Originally posted by bsdaddict
hrmmm, so for Hispano's with 303's, should it be the 303's that are set to converge a tad farther out?
This is a tricky one, and if I had the graphics skills I'd make a picture to show it. As I understand things, the key to the answer comes from thinking in terms of TIME more than DISTANCE, since distance convergence is built in to the convergence setting itself. Here's what I mean.
First, imagine your guns solution with you and the target in the same geometric plane, flying straight and level. In this situation, the only problem is the 3 dimensional geometry of gunnery. If your convergence is set the same for both gun types, the bullets and cannon shells will arrive at the same position in 3D space...although the slower bullets may have a little more "lob" to their flight path, they will end up at the same place. They will NOT, however, arrive at the same time. The cannon shells arrive sooner, and the bullets take a little longer to cover the distance from gun to target. When the geometry is flat, though, it doesnt matter all that much.
Now, however, imagine you are in a turn fight and you are taking a deflection shot. Suddenly the TIME component becomes much more important...because with your turning enemy, if the bullets take longer to get there the target will have moved. Since its in a different place in space, bullets that get there later will miss even if the cannon shells were perfectly placed. In short, adding the 4th dimension (time) to the equation means that when the targets position is changing relative to you, the correct aiming point will be different for different projectiles.
One way to get around this turn fight problem is to have different convergence settings to compensate for different muzzle velocities fired at the same time. Imagine now that you're in a Bf 109K4, with all its guns in the nose -- the slow 30mm shell and relatively quicker 12.7mm MG. Imagine also that you have your targeting pipper perfectly placed to get the 12.7mm MG rounds to hit the canopy. Here's the key point -- by the time the 30mm gets there, the target will have moved farther along its flight path, so you risk that the 30mm will pass behind the target, even though it is "converged" at the same position in space that the 12.7mm rounds got their hits!
In order to get the slower 30mm round to hit the target at the same fuselage position, you will have to set its convergence so the round is "lobbed" higher than the 12.7mm. To do this in AH2, you'd set the convergence distance farther out than the 12.7mm, but what you're really doing is NOT compensating for the "lob" (Remember, the whole idea of convergence is to get the rounds into the same physical space...so its already taken the lob effect into account.) Instead, you're allowing for the difference in TIME, which affects TARGET position in space.
Now, if I have this right, it means that having dissimilar rounds forces you to choose whether to get the rounds to hit together in a turning, out of plane situation (different convergences), or whether to set them to strike together better in a straight ahead, unchanging relative position (the straight shot (identical convergence).
Now if those of you with more knowledge catch an error in this thinking, please correct me -- I'd hate to lead anyone astray, and I'm always open for more learning!
