Modelling the effects of gun-recoil

[Thunderbolt56]

I've been doing a good bit of reading lately (always do right after Christmas as my family finally listens and gets me some of the selected reading material on my "list") and in reading 2 of Eric Hammel's books Aces Against Germany and Aces Against Japan, I've realized that recoil from firing all your guns at once was a real concern for many (especially in low-speed combat on the deck) because the recoil was so pronounced that it could actually contribute to a severe stall.

One pilot of a P-51 stated that firing all 6 guns was the equivalent of reducing horsepower by 400!

This brings me to a somewhat rhetorical question with 2 parts;

A. To what extent is this phenomenon modelled in IL2?

and

B. How well do you think it will be modelled in newer-gen sims like SoW and RoF?


I realize any answers to these questions will be speculative as the ones equipped to answer them accurately likely won't/can't respond. Nonetheless, I'm interested to find out.

TB

[Igo kyu]

Originally Posted by Thunderbolt56

A. To what extent is this phenomenon modelled in IL2?

Somewhat, maybe not that much, but I remember firing in a I16/24 with one of the SHVAK disabled by enemy fire, and it did tend to turn you toward the firing gun, which made achieving hits much more difficult. That was a while ago, maybe in the original FB, I couldn't swear it still happens now, but it could be that it does, I don't remember having a wing cannon disabled recently.

B. How well do you think it will be modelled in newer-gen sims like SoW and RoF?

That is entirely up to the developer. All other things being equal, which they never are, I'd prefer it was, but I don't know what I'd be prepared to give up in order to have it.

[robtek]

Recoil is modelled in il2, a standing 110 rolls backward when you fire the guns.

[choctaw111]

Gun recoil is modeled in Il2. As already stated, if you loose one wing cannon, your aircraft will slip to that side when firing.
Another and even better test is to land your plane, shut down the engine, and fire your guns. You will start to roll backwards. Of course this is more pronounced on the larger guns.
I would think that any and all effects present in Il2 (and many new ones) will be improved and implemented in SoW.

Edit...Sorry robtek. I see you already mentioned this.

[Thunderbolt56]

I realize it's modelled in IL2, but is it even close to the equivalent of reducing the effective horsepower on a P-51 by 25%? My experiences are that it's more of a shooting issue than an actual FM issue, even at low altitudes in a stall fight. I've lost a cannon or even a bank of guns on one side and had the resultant yaw skew my marksmanship enough to realize there is something there but firing my guns (even a pair of MK108's) in a low scissor doesn't seem to affect my forward momentum or contribute to one of my wings dropping off from lack of lift.

[BadAim]

As pure speculation, I doubt that the actual recoil of even 6 .50 cals is that great. I'm sure it is significant but compared to the inertia of a several thousand pound aircraft, I'd estimate the effects to be on the more conservative side. IMHO I'd say IL2 has got it pretty close.

That said I would be interested in some more scientific calculations. I'm definitely not the man for that job.

[II./JG1_Krupinski]

~SALUT~ Thunderbolt!

This is a rather interesting thread! I prompted me to do a little technical research on the 50 cal. Have to say it been fascinating!

While it wasn't my intention, I found some details that makes me wonder how the author came up with 400 hp reduction because of recoil.

If we consider a 50 cal bullet, 800 gr / 52 g with a muzzle velocity of say, 2895 ft/s or 882 m/s, this would result in 15000 ft-lbf or 20,000 J of energy stored in that bullet (E=1/2 MV^2).

Since Sir Isaac Newton states that for every action there is an equal and opposite reaction, this energy has also been exerted to the recoil system, the slides and ultimately the plane.

Since horsepower is a unit of work over time, we need to depress that trigger for a specified amount of time so we can compare energy (Joules) to Power (Horsepower/JoulesPerSecond)

So if we fire 1 gun for 1 second that equates to about 27 horsepower exerted on the recoil system. If the recoil system of the gun was fixed no moving parts, and strong enough to not break - then all that energy / work would be transferred to the plane - thus slowing it down. But, the recoil system of the gun takes that energy and converts it to heat and uses some of the power to reload the gun. So, it's safe to assume not all 27 HP is transferred to the plane, slowing it down. But of course, some amount is actually slowing it down.

Multiplying 27 HP for one gun by a total of 6 guns we'd get 162 HP. Now, I thought this couldn't be right but when I thought about it, it really makes sense.

If 6 guns did in fact exert 400 HP of power on a P51, then a single gun would be exerting 66 HP. We as humans, would not be able to fire a BMG. 66 HP is the equivalent lifting 36000 pounds, one foot in one second.

So I wonder want additional factors the author is considering? maybe additional forces created by drag induced from maybe the guns causing the plane to slip?


