20mm cannon, best, worst, specs, comparison to LMG, HMG etc.
- Thread starter claidemore
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This assumes you know how many bullets per square foot would be required to achieve 'lethal density' on the modern enemy aircraft, which the Air Tactics Department—after thorough testing—thought they did in 1938. We can all scoff at the thinking in certain British circles in the late 30s and early 40s now, but at the time gun harmonization was an intensely debated subject with very thoughtful arguments on each side.
The problem is, a stray bullet or two can bring down an enemy aircraft. The tough part is deciding at what point do you stop sacrificing optimal bullet group size and shape for density.
Shortround6
Major General
If we are discussing the effects of guns and ammunition it is one area of discussion. Saying that one type of armament, the eight .303s, is no good because they all pointed in different directions, is introducing a different component into the discussion, "how the armament was actually used (or miss used)".
It also needs a little backing up. For those who are interested in this subject I would recommend VERY STRONGLY, Tony William's and Emmanuel Gustin's book "Flying Guns World War II".
Unless somebody claims they are faked, in it are several pattern diagrams for the early Spitfires and I would imagine that similar diagrams exited for a variety of aircraft. One diagram shows the 75% and and 100% zones for each gun superimposed over a Heinkel 111 from the rear at 100, 200, 300 and 400yds range while using a 350 yd harmonization point.
At 400yds the 75% zones have crossed over but are still forming an overlapping sideways figure 8. the 75% zone from each gun is perhaps a foot or two larger than the diameter of the 111s fuselage. the 100% zone is obviously much larger. Shorter distances mean much smaller impact zones. This 350yd harmonization may have looked good on paper against a bomber but it wasn't so good in practice against fighters. But the guns were no more pointed in different directions than any US fighters wing guns were pointed in different directions. The harmonization point was changed to a shorter distance with combat experience.
The British may have also experimented with different dispersion patterns for the guns. Not pointing them in different directions but playing with mounts and buffers and such so that each gun produced a certain sized cone of fire, which were all pointed at a single harmonization point but affected how big the group was at that point. The small Browning was certainly capable of much better grouping than the British got out of it but not only did it require careful tuning and mounting to do so but too tight a group may be counter productive. A properly tuned and mounted water cooled .30 cal Browning could make a 10 shot-one ragged hole group at about 80 feet (1000in) but such a tight group is either hit or miss. Devastating if it hits, a total waste if it does not.
Trying to aim a too tightly grouping armament from a fast moving, vibrating, aircraft at another fast moving aircraft may mean a lot of near misses. the trick is in figuring out what cone of fire gives a good increase in the chances of hitting without dissipating the firepower too much.
The eight rifle caliber machinegun armament was a pretty effective armament for it's weight, all things considered. Trying to stretch it to twelve guns or increase the ammo from 300-350rpg to 500rpg (or more) may have been counter productive if other armaments options were available.
A problem with the whole .303 vs .50cal argument is not super bullets for the .303 or any other such nonsense. There is no question that the .50 cal round is more powerful and does more damage than the .303 round, the question is wither a single .50 bullet does more damage than Three or FOUR .303 bullets. for the same weight of guns and ammo you can have eight .303s with 350rpg or four .50 cal guns with 140rpg. you can have a firing rate of 146-160 rounds per second vs 40-56 rounds per second (pre 1940/post 1940). If the guns are set up with similar convergence points and similar cones of fire, which is a matter of doctrine or policy and not a characteristic of the guns and ammo, the .303 battery will give 3 to 4 times the number of hits as the .50 cal battery in the same firing position/situation.
It also needs a little backing up. For those who are interested in this subject I would recommend VERY STRONGLY, Tony William's and Emmanuel Gustin's book "Flying Guns World War II".
Unless somebody claims they are faked, in it are several pattern diagrams for the early Spitfires and I would imagine that similar diagrams exited for a variety of aircraft. One diagram shows the 75% and and 100% zones for each gun superimposed over a Heinkel 111 from the rear at 100, 200, 300 and 400yds range while using a 350 yd harmonization point.
