About WW2 fighter aircraft firing power

[Harri Pihl]

Originally Posted by Tony Williams

To be precise, the M2 was a moderately high-velocity gun (the muzzle velocity was little more than the 20mm Hispano's) and they rejected an extremely high-velocity one (the T17 - the MG 151 copy - was chambered for the US 15.2x115 round, far more powerful than the MG 151's 15x96).

The point is that USAF did not go towards lower velocity weapons like the Germans; possible replacements of the M2 had about same or higher muzzle velocity.

Originally Posted by Tony Williams

I suspect that there were two reasons why the US stayed with the .50: it was the only reliable aircraft gun they had, and it proved adequate as long as they fitted at least six of them. That is not exactly a ringing endorsement.

My impression is that good combat results were the main reason why USAF (and NAVY) continued with the M2 despite obvious benefits of the possible replacements. Note that at spring 1944 the P-51B, with only four M2s, proved to be extremely succesfull despite the problems with gun feed etc. some pilots prefered it over the P-51D.

Originally Posted by Tony Williams

The following extract from a 1944 US evaluation may be of interest:

"As it is now, we have the 50-cal. gun which has reached its peak. The only improvements will be minor. The only good increase is to increase the number of guns. So it seems to be just about the right time to look for a better weapon. There are two possibilities here - the one we have and the one we might get shortly. The one we have is a 20-mm gun. I think very highly of it. In fact, it is one we have here, and it is one in hand. It won't do what the 60 will do, but we haven't got the 60, and we won't have it for a year. So, we are gradually working into all of our aircraft the 20-mm gun. To give you some idea of the 50 versus the 20 and dispel a lot of ideas that have bothered us, I would like to give you a comparison. When somebody goes from four 50's to two 20's, to the layman that means a decrease in fire power. Actually, quite the reverse is true. In the horsepower of the gun, one 20 is equal to three .50-calibers. In the actual rate of fire delivered at the target, one 20 equals three 50's; in kinetic energy at 500 yards, one 20 equals two and one half 50's.[N.B. This takes no account of the effect of the HE content of the 20mm shells]

That adds up to four 20's equaling twelve 50 calibers, judging by those standards. Of course you have other advantages of the 20. You have the much greater penetration of armor. The 20 will go through 3/4 inch of armor at 500 yards, while the .50 cal, will go through only .43. In addition to that you have one more great advantage - that is you can have longer and more frequent bursts without damage to the gun with the 20 than you can have from the .50 cal. That is important for the strafing airplane, because they are burning up their barrels and ruining their guns on one flight. Sometimes it is long before that one flight is over. They will come down with screaming barrels and get trigger happy, and then all the barrels are gone in one flight. It should not happen in a 20mm. Of course, you have disadvantages. You have a heavier installation, one-half as much ammunition for the same weight. Our standard ammunition in the Navy is 400 rounds in one gun. The Fleet has set up 30 seconds of fire as a minimum requirement for the .50 cal gun. We can't do that with the 20, so we give them 200 rounds. The 20 is lethal enough to get far more results out of that 200 rounds than the .50 ever will out of 400 rounds."

From: "USN Report of Joint Fighter Conference NAS Patuxent River". (October 1944)

From hindsight we know that the 50-cal gun had not reached it's peak 1944; M3 entered service next year and offered about 50% increase in fire power. Infact there was allready a 1100rpm version of the original M2, twice the rate of the original MG53-2, in production three years before US entered war as you probably know. The design had some potential left, USAF was just slow to utilize it.

However, as noted above, I agree that the cannons had great advantages over the M2 but it's not the point of this discussion.

[Harri Pihl]

Originally Posted by Rob Philips

Does any of the forum visitors have any of the documents mentioned by Harri available, as that would be the fast way to obtain the information?

I have some pages which looked interesting photographed, not entire docs. I'll PM some samples sooner or later. As an example I can list some Radial sighting errors in dead astern attack. Source first, gun sight type, radial error in Mills:

WWII (RAF gun camera, flying bombs), fixed, 4.4-5.5
Squadron training exercise, fixed, 5.7
A&AEE trial with average pilots, gyro, 9.12
Fighter Command Trial with experienced pilots, fixed, 2.2
A&AEE trial with experienced pilot, gyro, 1.6

As you can see, there is quite a variation depending on pilot.