*** EDIT ***

This may come in use when comparing aircraft. This is how we can compare the weight of force between plane X and plane Y. Of course, it doesn't take into account the explosive power of exploding cannon rounds. But WoF, is a key element in determining a plane match up.

Best regards,

Raven

[JG27CaptStubing]

Some interesting reading....


WORLD WAR 2 FIGHTER GUN EFFECTIVENESSWORLD WAR 2 FIGHTER ARMAMENT EFFECTIVENESS

© Anthony G Williams & Emmanuel Gustin (with acknowledgements to Henning Ruch)
Revised 28 June 2004
The comparative effectiveness of fighter guns in the Second World War is a
subject of perennial fascination (and a great deal of argument) among technical
military historians. This is an attempt to take a fresh and objective look at
the evidence in order to draw up comparative tables of cartridge
destructiveness, gun power and gun efficiency. The effectiveness of typical day
fighter armament fits is also considered.
CARTRIDGE DESTRUCTIVENESS
There are two types of energy that may be transmitted to the target; kinetic and
chemical. The kinetic energy is a function of the projectile weight and the
velocity with which it hits the target. This velocity in turn depends on three
factors: The muzzle velocity, the ballistic properties of the projectile, and
the distance to the target. There are therefore two fixed elements in
calculating the destructiveness of a projectile, its weight and chemical (high
explosive or incendiary) content, and one variable element, its velocity. The
key issue is the relationship between these three factors.
A high muzzle velocity will provide a short flight time, which is advantageous
in increasing the hit probability and extending the effective range, and will
also improve the penetration of AP rounds. However, it might not add much to
destructiveness, as unless an AP projectile hits armour plate (and not much of
the volume of an aircraft was protected by this), a higher velocity just ensures
that a neater hole is punched through the aircraft; the extra kinetic energy is
wasted. Also, if the projectile is primarily relying on HE blast or incendiary
effect, the velocity with which it strikes the target is almost immaterial.
Provided that it hits with sufficient force to penetrate the skin and activate
the fuze, the damage inflicted will remain constant. In contrast, AP projectiles
lose effectiveness with increasing distance.
It is sometimes argued that a projectile with a high muzzle velocity and a good
ballistic shape (which reduces the rate at which the initial velocity is lost)
provides a longer effective range. To some extent this is true, but the greatest
limitation on range in air fighting in the Second World War was the difficulty
in shooting accurately. The problem of hitting a target moving in three
dimensions from another also moving in three dimensions (and probably at a
different speed and on a different heading) requires a complex calculation of
range, heading and relative speed, while bearing in mind the flight time and
trajectory of the projectiles. Today, such a problem can easily be solved by a
ballistic computer linked to a radar or laser rangefinder, but at the time we
are examining, the "radar" was the human eyeball and the "ballistic computer"
the human brain. The range, heading and speed judgements made by the great
majority of pilots were notoriously poor, even in training. And this was without
considering the effects of air turbulence, G-forces when manoeuvring, and the
stress of combat. These factors limited the effective shooting range to around
400 m against bombers (longer in a frontal attack) and against fighters more
like 250 m.
For all of these reasons muzzle energy (one half of the projectile weight
multiplied by the square of the velocity) has not been used to calculate kinetic
damage as this would overstate the importance of velocity. Instead, momentum
(projectile weight multiplied by muzzle velocity) was used as an estimate of the
kinetic damage inflicted by the projectile. It might be argued that even this
overstates the importance of velocity in the case of HE shells, as noted above,
but the effect of velocity in improving hit probability is one measure of
effectiveness which needs acknowledging, so it is given equal weighting with
projectile weight.
Chemical energy is generated by the high explosive or incendiary material
carried by most WW2 air-fighting projectiles. First, there is the difference
between HE and incendiary material, which were often mixed (in very varying
proportions) in the same shell. HE delivers instant destruction by blast effect
(plus possibly setting light to inflammable material within its blast radius),
incendiaries burn on their passage through the target, setting light to anything
inflammable they meet on the way. The relationship between the effectiveness of
HE and incendiary material is difficult to assess. Bearing in mind that fire was
the big plane-killer, there appears to be no reason to rate HE as more
important, so they have been treated as equal.
The comparison between kinetic and chemical energy is the most difficult and
complicated subject to tackle. This complexity is revealed by the example of a
strike by a delay-fuzed HEI cannon projectile. This will first inflict kinetic
damage on the target as it penetrates the structure. Then it will inflict
chemical (blast) damage as the HE detonates. Thirdly, the shell fragments sent
flying by the explosion will inflict further kinetic damage (a thin-walled shell
will distribute lots of small fragments, a thick-walled shell fewer but larger
chunks), and finally the incendiary material distributed by the explosion may
cause further chemical (fire) damage.
There will therefore always be a degree of arbitrariness in any attempt to
compare kinetic and chemical energy, as it all depends on exactly where the
projectile strikes, the detail design of the projectile and its fuze, and on the
type of aircraft being attacked. To allow a simple comparison, we will reduce
all these factors to an increase in effectiveness directly proportional to the
chemical content of the projectile. We assign to projectiles that rely
exclusively on kinetic energy an effectiveness factor of 100%. For projectiles
with a chemical content, we increase this by the weight fraction of explosive or
incendiary material, times ten. This chosen ratio is based on a study of many
practical examples of gun and ammunition testing, and we will see below that it
at least approximately corresponds with the known results of ammunition testing.