At 400yds the 75% zones have crossed over but are still forming an overlapping sideways figure 8. the 75% zone from each gun is perhaps a foot or two larger than the diameter of the 111s fuselage. the 100% zone is obviously much larger. Shorter distances mean much smaller impact zones. This 350yd harmonization may have looked good on paper against a bomber but it wasn't so good in practice against fighters. But the guns were no more pointed in different directions than any US fighters wing guns were pointed in different directions. The harmonization point was changed to a shorter distance with combat experience.
The British may have also experimented with different dispersion patterns for the guns. Not pointing them in different directions but playing with mounts and buffers and such so that each gun produced a certain sized cone of fire, which were all pointed at a single harmonization point but affected how big the group was at that point. The small Browning was certainly capable of much better grouping than the British got out of it but not only did it require careful tuning and mounting to do so but too tight a group may be counter productive. A properly tuned and mounted water cooled .30 cal Browning could make a 10 shot-one ragged hole group at about 80 feet (1000in) but such a tight group is either hit or miss. Devastating if it hits, a total waste if it does not.
Trying to aim a too tightly grouping armament from a fast moving, vibrating, aircraft at another fast moving aircraft may mean a lot of near misses. the trick is in figuring out what cone of fire gives a good increase in the chances of hitting without dissipating the firepower too much.
The eight rifle caliber machinegun armament was a pretty effective armament for it's weight, all things considered. Trying to stretch it to twelve guns or increase the ammo from 300-350rpg to 500rpg (or more) may have been counter productive if other armaments options were available.
A problem with the whole .303 vs .50cal argument is not super bullets for the .303 or any other such nonsense. There is no question that the .50 cal round is more powerful and does more damage than the .303 round, the question is wither a single .50 bullet does more damage than Three or FOUR .303 bullets. for the same weight of guns and ammo you can have eight .303s with 350rpg or four .50 cal guns with 140rpg. you can have a firing rate of 146-160 rounds per second vs 40-56 rounds per second (pre 1940/post 1940). If the guns are set up with similar convergence points and similar cones of fire, which is a matter of doctrine or policy and not a characteristic of the guns and ammo, the .303 battery will give 3 to 4 times the number of hits as the .50 cal battery in the same firing position/situation.
The crank and rods are there, very robust pieces of metal, some of it forged steel, when you consider just a few inches above,( or below in the DB's ) is a cast aluminum block that just about no bullet would have any trouble punching a hole thru, to get at those same rods and crankshaft. I see no benefit in armoring a oil pan.yep, nothing important inside the crankcase
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Mustang nut
Banned
- 200
- Jun 14, 2011
Great info Shortround. Another point about harmonisation is that harmonising at 350yds meant that if you were to get in behind directly behind a Bf109 at close range the only thing you would hit is the propellor. The RAF reconed that you needed to put enough bullets into a bomber in 2 seconds to bring it down so they doubled the number of guns. For a brief period the Hurricane and Spitfire were the most heavily armed fighters in service. 8x 303s was initially good enough to bring down most bombers, but very quickly the LW started installing armour and brought the Ju88 in service which was harder to take down. The Hurricane and Spitfire may have had the same guns but they had different installation. The spread of the Spits guns in the wings meant it fired like a "shaken pepper pot" according to one veteran, the Hurricanes was much more concentrated.
- Thread starter
- #147
claidemore
Senior Airman
Hi Mustang nut...., if you shoot off the propeller the plane isn't going to go very far!
Seriously though, the 'get right behind a 109 and miss everything but the propeller tips' is a common and cute 'image', but it has no bearing in reality. The prop on the Spitfire was bigger than the 109, so if the illustration were correct the Spit prop would get hit as well as the 109 prop. Fact is the Spit would have to fly perfectly line astern about 80 feet behind the 109 in a slightly rotated configuration (so the 109 wings don't get hit) in order for all 8 guns to miss. You would have to be an extremely skilled pilot and an extremely stodgy one, to maintain that position behind an enemy fighter while you poured 2400 rounds into the ozone. It also requires the 109 pilot to maintain his position all the while laughing merrily as 2400 rounds buzz past his ears like so many angry bees.
All it takes is a little rudder to have 2 or 3 guns from one wing bearing on the fuselage of the target.
