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Consider we have the exactly same turbine which is possible to be mounted to the tail (left picture) and to the wing (right picture) as picture below. Which one will produce more power to the airplane? Need physics analysis.

Two kind turbine placement

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The power will be the same. But the aircraft with wing mounted engines will have less drag. Contributing factors are:

  • Engines are heavy. Putting them aft means there is a big difference in centre of gravity between empty and loaded aircraft, so larger horizontal stabilizer is needed to keep it in trim over the range of centres of gravity. It is also needed for rotation on take-off with forward CoG, since the main gear must be behind the aft-most CoG position. That means more trim drag.

  • Putting something heavy, like engines, on the wing ahead of it reduces flutter, so the wing can be less stiff, and thus lighter. This means more payload, or less induced drag at the same payload.

  • Engines ahead of the wing fit nicely with the Whitcomb area rule. At the tail they add a lot of cross-section where it should be tapering off already, slightly worsening the transsonic performance.

So engines tend to be wing-mounted on all but small low-wing aircraft where they would have too little ground clearance.

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The power will be more or less the same but probably favours the wing engines. The only major difference is the pitching moment created by thrust is nose-up with underslung engines (low thrust line) and mildly nose down with the tail engines (high thrust line).

You could say the tail mounting creates a tiny bit more trim drag (because a little bit of extra tail downforce is required to counter the nose down pitching moment) than the wing mounted engines on two otherwise similar aircraft, so there is probably an argument that wing mounted engines are slightly more efficient overall because of lower trim drag losses. The tail mounting also requires the gear to be farther aft at a less than optimum position, to keep it from tipping on its tail when empty. This requires more tail power for rotation, with a bigger surface than would otherwise be necessary, and again slightly more drag.

So with two identical airframes, you could say the wing mounting does win out from a net power available to push the airplane along perspective, but I'm sure the difference is quite small.

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  • $\begingroup$ More than a couple of aircraft have a tail prop-stick to prevent tipping back when empty. That could be employed to help (at least somewhat) offset the gear location. $\endgroup$ – FreeMan Feb 19 at 21:00
  • $\begingroup$ Perhaps, but it's a really impractical solution. If you tour a typical gate area and observe all the tail engine airliners, Embraers, RJs, DC9s, you won't see too many tail struts. $\endgroup$ – John K Feb 19 at 21:22

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