To illustrate how this works: a typical cannon shell consists of 10% HE or
incendiary material by weight. Multiplying this by ten gives a chemical
contribution of 100%, adding the kinetic contribution of 100% gives a total of
200%. In other words, an HE/I shell of a given weight that contains 10%
chemicals will generate twice the destructiveness of a plain steel shot of the
same weight and velocity. If the shell is a high-capacity one with 20% chemical
content, it will be three times as destructive. If it only has 5% content, the
sum will be 150%, so it will be 50% more destructive, and so on.
The following table for the most common cartridges and loadings used in aircraft
guns shows the consequences of these assumptions and calculations. The first few
columns should be self-explanatory, as these are basic statistics about the
ammunition. HE(M) means Minengeschoss, or high-capacity mine shell. The 'DAMAGE'
column shows the results of the calculations described above. To run through an
example, let us look at the case of the 7.7x56R (.303") incendiary. The
projectile (a "De Wilde") weighs 9.8 g, (which equals 0.0098 kg) and was fired
at 747 m/s. Multiplying these gives 747 x 0.0098 = 7.3206, so you have a
momentum factor of 7.32. As the bullet contains 5% by weight of incendiary
material, the momentum is multiplied by 1.5 to give a destructive power score of
10.98 - rounded to 11.
The last column - 'POWER' - takes into account that different types of
ammunition, with different destructiveness scores, were commonly loaded into an
ammunition belt or magazine. Many cannon shells were also available with
tracers, which reduced the weight of HEI mix. This column therefore shows an
average score for the different types to give an overall destructiveness
assessment for that calibre. For convenience, the result is divided by ten and
rounded to the nearest whole number (except for HMGs), which helpfully leaves
the least powerful cartridges, the rifle calibre rounds, scoring 1.
TABLE 1: CARTRIDGE DESTRUCTIVENESS
CARTRIDGE TYPEROUND WEIGHTMV M/SECPROJECTILE WEIGHT GM% HEI
CONTENTDAMAGEPOWER
7.7x56RAP / I24762 / 74711.3 / 9.8- / 58.6 / 111
7.92x57AP-v2486511.5-10 1
13x64BAP / HE76 / 72710 / 75038.5 / 34- / 3.527 / 343.2
12.7x81SRAP / HE82760 / 77035.4 / 33- / 2.227 / 313
12.7x99API112890432464.6
12.7x108API125840484.2575.7
15x96AP / HE166 / 151850 / 96072 / 57- / 4.961 / 827.8
20x72RBHE200600128612312
20x80RBAPI / HEIT / HE(M)182 / 162585 / 585 / 700117 / 115 /
923.1 / 3.2 / 2290 / 89 / 20614
20x82API / HET / HE(M)205 / 183720 / 720 / 800117 / 115 /
923.1 / 3.2 / 22110 / 109 / 23616
20x94 AP / HE250 / 213700 / 730112 / 79- / 1278 / 12711
20x99RAPI / HEI183750 / 79096 / 952 / 686 / 12011
20x101RBHE222750128615415
20x110RBHE240830122818218
20x110HE (Mk II / Mk V)257860 / 8301308201 / 19420
20x125HE290820127717718
23x152BAPI / HE467880 / 880200 / 2003 / 7228 / 30026
30x90RBHE (M) 4805053302558058
30x184BHE (M)7808603302599099
37x145RHE9006106087.464564
37x195HE157090073561060106
40mm CLHE5872465858.726927