Or even better, if the 109 guy realizes he's being shot at and slams the throttle foreward, he's going to increase the range and fly directly into the harmonization zone, which will ruin his day.
Of course the RAF soon deleted half of the .303 guns and substitued two 20mm Hispanos.
Question is, why? And why keep 4 of the .303s?
Seriously though, the 'get right behind a 109 and miss everything but the propeller tips' is a common and cute 'image', but it has no bearing in reality. The prop on the Spitfire was bigger than the 109, so if the illustration were correct the Spit prop would get hit as well as the 109 prop. Fact is the Spit would have to fly perfectly line astern about 80 feet behind the 109 in a slightly rotated configuration (so the 109 wings don't get hit) in order for all 8 guns to miss. You would have to be an extremely skilled pilot and an extremely stodgy one, to maintain that position behind an enemy fighter while you poured 2400 rounds into the ozone. It also requires the 109 pilot to maintain his position all the while laughing merrily as 2400 rounds buzz past his ears like so many angry bees.
All it takes is a little rudder to have 2 or 3 guns from one wing bearing on the fuselage of the target.
Or even better, if the 109 guy realizes he's being shot at and slams the throttle foreward, he's going to increase the range and fly directly into the harmonization zone, which will ruin his day.
Of course the RAF soon deleted half of the .303 guns and substitued two 20mm Hispanos.
Question is, why? And why keep 4 of the .303s?
fastmongrel
1st Sergeant
All this talk of punching holes in engines seems to be missing out the fact that the squidgy bag of water wearing a flight suit sitting in the cockpit is the best thing to hit in a plane. A plane can escape with a hole in the radiator or engine it cant with a leaking pilot.
split s is the faster way to get out of there... no?
the was still shivery in WWII, and yes, even from the Germans.
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Shortround6
Major General
Rhetorical question?
The RAF knew that 20mm cannon were better than MGs. Once engine power improved so that the heavier guns could be carried without a performance penalty (and the reliability of the cannon improved) the cannon were fitted. Round for round a 20mm Hispano has 2 3/4 to 3 times the kinetic energy of a .50 caliber bullet. Some times this just means a neater, cleaner hole. Sometimes it means breaking parts that even a .50 cal cannot. And sometimes the explosive charge even goes off
While we may argue about the relative effectiveness of an equal weight of .50cal and .303 caliber machine guns and ammo there is no doubt that the 20mm Hispano was more destructive for it's weight than either of those two choices. The Problem was the buy in weight was rather high to start with. Perhaps too high for 4 such guns with a good supply of ammo until engine power increase yet again. Combat duration may have been a reason for keeping the the four .303s. Drum feed Hispanos were good for about 6 seconds. The belt feed Spitfires were good for about 12 seconds. with about another 5-6 seconds of firing time with the .303s. Hurricanes with four 20mm guns were good for about 9 seconds.
There are stories about gun heating issues, better roll response with the MGs vs four cannon, shortage of cannon and a host of others. Mix and match-take your pick. Four 20mms were used in some locations/theaters and with the new wing on the MK 21 it was four 20mm from then on. A single 20mm Hispano weighs 5 times a .303 Browning and the ammo weighs about 10 times as much per round. Not figuring for mounts, ammo boxes, feed chutes cocking mechanisms and so forth.
Depends on how badly the pilot is leaking. Saburo Sakai flew back several hundred miles to his home base after being shot in the HEAD with a 3006. I believe he said he reached up and removed the bullet himself, if I remember correctly. A doubt he would have made it home if that was a .50 Browning.
With all the twisting and turning relative to each other, most pilots were probably satisfied with just getting the sights on anything enemy. Where the bullets hit , they hit.
Edgar Brooks
Senior Airman
Because cannon shells go bang, and are liable to blow your enemy apart, but, once you've run out of them, it pays to have even some of the pea-sized .303" bullets as back-up. There was also nothing that could replace the outer .303", either; the .5" barrel was 18" longer than that of the .303", so would have stuck out in front of the leading edge, causing immense drag. And, no, you couldn't just slide them backwards, since 1) there wasn't room, and 2) the ammunition feeds must lie on the CofG, as near as possible, otherwise, as the ammunition is used up, the CofG can move out of limits, and make the aircraft unflyable.
