes can fly faster in the thinner air. They may provide thrust in one of several ways: from their exhaust (pure jet), by driving a fan (fan jet), or a propeller (prop jet). To learn more about jet engines, check out the links below.


J47 and Jet Engine Links
General Electric J47 Turbojet Engine
This page from the Air Force Museum's Engine Gallery shows a photo of a J47 engine, engine stats and even the engine cost.

How Gas Turbine Engines Work
How Stuff Works offers a great collection of pages explaining the workings of gas turbine engines, including jet engines. You'll also find a very helpful listing of advantages and disadvantages to turbine engines and links to related books.

Ultra-Efficient Engine Technology Kid's Page: Engines
NASA created this page on how jet engines work. The page features a list of the major parts of a jet engine along with definitions and illustrations, a history of jet engines, and information about many different types of jet engines. If you're interested, you can also follow links to plane-inspired online games.

Beginner's Guide to Propulsion
Despite the title, this page (designed for secondary school teachers as part of the Glenn Learning Technologies Project) features some detailed information about propulsion. The page includes links to definitions of important terms, and even an EngineSim that lets you design and test jet engines on your computer.

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