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The CFM 56-7BE (on the 737) has a long and narrow nozzle, the RR Trent 900 (on the A380) has a sharper nozzle, and the CF-6 (on the 767) has a wider opening at the nozzle. Why do the nozzle sizes vary among turbofans?

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    $\begingroup$ What do you exactly mean by nozzle? Are you talking about nacelle design, nacelle inlet or nacelle exhaust? $\endgroup$ – Farhan May 15 '15 at 19:06
  • $\begingroup$ I think the question is about nacelle exhaust section, but pictures illustrating exactly what you are asking about would be helpful. $\endgroup$ – fooot May 15 '15 at 19:27
  • $\begingroup$ Thank you @Farhan for correcting me, I meant the nacelle exhaust. $\endgroup$ – Madhav Sudarshan May 16 '15 at 7:16
  • $\begingroup$ If you can add pictures ilustrating exactly which differences are you looking for be explained will allow us to provide you a better answer. $\endgroup$ – Trebia Project. May 16 '15 at 11:26
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The nozzle, apart from its main function, that is accelerating the air in order to propel the vehicle, it determines what goes into the front of the engine, it is a downstream restrictor along with the turbine nozzle.

The areas of both the propelling nozzle and turbine nozzle set the mass flow through the engine and maximum pressure. For different engine operational purposes, it is used one shape or another. These engines have different shapes due to optimization reasons; the engine, is designed in such a way that the aircraft features will have the best balance in terms of fuel consumption, thrust needed, and many other parameters.

Each manufacturer design their engines in the most convenient way and then, it is determined which engine is better for a given aircraft.

Different kind of geometries, (e.g. convergent-divergent) also affect on the engine operation regime (supersonic, subsonic, transonic), but this does not affect here since all the engines are turbofans and thus, subsonic.

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  • $\begingroup$ Depending on what the question is referring to, the part may not be made by the engine manufacturer. $\endgroup$ – fooot May 15 '15 at 19:29
  • $\begingroup$ The nozzle shape also has quite an effect on engine noise. Some older engines have been equipped with "hush kits", which change the shaping a lot. $\endgroup$ – Sami May 15 '15 at 19:58

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