I used to have regular success with the rockets on the 110 - now I don´t have much time for playing anymore. Here is how I did it:
Approach the bombers from dead six. Zoom in a little, and keep the formation about two thirds down the line wich extends down from the circle in the aiming reticule. In other words, one third of that little line is below the bombers, two thirds above. Keep the bombers there, be smooth on the controls. If you keep them there for lets say 45 seconds while you approach, you will enter a stable altitude relationship with the target, i.e. both target and shooter are in level flight, taking vertical velocity out of the equation. Once the range drops from 1.5 to 1.0 let loose with maybe a 1 second spacing.
The parameters will change with altitude, speed, and rate of closure, but this is a good setting to start. Film your attack run, later you can review it and see to which side you erred.
The 110 is a fairly big target, and the 50 cals will start hitting you almost at that range. If the bomber isn´t suspecting a rocket attack he might wait to open fire and you might get lucky. In other words don´t linger and watch, at 900 and closing you are dead against mediocre and better gunners.
Litjan, 1.hessische Freibierstaffel
