Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Saxman on July 24, 2010, 08:34:50 PM
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Now that we have sight reticles that are accurate to the mil across all aircraft, does anyone have a calculation that can be used to determine how many mils of lead would need to be given to a target?
I know it's a function of the target's deflection, range and airspeed, and the flight time of the round, but I'm not sure of the actual formula.
I'd REALLY like to be able to put together a "lead chart" for the Mk.VIII sight showing lead in mils at various target deflection angles, ranges and airspeeds.
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You mean something like this? :)
(http://332nd.org/dogs/baumer/BBS%20Stuff/SightQuestion/leadtable.jpg)
I'm working on a write-up using the WW2 fighter gunnery manual, and it will have tables like this for some of the common Mil sights (35/50/75/100/105).
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doesn't anyone use the force anymore?
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Something like that, yeah, although that I can tailor specifically to the Mk.VIII sight with its 5mil increment marks.
More along the lines of::
| Range (Yds) | Deflection | Airspeed | Lead |
| 200 | 30 | 250mph | 25mil |
Obviously this isn't accurate and just an example of what I'm looking for. Like I said in the OP, I'm just looking for whatever formula is involved in calculating the estimates so I can put my own chart together.
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doesn't anyone use the force anymore?
na man
all the cool kids are using magnets these days
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doesn't anyone use the force anymore?
since day one brother! :D
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Well given that we get an incredible amount of practice gunnery compared to real WW2 pilots, it's no wonder so many of us have used the force.
Saxman here is the formula for calculating lead in Mils, feel free to run the numbers and post a table.
(http://332nd.org/dogs/baumer/BBS%20Stuff/SightQuestion/Lead/4-6.jpg)
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Do you have the ballistics chart for the M2 .50cal they reference as well? I think I'll need that, too, unless Aces High gives the .50cal a constant velocity regardless of range.
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Nope, I'd just use the range and speed they used in the example.
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Problem is I'm wanting to make something more comprehensive than a lead chart that only works when you're traveling at 455mph TAS and 333yds range (for one thing, my own convergence is at 200yds. This would be useless for me).
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Another article about sights from SimHQ that might be an interesting read also
http://www.simhq.com/_air/air_031b.html
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I've seen that site. The problem is it doesn't have the missing information I need to make my own lead tables (the velocity of the Browning .50cal at various ranges).
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I've seen that site. The problem is it doesn't have the missing information I need to make my own lead tables (the velocity of the Browning .50cal at various ranges).
I think a big part of the reason those aren't easy to find, is that they're going to be highly variable.
I think the best you'll be able to do is get a basic, generic trajectory table from a common, modern firearm and base your tables on that. I'd guess the 30-06 isn't probably that far off, but I'd have to look into it to know for sure. I think it has similar muzzle velocity, but I have no idea how similar the ballistic coefficients are...
Bullet velocity is normally measured near the muzzle, and sometimes you can find information for common rounds, out of common firearms, out at various distances. Even then, they need to be taken with a healthy bit of speculation. For the 30-06, you should be able to find some rough velocities out at common deer hunting ranges. Don't take them as "gospel" though.
In AH, I'd think some extensive use of the dot target coupled with the film viewer would give you a good idea of what the "times" would be.
There are so many variables at work that it's pretty pointless (and highly likely to be inaccurate anyway) to get that in-depth on a particular round. Just at the "gun end" there are a lot of variables that can effect velocity, starting with barrel length (and how it's mounted), and even action-type. In the round itself, the shape of the bullet, weight and speed all effect its trajectory. How the bullet fits the chamber even has an effect, which isn't minor. Bullets are mass produced to be on the "small side", while actions are mass-produced to be spacious enough to allow the largest commonly produced bullets to fit. Sure there are tolerances to follow, but there are allowable deviations. That means that almost all bullets are too small to fit the chamber ideally. Two bullets, identical in components but seated differently, won't fly the same. Two identical bullets, but fired out of two guns built by the same manufacturer won't fly quite the same...
Rifle manufacturers don't sell pre-sighted rifles because there's no way for them to compensate for the variables at hand. They leave that up to the guy that buys the rifle and ammo. They'll provide a sample trajectory table, but if you "live" by that table, you'll "die" by it too.
Even in the game, I suspect you'll find that as soon as the muzzle is pointed up or down a few degrees, it'll throw your table off. And if the altitude isn't always the same, that will throw it off too. Or if somebody fires while their wings are banked. Or while at anything other than 1G. If those things don't throw your table off, there's something wrong with the way the ballistics are modeled.
