As you say, some do some don't. I've always had mine internally with no problems. To me, it spoils the tidy look of a well made pattern plane to have it run externally...

The Twister I have just bought from ZN comes with a tube set into the fuz for an internal aerial - saves me a job!! As long as there is no carbon in the fuz surrounding it you will have no problems with reception with an internal aerial. Most are kevlar, glass or balsa so you should be fine.

James