Comments on Table 1
Clearly, the resulting scores can only be approximate, and in particular will
vary depending on the particular mix of types included in an ammunition belt.
The power calculation takes a typical mix of ammunition, where known. They also
take no account of the fact that some incendiary mixtures, and some types of HE,
were more effective than others were. However, they do provide a reasonable
basis for comparison. There is no point in trying to be too precise, as the
random factors involved in the destructive effects were considerable.
If we compare the values with the few data known from ballistic tests, we have
some indications that the factors assumed in the calculations are realistic. The
20x80RB M-Geschoss and the 20x110 (Hispano) HE were rated as about equal; the
greater blast effect of the M-Geschoss was countered by the greater penetration
and kinetic damage inflicted by the Hispano. They do indeed emerge with similar
scores. Also, the Luftwaffe reckoned that it took about four or five times as
many 20 mm shells to destroy a heavy bomber as it did 30 mm rounds. The power
relationship here is 3.6 times for the MK 108 and 6.2 times for the MK 103,
which neatly brackets this observation.
Cartridge illustrations
These photos illustrate the different cartridges listed above (with the
exception of the 40mm CL). The first PHOTO includes rounds from 7.7x56R to
20x101RB; the second PHOTO starts with the 20x101RB and finishes with the
37x195.
GUN POWER AND EFFICIENCY
The cartridge destructiveness table above only shows the relative effect of one
hit. When comparing the guns that fired the cartridges, other factors come into
play, namely the rate of fire (RoF) and the gun weight.
To calculate the destructive power of the gun, the 'POWER' factor from the above
table has been multiplied by the RoF, expressed in the number of rounds fired
per second. This gives the relative 'GUN POWER' figures in the table below. It
is important to note that all of the RoF figures are for unsynchronised guns;
the exception is the 12.7 mm UB (Soviet Berezin) where the lower RoF figure is
for a synchronised gun (which it commonly was in fighters), the higher for
unsynchronised. The effects of synchronisation on other guns varied
considerably; for German weapons, which used an efficient electrical system, the
reduction in RoF was around 10%. For other systems it typically varied between
20 and 40%.
To judge how efficient the gun was, the 'GUN POWER' result is divided by the
weight of the gun in kilograms to provide the 'GUN EFFICIENCY' score in the last
column. This is, in effect, a measure of the power-to-weight ratio of the gun
and ammunition combination.
TABLE 2: GUN POWER AND EFFICIENCY
GUNCARTRIDGERoF RPSCARTRIDGE POWERGUN POWERGUN WEIGHT KGGUN EFFICIENCY
Browning .3037.7x56R20120102.1
MG 177.92x5720120121.75
MG 13113x64B153.248172.82
Breda-SAFAT12.7x81SR12336291.24
12.7mm Scotti12.7x81SR12336221.64
Ho-10312.7x81SR15345231.96
.50 Browning M212.7x99134.660292.1
12.7mm UB12.7x10813 - 17674 - 97253 - 3.9
MG 15115x96127.894422.2
20mm Type 99-120x72RB812108244.5
MG-FF20x80RB814126284.5
MG 151/2020x821216192424.6
20mm Ho-520x941410154374.2
20mm ShVAK20x99R1311143423.4
Berezin B-2020x99R1311143255.7
20mm Type 99-220x101RB815120353.4
HS.7 and 920x110RB6.518117482.4
Hispano II20x1101020200504
Hispano V20x11012.520250426
Ho-1 / Ho-220x125718126452.8
VYa-2323x152B926234683.4
MK 10830x90RB1058580609.7
MK 10330x184B7996931414.9
37mm M437x145R2.564160961.7
NS-3737x19541064241702.5
Ho-30140mm CL7.5272021321.5


