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Given the fact that podded engines on the wings of airplanes cause much drag (and thereby contribute to a lot of loss of efficiency), why do airliners still prefer podded turbojet engines over turbojet engines fitted inside the fuselage (or inside the wing) ?

Edit

This question is not regarding "What is the role of Pylons in a podded jet engine", but this is about "Why podded engines in the first place?"

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    $\begingroup$ Who says engines cause drag? For me, they create thrust (if they run), quite the opposite. Placing faired engines in the free flow gives them the best efficiency, again quite the opposite of what you claim. See here for the answer. Buried engines have higher losses due to distortions in the intake flow and long exhaust tubes. $\endgroup$ – Peter Kämpf Jun 3 '15 at 7:53
  • $\begingroup$ What about engines placed inside the wings (contrary to the engines below the wings) $\endgroup$ – Victor Juliet Jun 3 '15 at 7:54
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    $\begingroup$ Efficient engines need much air to work with, and are consequently too big to fit inside a wing. $\endgroup$ – Peter Kämpf Jun 3 '15 at 7:58
  • $\begingroup$ Have a look at this link : en.wikipedia.org/wiki/De_Havilland_Comet $\endgroup$ – Victor Juliet Jun 3 '15 at 8:00
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    $\begingroup$ Ad Comet: It was construction nightmare (the wing root carries all the weight of the aircraft), maintenance nightmare (engines need lot of maintenance and sometimes replacing), horribly noisy (no structure that could damp vibrations between engines and cabin) and the wings are not thick enough to host modern high-bypass turbofans anyway. $\endgroup$ – Jan Hudec Jun 3 '15 at 8:06
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Most important factor affecting drag is frontal area. Almost all frontal area of the engine pod is the intake and it has to have the size it does to collect the air the engine needs. So there is not so much drag to be saved.

Beside that, embedding the engine in wing roots like De Havilland Comet did has many disadvantages, most of which also apply to the central engine of three-engined jets (B727, DC-10):

  • The wing root carries the weight of the aircraft, so weakening it by embedding the engine is design and construction complication.
  • Access for maintenance is difficult. Engines need a lot of maintenance and sometimes need to be replaced.
  • Uncontained failure is more dangerous (see UA232).
  • There is not much structure to damp vibration, so it is awfully noisy.
  • And last but not least, modern high-bypass turbofans are huge. They would not fit in the wing anyway.

And reasons for not attaching the engines directly to the fuselage or wing are already mentined in Why do we use pylons to mount the engines on jetliners?. Mainly, the inlet needs:

  • Free space around it from which it can draw air at slow speed.
  • Free space around it to which it can spill the excess air at high speed.

And the engines mounted forward of wing actually improve the distribution of cross-sectional area according to the Whitcomb area rule and they dampen flutter, so the wing can be slightly less stiff and thus slightly lighter.

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