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General Forums => Aircraft and Vehicles => Topic started by: beet1e on November 04, 2005, 02:19:22 AM

Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: beet1e on November 04, 2005, 02:19:22 AM
In a recent discussion in the GD forum, Lazs and I were debating the viability of long range gunnery. We all know that WW2 aircraft guns had bullet dispersion built into them to give the pilots a better chance of hitting the target, but my question is: What was the dispersion angle of various weapons, eg. .50 cal, cannon, .303 etc. Was it 1°? 5°? 10°? I would have thought it was the low end of that range, but I really don't know.

I tried a google search for a discussion about this, and it turned up this thread (http://www.hitechcreations.com/forums/showthread.php?threadid=43507) on this very board from a few years ago! Quite a good thread really, and worth another look for those interested.
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Charge on November 04, 2005, 05:11:43 AM
"We all know that WW2 aircraft guns had bullet dispersion built into them to give the pilots a better chance of hitting the target"

I didn't know that. I thought it was mostly a negative side effect of high MV and high ROF usually accompanied by a too flexible mounting of the gun (eg. wing).

-C+
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Grendel on November 04, 2005, 06:01:37 AM
Plus heating of gun barrels, again increasing dispersion.

No, there was so such thing as "built in dispersion". The idea was to have the gun shoot its bullets in as tight pattern as possible.

In reality the factors mentioned above and others caused dispersion.

The guns could be of course set to shoot different patterns, that would give lessed skilled pilots larger effective area - but with less bullets hitting the target.
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 04, 2005, 06:48:42 AM
Quote
Originally posted by Grendel

No, there was so such thing as "built in dispersion". The idea was to have the gun shoot its bullets in as tight pattern as possible.


Hm... I can certainly say that some guns have purpose built dispersion in mountings, and some of these are used still used today with notable succes (like the GSh-23). I don't know the excat value of the dispersion, but around couple degrees.

In ideal conditions (assuming that aiming was perfect and not systematically off) dispersion is bad. But in reality during WWII aiming was nearly allways systematically wrong because there was no way to determine correct lead until early gyroscopic sights arrived (and these still required some pure aproximations for range measurement). Basicly most pilots used too little lead and aiming point was behind and below correct point specially at long range. Therefore some amount of dispersion actually improved probability of the hit and also percentage of the hits.

It should be noted also that aiming error was generally much larger (say 10-30x)  than dispersion at longer ranges.

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: beet1e on November 04, 2005, 06:57:03 AM
Quote
Originally posted by Grendel
No, there was so such thing as "built in dispersion". The idea was to have the gun shoot its bullets in as tight pattern as possible.
Ah rgr that. An army guy I used to know told me about how a belt fed machine gun was set up on the ground to provide cover for the guys moving behind it. Initially, it discharged over too small an area, so the rifling was adjusted (bored out?) to give the gun less accuracy but distribute the bullets over a larger area, which is what was needed in this case. I assumed that they doctored aircraft guns the same way - I guess they'd have to if the guns were naturally as accurate as laser beams.

Gripen! - you wrote a lot in that thread I linked. So - a couple of degrees total spread, ie. 1° in any direction away from dead centre?
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 04, 2005, 08:06:02 AM
beet1e,
Couple degrees is just a wild quess, in fact it might have been less. In the case of the ZU-23 (AA gun, not GSh-23, I forget the designation), the mounting is built to have something like couple mm loosenes in the support point. Notable thing is that support point is actually rectangular so I quess the pattern is also rectangular. While shooting the jumping of the gun in the support point is quite well visible as well as dispersion of the projectiles.

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Oldman731 on November 04, 2005, 11:46:52 AM
Quote
Originally posted by Grendel
No, there was so such thing as "built in dispersion". The idea was to have the gun shoot its bullets in as tight pattern as possible.

I think Beetle is referring to the practice followed by the RAF at the beginning of the war to deliberately arrange their guns to fire in a circular pattern, similar to a shotgun pattern.  It was called the "Dowding Spread," if I recall correctly.  The idea was that pilots wouldn't be able to shoot an accurate stream of bullets and hit a fast enemy plane.
Each of the eight guns was therefore aimed a slightly different direction from the others.

- oldman
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Treize69 on November 04, 2005, 12:02:01 PM
I think I recall reading about either 8th or 9th AAF P-47 pilots doing pretty much the same thing (spreading the bullets) when they were flying predominantly ground-attack missions in the summer and fall of 1944. I forget the specifics, but I'm assuming it was similar in concept and application to the aforementioned "Dowding Spread".

They wanted to spread the destruction at ground level over as wide an area as possible without having to make multiple runs at the target area.
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 04, 2005, 12:09:50 PM
Quote
Originally posted by Oldman731
 The idea was that pilots wouldn't be able to shoot an accurate stream of bullets and hit a fast enemy plane.
Each of the eight guns was therefore aimed a slightly different direction from the others.


That's infact a different way to reach same advantage as built in dispersion in the mounting of a single gun but the result is almost same except the pattern would be slightly different (wider).

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: hitech on November 04, 2005, 03:21:41 PM
beetle: Typicly less than 1 deg.

To visulize what 1 deg is.

The sun and moon are both 0.5 degs across.


HiTech
Title: Re: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 04, 2005, 03:26:53 PM
Hi Beet1e,

>In a recent discussion in the GD forum, Lazs and I were debating the viability of long range gunnery.

It seems that the term "effective range" is lacking a clear definition in air combat. Accordingly, it's not suprising there is so much contradictory material around.

>We all know that WW2 aircraft guns had bullet dispersion built into them to give the pilots a better chance of hitting the target, but my question is: What was the dispersion angle of various weapons, eg. .50 cal, cannon, .303 etc. Was it 1°? 5°? 10°? I would have thought it was the low end of that range, but I really don't know.

I guess you're going to enjoy this thread:

http://www.hitechcreations.com/forums/showthread.php?s=&threadid=131669

The answers:

"Built-in" dispersion does not make much sense, though it was used initially in WW2. The RAF at some point appears to have adjusted the Spitfire's cannon so that their lines of fire crossed the centreline at different points in the vertical, which could be understood as a way of creating one-dimensional dispersion. Most harmonization patterns, however, were simply set for the greatest density of fire at the most common engagement range.

Here is a link to a highly interesting Luftwaffe gunnery training booklet:

http://rafiger.de/Homepage/Pages/Schiessfibel.html

Page 14 re-inforces I point I've just made: Dispersion doesn't help you. The Schießfibel:

"Accordingly [referring to example illustrations for faulty deflection shooting], don't rely on weapon dispersion - it won't help you if your aim is flawed! You can see here clearly how ACCURATELY you have to know and to apply deflection, or your fire will miss. But if you think now that you could simply adjust your MGs for a larger pattern to hit more reliably, then you're making a mistake. Your experience will be similar to that of the wild hunter in the picture on the right."

The latter advice is repeated on page 28:

"Another thing: Please don't invent new harmonization patterns, for example by adjusting the trajectory cross-over 100 m out etc. The ordered harmonization has been carefully devised by combat veterans and is good."

Here are dispersion values for different types of guns, partly from historical data and partly calculated. These values assume a rigid mount, such as in the aircraft nose - wing mounts usually are less rigid and lead to a higher dispersion. Flexible mounts are just that ;-) so defensive weapons have a much larger dispersion. (There are large differences depending on the mounting - I believe in this regard the Sperry ball turrets were the best of the US turrets.)

The units are mils, with 1 mil = 1 m error at 1000 m range


MG-FF:             1,0
20mm Type 99-1:    1,0
MK 108:            1,5
20mm Type 99-2:    1,5
Ho-1 / Ho-2:       1,5
12,7mm Scotti:     1,6
Breda-SAFAT:       1,7
MG 131:            1,7
20mm Ho-5:         1,9
MG 151/20:         1,9
MK 103:            2,0
20mm ShVAK:        2,0
Hispano V:         2,1
37mm M4:           2,1
Ho-103:            2,2
VYa-23:            2,5
12,7mm UB:         2,7
Hispano II:        3,0
NS-37:             3,3
MG 151:            3,4
,50 Browning M2:   4,0
Browning ,303:     4,2


With regard to long range fire, it's a combination of three factors:

- Trajectory
- Dispersion
- Divergence

(The latter simply describes what happens if you pass the convergence point - the lines of fire diverge.)



Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: straffo on November 04, 2005, 03:38:24 PM
Hohun do you have a link or data for  the 190A8 convergence ?
I've lost the drawing somewhere and I'm unable to put my hand on it.
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 04, 2005, 03:47:07 PM
Hi Straffo,

>Hohun do you have a link or data for  the 190A8 convergence ?

Quick summary:

MG 131 (cowl): max 57 cm above the sight line at 220 m range, sight line crossed at 30 m and 400 m. No convergence (parallel).

MG 151 (wing roots): max 82 cm above the sight line at 360 m range, sight line crossed at 120 m and 550 m. Convergence 600 m.

MG 151 (wings): max 84 cm above the sight line at 360 m range, right line crossed at 135 m and 550 m. Convergence 400 m.

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: straffo on November 04, 2005, 03:48:31 PM
Merci beaucoup :)
Title: Re: Re: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 04, 2005, 05:15:17 PM
Quote
Originally posted by HoHun


I guess you're going to enjoy this thread:

http://www.hitechcreations.com/forums/showthread.php?s=&threadid=131669



Well, let's take a quote from HoHun's post in that thread:

"If you consider the aiming errors random, there's no total advantage for the larger dispersion weapon at all because random errors are centered at the correct aiming point, and large dispersion gives you a big disadvantage there."

The problem is that there is no reason why random errors should be centered at the correct aiming point at long range. The error is probably systematical in most cases because there is no way to determine correct aiming point at long range. Therefore some amount of dispersion gives an advantage.

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 04, 2005, 06:15:31 PM
Quote
Therefore some amount of dispersion gives an advantage.


Not really.  Have you read any vunerability reports? Basically you need concentrated firepower and/or realtively large amounts of explosive force to ensure an immediate shoot down.

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 04, 2005, 06:34:01 PM
Quote
Originally posted by Crumpp
Not really.  Have you read any vunerability reports? Basically you need concentrated firepower and/or realtively large amounts of explosive force to ensure an immediate shoot down.


Actually in the case of systematical error some amount of dispersion gives more concentrated firepower. And at long range the aiming error is probably systematic.

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 04, 2005, 06:41:14 PM
Quote
Actually in the case of systematical error some amount of dispersion gives more concentrated firepower


Greater dispersion does not give you greater concentration, Gripen.  That is an oxymoron.  Sort of like being an "accurate estimate".

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 04, 2005, 06:52:12 PM
Quote
Originally posted by Crumpp
Greater dispersion does not give you greater concentration, Gripen.  That is an oxymoron.  Sort of like being an "accurate estimate".


Actually it gives if the aiming error is systematic as it probably is at long range. Just think dispersion patterns and systematical error.

gripen
Title: Re: Re: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 04, 2005, 07:17:32 PM
Hi again,

>

The dispersion values I posted above are for 100% dispersion diameters. As a rule of thumb, wing mountings have about 1.5 times the dispersion indicated above.

After sorting it out, here my example:

With regard to long range fire, it's a combination of three factors:

- Trajectory
- Dispersion
- Divergence

(The latter simply describes what happens if you pass the convergence point - the lines of fire diverge.)

So let's have a look at three different batteries to estimate the long-range fire capabilities (against a fighter-sized target held perfectly stationary in the centre of the sight):

1.) 1 x MK108 engine cannon
2.) 8 x Browning M2, wing mounted
3.) 4 x Browning M2, nose mounted

The MK108 has low dispersion and no divergence problem. Out to 500 m, its fire will strike the target with hardly any misses (as long as the crosshairs are perfectly aligned with the target centre), but beyond that, the trajectory drops far below the sight line, so with our setup, the fire will miss completely.

The wing-mounted Brownings, set to 250 m convergence for our example, have a high dispersion, large convergence/divergence effects and a very flat trajectory. At 100 m, some of the fire will hit both wings of the target, at 200 to 300 m, most of the fire will strike the fuselage (with enough bullets missing to be helpful in a realistic situation where the aim is not perfect :-), and at 400 m, the tips of the horizontal stabilizer will be showered. At 500 m and beyond, the greatest share of the bullets will miss, but you will still get strikes on the wings out to 900 m. (Realistically, you could deliberately aim at one wing tip to hit the fuselage, accepting that 50% of the fire will miss. In simulators, I do occasionally use this technique :-)

The nose-mounted Brownings combine low dispersion, centreline fire and flat trajectory. Out to 300 m, the fire will hit virtually without a miss, then the hit ratio will begin to drop very gradually, but even at 700 m about 80% of the fire will be on target. At 800 m, trajectory drop will become apparent, reducing target coverage to maybe 40%, and even less at 900 m. (Realistically, this drop is so slight that the pilot could probably compensate for it.)

So our three example batteries, modelled roughly after those of the Me 109, P-47 and P-38 (leaving out the 20 mm cannon of the latter) show rather different problems with long range fire.

The Me 109 enjoys great accuracy out to 500 m, but trajectory drop beyond that is very sharp, and it probably would not be worth trying to hit something at beyond 600 m.

The P-47 is limited in its range primarily by the divergence of its fire, and secondarily by the dispersion which means that even when hits are scored, a kill will not be guaranteed. Realistically, we can expect the pilot to be able to compensate a bit for the divergence problem, and while the fire won't be instantly lethal the dispersion means that he's still likely to hit and damage his target. (Note that barrel overheating limits firing duration, so he can't expect to use more than a fraction of his total ammunition load this way. Realistically, this is not really a limitation as the attacked pilot probably would see the tracers after a very few seconds and begin to evade.) An longer convergence range would improve long range firing capabilities, but historic combat experience obviously favoured short range fire.

The P-38 features a very accurate battery, and should be able to consistently score hits (admittedly on "sitting ducks", but these are a must for successful long-range attacks anyway :-) at up to 800 m, and with a bit of luck to 1000 m or more. Beyond 500 m, its fire will also be more effective than that of the P-47 due to the much higher density of the pattern. Add the Hispano, and you have a real long-range killer here :-)

Of course, pilot capabilities and "aim point wander" - the impossibility of keeping the crosshairs centered on the target - means that even in a situation where I have listed "100% hits" will not result in 100% hits. However, a tracking accuracy of 1 mil has been demonstrated by a highly trained fighter pilot during deflection gunnery tests, so the "ideal" situation above is not very far from the optimum human capabilities. Of course, a hastily trained wartime pilot might be very far from the expert I have just described :-)

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Bruno on November 04, 2005, 09:11:21 PM
Quote
Verlaß Dich also nicht auf die Waffenstreuung - sie hilft Dir nicht, wenn Du falsch gezielt hast!


Do not rely on weapon dispersion - it will not help you, if you aim badly!

Page 14 Die Schiessfibel

Was nutzen all die Kugelspritzen,
Wenn sie nur in die Gegend blitzen!

(http://bellsouthpwp.net/w/o/wotans/DSpG15.jpg)

Dispersion does not increase hit probability. A sporadic hit or hits, especially by heavy machine gun rounds, will be far less likely to bring down an aircraft then a well aimed concentrated burst. If you want to increase hit probability, and lethality, get in close and aim well...
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Squire on November 04, 2005, 09:25:29 PM
"If you want to increase hit probability, and lethality, get in close and aim well..."

Sums up air combat from 1915-1953.
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Bruno on November 04, 2005, 09:34:26 PM
Ah heck, I didn't read Hohun's first post, he posted the exact same I did...


Just ignore it...:furious
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Tony Williams on November 05, 2005, 12:16:05 AM
From Flying Guns – World War 2: Development of Aircraft Guns, Ammunition and Installations 1933-45:

When more powerful armament was installed, advantages were again seen in some dispersion of fire. The strongest argument in favour was that very flew pilots were able to judge correctly the amount of lead required for deflection shooting. In May 1942 the RAF would again opt for a greater dispersion of fire to generate more hits.