[Juha]

Rob
There at least has been Des Jägers Schiessfibel somewhere in net: It’s an official LW guide for aerial gunnery from 1944.

And in Fighting in the Air. The official combat technique instructions for British fighter pilots, 1916-1945. ISBN 0 85368 3921 there are:
some 90 pages long Notes on Air Gunnery and Air Fighting by WinCo E. M. Donaldson from 1943
some 20 pages long Bag the Hun! (estimation of range & angle off) from 1943.

Juha

[Rob Philips]

Thanks, Juha, first class. What I'm after is more likely in research notes than in pilot's instructions, but we'll know that once these works have been studied. Shall try to get them.

Regards,

Rob

[Rob Philips]

Have found in the web "Horrido! - Des Jägers Schiessfibel", ed. June 1944, German doc D. (Luft) 5001, approved by A. Galland.

The title translates as "The hunters shooting manual". "Horrido!" is a German hunters expression when greeting the other, or when calling all present to attention. This 36 page brochure is written in a P/O. Percy style used by the RAF, designed to explain complicated matters in the easiest possible way to many, using cartoons to make certain points stick. The matter has even been translated into a deck of cards, with which the basics are explained in an easy way, and with which you can gain money too! Call the General der Jagdflieger (Galland) to get the cards...

Hit probability is explained almost entirely as a function of pilot skills, so there is little answer here to the question I raised. However, the following remarks are noteworthy:

1. Page 7, shooting distance. It is explained that at a range of 600 meters perhaps one hit is scored. This changes to 4 hits at 300m, 9 at 200m, and 36 at 100m. This increase is not proportional but exponential, leading to only one conclusion: "Also ran!", meaning "go close!".
Obviously pattern density has been considered to come to this statement.

2. Page 14 shows drawings, that suggest that the pattern size was small for the Me.109, the main German fighter aircraft. There are no explanations or technical details given, but I assume that this is the results of the limited number of guns, their grouping close together, and the firing rate of the average model of Me.109. From this it follows that aiming has to be good; letting the attacked aircraft fly into the pattern is bound to fail. Trusting barrel wear and poor harmonisation to produce a wider, and more effective, pattern, is a bad idea. The pattern will be wider, but pattern density shall be reduced, leading to less effectiveness. For the same reason the following two advises are given:

A. Harmonisation should be as prescribed, and be checked on a regular basis. Tracer ammo can be used to check in flight, as opposed to on the firing range at base.

B. Harmonisation experiments are discouraged. Harmonizing the guns to longer ranges is called counterproductive. Reasons are not clearly stated; reference is made to results of the research work done by the specialists.

The ins and outs of the use of tracer ammo are mentioned too. Tony Williams mentioned that Allied pilots had objections against the use of tracer, as it would give away to the enemy that shots were being fired. In this German document the matter is seen in a different light:

A. Most aerial combat firing was done, not with too much, but with too little deflection. From that we can deduce that chances are much smaller that the attack is reported by tracer to the target pilot. In any case, the German document does not report this.

B. At longer ranges, tracer appears to represent curved projectile trajectories, that can be confusing. These curves do not result from projectile flight, but from the aircraft flying curves whilst firing bursts. Each projectile flies in a basically straight line, but the sum of these lines produced by firing in a curve is seen as a curve. It is advised to use the additional info given by tracer only on short ranges - both eyes open.


Therefore, hit probability is explained in this work mainly as a function of pilot skills, with reference to the armament characteristics of Germany's main fighter aircraft. Nevertheless, it offers some useful points when looking for ways that would increase hit probability, ways that would not be dependent on pilots skills.

"Fighting in the Air. The official combat technique instructions for British fighter pilots, 1916-1945" cannot be downloaded from the web. Shall order it.

Rob

[Rob Philips]

Have made an application in Excel, that calculates and graphically shows pattern density and size, as a function of
- number of guns
- their firing rates
- the distances between the guns
- the harmonisation type
- the harmonisation distance
- the distance to target
Leading to pattern densities and sizes per second of firing.

This is to be expanded with more harmonisation strategies, and all other parameters that are not related to pilot skill. This should enable to play with parameters, and see what comes up best under selected conditions. The ambition is to include ammo effectiveness parameters after that. Results, if any, shall be shared here. Right now I'm struggling with a silly "division by zero" error...

