Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: GODO on September 27, 2004, 01:20:26 PM
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These images come from luftarchiv:
(http://www.luftarchiv.info/bordgerate/me109_s.jpg)
(http://www.luftarchiv.info/bordgerate/brett.jpg)
Even with low ROF and low muzzle velocity, MG-FF was a very accurate weapon. MG151/20 mounted in hub or wing roots probably were as accurate if not more.
With dispersion like that, a gunsight is a very usefull tool, but not with current AH2 dispersion.
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What is the range on that?
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Wondering the same. My guess is no more than 120 yards.
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The wings probably don't vibrate as much as when in flight.
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Originally posted by ra
The wings probably don't vibrate as much as when in flight.
Why, are the wings attached to some fixed structure? Or just the opposite due the "bouncing", if any, of landing gear?
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Another thing to note is that ballistics are different depending on the type of round. HE and AP travel different paths. I'm not sure what those rounds in the photo are.
Also the two guns had distinctly different dispersions.
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Hi Godo,
>Even with low ROF and low muzzle velocity, MG-FF was a very accurate weapon. MG151/20 mounted in hub or wing roots probably were as accurate if not more.
There are several parameters for accuracy. The MG FF/M was very good with regard to dispersion. Mounted in a fuselage mount, dispersion was 1.0 mil, compared to 1.5 mil for the MK108, 1.9 mil for the MG151/20 and 2.0 mil for the MK103.
As a general rule, long-barreled high-velocity weapons had a higher dispersion due to the greater effect of barrel oscillations (and the greater recoil). Their benefit obviously was a flat trajectory, but as with everything in aviation, you've got to pick your compromise :-)
In a wing mount, dispersion was much higher. It was 5 mil for the MG151/20, for example. That's a dramatic difference - it means that the pattern is 7 times larger for the wing mounted guns.
For the US 12.7 mm MGs in a wing mounting, I've seen a 6 mil dispersion figure. (Mounted in B-17 turrets, dispersion ranged from 8.3 mil in the Ball turret to 25 mil in the manual tail turret.)
Additionally, wing guns had to be harmonized, adding on offset of around 10 mil to the dispersion. This was systematical so it isn't directly comparable to random dispersion, but beyond convergence range, the projectiles diverged pretty badly.
Likewise, you can measure trajectory curvature in mil - for example, for the Fw 190A-7/A-8, the MG151/20 trajectory peaks at about +2 mil above the sight line, and drops to -1 mil below at 600 m. For the P-47D, it's maybe +0.5 mil at both distances.
The low-velocity MK108, I don't have the type-specific graph so I've got to make an estimate, but it seems it could peak at +1.5 mil and descend to -1.5 mil at 540 m (-3.5 mil at 600 m though - from there on, the drop becomes sharp).
(With decreased air density at higher altitudes, the trajectory tended to become even flatter for all weapons. Shooting from a moving platform also made the trajectory flatter, though shooting at a moving platform made matters worse again :-)
That's all pretty difficult to visualize, but oversimplifying it for a moment, I'd say centreline guns beat wing guns for accurate long range shooting any day, regardless of which guns are mounted.
Regards,
Henning (HoHun)
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HoHun, you hit the nail. And this is what should be included in AH. I would expect little dispersion from wing root MG151/20 compared to outer ones un 190A8 or any 109 with gondolas. But then it should be applied also to the currently hispanos or 50", and that should make a clear difference between dispersion in a Spit and dispersion in a P38 or mosquito for MGs and for guns.
As we have currently a "punch" power and trajectory particular for each gun, we should also have a dispersion depending on the gun type and gun mounting.
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Are you sure we don't? Compare the dispersion from say a nose mounted Hispano or MG-151 vs the wing-mounted ones. I'll go do that now actually, although I can't post the pics.
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I did the test with 109 x3 20mm and all the guns got pretty similar dispersion patterns with cnv set to 300 yards. Now take into consideration the dispersions posted by HoHun and compare current dispersion from wing root or hub 151/20 with wing mounted 50", that is, 2 mil vs 6 mil.
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What is the range on that?
About 250 meters off hand.
You can figure it out exactly by "mil' ing" a known portion of the target with a known object mil size at that range.
