Quoting Dave from his blog at http://http://daveshangar.blogspot.com/:
I'm stopping my FG/JSBSim work for a while, maybe a long while. I need a break and have lots of work coming up anyway, so I won't be posting anything here, and won't be updating models. Grab them while you can because the hangar goes off the air in early December
I think the only thing we can do is hope Dave will be back at some point and for his work to stay available for download.
In the mean time you can still, using Dave's words "grab them while you can", at http://http://members.cox.net/davidculp/hangar.html