Aces High Bulletin Board
General Forums => Aces High General Discussion => Topic started by: Spazzter on November 08, 2007, 08:35:19 AM
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Hey All,
I am hoping some of you experts might be able to help me with a question about convergence. My main ride has been a Spit 9 lately, and I have my convergence for all guns set at 275. I like this range as I work to get close before taking my shots and want my bullets to count. I will shoot at max 600 on a dead six shot, but will only make a short spray in hopes to make a bogie break at any range beyond that. My question is this, I have noticed that the 20mm cannon runs out well before your 303's especially if you have multiple kills under your belt. I have many times found myself with only 303's left and still engaged with the enemy. I have been fairly successful in killing planes with the 303's, but find that the lead is much greater to get hits than when I am shooting the 20mm. This would make me think that my 303's are not hitting when I am firing both cannon and BB's and that maybe I should not have my convergence set the same distance for both guns. Any thoughts???
Thanks in advance for your input. I just want a better understanding.
<>
Spazz
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Use the .target command in TA or offline to visually check bullet dispersion at various distances.
I have my cannons at 350 and my .303 at 200.
As long as I still have 20mm ammo, I'm usually shooting cannon only, I don't need that added "punch" of the BBs. After cannon ammo is gone, I use the .303, getting as close as possible before firing, thus the short convergence for them.
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303s are lower velocity, and have wider dispersion than the hispanos. Also, while the convergence setting centers the guns at a specific PLACE, the bullets travel at a different SPEED than the cannons, so for deflection shots the lead will be a bit different.
That's the head knowledge -- to see the gut impression, use that .target command Lusche talked about and see how the rounds spread out differently. It'll make it even more clear.
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by no means am I an expert, but two suggestions I'd make would be:
1) tickle/range-find with the 303's, add cannon when you know you're gonna hit.
2) set the 20mm to converge 25 yards farther out than the 303's. When I fly the spitVIII I have the 303's at 250 and the 20's at 275.
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Originally posted by Simaril
303s are lower velocity, and have wider dispersion than the hispanos.
I think you got the velocities wrong there - the 303s go faster.
Trip
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Originally posted by Trip01
I think you got the velocities wrong there - the 303s go faster.
Trip
Nope.
The Hispano's 20mm 20/110 cartirdge delivered either 830 or 860 meters per second muzzle velocity, depending on the Mark. Meanwhile, the 7.7/56R cartridge used in the 303s left the muzzle at 762 mps for the AP round, slower for the incendiary. So the Hispano is 10-12% faster.
Not a gun expert, but if I recall that's a big part of why the Hispanos are so stinking deadly. Their higher velocity does more kinetic damage than many other 20mm, and it flies straighter and truer. (Quick comparison to a bad one -- the German 20mm round from the FF cannon has a velocity of only c.550 mps.) It also explanins why the US 50cal and Hispano pairing is so effective -- the Hipanos velocity is very close to the 50cal round, so matching those two guns means everything will be hitting nearly the same place AND time, with explosive and kinetic energy. Ouch.
(Data thanks to Tony Williams, who has on occasion dropped in to pay a virtual visit. If you haven't come across his work, he's a world authority on the guns and ammunition of WW2 era, having written a number of books on the subject. His website is HERE (http://www.quarry.nildram.co.uk/index.htm))
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Actually I think it was 840m/s versus 778 m/s. The .50 cal hits 930 m/s which is all I care about.
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Originally posted by Simaril
The Hispano's 20mm 20/110 cartirdge delivered either 830 or 860 meters per second muzzle velocity, depending on the Mark. Meanwhile, the 7.7/56R cartridge used in the 303s left the muzzle at 762 mps for the AP round, slower for the incendiary. So the Hispano is 10-12% faster.
hrmmm, so for Hispano's with 303's, should it be the 303's that are set to converge a tad farther out?
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Originally posted by Simaril
303s are lower velocity, and have wider dispersion than the hispanos. Also, while the convergence setting centers the guns at a specific PLACE, the bullets travel at a different SPEED than the cannons, so for deflection shots the lead will be a bit different.
That's the head knowledge -- to see the gut impression, use that .target command Lusche talked about and see how the rounds spread out differently. It'll make it even more clear.
So when you turn on the targeting computer in the TA, what is it calculating off of if you have both MG and cannon?
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Originally posted by Donzo
So when you turn on the targeting computer in the TA, what is it calculating off of if you have both MG and cannon?
there's separate crosshairs for each. one green one red IIRC.
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Originally posted by Donzo
So when you turn on the targeting computer in the TA, what is it calculating off of if you have both MG and cannon?
Both,you will see 2 sets of crosshairs.
even the spit 1 shows 2 sets of crosshairs for it's 8 mg's
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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!
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thanks for the explanation, Simaril. I'm definitely going to have to reread that sober... :confused:
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Originally posted by Simaril
The Hispano's 20mm 20/110 cartirdge delivered either 830 or 860 meters per second muzzle velocity, depending on the Mark. Meanwhile, the 7.7/56R cartridge used in the 303s left the muzzle at 762 mps for the AP round, slower for the incendiary. So the Hispano is 10-12% faster.
I stand corrected, thanks.
Trip
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Very well explained, Simaril. I didn't know the peas were faster than the Hizookas... I'll have to change my convergence on Spits! :)
Bsdaddict, the Latin in your signature is wrong. It's "Carpe libertatem". ;)
EDIT: I was probably drunk (in the morning!) I confused peas and shells! :D
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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!
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All,
Thank you very much for your informative posts and input.
<>
Spazz
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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)
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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?
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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.
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<---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
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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?
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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!
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(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.
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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?
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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:
(http://i231.photobucket.com/albums/ee35/lengro/sizeoftarget.jpg)
From the known wingspan of the 109 I could estimate the circle diameter to 12 meters.
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CC, considered setting up such a scenerio myself. Looks like it could be diameters of 20ft, 40ft, 60, 80...ect. Thanks.
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Mudr: You are correct Radius increases 10 feet each circle.
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Nice to see another Cragganmore, or just Scotch fan.....Right On, HiTech!:aok
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Thanks!