Centerline weapons vs wing mounted weapons.

[davebender]

Found this historical tidbit on the Kurfurst site.


In spite of our superiority of fire power over that of the enemy, many pilots would prefer the armament of an Me.109 with its one cannon firing through the airscrew hub and two machine guns mounted in the fuselage. They feel that despite its inferiority to our armament the concentration of parallel fire more than counter-balances our criss-cross pattern.

Wing Commander (Tactics) W.M. Churchill
31 Dec 1941

 

[Shortround6]

Please note the words "They feel".

No test results, no experiments.

And in 1940-41 in controlled tests many British pilots were opening fire at ridiculously long ranges. Instead of the 300yd opening range that was asked they were opening fire at 800-1200yds. Shooting at 3-4 times the effective range of the guns sin't going to work no matter how they were arranged.

 

[dobbie]

That is one big advantage, having your firepower in line with the fuselage. Especially if its something with good range. One big advantage to flying fighters like the P-38 is that with the weapons in the nose, there is no convergence to contend with, and some of the higher scoring aces made some pretty long ranged kills because of the concentration of fire.

 

[davebender]

JG26 pilots flew both Me-109s and Fw-190As. That puts them in a good position to evaluate merits of wing mounted vs centerline mounted weapons.

The unit must have written one or more technical evaluations of the weapons issue. Where are those reports?

 

[stona]

JG26 pilots flew both Me-109s and Fw-190As. That puts them in a good position to evaluate merits of wing mounted vs centerline mounted weapons.

The unit must have written one or more technical evaluations of the weapons issue. Where are those reports?

Why would they?

Any official report on the armament would emmanate from the Luftwaffe's armaments test centre.

If they were happy with the armament I very much doubt that such evaluations were made by front line units. Pilots may very well have expressed their opinions but that's all they are.....opinions. I don't remember a Bf 109 or Fw 190 pilot complaining about the standard armament of the various types,with the possible exception of the Bf 109 F.

Other problems were reported by units "breaking in" a new type to the manufacturer's engineers who would arrive with the new aircraft. These men reported to their employer who reported to the RLM (who were footing the bill).

In any case the armament is very similar. The guns mounted above the engine are effectively centre line on both. The Fw 190's inner wing weapons are firing through the propeller disc with minimal offset. It is only the outer wing weapons on both which would have much convergence. The only real difference is the cannon firing through the spinner of the Bf 109 (post E).

I heard Bader praising the centre line cannon on the Bf 109 F in an interview years ago. I have always suspected that there is a touch of "the grass is always greener....." about this.

The earliest 1940 gun camera footage from the RAF showed even worse results than those tests referred to by Shortround 6. Pilots were often opening fire at 1500 yards and underestimating deflection by at least 50%. In other words,whatever guns they were using,they had zero chance of hitting their intended targets.

Whilst it is true that some pilots did score long range victories with centre mounted weapons (I've seen those P-38 accounts too) the limiting factor on accurate air to air shooting was the gun sights. Every pilot who I've heard express an opinion says that the easiest/best way to shoot down an enemy aircraft was at close range and zero deflection. There was no huge improvement in gun sights until the gyro stabilised sights started to be fitted late in the war (at least for the RAF and Luftwaffe,don't remember what the USAAF was using).

Cheers

Steve

 

[davebender]

Because Krauts believe in scientific management and that's doubly true for German military. They performed extensive tests on everything from camouflage value of field gray to accuracy of Ju-87 and Ju-88 dive bombers. Reports from these tests were typically just as thorough as tests themselves. So unless JG26 was manned by slackers there should be plenty of historical reports to read.

 

[Shortround6]

The "long range" shooting is pretty much pie in the sky stuff. Anything over 600yds needs an awful lot of luck. It happened, but being able to do it consistently is another matter.

Consider the 117gram shell from a MG 151/20. It starts at 720m/s but by the time it gets to 300 meters ( 0.477 sec) it has slowed to 552m/s. This is still well within it's effective range. By the time it gets to 600 meters (1.10 sec) it is down to 422m/s velocity. depending on target this may still be in the effective range. However it is obvious that it will take another full second (if not considerably more) to make it to 1000meters. How far can the target aircraft move in just over 2 seconds?

