# A wing-mounted gun synchronization



## Milsurp (Aug 21, 2016)

Hi, I joined to ask a question about wing-mounted gun synchronization (or desync, actually). Please note this has nothing to do with propeller synchronization, which is the most common topic when I searched.

I had always thought multi-gun installations on wings had their firing normally desynchronized (ripple-firing) to reduce the stress on the wing structure. For example, the quad-cannon fighters like the British Firefly and the American P-51A and F8F-1B - it seems that firing twin 20mm in sync would have generated a lot of vibration and stress.

But in looking to confirm my assumption, I can't find any actual data via basic searching. All I get are redundant articles about gun-propeller sync mechanisms. Can someone give me some leads on where I might find this information? Credible references would be fantastic 

Thanks for any help!

Mil


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## Shortround6 (Aug 21, 2016)

It probably wasn't necessary. You have enough trouble getting the guns to fire at exactly the same time to begin with for the first shot let alone the following shots. Most aircraft guns fired "open bolt" which means the bolt is held the rearward position. When the "trigger" is pressed in the cockpit a signal has to be sent to the guns, Usually electric to a solenoid (or to pneumatic or hydraulic systems) to release the bolt/s which moved forward under spring pressure feeding a round into the chamber and releasing the firing pin once the bolt was in position. 
Not all springs had the same tension or moved the bolts at the same speed. Not all firing pin springs moved the firing pins at the same speed. And once the cap was hit not all primers ignited the charge with the same speed and not all powder charges burned at exactly the same rate. The last is why large 30mm cannon were never synchronized to fire though propeller discs. The large powder charges showed too much variation in the time from cap strike to round exiting the barrel. Please note that this is different than a variation in velocity of the projectiles. 
Cycle rates shown in books are an average of many guns, It was not unheard of for some guns to be off quite a bit from the nominal "book" rating. Some faster, some slower. 
Given all the naturally occurring variations in firing rates/times it would seem that spending much time devices to do it on purpose would be a waste of time. 
If you are worried about recoil forces damaging the plane investing in better mounts, like buffered ones, would seem to be a better use of time/man power.

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## Milsurp (Aug 22, 2016)

Thanks for the reply Short, but I wasn't asking from a theoretical standpoint. I was interested to know if it had actually been done in WW2 aircraft, and if so, where I could find citations for it. Do you happen to have any info on that? 

As a side note, during my research I found that Spitfires that experienced jamming with one of their two wing-mounted 20mm cannons were actually being yawed by the recoil of the other. So that speaks to how much recoil a fully-automatic 20mm weapon produces. 

This makes me even more interested in whether quad-cannon weapons had desynchronization to reduce vibration - 4x20mm going off all at once has to produce some serious shock to the airframe.

Thanks for any help!


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## pbehn (Aug 22, 2016)

/


Milsurp said:


> As a side note, during my research I found that Spitfires that experienced jamming with one of their two wing-mounted 20mm cannons were actually being yawed by the recoil of the other. So that speaks to how much recoil a fully-automatic 20mm weapon produces.
> 
> !



There were many reasons for the Spitfire cannons jamming when initially installed.

Supermarine Spitfire - the gun wings
The response was to fit the Spitfire with the 20mm Hispano cannon. This poses a variety of problems, not least of which was the size of the cannon. The only way to fit it in the Spitfire wing was to mount it on its side. A second problem was that the early cannons were prone to jam under the pressure of combat. If one cannon jammed, the recoil from the other one was enough to push the Spitfire off course.


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## stona (Aug 22, 2016)

SR6 gave the answer. The guns were neither synchronised (which would be impossible) nor desynchronised (which was therefore not necessary) by any intention or control. They fired in a desynchronised way by the very nature of the weapons.

The solutions to lack of reliability in many aircraft weapons, and not just wing mounted ones, was almost invariably better installation covering everything from gun mounts, heating, ammunition feeds, to ejection shoots and then some.

Cheers

Steve


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## pbehn (Aug 22, 2016)

Unless guns are somehow restricted if any two guns have different rates of fire they will eventually fire at the same time, I presume any set of guns fired by the same button will start of firing at nominally the same time anyway.


