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Gun Installation fuselage vs. wing


dov

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Hallo

After reading literature about P-38 and P-47 one question results:

If you have a fuselage installed gun, which shoots through the propeller arc. How much does the synchronisation reduce the amount of shots?

Take German MG of the late or early 109s or 190s. In percrntage, how much was the reductipn in firepower shopting through the arc, in opposition to a wing mounted gun which could fire full?

Since there is a reduction, you stay a longer time in the opponents line of fire!

Happy modelling 

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4 minutes ago, dov said:

If you have a fuselage installed gun, which shoots through the propeller arc. How much does the synchronisation reduce the amount of shots?

Rather depends on rate of fire, number of propeller blades, engine speed and arc of cam cutout for the interuptor gear

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Ooh, great question, I will be genuinely interested to hear a reply!

As per Dave's answer, bearing in mind the prop is probably doing between 2-3000 rpm, depending on power setting, with 3 blades/gaps, with a MG fire rate of 1000-1500 rounds per minute? These are back of a fag packet numbers, but even so, I wonder if there was any noticeable change in rate of fire? And I presume that would be affected by the larger 13mm type of guns?? Were cannon centreline mounted (other than the infamous breech mounted variety)??

Great question!!

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On the Ki-61-Id with the fuselage-mounted 20 mm Ho-5 guns - which b.t.w. were some of the best 20 mm guns of WWII - the rate of fire was reduced by appr. 50%. (3-blade prop, ca. 750 rpm fire rate). This was much resented by Japanese pilots who would have preferred to have this superior gun in the wing, but not enough space.

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16 minutes ago, isaneng said:

Ooh, great question, I will be genuinely interested to hear a reply!

As per Dave's answer, bearing in mind the prop is probably doing between 2-3000 rpm, depending on power setting, with 3 blades/gaps, with a MG fire rate of 1000-1500 rounds per minute? These are back of a fag packet numbers, but even so, I wonder if there was any noticeable change in rate of fire? And I presume that would be affected by the larger 13mm type of guns?? Were cannon centreline mounted (other than the infamous breech mounted variety)??

Great question!!

I was thinking along similar lines re rpm when we discussed visibility of the Kullerschnauze some time ago, but was reminded that the engines would have reduction gear, at something like a 1:14 ratio IIRC. I think this all is pretty complex, as the speed of the round/muzzle velocity would have to be factored in with prominence. And safety margins, due to mechanical tolerances. 50% would sound credible, if only as it "feels" right. I would imagine possibly more for the wing-root mounted 151s of the 190, though I think the firing would be done electr(on)ically controlled.

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However the trajectory is more predictable because the wing-mounted guns will suffer from the wing twisting under g in a turn, and wing mounted guns reduce the agility of the aircraft.  Yakovlev was very strongly against them, and this carried over to Lavochkin.  But then he had engine mounted cannon, best of all.

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Very interesting topic!

 

I have read that Italian pilots also complained about this. The C.200, C.202, and Re.2001 didn't have the most robust armament fit to begin with - two 12.7mm machine guns - and they fired through the prop.

 

But one advantage of centrally-mounted guns is they always shoot straight ahead! Widely-separated wing-mounted guns were calibrated to converge at a given distance, adding more interesting variables to their setup.

Edited by MDriskill
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I just would like to say:

If a 109 or 190 had only wing mounted guns clear of the prop arc, in contrary to a fighter with wing mounted guns only. Would it be more equivalent to a P-51 in firerpower?

 

A P-51 vs 109 (as it was) rounds fired in a certain amount of time. Which fighter could fire more rounds per time equivalent?

Or mass per time?

If the fuselage mounted were reduced to 50% in rate of fire, so I would have to stand twice the time in fire of my oponent.

Sounds not good!

The other fact is complicated maintenance! If guns are close to the engine!

The clear mathematical and physical facts I ask!

Maybe it is more phsychology as facts?

Happy modelling 

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5 minutes ago, dov said:

 

If the fuselage mounted were reduced to 50% in rate of fire, so I would have to stand twice the time in fire of my oponent.