Edgar
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- Thread starter
- #156
claidemore
Senior Airman
Hi Edgar
Actually they did mount .50 brownings in the Spitfire. The Mk XIV and XVI had them as well as some Mk IXs. They put the .50s inboard of the Hispano. This should have resulted in an improvement in rollrate with the .303s removed from the outer wing. Pilots liked this mix for shooting up rolling stock.
My thoughts on Hispanos in Spitfires.
Mk II Spit:, Hispanos were new, limited supplies available, so only two per kite plus four .303s (B wing). A lot of Mk IIs still had the A wing with the old 8 x .303 armament.
Mk V: Hispano production catching up, very few A wings, lots of B wings, and finally some C wings with 4 x 20mm Hispanos (most of the C wing Mk V's went to the MTO)
Experience in MTO (Malta in particular) showed some problems with the 4 cannon wing, as well as some supply issues, so a lot of MkVC's had half their guns removed and fought with only 2 cannons. This gave the Mk VC slightly better performance, which it needed against the similar performing 109F and Macchi 202.
Mk IX, VIII, XIV: mostly B wings, 2 x 20mm and 4 x .303. Eventually some E wings, which featured two 20mm and two .50 Brownings. (I believe all of the Mk VIIIs were B wing)
By the time these later models came out they were putting 4 x 20mm in Typhoons, so availability didn't seem to be an issue. At this point it seems that the poor reliability of the 4 cannon Mk VC's had caused the RAF to give up on that loadout in the Spitfire.
With the Typhoons it didn't take long for the RAF to give up on the 12 gun .303 armament and concentrate solely on the four cannon rig. They didn't seem too concerned about not having the longer firing time that the light mgs provided, of course the Tiffie had 140 rounds per cannon, while the MkIX Spit had only 120 per gun. My understanding is that the switch was made to cannons because cannon production had finally caught up. AFAIK no consideration was ever given to a mix of guns on the Typhoon. The differnce in speed between the 'clean winged' 12 x.303 MkIa and the long protruding cannon barrel winged MkIb was 4 or 5 mph.
Actually they did mount .50 brownings in the Spitfire. The Mk XIV and XVI had them as well as some Mk IXs. They put the .50s inboard of the Hispano. This should have resulted in an improvement in rollrate with the .303s removed from the outer wing. Pilots liked this mix for shooting up rolling stock.
My thoughts on Hispanos in Spitfires.
Mk II Spit:, Hispanos were new, limited supplies available, so only two per kite plus four .303s (B wing). A lot of Mk IIs still had the A wing with the old 8 x .303 armament.
Mk V: Hispano production catching up, very few A wings, lots of B wings, and finally some C wings with 4 x 20mm Hispanos (most of the C wing Mk V's went to the MTO)
Experience in MTO (Malta in particular) showed some problems with the 4 cannon wing, as well as some supply issues, so a lot of MkVC's had half their guns removed and fought with only 2 cannons. This gave the Mk VC slightly better performance, which it needed against the similar performing 109F and Macchi 202.
Mk IX, VIII, XIV: mostly B wings, 2 x 20mm and 4 x .303. Eventually some E wings, which featured two 20mm and two .50 Brownings. (I believe all of the Mk VIIIs were B wing)
By the time these later models came out they were putting 4 x 20mm in Typhoons, so availability didn't seem to be an issue. At this point it seems that the poor reliability of the 4 cannon Mk VC's had caused the RAF to give up on that loadout in the Spitfire.
With the Typhoons it didn't take long for the RAF to give up on the 12 gun .303 armament and concentrate solely on the four cannon rig. They didn't seem too concerned about not having the longer firing time that the light mgs provided, of course the Tiffie had 140 rounds per cannon, while the MkIX Spit had only 120 per gun. My understanding is that the switch was made to cannons because cannon production had finally caught up. AFAIK no consideration was ever given to a mix of guns on the Typhoon. The differnce in speed between the 'clean winged' 12 x.303 MkIa and the long protruding cannon barrel winged MkIb was 4 or 5 mph.
