Finishing the CPACS 3 wing structure implementation

CPACS 3 offers many new ways to define wing structural elements. Spars can now be defined between two ribs. Ribs also have a multitude of ways to be positioned, including the positioning

  • at a dedicated spar positioning,
  • at arbitrary eta/xsi coordinates,
  • at any position on a spar, the leading edge or the trailing edge
  • and any combination of them.

The implementation of all these new features took us a while and was the main issue, why TiGL 3 is not yet released.

The good news: We have to everything in shape and support all these new features. Here's a first glimpse of what you can expect with the new structural definition:

New ribs and spars features

Automatic conversion to CPACS 3

The new CPACS definition comes to the price of more complex CPACS files. Converting a CPACS 2 file into the new format can be very time consuming and error prone, if many ribs and spars are defined in the file.

To help you with the conversion process, we developed a small cpacs2to3 utility. Like TiGL, this converter is open source and hosted on github:

cpacs2to3 can be installed with the Conda package manager. Just create a new virtual environment and install cpacs2to3 in it:

conda create -n cpacs2to3 python=3.5 cpacs2to3 -c dlr-sc

To convert a cpacs file, use cpacs2to3 as follows

activate cpacs2to3
cpacs2to3 myaircraft.xml -o myaircraftv3.xml

Limitations of the conversion

CPACS 2 allowed to explicitly placing a rib in a wing section element. With the new definition, ribs can be placed with arbitrary eta/xsi coordinate combinations, which also enables to place a rib in a section.

In TiGL 2 however, ribs that have been placed into a section were not affected by a rib rotation around the z axis. Meaning, the rib kept always to be in the section. With the new definition, this is not the case anymore. The cpacs2to3 converter will return a warning in this case. Then it is up to the user to decide, what to do.

If you really want to have a rib inside a section, there is still the explicit rib positioning, which allows an exact rib positioning inside a section.