Standards for Using Airplane Coordinate Systems 1

[swertel]

I'm looking for standards, industry or corporate, that define the use of Airplane Coordinate Systems inside of CAD, CAM, and FEA programs.

It has been a long while since I used ACS and I'm now in the position where they would benefit a significant number of product designs I'm working on. Rather than re-invent the wheel from my fading memory, I'm looking for leads to standards I can review to create my own company standard on the technique and use of airplane coordinate systems.

Does anyone have a link, lead, or document they can share?

--Scott
www.wertel.pro

 

[rb1957]

i don't know that there's one standard. a reasonably logical one is ...
x aft, y stbd, z up
or
x aft, y port, z down

Quando Omni Flunkus Moritati

 

[49again]

Maybe I underthunk it too much....all I did was rename my standard SolidWorks planes from "Front" to "STA" (station), "Top" to "WL" (waterline), and "Right" to "BL" (buttline)

Steve R.

 

[IRstuff]

This is from ANSI/AIAA R-004-1992 Recommended Practice "Atmospheric and Space Flight Vehicle Coordinate Systems" for

Vehicle-carried orbit-defined axis system

A system with the origin fixed in the vehicle, usually the center of mass, in which the z_o-axis is directed from the spacecraft toward the nadir, the y_o-axis is normal to the orbit plane (positive to the right when looking in the direction of the spacecraft velocity), and the x_o-axis completes the right-hand system. (See Figure 1A.)

n.b. x_o is in the direction of the velocity vector from Figure 1A

Note that this is one of 11 coordinate systems listed in the document.


TTFN
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[rb1957]

yeah, that's what i'd describe as an external axes system, like for airloads (*once you figure out what "nadir" means !) ... a longitudinal axis fwd is not the most rational for an internal axes system (ie, for describing the vehicle itself).

Quando Omni Flunkus Moritati

 

[IRstuff]

Then, there's:
The standard axes for surface ships are shown in Figure 1. The roll axis for surface ships is the x-axis. It is oriented along the centerline of the ship, running forward and aft. Longitudinal dimensions are measured along or parallel to this axis. The pitch axis is the yaxis. It runs transversely port and starboard. Besides being the axis for pitch, transverse dimensions are measured along or parallel to this axis. The yaw axis is the z-axis. It runs vertically and dimensions are measured along or parallel to this axis.

Figure 1 shows positive x pointing aft, and positive y pointing port. Since ships have a similar "station" terminology as airplanes, this might be more appropriate. The above is from INTERNATIONAL SOCIETY OF ALLIED WEIGHT ENGINEERS, INC, RECOMMENDED PRACTICE NUMBER 13 Standard Coordinate System for Reporting Mass Properties of Surface Ships and Submarines

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[swertel]

Thanks for the ANSI reference, IRStuff. That is half the battle. Let me clarify with more details and turn my original question into a 2-part topic.

The first part is more or less answered. I remember reading a specification a long time ago that missiles point right, cars point left, etc. etc. And I know that zenith/nadir is waterline, port/starboard is butt line, and forward/aft is station line. But I was interested in knowing if modeling in the Z-axis is always zenith/nadir or if the Y-axis is.

That leads to the second part of the question. What CAD standards are followed to actually implement successful use of airplane coordinate systems?

For example, one ASME drafting standard says that the "front" view should show the most detail of the part. But that orientation may not be pointing FWD on an aircraft. I want to model the component part symmetric about the local coordinate system (default CS/orthographic planes in a solid CAD model), but I need to be able to relate it to the part's position in airplane coordinate system (ACS).

Do I have to manually perform the CS transform and create a coordinate system in each part file? I can't imagine that being sustainable. For example, if I lengthen a mating part by an 1/8 inch. Every single consecutive part would require a new ACS transform.

Is there even much benefit in a modern solids modeling (master model concept) system to use ACS?

--Scott
www.wertel.pro

 

[drawoh]

swertel,

Back in my drafting board days, I marked station numbers all over some complex optical systems I was working on. I need a precise definition of the position of everything, and the station numbers provided it. I have not done this on CAD.

What problem is it you are trying to solve?

--
JHG

 

[swertel]

What problem is it you are trying to solve?

Trying to do this on CAD.

--Scott
www.wertel.pro

 

[tbuelna]

Most current CAD applications use a system of discrete part models that are combined into a product/assembly model, and they are positioned relative to each other using geometric constraints. Thus, there is no global coordinate system need for most parts and sub-assys models. The only time a coordinate system would be applied is at an end item level. A typical aircraft configuration may use numerous coordinate systems for end items like the fuselage, engines, etc. The most common description of the primary aircraft coordinate system axes are "butt line" (BL) in the lateral direction, "water line" (WL) in the vertical direction, and "station line" (STA) in the longitudinal direction. WL=0.00 is usually located below what would be ground level and positive oriented upward, so that all WL dimensions have a positive value. STA=0.00 is located at a point ahead of the nose and positive oriented aft, such that all STA dimensions have a positive value.