Edgar Brooks
Senior Airman
I was talking about the two outboard stations, where the wing tapered; I did say "outer." One of the biggest considerations was weight, and its effect; as early as 1940, erks were being told to watch out for skin wrinkling, with nothing above 1/8" being permissible. Wing skinning was beefed up in later Marks.
No Spitfire Marks, other than the II, V VI, ever had a "B" wing; there has been a lot of mis-identification of "C" (actually known as the "universal") as "B," because there was a (fairly short-lived) modification, which had the outer cannon fairing cut off, leaving a smooth leading edge + a single cannon fairing. The mod was rescinded in anticipation of the arrival of the "E" armament, when both fairings would again be needed.
The IXc could not carry 2 x 20mm in the cannon bay, because the heating pipes ran through the outer compartment, before exiting to go to the outer 2 x .303". The VIII could have taken 4 x 20mm, but, apart from a very few, carried the "normal" "C" armament.
The RAF did not give up on the 4 x 20mm armament, since the 21 had that set-up, and saw action just before the end of the war.
Edgar
No Spitfire Marks, other than the II, V VI, ever had a "B" wing; there has been a lot of mis-identification of "C" (actually known as the "universal") as "B," because there was a (fairly short-lived) modification, which had the outer cannon fairing cut off, leaving a smooth leading edge + a single cannon fairing. The mod was rescinded in anticipation of the arrival of the "E" armament, when both fairings would again be needed.
The IXc could not carry 2 x 20mm in the cannon bay, because the heating pipes ran through the outer compartment, before exiting to go to the outer 2 x .303". The VIII could have taken 4 x 20mm, but, apart from a very few, carried the "normal" "C" armament.
The RAF did not give up on the 4 x 20mm armament, since the 21 had that set-up, and saw action just before the end of the war.
Edgar
fastmongrel
1st Sergeant
I take it you mean chivalry. I doubt there was any chivalry in air warfare because if you go round trying not to kill people they will turn round and kill you. Hartmann the most succesful pilot talked about his technique as "put the nose of your plane in his cockpit and press the firing button". I doubt he was deliberately trying to go round killing people but he knew the best way to knock down a well armoured plane was to knock out the pilot.
Chivalry was a myth anyway even at its peak it never stopped chivalric knights going round killing, raping and pillaging they just sang flowery songs about it
Shortround6
Major General
I don't know if Hartman was trying to kill the pilot or if, buy using the cockpit as an aiming point and cockpit usually being at or near the center of a single engine plane, a fair amount of the rounds that missed the cockpit would at least hit something else on the plane. Aiming at the engine or rudder leaves an awfully big area of empty space around the aiming point and aiming at the entire airplane usually means you are firing from too far away.
As far as firing time goes I believe that at some point, after analyzing a lot of gun camera footage, The British found that the average cannon burst was about 17 rounds.
It may have been a pre war calculation that figured a 3 second burst was needed, or that a pilot could only stay on target for 3 seconds that lead to those charts that show how much weight of projectiles could be fired in 3 seconds. With multiple 20mm cannon less firing time was needed. to inflict the needed damage compared to the mg armament, it may also be that the faster aircraft in the later war period didn't allow for the 3 second "hold" as often. This also depends on the targets, single engine fighters needed few hits than multi-engine bombers.
If we use the 17 round burst length as a 'standard' then the early Spitfires were good for 3 1/2 bursts, Hurricanes were good for 5 and a burp. Later Spits good for 7 bursts, Typhoons and Tempests 8 and a burp (unless fitted with MK V guns).
Now how may "bursts" should the pilot have available to him? we do want more than what was used on 'average' because for every pilot who got in a fight and returned with ammo there is another pilot who pressed his trigger and said "OH, XXXX, out of ammo" that is just the nature of "averages". #-4 is obviously too few and 7-8 seems OK, at least there wasn't demand for more. And 14 seconds of firing time for a Typhoon or tempest isn't that far off the 17-18 seconds of the .303s.