Tony Williams: Military gun and ammunition website (http://www.quarry.nildram.co.uk) and discussion forum (http://forums.delphiforums.com/autogun/messages/)
Title: Re: Re: Re: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 05, 2005, 04:22:42 AM
Quote
Originally posted by HoHun

So let's have a look at three different batteries to estimate the long-range fire capabilities (against a fighter-sized target held perfectly stationary in the centre of the sight):


If one wants to show that dispersion gives no advantage, he/she uses perfect aiming for the analysis. At long range shooting the exact range is not known, merely aproximated by the pilot even in the case of the early gyroscopic sights. And the target is keeped in the centre of the sight (or slightly below) only in the cases when the planes have exactly same flight path or exactly opposite (directly behind or head on). In the all other cases various amount of lead is needed in long range shooting (in addition to drop of bullets due to gravity)

Basicly the advantage of the dispersion is caused by aiming error which is completely ignored in the HoHun's analysis. Infact this has nothing to do with the original subject of this thread ie amount of purpose built dispersion to increase probabbility of the hit due to aiming errors.

Quote
Originally posted by HoHun

Of course, pilot capabilities and "aim point wander" - the impossibility of keeping the crosshairs centered on the target - means that even in a situation where I have listed "100% hits" will not result in 100% hits. However, a tracking accuracy of 1 mil has been demonstrated by a highly trained fighter pilot during deflection gunnery tests, so the "ideal" situation above is not very far from the optimum human capabilities. Of course, a hastily trained wartime pilot might be very far from the expert I have just described :-)


Here we go again; in the deflection shooting there is no crosshairs to center to the target. And even in the case of the early gyroscopic sight, the range measurement was quite unaccurate regardless how accurately the the target was keeped in the sight.

Basicly there is allways some error and there is no reason to believe that error is evenly distributed around correct aiming point ie the error is probably allways systematical.

Quote
Originally posted by Bruno

Do not rely on weapon dispersion - it will not help you, if you aim badly!


In other words: Dispersion will help you if you aim good enough.

Quote
Originally quoted by Tony Williams

When more powerful armament was installed, advantages were again seen in some dispersion of fire. The strongest argument in favour was that very flew pilots were able to judge correctly the amount of lead required for deflection shooting. In May 1942 the RAF would again opt for a greater dispersion of fire to generate more hits.


That's quite rational, at short ranges some amount of dispersion does not make difference but at longer range some amount of dispersion will increase probability of the hit as well percentage of the hits due to aiming errors.

gripen
Title: Re: Re: Re: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: beet1e on November 05, 2005, 04:31:26 AM
Quote
Originally posted by HoHun
but even at 700 m about 80% of the fire will be on target.
If a gun could be aimed that accurately, then to hit a target such as a wing from the dead 6 position would require that the aircraft be aimed extremely accurately, by which I mean to within 0.02°. Deviation beyond that limit would result in a miss.
Quote
Dispersion does not increase hit probability.
I'd say it does, but it may not increase the bring down the target aircraft probability.
Title: Re: Re: Re: Re: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 05, 2005, 05:01:11 AM
Quote
Originally posted by beet1e
I'd say it does, but it may not increase the bring down the target aircraft probability.


That depends on aiming error; if the error is systematic as it probably is in the case of the deflection shooting, the dispersion will increase probability of the hit as well as percentage of the hits.

gripen
Title: Re: Re: Re: Re: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 05, 2005, 06:48:22 AM
Hi Beet1e,

>>but even at 700 m about 80% of the fire will be on target.

>If a gun could be aimed that accurately, then to hit a target such as a wing from the dead 6 position would require that the aircraft be aimed extremely accurately, by which I mean to within 0.02°. Deviation beyond that limit would result in a miss.

I didn't say it was all on the wing :-) Due to the centreline mounting, the 75% dispersion circle will cover the target's fuselage at 700 m, and the extra 5% hits are from the outer 25% hits hitting wing roots and stabilizer.

Tracking accuracy achieved by a highly trainge pilot under good conditions has been proven to be 1 mil (ca. 0.057 degree). For the example, which was meant to illustrate the technical properties of the guns, I used 0 mils :-)

Name any aiming (in-)accuracy you consider realistic, and I will re-evaluate the example to show pilot influence.

Note that the requirement is to put the crosshairs smack in the middle of the target. I don't think there would be noticable difficulties with this, so I'll take your inaccuracy figure as random error :-)

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 05, 2005, 07:23:02 AM
Hi Tony,

>When more powerful armament was installed, advantages were again seen in some dispersion of fire. The strongest argument in favour was that very flew pilots were able to judge correctly the amount of lead required for deflection shooting. In May 1942 the RAF would again opt for a greater dispersion of fire to generate more hits.

The firing setup the RAF boffins had in mind was a stable tracking shot with the target stationary in the sights, but the wrong amount of lead selected. The pilot was to push the button while keeping the target stationary, and if he was pulling just the right amount of wrong lead, half of the fire would hit the target.

To get this kind of results, you actually don't need an artificially enlarged pattern size, which will dimnish your firepower in other situations.

The standard piloting technique in deflection shots is NOT to have the target stationary in the sights, but to begin firing with the crosshairs just short of the correct deflection while pulling them through the (not accurately known) correct deflection to a position of excessive deflection.

A bit difficult to describe, but it's just the same as the RAF boffins' technique except for pulling back the stick a little to make the target slide through your sight.

(Of course, it's also possible to start with excessive lead and drop back a bit in the turn to run your fire backwards over the target.)

Dispersion on demand ;-)

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: straffo on November 05, 2005, 10:13:42 AM
Don't get me started on Gaussian distribution or I'll crush this thread with statistics !

<= Le statistician
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 05, 2005, 11:42:15 AM
Quote
When more powerful armament was installed, advantages were again seen in some dispersion of fire.


I would agree with this given the vulnerability reports for explosive cannon rounds.

.50 cal and below or Armour piercing rounds gain no benefit from dispersion and rely on concentration of firepower to achieve an immediate shoot down.

But to make a blanket general statement that "more dispersion is good" is not correct and greatly depends on the type of armament being used.

All the best,

Crumpp
Title: Re: Re: Re: Re: Re: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: beet1e on November 05, 2005, 12:33:13 PM
Quote
Originally posted by HoHun
Tracking accuracy achieved by a highly trainge pilot under good conditions has been proven to be 1 mil (ca. 0.057 degree).  
Well, the pilots of WW2 were not highly trained. In addition to that, we know that dogfights took place amongst the clouds because hiding in cloud was a well known evasion tactic. At cloud height, there can be considerable turbulence, especially when passing through or under cloud. In a relatively small plane, turbulence is much greater than it would be in a large aircraft like an airliner. In my view, these factors cast considerable doubt on your claim that pilots could fly accurately to within 0.057°.
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 05, 2005, 02:54:48 PM
Quote
Originally posted by HoHun

Tracking accuracy achieved by a highly trainge pilot under good conditions has been proven to be 1 mil (ca. 0.057 degree).


To give some perspective it should be noted that according to Luftwaffe gun camera analyses an average LW pilot got only 2% hits when shooting a heavy bomber size target and here in Finland an experienced pilot could reach about 40-50% hits to a 6x6m ground target.

Quote
Originally posted by HoHun

Note that the requirement is to put the crosshairs smack in the middle of the target.


Actually in the real life deflection shooting the pilot could just quess the needed lead.

Quote
Originally posted by HoHun

The standard piloting technique in deflection shots is NOT to have the target stationary in the sights, but to begin firing with the crosshairs just short of the correct deflection while pulling them through the (not accurately known) correct deflection to a position of excessive deflection.


That system is plain waste of ammo, there is no way to tell correct deflection. Besides the standard piloting technique is estimate lead and shoot a short burst and correct the lead. Actually I just tested that with the AH Spitfire V and B-24 drone; I got much more hits with short aimed bursts and correcting the lead.

Quote
Originally posted by Crumpp

But to make a blanket general statement that "more dispersion is good" is not correct


No one has made such statement here, what I have stated here is that some amount of dispersion is good and that is exactly what the RAF did and it can be easily proved with aiming error.

Quote
Originally posted by beet1e

In my view, these factors cast considerable doubt on your claim that pilots could fly accurately to within 0.057°.


Note that tracking is not same as shooting accuracy, basicly the advantage of the dispersion comes from unaccuracy of the aiming in the deflection shooting.

BTW if you want have some fun with HoHun's offer to calculate with your parameters, just use what ever parameters you want but don't forget to add assumption that due systematical aiming error, the centre of the aiming points set is say 5m behind the correct aiming point ;)

gripen
Title: Re: Re: Re: Re: Re: Re: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 05, 2005, 04:33:52 PM
Hi Beet1e,

>Well, the pilots of WW2 were not highly trained.

It's just one data point (probably the "best case" data point) to help you to decide which dispersion figure you would consider realistic for the long-range fire situation.

Name any value you want, it's your decision :-)

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Tony Williams on November 05, 2005, 06:06:17 PM
I understand that most WW2 pilots were consistent in that they underestimated the amount of lead needed in deflection shooting. So in most cases the average aiming point would have been some way behind the required one. That would clearly give an advantage to a wider dispersion, provided the projectiles were destructive enough to do the job with few hits.

Of course, in a direct 6 o'clock attack (tail chase or head-on) the advantage goes to the plane with the guns tightly clustered in the nose, with minimal dispersion - except possibly vertically, to allow for errors in range estimation.

Tony Williams: Military gun and ammunition website (http://www.quarry.nildram.co.uk) and discussion forum (http://forums.delphiforums.com/autogun/messages/)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 05, 2005, 06:16:48 PM
Quote
No one has made such statement here, what I have stated here is that some amount of dispersion is good and that is exactly what the RAF did and it can be easily proved with aiming error.


Your statement is only true for specific conditions Gripen.  For a weapon requiring concentration any amount of dispersion is bad.

The RAF were in the process of adopting cannon.

You did claim:

Quote
But in reality during WWII aiming was nearly allways systematically wrong because there was no way to determine correct lead until early gyroscopic sights arrived (and these still required some pure aproximations for range measurement). Basicly most pilots used too little lead and aiming point was behind and below correct point specially at long range. Therefore some amount of dispersion actually improved probability of the hit and also percentage of the hits.


Which the highlighted portion is not correct for rifle caliber Machineguns.  Given the extremely low percentage chance an individual .50 cal and below rounds have of causing an immediate shootdown combined with the size and dispersion of the vunerable areas of the target, bullet dispersion is not a good thing for a weapon requiring concentrated firepower to cause an immediate shootdown.

Such weapons need to put multiple rounds into the same vunerable area of the target.  Just landing a few will not achieve a shootdown.

For example, in the Bf109F:

Target size = 33 sq/ft

Areas vulnverable to the .50cal API are the pilot and the fuel tanks.

Pilot = 3.0 sq/ft of vulnerable area with a 2 % chance of a hit causing vital damage to the target

Fuel tanks = 6 sq/ft with a 0% chance of a hit causing a fire and a 10% chance of a hit causing a leak.

You have to put multiple rounds into a vunerable area for a .50 cal API equipped fighter to achieve an immediate shootdown.

Dispersion does not help.  

For the FW-190 from direct astern, a single .50 cal API round has no chance at all to cause an immediate shootdown.

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 05, 2005, 06:21:37 PM
Quote
That would clearly give an advantage to a wider dispersion, provided the projectiles were destructive enough to do the job with few hits.


Key words Gripen.

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Squire on November 05, 2005, 07:18:52 PM
Just some general comments.

Clouds. Well, sometimes there were clouds and sometimes there were not, just like in any place on earth. Clouds were not omnipresent in all WW2 skies.

Training. WW2 pilots were well aware of what deflection shooting was, they were not stupid. In addition, specialist gunnery schools were setup in many air forces, specifically to tackle issues of deflection shooting theory.

Deflection shooting was, and is, a talent, and thats why 10 percent of the pilots in WW2 accounted for 2/3 of all the kills scored (I am generalising, but its close). Coupled with natural aggressiveness and the ability to remain cool headed, were the keys to success. Aces tended to be the "natural fighters" in the group.

Gyro gunsights did help average to below average shots immensly in judging lead, those with a lot of natural talent probably didnt benefit all that much. They also tended to help score hits at longer ranges.

Dispersion was never a "fix" for problems of poor air gunnery. A pilot relying on that I doubt scored many victories. When you "connect" with a "stream", dispersion affects how the hit pattern is likely to cause damage, but it relies on getting a hit *in the 1st place*, thats the hard part.
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 05, 2005, 07:36:55 PM
Hi Tony,

>I understand that most WW2 pilots were consistent in that they underestimated the amount of lead needed in deflection shooting. So in most cases the average aiming point would have been some way behind the required one. That would clearly give an advantage to a wider dispersion, provided the projectiles were destructive enough to do the job with few hits.

If you'd quantify all these factors, you'd see that this is true only for a very narrow cone section around the target's tail, and wrong for the core of the cone where no deflection is clearly superior. You'd also see that the distance at which dispersion would tell even in its "sweet zone" is beyond normal engagement range, so that the prerequisite of being able to score a few hits probably can't be met.

>Of course, in a direct 6 o'clock attack (tail chase or head-on) the advantage goes to the plane with the guns tightly clustered in the nose, with minimal dispersion - except possibly vertically, to allow for errors in range estimation.

I believe you do not fully understand the beauty of my example ;-)

The pilot does not need to perform any range estimation at all. He just puts the crosshairs on the centre of the target and pushes the button.

For the Me 109, the MK108 will hit the target out to 500 m. At 600 m, the trajectory is so far below the target that even twice the vertical dispersion won't generate any hit.

For the P-47, the problem is not trajectory drop but divergence. Vertical dispersion is not necessary even at 800 m, but divergence at 800 m means that only the target's wingtips are endangered at all.

For the P-38, hits out to 800 m are possible without any need for range estimation. Introducing vertical dispersion would make fire at ranges shorter than 800 m much less lethal, but push out the "crosshairs-on-target-centre" range by no more than 100 or 200 m. That's not a good trade-off I'd say :-)

Regards,

Henning (HoHun)
Title: Re: Re: Re: Re: Re: Re: Re: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 06, 2005, 03:59:35 AM
Quote
Originally posted by HoHun

It's just one data point (probably the "best case" data point) to help you to decide which dispersion figure you would consider realistic for the long-range fire situation.


The aiming error is far larger than dispersion and the error is probably systematical. To give some pespective, the largest dispersion claimed above (for the 7,7mm Browning) is less than 1m in the normal shooting range (150-200m) while the size of the heavy bomber is several times amount of dispersion depending on angle.

Quote
Originally posted by Crumpp
Your statement is only true for specific conditions Gripen. For a weapon requiring concentration any amount of dispersion is bad.


These "specific conditions" cover probably more than 90% of normal shooting situations. At short range even the largest dispersion claimed by HoHun is pretty much neglible and at long range the aiming error is probably far larger than dispersion. The only condition when you don't benefit from the dispersion is that you somehow are able to aim extremely accurate at long range.

Quote
Originally posted by Crumpp

Key words Gripen.


If you can roughly aim better than amount of dispersion at long range, you won't benefit from the dispersion. In the other cases you at least get more hits.

Quote
Originally posted by HoHun
I believe you do not fully understand the beauty of my example ;-)


Hm... the example has nothing to do with the real life.

Quote
Originally posted by HoHun

For the Me 109, the MK108 will hit the target out to 500 m. At 600 m, the trajectory is so far below the target that even twice the vertical dispersion won't generate any hit.


I tested the AH G-10 with the MK 108 and it appears to be extremely difficult get any hits at long range (around 400) regardless the deflection angle (even almost directly behind) when shooting a drone B-24. In the case of the AH Spitfire V, I could quite easily get hits even at 600.

