A brief explanation.
Jon set it up so that you must join the fleet to download his ships in order to keep tighter control over his work. Piracy has become an issue as of late. Fleet members act as beta testers and only get a crack at the new stuff after it has been tested by the staff.
We do have a new program underway for Test pilots who wish to help out with ship development through beta testing for fleet usage. You can find out all the details in the RTF Fleet forum.
Other developers also have hanger space at the fleet where you can find add ons that work with the fleet or as stand alone add ons. Due to lack of feedback on beta ships, I have restricted my hangar access to member level Nugget or higher. I hope to be able to allow all members back in soon.