This is a continuation of Airplanes Engines (part 1) – Piston Engines, and as promised I will start with the Me 262. Though the Messerschmitt Me 262 “Schwalbe” (Swallow) was not the first aircraft to use a turbojet as means of propulsion, but its tremendous speed and use against the American P-51 Mustang – which many consider the greatest fighter plane of the war – gave the post-war world a sense of urgency to develop more jet powered aircraft.
The turbojet also uses the ignition of a compressed air-fuel mixture to produce thrust, but unlike the piston engine, the turbojet has a series of blades and a controlled internal geometry that compresses the air. Incoming air enters the inlet of the engine and reaches the compressor blades. Some of these blades are rotating around a central driveshaft, while others are stationary (called stator blades) and are fixed to the inside surfaces of the engine. As the air becomes more compacted by the blades the inside surfaces of the engine squeeze the air further. Once the fuel is introduced, the mixture is ignited. At this point, the gases expand and so does the internal geometry. One way to visualize this is by imagining the cross-section of the engine from a side-view as two parallel lines. Then take your fingers and just squeeze the middle of them closer together. Another way to visualize this is by using the endless information on the internet to “google” a diagram of one. Like the one below:
The expansion of the gases causes an acceleration of the in the airflow, and conservation of linear momentum (or any other derivative of Newton’s 3rd Law) explains that thrust is generated. Before leaving the engine the gases go through a series of turbine blades which causes the blades to rotate and intern the turbine blades rotate the compressor blades from before. Finally, a nozzle at the back end of the engine helps create more thrust, and the air escapes out of the engine. The turbojet does not have cycles like the piston engine. Instead, this process happens continuously, so when some part of the air is being compressed in the compressor blades, another part of the air is in the nozzle, and another is turning the turbine blades.
Turbojets can manufacture more thrust and operate at higher speeds than a propeller powered aircraft, but that does not mean that is not without room for improvement. This leads to the next two types of airplane engines, which are probably some of the most common styles used today. There is one more part left. Next time we will talk about these variations on turbojets.
Until next time,
-T
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