Then you have the drop problem. The shell will drop 16 ft in the first 1 second of flight, this is allowed for by pointing the muzzle up slightly and the shell will cross the line of sight twice. once somewhere between 150-200 meters in front of the plane and once somewhere about 450-550 meters in front of the plane. The shell will never be more than a couple of feet from the line of sight. The problem comes after that, the shell (accelerating at 32ft per second squared towards the ground) will fall 48 feet in the 2nd second of flight. In order to get hits the pilot needs to KNOW the exact distance to the target, even 10% off isn't good enough. He needs to have the correct lead, even a 200mph bomber is covering 587 feet in 2 seconds. getting the speed wrong on a twin engine bomber by 10% means a complete miss. He needs to KNOW the exact course relative to his own and he needs to KNOW if the plane is flying level or descending or ascending.
Tracers tell the pilot where he SHOULD have been aiming 2 seconds earlier.
The difficulty of getting hits goes up at something over the cube of the distance. Center line guns may have some advantage but it is nowhere near as big as some people make it out to be.

It also helps if the guns have similar ballistics, the guns in the P-38 are a very good match, at least to 500-600yds so they may work well together a few hundred yards beyond that. The German guns ( some of the Soviet guns) had rather different flight times and trajectories from each other and are a lot harder to coordinate at long range no matter ho close together the muzzles may be.

Pilots estimates of range are all over the map which doesn't help with analyzing combat reports.

 

[GregP]

I beileve it is well documented that the top Aces like Hartmann, Barkhorn and Rall all preferred fuselage armament. They thought one in the fuselage was worth two in the wings. You'll note that virtually all modern fighters have fuselage-mounted guns, if they have guns.

Boy, Shortround, it's a good thing the pilots in WWII knew all that, huh?

 

[Shortround6]

And Hartmann, Barkhorn and Rall flew planes with wing mounted armament how many times in combat???? And what kind of of wing mounted armament?

"They thought one in the fuselage was worth two in the wings"

I am not saying they didn't think it. the questions are if they were right to think it or why they thought it.

I will note that "virtually all modern fighters have" NO propellers and do not have to worry about synchronizing guns, and many modern aircraft guns would be difficult if not impossible to synchronize.

I will note that "virtually all modern fighters have" rather large cannon and ammo feeds that are rather difficult to place in a wing.

I will note that "virtually all modern fighters have" no more than two guns which means that there is no reason to stick them in the wings.

I will note that "virtually all modern fighters have" cannon with much higher rates of fire than WW II aircraft cannon which means that they don't need multiple ( as in 3 or more guns) to get the weight (or rate) of fire desired.

I will note that "virtually all modern fighters have" computer assisted aiming systems and some even have a correction programmed into the fly-by-wire to prevent the gun recoil of an off-center mounted gun from slewing the plane off target.

Gee whiz, at least 5 differences from WW II aircraft to "modern fighters" that affect gun placement.

British WW II pilots (at times) were subject to some rather strange thinking by the "powers that be" which assumed that the average pilot wasn't going to be able to hit much anyway and had the planes set up for a "shotgun" approach to air to air combat. Guns were set up to point in slightly different directions to cover a bigger area of the sky but meant that seldom, if ever, would more than two guns actually hit in the same place unless the plane was at very close range (and then each gun hit different parts of the target aircraft). Guns were also mounted to give "dispersion" patterns (loose mounts?) of 1/3 of degree or even 1 full degree (5 ft at 100yds) which while increasing the chances of a single hit, did absolutely nothing for getting a large number of hits.

One "official" pattern for the Spit MK VB has (at 100 yds) left hand outer MG hitting higher than the line of sight, the inner mg hitting low, the cannon hitting low but higher and just inside the the inner mg with the right wing guns being a close but not exact mirror image. Right hand 20mm hits lower than right hand inner MG.
When superimposed on an He 111 silhouette from the 6 o'clock position at 250 yds the inner mgs overlap almost exactly at the bottom of the fuselage. the left 20mm is hitting the fuselage on the left side just over the wing root and the right 20mm is hitting the fuselage on the right side just under the wing root. the outer MGs are missing the fuselage on either side almost at the level of the top of the fuselage.
At 300yds the the inner mgs have crossed over and are missing (just) the bottom of the plane, the impact areas of the 20mm guns now form a figure 8 cented on the plane left gun upper circle and right gun the lower. the outer Mgs are no hitting the fuselage on each side about cockpit height.
At 400yds the the outer MGs are now coinciding but just over the top of the fuselage ( impact circle overlaps a bit) the inner MGs are missing just under and inboard of the engines and the left 20mm is hitting the upper right fuselage and space and the right hand 20mm is hitting the left wing root.