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: beet1e on November 06, 2005, 05:33:16 AM
Squire - good post - thanks for posting. I have a few comments to make.
Quote
Clouds. Well, sometimes there were clouds and sometimes there were not, just like in any place on earth. Clouds were not omnipresent in all WW2 skies.
I mentioned clouds because there tends to be some turbulence in their proximity because of thermals. A cumulus cloud exists because of warm moist air rising rapidly from the surface. As the air rises, it cools. And as it cools, it can no longer retain its moisture, which condenses into the atmosphere, and a cumulus cloud is formed. The point I was trying to make was that in the presence of said cumulus clouds, there would have been strong upward air currents and/or turbulence, making it difficult for even the most accomplished pilot to aim accurately by pitching the aircraft's nose to within 0.057° that HoHun suggested was possible. As a former glider pilot I'd be actively looking for thermals, and I know how rough it could get when I found one. As any other glider pilot will tell you, you'll get bounced all over the place.

Now, the absence of clouds does not mean there are no thermals. In very hot, arid climates such as can be found in desert areas like Australia or Arizona, there are still thermals! It's just that the rising air does not cool enough to condense out what little moisture it was retaining. But the thermals there will be much stronger than the ones to be found in places like Britain. Even in Britain, I was able to find thermals rising at 10 knots on a relatively warm July day.
Quote
Training. WW2 pilots were well aware of what deflection shooting was, they were not stupid. In addition, specialist gunnery schools were setup in many air forces, specifically to tackle issues of deflection shooting theory.
Not here they weren't. Britain got rushed into the war. I believe at one time the German bombers were faster than our fighters! We were desperately short of trained pilots in 1940, some of whom went into active duty with as little as 10 hours on type. I have seen interviews/read accounts of newbie pilots being told to just get up there, point and shoot!

As I said earlier, to hit a wing (assuming 6" thickness) at 800 yards would require gun accuracy of 0.012°, and that's being generous by assuming laser gunnery and no bullet drop due to gravity or air resistance. As was pointed out, the wing was not the only target. How high did a typical fighter plane stand? - probably about 10ft - do you agree? In which case, the shooting aircraft would have to be aimed accurately with within 0.25° to achieve any hits on the target at 800yds.  Given the environmental factors I've just described, this would seem incredible for any pilot to achieve. And even if he could, dispersion would account for 75% of the rounds missing the target no matter how could the aim was. And this scenario doesn't even take into account loss of kinetic energy and bullet drop due to gravity and air resistance.
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 06, 2005, 06:40:17 AM
Quote
These "specific conditions" cover probably more than 90% of normal shooting situations.


Most of the world's air forces moved to cannon armament by the end of the conflict, Gripen.

In the begining when rifle caliber machineguns prevailed your statement is incorrect but only for a short period of time.  The majority of the war cannon were the fighter armament of choice for most air forces.

So in that sense disperision is not as detrimental as it is to a rifle caliber weapon.  

Quote
At short range even the largest dispersion claimed by HoHun is pretty much neglible and at long range the aiming error is probably far larger than dispersion. The only condition when you don't benefit from the dispersion is that you somehow are able to aim extremely accurate at long range


Your speculating and do not know.

Do not pass guesses or personal theory off as fact.

Like any shooting problem, the more errors than can be eliminated the more accurate the system.  Aerial gunnery by it's nature is fraught with errors.  Building in more shooting error would be rather stupid, IMHO.  There is already plenty to go around.

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 06, 2005, 07:01:28 AM
Quote
Originally posted by Crumpp
Most of the world's air forces moved to cannon armament by the end of the conflict, Gripen.


Yep, a good and rational decision.

Quote
Originally posted by Crumpp
Your speculating and do not know.


Hm... I'm not speculating, or do you see the reason why the pilots should have been able aim correctly in average at long range ie without systematical error.

Quote
Originally posted by Crumpp
Do not pass guesses or personal theory off as fact.


There is no quesses, simply a large probability that an average pilot aimed pretty much allways with some error.

Quote
Originally posted by Crumpp
Aerial gunnery by it's nature is fraught with errors.  Building in more shooting error would be rather stupid, IMHO.


Actually the dispersion decrease the effect of aiming error increasing the probability of the hit. Aircraft guns are burst type weapons, not single shot types as rifle.

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Kurfürst on November 06, 2005, 07:44:20 AM
Quote
Actually the dispersion decrease the effect of aiming error increasing the probability of the hit.


That's why people use high-dispersion shotguns to shoot down little birds. There's one difference however, a fighter was generally 3-4 tons heavy in WW2 and would not go down just because it was hit. Big dispersion is great for hitting a fighter randomly on occasion, and making some holes in it. OTOH, that's just a f. useless thing to do. You basically don't see the forest from a tree, arguing on one small detail and don't get the big picture, that we are aiming to destroy the enemy plane, not just hit it, with a few exceptions of extremely powerful board weapons.

It had to be hit repeatadly, preferably on the same place to have good effect and to cause enough damage on a certain area that something critical would fail, either the structure itself, or some vital part. If you don't get your hits concentrated, you don't get good effect and the target will just swallow the hits - a fighter would rarely go down because 1-1 cannon shell hit each of the wings, and the fuselage. But if it gets 3-4 of those shells in the same plane, it WILL go down, or at least written off. If you have high dispersion, or wing guns (which generally comes together), you can't control what you want to hit - hence 'spray and pray' that you hit something important, but I'd rather aim myself to something important instead of letting the  prayers do it.
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 06, 2005, 07:51:32 AM
Quote
Originally posted by Kurfürst

You basically don't see the forest from a tree, arguing on one small detail and don't get the big picture, that we are aiming to destroy the enemy plane, not just hit it, with a few exceptions of extremely powerful board weapons.


If the pilots aiming error is systematical as it probably is, some amount dispersion will actually increase probability of the hits as well as nunber of hits ie probability to destroy the enemy plane..

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 06, 2005, 08:19:34 AM
Quote
There is no quesses, simply a large probability that an average pilot aimed pretty much allways with some error.


Gripen you’re guessing that designers purposely built in dispersion to increase the hit probability when facts are they do not.

That is not true.

Quote
Couple degrees is just a wild quess, in fact it might have been less. In the case of the ZU-23 (AA gun, not GSh-23, I forget the designation), the mounting is built to have something like couple mm loosenes in the support point. Notable thing is that support point is actually rectangular so I quess the pattern is also rectangular. While shooting the jumping of the gun in the support point is quite well visible as well as dispersion of the projectiles.


Design flaw not a feature when it comes to accuracy.  Simply examine the number of high performance aircraft that have been brought down by ZU-23 fire.  While considered a threat, it is hardly an effective one.  The advantage lies in the "bang for the buck" factor.  ZU-23's are realtively inexpensive compared to other AAA platforms.

Quote
I didn't know that. I thought it was mostly a negative side effect of high MV and high ROF usually accompanied by a too flexible mounting of the gun (eg. wing).


Correct.  The dispersion found in a design automatic weapon is a function of the engineering tradeoffs to achieve sustainable automatic fire.  Not a feature to improve hit probability.  

Looks to me like people are confusing the convergence of fighter’s weapons with the dispersion of the weapon itself.

When a suitable picture hanger becomes available again, I will post various convergence adjustments, individual weapon dispersion charts, and vulnerability reports.

Facts are the aerial gunnery problem was inherently difficult.  No individual weapon is purposely designed with "built in dispersion".  All weapons are engineered to eliminate as much dispersion as is possible within the design limits.

Convergence patterns can be changed to increase a pilot with poor aim chances of placing a vital portion of an enemy aircraft into the beaten zone of the individual weapons in the array.  This would increase his chances of achieving concentration of firepower on a vulnerable portion of the target.

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 06, 2005, 08:57:58 AM
Quote
Originally posted by Crumpp
Gripen you’re guessing that designers purposely built in dispersion to increase the hit probability when facts are they do not.


I'm not quessing, I have seen that in the ZU-23. And the reason for the loosenes is actually described in the documentation. And the reason for dispersion can be proved with aiming error.

Quote
Originally posted by Crumpp

Simply examine the number of high performance aircraft that have been brought down by ZU-23 fire.  While considered a threat, it is hardly an effective one.  The advantage lies in the "bang for the buck" factor.  ZU-23's are realtively inexpensive compared to other AAA platforms.

 
The ZU-23 is probably one of the most succesful gun in it's class and it brought down plenty of high performance aircraft in Vietnam, Afganistan, Midle East etc. Current versions used by Finnish army feature motorized aiming as well as laser range seeker. Shortly a very succesfull and reliable weapon.

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 06, 2005, 09:21:34 AM
Quote
I'm not quessing, I have seen that in the ZU-23. And the reason for the loosenes is actually described in the documentation. And the reason for dispersion can be proved with aiming error.


I have seen them too, Gripen.  

You should probably check your statistics on the effectivenss.  There is a pretty good reason most first world armies do not rush out and buy them.

If you have original documentation please post it.  Getting it translated is no problem.

I would think the "looseness" of the mount has more to do with recoil forces not destroying the light mount of the weapon.

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Bruno on November 06, 2005, 10:37:29 AM
Quote
If the pilots aiming error is systematical as it probably is


Where does this assumption come from?
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 06, 2005, 12:13:41 PM
Hi Beet1e,

>Given the environmental factors I've just described, this would seem incredible for any pilot to achieve. And even if he could, dispersion would account for 75% of the rounds missing the target no matter how could the aim was.

Do you think you could come up with a number for the random aiming error you would consider credible?

>And this scenario doesn't even take into account loss of kinetic energy and bullet drop due to gravity and air resistance.

Hm, I'm not sure what you are talking about, but my example does.

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 06, 2005, 12:31:03 PM
Hi Bruno,

>>If the pilots aiming error is systematical as it probably is

>Where does this assumption come from?

As far as my example is concerned, certainly from a misunderstanding.

Out to the distances described above, the pilot can simply put his crosshairs on the centre of the target and push the button. The hit results described above are what they are because the trajectory does not deviate far from the sight line.

So all the pilot has to do - since it's so difficult to grasp, I'll have to repeat it once again - is to put his crosshairs on the centre of the target and push the button.

Only beyond 500 m for the MK108 and beyond 800 m for the Browning M2, trajectory drop becomes a factor, and range estimation and possible systematical errors in range estimation would have to be considered.

With the standard technique "Put the crosshairs on the target and push the button", systematical errors are not a factor.

(If you were bent on it, you could of course produce a systematic aiming error even for that technique. For example, you could suggest that the pilot never pushes the button when the crosshairs are on target, but only when they are off target. Instant systematic error :-) Not a very realistic suggestion, though.)

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: beet1e on November 06, 2005, 01:45:53 PM
Hohun,

My interest in this topic has a lot to do with the viability of killer 800yd shots, and the way that in some versions of some aerial combat games, ;) wings could be shot off with consummate ease at awkward trajectories at ranges of as much as 800yds or even more.

Gripen has estimated the total dispersion spread as a couple of degrees, maybe less. I did my own calculations based on a total spread angle of 1°, which is to say ½° in any direction from dead centre. Let us set aside the effects of gravity and air resistance until later...

In theory, the bullets would be discharged from the barrel of the gun(s) and would create a circular pattern on the target. The bullet stream would be conical in shape, with the point of the cone being at the gun barrel. But, at 800yds or 2400ft, the radius of that circle would be 2400xtan(½) = 20.94ft, and therefore the area of that circle would be just over 1377 square feet!! How much surface area is visible to an attacking pilot in the dead 6 position at 800yds? Well, the wingspan of a Spit V was in the order of 37ft. I don't know what the exact wing thickness was, what with fuel tanks - can we say an average wing thickness from tip to root of 4 inches? In this case, the surface area would be 37x0.33333 square feet = 12.33 square feet. Add to that the visible surface area of the tail and fuselage - asymmetrical, so difficult to calculate. Let's say the surface area was twice as much as the visible wing surface area - and that's being very generous. We end up with a value of 37 square feet, but as I have already shown above, the area covered by the guns at 800yds would be 1377 sq.ft.  Therefore, only one out of every ~37 bullets would find the target at a range of 800yds...

...and that's assuming perfect conditions - no bullet drop due to gravity, bullets that fly as straight as laser beams and which are unaffected by air resistance. It also assumes that the pilot can at all times keep the plane aimed to within a small fraction of a degree of the required attitude throughout the entire period needed for his guns to deliver the necessary destructive power to bring down the target. When these other factors are taken into account, it's clear to see that the chances of downing an enemy plane at such a huge range is infintesimal. Granted, a random ping could create an oil leak, to be followed soon afterwards by a forced landing, but that's about it.

The only way it could be done is if the bullets were as big as marrows - in some games, they were! :lol
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: 2bighorn on November 06, 2005, 02:53:57 PM
US Navy gunnery manual for pilots from 1944 says .50 cal dispersion was from 6 to 10 mil and max effective range was 1000 ft (333 yards).

Bullet drop due to gravity was about 15 ft at 900 yds (calc 11 ft at 800 yds)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 06, 2005, 03:59:36 PM
Hi Beet1e,

>But, at 800yds or 2400ft, the radius of that circle would be 2400xtan(½) = 20.94ft, and therefore the area of that circle would be just over 1377 square feet!!

Well, you're assuming that the bullets would spread out evenly over the entire area. However, with a random deviation caused by erratic movements of the aircraft nose, the crosshairs will be near the centre of the pattern much more often than on the edges.

Relying on the Gaussian distribution, I'll take your deviation of 0.5° as 3*sigma so that 99.7% of all hits are in the circle you describe.

With this, we arrive at the following hit distribution:

central 1/6° radius circle: 68% of the hits, 1/9 of the area => 153 sqft
ring 1/6° to 2/6°: 27.5% of the hits, 3/9 of the area => 459 sqft
ring 2/6° to 3/6°: 2.7% of the hits,  5/9 of the area => 765 sqft

So to hit the assumed area of 37 square feet, we get the following hit ratios:

central 1/6° radius circle: 68% of the hits => 24% strikes
ring 1/6° to 2/6°: 27.5% of the hits, 3/9 of the area => 8% strikes
ring 2/6° to 3/6°: 2.7% of the hits,  5/9 of the area => 0% strikes (rounded down :-)

The resulting total hit probability is:

Ph = 68% * 24% + 27.5% * 8% + 2.7% * 0% = 18.52%

That is closer to one out of every five bullets striking than to one out of every 37. With that kind of hit percentage, firing at 800 yards probably would be worthwhile.

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 06, 2005, 04:08:12 PM
Quote
Originally posted by Crumpp

You should probably check your statistics on the effectivenss.  


I wonder what should I check, during last 40 years no other AA gun has seen as widespread use as the ZU-23 and probably no other AA gun has brought down as many aircraft (planes or helicopters) as the ZU-23 during that period.

Quote
Originally posted by Crumpp

There is a pretty good reason most first world armies do not rush out and buy them.


I can certainly say that Finnish army has been very happy with the weapon itself   and in it's current form (http://www.mil.fi/maavoimat/kalustoesittely/index.dsp?level=54&equipment=79) will remain in service maybe next 10-20 years.

Quote
Originally posted by Bruno

Where does this assumption come from?


There is no reason to believe that the centre of the aim point set of a pilot is same as the correct aim point in long range deflection shooting.

Quote
Originally posted by Hohun

As far as my example is concerned, certainly from a misunderstanding.


The "example" has absolute nothing to do with the long range deflection shooting.

Quote
Originally posted by Hohun

With the standard technique "Put the crosshairs on the target and push the button", systematical errors are not a factor.


At long range deflection shooting the target is never in crosshairs except with gyroscopic gunsight.

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 06, 2005, 04:48:39 PM
Quote
I wonder what should I check, during last 40 years no other AA gun has seen as widespread use as the ZU-23 and probably no other AA gun has brought down as many aircraft (planes or helicopters) as the ZU-23 during that period.