Comments on Table 2
Two factors not included are gun reliability and total ammunition weight. The
former is simply not available in most cases. The latter involves too many
variables. First, the ammunition supply for most guns varied according to the
installation. Furthermore, in searching for comparators, there would be the
problem of which measures to take: the weight of the number of rounds fired per
second, or the weight of the number required to inflict a certain amount of
damage? There would be a case for either of these, but they would produce very
different results. This issue is however addressed in the next table.
The lower rate of fire of many of the larger guns tends to reduce their power
advantage over the smaller calibres. However, in power-to-weight ratio, larger
guns are generally better performers (the slow-firing American 37 mm M4 and
low-velocity IJA Ho-301 excepted).
Most of the Soviet guns show up as being remarkably efficient, with scores of
around 4, but the Hispano and the MG 151/20 also show up well, as do the simple
MG-FF and Japanese Type 99 API blowbacks because of their light weight.
The American Browning .50 M2 is an undistinguished performer, particularly when
compared with its closest competitor, the 12.7 mm Berezin. The relatively small
incendiary content in the .50 API (0.9 g instead of 2 g) gives the Soviet round
a flying start, which it adds to by its usefully higher rate of fire, then
finishes off in style by being lighter as well, and thereby almost twice as
efficient overall. The Browning also makes an interesting comparison with the
Japanese Ho-5, which was basically the M2 slightly scaled up to take 20 mm
cartridges.
It may appear that this low score of the .50 M2 is in disagreement with the
satisfactory experience the USAAF had with this weapon. The answer to this
apparent contradiction is that the .50 M2 proved very effective against fighters
and (not too sturdy) bombers, if installed in sufficient numbers. Six or eight
guns were specified as standard armament, resulting in a destructive power total
of 360 or 480, at the cost of a rather high installed weight. Most American
fighters were sufficiently powerful to have a high performance despite this
weight penalty. Incidentally, the mediocre efficiency score of the .50 M2 is not
only an effect of the low chemical content of its projectiles. Even if only the
kinetic energy were considered, the efficiency of this gun would remain inferior
to that of the UBS, B-20, ShVAK or Hispano, although better than that of the MK
108 or MG-FFM. To sum up, the preferred US armament fit was effective for its
purpose, but not very efficient by comparison with cannon.
A further validation of the calculations is provided by the outcome of tests by
the USN, which stated that the 20 mm Hispano was about three times as
destructive as the .50 M2. In the above table, the ratio between their scores is
3.3.
The outstanding performer is clearly the German 30 mm MK 108, which achieves ten
times the destructiveness of the .50 M2 for only twice the weight. It makes a
particularly interesting comparison with the MK 103, which fired the same
M-Geschoss projectiles. The MK 103 gains an advantage because of its higher
velocity, but loses most of it due to its lower rate of fire, then is finally
eclipsed in efficiency because of its much greater weight. No surprise that the
Luftwaffe considered the MK 108 their premier air-fighting gun despite its low
muzzle velocity. The Me 262 jet fighter, with four of these guns clustered in
the nose, completely outclassed the firepower of every other WW2 fighter.
FIGHTER FIREPOWER
Finally, a consideration of how the firepower of day fighters compared with each
other, and in particular how it increased during the war. The aircraft have been
grouped in early-war, middle-war and late-war fighters, and have been chosen to
be representative of their period.
TABLE 3: FIGHTER FIREPOWER
NameArmamentWeight (kg)AmmoPowerGunPowerTime to fire 2320
1939 - 1941
Morane-Saulnier MS.4061 x HS.7 (e)
2 x MAC 1934 911680163(14.2)
Messerschmitt Bf 109E-42 x MG 17 (s)
2 x MG-FFM14936802868.1
Fiat G.50 Freccia2 x Breda-SAFAT 12.7 (s)107180054(43.0)
Hawker Hurricane Mk.I 8 x Browning .303144267216014.5
Supermarine Spitfire Mk.VC2 x Hispano Mk.II
4 x Browning .30323562004804.8
Lavochkin LaGG-31 x ShVAK (e)
2 x ShKAS (s)931970189(12.3)
Yakovlev Yak-1B1 x ShVAK (e)
1 x UBS (s) 178290821710.7
Curtiss P-40C2 x Browning .5 M2 (s)
4 x Browning .30230545616314.3
Brewster F2A-3 Buffalo 2 x Browning .5 M2 (s)
2 x Browning .5 M2318828020211.5
Bell P-39D Airacobra1 x 37 mm M4
2 x Browning .5 M2 (s)
4 x Browning .30 M236778983237.2
Mitsubishi A6M2 Reisen 2 x Type 97 Fixed (s)
2 x Type 99-1 12024402389.7
Nakajima Ki-43-Ib Hayabusa1 x Type 89 Fixed (s)
1 x Ho-103 (s)70131038(61.1)
1942 - 1943
Messerschmitt Bf 109F-41 x MG 151/20 (e)
2 x MG 17 (s) 129420022610.3
Messerschmitt Bf 109G-6/R61 x MG 151/20 (e)
2 x MG 131 (s)
2 x MG 151/2028686407143.3
Focke-Wulf Fw 190A-42 x MG 151/20 (s)
2 x MG 17 (s)
2 x MG-FFM310100806663.5
Macchi C.205V series III Veltro2 x Breda-SAFAT 12.7 (s)

