| Tomb on Guns and Damage |
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| Last update - 26 April 1999 |
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Tomb posted 04-23-99 02:54 AM Im going to open this discussion by presenting my reading of the facts as explaIned by the RAF air to air gunnery manuals volume 7 from 1940 and 1943 and items from the instructOr training course from the RAF Central Gunnery School from this period. Most of you are aware that the bullets from a gun do not all go to the same place and this is due to several factors: mechanical factors such as barrel whip, recoil, mounting points, etc location factors such as wing mounted or fusalage mounted...fixed or free enviromental factors such as day or night low or high altitiude. all these effects cause the bullets to spread around the gun axis and this is known as a BULLET GROUPING this bullet grouping for a world war one aircraft at 250yds is a 20ft diameter circle and for world war two aircraft at 400yds is a 20ft diameter circle below 1000ft this becomes a 25ft diameter circle due to turbulence and at night is some value less (no value given) effects which can increase the dispersion values are unsyncronised guns, a gun stoppage, aircraft control inputs. these affect light aircraft more than heavy aircraft. it is important to note this effects all guns equally MG or cannon. so if i have explained this correctly you should grasp the idea that the bullet stream comes from the gun in a cone from the gun which is all things being equal (mountings etc) is equal no matter where the gun is mounted fusalage or wing...what can make it unequal is a wing mounted gun will have more of an effect on dispersion if one jams/does not fire/not sychcronised or the wings are not held steady over fusalage mounted guns while any pitch or yaw input will affect both fusalage or wing guns equally ..further more a heavy bomber will not be tossed around like a light fighter in turbulence..there is more turblence at low level and less at night. Ok the next important concept is BULLET DENSITY to save a lot of sums i am going to cite the example from the manual and that is an eight gun browning system puts out 200 rounds a second so that at 200yds the bullet density is 12 rounds per square foot and at 400yds is 3 rounds per square foot. its not hard to see from that that that bullet concetration drops off with range very dramatically... Ok to illustrate this point if you stand with a torch about 5 foot and shine it on a wall notice how how bright and compact the light pattern is..now stand back 20ft and notice how much bigger and dimmer the light pattern is..remember this for our next point of discussion. HARMONISATION this comes in two main flavours "POINT" and "PATTERN" in WB this is called convergance and you may only do "point" back to our torch example if you have a torch in each hand and spread your arms wide and shine the torchs you can see two light circles on the wall if you tilt both beams inwards till they overlap then they are "converged". back to guns using the same principle we do the same with the guns and the primary reason for this with an MG is to increase bullet density and this fact makes them more lethal. this is an important concept because guns with a convergence setting of 200 yds is not the same as a setting of 400yds..over all fire power(bullet density) is down by 75% at 400yds..thats a big drop. lets put that together in a single engined fighter which has say 2 fusalage MG and 2 wing Cannon we will also to keep it simple and use our above numbers of 12 rounds per sq/ft at 200yds and 3 rounds per sq/ft at 400 yds..but it will be per gun for our example. fusalge mounted guns would lose some rounds due to the prop interupter gear ..to keep my numbers easy im going to say 30% the two fusalage guns are close together so it reasonble to combine them so at 200yds 12 bullets less 30% equals 8 bullets per gun x two guns equals 16 rounds per sq/ft at 200 yds and 4 rounds per sq/ft at 400yds our two wing guns with no propellor in the way will obtain 2x12 =24 rounds per sq/ft at 200yds and 6 rounds per sq/ft at 400yds for a total of 40 rounds per sq/ft at 200yds and just 10 rounds per sq/ft at 400yds. factors to consider if a fusalage gun malfuntioned it would most likley drop the bullet density by 8 rounds at 200yds and 2 rounds at 400yds which is much less of a loss..if a wing gun malfuntioned it would not only throw the aim point off but also increase the bullet spread which would also reduce the bullet density by a significant amount. lets look at some other factors a low and high velocity mg round a low and high velocity cannon round a AP and a HE round this comes from other documents as well as the document mentioned at the start from a recovered me109 fighter which had been shot by an AP 20mm cannon shell from a hispano suiza cannon This shell had penetrated through the rudder ,sternpost,through various members of the