Losses to AAA have been insignificant.

http://www.au.af.mil/au/afhra/wwwroot/short_studies/USAFMannedAircraftCombatLosses1990_2002.pdf

Considering the quantity employed and produced, the ZU-23 can hardly be considered a success.

Quote
can certainly say that Finnish army has been very happy with the weapon itself


Happy for them.  Hope they enjoy using them in combat.

Quote
At long range deflection shooting the target is never in crosshairs except with gyroscopic gunsight.


Where do you get deflection shooting from HoHun's post?

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: 2bighorn on November 06, 2005, 05:12:57 PM
Quote
Originally posted by HoHun
firing at 800 yards probably would be worthwhile.

Typical ww2 .50 cal M2 type 2 machine gun has only 13% hit rate (at 800yds) with a target area of 45 square feet. That would be with dispersion of a single gun.

If you would calculate in gunsight/guns harmonization error at typical distance of 350/400 yds of 6 guns package, aim of a typical airman, atmospheric conditions, speed of aircraft, bullet drop, different trajectory/balistics for mixed ammo loads, the fact that 90% of airman would completely miss banner target between 1000 and 1500 feet, then shooting at target at 800 yds for all practical purposes, was complete waste of ammo.

Quote
by US Navy 1944
Browning Aircraft Machine Gun, .50 Cal..,  MK 2, Mod 2. Range: Maximum effective - 1,000 feet.

Conservation of ammunition - don't waste ammunition firing out of range - only limited supply - main problem of combat fighters.
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 06, 2005, 05:31:21 PM
Quote
Originally posted by Crumpp
Losses to AAA have been insignificant.


Please check Vietnam.

Quote
Originally posted by Crumpp

Where do you get deflection shooting from HoHun's post?


I don't understand your (or HoHun's) logic here at all; Bruno asked from me from where comes my assumption that at longe range deflection shooting the error is probably systematical. HoHun answered and some how mixed in his "example" which has nothing to do with the deflection shooting.

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 06, 2005, 05:41:26 PM
Hi 2bighorn,

>Typical ww2 .50 cal M2 type 2 machine gun has only 13% hit rate (at 800yds) with a target area of 45 square feet. That would be with dispersion of a single gun.

Interesting data point! :-) That would be a 100% dispersion circle of roughly 7.6 mil. For which type of mount is this data valid?

For my example, I'm using 4 mil for the P-38 and 6 mil for the P-47, which is a bit lower, but seems to match historical data from various sources.

(Of course, with half the dispersion, I get four times the hit percentage.)

>the fact that 90% of airman would completely miss banner target between 1000 and 1500 feet

Well, banner shooting was not from the dead six position against a stationary target, but involved dynamic pursuit-curve attacks and lead estimation, so the level of difficulty is considerably higher than in my example.

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 06, 2005, 06:00:25 PM
The USAF maintained a .65% loss rate due to all enemy action causes.  

http://www.fas.org/man/crs/RS21141.pdf

Far more appear to have been brought down my SAMS and Air to Air Combat:

http://home.sprynet.com/~anneled/usloss.html

All in all, it seems pretty ineffective even back then.  

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 06, 2005, 06:15:56 PM
Quote
In ideal conditions (assuming that aiming was perfect and not systematically off) dispersion is bad. But in reality during WWII aiming was nearly allways systematically wrong because there was no way to determine correct lead until early gyroscopic sights arrived (and these still required some pure aproximations for range measurement). Basicly most pilots used too little lead and aiming point was behind and below correct point specially at long range. Therefore some amount of dispersion actually improved probability of the hit and also percentage of the hits.


While you are correct in this assumption Gripen for convergence adjustments, it does not improve the chances of achieving an immediate shoot down.

It is not correct for individual weapon dispersion.  Guns are designed to be as accurate as engineering allows and eliminate as much dispersion as possible.

More individual weapon dispersion simply means more chance to waste ammunition.

Quote
Ah rgr that. An army guy I used to know told me about how a belt fed machine gun was set up on the ground to provide cover for the guys moving behind it. Initially, it discharged over too small an area, so the rifling was adjusted (bored out?) to give the gun less accuracy but distribute the bullets over a larger area, which is what was needed in this case.


I would have to throw out the BS flag on this one, beetle.  

Think about the situation, if you were moving under covering fire wouldn't you want that fire to go exactly where the gunner aims?  Or at least as close as possible?

Covering fire is only effective if you are moving closely behind it.  From my experience you want it to be accurate as possible so that the gunner knows exactly where his bullets are going.  This ensures they do not go into you or anyone else they are not supposed too.

Additionally ask any soldier what would happen if he purposely bored out his weapons barrel or damaged his weapon.  The military uses terms like "statement of charges" and "Uniform Code of Military Justice" in the answer.

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 06, 2005, 06:17:17 PM
Quote
Originally posted by Crumpp
The USAF maintained a .65% loss rate due to all enemy action causes.  


Hm... US forces lost thousands of planes (fixed wing and helicopters) in Vietnam, most of them to the AA, the ZU-23 being the one of the main weapons.

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 06, 2005, 06:23:16 PM
Quote
Originally posted by Crumpp
While you are correct in this assumption Gripen for convergence adjustments, it does not improve the chances of achieving an immediate shoot down.


More hits, better chance to shoot down.

Quote
Originally posted by Crumpp
Guns are designed to be as accurate as engineering allows and eliminate as much dispersion as possible.


Some succesful guns are designed with some dispersion built in.

Quote
Originally posted by Crumpp
More individual weapon dispersion simply means more chance to waste ammunition.


No, some amount of dispersion increase probability of the hit as well as amount of hits in the deflection shooting.

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: 2bighorn on November 06, 2005, 06:26:14 PM
Quote
Originally posted by HoHun
Interesting data point! :-) That would be a 100% dispersion circle of roughly 7.6 mil. For which type of mount is this data valid?
Wing mounted various Navy AC types. I guess they took middle value of 8 mils (hit percentage was actually 13+, I rounded the value), since they stated dispersion values from 6 to 10 mils.

Quote
Originally posted by HoHun
For my example, I'm using 4 mil for the P-38 and 6 mil for the P-47, which is a bit lower, but seems to match historical data from various sources.
Interesting how AF and Navy got different numbers.

Quote
Originally posted by HoHun
Well, banner shooting was not from the dead six position against a stationary target, but involved dynamic pursuit-curve attacks and lead estimation, so the level of difficulty is considerably higher than in my example.
True.
However, I still believe that disabling enemy plane at 800 yds with .50 cals was extremely difficult. I'm not saying it didn't happen, it's just that probability is very low.

Here in AH I get often kill with 70-80 degrees deflections shots at 400-500 yds. Even with all the practice, it seems too easy.
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 06, 2005, 06:26:29 PM
Quote
Hm... US forces lost thousands of planes (fixed wing and helicopters) in Vietnam, most of them to the AA, the ZU-23 being the one of the main weapons.


Sure they did but they had tens of thousands of aircraft flying and rotating through the war zone over the decades the Vietnam war was fought.

Proportionally AAA is not very effective.  Certain tactics make it a neglible threat.  It is certainly much more dangerous to be the AAA gunner than the aircraft pilot in modern war.

Most of the Ground fire casualties appear to be Helicopters.  I seriously doubt the NVA were hauling 23mm systems through the jungle.  Most likely these are just MG's from fairly close range on a pretty much stationary helicopter landing or taking off.

You have any documentation on the ZU-23 being the main weapon used?  IIRC the North Vietnamese employed a variety of AAA systems with a PK and DSHK being the most common.

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 06, 2005, 06:28:00 PM
Quote
However, I still believe that disabling enemy plane at 800 yds with .50 cals was extremely difficult. I'm not saying it didn't happen, it's just that probability is very low.


I think that is a very true statement.  The vunerability reports, convergence charts, and dispersion patterns seem to point to that conclusion.

Quote
More hits, better chance to shoot down.


No one is arguing that Gripen.  Your statement that weapons have design purpose dispersion is not correct.

Additionally, a projectile has to capable of inflicting enough damage to a vulnerable area of the target.  The chances of randomly achieving the required number of hits from a .50 cal or below on a vulnerable area are pretty slim.

Quote
Some succesful guns are designed with some dispersion built in.


Name them.

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 06, 2005, 06:37:28 PM
Quote
Originally posted by Crumpp

You have any documentation on the ZU-23 being the main weapon used?  IIRC the North Vietnamese employed a variety of AAA systems with a PK and DSHK being the most common.


http://www.ausairpower.net/TE-Helo-Mar-05-P.pdf

"After the Vietnam experience
where thousands of UH-1/AH-1 family helicopters
were lost to a combination of AK-47/AKM rifles, ZPU, ZU-23
and ZSU-23-4P guns and MANPADS, the US embarked on a
major rethink of helicopter design.
"

Note that the gun itself is same in the ZU-23 and ZSU-23-4.

Quote
Originally posted by Crumpp

Your statement that weapons have design purpose dispersion is not correct.


The ZU-23 is designed with built in dispersion and for a rational reason.

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 06, 2005, 06:43:16 PM
Quote
After the Vietnam experiencewhere thousands of UH-1/AH-1 family helicopters were lost to a combination of AK-47/AKM rifles, ZPU, ZU-23
and ZSU-23-4P guns and MANPADS, the US embarked on a
major rethink of helicopter design."


Hardly proof of the Zu-23's effectiveness.

Quote
The ZU-23 is designed with built in dispersion and for a rational reason.


Yes, you have claimed this earlier.  And I replied that I doubted the dispersion was "built in" to increase hit probability.  More likely the mount is flexible to reduce the force of recoil so that it does not crack the mount.

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 06, 2005, 06:49:06 PM
Quote
Originally posted by Crumpp
Hardly proof of the Zu-23's effectiveness.
 


http://www.globalsecurity.org/military/library/report/1984/CSJ.htm

" What can be seen can be hit."  For attack helicopter
pilots these words suddenly had real meaning in 1973.  The
event that gave meaning to these words was the 1973 Mid-East
War; the weapon was the ZSU-23-4.  During that conflict,
nearly one-half of all the aircraft that the Israeli forces
lost were to the ZSU-23-4.1  The significance of that
accomplishment was not lost on the attack helicopter com-
munity.  No single event has had such a profound effect on
the tactics of the AH-1.
     The ZSU-23-4 is the backbone of a Soviet maneuver
echelon's formidable air defense system.  Although it first
appeared in the mid-sixties, it was not until the 1973
Mid-East War that the ZSU's capabilities became widely known
and appreciated.  It immediately became apparent that the
ZSU-23-4 was a deadly threat to any low flying helicopter
that came within its sight and range.  This disconcerting
development quickly became a source of concern to attack-
helicopter pilots who had previously enjoyed a relatively
free rein during the Vietnam conflict.  As a result of that
concern, radical changes in tactics and increased emphasis
on survivability equipment evolved.
"

Quote
Originally posted by Crumpp
Yes, you have claimed this earlier.  And I replied that I doubted the dispersion was "built in" to increase hit probability.  More likely the mount is flexible to reduce the force of recoil so that it does not crack the mount.


It's 100% certainly built with loosenes in the support points to give some amount of dispersion. Go and check one.

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: zorstorer on November 06, 2005, 07:12:20 PM
Quote
Originally posted by gripen
http://www.globalsecurity.org/military/library/report/1984/CSJ.htm

" What can be seen can be hit."  For attack helicopter
pilots these words suddenly had real meaning in 1973.  The
event that gave meaning to these words was the 1973 Mid-East
War; the weapon was the ZSU-23-4.  During that conflict,
nearly one-half of all the aircraft that the Israeli forces
lost were to the ZSU-23-4.1  The significance of that
accomplishment was not lost on the attack helicopter com-
munity.  No single event has had such a profound effect on
the tactics of the AH-1.
     The ZSU-23-4 is the backbone of a Soviet maneuver
echelon's formidable air defense system.  Although it first
appeared in the mid-sixties, it was not until the 1973
Mid-East War that the ZSU's capabilities became widely known
and appreciated.  It immediately became apparent that the
ZSU-23-4 was a deadly threat to any low flying helicopter
that came within its sight and range.  This disconcerting
development quickly became a source of concern to attack-
helicopter pilots who had previously enjoyed a relatively
free rein during the Vietnam conflict.  As a result of that
concern, radical changes in tactics and increased emphasis
on survivability equipment evolved.
"

 

It's 100% certainly built with loosenes in the support points to give some amount of dispersion. Go and check one.

gripen


CC Grippen....

I can only speak about my time in the Army as a gunner in a M2A2 ODS Bradley.  The 25mm M242 Bushmaster chaingun had a built in flexability in the mounting.  This was done (as told to me by our master gunners) to aid in supression of the enemy and our secondary ability (anti-air).  If anyone remembers seeing the AH-64 attack on the guy under the truck you can see the circular pattern that the 30mm shells make (the M242 was designed as a smaller version of the AH-64's cannon).  That being said I only found that firing at a stationary target at 1500m my grouping was usually less than 3ft.  Not sure what you number crunchers out there can make of it :)  I'll try to dig out some pics.
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Squire on November 06, 2005, 07:16:45 PM
Big difference between the campaign in the North vs fixed targets and the missions flown in the south. Crew served weapons were not a big part of the VC or NVA arsenal in S. Vietnam, at least, not prior to 1973.

I have seen several books on the percentage of hit in 1972 for SA-2s and 57mm and 85mm AAA guns, and it would seem the AAA guns are actually more effective, and less costly, over the long run, when deployed in large #s.  

Of course that changes over time, with technology, but its interesting to note that many of the Coalitions losses suffered in 1991 were as a result of "blind fire" AAA, and not the very expensive, and vulnerable SAM systems that so many governments spent billions on.  

The SA-6s in 1973 (Arab-Israeli), had a "sweet time" where they were a novelty. A mobile, high end SAM system. After countermeasures technology started coming into its own, and tactics changed, they were reduced in effectiveness greatly. In the 1982 Bekaa Valley campaign, they were taken out completely.

As for the ZSU-23-4 gun system, again, its impressive untill you jam it with countermasures, and its radar cant lock on to targets. Then its just a big target on tracks. To a UH-1 with no countermeasures im sure its a dangerous foe, but things change. Same with shoulder fired I-SAMs, they scare commercial airline pilots, not attack pilots. I think during the Falklands war a stinger managed to down a single Pucara turboprop...  

Since 1973, SAMs have not delivered the goods. They promise much and often fall short. Just an observation. Im not saying they dont belong in militaries, just pointing out they have not done nearly as well as advertised.
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 06, 2005, 07:43:48 PM
Quote
It's 100% certainly built with loosenes in the support points to give some amount of dispersion. Go and check one.


I have seen plenty of them Gripen.

The ZU-23 is a large caliber gun on a very light mount.  When it is fired, the weapon jumps around considerably.  

Yes the looseness of the mount adds dispersion.  It was NOT designed to add dispersion.

It is a flaw not feature when it comes to accuracy.  It my very well be an engineering feature designed to mitigate other parameters.

Show some documentation proving this was a "design feature" to add dispersion.  You said you had it.

Notice the definition of Ballistic Dispersion:

Quote
BALLISTIC DISPERSION— The variation of a path of a bomb or projectile which is attributed to physical tolerances in the weapon dimensions and to the stability of the weapon. The error produced by this variability is commonly stated as standard deviation in range and deflection of the error with respect to the mean point of impact.


Notice it does not say "the feature" produced.

http://www.fas.org/irp/doddir/usaf/afpam14-210/part14.htm


Quote
Employment Of The AH-1T (Tow) Against The ZSU-23-4
CSC 1984
SUBJECT AREA Strategic Issues
                     EMPLOYMENT OF THE AH-1T(TOW) AGAINST
                                 THE ZSU-23-4
                                 Submitted to
                                  Dr. Berens
                    In Partial Fulfillment of Requirements
                           for Written Communication
                  The Marine Corps Command and Staff College
                              Quantico, Virginia
                            Major S. J. Cobain, Jr.
                          United States Marine Corps
                                 April 6, 1984
            EMPLOYMENT OF THE AH-1T(TOW) AGAINST
                        THE ZSU-23-4
                           Outline
Thesis Sentence:  The AH-1T(TOW) is well suited to counter
                  the ZSU-23-4 on the modern battlefield.