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## stona (Aug 22, 2016)

pbehn said:


> Unless guns are somehow restricted if any two guns have different rates of fire they will eventually fire at the same time, I presume any set of guns fired by the same button will start of firing at nominally the same time anyway.



Correct, and there will inevitably be a time when any two guns will fire at exactly the same time, at least for one round, before they start falling out of synch. Whether all eight machine guns in a Spitfire/Hurricane wing ever fired exactly in synch seems extremely unlikely given the amount of ammunition provided and length of time they could fire continuously. It must be statistically possible.
Cheers
Steve


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## Milsurp (Aug 23, 2016)

Thanks for all of the answers! It sounds like nobody's ever seen an official reference for this subject, so I have to assume they just hit the button and hoped for the best  Too bad, as desynching would double the coverage and increase the chance of hits. Thanks for your help!


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## GrauGeist (Aug 23, 2016)

I might point out that any mechanism that intentionally regulated the MG or cannon firing would have slowed the RPM considerably.
Much like the a sync mechanism on MGs firing through a prop arc.

The reason I say this, is that when the MGs or Cannon are set in motion, they fire as fast as their cyclic rate allows: cartridge is fired, gasses blow back the breach, eject the empty casing and the breach closes, loading the next round.
If you interrupt this process by a "de-sync' mechanism, you are slowing the firing rate by a great deal resulting in a reduced amount of rounds being placed on target, all for the sake of a "ripple effect" which really has no bearing on the aircraft's performance.

As it happens, when a pilot of a P-47 presses the trigger on his 8 .50 MGs, they all fire at the same time initially, but due to varying weapon wear, slight variances in gas pressures and other variables, will see those 8 .50 MGs fall out of sync if he holds the trigger long enough.


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## Micdrow (Aug 23, 2016)

I haven't read through it but this might help you as well.

Manual on Harmonization of fixed aircraft guns

Thanks Paul


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## stona (Aug 23, 2016)

Milsurp said:


> Too bad, as desynching would double the coverage and increase the chance of hits. Thanks for your help!



How can desynching the weapons (which were never synchronised on any British aircraft anyway) achieve this? Please explain.

Are you confusing synchronisation of firing time and harmonisation of aiming point? There was plenty of discussion, and plenty of paper generated about the latter.

Cheers

Steve


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## Shortround6 (Aug 23, 2016)

The only "synchronized" automatic weapon installation that I have heard of was the British octuple 2pdr AA mount on ships. While the guns loaded automatically the firing was controlled by a crank arrangement. Ir did slow the rate of fire and was later done away with, in part due to maintenance issues.
Just think about trying to link guns in the wings on opposite sides of the fuselage with mechanical gear, or electric (which has a whole can of worms of it's own) Hydraulic or pneumatic would be maintenance nightmares even they worked at all. you are trying to send signals to the guns at a minimum of 10 times a second. How does the "firing unit" know when the loading is finished? and the loading of the slowest gun, which may change in flight or from shot to shot due to fouling, belt binding, hard pull of round from belt or other reasons.


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## Glider (Aug 24, 2016)

The book ROF for the 20mm as used in the RAF was between 570 and 620 RPM which gives some idea of the difference.


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## chuter (Aug 28, 2016)

stona said:


> How can desynching the weapons (which were never synchronised on any British aircraft anyway) achieve this? Please explain.
> 
> Are you confusing synchronisation of firing time and harmonisation of aiming point? There was plenty of discussion, and plenty of paper generated about the latter.
> 
> ...




I believe he's saying that a stream of bullets from guns firing at separate times (like a single gun with two/three times the rof) would be more difficult to fly through than clumps of bullets fired at the same time. The clumps would do more damage if they hit something crossing the line of fire but the steady stream would be more likely to hit.


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## stona (Aug 28, 2016)

chuter said:


> I believe he's saying that a stream of bullets from guns firing at separate times (like a single gun with two/three times the rof) would be more difficult to fly through than clumps of bullets fired at the same time. The clumps would do more damage if they hit something crossing the line of fire but the steady stream would be more likely to hit.




