aircraft is an odd duck. I'm not sure it's a bad tag (certainly there are some generic things that apply equally to a glider, an airship, and a transport-category jet for which "aircraft" may be the best tag), but I'm at a loss how to describe it.
I feel like the tag wiki needs to describe not only what "aircraft" means (we can steal the FAA definition for that), but how we want the aircraft tag used on the site.
Anyone want to take a swing at a Wiki entry, or weigh in with ideas?