I think that is a true statement borne out by experience in Vietnam, Aghanistan, and Iraq.

http://www.globalsecurity.org/military/library/report/1984/CSJ.htm

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 06, 2005, 08:15:15 PM
Quote
The 25mm M242 Bushmaster chaingun had a built in flexability in the mounting.


Whoever told you that fed you some BS.  Sounds cool though.

The M242 needs 12mm of recoil movement in order to cycle the gun.  The mount is flexible to allow the gun to move that 12 mm.  

Served quite a few years in Uncle Sugar's Ain't Released Me Yet....

Check FM 3-22-1.

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: zorstorer on November 06, 2005, 08:50:42 PM
Quote
Originally posted by Crumpp
Whoever told you that fed you some BS.  Sounds cool though.

The M242 needs 12mm of recoil movement in order to cycle the gun.  The mount is flexible to allow the gun to move that 12 mm.  

Served quite a few years in Uncle Sugar's Ain't Released Me Yet....

Check FM 3-22-1.

All the best,

Crumpp


CC it does need the 12mm of recoil movement to the rear to allow the gun to cycle.  If it doesn't the gun knows that a round didn't fire and stops the firing cycle.  BUT this recoil is to the rear, inline with the barrel.  The play I am taking about is in the mounting pins on the bottom front of the mounting.  You know the one you tore up your hands trying to release ;)

So were you a crunchy when you were in?  :D
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Tony Williams on November 06, 2005, 09:24:28 PM
Whether SAMs or AAA shoot many planes down isn't necessarily the issue. What does matter is that their existence makes the job of pilots much harder, forcing them to adopt tactics which reduce their ability to attack the targets they're after. So they can be effective even if they shoot nothing down.

Of course, if there's a big technology imbalance between attacker and defender, the pilots can overcome this - to some extent - with SEAD. Even so, that doesn't work against manually aimed guns like the ZU-23 (as opposed to the ZSU), which remain a serious threat to low-flying helos in particular. After all, if a burst of small arms fire can force an entire unit of AH-64s to retreat in disarray, think what ZU-23s could have done to them...

Tony Williams: Military gun and ammunition website (http://www.quarry.nildram.co.uk) and discussion forum (http://forums.delphiforums.com/autogun/messages/)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 06, 2005, 10:11:38 PM
Quote
The play I am taking about is in the mounting pins on the bottom front of the mounting.


It's not there for added dispersion, that is for sure.  It is there because it is very difficult to make pins that do not move that can removed easily.

That is why you do not see removable breakdown pins on an M24 SWS or any rifle designed for maximum accuracy.

For aerial targets ammunition (HE-T preferably if less than 1200 meters or APDS-T if farther out) and proper ranging are the key using the ADR sight.

Think about how much "built in" dispersion would help you engaging a BMP?

Quote
So were you a crunchy when you were in?


Yep

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 06, 2005, 11:06:18 PM
Quote
Originally posted by Crumpp

Yes the looseness of the mount adds dispersion.  It was NOT designed to add dispersion.


Read my lips: There is built in dispersion in the mounting of the ZU-23. It's purpose built to the rectangular support point.

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 07, 2005, 02:01:03 AM
Hi 2bighorn,

>Wing mounted various Navy AC types. I guess they took middle value of 8 mils (hit percentage was actually 13+, I rounded the value), since they stated dispersion values from 6 to 10 mils.

Ah, thanks, that makes sense! :-)

>Interesting how AF and Navy got different numbers.

Historically, the USAAF seems to have been a bit more optimistic about the capabilities of the Browning M2 than the Navy. I wouldn't be suprised if that subconsciously influenced the numbers, but there seems no way to verify this :-/

>However, I still believe that disabling enemy plane at 800 yds with .50 cals was extremely difficult. I'm not saying it didn't happen, it's just that probability is very low.

Remember that my my statement on fire at 800 yards being possibly worthwhile is for a P-38 with nose-mounted armament only - the more common layout with the guns in the wings would be rather disadvantaged at that range, since convergence was normally set at 200 to 300 yards.

Even with a P-38, there'd be two different situations: The target is flying away from you because it has not discovered you yet,  or the target is flying away because it has discovered you and attempts to run away.

In the former situation, it would be sensible to get much closer to the target before firing because hit chances increase at shorter range, and you'll be in a better position to catch up with the target if it dives.

In the latter situation , it's not likely that the target will fly the perfectly straight path required for long range shooting, and even "drifting around" slightly will make hits much less probable than against an unaware target.

So I don't believe my estimate (which was aimed at the technical side of long range shooting) is necessarily unrealistic. However, long range fire might have only been possible under specific circumstances which did not occur very often.

>Here in AH I get often kill with 70-80 degrees deflections shots at 400-500 yds. Even with all the practice, it seems too easy.

Hm, one would have to check the number of hits required for such a kill to see whether it's a damage model or an aiming question. It would also be interesting to have a look at the hit ratio - it might very well be that you're expending a lot of ammunition for very few hits, which is another way to score with low probability shots :-)

I know that in games, gunnery appears too easy to me, too, but when I check my total hit ratio at the end of the day, it's usually not much better than 5%, which appears realistic. I'm sure that count is right, but the contrast has me puzzled anyway :-)

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 07, 2005, 04:12:16 AM
Quote
Read my lips: There is built in dispersion in the mounting of the ZU-23. It's purpose built to the rectangular support point.


Read my lips:  Your full of it.  

You said you could prove it and had documentation:

Quote
Gripen says:
And the reason for the loosenes is actually described in the documentation.


Post it, that is all I have asked.  Instead you respond with an attack.  Typical Gripen.

 
Quote
Show some documentation proving this was a "design feature" to add dispersion. You said you had it.


All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: beet1e on November 07, 2005, 04:24:53 AM
Quote
Originally posted by HoHun
Well, you're assuming that the bullets would spread out evenly over the entire area.
Yes I was assuming that, for the purposes of my example. I was also assuming that the pilot could fly the plane accurately to within ¼° nose pitch, that the bullets would fly as straight as laser beams unaffected by gravity or air resistance, and that the plane was being flown in smooth air conditions with zero turbulence. As I said before, the introduction of these environmental factors makes the likelihood of scoring hits much less likely, and as 2bighorn has quoted from the US Navy manual, the .50 cal was effective to a maximum of 333 yards. Gabreski claims to have got kills at 400yds, using the 8x.50cal wing mounted on his P47. But he also says in his book that getting in close made the guns much more effective.

I accept that the dispersion pattern was asymmetrical, as you described, but then we're back to the opposite problem - if the majority of the hits passed through the inner portion of the circle, an area of 153 square feet in your example, then the diameter of that circle would be 14 feet. The aim would have to be accurate to within about 0.34° for any part of the "inner dispersion disc" to bear upon any part of the 153 square foot target area. But... I don't think you've allowed for the fact the attacking pilot would not see the target as a circle, but as two wings and a fuselage in the middle. In my example, the wings represent one third of the target area, but with an average thickness of 4 inches, a value which you did not dispute, even with perfect aiming, less than 5% of these hypothetical laser bullets would find the wing, and for any of them to find the wing at all, the aircraft would have to be flown and aimed accurately to within that 0.34°. Sorry, but I just don't buy it.

I'd like to hear more from 2bighorn about that USN manual, and the reasons given for the effective range of the .50 cal.

Some of you guys are expressing dispersion values as "mil". Can you indicate what this value would be expressed as degrees of variation from perfect centre?

Crumpp - About the army guy with the bored out machine gun. No, he didn't do it himself. :lol It's a long time since I heard the story, but I think what he was trying to say was that the British Army experimented with a particular type of gun which they intended to deploy in jungle conditions. What they wanted was to be able to fire many rounds into a sizable area, ie. not all at one spot, to provide covering fire. That's all I can remember. Come to think of it, I used the word "friend" loosely when referring to this guy. He was actually a bit of an arse, and a lot of what he said was BS.

After all these calculations, I can see why the authors of the early game sims used "hit bubbles"! :rolleyes::D
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Kurfürst on November 07, 2005, 04:44:56 AM
Quote
Originally posted by gripen
If the pilots aiming error is systematical as it probably is, some amount dispersion will actually increase probability of the hits as well as nunber of hits ie probability to destroy the enemy plane..

gripen


Disagree, that's quite a bit reaching out of the boundaries or reality. It'd would be correct to assume that if the dispersion is greater, than the probability to achive a hit is greater. Shotgun effect : out of many small pellets one or two will hit.

Hit percentage is entirely different thing, there dispersion works against you. Shotgun example again : even if you're aim is correct, out of say 30 fired pellets only 1-2 did hit (high dispersion). Use a machinegun (tight dispersion) with the correct aim, and almost all bullets will hit. Does HK G11 rifle ring a bell? It was built around to hit the target with several bullets at the same time with very tight dispersion. Curiously, you don't find many shotguns in armies firing small pellets, with great chance of hitting once, but doing very little damage overall.

I think even you wouldn't argue against that the hit percentage is the highest when you're aim is correct. And when your aim is correctly laid on target, higher dispersion would only lead to lesser percentage of hits achieved against when the fire pattern is tight, obviously. You're basically arguing on the basis that WW2 pilots never ever hit anything, and had to rely on high dispersion, in other words, pure luck to hit something. That is just blatantly false. Higher concentration of fire (=low dispersion) was seeked by everyone. The P-38 to name one allied example, was described to be lethally effective with it's nose mounted, highly concentrated firepower as compared to US fighters with the 'high dispersion' way with wing mounted guns. Another example being the RAF, which opted - initially - for the 'blunderbuss' effect. Even they decreased the harmonization range of the guns, again high fire concentration, lower dispersion was choosed instead of covering a larger area with higher dispersion.
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 07, 2005, 05:29:05 AM
Quote
Originally posted by Crumpp

You said you could prove it and had documentation:


There are thousands of ZU-23s around the world, all you need to do is go and check one out. AFAIK there is some ZU-23s owned by collectors in the USA.

And documentation is training material of Finnish army, not available in the net nor trough me.
 
Quote
Originally posted by Crumpp

Post it, that is all I have asked.  Instead you respond with an attack.  Typical Gripen.


I have pointed out where to find the evidence if you want to check it out. Generally I have no need to prove something in practice if I can prove it with theory.

Actually it's you who responds with attack when me and zorstorer tell what we have learned in service. The point here is that we (me and zorstorer) know what we are talking about and you don't.

Quote
Originally posted by Kurfürst

Disagree, that's quite a bit reaching out of the boundaries or reality. It'd would be correct to assume that if the dispersion is greater, than the probability to achive a hit is greater. Shotgun effect : out of many small pellets one or two will hit.


No, if the error is systematical, some amount dispersion gives more hits.

Quote
Originally posted by Kurfürst

I think even you wouldn't argue against that the hit percentage is the highest when you're aim is correct.


From my first post to this thread:

"In ideal conditions (assuming that aiming was perfect and not systematically off) dispersion is bad. But in reality during WWII aiming was nearly allways systematically wrong because there was no way to determine correct lead until early gyroscopic sights arrived (and these still required some pure aproximations for range measurement). Basicly most pilots used too little lead and aiming point was behind and below correct point specially at long range. Therefore some amount of dispersion actually improved probability of the hit and also percentage of the hits."

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: 2bighorn on November 07, 2005, 01:41:18 PM
Quote
Originally posted by beet1e
I'd like to hear more from 2bighorn about that USN manual, and the reasons given for the effective range of the .50 cal.

Reason were more or less practical and most of them influenced accurate aiming and/or hitting power above 1000'.
Bullets travel time: about 4/10 of a second for first 1000'
Bullets speed decrease: roughly 530fps for the first second
Bullets drop due to gravity: roughly a foot for first 1000' and whooping 14-15' at 2400' (800yds)
Sights were typically boresighted at 750' (wing mounted) - rarely above 1000' (convergence issues at greater ranges)
Different ammo types had different balistics (AP vs Tracer) which wasn't an issue at shorter ranges (1200' and bellow).
Gunsight resolution: at 600' bf109 wingspan would fit into inner 50 mils ring, at 2400' (800 yds) its wingspan would cover 12,5 mils only, fuselage would be completely covered with pipper. Corrections to accurately adjust for bullets drop would be nearly impossible.

Lets say that you would be able to accurately aim at 800yds. You have nose mounted 6x.50 cal guns (no conv. issues). Fire rate is max 850 rounds per min per gun, that's about 14 per sec per gun. Hit percentage at that distance into twin engined me110 would be 15% due to dispersion.

To get 50 rounds into target, you would need to fire aprox 330 rounds. 6 guns can fire only 84 rounds per second. At that rate you would need 4 seconds burst.



Quote
Originally posted by beet1e
Some of you guys are expressing dispersion values as "mil". Can you indicate what this value would be expressed as degrees of variation from perfect centre?


During World War II the U. S. Army often used a mil equal to 1/1000 of a right angle, 0.1 grad, 0.09°, or 5.4 arcminutes.
One mil equals 1 foot at 1000' and 35' wingspan at 1000' equals 35 mils.

For example, outer ring on standard gunsight was 100 mils and inner ring was 50 mils, refective gunsight pipper itself was 2.5 mils or 5 mils, depends on gunsight.
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 07, 2005, 03:01:48 PM
Hi Beet1e,

>>Well, you're assuming that the bullets would spread out evenly over the entire area.

>Yes I was assuming that, for the purposes of my example.

The problem with that particular assumption is that it is not realistic, and that it has a major impact on the final result.

The Gaussian bell curve universially applies to all statistic events that are determined by a large number of independend random events, such as all the small effects we can't account for individually that contribute to moving the crosshairs off the aiming point.

Probably le statistician Straffo could explain it better than I can ;-) Anyway, the result of complex random events is not an even distribution as the one in your original example, but one with a noticable peak around the average value, which - due to the marksman's efforts - is the position in the centre of the sight.

>as 2bighorn has quoted from the US Navy manual, the .50 cal was effective to a maximum of 333 yards.

Well, the problem is that "effective range" is not a clearly defined terminus. I'd agree that with wing guns, divergence problems lead to a noticable drop in effectiveness somewhat beyond convergence range. So if the Navy was using a convergence range of 250 yards, 333 yards would be about the point where the effectiveness begins to drop off. It's not yet the point where it's zero, though. (If I remember correctly, the Navy was more into deflection shooting than the USAAF, too, so they might have had more complex situations in mind than the straight six shot our discussion started off with.)

>Gabreski claims to have got kills at 400yds, using the 8x.50cal wing mounted on his P47. But he also says in his book that getting in close made the guns much more effective.

I believe that's an accurate description of the drop in effectiveness resulting from divergence beyond the point of convergence, and well in line with the Navy observation.

Here's a quote from my original analysis near the beginning of this thread:

"At 200 to 300 m, most of the fire will strike the fuselage (with enough bullets missing to be helpful in a realistic situation where the aim is not perfect :-), and at 400 m, the tips of the horizontal stabilizer will be showered. At 500 m and beyond, the greatest share of the bullets will miss."

In my opinion, that agrees with the Navy advice and Gabreski's experience.

(If the target does not fly perfectly straight at 400 m, it can easily be hit in the fuselage by one wing's guns, so please don't focus on the small size of the tips of the horizontal stabilizer :-) But then the fire of the other wing's guns would miss almost completely, which explains the sharp drop in effectiveness compared to the convergence situation where both wings' guns can hit.)

>But... I don't think you've allowed for the fact the attacking pilot would not see the target as a circle, but as two wings and a fuselage in the middle.

You are right,  I didn't account for that in my version of your example. In fact, I applied the "even distribution" logic I criticized, only divided in three uneven zones :-) I didn't mean to provide a final hit probability figure, just to illustrate the effect of the bell curve distribution.