Just eyeballing it and comparing the torso of a man (about 1 mil at 700 meters) and run it through the mil-dot formula.
I got a slide rule at work that will figure it out exactly.
Height of target (meters) X 1,000/Height of target (mils) = Range (meters)
It will give you good approximation. Even better is to look in the POH and see what range they set the convergence too.
Crumpp
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Tested also 109 1x20, 190A8 2x20 and SpitIX 2x20, all got the very same dispersion per weapon with target set to 200 and convergence to 300. SpitIX 50" dispersion was clearly inferior to any of the tested guns. I would post the target image, but while testing mk108 the hit marks of previous guns were reset and I had no patience to repeat all the tests.
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The main problem in hitting with MG/FF is its low velocity.
In real fight the target moves thus it is very hard to make correct aiming with low speed of canon's rounds.
I have mostly problems in deflection shoots - so you need to come closer.....
In labaratory conditions all is much better and simpler.....
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Hi again,
>That's all pretty difficult to visualize,
... but I'm working on it :-)
Have a look at this diagram, showing the view through a gun sight with 70 mil ring at a P-47-sized target, with the dispersion circles of 6 mil and a convergence of 300 m.
The top diagram is for 700 m distance, the following ones are 100 m closer each. The bottom diagram is 100 m.
Regards,
Henning (HoHun)
PS I've got to find a quick way to generate these diagrams, it's way too much work.
(http://www.x-plane.org/users/hohun/p47guns.gif)
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Hi Artik,
>The main problem in hitting with MG/FF is its low velocity.
I'd agree, but that's a different problem :-) Firing at a static target is difficult enough for now ;-)
Regards,
Henning (HoHun)
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HoHun, If you have a dispersion of 6 mils at 100 yards with a gun, that dispersion would increase further than 100 yards more and more. In your example I can imagine 21 mils dispersion at 700 yards starting with 6mils at 100 yards, that considering dispersion inducted by gun alone.
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Hello again,
Here's the corresponding diagram for a nose-mounted MK108.
(http://www.x-plane.org/users/hohun/nose_mk108.gif)
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Hi Godo,
>HoHun, If you have a dispersion of 6 mils at 100 yards with a gun, that dispersion would increase further than 100 yards more and more. In your example I can imagine 21 mils dispersion at 700 yards starting with 6mils at 100 yards, that considering dispersion inducted by gun alone.
Hm, mil is a polar reference system, so the dispersion induced by barrel oscillation should stay the same expressed in mils downrange.
There might be aerodynamic effects I'm not accounting for, though.
Regards,
Henning (HoHun)
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Ok HoHun, lets say the dispersion circle would be about 3 times bigger at 700 yards than at 100 yards.
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Hi Godo,
>Ok HoHun, lets say the dispersion circle would be about 3 times bigger at 700 yards than at 100 yards.
Through aerodynamic effects, that is?
Regards,
Henning (HoHun)
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Originally posted by HoHun
[BThrough aerodynamic effects, that is?
[/B]
No, due dispersion inducted by guns alone. Then we can add dispersion due temperature, wing, aerodynamics, etc, but all these factors may affect the same way to every round. The movements of the guns in their mountings generate a cone of dispersion starting at soon as the bullets exit the guns, that is, we have rounds with very similar, but, in fact, different trajectories along these dispersion cones.
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Hi Godo,
>No, due dispersion inducted by guns alone.
Hm, I fail to understand how that would increase the mil size of the dispersion downrange.
(It could be a geometric effect due to the parabolic trajectories, but that affects only elevation, and would be noticable only far beyond the ranges we're interested in.)
In short, I think the gunfire should disperse in a cone, while the way I understood your statement, it should disperse in a trumpet shape with dispersion increasing downrange.
Is that idea correct?
Regards,
Henning (HoHun)
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Originally posted by HoHun
Is that idea correct?
Absolutely, and the trumpet example was perfect :aok (<- first time I use that ugly emoticon).
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Hi Godo,
>Absolutely, and the trumpet example was perfect
I see :-)
Do you have a mathematical function describing the trumpet?
From 100 m; 1.9 mil to 700 m; 5.7 mil I get dispersion ~ range^0.56.