It strikes me that "harmonisation" (-zation?) is a subject that can do with some more thoughts. It is usually understood as meaning trajectories from multiple guns converging at a set point in space. We have already learnt that harmonisation to two or more points has been done. To this I shall add harmonisation to infinity, and negative harmonisation, meaning diverging trajectories. Furthermore, it seems that harmonisation is usually considered in a single surface, parallel to the trajectories of guns that are basically located in one plane (meaning surface here, not aircraft). It seems that this x-distance notion of harmonisation leaves out an y-spread notion that is important too. This already gives one preliminary conclusion: more guns enable better harmonisation in the y-axis than fewer guns can do. Shall explain with drawings later.

Rob

[Stewart]

You have posted an interesting article. There are how ever some glairing mistakes.

Sycronisation was the act of fixing the weapon to fire in between the spinning propellor blades with out hitting them. The term that you need is "Harmonisation" or Zeroing. This is probably the single largest factor in dertemining the effectiveness of any planes weapons system.

Many pilots tried many systems for this and three general trends emerged based on the type of fit in the plane.

1. Widely spaced wing guns, like in the early model Spitfires were the worst possable solution to the problem. This lead to pointing all of the guns at either one point in space ahead of the fighter at some range that coincided with the phylosiphy in force. This varied between 200-250 Yards, with some very few exceptions as close as 150 or as far as 400 Yards. This was not very successfull because at other ranges, even perfectly aimed shots would, because of the range they were "Hamonised" at be absolutely guaranteed to miss at other ranges!

This lead to the idea of pointing each of the four pairs of guns at a slightly different range, so that at least some of the bullets would hit if the piper covered the target. This was also a failure because it did not consentrate the fire enough, to cause significant damage durring the very short time that the target was passing threw the leathal point of aim.

The other type of wing mounted gun system was to cluster all of the guns in each wing into a small group and then point the entire group at the Harmonisation range. This was done in the Hurricane and all most all American Fighters. This was universaly aknowledged to be the far supirior solution for wing mounter guns. But this suffered from the same faults as the Spit's fit above, but to a lessor but still unsatisfactory degree.

The Russians, American P-38/39 and to a very much larger degree the Germans TENDED to mount all the guns in or very close to the nose, which tended to put ALL the bullets/shells into the same stream regardless of range. This was found to be many times more effective than any type of wing mounted guns, with planes like the P-38s, later Me-109s and the D model 190 found to be particularly devistating in this regard.

The second factor of grate import was the single gun's dispersion and this had two causes;
1. The basic design of the weapon, recoild opperated guns have more dispersion than gas opperated guns.
2. The strength of the mounting system in wing guns. Some planes had very flimsy structures like the Spitfire which caused very large dispersions beyond what is normal for the gun. IE, 100-110Cm at 100 yards, Vs 50-60Cm at 600 yards in other planes with stronger wings like the P-47 and -51.

3. This was much less of a problem for planes with the guns mounted in clusters or attached to very solid parts of the basic structure like wing roots or engine mounts.

Then there is rate of fire. Because of the inhearant difficulty in pointing the figher plane at any target, even those stationary on the ground or flying in formation WO maneuvering, the rate of fire must be as high as possable. Given a projectile of certain minimum energy dencity required to provide a minimum level of damage to the average un-armored target plane, it matters very little wether it is .30 or .50 caliber. Having said that, balistics comes into play, where the typicle ~.30 caliber slug has that much energy at 300-400 Meters and the typicle .50 caliber will do more damage at 2000M. Cannon shells will meet that minimum level of damage at any range at which they will still reliably detonate. So regardless of caliber, IF the range is short enough, the more bullets the better.

To find out the effective relationship between any two weapons systems, simply square the ratio between their rates of fire. IE, a plane that fires twice as many bullets as another will be four times as effective, ALL OTHER THINGS BEING EQUIL!

That brings up the issue of armor plating protecting vital parts of the plane. This rases the damage level high enough that ~.30 caliber weapons are no longer effective. Armor also greatly reduces the effect of cannon shells which explode on or just after perforating the air craft's skin and fail to damage vital items protected by even the thinest armor. Again having said all that, there was no armor fitted to any plane which could provide protection from .50 caliber fire at common combat ranges!

