What is the drag induced by a turbo bypass jet engine in a typical most modern airliner like the 777, the Jumbo Jet (Boeing 747-8) and the Airbus A380?

Given that the jet is travelling faster than the replacement of the air displaced by the engine suction, do parts in close proximity to this area where suction is largest cause less drag to the aircraft because of this micro second vaccum period occuring at all times when the aircraft is in cruise mid air? I refer to turbo bypass engines because they are the ones most used because of fuel efficiency, noise, etc., in airliners, I do not ask about bypass ratio. I ask about the displaced air outside the engine, and the overall effect on drag caused by the engine as a physical component attached to the plane colliding with air.

Does the fact that it is sucking a very large amount of air around it reduce this drag and by how much compared to if it were not sucking any air at all?

  • $\begingroup$ I'm not asking about the bypass ratio and drag I'm asking about the engine as a physical part of the airframe, its close proximity to the displaced air by suction of the jet its under aerodynamics not drag and spinning parts like the propeller blades $\endgroup$ Oct 13, 2017 at 11:48
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    $\begingroup$ Ok, I've voted to reopen after your edit. It's not a duplicate from what you explain. However after it'll be reopened it may be closed again for unclear, so maybe you should try to improve/refine the question. Good luck. $\endgroup$
    – mins
    Oct 13, 2017 at 11:59
  • $\begingroup$ The first line of your question is confusing - engines deliver thrust, the opposite of drag. The second paragraph further enhances the Huh? factor. The last paragraph does not seem to account for the fact that the aircraft is at cruising speed, and air is blown into it. I'm sorry but I have no clue what you're asking about. $\endgroup$
    – Koyovis
    Oct 17, 2017 at 2:05
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    $\begingroup$ @Koyovis Engines deliver net thrust. But it still makes sense to ask about drag caused by them, just as it makes sense to ask about the expenses of a profitable company. $\endgroup$ Oct 20, 2017 at 15:19

1 Answer 1


What you are asking about is inlet performance.

Instead of sucking air, think of it as eating air, that's a better more correct analogy (like Pac-Man eating dots). As the plane flies through the air, it may literally bite off more than it can chew. Causing spillage. The extra air stuck in the inlet tries (but fails) to go out. Creating drag.

But this drag for the subsonic airliners you ask about is offset by the suction at the inlet due to the inlet's design.

See here for how they cancel each other: How does inlet spillage drag produce a lip suction effect?

Related: Does the air resistance of a jet engine air intake count towards the jet's total air resistance?


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