At no point do more than 2 guns of any type hit the same place. While this greatly increases the chances of hitting with something it also means that no matter how good the pilot is he cannot bring the full fire power of the Spitfire to bear on even a He 111 (from 6 oclock) let alone a single seat fighter. Please note that this has NOTHING to do with the guns being in the wing as the guns could be adjusted to ALL hit the same point at one distance if so desired.

Lets not confuse cause and effect here when talking about the benefits or problems of fuselage and wing mounted guns.

For the Germans let us also note that there is a 100mps difference in velocity using the 92gm mine shell between a MG 151/20 and a MG/FFM and a 125mps velocity difference using the 115-117gm shells, the heavier shells retain velocity better than the light shells and are better for "long range shooting".
Germans figured the heavier shell had a "max" range of 750 meters at 3000 meters altitude compared to a "max' range of 600 meters for the mine shell. Effective range for the mine shell was considered 400 meters against bombers.

What were the German pilots comparing?
The wing mounted MG/FFM to the engine mounted MG 151? Wing mounted MG 151s to the engine mounted MG 151 (under wing gondolas?) Please note the under wing cannon are mounted a bit lower than the engine mounted cannon and have a vertical convergence problem as well as lateral.
Fw 190 pilots with the early models had 20mm cannon firing at different velocities in the same plane. getting the MG 151s and the MG/FFMs to hit a fighter using a deflection shot when they had different flight times and needed different amounts of "lead" to hit the target may have been difficult?

 

[GregP]

Well, the three top aces combined shot down almost a thousand aircraft among them and I think their opinions are probably good ones. You obviously disagree. Want to know what they're comparing? Ask them. I don't know ... but around 1,000 planes shot down by three guys speaks volumes for their choice in my book, especially when they had a coice of whatever they wanted to fly and stuck with the 109.

You and I don't have a great history of seeing eye to eye, do we? So, I suppose it's no surprise this time, is it?

Either way, looks like the fuselage-mounted armament idea has won out for SOME reason. Take your pick of why and welcome to it, no argument here. I have my own ideas why. Unsurprisingly, we have Korean War pilots give talks at the museum and they love the fuselage-mounted armament in the P-80 and F-86 way more than the wing guns in Mustangs, at least the ones who commented on it at all. Some didn't mention armament one way or the other, but had some good flying stories that were more interesting anyway.

But, Gee Whiz ... you could be right ... if we all thought the same, it'd be a dull world.

 

[Greyman]

It's always been known that centreline weaponry is better. There are plenty of reasons for WWII aircraft to have wing-mounted weaponry, but that doesn't change the fact that a gun centred with the pilot and gunsight is better than a gun three metres off axis.

Guns were also mounted to give "dispersion" patterns (loose mounts?) of 1/3 of degree or even 1 full degree (5 ft at 100yds) which while increasing the chances of a single hit, did absolutely nothing for getting a large number of hits.

You're always going to get a dispersion pattern, that's just the nature of the game. To what degree is the question. The mounts weren't intentionally loose, there are dozens of variables that cause a particular dispersion pattern size.

Take eight Brownings in a Spitfire I to the butts and you're going to get eight different group sizes. Sometimes very, very different. The standard RAF 1/3 degree is a reasonable average of how the Browning .303in and Hispano 20mm would perform.

 

[Shortround6]

It's always been known that centreline weaponry is better. There are plenty of reasons for WWII aircraft to have wing-mounted weaponry, but that doesn't change the fact that a gun centred with the pilot and gunsight is better than a gun three metres off axis.

It is better, the question is, is it twice as good?

for an answer we get "Ace ____________ (fill in the blank) SAYS so." which isn't really a very good answer.

You're always going to get a dispersion pattern, that's just the nature of the game. To what degree is the question. The mounts weren't intentionally loose, there are dozens of variables that cause a particular dispersion pattern size.

True. perhaps "loose" was not a good choice of word. The British could "apparently" adjust the dispersion pattern somehow though. They have hit diagrams for 1/3 degree and 1 full degree of dispersion.

