Barrel rolls, or Lag rolls help give you a snapshot on an enemy that is coming with a lot of speed. Usually, when he's about 600 or so off, you begin the lag roll, he has way too much E to try and do the same maneuver, so most likely he will pull back out. By the time he realizes that, you already have pulled out of the roll and are on his 6, 200 out. probably, he will pull straight up to avoid the shot, but again, you are much more maneuverable than this con, so you can quickly get a shot on him, hoping that either you hurt him, or you kill him.
These usually only work on a diving con, if you got a con on your 6 with the same speed, I would suggest, for a quick reversal, would be to pull him into a scissor. Most of the time, you will have inexperienced pilot on your six and its a quick kill, but someone that has More experience, may avoid the shot once or twice. you will have more advantage because you have made the first move, and he may not expect that at all, but there are a few people that would know what to do in that position. Depending on the plane that you or what he is flying, your going to have to use every advantage that you can. if its a spixteen P51, fight vertical. If its a spixteen K4, out turning is the best way because he has more vertical.
That's just some of the things that can help. SA is very important in situations like this.
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