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Already tried using the target + film viewer combo. Target doesn't show in the film viewer.
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Already tried using the target + film viewer combo. Target doesn't show in the film viewer.
How about parking a friendly right next to a hanger, so that from the ground you can fire at the hanger? That way, you'd know the range to the hanger.
Just guessing on an idea that might work.
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Too bad Off line missions is not working, you could just send a drone out and scale sight on it.
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I was going to say about what Mtnman said about ballistics. There are way too many variables to even accurately guesstimate velocity loss and bullet drop at certain distances in game. But if it helps, modern API M8 round for the M2HB have a muzzle velocity of approximately 2810 fps. Historical data puts the velocity loss at approximately 29% at 600m. I'm not sure what factors are used in calculating the velocity loss, because a lot of different things can make the numbers change. I believe that the British .50 BMG used a slightly different ammunition with a higher chamber pressure and velocity. Are the different 12.7/13mm modeled differently ballistically or is it the same model for all of them in game?
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Best bet on bullet speed is going to be a reloading book.
Although it might vary somewhat from gun to gun, by far the biggest variables are bullet weight, shape, and powder load.
Those for WWII .50 ammo should not be hard to find.
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Here you go.
(http://beta.hitechcreations.com/pyro/50chart.jpg)
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Pyro you are the man sir! <S>
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Thank you Pyro, it's much appreciated.
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Ok, if I'm reading the chart right, we want to use the line for the 36" barrel, which yields approximate bullet velocities of:
Range (YDS) | Velocity (FPS) | Average Velocity (FPS) |
Muzzle | 2850 | - |
200 | 2600 | 2725 |
400 | 2350 | 2600 |
600 | 2100 | 2475 |
800 | 1875 | 2355 |
1000 | 1675 | 2241 |
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You read the velocity right but I don't know what your average velocity column is or how you came up with that. The graph is two graphs in one. One graphs out the relation between distance and velocity for the aircraft and GV versions of the M2 .50. You read that part right. The next piece of the graph shows the relationship between striking velocity and armor penetration at various degrees of obliquity. Look horizontally along your velocity line until it intersects the strike angle you want to look up. Go straight down along the the vertical axis of the intersection point between the striking velocity and the degrees of obliquity that you're looking up and it will take you to the Penetration - Inches scale showing you how much armor penetration you can get at that velocity and that angle.
Example: I want to know how much armor the .50 on my M8 will penetrate at 100 yards. First find the point where the line for the 45" M2 intersects the 100 yard scale at the bottom of the graph. Look at the velocity scale and on the left and we have a striking velocity of about 2800 f/s. Now following the 2800 f/s line horizontally out to the obliquity angle you want to look up. In this case we'll look at 0 degrees which would be a straight on shot. At the point that the 2800 f/s line intersects the 0 degree obliquity curve (which is about where that curve starts), go straight down from that point and see where that ends up on the Penetration scale. In this case it would be about 1.06". Multiply by 25.4 and you end up with 27mm of penetration by an GV .50 at 100 yards with no obliquity. With 60 degrees of obliquity I would get a whopping .2" or 5mm of penetration at the same range according to the graph.
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I calculated the average velocity under the assumption that each point on the graph where the range and velocity intersect the curve is the velocity at which the round is traveling at THAT particular range. However because the round isn't traveling at that particular velocity over the ENTIRETY of its flight, the indicated velocity would therefore not be accurate for the lead calculations (which calls for the average velocity of the round over the entirety of its flight).
For example:
I have my guns set to a convergence of 200yds, and this is the range at which I typically fire. At 200yds the round is traveling 2600fps, however this is its approximate velocity AT 200yds, and does not account for the velocity of the round as it leaves the muzzle and for every foot it travels between the moment it's fired and the moment the round reaches this range. If I were to attempt to calculate my lead based on the speed of the round AT 200yds my rounds would be falling short. So I used those two known data points--velocity at the muzzle and velocity at 200yds--to average the bullet speed over the entirety of its flight, ( (2850 + 2600) / 2 ) which is what the lead calculations call for.
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Can you figure out an average velocity if you don't know how long it takes the round to get to a given point? You need to know the time of flight to figure that out accurately.
Doing the math as you have gives a possible answer, but it relies on the round slowing at a constant rate, right? Does the round decelerate at a constant rate?
I'd expect the round to hold velocity briefly, then decelerate at an increasing rate, before finally decelerating at a reduced rate. Once it reached a certain point (falling nearly vertically), I'd expect it to not decelerate any more at all until it hit the ground.