 

Only if head on.  And even then all your fire would be heading to your opponent all the time, rather than spraying around and only concentrating at one specific range.  And doing more damage when they hit, if cannon.  But most combats are not head-on.

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I have the calibration pattern of a few fighters. As download manuals. Since I never shot in real life, I know maths and physics.

All calibration is done to a fixed distance. Beyond and before you are off. If you have an 109E with MG FF in the wing, you have the same problem as in a Spitfire.

Was the Spitfire more effektiv in firerpower as a 109 Emil in the BoB? This qiestion could be part of the answer. 

Had a Gustav more or less effektiv firerpower as a P-51?

We will see what our experts say!

Happy modelling 

 

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"Es hat alles seine Vor- und Hinterteile!"

 

With the guns in the nose you have "concentrated" firepower and that is good to have in case you aimed well, including the deflection (Vorhalt)

with the guns (plus ammo) in the wings you have a disadvantage in maneuverability and have to decide wether you shoot "straight" or have the barrels converging at "the usual distance".

 

With a high rate of fire you have concentrated firepower in short moments of engagement (good in case you aimed well)

with slower rate of fire you can fire longer (if you follow your tracer rounds this may help).

 

In case you are engaging heavy bombers it might be nice to have a 30mm canon to saw off a wing, in case you intend to shoot into the He 111's glasshouse one .30 round in the pilot's head might do the job.

Sometimes an incendiaray .50 round is just the right thing.

 

So, if the 109's and 190's job is to engage heavy bombers and the P51's job is to engage fighters they have different targets demanding a solution.

 

Later in the F-86 the guns were all mouted in the nose and even later in the F-104 it was only one gun.

 

It's a bit late to quarrel about this and other things were more decisive (probably).

 

For the first question (rate of fire with synchronised guns) there will be diagrams somewhere (including a safety margin for high and low propeller rpm), maybe it was the reason we never saw a four- or five-bladed 109 propeller.

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A quick look at Wiki suggests the M2 had a cadence of 500rpm, the 151/20 of between 550 and 750 synchronised and up to 800 elsewhere, 131 930rpm (no indication whether "free" or synced). If this data is correct, the 151 would still deliver more rounds with a much heavier weight and explosive charge in a given time than the M2. Would need some calculation, but 2*151 vs. 6*M2 may net out.

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19 minutes ago, tempestfan said:

A quick look at Wiki suggests the M2 had a cadence of 500rpm, the 151/20 of between 550 and 750 synchronised and up to 800 elsewhere, 131 930rpm (no indication whether "free" or synced). If this data is correct, the 151 would still deliver more rounds with a much heavier weight and explosive charge in a given time than the M2. Would need some calculation, but 2*151 vs. 6*M2 may net out.

 

The aircraft variant of the M2 had a rate of fire of around 800 rpm. This increased to almost 1200 on the later AN/M3, that came at the end of WW2 and later served in the Korean War.

 

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If you want to read more about the development of guns for aircraft use, including the aspects discussed here, I suggest to look at the work of Anthony Williams. He wrote a number of books on the subjects but also published several articles on his website. This is now being rebuilt so not all are available, in any case the site is here:

 

https://quarryhs.co.uk/home/index/

 

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19 hours ago, MDriskill said:

Very interesting topic!

 

I have read that Italian pilots also complained about this. The C.200, C.202, and Re.2001 didn't have the most robust armament fit to begin with - two 12.7mm machine guns - and they fired through the prop.

 

But one advantage of centrally-mounted guns is they always shoot straight ahead! Widely-separated wing-mounted guns were calibrated to converge at a given distance, adding more interesting variables to their setup.

Not an advantage though. I'd far rather try to hit a duck with a shotgun than a sniper rifle! And what do you want to hit? On a multi-engine target you might want to hit engines rather than whats straight in front of the nose.

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The argument for the target area, big or smal targets, I supose this was no thought during developement!

Get on two facts at the same time: Head on attack 12 o'clock and a Rammjäger at 6 o'clock!  So far as I understand the point is to calibrate your guns for the desired distance! If the distance does not match with your tactics, so something is wrong! The paper? Or the paper is not up to date?