Is the downrange dispersion always proportional to the initial dispersion? I. e. does
100 m; 1.9 mil to 700 m; 5.7 mil
translate to
100 m; 6.0 mil to 700 m; 18.0 mil for the wing-mounted Brownings?
Regards,
Henning (HoHun)
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Current AH 109 nose mounted mk108 dispersion with target at 100 yards:
(http://www.terra.es/personal2/matias.s/mk108dispersion.jpg)
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Mandoble, you made that test standing still, right?
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fyi that center circle on the .target is 20ft dia, the next 40 then 60 etc....
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Need some one to check my calcs and estimations on the targets range.
The target is Aproximatly 8' accross. I.E. 4' center to edge
Dimention on the 109 tail is 4.9' center line to edge.
From the picture the 109 tail is 144 pixels center to edge.
Target is 12 pixels center to edge.
That would give a tangent of aproximatly 0.1
Hence the target is apox 40' - 50' away.
Radius of dispersion on the target is aprox 6" at 50'
At 100 yards that would translate into 3 feet
Per the 100 yard test in ah it shows a radius of about 2' at 100 yards.
Did I miss somthing?
HiTech
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That target is about 150 meters away.
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50' would be only 1 1/2 wingspans. That target must be farther away than that.
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Originally posted by hitech
Did I miss somthing?
HiTech
The focal used ?
The field of view is perhaps not the one for a 50 mm lens.
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Originally posted by moot
Mandoble, you made that test standing still, right?
Flying at 5000 feet and about 350 mph.
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I recant my previous estimate. I'd say it is 200 meters.
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Originally posted by hitech
Did I miss somthing?
At 100 yards the P47D40 wingspan covers all the horizontal yellow line (extreme to extreme) of the default gunsight.
in the 109 gunshight image, dispersion is 38x39 pixels, the lenght of the P47 wingspan at 100 yards would be about 300 pixels.
In the HoHun 100 yards image, the P47 wingspan covers 440 pixels and the dispersion yellow circle is 15x13 pixels. Translating that into the 109 gunsight picture, mk108 dispersion would be 10x9 instead of the current 38x39. This is four times the dispersion calculated by HoHun.
What did I miss?
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Mand, I thought your position has always been that there isn't enough dispersion?
In the model, I can set dispersion figures individually for each gun. As it is, I don't have figures for all guns and have just used a generic figure for each caliber of weapon. I'd be interested in knowing more about Hohun's figures, I don't recall seeing those before.
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About the range:
Did the top MG shoot straight on a 109? then you should be able to know the width of the inner circles in the target. This will give you a hint about the width of the outer circles where they shot at.
Then you have to know the width of the mounted guns and you probably will be able to calculate the shooting distance with some simple geometric formulas, counting pixels in the first picture for target and wing guns width
niklas
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I truly and honestly can NOT believe how bad 30mm dispersion is!!
What the heck!??! It disperses at 100d more than most planes span!! It's got a large, round, cone of 10 yards across, and that's NOT taking into account how SLOW the round is, nor how BADLY it drops in flight.. Deflection shots are almost impossible, as it is, and you add this humungous "cone-o-bullets" into the mess and I have to ask.. WHY was the 30mm nerfed like this?
I know for a fact in AH1 you could get hits with it, but in AH1's super-simplistic over-size hit bubble world, it could get away with it. In AH2's hyper-accurate aiming and hitting system, such an overblown random cone is unacceptable. I believe somebody in HTC said that 30mm hasn't changed since AH1.
Well there's your proof. It *hasn't changed*, but all other gunnery aspects have. I think 30mm *needs a change*, because as of now it is a throwback to the older engine, and ONLY worked in the older engine, with huge-arse hit bubbles that spanned 10 yards around every plane. Now we don't have those, but the bullets still fly like we do. The result? 5% of those bullets may hit now, in reality, where about 70%+ may have hit in AH1.
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on a P-38 the M2 100% dispersion pattern was 8 mil (official value).
I agree with Hohun's values on the MG-FF (mine from actual tests being 1.2-1.3) but the the nose mounted MG-151/20 seems a tad too precise. Indeed from tests i have the MG 151 (15mm) was in the 3-3.5 mils for a centerline mounting.
The MG-17 values were around 6-7mils for cowling mounted weapons.
