Convergence Question

[Simaril]

OK, after a night thinking about it more, I have a correction.

Getting the rounds to target is about TIME and DISTANCE. We're always thinking about the distance part of the equation, but I've been pointing out the role of time. In fact, I got so busy with the time aspect that I overlooked the role of distance in the straight on shot...

Here's what I mean:

Imagine that straight on shot again, but this time pay attention to the range. Acoording to Tony Williams, the Mk 108 30mm cannon had a muzzle velocity of 505 m/s, while the 13mm MG 151 had a velocity of 710 m/s. Now consider the guns range -- which is different than the range to target at the time of firing, since you are both in airplanes travelling hundreds of miles per hour.

OK, for simplicity lets make the planes flying at 280 miles per hour, which is 125 meters per second. Lets place the plane 288 meters ahead of you, having just clicked the AH range marker from 400 to 200. (Please let me ignore the difference between AH range in yards and velocities in meters -- this is hard enough already!)

The 13mm rounds are moving at 700 m/s. They will strike the target in 0.5 seconds, because in that time the target will have moved an extra 62 meters to make the total bullet flight distance 350 meters. But, in the same 0.5 seconds the 30mm round will still be 100 meters away, and it will take it another 0.25 second to reach the preset convergence DISTANCE. In that extra 0.25 seconds, the target will have flown another 30 meters, and the 30mm will miss. So, at speed of 280mph and range of ~300 yards, you'd need to set the 30mm cannon  convergence 25 meters farther to get the rounds to hit nearly together ON THE TARGET. They will hit at different times, and at different map coordinates, but they will land nearly together on the target aircraft.


At very short TARGET RANGES, the rounds' flight times are so short that the time element doesn't matter nearly as much -- which is why it's easier to get 30mm hits up close. On the other hand, when the target is moving faster, the difference in convergence will need to be greater to get them both to hit.



Now on to turn fights. Here, the calculations get incredibly tangled by the target actually moving upward relative to the firing plane, the apparent size of the aircraft when viewed at angles, guns firing across the chord of the turning arc, the need to adjust convergence thinking about vertical position instead of the horizontal geometric plane the setting was designed for, and so on. Frankly, calculations just aren't worth it. Instead, understand the qualitative situation I outlined in the first post and adjust by the seat of your pants!

[Spazzter]

All,

Thank you very much for your informative posts and input.

<>
Spazz

[lengro]

Simaril,

Imagine a train with a lenght of 200 meters.

Attach an la7 at the front of the train and a 109k4 at the back. (randomly chosen - promise!)

The 109k4 has the 13mm and 30mm convergence set to 200 meters - and the la7 centered in the gunsight.

If the train is stationary - the 13mm and 30mm will hit the same spot - at different times.
If the train is running at full speed - the 13mm and 30mm will still hit the same spot - at the same times as before. (Neglecting the impact of change of wind resistance)

(In your calculations you should add your planes speed to the bullets muzzle speed)

[BaldEagl]

While everyone here would agree that the modeling in AH2 is the best out there, I have to wonder if the guns are modeled to the exact level of detail descibed in this thread, or if, in fact, they've been modeled to "keep it simple" in terms of gameplay.  Certainly general ballistic properties in terms of flight arc, rate of fire, etc. have been modeled.  I'm not as sure about muzzle velocity and frictional loss being modeled exactly.

Another issue/question in regards to this is the "lob" or flight arc of the ordinance because, in reality, if the plane is laid over on it's side in a turn, the arc should become horizontal relative to the plane rather than vertical (your shots would drop toward your lower wing) with the vertical component of converrgence actually producing built in lead.

I'm not arguing that what's been said in this thread is theoretically true or not.  Simply wondering just how accurate the modeling is or if it's "close enough for gameplay".

Maybe someone's tested this?

[E25280]

Originally posted by BaldEagl
While everyone here would agree that the modeling in AH2 is the best out there, I have to wonder if the guns are modeled to the exact level of detail descibed in this thread, or if, in fact, they've been modeled to "keep it simple" in terms of gameplay.  Certainly general ballistic properties in terms of flight arc, rate of fire, etc. have been modeled.  I'm not as sure about muzzle velocity and frictional loss being modeled exactly.