2 x MG 151/20 28588004385.3
Hawker Typhoon Mk.IB4 x Hispano Mk.II344112008002.9
Lavochkin La-5FN2 x ShVAK (s)157440022010.5
Yakovlev Yak-9T1 x NS-37 (e)
1 x UBS (s) 27045324984.7
Curtiss P-40E Warhawk6 x Browning .50 M233264863606.5
Lockheed P-38J Lightning1 x Hispano M2
4 x Browning .50 M2429122004405.3
Republic P-47D Thunderbolt8 x Browning .50 M2613156404804.8
Mitsubishi A6M3a Reisen2 x Type 97 Fixed (s)
2 x Type 99-2 16240002628.9
Kawasaki Ki-61-I-KAIb Hien2 x Ho-103 (s)
2 x Ho-528070003626.4
Nakajima Ki-44-IIc Shoki2 x Ho-103 (s)
2 x Ho-3013632040459(5.1)
1944 - 1945
Messerschmitt Me 262A-1a4 x MK 1084132088023201.0
Focke-Wulf Fw 190A-82 x MG 131 (s)
2 x MG 151/20 (s)
2 x MG 151/20431161608262.8
Focke-Wulf Fw 190A-8/R82 x MG 131 (s)
2 x MG 151/20 (s)
2 x MK 1084581742016081.4
Supermarine Spitfire Mk.XIVE 2 x Hispano Mk.II
2 x Browning .50 M2 276 7100 520 4.5
Hawker Tempest Mk.V 4 x Hispano Mk.V 374 16000 1000 2.3
Lavochkin La-7 3 x B-20S (s) 147 4290 330 7.0
North American P-51D Mustang 6 x Browning .50 M2 385 8648 360 6.5
Kawanishi N1K2-J Shiden 4 x Type 99-2 255 7800 480 4.8
Kawasaki Ki-84-Ib Hayate 2 x Ho-5 (s)
2 x Ho-5 291 6600 484 4.8


