Lazy 30mm question

[Muzzy]

I know this has been mentioned before, but I can't find the post...

What happens to the K4 tater gun when you extend the convergence setting?  I've heard talk about 'loft' but what exactly does that mean?  Do the rounds curve, or do they drop less?

[Spork]

The muzzle velocity on the round never changes. So, for it to travel farther you need to put extra loft on the round. Picture throwing a baseball at 80 mph. You can't throw harder or softer. How much trajectory you put on the ball determines how far you can throw it. Want to  hit something farther out? Throw it a bit higher. Same concept.

On a side note: If you have your convergence set at 600, based on what I said earlier, it will have a lot of loft on it. So on a close target, say 200m, you will actually have to aim BELOW the target because of this.



Spork

[The Fugitive]

The theory is that if you set it at 300 you will hit the center of a target AT 300. If you set the convergence at 600 you will hit ABOVE center at 300 due to the lob. The idea is that if your pulling G's in a tracking shot you shouldn't have to lead as much.

[Muzzy]

So it seems, like all convergence issues, I have 3 choices.

1. I can set the convergence at the point where I find I'm getting most of my target shots in the K4, which is around 200.

2. I can set the convergence at 600 to try and improve my distance shots, compensating for loft when I take close in shots.

3. I can set for around 300 and split the difference.

Regarding option 3, at setting 300, is there much loft at 200 and is there much drop at 400? 

[The Fugitive]

You can check it using the ".target" command. On-line or off-line type .target xxx with "xxx" being the distance you want to check (400 and 200) turn your plane north steady it in level flight, and fire a burst. Reset the distance, and do it again and then check the hit patterns.

[Tophat23]

Me neither

[Muzzy]

Yes but I said this was a lazy 30mm question.

Seriously though, thanks very much for the answers. I'll try to put them to good use.

[The Fugitive]

LOL!!! well set your convergence at 300 and do the test on your next climb out....you do play to fly it again don't you?

[Muzzy]

LOL!!! well set your convergence at 300 and do the test on your next climb out....you do play to fly it again don't you?

And waste 2-4 perfectly good taters??? Are you insane??? 

[grizz441]

So it seems, like all convergence issues, I have 3 choices.

1. I can set the convergence at the point where I find I'm getting most of my target shots in the K4, which is around 200.

2. I can set the convergence at 600 to try and improve my distance shots, compensating for loft when I take close in shots.

3. I can set for around 300 and split the difference.

Regarding option 3, at setting 300, is there much loft at 200 and is there much drop at 400? 

For what it's worth, I have mine set at 350 to "split the difference" if you will.

[BillyD]

I like the 200 since I try to set up close crossing shots and dont want to loft over the tar-get. Find something that works and run with it. If you try not to get into too many tail chase scenarios and work on getting the crossing shot or a windscreen filling overtake shot you will have no problems connecting taters.

[mtnman]

So it seems, like all convergence issues, I have 3 choices.

1. I can set the convergence at the point where I find I'm getting most of my target shots in the K4, which is around 200.

2. I can set the convergence at 600 to try and improve my distance shots, compensating for loft when I take close in shots.

3. I can set for around 300 and split the difference.

Regarding option 3, at setting 300, is there much loft at 200 and is there much drop at 400? 

Laziness will practically ensure you get a bunch of misses when it comes to gunnery, plain and simple.  There's no "magic" answer to your question, so no tidbit of advice will allow you to be lazy and successful at the same time.

From an "aim-point" perspective, you have it pretty easy with a nose-mounted gun, because it's mounted so close to eye-level and the trajectory "behaves" the way you think it should.  It makes the trajectory behave the way Fugitive states-

If you set the convergence at 600 you will hit ABOVE center at 300 due to the lob.

With wing-mounted guns though, his statement isn't necessarily true though.  With a 600yd convergence you'd hit LOW at 300 with the F4U's .50's, for example.

What makes it difficult to get hits with the 30mm's is the time or "space" between the rounds.  Due to that, having a "perfect" convergence setting, along with "perfect" aim, is far from enough to ensure hits.  You also need to time your shots perfectly, unless your target is going straight away and has no apparent motion from your perspective.  An absolutely perfectly-aimed shot on a crossing target will miss every single time, if you squeeze the trigger a fraction of a second too early or too late.

The three convergence options you mention are only valid for discussion assuming you have the required timing down, or are shooting at targets that appear stationary.

Assuming you're doing that, what are the merits of each of the options you list?

1- Pro's... targets are bigger when you get closer.  Less time is required for the round to travel a lesser distance.
    Con's...  A convergence set in super close doesn't take advantage of the trajectory to it's fullest.  It's like sighting-in a center-fire deer rifle at 100 yards.  It work's, but isn't optimal.  It leads to more guesswork at a larger variety of ranges.

2- Pro's- It'll let you aim directly at some targets at 600yds.
    Con's- You may need to adjust your aim-point for every other shot distance.  It may actually be harder to hit a target at 200-300 yards, than it would have been to hit one at 600 with a 300 yard convergence.