fusalage ,the wireless set, two thicknesses of armour plate , both sides of the fuel tank,the back of the pilots seat,through the pilots chest removing the ribcage,through the dashboard,and out the front of the airplane, a most effective demostration of the power of penetration of the cannon shell.. while we are on the grisly bits the effect of 8x.303 on the human body ...total disintergration..not a body riddled with bullets...total disintergration... as you can imagine you wont find this sort of manual in your local libary...they are written by the military for the military and dont pull any punches..they were written during a war and are not polite or politically correct in any way..they occasionaly surface in old book shops when someone hands over old documents/books/training manuals etc. MG rounds it would appear unless they hit a critical system such as the pilot or engine/fuel/oil system are very unlikey to bring down a fighter... pilots are encouraged to aim at the cockpit area in the 109 as this is where the pilot is and he is surrounded by a fuel tank behind and underneath. MG loads outs appear to be a mix of ball,AP,incendiary, and tracer..often many tracer rounds near the end of the ammo to tell you you were about to run out..operationaly it appears the last tracer rounds were not put in because the enemy would also know you are about to run out incendiary rounds were put in because the greatest hazard from fuel hits/leaks was fire. cannon rounds: the RAF seemed to favour AP/API rounds and the Luftwaffe HE/HEI off the manuals now lets look at this...the bombers the RAF faced were generally twin engined no/light armour/lightly armed/and the crew handily placed next to each other.. the lufwaffe on the other hand faced 4 engined bombers with many guns and the crew and engines spread over a much bigger area. while MG was adequate for the light to medium single/twin engine at close range a cannon was needed against medium to heavy twin/quad engined planes.. from the luftwaffe/RAF accounts many have seen these numbers.. i wont quible over exact numbers fighters 5 to 7x 20mm shells bombers 20 to 25 x20mm shells fighters/medium twins (b25) 1 to 2 x30mm bombers 4 to 5x 30mm sample damage accounts a lancaster hit by over 20 x20mm and many other MG rounds between the tail gun and trailing edge of the wing...nothing vital hit..no repairs other than patching needed a whitely twin engine bombers entire port wing upper surface missing...reskinned a wellington direct hit by an 88mm..all fusalge covering missing from aft of the trailing edge to just infront off the tail..written off (it made it home with severe damage..it is doubtfull if any other aircraft could take this kind of hit in this area) lancaster hit by 88mm in port wing tip port outer wing replaced He111 over 200 mg holes nothing vital hit repairs not noted whitley over 700mg rounds nothing vital hit repairs patches and electric cabling p47 hit by 4x20mm one in prop/rudder/ starboard flap/starboard gear well repairs not noted p47 hit by 5x20mm in starboard wing root trailing edge removing flap and surrounding wing skin..failed to penetrate aft spar, repairs not noted there are many more plus the usual b17 damage loss of nose/fin/tail etc the point is while many aircraft could and did take more than average many also took less. where you were hit mattered a lot especially with mg rounds... an Mg round lets say low velocity hit a single enging fighter just in front of the trailing edge by the fusalage at 8oo yds say..lets say the fighter is made of metal most likley result is a dimple in the metal a high velocity round may even go straight through...result to aircraft of hit ..not noticable..now a 30mm round hit in the same place..that round will explode removing nearby wing panels spraying shrapnel into the adjacent fusalge with disasterous results for any fuel tanks or pilot sat nearby..you get the idea and those 30mm rounds could contain 11oz of incendiary material. penetration of the 20mm HE round was fairly low in fact one account i have here shows a 20mm shell exploding just one inch above a b17 crew man head ..he had a helmet on so the force of the explosion forced his head down but failed to do more than dimple his helmet..there are other examples of 20mm HE failing to penetrate seat armour but equally there are accounts of a 20mm shell hiting a cockpit and spraying the occupents with shrapnel ..those helmets and flack jackets which appeared on crew members of buffs later on in the war were worn with good reason. so to add that lot up into a few salient facts and to first state from the gunnery manual light MG rounds are considered ineffective beyond 300yds (penetration) and heavy beyond 400yds (bullet density) HE cannon rounds will be equally effective at any range but will suffer more so from bullet density (due to generally lower rates fire). if any one cares to crunch the numbers you will find that most aircraft weapon systems from