Comments on Table 3
The armament installations are listed in the second column. In some cases there
were several alternative armament installations for the specified type of
aircraft; of these one has been chosen. The (e) and (s) in the armament column
indicate engine cannon and guns synchronised to fire through the propeller,
respectively. Where the rate of fire for the synchronised installation is not
known, a reduction of 25% of the unsynchronised rate of fire has been assumed.
An exception was made for the MG 131 and MG 151/20 with their electrical priming
systems (10%) and the big Browning .50 M2, Ho-103, and Ho-5 (40%), as these
weapons reportedly suffered badly when synchronised.
The specified weight is the weight of the bare guns and the ammunition. It does
not include belt links, ammunition tanks, gun mounting points and recoil
buffers, synchronisation systems and trigger gear, et cetera. Realistic figures
for the weight penalty would probably be 30 to 60% higher; for example, values
are known of 685 kg for the P-38J and 495 kg for the P-39D.
The ammunition power value is the cartridge power value from Table 1, multiplied
by the number of cartridges carried. The gun power value is the sum of the gun
powers as in Table 2, but recalculated to take into account the effects of
synchronisation.
The final column gives the time in seconds, needed to fire the equivalent of an
ammunition power of 2320. The choice of this value is somewhat arbitrary; it was
selected simply because the heaviest armed fighter - the Me 262 - was capable of
delivering this firepower in one second, so it enables easy comparisons to be
made. Not all fighters carried that much ammunition; for those aircraft that did
not the time has been put between brackets.
During 1939 - 1941 we see that all fighters of the Axis nations and the USSR
have fairly modest firepower. This characteristic is also shared by the
Hurricane Mk.I (and of course the Spitfire Mk.IA). Near the end of this period
the UK and USA started to build fighters with much more firepower, and by 1942
the Curtiss P-40E and Hawker Typhoon were established in service. With those
fighters the armament pattern preferred by these two nations emerged: six .50 M2
guns and four Hispano cannon, respectively. We see that these choices are
approximately the same in weight, but the second offers twice the firepower.
Armed with six .50 guns in the wings were also the F4F-4, P-51D, and most of the
production of the F6F and F4U. Some US fighters - the most important of them was
the P-51B - had only four .50 M2 guns, resulting in a firepower value of just
240, well below average after 1941.
In the second period the firepower of Axis fighters is substantially improved,
mostly by the introduction of multiple and better 20 mm cannon: the MG 151/20,
Ho-5 and Type 99-2. The weight of their armament installations remained fairly
low, especially compared with that of the new American fighters, the P-38 and
P-47. But the empty weight of these aircraft was 5.8 and 4.5 tons, compared with
2.6 tons for a Bf 109 and 3.5 tons for an Fw 190A, so the weight of the armament
was roughly proportional. The Japanese made an interesting attempt to improve
the firepower of the Ki-44 by installing the 40 mm Ho-301 cannon, firing
caseless ammunition. But the 245 m/s muzzle velocity of these weapons was far
too low, and they failed in combat. Not many of these Ki-44-IIc aircraft were
built.
In the final period specialised bomber-killers such as the Fw 190A-8/R8 and Me
262 appeared, with impressively high firepower values due to their MK 108
cannon. These too had a relatively low muzzle velocity, but at 505 m/s this was
still sufficient for engaging bombers. Exchanging two MG 151/20 for MK 108
cannon nearly doubles the firepower of the Fw 190A-8. It is also obvious that
the armament installations of these fighters are quite heavy, especially for the
small Fw 190; the A-8/R8 was heavily armoured as well. The need to destroy heavy
bombers had an adverse effect on the performance of German fighters.
An obvious overall tendency is that towards steadily increasing firepower: The
average gun power in the three periods is 210, 460 and 870. This comes with a
rise in the average weight, which climbs from 175 kg over 300 kg to 340 kg. In
the first years of war a third of the selected fighters fails to reach the 2320
ammunition limit, but in the last years they all carry much more than that.
Of course, the projectiles could only inflict damage if they hit the target, and
in aerial combat the great majority missed (estimates for an average pilot's hit
rate varying between two and five percent). Pilot skill was by far the most
important factor in this, in combination with the quality of the gunsight; it
was claimed that the gyroscopic sight (which entered UK/USA service in 1944) put
deflection shooting within the ability of the average pilot and thereby doubled
armament effectiveness. Other factors were the nature of the target (its size
and whether or not it was manoeuvring), the steadiness of the fighter as a gun
platform, the muzzle velocity of the guns (the higher, the better) and the
location of the guns, centre-mounted ones being more efficient than wing-mounted
over a wide range of target distances.
Criticisms and Alternatives
The publication of this study has created much interest and comment.
Unsurprisingly, the most vocal commentators have been those with criticisms of
the methodology used. This section has therefore been added in order to describe
and answer the criticisms.
There are four principal criticisms, which are mainly centred on the validity of
the comparison between the .50 Browning and the rival cannon. In these tables,
the Browning compares rather poorly and this is sometimes, of itself, taken to
discredit the entire comparison on the grounds that the USAAF was the most
successful air force, so its chosen armament had to be much better than this
study suggests. This general point will be returned to later. The specific
criticisms are:
1. The kinetic element of destructiveness is measured at the muzzle, not at
combat range. The subtext of this argument is that the .50 Browning, having
better ballistics than cannon, retains a higher percentage of its
destructiveness at long range than cannon.
In fact, while it is true that most cannon shells slow down more quickly than
the .50 calibre bullets, it is not true that their destructiveness reduces pro
rata. As has already been pointed out in this study, much of the destructiveness
of cannon shells lies in their HE/I content, which is not affected at all by the
striking velocity as long as it is sufficient to actuate the fuze. So while both
.50 bullets and cannon shells lose kinetic effectiveness with range (the cannon
shells at a faster rate), in overall destructiveness (kinetic +chemical) most
cannon shells actually lose effectiveness more slowly than the bullets.
It is also worth pointing out that most successful attacks in WW2 took place at
fairly short ranges at which different projectile ballistics would not have had
a major effect on destructiveness. During 1940 the RAF rapidly dropped the
harmonisation distance for their fighter guns from 370 to 230m, and were annoyed
that the narrow gun bays in the Spitfire's wing prevented them from harmonising
the 20mm cannon down to their preferred distance of 180m (at which they did most
ammunition effectiveness testing). Although successful attacks at longer ranges
were possible, particularly against large, stable targets like heavy bombers (as
the Luftwaffe discovered), it seems probable that the great majority of
shoot-downs took place between 100 and 300m. This is often not appreciated by
players of combat sims, who think that the ability to score routinely at ranges
of 1,000m or more in their games reflects WW2 reality – it doesn't!
2. The way of calculating the chemical destructiveness is too crude. It is
suggested that instead of just adding an arbitrary percentage to the kinetic
destructiveness depending on the percentage weight of HE/I filling, an energy
calculation should be produced. This would calculate the kinetic energy of the
projectiles (in joules) at some typical combat range, then add to this a
calculation of the chemical energy (also in joules) contained within the high
explosive (if any).
There is a lot of merit in this suggestion, which is more scientific in its
approach. However, there are some drawbacks also. First, there is the question
of what constitutes a typical combat range. And whatever range was selected, the
kinetic energy with which the projectiles struck the target would vary
considerably depending on whether the engagement was a tail chase, a beam attack
or a head-on attack.
Second, there is the comparison between the various HE and incendiary compounds
used. Some of the information required as to their chemical energy is difficult
to obtain, and in any case the filling of some shells varied through time, in
ways which have not always been recorded.
The final response is the simplest: this approach, while affecting the relative
scores of some of the projectiles, doesn't actually change the 'order of merit'
very much. Basically, the lower-powered AP or small-HE-capacity cannon shells
(which derive most of their effectiveness from kinetic energy) tend to show up
as less effective than in Table 1, while the high capacity HE shells show up as
being more effective. As these types were typically mixed in an ammunition belt,
the net result is no significant change in the rankings.
Henning Ruch has done some calculations on the basis of the 'kinetic+chemical
energy' equation and compared the results with those in Table 1. If the .50
Browning is taken as the baseline and given a score of 1.00, the following are
some results for other rounds: As you will see, the 'total energy' calculation
as much as doubles the performance of the high-capacity cannon shells, while
almost halving the score of the AP projectiles.
CALIBREPROJECTILE TABLE 1 SCOREENERGY SCOREENERGY / TABLE 1
40mm CLHE5.8713.832.36
20 x 82HE (M)3.486.531.88
30 x 90RBHE (M)12.6123.031.83
20 x 94HE2.393.391.42
30 x 184BHE (M)21.5226.691.24
37 x 145RHE13.9116.691.20
7.7 X 56RI0.220.251.15
15 X 96HE1.701.921.13
20 x 110 (Mk II)HE4.354.861.12
37 x 195HE23.0424.921.08
13 x 64BHE0.700.741.07
12.7 x 99API1.001.001.00
12.7 x 81SRHE0.650.630.97
7.92 x 57AP-v0.220.200.91
23 x 152BAPI5.655.080.90
15 x 96AP1.701.190.70
20 x 82HET3.482.310.66
13 x 64BAP0.700.440.64
20 x 94AP2.391.260.53