I do not know for instance if it is possible to calibrate guns and revi to a commander desired distance for new tactics?

If you can calibrate you a/c an individual mode including camera, so fine. Just the next question is, was it done?

As you see I am on this matter not familiar.

Thank you in forward for ideas and thoughts.

Happy modelling 

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Just a thought, a P-47 carried 8 .50cal machine guns, at 500 rounds per minute, that's 4000 RPM.  With approximately 16 Feet between the outboard most guns, converging to a single point at 150 yards, at 75 yards behind a target, the spread is only 8 feet. With a wingspan of 32 feet on the BF-109, the entire firepower is concentrated in an area between the two wing mounted radiators (and fuselage). A 3 second burst puts 200 rounds into an area slightly larger than a fuselage cross section. 

Fuselage (nose) mounted weapons could not come close to this level of mayhem. 

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This assumes that there is no scatter from a single gun, which is unrealistic.  Every machine gun does not fire out a single line of slugs but a fan.  This certainly does not stop a level of mayhem, but not to that extent.  Otherwise there would be myriads of stories of enemy fighters simply disappearing under a hail of bullets, which is rarely the case.  However a single hit from a 30mm cannon does indeed rip the tail off a small fighter.

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44 minutes ago, dov said:

+++

I do not know for instance if it is possible to calibrate guns and revi to a commander desired distance for new tactics?

If you can calibrate you a/c an individual mode including camera, so fine. Just the next question is, was it done?

As you see I am on this matter not familiar.

Thank you in forward for ideas and thoughts.

Happy modelling 

Part of the answer:

https://en.wikipedia.org/wiki/Gyro_gunsight

 

Revi 16 (xyz) was adjusted on the ground.

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A few general comments on the matter of where guns hit: guns were routinely checked to verify they hit where they aimed at the desired distance. This was of course true for those mounted in the wings as they had to be arranged to converge at a certain distance. This could have been the same for everyone but there were pilots who preferred a specific distance.

Fuselage mounted guns however also had to be adjusted to verify that they hit where aimed as vibrations could lead to misalignments. It was just part of the maintenance regimen and the instructions for this can be found in all aircraft operating manuals. There are also several pictures showing this operation that make for interesting diorama subjects..

Then there's the matter of calibrating guns and sight so that the guns hit where the sight aims. Afterall bullets drop as soon as they leave the muzzle while the line of sight is a straight line. By calibrating the sight it's possible to choose the distance at which the two lines meet.

Distance: yes all guns were arranged to converge at a certain distance but clearly getting the distance right is very hard in combat. The solution is to have a very flat trajectory of the bullets (with a high muzzle velocity) and a pattern that will spread but not too much. In this way even if the distance is say 300m instead of 250 there will still be a good number of bullets hitting the target. 

Of course the introduction of more modern sights made things much easier, at the same time however the increased speed of aircraft made them harder for the pilot. That's the reason for the very high rate of fire of late-war and postwar aircraft guns, to try have a high number of bullets toward the target hoping that at least a few will hit something. 

What to aim for? Realistically, unless the pilot is in a very lucky situation (target unaware of the presence of the fighter and not maneuvering etc.), the guns are aimed at center of mass. For 2 reasons: 1) if I shoot at the centre of the target I will hit something, may be a fuel tank, may be a linkage, may be a structural component 2) it's the easiest thing to aim at and in most combat situations it will be the only thing I can realistically hope to aim at.

 

Edited by Giorgio N
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On 12/7/2023 at 3:58 PM, dov said:

Hallo

After reading literature about P-38 and P-47 one question results:

If you have a fuselage installed gun, which shoots through the propeller arc. How much does the synchronisation reduce the amount of shots?

Take German MG of the late or early 109s or 190s. In percrntage, how much was the reductipn in firepower shopting through the arc, in opposition to a wing mounted gun which could fire full?

Since there is a reduction, you stay a longer time in the opponents line of fire!