I'd also expect that if you knew the time of flight to different yardages, the actual velocity at those yardages wouldn't matter, since all you're trying to do at this point is hit something, rather than figure out how much damage the round does when it gets there.
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This is really the best I could do to figure it without having access to or knowing how to accurately test for time of flight data (considering you're getting into 10ths of a second or less I don't have the tools to try to test this myself in the game). Perfect? No, but it's what I have to work with so far, and a little bit more accurate than going strictly by actual round velocity at Range X.
I've put together a quick Excel spreadsheet that automates much of the calculation, so it's really just a matter of getting more accurate average velocity data to plug into the formulas if someone can provide it.
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This is really the best I could do to figure it without having access to or knowing how to accurately test for time of flight data (considering you're getting into 10ths of a second or less I don't have the tools to try to test this myself in the game). Perfect? No, but it's what I have to work with so far, and a little bit more accurate than going strictly by actual round velocity at Range X.
I've put together a quick Excel spreadsheet that automates much of the calculation, so it's really just a matter of getting more accurate average velocity data to plug into the formulas if someone can provide it.
Yea, it's probably close enough anyway.
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This is really the best I could do to figure it without having access to or knowing how to accurately test for time of flight data (considering you're getting into 10ths of a second or less I don't have the tools to try to test this myself in the game). Perfect? No, but it's what I have to work with so far, and a little bit more accurate than going strictly by actual round velocity at Range X.
I've put together a quick Excel spreadsheet that automates much of the calculation, so it's really just a matter of getting more accurate average velocity data to plug into the formulas if someone can provide it.
Yea, it's probably close enough anyway.
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Sorry, my brain got tripped up and I was thinking you were reading too far into the chart.
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If I'm reading the graph right, you used the MV for the 36" barrel, but the in-flight velocities for the 45" barrel. Am I reading it wrong too?
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Yea, it's probably close enough anyway.
I could probably make it closer by using more data points (IE, every 50-100yds rather than ever 200). I just used the 200yd intervals since that seems to be where most people set their guns (I hear more guys use 200, 400, 600, etc. as their convergence than 250, 300, 500, etc).
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Disregard, I noticed a MAJOR error in the chart I must fix....
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I could probably make it closer by using more data points (IE, every 50-100yds rather than ever 200). I just used the 200yd intervals since that seems to be where most people set their guns (I hear more guys use 200, 400, 600, etc. as their convergence than 250, 300, 500, etc).
I think they do that because the icons counters switch at 200, 400, 600, etc.
It's a shame, since 300 and 500 are "sweet-spots", and from what I've read, 300 was a pretty commonly used setting historically.
I'm curious to see what you come up with, because I'd like to see how close it coincides to what I've seen on running shots on deer. I'd be surprised if you come up with something much different than I've figured out for my .270 at 100 and 200 yards, and my muzzleloader at 50 and 100 yards. The .270 is shooting slightly faster than the .50's (at just over 3000 FPS MV, 1800 FPS AT 200 yds), and the .54 flintlock is probably not too far off of the cannons (1800 FPS MV, roughly 1/2 that at 100 yds).
While I've taken the time to figure those points out for 90 degree shots on "full-speed" deer and coyote (about 35 mph), I actually do better if I block those ideas out of my mind and just watch the target very intently. It's too hard for me to figure out the combination of angle (they're never really running at 90 degrees), speed (they're never really at full speed) and range (they're never really at 50, 100, or 200 yards, and even if they are, it takes me too long to really estimate that accurately; by the time I do that, the shot opportunity is past). If I have time to range them, they're not running.
An exception is when I'm a "stander" for drives. In that case, I take to time to range landmarks, and figure that aspect out. Then remind myself of the leads needed for a full-speed target at 90 degrees. In the end though, when it comes down to the shot, there's not a lot of time to think about those things. The biggest questions I'm thinking about are "is it safe to shoot" and "is it in range?". Beyond that, I just intently concentrate on the target. I think that's how quarterbacks do it too.
I'm very interested in what you come up with.
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Ok, here it is. It's not pretty, but should be very comprehensive. This JUST covers a range of 200yds, however I can very easily adapt it to other ranges, as well. You'll want to R-Click -> View, or save the image as it's very large so doesn't fit the window. It covers a wide range of both target and shooter airspeeds, from 200mph TAS up to 450mph TAS in 50mph increments. Note that the average round velocity figures factor in the shooter's airspeed.