this era would be hard pushed to fill that 20ft diameter circle with just one round per sq/ft per sec... at 400yds so if you aim with perfect control and make a perfect aim..your still going to have your rounds spread over a 20ft diameter at 400yds ..bring the range down to 200yds and the bullet densisty increases dramatically. some things begin to match the accounts of what happend during various combat accounts if you take into account bullet density. no doubt a high velocity round such as a .50 is quite capable of going a long way..but is unlikey to bring a fighter down at long range due to the effects of dispersion on bullet density..it would have to hit one of the vital parts such as the cockpit..the pilot for instance...very very unlikely though possible..on the other hand a 30mm shell though less likley to hit due to even less bullet densisty (though EQUAL dispersion notice)will almost certainly bring down a fighter unless perhaps it hits a wingtip. velocity is much less of a factor to damage caused than bullit density ...many bullets ariving in a given area are more likely to hit something critical than a single high velocity MG or cannon AP round..a hit just about anywhere with a 30mm or larger round will bring down a fighter again velocity is less of a factor i have only ever found one battle damage survey and it covers 501 single engine aircraft and 354 4 engine liberators all hit in air to air action with mostley 20mm cannon (reposted on imols main board..if any one would care to add it to this discusion for me i would appreciate it.. i dont know how. [added to this thread and figures placed into tables below - front]) basically the primary cause for single engine fighters going down is the dreaded cockpit kill..for a buff its the loss of engines..losses due to wing/fuse/tail being blown off for a fighter is just 10% and 3% for a bomber..any way see the repost for full details. there is very little evidence to support the kinectic kill dynamic...much to support the cannon kill dynamic and much to support close range MG kill dynamics and much to support critical hit dynamics it would apppear due to kinectic kill dynamics that high velocity rounds such as the .50 cal become plane destroyers at long range while lower velocity cannon is weaker at long range..the evidence suggests the opposite is fact true mainly i suspect due to BULLET DENSITY...there simply would not be enough rounds per sq/ft to make a damaging hit to structures while most of a HE/HEI rounds effect is effective at any range low or high velocity. the old way of gunfire/damage modeling is wieght of fire assigned a point value and everthing extrapolated from then on for example a rifle size round round is given a value of 1 for a 1 sec burst and is about .4 lbs a second wieght of fire while a 30mm which is not quite 8lbs a second is 20 times greater so we give it a value of twenty and we know that 1 30mm round will destroy a fighter plane structure so we assign a value of 20 to the structure we also know that a 3 sec burst from a hurricane will also destroy a fighter 8x .303 = 8x 1 point in our system x 3 seconds = 24 points of damage..its looking good ..the sums add up factor in range against bullet densisty for the probabilty of a hit and we have a working combat model..a complete damage map is made out adding engines, fuel tanks etc a computer game may use such a method and in the early days warbirds felt like it did. while this is good for a game its not good simulation ..the available facts show that that in fact very few aircraft went down to structure failure so several spit/ or hurris could fire there ammo loads into a HE111..the structure is unlikely to fail ..those rounds would be directed at the crew compartment/engines/fuel tanks/etc the next generation of RAF plane had cannons after this and to quote from the manual "the MG is like the infantrys bayonet..for close range work" another major flaw of a size/points damage model is the well known glass elevator syndrome such as the p38/mossie/b17 as has already been shown it is bullet density/shell size that counts not size of target so much..the large size elevator acts as a bullet collector ...from the survey of 855 aircraft not one single one was lost to control surface damage..not one. a second major flaw is japenese planes noted weakness was lack of pilot armour and self sealing fuel tanks..not airframes falling apart...this is well documented..again lightly built is mistaken for weakly built and heavily built is not always strongly built for example a zero can out dive and pull far more G than a heavily built b17 while the heavily built p47 could go faster and pull more G than both of them ...certain aircraft were noted for certain vunrabiltys such as the betty bomber (G4M) to fire. there are many other factors too numerous to mention in the time availble about other aircraft. the quad .303 rear turret was very effective in lancaster and other bombers because