I'm trying to decrypt a US aircraft manufacturer's plan. Could W.L. (waterline) and Sta. (station) references use different units?

For example, I have different distances from W.L. 0 to W.L. 200 and from fuselage Sta.3000 to Sta.3200. Are these references always in inches?

  • $\begingroup$ If I had to guess, I would say that imperial units aren't used, and what you are looking at is millimeters. If the fuselage started at Station 0 and ended at Station 3200 and was in inches, that would mean the fuselage was 266 feet long. An A380 is only 239' long. $\endgroup$ – Ron Beyer Sep 15 '16 at 14:07
  • $\begingroup$ Thanks for your response. It is a plane longer than the A380 indeed, never build , Boeing 2707-200. Found it was supposed to be 318' long. On the plan i'm working on , the nose starts at Sta.200 and fuselage ends at Sta.4016. It can't be millimeters. $\endgroup$ – galgot Sep 15 '16 at 15:27
  • $\begingroup$ Edit : 4016 - 200 = 3816 and that is 318' , so Stations are in inches for sure... But I don't understand that smaller W.L units. $\endgroup$ – galgot Sep 15 '16 at 15:34
  • $\begingroup$ What is the distance that you measure for the water line? $\endgroup$ – Ron Beyer Sep 15 '16 at 15:36
  • $\begingroup$ OK… I think I understand why. That line noted W.L. is not the true WaterLine on the Plan, it’s used to mark the angle with another angled line noted « Ground line for minimum ventral clearance… » starting at the base of the main LG. Just for angle reference with the clearance line. Should have noticed that , the same W.L line is legended as « W.L. (ref) » on another sheet . So the true W.L. is lower, but not traced on the plan. Thanks for your help anyway :) And sorry for the inconvenience. $\endgroup$ – galgot Sep 15 '16 at 17:19

Coordinates should always be in the same units. For a US manufacturer, that will be inches. The SI units are generally millimeters. This makes it much easier to locate coordinates, and for calculating things like volumes or distances.

  • $\begingroup$ Imperial units of millimetres? $\endgroup$ – Nij Sep 18 '16 at 19:35

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