Nearly all modern transport aircraft are designed with a plug-system fuselage, allowing longer and shorter variants to be built by adding or removing plugs.

In addition, the plug system simplifies construction, as large sections of the aircraft can be assembled from modular parts.

What was the first aircraft to employ this system?

And what was the reason for adopting it in the first place:

  • to make possible the construction of variants
  • to enjoy efficiencies and economies of design and manufacture
  • both of the above?
  • $\begingroup$ For the why part of the question: Why does an airliner fuselage have a constant section over its length rather than a tear drop shape? $\endgroup$
    – user14897
    Commented Oct 13, 2018 at 13:40
  • $\begingroup$ @ymb1That does not say anything about why the designers of the first airliner to adopt the plug system did so. $\endgroup$ Commented Oct 13, 2018 at 14:00
  • $\begingroup$ It does not specifically mention the first, but the reasons there are valid, and it may have been the same. It is not a duplicate, rather a helpful related post, that's all. $\endgroup$
    – user14897
    Commented Oct 13, 2018 at 14:05
  • $\begingroup$ Side note: This comes from marine ships, which have used this even before airships. $\endgroup$
    – Therac
    Commented Jan 29 at 7:37

2 Answers 2


This should be a Zeppelin. You said "aircraft", not "airplane", so lighter-than-air systems qualify also.

Already the model submitted with the patent application in 1895 (yes, back then the inventor had to demonstrate that the invention is actually implementable!) showed several cylindrical sections, akin to a train of cylindrical balloons. The final patent (Reichspatent No. 98580) was for a "Lenkbarer Luftzug" (dirigible aerial train). Adding more sections would increase length and payload.

Later, when the maximum diameter of Zeppelin airships was limited by the size of available hangars, their mid section was of constant size and allowed to add plugs to increase payload and range. This was, among others, the case with LZ 104 which turned out 30 m longer than initially planned.

The last big airliner not designed for stretching was the Lockheed Constellation. It had a continuously varying cross section from tip to tail.

  • $\begingroup$ Interesting, though if it is the balloon that is made of sections, does that count as a fuselage? $\endgroup$ Commented Nov 13, 2018 at 11:31
  • $\begingroup$ @DanieleProcida: Good question! At least it was the part holding the payload, and the idea was to spread the payload over the length of the airship. Only it is not called a fuselage. $\endgroup$ Commented Nov 13, 2018 at 19:47

In the US, that was most likely the Douglas DC- series of aircraft. Douglas used the plug-stretch design principle throughout the series, as more powerful engines became available over time which permitted more payload.


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