The CPACSCreator added a new abstract base class CreateConnectedElementI for both wings and fuselage, which seems a bit intrusive to me. In addition the Open-Closed principle is violated, because we had to modify the existing classes for the new functionality in the TiGLViewer. In addition, neither a wing, nor a fuselage "is a" CreateConnectedElementI.

An alternative solution would be to have the TiGLViewer code use std::variant and std::visit (or boost::variant, if we still want to stick to C 14).

using ElementModificatorInterface = std::variant<Fuselage, Wing>; // could be apended with Duct, Pylon, tank in the future

The code changes are limited to the calling code, i.e. TiGLViewer.