>Some of you guys are expressing dispersion values as "mil". Can you indicate what this value would be expressed as degrees of variation from perfect centre?

1 mil = 0.057 degrees as it's defined as 1 unit of lateral displacement at 1000 units distances.

2bighorn seems to have found a different definition :-/ We had different definitions in some earlier thread, too, but the differences were small enough to be insignificant. However, if 2bighorn uses 0.09° and I use 0.057°, that's a bit of a problem.

The USAAF's K-14 LCOS (lead computing optical gunsight) as used for example in the P-51D had a 70 mil ring, by the way.

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: 2bighorn on November 07, 2005, 03:24:00 PM
Quote
Originally posted by HoHun
1 mil = 0.057 degrees as it's defined as 1 unit of lateral displacement at 1000 units distances.

2bighorn seems to have found a different definition :-/ We had different definitions in some earlier thread, too, but the differences were small enough to be insignificant. However, if 2bighorn uses 0.09° and I use 0.057°, that's a bit of a problem.

The USAAF's K-14 LCOS (lead computing optical gunsight) as used for example in the P-51D had a 70 mil ring, by the way.

Regards,

Your definition of a mil wasn't used in ww2. That came later.

ww2:
mil equal to 1/1000 right angle, or 0.09° (5.4 moa)

NATO after ww2:
mil equal to 1/1600 right angle, or 0.05625° (3.375 moa)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 07, 2005, 03:50:31 PM
Quote
I have pointed out where to find the evidence if you want to check it out. Generally I have no need to prove something in practice if I can prove it with theory.


In otherwords, you cannot prove it and do not have the documentation.

Fine.  Say so and state it is a theory of your own making.  Do not claim it as fact.

It can then be discussed and the merits examined.

Quote
Crumpp - About the army guy with the bored out machine gun. No, he didn't do it himself. It's a long time since I heard the story, but I think what he was trying to say was that the British Army experimented with a particular type of gun which they intended to deploy in jungle conditions. What they wanted was to be able to fire many rounds into a sizable area, ie. not all at one spot, to provide covering fire. That's all I can remember. Come to think of it, I used the word "friend" loosely when referring to this guy. He was actually a bit of an arse, and a lot of what he said was BS.


No problem beetle.  I just did not want you to get the wrong impression dispersion is a good thing to have in a direct fire weapon.

As Tony points out on his website, the perfect gun would be a laser beam.

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: straffo on November 07, 2005, 03:52:23 PM
Quote
Originally posted by HoHun
Hi Beet1e,

>>Well, you're assuming that the bullets would spread out evenly over the entire area.

>Yes I was assuming that, for the purposes of my example.

The problem with that particular assumption is that it is not realistic, and that it has a major impact on the final result.

The Gaussian bell curve universially applies to all statistic events that are determined by a large number of independend random events, such as all the small effects we can't account for individually that contribute to moving the crosshairs off the aiming point.

Probably le statistician Straffo could explain it better than I can ;-) Anyway, the result of complex random events is not an even distribution as the one in your original example, but one with a noticable peak around the average value, which - due to the marksman's efforts - is the position in the centre of the sight.


You called ? ;)

It's exact if an only if the distribution is a normal distribution and more than often if we except measurement artefact (the usual suspect) it's true.
A picture is better than thousand words :

(http://www.robertniles.com/stats/graphics/normal.gif)

Enought for now I've to see the "rois maudits" on TV.
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 07, 2005, 03:53:23 PM
Quote
Well, the problem is that "effective range" is not a clearly defined terminus.


Hey Hohun,

IIRC The US Military defines effective range as the point at which an average shooter can achieve 50% hit probability.

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 07, 2005, 04:09:54 PM
Hi Straffo,

>A picture is better than thousand words :

Merci beaucoup! :-)

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Bruno on November 07, 2005, 04:22:47 PM
Quote
Some of you guys are expressing dispersion values as "mil". Can you indicate what this value would be expressed as degrees of variation from perfect centre?


take your pick...

Angle Conversions (http://www.engnetglobal.com/tips/convert.asp?catid=6)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 07, 2005, 04:31:45 PM
Hi 2bighorn,

>Your definition of a mil wasn't used in ww2. That came later.

>ww2:
>mil equal to 1/1000 right angle, or 0.09° (5.4 moa)

>NATO after ww2:
>mil equal to 1/1600 right angle, or 0.05625° (3.375 moa)

Hm, that would of course overthrow my results for the US guns!

It would also invalidate my weapon dispersion table since it is based on the assumption that the historic dispersion would be expressed in identical units.

However, going back to the old thread, I found that two different definitions were used by the US in WW2, with one being 1/1000 of a right angle, and the other being 1/1000 of a radian, which is exactly the 0.0573° of the 1/1000 of range definition.

(The Germans used the fraction of range definition, too, and I would be suprised if the US weapons had that much more dispersion.)

So I'll continue to use the 0.0573° for now, but I'll keep my eyes peeled for an example where range and deviation are named in absolute figures so we can cross-check it!

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Sable on November 07, 2005, 04:33:05 PM
Quote
Originally posted by 2bighorn

During World War II the U. S. Army often used a mil equal to 1/1000 of a right angle, 0.1 grad, 0.09°, or 5.4 arcminutes.
One mil equals 1 foot at 1000' and 35' wingspan at 1000' equals 35 mils.

For example, outer ring on standard gunsight was 100 mils and inner ring was 50 mils, refective gunsight pipper itself was 2.5 mils or 5 mils, depends on gunsight.


So if we say:

a= size of object in feet
b= distance to object in feet
x= size of practice target or model in feet
y= mils
z= distance of practice target or model from viewer in feet

Then we can use 1000ft/b * a = y to determine the mils of the object we want to simulate, and then z/1000ft * y = x to determine the distance we need to place our model at from the viewer to simulate the object.

So if we use a Bf109, and a 1:48 scale Bf109 model then we know

a= 32.5ft (Bf109 wingspan)
b= 300ft (100yds)
x= .677ft or 8.125" (wingspan of 1:48 Bf109)


Then we can say 1000ft/300ft * 32.5ft = 108.3 mils

and

z/1000ft * 108.3 mils = .677ft

Z = 6.25ft

So we can say that a 1:48 scale Bf109 viewed from 6.25ft looks the same as a real Bf109 at 100 yards?  Does that math look right?
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 07, 2005, 04:40:13 PM
Hi Crumpp,

>IIRC The US Military defines effective range as the point at which an average shooter can achieve 50% hit probability.

Thanks a lot! :-)

That's quite interesting because it fits very well with the US Navy idea of effective range being just beyond convergence range. As I pointed out above, you are not going to get more than 50% hits once the bullet streams from both wings start to diverge noticably, and if 50% was indeed the criterion, that would coincede with my explanation attempt.

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: 2bighorn on November 07, 2005, 05:22:56 PM
Quote
Originally posted by HoHun
Hi 2bighorn,
However, going back to the old thread, I found that two different definitions were used by the US in WW2, with one being 1/1000 of a right angle, and the other being 1/1000 of a radian, which is exactly the 0.0573° of the 1/1000 of range definition.

(The Germans used the fraction of range definition, too, and I would be suprised if the US weapons had that much more dispersion.)

So I'll continue to use the 0.0573° for now, but I'll keep my eyes peeled for an example where range and deviation are named in absolute figures so we can cross-check it!

Regards,

Henning (HoHun)
Yes, it gets confusing because of different definitions. Some ww2 documents have clear definitions of a mil, some don't.
Either way, values given by me were already calculated, so the differences in results are more or less differences in approach by USAF and Navy, like dispersion values for example.
On the other side, difference  in dispersion in mils by USAF (4 mils for .50) or by Navy (6-10) might be because of different mil definitions.
Taking off 30% from average Navy value of 8 would bring it down to 5.6 which better corresponds with USAF values. The rest might be contributed to stricter Navy standards.
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 07, 2005, 10:59:46 PM
Quote
Originally posted by Crumpp
In otherwords, you cannot prove it and do not have the documentation.


I have given the source ie thousands of ZU-23s around the world. If you want to check if my claims (or zorstorer's) are true, just go and check one.

Basicly the source is given it's up to your footwork to check it, normal academic procedure.

Quote
Originally posted by Crumpp
Say so and state it is a theory of your own making.


Actually if you examine the thread (http://www.hitechcreations.com/forums/showthread.php?threadid=43507) claimed by beet1e in the opening of this thread, it's me who showed to HoHun how to calculate probabilities of shooting.

And it's not my theory, just basic statistics.

Quote
Originally posted by HoHun  
Anyway, the result of complex random events is not an even distribution as the one in your original example, but one with a noticable peak around the average value, which - due to the marksman's efforts - is the position in the centre of the sight.


How a pilot, (marksman or novice) can aim in long range deflection shooting without systematical error if there is no way to determine correct aiming point?

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: straffo on November 07, 2005, 11:50:42 PM
Quote
Originally posted by gripen

How a pilot, (marksman or novice) can aim in long range deflection shooting without systematical error if there is no way to determine correct aiming point?

gripen


Because he is aiming with punctiform sight not considering the spread of the bullets.
And luckily this point is at the apex of the gauss curve :)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Tony Williams on November 08, 2005, 12:08:39 AM
A quote from the article on the .5" Vickers on my website, concerning the four-gun naval mounting:

"The four-barrel mounting had its guns adjusted to provide a spread of fire, amounting to 60 feet wide and 50 feet high at 1,000 yards (15-18 m at 915 m)."

That showed a touching if misplaced faith in the destructive capability of a .5" calibre bullet...

Tony Williams: Military gun and ammunition website (http://www.quarry.nildram.co.uk) and discussion forum (http://forums.delphiforums.com/autogun/messages/)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 08, 2005, 04:16:56 AM
You calimed to have the manual and knowledge of a specific design detail of the ZU-23.  

Quote
Gripen says:
And the reason for the loosenes is actually described in the documentation.


You then admit you do not have specific design detail knowledge but are simply taking a guess.

Quote
Gripen says:
Generally I have no need to prove something in practice if I can prove it with theory.


And you admit you do not have access to the material in the first place when you made your calim.

Quote
Gripen says:
nd documentation is training material of Finnish army, not available in the net nor trough me.


Quote
And it's not my theory, just basic statistics.


It is your theory on the ZU-23.

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 08, 2005, 08:35:54 AM
Quote
Originally posted by straffo
Because he is aiming with punctiform sight not considering the spread of the bullets.
And luckily this point is at the apex of the gauss curve :)


That is the situation in his example ie stationary target, no lead needed.

But I'm asking about the situation when some lead is needed (deflection shooting). Why the apex of the gauss curve should be the same as correct aim point then?

Quote
Originally posted by Crumpp

You calimed to have the manual and knowledge of a specific design detail of the ZU-23.


No, such claim I have not done. I have seen training material of Finnish army which states that (as well as our instructors BTW). And I do have knowledge on the ZU-23 because I served in the AA of the Finnish army and the ZU-23 was one of the weapons we got training for. I have put it to pieces and assembled it, I have done aerial shooting as well as ground target shooting with it.

Quote
Originally posted by Crumpp

It is your theory on the ZU-23.


Actually the theory has nothing directly to do with the ZU-23, the built in dispersion in it just utilizes theoretical fact that some amount of dispersion gives better probability of the hit as well as more hits if there is some error in aiming.

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 08, 2005, 08:59:46 AM
Quote
No, such claim I have not done.


Ok then you do not know.

Quote
Actually the theory has nothing directly to do with the ZU-23, the built in dispersion in it just utilizes theoretical fact that some amount of dispersion gives better probability of the hit as well as more hits if there is some error in aiming.


So far you have no shown one individual weapon which has "built in" dispersion.

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Tony Williams on November 08, 2005, 10:31:17 AM
Quote
Originally posted by Crumpp
So far you have no shown one individual weapon which has "built in" dispersion.


You could get different barrel clamps for the M61A1, which gave different dispersion patterns (including a wide one) by varying the spacing between the barrels. Don't know if that saw any use, though.

Tony Williams: Military gun and ammunition website (http://www.quarry.nildram.co.uk) and discussion forum (http://forums.delphiforums.com/autogun/messages/)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 08, 2005, 01:50:30 PM
Quote
Originally posted by Crumpp
Ok then you do not know.


Hm... I do know what I learn during my service and I wonder why you try claim otherwise.

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 08, 2005, 03:58:33 PM
Quote
You could get different barrel clamps for the M61A1, which gave different dispersion patterns (including a wide one) by varying the spacing between the barrels. Don't know if that saw any use, though.


Hi Tony!

You got a link or documentation showing this was done specifically for the purpose of adding dispersion and not some other engineering purpose?

Quote
Hm... I do know what I learn during my service and I wonder why you try claim otherwise.


I guarantee you Gripen those pins are there for the exact same reason, ease of deployment or removal.  Although they add dispersion that is a flaw not a feature.

The ZAP 23 cannons have plenty of dispersion just due to the fact they are mass manufactured automatic weapons firing mass production ammunition.

The M2 is considered a very flat trajectory MG and very accurate.  It has a 4 mil dispersion cone.

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: straffo on November 08, 2005, 04:24:39 PM
Quote
Originally posted by Crumpp
The M2 is considered a very flat trajectory MG and very accurate.  It has a 4 mil dispersion cone.

All the best,

Crumpp


sustened fire ?
what king of mounting ?
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 08, 2005, 04:35:48 PM
Quote
sustened fire ?


Yes.  I assume that is at max rounds per burst.  "Sustained" rpb is 10 rpb every 30 seconds for a maximum of 21 consecutive bursts.

Mounted in the wing of a P51D.

Picture hanger ever comes back up I can post a slew of documents on this subject.

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: straffo on November 08, 2005, 04:43:07 PM
Thank you :)

At least I didn't put an accent in sustainèd fire ... oops I just did :D
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 08, 2005, 05:16:25 PM
Quote
Originally posted by Crumpp

I guarantee you Gripen those pins are there for the exact same reason, ease of deployment or removal.  Although they add dispersion that is a flaw not a feature.


If you disassemble the gun, you can even measure couple mm loosenes from the rectangular mounting supports. It wont make any easier or difficult to assemble the gun if these were tighter.

Besides, our instructors as well as documentation told that it's there for dispersion.

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 08, 2005, 05:17:40 PM
Quote
You could get different barrel clamps for the M61A1, which gave different dispersion patterns (including a wide one) by varying the spacing between the barrels. Don't know if that saw any use, though.


Hi Tony,

Looks like those may have been an attempt to reduce the dispersion which is usually the case in gun design.

Check out this Raytheon advertisement for the Phalanx system under "optimized barrels":

http://www.raytheon.com/products/stellent/groups/public/documents/content/cms01_055720.pdf

"Original M61A1 gun barrels were designed for short bursts and subject to wear and increased dispersion patterns."

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Tony Williams on November 09, 2005, 01:01:20 AM
I have an original GE '20mm Weapons Applications Data' handbook, with lots of technical stuff about the M61 family. It includes information about three different muzzle clamps which were available, together with nice shot pattern diagrams to show the effects of them. They are (for 100% of shots):

1 - Standard: circular pattern, 4.5 mils.

2 - Oval: 8 mils high by 38 mils wide.

3 - Large Dispersion: circular pattern, 16 mils.

The text states that: "The M61A1 gun normally produces a small circular dispersion pattern at the target. However, certain missions or targets may call for greater than normal dispersion. Still other targets may call for an oval pattern for increased hit probability. Such increased dispersion or pattern distortion can be obtained by substitution of a special muzzle clamp."

As I said, I have no idea whether any of these special muzzle clamps were ever used, but GE obviously thought that there might be a demand for them.

Tony Williams: Military gun and ammunition website (http://www.quarry.nildram.co.uk) and discussion forum (http://forums.delphiforums.com/autogun/messages/)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Tony Williams on November 09, 2005, 01:13:23 AM
Quote
Originally posted by Crumpp
The M2 is considered a very flat trajectory MG and very accurate.  It has a 4 mil dispersion cone.


