This technique can be implemented in different ways and for different objectives. Thus it was divided in three lessons covering the positioning of plane parts asymmetrically displaced, the building of plane parts asymmetrically shaped and the building of plane parts asymmetrically paired. Seek for the other two lessons at the Tutorials index page.

Lesson Three - the building of plane parts asymmetrically paired:

When a tank/float part is placed off-center in the airplane's frame, that is using any lateral arm value different than 0 (zero), that part is mirrored in both sides of the airplane relative to its longitudinal center axis. The TXT definition file contains two set of arrays with nodes coordinates for both the right and the left part but while modeling in Plane-Maker both parts are shaped equal.

Fortunately, both left and right nodes values are saved in separate and X-Plane engine renders the parts relaying on the data of these nodes, not forcefully mirroring them. Because this, it is possible to edit these nodes values directly in the TXT and then build an asymmetric pair of parts.

As a technique demonstrator I used a beautiful FA-18 model from Greg Hofer. It was modified to transport an asymmetric payload below its wings: one fuel tank and one GBU bomb, shown in the following image.

Caution: Once the plane is modified and converted back to ACF format it cannot be saved through Plane-Maker because doing so will reset the left part to be symmetric mirrored for the right one.

How-to steps:

1. Start a fresh ACF file in Plane-Maker (let's call it "gbu-bomb.acf") and model one of the parts desired, in this example the GBU bomb. This will create a symmetric part (as usual). See the following left image;
   
   
2. Start another fresh ACF file in Plane-Maker (let's call this one the "fuel-tank.acf") and do the same of step 1 for the other desired part, in this example the fuel tank. This will too create a symmetric part. See the following right image;
   
   

3. Use the ACF2TXT utility to convert both these ACFs files and also the plane ACF file to TXT format;
   
   
4. Search the TXT files for the set of arrays named "body_XYZ"*. These arrays are tridimensional where the first element relates to the plane's part, the second element relates to each part section and the third element relates to each section node. The values that go along with them are the respectively "X", "Y" and "Z" coordinates for that node;
   
   (*) For the tank/float pair, the target arrays would be the ones named "body_XYZ[23]" and "body_XYZ[24]";
   
   
5. For this plane part only the section elements from #0 to #6 are used by X-Plane render engine (they correspond to the seven section ribs of the part) and all node elements from #0 to #15, for each section;
   
   
6. Copying the values of the arrays elements that define the tank/float part* from both TXT files and pasting them in the correspondents arrays elements in the plane TXT file will result in having a different pair of tank/float parts;
   
   (*) For this demonstrator, values from array "body_XYZ[23][1][0]" to "body_XYZ[23][6][15]" were copied from "fuel-tank.txt" and values from array "body_XYZ[24][1][0]" to "body_XYZ[24][6][15]" were copied from "gbu-bomb.txt" and they all were pasted into "FA18.txt" file in the respective sets of arrays.
   
   
7. Finally convert the plane TXT file back to ACF format. Opening the modified plane in Plane-Maker will show both tank/float parts equal because it uses only one set of array to identify the part's shape, but when opening the plane directly in X-Plane it will be possible to see the asymmetric results, as shown in the following image;
   

Almost everything here done by me: Marcelo M. Marques - codename 31 M.M.M
mmarques@frontier.com.br