Principles of Operation
- A nozzle operates by using its narrowest part, or 'throat', to increase pressure within the engine by constricting airflow, then expanding the exhaust stream to, or near to, atmospheric pressure, and finally forming it into a high speed jet to propel the vehicle.
- The energy to accelerate the stream comes from the temperature and pressure of the gas- the gas expands adiabatically, when done against a nozzle, this largely reversibly (and hence efficiently) cools, expands, and accelerates the gas, with the heat and pressure of exhaust gas being proportional to its speed.
- Airbreathing engines create forward thrust on the airframe by imparting a net rearward momentum onto the air via producing a jet of exhaust gas, which, when fully expanded, has a speed that exceeds the aircraft's airspeed.
- Engines that are required to generate thrust quickly from idle use propelling nozzles with variable area. While at idle, the nozzle is set to its open configuration for minimum thrust and high engine rpm, but when thrust is needed, (e.g., while initiating a go-around) constricting the nozzle will quickly generate thrust.
Read more about this topic: Propelling Nozzle
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