Take eight Brownings in a Spitfire I to the butts and you're going to get eight different group sizes. Sometimes very, very different. The standard RAF 1/3 degree is a reasonable average of how the Browning .303in and Hispano 20mm would perform.

I have shot enough guns to know that you would get different group sizes. You are also NOT going to get a 1/3 degree group without some sort of "help". Guns that were that BAD on their own should have been junked or overhauled.

The US used the very similar .30 cal Browning as a ground gun and the water cooled version on a sand bagged tripod could be made to shoot a 10 round group at 1000 inches (83 feet) with all ten bullet holes touching. It was almost a requirement that the guns do so in order for the unit machine gunners to pass their annual qualifications. Some of the suggestions for reducing group size don't apply to aircraft guns (like placing a tent stake behind the rear tripod leg to reduce vertical stringing) but suggest teh larger groups were not always the fault of the gun itself.

A several inch (between 2 and 3) group at 83 feet does NOT equate to a 20 in group at 100yds.

The "Spitfire Bullet Pattern 1" (which implies there was a No 2?) shows a 75% impact zone for each gun at about 3 feet at 200yds and a 100% zone of about 6 feet. It also shows the patterns at 100, 300 and 400 yds and where each gun should hit (or miss) with a 350 yd convergence pattern.

While a little dispersion is a good thing too much dilutes the possible impact. They were intentionally trading the possibility of getting more hits from poor shots for the inability of the better shots to get even the majority of their guns/bullets on target at any given time.
They did the same thing with the quad .50 Naval AA gun. Each barrel pointed in a slightly different direction to increase the chances of getting hits, it meant that only one barrel of the four was actually "on target" at any given time and that not enough bullets could be put into a target to ensure destruction in a reasonable period of time, like several seconds on target.

 

[tomo pauk]

About the 3 aces with 1000 claims: is there a reason to believe they would not accomplish the same with wing mounted battery? Put Hartmann in Spitfire IX and he will have no problems to score as he did.

 

[Kryten]

centerline weps on a p38, me110 or Mossie or a whirlwind may have some advantage over wing mounts due to convergance, but on a single engined plane you have to factor in the reduction in rate of fire due to harmonisation!

secondly FW190 pilots had no difficulties with thier wing mounted armament!

Hartman racked up high scores because he was a top shot and more importantly a superb tactitian!
simple fact is very few pilots could even shoot straight , let alone accurately, top scorers were top shots, Beurling for instance pulled off some spectacular deflection and range shots with wing mounted weapons!

 

[GregP]

Hi Tomo,

There's that theory, yes. Hartmann himself said otherwise. He was thoroughly familiar with the 109 and knew exactly what he could get out of it, and said that if has switched to an Fw 190, he might have been killed right away since he'd be a beginner in it. I'd tend to believe he'd feel the same about a Spitfire, but maybe not. In the war it wasn't an option, was it?

So ... it's a "what if" that I won't even take a crack at. We've had too many pilots give talks about planes and battles and express opinions that support the notion that center-mounted guns were preferred when available, even with the loss in fire rate due to synchronizer gear. I'll just take them at their word and let it go at that.

 

[stona]

Because Krauts believe in scientific management and that's doubly true for German military. They performed extensive tests on everything from camouflage value of field gray to accuracy of Ju-87 and Ju-88 dive bombers. Reports from these tests were typically just as thorough as tests themselves. So unless JG26 was manned by slackers there should be plenty of historical reports to read.

Have you ever seen a proper and rigorous scientific assessment written by a front line Luftwaffe unit about the standard fighter armament on the types they were flying?

The Luftwaffe had extensive test facilities and specialist test units to carry out that kind of duty. This was all done as part of an aircraft system's development,long before it went into service. Some of these units might ultimately test systems in combat,but they were not regular front line units as far as the Luftwaffe was concerned,that's why they were called things like "erprobungsgruppe" (even if the most famous one wasn't actually testing the aircraft it was set up to assess!).

There will surely be reports but not from JG 26.

Cheers

Steve

 

[davebender]

Have you ever seen a proper and rigorous scientific assessment written by a front line Luftwaffe unit

I've seen plenty written by Heer officers all the way down to company level. Luftwaffe more or less adopted Heer leadership methods so they probably write evaluations and after action reports too.

