One on one, as long as you're flying faster plane, AI doesn't stand much chance. They're annoying, though. Getting on their six is never a problem. But AI has eyes in their tail, and they are master of handling aircraft at stall speed (as matter of fact, they don't stall). You're now facing a dilemma: keeping your speed, you will overshoot, chasing them, you will be slowed down. Players tend to go the second way, it's quite boring having AI on your 6, extending for 15 minutes before you can loop around to go head-on and do everything again.
When fighting more than 1 AI, be careful since AI is master of drag-and-bag. You slow down for the kill and another will get you from behind. Sometimes, when my speed advantage isn't very great (P-51 vs. FW-190 for example), AI tries even more sinister tactic: one AI drags you down low, the others keep climbing. You can get one AI and find yourself 1000m under 3 other FW-190 circling above
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Another no-go when fighting AI is steep climbing when AI is on your six. AI will get you in no time with their excellent deflection shooting. But I know, AI can master substained climb rate without bleeding energy. I can't because my handling at slow speed is terrible.