Cobra Effect · Everyday machines
How a jet engine pushes a plane forward
How a jet engine drives a plane forward by throwing gas backward.
7 cards, read aloud in 2:40, with a test and sources.
In 1930, a young RAF officer named Frank Whittle applied for a patent on a jet engine.
He proposed a turbine engine that would drive a plane forward with a fast stream of gas. The Air Ministry showed little interest, and the patent lapsed in 1935 when its renewal fee went unpaid. In 1936, Whittle and his backers formed a company, Power Jets, to build the engine.
A jet engine does four things, over and over.
At the front, a compressor squeezes the incoming air. In the middle, fuel is sprayed in and burned, making the air very hot. The hot gas spins a turbine, whose job is to drive the compressor. Then the gas rushes out of the back far faster than the air came in.
The push comes from throwing gas backward, not from pushing against the air behind.
The engine speeds up a great mass of gas toward the back. The gas pushes back on the engine just as hard, and that drives the plane forward. A rocket works the same way, even in empty space.
In April 1937, Whittle’s first engine ran on a test bench.
Keeping the burning fuel steady was a struggle, and the early runs were hard to control. Meanwhile in Germany, Hans von Ohain was developing his own design, backed by the aircraft maker Heinkel. His demonstration engine ran in September 1937.
In August 1939, a jet powered plane flew for the first time.
It was a Heinkel test plane, powered by von Ohain’s engine. The flight lasted about six minutes, just days before the Second World War began. Whittle’s engine first flew in May 1941, in a Gloster test plane.
The two inventors worked separately, and later became friends.
Whittle’s engine ran first, and von Ohain’s flew first. In 1991, they shared a major engineering prize for their independent development of the jet engine. Jet engines went on to carry most of the world’s long distance air travel.
So when a machine moves forward, ask what it is throwing backward.
A jet throws air and burned fuel backward very fast. A rowing boat throws water back with its oars. The push forward is always matched by a push back.
Sources
- Turbojet thrust, NASA Glenn Research Center. How a turbojet produces thrust, explained simply.
- How do jet engines work?, Explain that Stuff. An illustrated explanation, including why jets do not push against the air.
- Frank Whittle, Wikipedia. His patent, the lapsed fee, the first run and the first flight.
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