The first point is to clarify whether we are talking about the figure for 100% or the often-quoted 75% of shots (the latter being typically half the size of the former). Then there is the question of the mounting.

Yes, the .50 M2 could achieve 4 mils for 75% of shots, from a rigid mounting. But that is not very accurate, in fact it is among the worst of WW2 aircraft guns.

That is not too surprising, as the Browning uses a short-recoil action which means that the barrel is not fixed but has to be free to move to and fro. That also helps to explain why the short-recoil MG 151 had far more dispersion than the fixed-barrel MG-FF (another part of the reason was that long barrels tend to 'whip' more than short ones, so have more dispersion).

And all that leaves entirely aside the issues already mentioned of the flexibility of the mountings (wings being worse than fuselages) or convergence effects for wing-mounted guns, or 'aim wander', all of which had a considerable effect on the overall shot pattern.

Tony Williams: Military gun and ammunition website (http://www.quarry.nildram.co.uk) and discussion forum (http://forums.delphiforums.com/autogun/messages/)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 09, 2005, 02:05:23 AM
Hi Tony,

>Yes, the .50 M2 could achieve 4 mils for 75% of shots, from a rigid mounting. But that is not very accurate, in fact it is among the worst of WW2 aircraft guns.

Are you certain that 4 mils is the 75% dispersion circle diamter and not the 100% one? I beleive that in the old thread referenced above, Butch2k quoted 4 mil for the Browning and 3 mil for the Hispano as 100% dispersion circles.

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: butch2k on November 09, 2005, 02:35:25 AM
Nope that was for the 75% dispersion
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 09, 2005, 04:18:59 AM
Quote
As I said, I have no idea whether any of these special muzzle clamps were ever used, but GE obviously thought that there might be a demand for them.


Hi Tony,

Interesting.  Guess there was not a demand for them if added dispersion was not needed to bring down a small fast moving target like a missle.

Quote
But that is not very accurate, in fact it is among the worst of WW2 aircraft guns.


Interesting.  Well that is a myth down the tubes then.


All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 09, 2005, 04:19:32 PM
Hi Butch,

>Nope that was for the 75% dispersion

Thanks for the correction! That does of course have a serious impact on my example!

I'll double all dispersion figures (including the German ones, after re-reading your post in the old thread) and re-run my example:

The MK108 will still hit accurately out to 500 m, but be virtually useless beyond.

The wing-mounted Brownings set to 250 m convergence will be a ineffective at 100 m if the pilot aims at the target fuselage because of convergence. (Easy to fix by kicking rudder, of course.) At 200 m, maybe 40% of the fire will be on target, at 250 m it's 80%, and at 300 m it's only 30%. (Note the way the hit ratio peaks at convergence range!) At 400 m, the horizontal stabilizer will be showered and there might be a few random hits on the fuselage. At 500 m and beyond, hit chances are very small.

With the nose-mounted Brownings, out to 200 m, the fire will hit virtually without a miss. At 300 m, the hit ratio will drop to maybe 80%, at 700 m it will only be about 20%. At 800 m, trajectory drop will roughly halve the hit chances, and at 1000 m they will be maybe 5% or less.

So the three example batteries still show the problems I orginally described, but the conclusions are a bit different.

For the Me 109, not much has changed because its dispersion is rather small.

The P-47 is limited in its range primarily by the divergence of its fire, and dispersion means that its fire loses effectiveness rapidly at long range. Firing at beyond 500 m probably won't be worth it, though it's still possible to envelop the target in tracers for tactical effect and score a handful of hits with a long burst.

The P-38's battery still is the best for long-range shooting, and a thee-second burst at that range might yield a fair chance of bringing an enemy fighter down. (The probability will, say, double if the Hispano cannon I neglected in my above consideration is added to the battery.)

So the P-38 is a real long-range killer if there ever was one! I stick to that comment ;-)

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 09, 2005, 04:27:17 PM
Hi Tony,

>I have an original GE '20mm Weapons Applications Data' handbook, with lots of technical stuff about the M61 family. It includes information about three different muzzle clamps which were available, together with nice shot pattern diagrams to show the effects of them. They are (for 100% of shots):

>1 - Standard: circular pattern, 4.5 mils.

>2 - Oval: 8 mils high by 38 mils wide.

>3 - Large Dispersion: circular pattern, 16 mils.

Thanks, that's interesting information! An A-10 pilot who usually provided very reliable information once told me about a similar purposefully increased dispersion for the 30 mm Gatling on the A-10. Of course, that was meant for attacking ground targets, and at least the wide oval pattern you quoted suggests that it was meant for ground attacks, too. A circular pattern does not suggest any particular target, but considering that the M61 is not a one shot MiG killer by any means, I'd suspect that the large dispersion setting was not really intended for air combat either. That's just my personal guess, of course :-)

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Tony Williams on November 10, 2005, 12:33:34 AM
Quote
Originally posted by HoHun
An A-10 pilot who usually provided very reliable information once told me about a similar purposefully increased dispersion for the 30 mm Gatling on the A-10. Of course, that was meant for attacking ground targets, and at least the wide oval pattern you quoted suggests that it was meant for ground attacks, too.


From Flying Guns – the Modern Era: Development of Aircraft Guns, Ammunition and Installations since 1945:

The 30 mm GAU 8/A in the A 10 "tankbuster" can get 80% of its shots within 5 mil, equal to 9 m dispersion at the 1,800 m maximum range. On test, the A-10 managed to hit a tank with about 10% of the shots fired at ranges varying between 500 and 1,340 m; a performance which has almost certainly improved since the LASTE package (low altitude safety and target enhancement), including a radio altimeter, autopilot and ballistic computer, was fitted in the 1990s. Incidentally, of the hits scored (against Russian T-62 tanks) just under 20% penetrated the armour (i.e. 2% of shots fired), although many others extensively damaged the track and suspension.

Tony Williams: Military gun and ammunition website (http://www.quarry.nildram.co.uk) and discussion forum (http://forums.delphiforums.com/autogun/messages/)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 10, 2005, 03:34:36 AM
Quote
Originally posted by HoHun
A circular pattern does not suggest any particular target, but considering that the M61 is not a one shot MiG killer by any means, I'd suspect that the large dispersion setting was not really intended for air combat either. That's just my personal guess, of course :-)


That certainly depends on your personal abilities; if you can aim more accurately at long range to the moving targets than stationary targets, then your personal quess is correct.

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 10, 2005, 01:09:51 PM
Hi Tony,

>Incidentally, of the hits scored (against Russian T-62 tanks) just under 20% penetrated the armour (i.e. 2% of shots fired), although many others extensively damaged the track and suspension.

Highly interesting! I'd say in conjunction with the info from the loss analysis linked by Crumpp (pointing out that 50% of the A-10 losses were due to SA-16 MANPADS), that suggests that gun-armed slow-movers are not a good choice for today's battlefield environment.

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 11, 2005, 04:24:15 PM
Hi again,

Some additional numbers on my example:

The Me 109's MK108 will hit with about 8 - 10 shells per second out to 500. That's equal to about 4 - 5 MW of total firepower on target. At 550 m, firepower on target will be down to 4 hits/s or 2 MW, at 600 m there will be no hits :-)

The P-47's wing mounted Browning are more complicated:

100 m*: 26 hits/s -> 0.57 MW
200 m: 42 hits/s -> 0.91 MW
250 m: 83 hits/s -> 1.82 MW
300 m: 31 hits/s -> 0.68 MW
400 m: 10 hits/s -> 0.23 MW

* aim laterally offset to hit fuselage

The nose-mounted Brownings yield the following results:

100 m: 52 hits/s -> 1.13 MW
200 m: 52 hits/s -> 1.13 MW
300 m: 42 hits/s -> 0.91 MW
700 m: 10 hits/s -> 0.23 MW
800 m: 05 hits/s -> 0.11 MW
1000 m: 2.6 hits/s -> 0.06 MW

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 15, 2005, 03:19:58 PM
I have compared the new AH K-4 to the AH P-47D-11. At long range between 600-800, I can definately kill the drone B-24 easier with with the P-47 than with the K-4. It's just much easier to get correct lead with the 8 mgs and the needed lead seem to be less ie there is less room for error. Generally it seems that in long range deflection shooting, the amount of bullets (more hits) and velocity of the bullets (less lead needed) are the most important factors.

gripen

edit: Convergence was default.
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Tony Williams on November 16, 2005, 02:51:53 AM
Quote
Originally posted by gripen
Generally it seems that in long range deflection shooting, the amount of bullets (more hits) and velocity of the bullets (less lead needed) are the most important factors.

I would agree that you will get more hits in those circumstances. However, when comparing with RL, you should bear in mind the following:

1. In RL, scoring hits at long range was uncommon. Scoring hits at any significant deflection angle was also uncommon. Scoring hits at long range and in deflection was virtually impossible. So your point is rather theoretical.

2. Also in RL, if you pulled off the remarkable trick of landing a few .50 hits in those circumstances it is unlikely that a B-24 would take any significant damage, let alone get shot down.

Tony Williams: Military gun and ammunition website (http://www.quarry.nildram.co.uk) and discussion forum (http://forums.delphiforums.com/autogun/messages/)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Kurfürst on November 16, 2005, 03:45:29 AM
Quote
Originally posted by gripen
I have compared the new AH K-4 to the AH P-47D-11. At long range between 600-800, I can definately kill the drone B-24 easier with with the P-47 than with the K-4. It's just much easier to get correct lead with the 8 mgs and the needed lead seem to be less ie there is less room for error. Generally it seems that in long range deflection shooting, the amount of bullets (more hits) and velocity of the bullets (less lead needed) are the most important factors.

gripen

edit: Convergence was default.


True for AH2, where the hit model is a joke, and I can score hits even when completely aiming stupidly in the 'general direction' of the airplane. That's becasue AH uses hit boxes, which are much larger than the actual aircraft.l

Try it in Il2FB, where the bullets only hit if the actually hit the 3d model of the enemy... your POV will change drastically. Someone getting regular 50% hit perctange in AH will be happy to get 5% in Il2FB's realistic gunnery model.
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 16, 2005, 04:08:45 AM
Quote
Originally posted by Tony Williams
I would agree that you will get more hits in those circumstances. However, when comparing with RL, you should bear in mind the following:

1. In RL, scoring hits at long range was uncommon. Scoring hits at any significant deflection angle was also uncommon. Scoring hits at long range and in deflection was virtually impossible. So your point is rather theoretical.

2. Also in RL, if you pulled off the remarkable trick of landing a few .50 hits in those circumstances it is unlikely that a B-24 would take any significant damage, let alone get shot down.


Ýep, overall I was just wasting ammo at ranges above 400. When I tried to shoot smaller targets (AH drones P-51D and Fw 190D-9), the results were even worse.

But the purpose of the test was just to show that in practice there is some "shotgun effect" which helps to find the correct lead and also the high velocity of the bullets helps to find the correct lead.

Quote
Originally posted by  Kurfürst

True for AH2, where the hit model is a joke, and I can score hits even when completely aiming stupidly in the 'general direction' of the airplane. That's becasue AH uses hit boxes, which are much larger than the actual aircraft.


So in real life deflection shooting at long range was actually even more waste of ammo, right?

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: hitech on November 16, 2005, 09:28:39 AM
Quote
Originally posted by Kurfürst
True for AH2, where the hit model is a joke, and I can score hits even when completely aiming stupidly in the 'general direction' of the airplane. That's becasue AH uses hit boxes, which are much larger than the actual aircraft.l
.


You are totaly miss informed and full of dog dodo.

HiTech
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Waffle on November 16, 2005, 09:32:26 AM
lol! made my morning!
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 16, 2005, 10:43:33 PM
Hi Tony,

>2. Also in RL, if you pulled off the remarkable trick of landing a few .50 hits in those circumstances it is unlikely that a B-24 would take any significant damage, let alone get shot down.

Based on total projectile energy, I'd say a figure of about 170 12.7 mm hits would be in line with the German expectations for a 95% kill chance.

With about 150 rounds per barrel being possible for a Browning M2 in a single attack run without overheating issues, and a battery of 6 - 8 barrels, this would require a hit probability of 14 - 19% for a 95% kill chance per attack run.

Evaluating the 8 x 12.7 mm Browning M2 battery according to the Luftwaffe scoring criteria (total battery weight multiplied by required firing duration) for anti-bomber weapons, I get a suitability factor of 0.055. That's about the same as 6 x 15 mm MG151 with 0.056. 2 x MK108 score 0.724, 2 x MG 213/30 1.00.

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 17, 2005, 03:36:19 AM
Quote
Originally posted by HoHun

With about 150 rounds per barrel being possible for a Browning M2 in a single attack run without overheating issues, and a battery of 6 - 8 barrels, this would require a hit probability of 14 - 19% for a 95% kill chance per attack run.


Actually I did my testing flying at about same speed as target (at various deflection angles) and shooting short bursts until all ammo was used. With the K-4 it was almost impossible to find the correct lead in deflection shooting, while with D-11 that was quite easy (less lead needed and more bullets in air). Notable thing here is that the AH D-11 can take 425rpg (8x12,7mm) while the K-4 can take only 68rpg (1x30mm). In practice most shooting runs (until the end of the ammo) at long range ended without single hit with the K-4, while with the D-11 I allways scored large number of hits and sometimes got a kill.

At short range the K-4 did well, I quess less than five hits is enough to destroy the drone B-24 but also the D-11 seem to be quite lethal at short range.

Quote
Originally posted by HoHun

Evaluating the 8 x 12.7 mm Browning M2 battery according to the Luftwaffe scoring criteria (total battery weight multiplied by required firing duration) for anti-bomber weapons, I get a suitability factor of 0.055. That's about the same as 6 x 15 mm MG151 with 0.056. 2 x MK108 score 0.724, 2 x MG 213/30 1.00.


Hm... I wonder if this criteria include aiming errors and differences between the guns caused by velocity of the bullets? It's quite obivious that at long range deflection shooting  it's much easier to get hits with the gun which can shoot high velocity projectiles.

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Charge on November 17, 2005, 06:08:58 AM
"Hm... I wonder if this criteria include aiming errors and differences between the guns caused by velocity of the bullets? It's quite obivious that at long range deflection shooting it's much easier to get hits with the gun which can shoot high velocity projectiles."

I think the question is more about the projectile destructiviness and how well does a light projectile retain its energy and thus how much it can cause damage after flying, say, 600 yards plus the result of the forward movement component of two a/c which is detrimental to the energy of the projectile. Then again the forward velocity component might have a very small effect as the drag builds up rather slowly after the projectile has been launched well above the speed of sound.

The German standard belting for 151/20 has 3 MG of the 5 (1AP+1HE+3MG?) and at least the AP and MGs have the same flight time to 400m which, consequently, is the standard convergence range for German a/c, IIRC that is. I'm not sure what is their drop to that range although I'll have that checked when I get back home.

HoHun, what is that score for 151/20? What is the required limit? Is it some certain amout of Joules after which the bomber is considered destroyed or what?

BTW i'm sure any modern gatling type aircraft cannon benefits of disperison as a single projectile can cripple the enemy a/c sufficiently and the RPM is what, 6000rpm? So the less RPM the gun has the more accurately it has to hit the center of the sight. (what is the dispersion caused by the sight? Which is better in this sense, fixed pipper of LCOS?)

Also with a gun with heavy drop to get a hit on enemy its not only to get a hit in long range in vertical plane but as the projectile starts to plummet downwards you have to hit it in horizontal plane, too.

Err, I mean that if you use a "friggin lazer beam" you aim only in vertical plane, where as firing a mortar you need to get a hit in both vertical, AND horizontal planes. So if you are lined just behind a bomber at long range and try to hit him with a large bore cannon you are actually trying to "drop" a huge grenade ON him. But of course your hit probabilty might as well stay the same as the probable hit area increases, too.
Am I making sense here? :confused:

More questions than answers...