Lastly, In some of your formula, you mentioned that energy was the product of velocity and weight, or mass of the projectile. This is not strictly true. Energy is the product of 1/2 of the mass and the velocity squared! This is vitaly import because velocity has two extreamly important effects on weapon effectiveness!

1. First is the stated effect on the energy available to damage the target plane.

2. Vastly more important is velocity's effect on the shooter's ability to hit the target!
The higher the MV the easier it is to hit a moving target!

Studies AND extencive testing back in the ~70s by the USAF concluded that the combination of MV and BC was so important that they spent dozzens of millions of dollars developing EACH of half a dozzen different gun weapon systems! 25MM Caseless, 25MM telescoped cased, 25MM liquide propellant, 20MM super velocity ammo for the standar Vulcan gun, which lead to the long barreled gun in the F/A-22 and both of the Mauser BK-27 and ADEN-25 guns when that data was shaired with our friends!

There are other factors, which have been found to be of marginal importance to modern gunnery, but they are not really realivant to WW-II because they are so far over shadowed by other factors.

Hope this helps. Sincerely, Stewart.

[Stewart]

The reason that small increses in MV/BC are so much more effective is not because of the differances between target and projectile velocities as you surmise, but because you required less lead on a target apearantly moving accross the line of fire.

The USAF made many studdies and determined that the third power of the differance between any two MVs would show the differance in probability to hit. In WW-II the Germans determined that the square of the differances in MV was equal to the differance in hit probability. The Ruskis came to much the same conclusions, but then determined that weight of shell Vs the heavy American Bombers was more inportant as they were very easy to hit. later guns had much higher MV/BCs!

[Stewart]

The example is the Hispano Suiza 20mm cannon, widely used in fighter aircraft in WW2. The cartridge is 110mm long, rimless. A HE (High Explosive) projectile weighs 130 grams, and carries 6 grams of TNT. A solid non-explosive projectile weighs 150 grams. Both are fired at a muzzle velocity of 850 m/s.( Should be 840M/S!) TNT has a detonation speed of 7.000 m/s.

Kinetic energy (Joules) = 0,5 x projectile weight (kg) x the square of the muzzle velocity (m/s)

The muzzle energy of the non-explosive round is calculated as follows:
0,5 x 0,150 x 850 x 850 = 54.188 Joules, or 54 kiloJoulesShould be = 52.92Kj.

The muzzle energy of an exploding round is calculated as follows:
0,5 x 0,124 x 7.000 x 7.000 = 3.038 kJ Should be = 840X840X130/2000 = 45.864Kj. Then the explosive content should be found by multipliing the energy yeald per gram, times the number of grams. The yeald of Grade one TNT is 4,185J/Gram or 25.11Kj for a total of 70.974 Kj or on the surface appierance 34.1% increase in energy effectivness! But this is false. The solid AP projectiles will drill right threw the target plane and unless it hits some very strong massive part will waist most of their energy on the air on the far side of the target.

This is important now, but not back in WW-II because the planes of that time had numerious single point failures which would down the plane and were vulnerable to plain bullets. Then the effect of bursting munitions is widely over stated as it relates to WW-II planes!

To this should be added the kinetic energy of the round directly prior to explosion:
0,5 x 0,130 x 850 x 850 = 47 kJ
Total = 3.085 kJ

Meaning that the explosive round has 3.085/54 = 57 times the energy of the non-explosive round.Massive failure of the math proccesses!

[Stewart]

However, with automatic guns, such as aircraft cannons, a round fired earlier, ie. in case of higher cyclic rate during a given time frame will reach the target earlier, than in a case of a higher velocity round fired at a slower cyclic rate. For practical applications, careful aiming and application of proper lead is less attractive than just let the target 'walked into' a sufficiently dense line of firepower applied - ie. point and shoot. Its a fail-proof method. No, it is not! actively "Dragging" the bullet stream accross the target is much better than waiting for the target to fly threw. The neccessary ingreadient is that the shorter the ToF, the more likely you are to be able to score hits!

There is a reason for using shotguns for hunting small game and birds with a high number of slow pellets instead of .223 bolt action rifles with 1200-1300 m/sec. This argument is faseeshious on it's face! There are numerious reasons why it is not true!