(http://vmf251-buccaneers.net/images/Media/Sights/LeadCalc200.png)
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Have you had a chance to put any of it to the test?
It's intriguing, but it seems like you'd need a computer running in the background to sort through the numbers before you fire. Don't get me wrong, my intent is not to "attack" your idea at all, I just have some questions on your thought process. Nobody else is posting/asking questions, and I don't want you to think I'm ignoring you or that I'm not interested.
For starter's I'm unsure of why you'd adjust the velocity of the round based on your forward speed. If you and your target are flying the same speed (lets use 200yds and 200mph) the apparent velocity of the round is the same as if you were stationary. I think I know where you're going with it, but holy cow will that get complicated! On the 200 yard, 200 mph shot, how far does the bullet travel from the time it was fired until it impacts? More than 200 yards, because the target is moving away, even if it's apparent motion is zero from your perspective. That's a small factor, but it matters more for longer shots, and when the apparent speeds change. How far does the bullet fly on a 1000yd head on shot with both pilots doing 350mph? Or, on a 20 degree head-on deflection shot, what is the lead required if you're flying 300, and your target is doing 200, and he's 400 feet lower than you?
A course in estimating target speed may be a prerequisite.
So far, your chart appears much simpler, but I'm a little unclear how you intend it to work. If you and your target are both going 200mph with him in a bit of a bank 200yds in front of you, with you matching his bank, how does his speed factor in? His speed would be almost an apparent 0mph from your perspective.
You'd still need to lead him, of course, but how much? He'd be holding at a "consistent" point on your nose, so there's no apparent "crossing" deflection. Is the lead required based on time/distance, or G-force (you'll need to fire at greater than 1G unless you pull the stick and then unload the G's). Would the same exact shot (at the same range) but with both of you at twice the forward speed require the same lead? Or double? Or other? What about twice the speed, and twice the range, and twice the bank angle?
How does the bank angle factor in? In a near 90degree bank (lufberry shot) the upward cant of your guns is now translating to "lead", and you've lost the tilt that's supposed to be opposing gravity. Hence, your shots in a left bank will trend too far to the left, and low. With a chart only looking at speed and deflection angle, would the mathematical lead required for a 30 degree deflection shot be equal for a target regardless of bank?
So, on a given 30 degree deflection shot at "x" distance and speed, would the lead be the same if your following your target through an immelmann vs. say a flat turn? Would the lead be the same on the "upward" side of a loop vs. the "downward" side? On the downward side, the cant of your guns is actually going to accelerate the apparent effect of gravity, rather than oppose it, since the guns are now tilted "down". The bullets trajectory would reverse from your point of view. They'd appear to curve upward rather than downward (this also happens when you fire with your nose straight up).
What about firing on an opponent that's diving away? If you tilt your nose up or down, your bullets will hit high. Even on a 0 degree deflection shot, with both pilots "wings level", same speed (but accelerating) and maintaining 200yd separation, in a 45 degree dive you'd need to aim low to hit him (assuming 200yd convergence, because otherwise it'll get too complicated; for the same 200yd shot with 300yd convergence you'd want to hold right on him). Now, since he's diving and you need to hold under him, you're leading him, but the apparent deflection is zero...
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Dear mtnman,
Please stop shooting me down.
Regards, Jam.
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Dear mtnman,
Please stop shooting me down.
Regards, Jam.
I would never shoot you down Jam! If you think i have, you must be mistaken!
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I have a program that will calculate external ballistics giving time of flight (among other things) for various distances. The program has the following limitations:
BC <1.2
Max wind speed 30 mph
Max altitude 15000 feet
Max bullet weight 1200 grains
With these limitations, the only rounds in AH that can be calculated are the vehicle mounted machine guns. If you want me to run any numbers, let me know which one and I'll do it for you.
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Now that we have sight reticles that are accurate to the mil across all aircraft, does anyone have a calculation that can be used to determine how many mils of lead would need to be given to a target?
I know it's a function of the target's deflection, range and airspeed, and the flight time of the round, but I'm not sure of the actual formula.
I'd REALLY like to be able to put together a "lead chart" for the Mk.VIII sight showing lead in mils at various target deflection angles, ranges and airspeeds.
Saxman,
wouldn't such a gunsite only be applicable to targets flying in a straight line? Once you start to turn, the quired lead (at the same distance to target, and speed of target) would change. And the change would be dramatic. Crossing shots on level flying bombers would be a good application for the gun sight you describe. Is that the objective? :salute