Hohun could you tell where you got those values from ?
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Hi Pyro,
The distance of the range test in the pictures is pretty accurately 100 m. The 109 Lair had a Me 109C-3 sighting data sheet up from which you can tell that the bare crosses are for the reference sighting points while the ringed crosses (OK, that was obvious :-) are the impact points. The Luftwaffe used either 50 m or 100 m test firing distances, and the position of the impacts slightly inboard of the reference points rule out the 50 m distance. In fact, they fit the 100 m distance for the 200 m harmonization suggested by the C-3 manual very well.
The second set of ringed crosses is a bit puzzling because they could only be hit at about 280 m, which seems excessive. As I only have a few pages from the manual and the appendix with the exact target layout is missing, I can't provide an explanation :-(
(The C-3 was a planned variant that was replaced by the E-3 before it entered production. Apparently, the manuals were already printed.)
>In the model, I can set dispersion figures individually for each gun. As it is, I don't have figures for all guns and have just used a generic figure for each caliber of weapon.
From what I've read, the difference between the usually very rigid nose/wingroot mounting and the more flexible wing mounting was far more important than the weapon type.
>I'd be interested in knowing more about Hohun's figures, I don't recall seeing those before.
The nose-mount figures are from a German memorandum on anti-bomber guns.
The wing-mount MG151/20 figures are from the Ju 87 harmonization procedure. (Only the D-5 was produced with 20 mm cannon, but the cannon armament also was shipped as Rüstsatz to retrofit exisiting Stukas.)
The wing-mount M2 figures were posted by someone else on some board. Maybe someone else has more details?
The bomber gun figures (B-17 and B-24) were posted by someone as scans from a USAAF bomber training manual respectively a modern compilation of interesting pages from one.
Note the difference in dispersion between the 1.0 mil for a nose-mounted MG FF/M and the roughly 2 - 3 mil for the wing-mounted MG FF/M in the photograph.
I've got to admit that there is a slight ambiguity in the German document about whether the 1.0 mil is dispersion radius or diameter - while the text says radius, the table uses the diameter symbol.
The Ju 87D-5 manual actually is clear in specifiying a 2.5 mil dispersion radius, though the calibration on the ground is considered OK with a 3.5 mil radius.
This fits well with a statement in the Baade report prepared for the Soviets after WW2 that dispersion as observed on the ground was worse than in the air. (I figure a three-point suspension allowed worse oscillations of the airframe structure than a continous suspension by aerodynamic lift did.)
Regards,
Henning (HoHun)
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Hi Butch,
>on a P-38 the M2 100% dispersion pattern was 8 mil (official value).
For which distance? It seems so high that I assume more than 100 m, so we might see the trumpet effect in action here ;-)
>I agree with Hohun's values on the MG-FF (mine from actual tests being 1.2-1.3) but the the nose mounted MG-151/20 seems a tad too precise. Indeed from tests i have the MG 151 (15mm) was in the 3-3.5 mils for a centerline mounting.
The MG-17 values were around 6-7mils for cowling mounted weapons.
Hm, could that be a question of radius vs. diameter?
Regards,
Henning (HoHun)
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Mine are calculated as diameters using the standard 1 mil = 1/1000th of rad and measured at 100m for German data and 228m for the M2. And those are the 100% dispersion cones.
Note that actual dispersion is ALWAYS considered as a CONE (see reasons below), and not an hyperbolic one ;). This could be seen for instance on USAAF dispersion charts for various vintage fighters.
Indeed it's the 75% dispersion cone (75% of the bullet go through this cone) which is generaly used because it prevents the weird magic bullet effect which could have an adverse effect on the 100% dispersion.
For M2 the 75% dispersion cone is 4 mils and 100% dispersion 8 mils, underlining the extreme dispersions of some bullets.
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Originally posted by Pyro
Mand, I thought your position has always been that there isn't enough dispersion?
In the model, I can set dispersion figures individually for each gun. As it is, I don't have figures for all guns and have just used a generic figure for each caliber of weapon. I'd be interested in knowing more about Hohun's figures, I don't recall seeing those before.