Happy modelling 

There are lots of misconceptions as to the nature and operation of an “Interrupter Gear” for a machine gun that fires through a rotating propeller.

The first and most prevalent misconception is that the “interruptor gear” stops the gun from firing when the propeller blade is in the way of the gun muzzle. It doesn’t. What the “synchronization gear” (which what is the correct term for the mechanism) does is actually fire the gun when the blade is not in the way.

To achieve this the first important thing to take on board is that the aircraft gun has to be converted from automatic operation (when the trigger is pressed the gun continues firing until either the trigger is released or it runs out of ammunition), to semi automatic operation (the trigger press fires one round only and you have to release the trigger and press again to fire the next round).

When the pilot presses his cockpit trigger he is not directly firing the gun, he is actually connecting the gun to the synchronization gear.

In basic terms the synchronisation cam system operation does not press the gun trigger when a blade is in front of the barrel. As the blade moves out of the way of the muzzle the cam system presses the gun trigger (actually via an item called called a trigger motor) and a round is fired. The trigger is released by the cam when the next blade passes in front of the barrel, and then is pressed again as it passes the gun muzzle firing the next round. And so on until the pilot releases his trigger or the gun runs out of ammunition.

This does obviously reduce the rate of fire of the gun. This is affected by two main factors. Firstly the engine (Propeller) RPM which obviously is a variable as this is affected by the throttle control that changes RPM, and secondly the cyclic rate of the gun (how long it takes for the gun to extract the empty case and feed the next round into the gun breech). A faster cycling gun will obviously fire at a faster rate (less blades between shots). Typically this usually resulted in the gun firing after an average every sixth blade with a two blade prop, or twelve blades with a four blade prop.

In WW1 there were many systems used but the system that became standard was the Constantinescu Colley (CC) gear, which was hydraulic in operation, which allowed multiple guns to be operated at the same time, previous systems could only operate one gun. This system was used by the RAF into the 1940’s (last use I think was the Gladiator?)

Another interesting factor is that you can only synchronise a gun with a closed bolt system. An open bolt gun (where the breech is normally empty, and on trigger press the breech moves forward and collects and then fires a round) won’t work because of the time delay between trigger press and the round firing. A typical example of this was the open bolt system Lewis gun on WW1 aircraft which had to use the top wing mounted curved Foster mount. that ensured the gun fired over the propeller arc.

As to gun alignment (correct term is Harmonisation) This ensures that the gun and sight converge at an imaginary point at a pre determined distance in front of the aircraft. Even with a single gun a fired round is affected by gravity so the gun and sight have to be adjusted to allow for “Bullet Drop.”

On multi gun installations such as the eight gun spitfire, all guns are aligned to this point so to give the pilot a killing punch by having the combined fire of eight machine guns hitting the same point in space at the same time. That is why determining range was such a factor, too close or too far away from your target dispersed your gunfire.

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6 minutes ago, Selwyn said:

As to gun alignment (correct term is Harmonisation) This ensures that the gun and sight converge at an imaginary point at a pre determined distance in front of the aircraft. Even with a single gun a fired round is affected by gravity so the gun and sight have to be adjusted to allow for “Bullet Drop.”

On multi gun installations such as the eight gun spitfire, all guns are aligned to this point so to give the pilot a killing punch by having the combined fire of eight machine guns hitting the same point in space at the same time. That is why determining range was such a factor, to close or too far away from your target dispersed your gunfire.

 

I was just about to post this example that fits with the above.
Accounting for both horizontal and vertical dispersion...

 

embed?resid=3BF77D171B0E492C!906761&auth

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Gustin has answered all your questions on his website The WWII Fighter Gun Debate: http://www.geocities.ws/gustin_e/fgun/fgun-in.html .

I posted the link here before, but it appears it is only accessible with a desk/laptop. On mobile devices it forwards to lots of aggressive and unwanted advert sites.

The site does have loads of info, so just copy-patse the address on your desk/laptop and enjoy!

 

After more searching, I think I've found the actual official site: https://flying-guns.com/ this one seems spam-free!

Edited by 48-Alone-Is-Great
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