If we compare to the American .50 caliber armed planes a few things should be noted. The US Navy estimated that either one 20mm hit was worth three .50 cal hits or one 20mm gun was worth three .50 cal guns, I forget which. Lets go with the one hit vs 3 hits since it is more conservative. Assuming an equal proportion of hits per unit of rounds fired (and at ranges under 300yds it should be close, better ballistics of the .50 cal don't really come into play until much longer distances) you need 102 rounds of .50 to equal the 34 rounds of 20mm from a Spitfire in our 'standard' burst. Due to the higher rate of fire of the .50cal this can be done with 4.6 guns and not 6 guns, or 4 guns firing for 2.0 seconds instead of 1.7 seconds. The .50 cal planes do have more combat duration. They only need 182 rpg to equal the Spitfire. Moving to the Typhoon or Tempest they are firing 68 rounds so the .50 cal planes need to fire 204 rounds, not a problem for the P-47 with it's eight guns. A 6 six gun fighter needs 2.6 seconds to deliver the 204 rounds though. Going on the assumption that they can stay on target ( in the sense that the target is at least in the gunsight enough to make it worthwhile to keep firing , not that many hits are being made at a given moment) this means the six gun fighter needs 270 rpg to equal the firepower/combat duration of the four 20mm gunned plane with 140rpg. Most late war .50cal armed fighters could do this.
Most .50 armed fighters do have an advantage in combat duration but it may not be as much as it first looks due to the need to be on target longer.
As far as firing time goes I believe that at some point, after analyzing a lot of gun camera footage, The British found that the average cannon burst was about 17 rounds.
It may have been a pre war calculation that figured a 3 second burst was needed, or that a pilot could only stay on target for 3 seconds that lead to those charts that show how much weight of projectiles could be fired in 3 seconds. With multiple 20mm cannon less firing time was needed. to inflict the needed damage compared to the mg armament, it may also be that the faster aircraft in the later war period didn't allow for the 3 second "hold" as often. This also depends on the targets, single engine fighters needed few hits than multi-engine bombers.
If we use the 17 round burst length as a 'standard' then the early Spitfires were good for 3 1/2 bursts, Hurricanes were good for 5 and a burp. Later Spits good for 7 bursts, Typhoons and Tempests 8 and a burp (unless fitted with MK V guns).
Now how may "bursts" should the pilot have available to him? we do want more than what was used on 'average' because for every pilot who got in a fight and returned with ammo there is another pilot who pressed his trigger and said "OH, XXXX, out of ammo" that is just the nature of "averages". #-4 is obviously too few and 7-8 seems OK, at least there wasn't demand for more. And 14 seconds of firing time for a Typhoon or tempest isn't that far off the 17-18 seconds of the .303s.
If we compare to the American .50 caliber armed planes a few things should be noted. The US Navy estimated that either one 20mm hit was worth three .50 cal hits or one 20mm gun was worth three .50 cal guns, I forget which. Lets go with the one hit vs 3 hits since it is more conservative. Assuming an equal proportion of hits per unit of rounds fired (and at ranges under 300yds it should be close, better ballistics of the .50 cal don't really come into play until much longer distances) you need 102 rounds of .50 to equal the 34 rounds of 20mm from a Spitfire in our 'standard' burst. Due to the higher rate of fire of the .50cal this can be done with 4.6 guns and not 6 guns, or 4 guns firing for 2.0 seconds instead of 1.7 seconds. The .50 cal planes do have more combat duration. They only need 182 rpg to equal the Spitfire. Moving to the Typhoon or Tempest they are firing 68 rounds so the .50 cal planes need to fire 204 rounds, not a problem for the P-47 with it's eight guns. A 6 six gun fighter needs 2.6 seconds to deliver the 204 rounds though. Going on the assumption that they can stay on target ( in the sense that the target is at least in the gunsight enough to make it worthwhile to keep firing , not that many hits are being made at a given moment) this means the six gun fighter needs 270 rpg to equal the firepower/combat duration of the four 20mm gunned plane with 140rpg. Most late war .50cal armed fighters could do this.
Most .50 armed fighters do have an advantage in combat duration but it may not be as much as it first looks due to the need to be on target longer.
He said that He'll close to within 150 yards, pull lead on the e/a nose and pull the trigger and run down the aircraft. bullets could hit the engine, cockpit, wingroot, etc. He also said that he wasn't a very good shot.
oh and BTW, Adolph Galland was ordered to shoot pilots that bailed. He out right refused a direct order, as he considered it murder. shivery? nah...