Just the correct dispersion per weapon and its mounting. Using generic dispersions for each caliber without considering mounting and specific weapon dispersion is like using generic ROF, muzzle vel or punch power for every weapon depending on caliber. The dispersion inducted by the weapon and the corresponding mounting (not the ballistics of the round) is the primary factor to measure the accuracy at medium and short ranges, where the round is still full of energy and external factors will still have little effect on the round trajectory.
Take a look at the common Spit or Typh real gunsights, just a generic circle oriented to spray enough to score some hits at short range. Now take a look at the 109 revis, carefully marked. 109s cant just press the trigger and hope to score hits with a single gun and small ammo clip, 109s depend much more on gunsight and accuracy of the gun. This is even more evident with 109K series with a single mk108.
Applying a generic high dispersion to multigunned planes may ensure to score some hits even being a poor aimer, but for single gunned planes like 109s with Mk108, the effect is probably the opposite, being unable to score a single hit after spending all the rounds.
IMO, every gun should have its correct dispersion depending also on the mounting placement, this is as important as any other gunnery factor already present.
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Hi Butch,
>Mine are calculated as diameters using the standard 1 mil = 1/1000th of rad and measured at 100m for German data and 228m for the M2. And those are the 100% dispersion cones.
Are they radius or diameter?
The Luftwaffe memo I've got my numbers from is for 100% dispersion, too.
>Note that actual dispersion is ALWAYS considered as a CONE (see reasons below), and not an hyperbolic one ;).
Hm, what are the reasons?
As far as I know, it's generally accepted that off-centre bullets actually fly a turn because they're a lifting body with an angle of attack that's sustained by the stability due to its spin. That would support the trumpet idea qualitatively, though I have no idea how much it is quantitatively.
>This could be seen for instance on USAAF dispersion charts for various vintage fighters.
I've never seen such a chart :-( I've got one for the Ju 87D-5, though.
>For M2 the 75% dispersion cone is 4 mils and 100% dispersion 8 mils, underlining the extreme dispersions of some bullets.
Thanks, that's about what I'd have suspected from a sort-of-Gauss dispersion!
Regards,
Henning (HoHun)
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Krusty,
15ft is more than most plane's spans? Wow. I've been reading some really wacked stats on these aircraft. All my sources put wingspans over 30ft for nearly every fighter.
Yes, 15ft is too much, way too much, but decending into hyperbole doesn't help.
I did a test last night using the MK108 at 100 yards while sitting on the ground. It did not look substantially different than MANDOBLE's image.
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Originally posted by GODO
Using generic dispersions for each caliber without considering mounting and specific weapon dispersion is like using generic ROF, muzzle vel or punch power for every weapon depending on caliber. The dispersion inducted by the weapon and the corresponding mounting (not the ballistics of the round) is the primary factor to measure the accuracy at medium and short ranges, where the round is still full of energy and external factors will still have little effect on the round trajectory.
No, it's not like that at all. First of all, things like velocity and mv is readily available information. Dispersion is not.
Second, you attach way too much importance to it. It would have to get extremely large before it could anywhere close to the other factors you put it in company with.
But having said that, I'm all for getting it more accurate. I don't remember if I have the fuselage guns set differently than wings, but I would prefer to redoing everything on an individual basis all at once. It would only take me about 15 minutes if I had all the numbers in front of me. So how about you gather all the numbers and post them for hashing out and then I'll stick them in. Sound good?
-edited for typo
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Originally posted by Pyro
No, it's not like that at all. First of all, things like velocity and mv is readily available information. Dispertion is not.
That is a different story. If information is unavailable, you may start with some basic aproach using a generic dispersion, just halve the dispersion for wingroot or nose mountings, and quadruple the dispersion for handed guns. But take also into consideration that caliber is a wrong aproach, energy may be a better one. It seems that the old MG-FF, even wing mounted, is more accurate than 50"s.
Originally posted by Pyro
Second, you attach way too much importance to it. It would have to get extremely large before it could anywhere close to the other factors you put it in company with.
I disagree. Dispersion is the primary factor to measure gun/mounting accuracy. As far as you can predict accurately where a round will land at 300m, your weapon will be effective, even having a single gun. If the round trajectory is not so flat or not so fast is, IMO, secondary, as far as it doesnt miss the target.
