Dispersion Angle for rapid fire WW2 aircraft guns

[Crumpp]

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

[beet1e]

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°.

[gripen]

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.

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.

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.

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.

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

[HoHun]

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)

[Tony Williams]

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 and discussion forum

[Crumpp]

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:

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

[Crumpp]

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

[Squire]

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.

[HoHun]

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)

[gripen]

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.

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.

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.

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.

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

[beet1e]

Squire - good post - thanks for posting. I have a few comments to make.

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.

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.

[Crumpp]

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.  

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

[gripen]

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.

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.

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.

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

[Kurfürst]

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.

[gripen]

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