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Check the MD80's empennage below.

enter image description here

Can easily tell it's not built on exactly centerline by naked eyes.

Is that because aluminum joint or consider aerodynamics?

I don't think it is manufacturing defects or imprecision.

Some of the small aircraft have the same construction like this.

Couldn't find the similar discussion online though.

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  • $\begingroup$ Welcome to av.se :) $\endgroup$
    – ymb1
    Mar 16, 2017 at 12:15
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    $\begingroup$ Looking at the picture, I see that the forward portion of the empennage fairing does not line up with what appears to be a joint in the skin structure. However, the joint may be off-center compared to the rivet placement. Looking at the empennage in person may reveal it to be off centerline, but this is not clear to me from the picture. Could you further explain or document how the empennage is not on centerline? $\endgroup$
    – J Walters
    Mar 16, 2017 at 13:04
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    $\begingroup$ This is a good question, because some aircraft do have off-center (or divergent or angled from the longitudinal axis) empennage. The C172 is an example of such an aircraft; I'm not sure that the DC-9/MD-80 series is. $\endgroup$
    – J Walters
    Mar 16, 2017 at 13:13
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    $\begingroup$ I haven't had my hands on a C172 in a few months, but if I remember right, the built in angle is to counteract some of the left turning tendencies and provide built in trim. The C172 doesn't have cockpit-adjustable rudder trim. $\endgroup$
    – J Walters
    Mar 16, 2017 at 13:25
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    $\begingroup$ You said "aircraft", not "planes", so you should look at helicopters because almost all of them are asymmetric by definition : ) $\endgroup$
    – Agent_L
    Mar 16, 2017 at 15:45

2 Answers 2

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The vertical stabilizer is on the centerline.

The line you see is not the centerline, it's the overlap of the aluminum sheets that form the circular fuselage.

enter image description here
(Source)

enter image description here
(Source) Non-aviation example of what I mean by overlap and centerline.

On the other hand, propeller aircraft may employ different methods to counter the left turning tendencies.

Tail

The tail group consists of a vertical stabilizer, a horizontal stabilizer, two elevators, and a rudder. The vertical stabilizer is mounted on the aft fuselage, and the horizontal stabilizer is mounted on the top of the vertical stabilizer. The rudder and elevators are mounted on the vertical and horizontal stabilizers, respectively.

The vertical stabilizer is fully cantilevered and sweptback. A scoop for cooling the air-conditioning systems is located on the lower leading edge section and is heated when the Airfoil Anti-ice is operating.

– MD-80 Flight Manual

Back to the MD-80 in the photo, from its manual there is no mention of an offset. I searched for multiple terms such as offset, angled, and off center.

Finally, from an official CAD drawing from Boeing's website:

enter image description here

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  • $\begingroup$ That make sense. Thanks very much. $\endgroup$
    – ReinFore
    Mar 16, 2017 at 12:02
  • $\begingroup$ @ymb1 nice editing :) $\endgroup$
    – ReinFore
    Mar 16, 2017 at 14:33
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    $\begingroup$ that link about left-turning tendencies is really interesting and high quality, thanks! $\endgroup$
    – cat
    Mar 16, 2017 at 17:33
  • $\begingroup$ Awesome, thank you for your effort! $\endgroup$
    – ReinFore
    Mar 16, 2017 at 23:43
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Its my first time seeing this kind of defects. For sure its not a defect caused by manufactures. It could be that this aircraft had gone through a skin change procedures. Its the overlapping of two skins that appear to be not center or could be the dorsal fin's anchor nuts not rivets properly i guess so (refer to my experience working with b737-family).

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  • $\begingroup$ this does not add anything to the already existing answer $\endgroup$
    – Federico ♦
    Mar 21, 2017 at 17:06
  • $\begingroup$ Are you suggesting that this is a defect? Are you familiar with the construction of the MD-80 type? Is this, in fact, an example of defective manufacture? I have seen nothing else that suggests the photo in question depicts a defect; my understanding is that the photo shows proper construction that differs from the expectations of the OP. $\endgroup$
    – J Walters
    Mar 21, 2017 at 17:09
  • $\begingroup$ I'm sure this section haven't been modified and other MD82 are the same. Have repairing experience on MD82/83. $\endgroup$
    – ReinFore
    Mar 21, 2017 at 23:36

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