And, of course, If I eventually get accurate information about dispersion for different weapons and different mountings, I will share it with you, as any of us will do. But, take into consideration that players usually expend its AH limited free time playing, not looking for info ;)
Said that, please, check all the current manned guns, on ships and ground, none of them has even the minimal dispersion configured, with the exception of the 5", these have a bit (very small bit) of dispersion.
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I think being mounted to a several-ton cement platform by heavy steel mounts would negate all problems for dispersion, providing a good, steady, stream of rounds.
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Having talked to Pyro about guns and how they are modelled in the game.. I kinda trust how he has it.
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I think being mounted to a several-ton cement platform by heavy steel mounts would negate all problems for dispersion, providing a good, steady, stream of rounds.
Actually not, bro. Depends on the actual gun cradle/mount. In a flexible mount, such as a waist gun, dispersion is greater than a pintle with T & E.
Crumpp
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Yeah, but on a field gun, which was what I meant by the heavy, sturdy, base, you don't aim by yourself, you aim by turning gears which lock the gun in place, even during recoil.
That's what I was thinking of, specifically.
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Hi Krusty,
>Yeah, but on a field gun, which was what I meant by the heavy, sturdy, base, you don't aim by yourself, you aim by turning gears which lock the gun in place, even during recoil.
Well, sounds logical, but have a look at this:
http://www.sadid.co.za/SADID_7/edition7/liw-nads/liw-nads.html
Modern 35 mm gun, 5.5 t total weight, still the 1 sigma dispersion is 2 mrads (= mils). The 70% dispersion we're talking about is 2 sigma, 100% dispersion more like 3 sigma, or 6 mils.
I don't think WW2 AAA would have been any better than that.
Regards,
Henning (HoHun)
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Originally posted by GODO
I disagree. Dispersion is the primary factor to measure gun/mounting accuracy. As far as you can predict accurately where a round will land at 300m, your weapon will be effective, even having a single gun. If the round trajectory is not so flat or not so fast is, IMO, secondary, as far as it doesnt miss the target.
If battles took place on the gun range against stationary targets, I would agree with you. Extreme accuracy is irrelevent if the target is no longer where you aimed when the bullet reaches that point. Some dispersion is not bad and was often intentionally put in with how the convergences were set up.
Originally posted by GODO
That is a different story. If information is unavailable, you may start with some basic aproach using a generic dispersion, just halve the dispersion for wingroot or nose mountings, and quadruple the dispersion for handed guns. But take also into consideration that caliber is a wrong aproach, energy may be a better one. It seems that the old MG-FF, even wing mounted, is more accurate than 50"s.
And, of course, If I eventually get accurate information about dispersion for different weapons and different mountings, I will share it with you, as any of us will do. But, take into consideration that players usually expend its AH limited free time playing, not looking for info ;)
So grab what info is readily available and volunteered here and see if a model can be made to extrapolate out a general but better arrangement. I'm not asking you to dig up the data on every plane, most of which is probably nonexistant. Just start up a thread on how dispersion should be modeled and I'm sure you'll get plenty of input and advice. And then when things are as good as they're going to get, I'll stick them in.
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"NATO 35 x 228 mm rounds at 1100 rounds per minute, with a muzzle velocity of 1175 meters per second."
30mm MK108 650 r/min with 525 m/s. Hardly similar as the weapon mentioned above. To me it seems that they produce quite a different amount of recoil energy as well.
-C+
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Charge,
Tony was comparing it to an MK103, not an MK108.
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Pyro, you can still have a far more accurate gunnery model even without real numbers per gun and mounting.
My proposal would be to start measuring the power of the guns, it should be easy to find that information, weight of the round, muzzle velocity and ROF would be the factors.
You can start with the less potent gun, probably MG-FF with the known 1 mil dispersion, then make the dispersion of any other weapon be a function of its power relative to the 1 mil dispersion gun (MG-FF?). It would be ideal to know the dispersion of the less potent gun and the dispersion of the most potent gun, and then scale any other dispersion depending on the each gun power between these two values.
Once you have the "base" dispersion of every gun, multiply by 2 or 3 (Hohun?) that dispersion for guns in half wing mountings, and multiply by 4 or 5 for manned guns.