at close range its bullet density was high and an oncoming fighter would be facing a wall of lead...this would be around 400yds or less.. also remember this aircraft flew largley at night where any nightfighter would be within the what i will call the lethal density range...compared with a twin .5 cal which though longer ranged would have a much lower bullet density but add in the top/bottom turret and you now have 4 guns bringing the lethal density up..add in the other planes in formation and the bullet density rockets to very lethal levels indeed i would suggest suggest one for one the 4 gun 303 turret is more effective out to 300-400yds than a twin .5 cal due to bullet densisty while in formation the .5 cal could maintain its more effective range to up the lethal density by having many guns firing at a target therby increasing bullet density..the key factor is number of guns x rate of fire. where bullet density drops below lethal values for MGs which appears to be after around 300-400yds then the cannon is the weapon of choice because even though the bullet density is lower the rounds effect is much greater due to explosive/incendiary effects note lethal density refers to aircraft structure and or systems a .5 cal can kill a crew member out to 7500yds..very very unlikly..but possible a good damage model in my view would reflect the critical system hit dynamic (supported by the damage survey of 855 aircraft) which would also allow an aircraft taking more damage than average if the those hits were spread all over the airframe while allowing a well aimed/lucky hit to down it in less than average such as a pilot hit in a single engine plane or a fuel tank fire in a multi or single with damage appropiate to the round fired for example mg rounds are unlikly or destroy the airframe though incendiary rounds could possibly start a fuel fire while 20mm is unlikley to destroy a four engined heavy it is more likley to injure crew or start fuel tank fires/wreck engines while a 30mm round is highly likley to produce a catastrophic result Bullet grouping or bullet density is a critical factor and determined by dispertion which is fairly standard for all guns types at 20ft diameter at 400yds and rate of fire becomes very important at close range i think i have covered most of it....if you understand the above you realise why the 262 had 4x 30 mm cannon in the nose over the me109g/k which was fitted with one which is surly enough if one hit would kill a fighter answer, it was simply to increase bullet density and therefore probabilty of a kill why the hurricane was regarded as a better gun platform than the spit though they both had 8x.303s..again bullet density..huricanes guns were close together why the marine corps rated the F4u as having 86% more firepower than the P51b (it had two guns more than the 51..sureley thats 50% more)...our old friend bullet density why Mg rounds being largley ineffective at long range, despite invidual rounds being highly effective ..bullet density the strange effect of having a MG armed fighter causing more damage than a cannon armed fighter at longer ranges...ahh perhaps that is lack of bullet density effects and or cannon effects coupled with a less than realistic damage model do we like 2.6 gunnery...OH YES..first time its felt like plane to plane combat for ages do we like the damage model...oh no its in the dark ages and not represenative did we read MOs post about updating the damage model at a later date..sure did so we can look for a superior combat model to match the superior flight model..i reckon we just might.. Tomb (people who dont make mistakes..dont make anything) i could write rather a lot more on this subject..several people have read anything by Mike Spick/Alfred Price/William Green if you want more..the other stuff is unobtainble by the general public and in private hands..mine actually also drag out those old wargames if you play them they are often extremely well researched and the quality ones often give their research findings and where to get it for yourself |
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Dslick posted 04-23-99 03:35 AM Great post Tomb!!! So, from what you wrote, I gather that a plane like the P-38 would have HUGE bullet density as 4X50 cal and 1X20mm all fire from the nose with no interrupter for a propeller. I would love to read that book!!! Dslick
Mercury posted 04-23-99 05:20 AM Wow! That was very informative. I think that you have a very valid point about the damage model, as I have often wondered how the fabric skined alierons on the Spit I and Fw-190 A series are "removed" in flight. I feel that the gunnery is a vast improvement over the previous versions, and don't get me wrong, I think that the aircraft are much more realisticly survivable, but the indvidual pieces seem to come off a lot! I'd be really interested in seeing some more stats on Weight of fire/Aircraft survivability if aby one has more? Thanks for the info!