I think they are, and as evidence I am linking below a thread where I not only make a fool of myself, but do the math to prove it.

http://forums.hitechcreations.com/forums/showthread.php?s=&threadid=172137

The basic arguement I was trying to make is that buff guns were not any more effective then a fighters guns when the fighter was firing from dead 6.  What I didn't account for was deceleration of fired rounds.

HiTech's first reply to me was:

E25280: Gunns firing reward are more lethal at range, not do to the resone given above, but because they are travling at a slower rate threw the air at launch time, and hence less drag, hence they are travling faster at impact time.

Take the most extream case both planes are travling at 1000 fps and the bullet is shot straight back with a muzzle vel of 1000 fps.

Hence relative to the ground and air it is not moveing other than it is starting to fall.

Now 2 secs later the plane impacts the bullet at 1000fps, notice the bullet did not slow down at all relative to the trailing plane.

This is why reward guns of bombers seem more lethal.


HiTech

A little later on . . .

E25280: Intial deacceration on the 50cal would be in the 1400 FPSPS Range

HiTech

So, long story short, in answer to your question, AH does model things like deceleration due to wind resistance, and that difference is, I am certain, modeled on a by-weapon basis.

[2Dizzy]

<---using the convergences form SODA's evaluations pages. Was a good start and were a big help. Didn't have to adjust much since then.
It should get you started.

Dizzy

[bsdaddict]

Originally posted by Gianlupo
Bsdaddict, the Latin in your signature is wrong. It's "Carpe libertatem".

Thanks Gianlupo.  I've never studied latin, just used an online English->Latin translator...  I'll trust that you're correct, but if you wouldn't mind, what's the difference between the two phrases, how do they translate literally?

[Simaril]

Originally posted by lengro
Simaril,

Imagine a train with a lenght of 200 meters.

Attach an la7 at the front of the train and a 109k4 at the back. (randomly chosen - promise!)

The 109k4 has the 13mm and 30mm convergence set to 200 meters - and the la7 centered in the gunsight.

If the train is stationary - the 13mm and 30mm will hit the same spot - at different times.
If the train is running at full speed - the 13mm and 30mm will still hit the same spot - at the same times as before. (Neglecting the impact of change of wind resistance)

(In your calculations you should add your planes speed to the bullets muzzle speed)

Lengro,

Good point, as applies to the straight and level flight example. The rounds will strike at fractionally different times in either situation, but if the firing plane's velocity matches the target plane's, then the target movement will exactly equal the extra velocity imparted by the firing plane's movement.


Time becomes much more of a factor in the off angle guns solution, which is the situation that first got me thinking about how projectile flight time become at least as important as convergence.

Thanks for the input!

[hitech]

(Neglecting the impact of change of wind resistance)

In the train example and assuming the above you are correct. But the change in wind resistance at normal airplane speeds, is not a trivial effect when shooting backwards or forwards.

[Murdr]

HT (or anyone else),

(dreaming here that I'll get an answer)

Do you know the specs on your .target?
eg. The center circle is X feet in diameter, and each subsequent circle is X feet larger?

[lengro]

Originally posted by Murdr
HT (or anyone else),

(dreaming here that I'll get an answer)

Do you know the specs on your .target?
eg. The center circle is X feet in diameter, and each subsequent circle is X feet larger?

Murdr,

I have also wondered about that, so I made the following picture with .target 1 and a 109k4 - with that distance, the target plane is actually slicing through the 109:



From the known wingspan of the 109 I could estimate the circle diameter to 12 meters.

[Murdr]

CC, considered setting up such a scenerio myself.  Looks like it could be diameters of 20ft, 40ft, 60, 80...ect.  Thanks.

[hitech]

Mudr: You are correct Radius increases 10 feet each circle.

[Angrist]

Nice to see another Cragganmore, or just Scotch fan.....Right On, HiTech!:aok

[Murdr]

Thanks!