You can only defeat the Red Baron on level 25. The trick to defeating him is not to shoot him down. Allow the Red Baron to get behind you. He is usually the second bogey you encounter. Go into vertical climb, then when you hit the ceiling, go into a nose dive (the more vertical the better). The Red Baron will follow. Immediately before you hit the ground, pull up. The Red Baron, being under-powered, will crash ending the game.