Machine gun synchronisation on WW 2 fighters.

exbluejob

LE
Book Reviewer
Google is your friend, took me 10 seconds.



 
The first war fighters used mechanical interruption for slow firing guns. World War 2 brought guns firing 1200 rpm through the prop, by electrical firing. How did that work?
 

exbluejob

LE
Book Reviewer
The first war fighters used mechanical interruption for slow firing guns. World War 2 brought guns firing 1200 rpm through the prop, by electrical firing. How did that work?
Wiki is your friend:

The Nelson gear[edit]​

The Marlin gas operated gun proved less amenable to synchronization than the Vickers. It was found that "rogue" shots occasionally pierced the propeller, even when the gear was properly adjusted and otherwise functioning well. The problem was eventually resolved by modifications to the Marlin's trigger mechanism,[71] but in the meantime the engineer Adolph L. Nelson at the Airplane Engineering Department at McCook Field had developed a new, mechanical gear especially adapted to the Marlin, officially known as the Nelson single shot synchronizer.[72] In place of the push rod common to many mechanical gears, or the "pull rod" of the Sopwith-Kauper, the Nelson gear used a cable held in tension for the transmission of firing impulses to the gun.[68]

Production models were largely too late for use before the end of the First World War, but the Nelson gear became the post-war U.S. standard, as Vickers and Marlin guns were phased out in favour of the Browning .30 calibre machine gun.

E-4/E-8 gears[edit]​

The Nelson gear proved reliable and accurate, but it was expensive to produce and the necessity for its cable to be given a straight run could create difficulties when it was to be installed in a new type. By 1929 the latest model (the E-4 gear) had a new and simplified impulse generator, a new trigger motor, and the impulse cable was enclosed in a metal tube, protecting it, and permitting shallow bends. While the basic principle of the new gear remained unchanged: virtually all the components had been redesigned, and it was no longer officially referred to as the "Nelson" gear. The gear was further modernised in 1942 as the E-8. This final model had a modified impulse generator that was easier to adjust and was controlled from the cockpit by an electrical solenoid rather than a Bowden cable.

 

Daz

LE
The first war fighters used mechanical interruption for slow firing guns. World War 2 brought guns firing 1200 rpm through the prop, by electrical firing. How did that work?
The basic idea is that the trigger mechanism follows a cam lobe that is tied to the propeller shaft. When the cam lobe spins, the trigger is allowed to fire the gun only when the propeller isn't "in the way".

More here Synchronization gear - Wikipedia

Of course, you could just lob the guns into the wings instead, solving that little problem :)
 
I can just imagine the trials for this gear.

“Right, here’s the latest prototype, get it installed”.

”OK boss, ready to fire”

”Brrrp”

”Fcuk’s sake!”

Repeat ad nauseum.

Or some bean counter in the Ministry of Aircraft Production. “I say, most units consume 1.2 propellers per aircraft per year. But 654 Sqn only have one, and they’ve gone through 50!”
 
Plates on prop, then cams, then oil-feed interrupters.
Then the electric version, which interrupted by way of the solenoid, for example on Bf 109.
Though Galland said it didn't work well, and there were bullet/prop incidents.
I'm sure a metal prop, though shot, wouldn't disintegrate like a wooden one.
 

Bubbles_Barker

LE
Book Reviewer
I can just imagine the trials for this gear.

“Right, here’s the latest prototype, get it installed”.

”OK boss, ready to fire”

”Brrrp”

”Fcuk’s sake!”

Repeat ad nauseum.

Or some bean counter in the Ministry of Aircraft Production. “I say, most units consume 1.2 propellers per aircraft per year. But 654 Sqn only have one, and they’ve gone through 50!”
More worryingly 654 Sqn flew helicopters...
 

Bubbles_Barker

LE
Book Reviewer
I just picked a number, but I suppose in actuality it would have been the “Aeroplane and Armaments Experimental Establishment”.
They flew Auster AOPs earlier and I don't think they were armed either!

Luckily the props are on the wings here, imagine synchronising that lot:

1638891279246.png
 

Bubbles_Barker

LE
Book Reviewer
In fact I originally thought this thread was about harmonisation of guns:

1638891714459.png


1638891726903.png

To get them to sing in tune...
 
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What about mid-upper turrets? Presumably they must have had stops to prevent accidental damage to tail fins. Or waist gunners on B-17s, stops to prevent engaging your own wings, presumably.
 

Bubbles_Barker

LE
Book Reviewer
What about mid-upper turrets? Presumably they must have had stops to prevent accidental damage to tail fins. Or waist gunners on B-17s, stops to prevent engaging your own wings, presumably.
Fairings, cams, interrupter bars, electrical solenoids. Apparently each one of a Defiant's four guns could be individually managed in that respect.
 

diehard57

War Hero
The Lancaster mid-upper turret used ‘Taboo Arms’ to ensure that the gunner didn’t accidentally shoot off the aircraft tail, I presume the other RAF ‘heavies’ - the Halifax and Stirling had a similar arrangement.
D18A7DEA-0AA7-4A1A-A4FE-3149A99A2310.jpeg
 
Just spoke to an ex SAAF chap, who has a world of knoweldge about such things.
He also pointed out that Galland had shot bits of his prop off in a Bf109, and explains thus...
The machine guns were 'synched' to fire through the prop, but the problem was that a) the ammunition wasn't that good in terms of consistency from striking the primer to the bullet leaving the barrel; and b) this problem was made worse when the aircraft had been at differing altitudes, and thus different temperatures.
Apparently cold Machine Guns fire fractionally slower than warm ones due to friction variation.
As he says 'one of those things you cannot replicate on the ground.'

Galland:
I fired, and I was infuriated by the constant jamming of the guns. Further I was amazed by the remarkable flames from the muzzle. I had never seen anything like it: real fireworks in front of my cockpit. Again the guns jammed. I could not coax one more shot out of them.
I was not very impressed when I received the report that three quarters of the propeller had been cut through. That was the explanation of the fireworks. The synchronization had been wrongly adjusted or was faulty. I insisted on a detailed technical inquiry, but in the shape of a personal report from the man responsible. Each shot that had been fired a fraction of a second too late or too early had hit the propeller and exploded there. At the neck of each blade there was a piece as big as a fist missing.
 

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