You may believe that development of a free software project is not easy, and you don't want to destroy them for any possible reason. One of my project, however, is the only one which I may destroy it within a few day. I will delete the git repository.
It is a Dornier 328 Jet FlightGear model. This model is free software and it is licensed by GPLv2. However, I finally realized that I used a non-free software to develop it, so in repository, it contains some files with non-free formats. This non-free software I used is called DATCOM+. DATCOM is free software which was developed and released by NASA in public domain. In contrast, DATCOM+ is based on DATCOM but the company which maintains DATCOM+ does not released the source codes of DATCOM+. This software also comes with DRM. The DRM restricts their users installing this software in more than one computer.
There is not legal issue to build software based on DATCOM, because it is in public domain. However, it has a lot of ethical issues. For example, this software includes no source code, so we do not know whether this software will harm our computer or not, and it may even upload your new designed aircraft model to others without your permission. There is another ethical issue which is not about free software but a misleading to customers. This software named DATCOM+. The name is very similar to the original DATCOM. Therefore, customers may be misled, so they may believe that the DATCOM+ and the original DATCOM is the same thing.
What I will do is develop a new FlightGear aircraft model by using totally free software. It means that I will try to learn the original DATCOM. It may not be easy. If I can develop a flyable aircraft model successfully, I will write some tutorials and articles about how to build a totally free software production and development pipeline to make a free flight simulator model. I may also maintain DATCOM and develop some extensions for DATCOM, and of course, release them under GPL.
I say I MAY do that, but I am not very sure if I have time or enough powerful programming skills to deal with such ancient software. Therefore, I encourage any of you to maintain and continue to develop DATCOM.
Have fun, be free.