In a 38, you're best bet at low altitude is probably a scissors. This works especially well if they enemy is going faster than you are. There really isnt much you can do at low alt other than keep moving.
I have realized flying in a Mosquito lately, which is kinda similar to the 38, that if an enemy con, lets say an La7 (which we see so much of), is going faster than you, yet is slow enough for a shot. Since the LA7 can turn better than you, you cannot break away from it. What I would do is this:
Begin a scissors move, and while entering the first roll, cut throttle to 25% which is not too slow, yet slow enough that the LA7 cant get a very clean shot. Continue the Scissors and try to keep the LA7's roll opposite of yours, meaning if he is banking left, you want to be banking right. Hopefully, the LA7 will overshoot, and pass you. Most likely he will try to loop back around, so hit full power and WEP and try to follow him in the loop, if there are no other enemy planes around. Use the superior stall fighting of the 38 to roll over and hopefully, take a clean shot at him.
Another move that I have noticed an enemy con may take after overshooting is loop halfway, then try to do a vertical scissors. If he does this, follow him, but do not lose too much E, then when he dives back down, use the long rudder movement of the 38 to manuever into a firing position, and with the superior firepower of the 38 you should easily down, or severly cripple him.
Let's say the enemy aircraft is a spit IX and he is not going faster than you. In this situation, since he is a better turner and is in the better aircraft, I would try to extend away from him and either 1) he will get tired of chasing and break off or, 2) you will get far enough away from him to turn back and fight him starting off clean with E and a merge.
You may already know this and not get anything out of it, but its just my 2 cents.
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Also remember, I've only been flying 2 years and have had MA for only 4 months, so take taht into consideration before you try anything this noobie tells ya.
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:edit I just saw the part where you say you have little E because you just finished off a different target. This is actually to your advantage because it will cause the enemy aircraft to overshoot even more, and give you a better shot.