Yes, it is obviously perfectly legal to make money off GPL'ed software.
Some of you folks (chris!) should really have a look into the GPL license, especially if you intend to contribute to FG.
There are some other contributors who specifically decided not to release their work under the GPL due to this possibility.
Making money off GPL'ed software is actually a good opportunity, this can for example be done by providing professional support services or by providing consultancy services. Another opportunity is contract work, i.e. doing paid open source development.
Many large open source projects use such opportunities to fund their development.
Unfortunately, there are also some simple "ripoffs", which just take existing open source software, rename it, re-brand it, re-package it and try to make money by selling it to UNINFORMED people.
this just disgusts me. I created my aircraft specifically so others wouldn't need to pay for them. Give to others freely without expecting anything in return; that's what being a good person is all about. Unless of course what you're giving has been taken by some prick to be sold to others. If I find my X-29a or X-02 on that list of included aircraft on the FPS site i'mma be pissed.
Just wonder if any other devs feel the same way.
This is explicitly allowed under the terms of the GPL.
If I were to take the FG release, put it on a CD, rename it to "The totally awesome Hooray Simulator" and started to sell it on ebay, it would still be perfectly fine.
Even if I took any of your contributions (GPL).
As long as FlightGear is GPL software, the only way to deal with this is an aggressive information campaign, by telling people about FlightGear, and by making it as easy as possible to track FlightGear related derivates.
For aircraft developers, one simple way would be to use custom splash screens that contain the
http://www.flightgear.org URL, including a short text saying "This is free software, under the terms of the GNU GPL".
In addition, you can print this information to the console using a Nasal script.
You could even display such information in a splash screen, or an about/help dialog.
Really, people are not going to pay any longer for FlightGear ripoffs, once they immediately see that they are dealing with scams.
Putting watermarks on your screenshots and videos (youtube) is another easy way for dealing with this.
People who are willing to pay for FlightGear, can do so by directly purchasing a set of DVDs using the official flightgear.org website.