Re: A/C Body Station Designations

Date:         03 Nov 97 02:18:53 
From:         "Richard L. Grubb" <>
Organization: 3-7DSL
References:   1
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JAK1959 wrote:
> Could someone please inform me as to where the reference point
> is that body stations are measured from on commercial aircraft?
> Is it the forward pressure bulkhead?  Is it the mounting
> structure for the weather radar?  Please let me know.
> Also, are there any publications that have aircraft diagrams
> that would include both body stations and stringers?
> And a final question.  How does Airbus designate the body
> stations?  Please let me know.

I have been told by a coworker who had this same discussion at another
aerospace company, that once, a long long time ago (in a place far far
away), Body Station 0.0 was placed at the tip of the nose and waterline
0 may have been placed at the point of contact between the main gear and
ground. But when the first 'stretch' or derivative was designed, 'they'
vowed never to do that again.

Today (i.e. in my experience over the last 23 years), the origin is
placed far enough in front of and below the airplane so as to never
require the use of negative values for any reasonable stretched
derivative. Of course, Butt Line 0 is placed on the centerline of
symmetry. I have also been told that McD planes had waterline 100 placed
at a prominent 'horizontal' feature and some other vertical feature such
as a bulkhead would be given an arbitrary value such as BS 112.0.

In this explanation, I have been using nomenclature for Boeing
fuselages. Other components such as wings and tails or even control
surfaces have their own reference systems. I believe Wing Stations are
perpendicular to the rear spar.

All of these coordinate systems are tied together on an airplane
centerline drawing. All drawings are company proprietary data, but you
may be able to write to the public relations department and request the
information for particular models.

On a side note, the loads engineers require that an 'all numeric'
coordinate system be used in their calculations. Why would a coordinate
system never be 'all numeric' you might ask? Well remember those
derivative models with stretched fuselages? The fuselages are generally
stretched by adding body plugs just in front of the wing and/or just
behind the wing. For instance, on the 737 family of airplanes, forward
plugs are placed between BS 500 and BS 520. The designers do not want to
relabel all of the frame drawings aft of the plug, so the first frame
aft of BS 500 is given the 'coordinate' 500A, and so on to BS 500I for
the 737-800. This system is impractical to use in engineering numerical
analysis. The loads group therefore define a coordinate system (referred
to by the terms balance arm or panel station) that has the same
numerical value for various derivative models at some point in the
center section of the body. A point near the tip of the 737-800 nose
then is at BS 130.0 or balance arm -68.0
Richard Grubb
BCAG, 737NG Stress, Wichita
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