I don't think this is relevant when even the slowest firing aircraft weapons have a rate of fire of several hundred round per minute.
A typical 20mm cannon might be firing 8-10 rounds per second (16-20 for two). The eight machine guns of a Spitfire or Hurricane would fire 130-140 rounds per second.
Cheers
Steve


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## Frank Stewart (Aug 30, 2016)

Shortround6 said:


> It probably wasn't necessary. You have enough trouble getting the guns to fire at exactly the same time to begin with for the first shot let alone the following shots. Most aircraft guns fired "open bolt" which means the bolt is held the rearward position. When the "trigger" is pressed in the cockpit a signal has to be sent to the guns, Usually electric to a solenoid (or to pneumatic or hydraulic systems) to release the bolt/s which moved forward under spring pressure feeding a round into the chamber and releasing the firing pin once the bolt was in position.
> Not all springs had the same tension or moved the bolts at the same speed. Not all firing pin springs moved the firing pins at the same speed. And once the cap was hit not all primers ignited the charge with the same speed and not all powder charges burned at exactly the same rate. The last is why large 30mm cannon were never synchronized to fire though propeller discs. Actually, the Germans had a weapons tray that mounted instead of the belly bomb rack and fired one or the other of the big 30s threw the prop disk of the Fw-190! The large powder charges showed too much variation in the time from cap strike to round exiting the barrel. Please note that this is different than a variation in velocity of the projectiles.
> Cycle rates shown in books are an average of many guns, It was not unheard of for some guns to be off quite a bit from the nominal "book" rating. Some faster, some slower.
> Given all the naturally occurring variations in firing rates/times it would seem that spending much time devices to do it on purpose would be a waste of time.
> If you are worried about recoil forces damaging the plane investing in better mounts, like buffered ones, would seem to be a better use of time/man power.


The gun camera and ground films show the Navy planes strafing Jap Positions to fire all four guns in synchronized manner! It seems that the interval between shots at only 600 R/M is so small that the muzzle blasts seem to be synchronized for the entire burst. IIRC, there were four American planes that used four 20s to see war service. Early A-36 (Mustangs), later Bearcats, and Corsairs and the Tigercat? Can not remember if the last actually saw any service late in the War?


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## Frank Stewart (Aug 30, 2016)

Milsurp said:


> Hi, I joined to ask a question about wing-mounted gun synchronization (or desync, actually). Please note this has nothing to do with propeller synchronization, which is the most common topic when I searched.
> 
> I had always thought multi-gun installations on wings had their firing normally desynchronized (ripple-firing) to reduce the stress on the wing structure. For example, the quad-cannon fighters like the British Firefly and the American P-51A and F8F-1B - it seems that firing twin 20mm in sync would have generated a lot of vibration and stress.
> 
> ...


Wing mounted guns were "Harmonized", or "Synchronized" such that each gun was pointed to put it's bullets under the Pipper at some very specific range! The Brits who fought the BoB with eight Rifle Caliber Machine Guns chose 200 yards for the most part, although there were other schemes, they were never very popular as they diluted the damage that the eight guns all pointed at the same target at the same range. We Americans with our larger .50 Caliber Heavy Machine Guns chose 400 yards for the most part although some of the Aces preferred to synchronize them all at 600 Yards. The P-38 and all of the German planes with nose mounted guns all chose 600 Meters, or yards for the P-38. At 720 meters, the trajectory of the P-38's guns sighted on the center of the target fighter plane, never rose to miss the top of the canopy, or fell low enough to miss the belly giving the longest point blank range of the War!


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## pbehn (Aug 30, 2016)

Frank Stewart said:


> Wing mounted guns were "Harmonized", or "Synchronized" such that each gun was pointed to put it's bullets under the Pipper at some very specific range! The Brits who fought the BoB with eight Rifle Caliber Machine Guns chose 200 yards for the most part, although there were other schemes, they were never very popular as they diluted the damage that the eight guns all pointed at the same target at the same range. We Americans with our larger .50 Caliber Heavy Machine Guns chose 400 yards for the most part although some of the Aces preferred to synchronize them all at 600 Yards. The P-38 and all of the German planes with nose mounted guns all chose 600 Meters, or yards for the P-38. At 720 meters, the trajectory of the P-38's guns sighted on the center of the target fighter plane, never rose to miss the top of the canopy, or fell low enough to miss the belly giving the longest point blank range of the War!



Friend,you have completely miss read or not read the whole topic of discussion

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