About air combat and gunnery, if you learn to aim, yo will easily predict where the engine of the enemy plane will be when the round reach the target with the target moving, not stationary. Some gunsights were well marked for that purpose. As far as you can follow the target with the sight and make the target "stationary" relative to a known mark in the sight, you will hit with a 0 mil dispersion weapon and with the very first round (unless the target changes violently its course or the turn is so tight that the target is obscured by the nose of your plane). It is like the old "trick" of aiming torps with PT boat against a moving ship, just make the moving ship "stationary" with your PT boat course and launch the 0 dispersion torpedoes, and, if inside range, you will hit always.
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Sounds good to me. Collect some basic info and see what relationships exist between the different data points.
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Originally posted by GODO
About air combat and gunnery, if you learn to aim, yo will easily predict where the engine of the enemy plane will be when the round reach the target with the target moving, not stationary. Some gunsights were well marked for that purpose. As far as you can follow the target with the sight and make the target "stationary" relative to a known mark in the sight, you will hit with a 0 mil dispersion weapon and with the very first round (unless the target changes violently its course or the turn is so tight that the target is obscured by the nose of your plane). It is like the old "trick" of aiming torps with PT boat against a moving ship, just make the moving ship "stationary" with your PT boat course and launch the 0 dispersion torpedoes, and, if inside range, you will hit always.
It is not quite that simple. The PT boats were cruising at the same speed as their torps, and that's how they could aim them by finding the angle of approach that kept the target stationary in their sights. Aircraft do not have the same capability, thus relative speed becomes a factor.
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So if all the guns have a certain dispersion factor there is no difference in ME262 firing 4xMK108 simultaneously and Bf109 firing single centerline MK108. They all have similar dispersion pattern.
I'd imagine the engine mounted MK108 to be quite accurate considering the placement on recoil point of view. Dunno how the engine vibration would affect it as it is not attached to engine but in forward fuselage and just fires "through" the engine.
On ballistics: It is, of course, good to have a streamlined greanade when flight speed is considered but in relatively light grenades it is also good to have a blunt tip so it more easily enters the fuselage of the target in shallow angles and does not bounce away.
-C+
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The "bounce away" myth is just that ... a myth. The skin of aircraft is in no way strong enough to deflect even the guns with lowest of muzzle velocities. Most pistol rounds would penetrate at 50-100 yards even at extremely shallow angles.
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So why didn't they put a bakelite cap to the Minengesch. tip to gain better ballistics?
-C+
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Originally posted by GScholz
The "bounce away" myth is just that ... a myth. The skin of aircraft is in no way strong enough to deflect even the guns with lowest of muzzle velocities. Most pistol rounds would penetrate at 50-100 yards even at extremely shallow angles.
I have to question that. If bullets - and even battleship shells - will skip off water if they hit it at a shallow enough angle, then a stiff alloy skin should be capable of deflecting very shallow-angle strikes. It was one of the reported problems suffered by USAF F-86's in Korea; their .50 cal bullets kept skipping off the tough skin of the MiG-15s.
Tony Williams
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Not so.
The Sabers in Korea had 50cal rounds that HIT but failed to blow their targets apart. Many a mig returned home with a huge freaking hole in its wing, tail, fuselage, or "insert part here". The 50cals HIT, but due to the tough-as-friggin'-nails Soviet jet construction, the planes could withstand almost anything.
Consequently, that is why later US aircraft began carrying cannon.
Also, the 50cal incendiary round could penetrate a large steel plate with ease. There was a post long ago on the forums that had detailed info about that, and a picture profile of a 50cal round doing so. Can't be arsed to search for it (was 3+ years ago, probably gone)
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I have no doubt that the .50 API can penetrate armour plate - in fact, around 20-25mm of it, if it hits it dead-on (i.e. at short range and 90 degrees impact). I also have no doubt that it shot many holes in the MiG-15s.
However, you are ignoring the question of striking angle, which is crucial. Even at short range, the .50's penetration of steel armour drops from 20+mm to only 5mm if it hits at 30 degrees. As the angle of the hits gets shallower, so the penetration falls off at an ever-increasing rate.
Any bullet which strikes a glancing below (i.e. it isn't the point which strikes first, but the body of the bullet) has very little penetrative power, and in those circumstances a stiff light-alloy skin could indeed deflect it - and did so, according to first-hand reports I have read from Korea.