Subject: Re: Battle damage USN survey 2nd repost (complete this time) Date: Fri, 23 Apr 1999 16:28:50 +0100 First off when looking at the figures to follow some things should be considered: The survey runs from September 1944 to August 1945. All aircraft losses/damage are due to air to air action only. A loss is considered any aircraft that did not make it to a base. A damaged aircraft is one that did..repairable or not. It is the PTO so a small fuel/oil/hydraulic leak would have more significance here than in the ETO. Most engines will be of the Radial type. This late in the war most Japanese fighters would be firing cannon No survey of twin engine types... only singles (all types fighter/bomber/torpedo/recce..etc) and only the four enginged Liberator are surveyed. Pilot losses would be higher but missing pilot/aircraft are not included (planes not observed to go down and no survivors) Also bear in mind the planes being shot/damaged are late war US so would have a full complement of protection such as self sealing tanks,pilot armour/deflector, plates armoured glass etc etc... The numbers: Single Engine Aircraft
From a quick look at the numbers... if you got damaged you had a 6 in 10 chance of getting home... lets re-order that list from most likely hit area to least.
Not a suprise that "structure" gets hit the most. Probaly not welcome is the pilot/controls is very high up on getting hit too. Its interesting to note hydraulics hits are only just behind the engine for a chance to be hit and ahead of fuel. Ok lets re-order the list once more into what actuall brought an aircraft down from highest to lowest:
Its pretty obvious from this that the cockpit area produces the most deadly results. It contains all the aircraft vitals in one nice big volume of space... a hit here can bust any aircraft system from the flight controls to the engine controls to the fuel controls to the gear controls..you name it in a single engined single crew fighter all the vital bits are neatly placed in one space... not to mention the pilot does not function too well after a few hits either. I would expect in a correctly "damaged aircraft" model to kill or be killed Thus out of 10 kills/deaths. 4 "cockpit kills" lets say 2 pilot kills and 2 total control loss kills (no controls at all) 1 engine kill (engine stops) 1 fuel kill (leak/fire/explosion) 1 oil kill (leak/fire) 1 hydraulic kill (leak/fire) 1 structure kill (loss of tail,wing,fusalage) 1 "other kill" (gear dropped,ammo explodes.etc ) A point to ponder is the fluids while hard to hit were highly fatal when they were and were flammable. This would have to be modified a little acording to aircraft type and period. Spits and Mossies for example had pneumactic rather than hydraulic flaps so hit here would not cause a fire but would render the flaps unusable immediatley on a Spit. They also had liquid cooled engines so a "coolant" leak could be added also non flamable... fluid leaks seem to be about a 1 in 10 chance (each). Early war Japanese did not have self sealing fuel tanks so the risk of leak, fire, explosion is that much higher or pilot armour so pilot/control kill would also be higher... pre-Battle of Britain LW aircraft carried little armour either nor many Brit buffs of this period had self sealing fuel tanks. A B17 with self sealing tanks is less likely than say a G4M Betty with a lot of fuel tanks not self sealing to go down in flames. Something like a IL2 which had an armoured bath tub around all the vitals would be much harder to get a pilot/control kill on than say a standard fighter such as F6/F4u which this survey covers. So this is what I would expect from an accurate damage model. Concerning single engine aircraft... obviously the better shots would go for cockpit kills (like DoA). For a realistic Simulation i would expect for every 25 missions where damage was recieved I would get home on 15 of them and get shot down the remaining 10 for the reasons above on AVERAGE. More later, but lets now look at a Four Engine Heavy for comparision:
From this it is immediatly obvious that engine kills brought down buffs the most and notice how fluid kills, while largly fatal in a fighter, have very much less effect in a "heavy" (multiple system redundancy) and structure kills are MUCH less... only 4% ( multiple load path redundancy). So lets re-order this list also as most hit area from most to least:
No suprise that again the structure is the most hit. Compared to single engine planes though the cockpits hits are well down the list though as there are more engines... so hits are more likely to occur. I would have expected far more fuel hits but suprisingly this is not the case. A second look shows a very big difference between what gets hit in a single engined aircraft and a multi engine aircraft. Why is this ? Well a bigger aircraft has a lot of space or "voids" in which no matter how may rounds you fire you are just putting a hole in the skin and hitting air... in the warbirds and others there appears to be no concept of an "undamaging hit"... all hits cause damage. This I feel is a fatal flaw in most damage models. A second reason is the cockpit/engine/fuel tanks in a single engined aircraft occupy significantly more percentage of the total volume of the airframe compared with a heavy bomber which has a higher volume of "empty" space. So lets re-order the numbers and see what actually caused a bomber to go down from most to least:
Straight away you can see that the primary cause of a buff loss is engines by some margin. Ok so lets review... If I'm in a buff i would expect if damaged to get home almost 9 times out of ten (compared with a fighters 6 out of 10) If i went down 10 times I would expect (rounding off) to go down: Engine kill 5 times (2 or 3 more engines stop) Fuel kill 2 times (leak,fire,explosion) Pilot/Control kill 1 (pilot/loss of all control) Structure kill 1 (loss of wing, fus, tail) Oil kill 1 ( leak,fire ) Hydraulic/Electrical (very unlikely but possible there would be redundant electrical and hydraulic systems) More importanly if I was killed/downed 10 times I would expect to survive the other 90 missions as survival rate if damaged is (almost) 9 out of 10. These figures were taken from the PTO in which the air fighting was still very fierce... the last stages of the ETO war was a virtual flypast as by now the LW was all but destroyed So lets now compare fighter to buff losses:
I have missed off control surfaces because from the sample of 854 aircraft damaged only 47 took hits there and NOT ONE was lost to this cause... this little piece of battle damage, while graphic, is completely unrealistic. Also propellor damage did not cause any aircraft losses from this sample I was puzzled for a while why electrical losses could bring down a heavy but after extensive reading i conclude that this is an electrical fire from an electric powered turret(s). Structure failure in WarBirds is the primary cause of shoot down and some aircraft suffer more than most such as the P38/mossie/B17. Bigger structure means easier to hit and destroy in WarBirds when in fact the opposite is the case as bigger structures are generally more solid and therefore harder to destroy... easier to hit yes but harder to destroy. I think the above figures bear that out... 11% for a fighter and 4% for a much bigger buff are the numbers for "structure" losses. "Others" is not specified but while fairly fatal for a fighter is not fatal to a bomber so I would suggest it consists of single systems such as oxygen in a fighter, a buff would have more oxygen system redundancy... I'm sure there are other systems too. As far as I am aware this is the only extensive WW2 battle damage survey. It clearly shows that the damage model needs reviewing. The method of counting damage pings and then busting off a piece of structure is quite clearly not simulation. I stated a while back that system failure brought down most aircraft not structual this USN survey quite clearly backs that up (for air to air). Imho a gunnery rewrite is less valuable unless you have a realistic damage model to apply it to..they go hand in hand. Care to accept the challenge dudes ??? Tomb | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||