Different jet airplanes mount the engines in different ways.
For example:
Under the wing
To the fuselage
How does the engine location affect aircraft performance? Is one better than the other?
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asked Jan 28, 2014 at 18:54
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5$\begingroup$ There's also the single engine, straight out the tail, like the cirrus sf50 $\endgroup$– falstroCommented Jan 29, 2014 at 8:29
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11$\begingroup$ First thing I saw when following that link was seven people digging a hole ;-) $\endgroup$– Rob VermeulenCommented Jan 23, 2016 at 9:52
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2$\begingroup$ @falstro Awesome, but where's the picture? $\endgroup$– user7241Commented Dec 26, 2017 at 19:41
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$\begingroup$ I believe the answers already given are more in line with what you are seeking. However, a minor point to remember is any propulsion out of line with the CG provides asymmetric thrust that must be compensated for aerodynamically. All other factors being equal, power supplied inline with the CG will be the most efficient. $\endgroup$– jwzumwaltCommented Dec 26, 2017 at 23:04
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4 Answers
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Engine location performance-affecting factors:
1. Mounted in the wing root
- low asymetric yaw on engine failure, less rudder required: less drag
- no engine pods: less parasitic drag
- engines closer to CG, less downforce needed from the tail: less drag
- very little reverse thrust available
- Little space for high-bypass-ratio engines
2. Mounted in pods under the wing
- high asymetric yaw on engine failure requires larger rudder: drag penalties
- engines provide bending relief on the wing, allowing better wing design (thinner wings): less drag
- at high incidence angles the pods can prevent spanwise flow: less drag and better stall characteristics
- full thrust can impose a large, undesirable, pitch up moment (think stall recovery)
- less freedom in roll on cross-wind landings
- Location ahead of the wing's elastic line helps to dampen flutter
3. Mounted inside the tail or on pods on the rear fuselage
- low asymetric yaw on engine failure, less rudder required: less drag
- wing design is freed from the need to accomodate engines, allows for more complex wing designs: better performance throughout the flight envelope
- heavy engines so far aft of the fuselage require wings mounted further aft, and a higher tail to support that: more drag
- Lower landing gear required, especially in case of short fuselages
That's about what I can come up from memory, maybe someone can merge all answers into a comunity wiki kinda post..
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2$\begingroup$ Pictures would be nice. Can you (or someone else) edit in some CC-SA photos or diagrams? $\endgroup$ Commented Jul 18, 2015 at 13:32
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$\begingroup$ Why does the landing gear need to be lower for rear fuselage engines? $\endgroup$– Radu094Commented Jul 18, 2015 at 19:52
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1$\begingroup$ @Radu094 I don't think it's about the landing gear having to be lower, but that the landing gear can be lower due to the fact that it doesn't have to extend past the engines anymore to avoid dragging them over the ground. $\endgroup$– JustSidCommented Jul 19, 2015 at 17:25
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$\begingroup$ What about the HondaJet style mounting above the wing on pods? $\endgroup$ Commented Aug 6, 2015 at 16:43
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$\begingroup$ Tail mounted are susceptible to less engine damage problems due to FOD I think. Maintenance etc. is easier on the wing mounts. Containment in case of turbine failure is also an issue for close to fuselage designs. $\endgroup$ Commented Aug 29, 2015 at 7:32
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Mounting jet engines above the wings (see: Antonov An 72, Boeing YC-14) takes advantage of the Coandă effect to increase lift and improve short-field takeoff and landing performance. The high-velocity engine exhaust (I'm hand-waving a bit here) adheres to the surface and allows the wing to produce lift somewhat longer than it could otherwise.
This layout also vastly reduces the amount of debris and spray that can reach the intakes and damage the engines.
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$\begingroup$ So it's much like using propeller slipstream on a piston/turboprop $\endgroup$– Radu094Commented Jan 31, 2014 at 12:23
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$\begingroup$ Yeah, it's similar in the end result, but I think it's due to a different aerodynamic principle. $\endgroup$– egidCommented Jan 31, 2014 at 16:53
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1$\begingroup$ What are disadvantages? Serviceability and more complicated structural analysis of the wing? $\endgroup$– user7241Commented Dec 26, 2017 at 19:49
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Generally there are 3 engine placements: In the tail, on the fuselage in the back, or under the wings. I'll go over the pros and cons of each.
On the tail
Pros
Not many pros, except that it lets one turn a four-holer into a three-holer which is usually more efficient.
Cons
Generally if you lose the engine in the tail, you risk losing rudder control and you also need a thoroughly reinforced tail, plus you have fuel lines running near the cabin, and you have a significant amount of weight not near the center of gravity.
On the fuselage in the back
Pros
Helps to prevent debris from entering the engine, allows for more room for flaps on the wing, and lighter, more aerodynamic wings since they are not holding up engines, generally allowing for slower approach speeds, also the thrust is closer to the center of the aircraft.
Cons
Fuel lines near the back of the aircraft,tail has to be a T-tail, as well as reinforced. and center of gravity issues.
Under the wings
Pros
Well centered with the center of gravity, allows for more weight shifting in the cabin, and with the bags. The fuel is also kept away from the cabin, and the noise is better spread out through the cabin. In the event that something goes wrong, debris is also less likely to enter the cabin.
Cons
Much easier to get debris swept into the engine, wings have to be reinforced, lose some area for flaps and slats, raising approach speed.
Some useful links
http://adg.stanford.edu/aa241/propulsion/engineplacement.html http://www.airliners.net/aviation-forums/general_aviation/read.main/750042/
Performance Wise
Tail: Generally not the best, as it has center of gravity issues and drag problems.
Fuselage: Good for poor quality runways or low approach speeds but can add weight in reinforcing the tail.
Under the wing: Good for getting more load as less center of gravity issues, but raises approach speeds.
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8$\begingroup$ Not sure your fuel points are really an issue. Many under-wing configurations have fuel tanks in the fuselage right under the passengers, and all of them have fuel cross-feed which means fuel lines are running through the cabin. $\endgroup$ Commented Jan 28, 2014 at 20:00
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2$\begingroup$ You also have fuel lines to the tail for the APU for the underwing configuration. $\endgroup$– caseyCommented Jan 28, 2014 at 20:42
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2$\begingroup$ How do the different configurations affect performance though? $\endgroup$ Commented Jan 28, 2014 at 21:16
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$\begingroup$ How does a rear engine arrangement require a t-tail? Look at Hawkers, Falcons, Caravelle, etc. $\endgroup$– egidCommented Jan 29, 2014 at 4:21
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3$\begingroup$ HondaJet - over the wing engine mount. They claim less cabin noise, & I forget what else. $\endgroup$ Commented Jan 29, 2014 at 23:16
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For tail side-mounted: I think there are issues with airflow to engines at certain angles, reducing stall-recovery options.
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4$\begingroup$ This is a valid point but this answer could be improved by providing more detail. $\endgroup$– foootCommented Jan 23, 2016 at 4:12
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$\begingroup$ I was under the impression that the greater problem was that tail-mounted engines necessitate a T-tail configuration, which is susceptible to entering a deep stall. $\endgroup$– VikkiCommented May 2, 2018 at 17:07