Tony Williams: Military gun and ammunition website (http://www.quarry.nildram.co.uk) and Discussion forum (http://forums.delphiforums.com/autogun/messages/)
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Some facts :)
(http://www.allaboutwarfare.com/files/pictures/tmp/50-face-hardened-plate-penetration.jpg)
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Originally posted by Tony Williams
I have to question that. If bullets - and even battleship shells - will skip off water if they hit it at a shallow enough angle, then a stiff alloy skin should be capable of deflecting very shallow-angle strikes. It was one of the reported problems suffered by USAF F-86's in Korea; their .50 cal bullets kept skipping off the tough skin of the MiG-15s.
Tony Williams
It's quite simple: Water provides more resistance than a thin sheet of aluminium at whatever angle. A sheet of aluminium can only offer a finite amount of resistance before breaking and yielding to the projectile. Water (depending on depth) offer an almost infinite amount of resistance and will continue to change the vector of the projectile until it either flies back up out of the water, or loses so much energy that it sinks. The projectiles do not really "skip" of the water surface, but rather dive under it and gets skewed back up by hydrodynamic forces. As someone pointed out, a bullet has an aerodynamic profile that creates lift.
The MiG-15 "flying tank" is also a myth. The .50 cals didn't skip of the though skin ... the MiG was simply so ruggedly constructed that it could take incredible amounts of damage and keep on flying, and the jet fuel didn't burst into flames as easily as the WWII aviation gas the US pilots were used to (many of them were WWII veterans).
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The graph above doesn't help as it only goes to 40 degrees from the vertical - what I'm interested in is what happens when you reach the 'glancing blow' stage - i.e. at 80+ degrees, such as you would get when hitting the fuselage skin of a plane you were firing at from dead astern (or close to it).
TW
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Very Interesting, How I wounder would Fused Shels such as say a Ho-5 20mm react in such an instance, would the impact from the strike in a situation whear a glancing blow ocured that would defelect a 50cal round, be suficient to cause the detonator to...well detonate? And Not just the mechanical fuses, how would the chemical detonator on again a later Ho-5 HEI round react?
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There was always a certain percentage of HE rounds which failedto detonate on impact. In many cases, this would have been because they hit at too shallow an angle. The later British Hisso used an air-column fuze (as did some of the Japanese shells) which required the nose to hit first to work. Other fuzes used inertia, which required the shell to be slowed down suddenly as when hitting something. Again, a graze might not have set it off.
Getting a fuze to be sensitive enough to work properly with graze hits while still being safe to fire was not easy - it still isn't today.
TW
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TY Tony, I was woundering though on the PETN fuse in the later model Ho-5 cannon rounds, would they of neaded to impact dead on in order to work? or would the shock from the crazing of been enough to set them off?
p. 181 Flying guns, their is an image of the round I am refering to.
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Well, you have to bear in mind that this fuze has no safety devices so needs to be insensitive enough to tolerate being slammed up a feed ramp as it's chambered. I don't think it would work with a grazing hit.
TW
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TY Tony. This is all very interesting realy, espichaly since one would think that a lage percentage of potential hits from a following posation could be grazing.
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Tony, I believe the German HE and HE(M) shells had a rotation activated safety and self-destruct. I don't know about other shells though.
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German fuzes for home defence fighters had a self-destruct mechanism (which normally operated at 800-1,200m) but they used simpler contact fuzes for ground attack.
TW
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The cannon was already a potential choice for fighters in WW2 but I guess the reliability of US hispano was not good enough and the rate of fire was not considered enough in jet dogfighting.
Considering the distances and speeds and durability of jet airframes I can easily believe that the bullet penetration was a real problem as well as the bullet being too light to be effective at those speeds as the bullet was constatly passing transonic speeds which probably caused them to be very inaccurate in longer ranges.
However, the combined rate of fire of 6x'50 cal and their "shotgun effect" was usually enough to score several turbine hits which were alone devastating. Their power was surely enough from close range but I'd believe it was very hard to get very close to an enemy a/c in jet dogfight.
Slightly blunt tip is good for penetration as it "cuts" through the skin of the a/c even in shallow angles so I'd think that is why it was a common shape in WW2 20mm grenades.
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