At the begining and at the final battle scene, when the fighting is for real, the Russian planes are actually repainted American F-5 Tiger 2s. Also there is not anything as a MiG-28s. All jet MiGs ave been odd numbered
That's really a non-issue.
American jets are used all the time to simulate enemy aircraft. (Tora! Tora! Tora! for example)
The MiG-28 is a contrived type - can't expect the filmmakers to design a whole new aircraft from scratch to flying model just for a movie right? Furhter, this was in 1985 (?); CGI wasn't extant then.
Lastly, juust like to add a point - the F-5 is (was) used by the Navy as an aggressor a/c.
Actually, Top Gun was filmed at Miramar in San Diego, Cali. in the autumn of 1984. I was born at Balboa Med. Center, and my family lived at the base during the filming of the movie.
The Soviets have always numbered their aircrafts oddly, never even, so there is no chance of a MiG-28 ever existing (eg. Mig 17, MiG 21, etc.). The fact that they are F-5 Tiger IIs given the Red Army markings(the bright red star on the tail indicates they are Russian) also disproves the MiGs.
They use F-5s for sim battles. In fact, the star on the tail was fake; it only simulates enemies to tell which is on your side and which isn't, because the star has a border around it, whereas the Russian star does not. Plus, they wouldn't let it go if it was a true enemy; they would either escort it back to the carrier or shoot it down. That's the one rule of Naval Aviation; NEVER LET THE ENEMY GO!