3. The shorter flight time of the .50 bullets, plus the larger number fired for
a given weight of armament, greatly improves the hit probability of this
armament by comparison with the slower-firing cannon, making shoot-downs more
likely.
The first part of this criticism is undoubtedly correct, but the second part
does not follow. The relative lack of effectiveness of the .50 bullets mean that
it is necessary (on average) to score many more hits to shoot down a plane than
with cannon armament. These two factors probably more or less cancel each other
out.
As has already been observed, hit probability is also affected by many other
things apart from gun performance: the quality of the gunsights, the location of
the guns, the stability of the aircraft as the gun platform, and above all,
pilot skill. These cannot be taken into account in a study of this type – there
are just too many variables.
4. That the calculations understate the effectiveness of cannon in general, and
large-calibre cannon in particular. This is partly because while a machine gun
bullet relying in kinetic energy has to hit something vital to have an effect
(or score so many hits close together that it shreds the structure) - it
otherwise just makes small holes - a single cannon strike anywhere on the
aircraft can inflict significant damage. It is also argued that a hit by one
large cannon shell is more effective than hits by several smaller shells
generating the same total damage score, as these will be spread across the
aircraft instead of being concentrated at one point.
These points are valid. However, it is also true that cannon shells did not
always explode when they hit – the fuze could sometimes fail to function – in
which case they were reliant solely on their kinetic damage. Again, it seems
likely that this would more or less counteract the criticism.
In Conclusion, while it is admitted that some elements of the calculations –
especially concerning the relative weighting given to kinetic and chemical
damage – are open to criticism, in practical terms the results stand up quite
well. Changing the method of calculation affects some scores but has
surprisingly little effect on the overall 'order of merit' of the
destructiveness rankings. Where it does have an effect, it is generally to boost
the scores of high-capacity HE shells while reducing those of lower-velocity AP
cannon shells, which is validated by the Luftwaffe's decision to focus on
chemical rather than kinetic energy in developing their aircraft weapons.
To return to the obviously controversial question of the relatively poor
performance of the .50 Browning: as has already been stated in this study, "the
preferred US armament fit [of six or eight .50 HMGs] was effective for its
purpose, but not very efficient by comparison with cannon". It is worth pointing
out that for as long as the battery of .50s proved adequate against the targets
usually encountered, there were strong arguments in favour of retaining the
weapon, as the standardisation of production, supply, maintenance and training
provided great logistic benefits by comparison with the plethora of different
weapons fielded by the Germans and Japanese in particular. Of course, the USA
did make some use of the 20mm Hispano cannon, but this was severely limited by
production problems: that is another story, told elsewhere on this website!
HOME

[Thunderbolt56]

Just to clarify, in the book I've read this information in, the author didn't really write it. It is interviews and memoirs of different aces (yes, all are aces) and while one pilot in particular quoted the number "400 hp" it was just his statement and gave the impression it was just a number he might have pulled out of his arse.

I didn't think too much about it until I read in at least 3 other exerpts where each pilot was concerned about firing all his guns at a particular angle of attack or at a particular low speed for fear of wing departure. It may have been a thought bordering on pilot's superstition (kinda like gremlins in bomber squads), but it was mentioned enough to actually get my attention...that's all.

I'll try to go back through and mark the individual sentences and post them here. They may clarify a bit.

[choctaw111]

Anthony G Williams & Emmanuel Gustin have some great books on Combat aircraft. I have two books. One from the first world war and another from the second.
I was going to do the math on this once I saw how this thread was turning out, but I was beaten to it. I may try some other math and see what I come up with.