Emty places

[alyster]

I was wondering why are names F-13(YF-13) and F-19 (YF-19) emty???
And why is JSF YF-35, not something like YF-24 

[Goose]

I don't believe they are empty. Most are used by experimental aircraft and others of sorts. For example the X-29 and another example is the F-21.

[alyster]

I know, I found stuff like YF-12, F-21, F-17 etc. But nothing on the F-19.
About the F-13, the J-13 was called F-13 I found. 

[Webmaster]

J-13? Chinese? it doesn't belong in the list anyway. But the X-13 was the Ryan Vertijet...it never succeeded to become a fighter, probably because of the number 13 

F-19 was skipped on request by Lockheed, they wanted to introduce the F-5 derivative (now F-20) and since it was intended as export fighter, they didn't an odd number because the soviet fighters used odd numbers.