3-  Pro's- It's about as good as it gets when looking for an overall "good" option for the largest range of shooting distances.  Aim a little high for long shots, maybe a little low for close (but it probably won't really matter) shots.
     Con's- it still won't allow for the differences you'll see in impact point for firing while in anything other than a straight and wings-level 1G configuration.  Firing while banked, inverted, nose up- or nose-down, or pulling anything more or less than 1G will render your sights inaccurate.

Regardless of the convergence you choose, the beauty of the matter is that for us, any laziness you exhibit in learning about aerial gunnery is to our benefit.  In the end, it means that the best, most accurate, and most truthful answer to your question is "It just doesn't matter".   

[grizz441]

What makes it difficult to get hits with the 30mm's is the time or "space" between the rounds.  Due to that, having a "perfect" convergence setting, along with "perfect" aim, is far from enough to ensure hits.  You also need to time your shots perfectly, unless your target is going straight away and has no apparent motion from your perspective.  An absolutely perfectly-aimed shot on a crossing target will miss every single time, if you squeeze the trigger a fraction of a second too early or too late.

I have to respectfully disagree with your post on the inference of the sensitivity of convergence.  You make some good points, but ultimately, convergence has minimal importance with shooting a proper Mk108.  I will list the order of importance to prove my point:

1.  Shot setup.  Creating a close quarters <200yd crossing shot.  This gives you the best chance to hit the target consistently.
2.  Firing early and in front of your target on center.  He will fly through your rounds in pieces most of the time.  I have to disagree with you here when you say he can easily squeeze through your rounds if not timed properly.  It can happen, but it is very unlikely.  The rate of fire on mk108 is around 6.5/second.  It fires slow but not that slow.  
3.  Last comes convergence.  If you are firing early, on center, and in front of your target, I'm sorry, but the probability of missing him is slim to none regardless of what your convergence is set at with this approach.  Convergence will only affect the fringe shots, that aren't on center, and this is ultimately a crap shoot, since sometimes you miss high and other times you miss low.

Having said all that, I prefer 350 because it still gives me the opportunity to land a long range tater instead of just dropping dramatically at the 450yd level.

[Muzzy]

Right, so, uh, I think I'm just gonna go with 300.

Thanks. 

 

[mtnman]

I have to respectfully disagree with your post on the inference of the sensitivity of convergence.  You make some good points, but ultimately, convergence has minimal importance with shooting a proper Mk108.  I will list the order of importance to prove my point:

1.  Shot setup.  Creating a close quarters <200yd crossing shot.  This gives you the best chance to hit the target consistently.
2.  Firing early and in front of your target on center.  He will fly through your rounds in pieces most of the time.  I have to disagree with you here when you say he can easily squeeze through your rounds if not timed properly.  It can happen, but it is very unlikely.  The rate of fire on mk108 is around 6.5/second.  It fires slow but not that slow.  
3.  Last comes convergence.  If you are firing early, on center, and in front of your target, I'm sorry, but the probability of missing him is slim to none regardless of what your convergence is set at with this approach.  Convergence will only affect the fringe shots, that aren't on center, and this is ultimately a crap shoot, since sometimes you miss high and other times you miss low.

Having said all that, I prefer 350 because it still gives me the opportunity to land a long range tater instead of just dropping dramatically at the 450yd level.

My point isn't that convergence matters much with nose-mounted guns.  It doesn't.  There are ways to adjust it to "make it" matter more than it should, one of which is to stretch it way out.  A handicap of sorts, willingly applied.

The timing aspect though, still plays out, and gets worse the further out you fire (simply because range estimation, and estimation of projectile travel time gets more difficult).  I've never looked at the specs for any gun on any German plane, so I'll just take your word for the 6.5 rounds per second rate of fire.  A gun firing at 6.5 rounds per second is firing one round every .1538 seconds.  By my math, a plane crossing in front of you at 250mph is moving at 340 FPS, which means it travels 53.2 feet in the time between rounds leaving the barrel.  An F4U is a pretty large fighter (at 33ft 4" length), and 250 is not too fast when it comes to an estimate of speed.  Plenty short to squeeze (albeit unintentionally) into a 53ft space.

That basically means that in a 90 degree crossing shot at a 250mph target, only one round really stands a chance of hitting it.  The round fired before will pass in front, the round after will pass behind.  That "golden" round, fired at roughly the right time, and aimed perfectly, stands about a 62% chance of hitting.  If the trigger squeeze is off by .09 seconds though, it's a miss.  If you're "off" by more than .09 seconds, your next perfectly-aimed round would be the one to stand a 62% of scoring a hit.  Odds of a hit would be worse if the target was a smaller plane, or was crossing at a higher speed, and would drop to zero if it wasn't aimed perfectly.

Of course, there are ways to improve your odds.  As you mention, getting close will help, as will reducing the crossing angle and/or speed.  Setting up a situation where you can hold (and adjust) a sustained lead would be even better.

And of course, setting up a sustained lead would totally blow any importance the convergence setting has, especially with nose-mounted guns.