 

[Greyman]

It is better, the question is, is it twice as good?

for an answer we get "Ace ____________ (fill in the blank) SAYS so." which isn't really a very good answer.

I think people might be after different things. From a bean-counting, 21st century, internet-grognard, scientific point of view in which we're after a study stating 'a 109F centreline MG151 is 2.024 times better than a Spitfire Hispano-Suiza' - pilot opinion certainly isn't the end all be all.

I always find pilot opinions fascinating, though. Pilot psychology isn't easily measured and in the final equation can be more powerful than a lot of scientific factors.

True. perhaps "loose" was not a good choice of word. The British could "apparently" adjust the dispersion pattern somehow though. They have hit diagrams for 1/3 degree and 1 full degree of dispersion.

I'd have to see these diagrams to know what's up for sure. As far as I know adjusting group sizes for individual guns wasn't a 'thing'. I would assume it's measuring different group percentages. For example; 1/3 degree might be a 75% zone and 1 degree a 100% zone.

I have shot enough guns to know that you would get different group sizes. You are also NOT going to get a 1/3 degree group without some sort of "help". Guns that were that BAD on their own should have been junked or overhauled.

Another reason centreline, engine mounted weaponry is better. A light-as-possible aluminum mounting isn't going to be as rigid as a one-ton engine or a heavy tripod sandbagged in the ground.

 

[stona]

so they probably write evaluations and after action reports too.

I'm sure they did but that's not the same thing as a comparative assessment of different weapon systems on different aircraft over which they had no control anyway.

In any case both the Bf 109 and Fw 190 had fuselage mounted weapons. I'm not sure what's to compare.

Front line units were equipped with aircraft with the standard armament for their role. They were limited in what alterations they could make. There are endless arguments about what they could or could not do but these are arguments about what those limits were,not whether they existed.

Cheers

Steve

 

[Shortround6]

going in reverse order.

Another reason centreline, engine mounted weaponry is better. A light-as-possible aluminum mounting isn't going to be as rigid as a one-ton engine or a heavy tripod sandbagged in the ground.

Cowl guns are not mounted to the engine, so only one gun out of three is mounted on the engine. The engine is mounted on elastic mounts (rubber bushings) to cut down on vibration transmitted to the airframe. The through the prop gun may be rigidly mounted to the engine (or not):

French planes did mount the Hispano cannon on the engine.

The "light-as-possible aluminum mounting" may not be aluminium. It has to not only withstand the the recoil but hold the gun in place while the plane does a 6-7 "G" pull out or turn ( 22lb gun is now putting 132-154lbs of load on the mount) wing gun mount is usually attached to the spar/s. Some later mounts incorporated spring buffers to reduce the recoil load.

The point of bringing up the tripod is that the mounts can affect the accuracy or dispersion of the guns and we should not confuse the accuracy/dispersion of the gun itself with the accuracy/dispersion or the entire system.

I'd have to see these diagrams to know what's up for sure. As far as I know adjusting group sizes for individual guns wasn't a 'thing'. I would assume it's measuring different group percentages. For example; 1/3 degree might be a 75% zone and 1 degree a 100% zone.

Three different diagrams are reproduced in Anthony Williams and Emmanuel Gustin's Book " Flying Guns of WW II". You may be right about the the group sizes but they don't appear to be exact fits.

I think people might be after different things. From a bean-counting, 21st century, internet-grognard, scientific point of view in which we're after a study stating 'a 109F centreline MG151 is 2.024 times better than a Spitfire Hispano-Suiza' - pilot opinion certainly isn't the end all be all.

We get into discussions of which airplane was better or which armament fit was better and the fact that a Spitfire carried double the number of guns as a 109F or early G (without under wing guns) is often blown off by the 109 supporters with this tired "centerline guns are worth two wing mounted guns" excuse. When asked for proof we get "because ace XXXX says so".

I don't need to know to 3rd decimal place the actual ratio of effectiveness but something beyond "pilots XXXXX and YYYYY shot down a lot of planes using centerline guns so it must be true" would be nice.

The whole long range shooting argument is a load of manure. 99% of the pilots flying in WW II had no business firing at more than 600 meters or so even at a 4 engine bomber flying straight and level.

Success for them in such a situation depended the position of the stars, sun and moon, what they had for breakfast and how fresh the dog poo they stepped in on the way to the plane was.