-C+
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 17, 2005, 08:16:13 AM
Quote
Originally posted by Charge

I think the question is more about the projectile destructiviness and how well does a light projectile retain its energy and thus how much it can cause damage after flying, say, 600 yards plus the result of the forward movement component of two a/c which is detrimental to the energy of the projectile. Then again the forward velocity component might have a very small effect as the drag builds up rather slowly after the projectile has been launched well above the speed of sound.


The original question of this thread was about the optimal dispersion angle of the gun. It can be theoretically proved that due to aiming error some amount dispersion is an advantage but how much, is a good question.

What I can say based on my not so scientific testing is that a large gun with a low velocity projectile, low rate of fire and low dispersion is quite uneffective at long range because aiming is extremely difficult, while battery of the smaller guns with high velocity projectiles, high rate of fire and rather high dispersion (due to installation and/or dispersion of the gun itself) appear to far easier to aim and seem to give much better results at least in the realm of AH.

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 17, 2005, 09:04:08 AM
Quote
It can be theoretically proved that due to aiming error some amount dispersion is an advantage but how much, is a good question.


I understodd your contention Gripen was that guns have purpose engineered dispersion as a feature.

Mass production automatic weapons have plenty of dispersion inherently especially when combined with mass production ammunition.  

Engineers work to eliminate dispersion not add it.

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 17, 2005, 12:03:14 PM
Quote
Originally posted by Crumpp
I understodd your contention Gripen was that guns have purpose engineered dispersion as a feature.


Well, it has been pointed out that in this thread that there is gun installations with purpose built dispersion as well guns which have different barrels for different dispersion patterns.

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 17, 2005, 01:35:20 PM
Hi Charge,

>"Hm... I wonder if this criteria include aiming errors and differences between the guns caused by velocity of the bullets?

The Luftwaffe used an average hit figure of 5% as basis for that comparison.

>It's quite obivious that at long range deflection shooting it's much easier to get hits with the gun which can shoot high velocity projectiles."

As reported by the USAAF bombers, the vast majority of Luftwaffe fighter attacks came from straight 12 or 6 o'clock positions and involved little to no deflection.

As Tony pointed out, "long range deflection shooting" was not a sensible tactic in WW2.

>I think the question is more about the projectile destructiviness and how well does a light projectile retain its energy and thus how much it can cause damage after flying, say, 600 yards plus the result of the forward movement component of two a/c which is detrimental to the energy of the projectile.

The total energy of mine shells is preserved pretty well downrange because it's primarily a function of its explosive content. 12.7 mm projectiles lose energy much more quickly. If the 12.7 mm API projectile starts with a muzzle velocity of 890 m/s and is down to 650 m/s 500 m downrange, it is down to 64% of its total energy. The 30 mm mine shell stores more than 90% of its energy in its explosive, so it hardly loses destructive power going downrange.

>HoHun, what is that score for 151/20? What is the required limit? Is it some certain amout of Joules after which the bomber is considered destroyed or what?

The 4 x MG151/20 battery scores 0.262. The main criterium seems to have been mass of explosive delivered, but apparently with some modification to account for the more uniform results delivered by a higher number of smaller projectiles. (Less overkilling with smaller projectiles.)

>Also with a gun with heavy drop to get a hit on enemy its not only to get a hit in long range in vertical plane but as the projectile starts to plummet downwards you have to hit it in horizontal plane, too.

That's accounted for in my initial example on lang range shooting that assumes that the pilot does not compensate for bullet drop at all. The MK108 is a "friggin lazer beam" out to 500 m, but beyond that - no way :-)

(As far as I know, the EZ42 was the only WW2 sight to compensate for bullet drop, and it saw only very limited use.)

>But of course your hit probabilty might as well stay the same as the probable hit area increases, too.
>Am I making sense here? :confused:

Yes, you are! Interesting consideration, I hadn't thought of that before :-)

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 17, 2005, 01:44:38 PM
Hi Crumpp,

>Engineers work to eliminate dispersion not add it.

Tony has pointed out one example of the RAF intentionally enlarging the bullet pattern for air-to-air combat, but this is an isolated recommendation which seems to coincede with the time at which the RAF was desperately trying to come up with a way to deal with the Fw 190.

The other examples probably are intended for air-to-ground or ground-to-air fire.

As all contemporary documentation on air-to-air firing technique stresses accuracy and none of it recommends "walking the rudders" to increase dispersion (as suggested in WW2 manuals for ground attacks), I'm highly sceptical of the claim that dispersion is helpful.

The Luftwaffe explicitely warned against that assumption.

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 17, 2005, 02:28:15 PM
Quote
Originally posted by HoHun

The Luftwaffe used an average hit figure of 5% as basis for that comparison.


That's for unspecified range. According to LW instructions posted by you and others, the max practical range was 400m so the average might be around 200 m (about convergence range). Dispersion is actually not issue at so close range particularly in the case of the bomber size target.

Quote
Originally posted by HoHun

As reported by the USAAF bombers, the vast majority of Luftwaffe fighter attacks came from straight 12 or 6 o'clock positions and involved little to no deflection.


So even assuming convergence range and no deflection, an average pilot could hit 5%.

Quote
Originally posted by HoHun

As Tony pointed out, "long range deflection shooting" was not a sensible tactic in WW2.


Yep, but as Tony also pointed out, adding dispersion to the 20mm installations, improved results in the deflection shooting.

Quote
Originally posted by HoHun

The total energy of mine shells is preserved pretty well downrange because it's primarily a function of its explosive content.


Yep, but explosive content does not help if you can't hit, an it's obivious that aiming is much easier with high velocity gun than with low velocity gun if the target is moving.


 
Quote
Originally posted by HoHun

The MK108 is a "friggin lazer beam" out to 500 m, but beyond that - no way :-)


The idea of the "lazer beam" term is to be able to shoot with minimum deflection to the moving targets using extremely high velocity of the projectile. The MK 108 is not such weapon.
 
gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 17, 2005, 03:10:59 PM
Quote
As all contemporary documentation on air-to-air firing technique stresses accuracy and none of it recommends "walking the rudders" to increase dispersion (as suggested in WW2 manuals for ground attacks), I'm highly sceptical of the claim that dispersion is helpful.


I agree, Hohun.

I have some ballistic diagrams for the Mk 108 I could dig out and send if you would like.

In the Ta-152C motor cannon installation, it crosses the vision line at 85m and 400m with a max ord of 66cm.

A surprisingly flat shooting weapon in comparision.

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Scherf on November 17, 2005, 03:34:06 PM
Quote
Originally posted by hitech
You are totaly miss informed and full of dog dodo.

HiTech



sig material at last!
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 17, 2005, 04:27:15 PM
Hi Crumpp,

>I have some ballistic diagrams for the Mk 108 I could dig out and send if you would like.

That would be great! :-)

>A surprisingly flat shooting weapon in comparision.

You're quite right - it's often forgotten that depressing the sight line (or elevating the bore axis) will help to make the weapon hit close to the aiming point  - which is just what the shooter wants.

When aiming right at the centre of the target without considering bullet drop makes the bullet strike the target, this is considered "point blanc range" I believe. Using your Ta 152 example, the MK108 really has a point blanc range of more than 400 m, which is not what you'd expect from the comments on trajectory curvature.

The point is that trajectory curvature begins to have a serious impact only at ranges far beyond what was normal engagement range in WW2.

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 17, 2005, 06:19:26 PM
Quote
Originally posted by HoHun

You're quite right - it's often forgotten that depressing the sight line (or elevating the bore axis) will help to make the weapon hit close to the aiming point  - which is just what the shooter wants.


In the deflection shooting, the shooter does not know the aiming point, it just had to be quessed if there is no gyroscopic sight or other similar device.  

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Crumpp on November 17, 2005, 06:32:59 PM
Quote
The point is that trajectory curvature begins to have a serious impact only at ranges far beyond what was normal engagement range in WW2.


Exactly!

I will scan those documents and email them to you soon.

All the best,

Crumpp
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Charge on November 18, 2005, 04:26:24 AM
"The total energy of mine shells is preserved pretty well downrange because it's primarily a function of its explosive content."

I'd say it fully retains its energy as upon impact the velocity it hits the target has no significance at all, its the chemical energy that counts. Even the shrapnel does not get any added energy of the impact speed as its only a very thin steel core with negligible mass.

"the MK108 really has a point blanc range of more than 400 m, which is not what you'd expect from the comments on trajectory curvature."

This is really surprising. Then again the 30mm HE grenade is probably rather light, so after that distance (400m) it is probably mostly aerodynamics which causes it to slow down quite rapidly. I wonder what is the trajectory like for MK103 which probably used the same grenade?

-C+
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: hitech on November 18, 2005, 08:57:09 AM
Gripen:

When considering the probabilty of a hit one must ask a slightly different question as regards to dispersion.

What is the probabilty of a hit or kill, in a given time frame.

This case represents large dispersion.

As an extreem case of what I am talking about, Assume have one gun that fires 100 rounds a sec. And has a 1 foot dispersion at 100 yards. And each round has a hit probablity of 10%.

This case represents 0 dispersion, but aiming errors.
In the second case assume you have 100 guns each firing 1 round a sec all at exatly the same point. But with each shot all guns disperse together to exatly the same point.

And just as before they have a hit probabilty of 10%.

Now do not look at the probabilty from each bullets perspective, because those chances are the same.

But wrather look at the chances of scoring a single bullet in in 1 sec.

This is more representive of how dispersion effects fire power.

Basicly the Bigger the round, (I.E. more damge each can inflict) will lower the average time required for a kill under the first example.

In the 2nd case bigger rounds would not improve your average time required for a kill, assuming 100 rounds is enof for a kill.
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: gripen on November 18, 2005, 01:46:11 PM
Hitec,
I'm trying to modify your example to the form of two planes with different armament to make sure we talk about same issue.

Plane A has 2 guns being able to shoot 20 rounds/second/gun ie 40 rounds/s with 1 m dispersion at 100 m causing each round having hit probability 10%.

Plane B has 8 guns being able to shoot 5 rounds/s/gun ie 40 rounds/s to the exactly same point with no dispersion but aiming error causing 10% probability of the hit.

So every single round in both planes has a 10% probability of hit but in the plane A it takes in average 0,25 s to get one hit. In the case of the plane B it takes in average 2 s to get 8 hits.

If we assume that it takes 8 hits to down the target with a given round and 4 hits with bigger round. Then increasing the size of the round would improve the effectivity of the plane A reducing the average time to for a kill to 1 s. The plane B does not benefit at all from the bigger round because when it hits, it got a kill regardless the size of the round.

I think that this kind of example can be extended further but notify if I got it right.

gripen
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 18, 2005, 06:10:23 PM
Hi Charge,

>I'd say it fully retains its energy as upon impact the velocity it hits the target has no significance at all, its the chemical energy that counts.

Well, naturally the kinetic energy of the projectile is present in the explosion gases too, increasing the blast damage. However, it's about 90% chemical 10% kinetic energy at the muzzle, and the kinetic energy decreases downrange, so you got the relative significance right :-)

>>"the MK108 really has a point blanc range of more than 400 m, which is not what you'd expect from the comments on trajectory curvature."

>I wonder what is the trajectory like for MK103 which probably used the same grenade?

Point blanc range about 650 m. (The Browning M2 is close to 800 m, for comparison.)

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Tony Williams on November 18, 2005, 10:05:02 PM
Quote
Originally posted by HoHun
You're quite right - it's often forgotten that depressing the sight line (or elevating the bore axis) will help to make the weapon hit close to the aiming point  - which is just what the shooter wants.

An important issue here is the height of the sights above the gun: the greater the vertical separation, the flatter the gun seems to shoot.

This is because the projectile trajectory is curved but the sightline is laser-straight. If the sights are at the same level as the gun, then to zero-in the gun for 400m (say) means that all of the trajectory will be above the sight-line, which in a low-velocity gun like the MK 108 would mean that at 200-250m the gun would be shooting very high. When the sights are mounted significantly higher than the gun (as they are in most aircraft installations) then the first part of the trajectory is below the sight-line, which means that the gun has two 'zero points'; one when the shells cross the sight-line on the way up (perhaps at 100m or so) and one on the way down, at 400m. The highest point of the trajectory is not as high above the sight line as in the first example, so the gun appears to shoot 'flatter'.

You get a similar effect in rifles with a scope sight high above the bore, as opposed to iron sights mounted on the barrel.

Tony Williams: Military gun and ammunition website (http://www.quarry.nildram.co.uk) and discussion forum (http://forums.delphiforums.com/autogun/messages/)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Charge on November 21, 2005, 07:56:22 AM
"Well, naturally the kinetic energy of the projectile is present in the explosion gases too, increasing the blast damage. However, it's about 90% chemical 10% kinetic energy at the muzzle, and the kinetic energy decreases downrange, so you got the relative significance right :-)"

If we consider the velocity of the explosion (gases) and the momentum component of the projectile I' day the significance of the kinetic energy upon impact is very very small, so I'd say, without calculations, that 10% is very much exaggarated. I'd be surprised if it is even as much as 1% of the full energy of the blast on target.

;)

-C+
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 21, 2005, 01:41:36 PM
Hi Charge,

>I'd be surprised if it is even as much as 1% of the full energy of the blast on target.

Time to be suprised then ;-)

MK108 330 g mine shell @ 505 m/s:

Kinetic Energy: 42.1 kJ
Chemical Energy: 461 kJ

Regards,

Henning (HoHun)
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Charge on November 22, 2005, 03:40:42 AM
Thx HoHun.

But my point is, what does that kinetic part consist of? If half of it consists of the weight of the chemical part so upon explosion that part of mass is actually reduced of the damage as it is transformed into chemical energy? OR That mass is added to the forward velocity component of the explosion and the other half is reduced as it works against the explosive force, so what remains?

Can you just add the kinetic energy to chemical energy like that?

That is the energy at muzzle?

-C+

:confused:
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: Charge on November 22, 2005, 05:44:41 AM
Then again, the energy does not disappear... ;)

-C+
Title: Dispersion Angle for rapid fire WW2 aircraft guns
Post by: HoHun on November 22, 2005, 01:41:45 PM
Hi Charge,

>That mass is added to the forward velocity component of the explosion and the other half is reduced as it works against the explosive force, so what remains?

It's tricky to visualize, so here is a simplified example: Let's assume we have not an explosion, but rather a recoilless rifle firing a slug of equal weight out of both ends of the barrel.

Let's say it fires 200 g each way at 500 m/s, so we get Ekin0 = 2 * 1/2 * 0.2 kg * (500 m/s)^2 = 50 kJ.

As the kinetic energy of both projectiles was zero before we exploded fired the rifle, these 50 kJ obviously were stored in the driving charge as chemical energy (Ekin0 = Echemical).

Now fire the entire recoilless contraption as a single projectile. Let's assume we fire it at 200 m/s. Barrel mass and explosive are assumed to be 0 kg.

We get a kinetic energy of Ekin = 1/2 * 0.4 kg * (100 m/s)^2 = 2 kJ.

On firing the rifle, both projectiles now travel at different speeds:

Foward fired projectile: EkinForward = 1/2 * 0.2 kg * (500 m/s + 100 m/s)^2 = 36 kJ

Rearward fired projectile: EkinRearward = 1/2 * 0.2 kg * (500 m/s - 100 m/s)^2 = 16 kJ

So the balance:

Echemical + Ekin = EkinForward + EkinRearward

or 50 kJ + 2 kJ = 36 kJ + 16 kJ

In short: The forward-fired projectile gains more destructive energy than the rearward-fired projectile loses.

You could run a similar sum for all molecules of the blast cloud of a mine shell, and would of course find a perfect analogy there. The forward traveling front of the blast wave would gain more destructiveness than the rearward traveling front would lose.

Regards,

Henning (HoHun)