Another question on synchronisation

[MikeW]

If we assume that a Vickers Mk1* could fire at something between 450 to 550 rounds per minute, depending upon how it was adjusted, what sort of hit did the purely mechanical interrupter gears have on the firing rate? The interrupters *that I am interested in are Scarff-Dybovsky, Sopwith-Kauper (which I believe was better than Scarff-Dybovsky), and Alkan-Hamy.

And before anyone states the obvious, yes I know that the gun won't be firing for the width of the propeller blade + 4" twice every engine revolution - what I want to know is the limitations imposed by slop and inertia in the mechanical linkages.

[RLWP]

The secret here probably lies in the rotational speed of the engine, and the number of lobes on the syncronisation cam.
Erudite start, but I don't have either of those two numbers....

Richard

Damn engineers...

[EdStevens]

Isn't that what the +4" allows for?

[Darryl]

MikeW,

Given that most synchronisation gears were, I believe, *not "interupter" gears but "activating" gears, there should be no effect on rate of fire.

I believe only one "firing" was rigged each revolution so there are 1200 "triggers".

Garros apparently calculated that 1 bullet in 15 would hit his deflector plates. So you need to take off time for about 80 shots per minute from a possible 1200. There is ample time for 450-550 effective firings in a minute.

The gun was the real limitation. The Lewis was apparently not consistent enough in its rate of fire to ever allow synchronisation.

There is an old article on CC gear lying around here somewhere, I'll dig it out if you like. (I know it was hydraulic but the principle is the same)

best regards

Darryl
*

[TonyWilliams]

Darryl,

In theory what you say ought to be true, but in practice it didn't work out that way. See the last info I posted on the previous thread on this subject. The very best performance I have found represented a loss of 10% of RoF, for WW2 German installations using electric priming for maximum precision. Others run between 15% and 40%.

Tony Williams
Author: "Rapid Fire: The development of automatic cannon, heavy machine guns and their ammunition for armies, navies and air forces"
Details on my military gun and ammunition website:
http://www.quarry.nildram.co.ukMilitary gun and ammunition discussion forum:
http://forums.delphiforums.com/autogun/messages/

[MikeW]

Darryl,

the Scarff-Dybovsky most definately interrupted the firing linkage - when it was on the lobe of the cam the mechanism "locked out" the firing lever. When it moved off the lobe onto the root, the firing lever was free to rotate the pecker lever which impinged on the trigger lever at the back of the gun. There was a 90 degree bellcrank, and three hinge pins in the mechanism - there was going to be slop in every one of those joints.

Tony,

is it safe to assume that the S-D gear would give a reduction close to 40%? Say 200 rounds per minute. Many period accounts relate that you could hear the individual rounds being fired on a Pup or a Triplane.

[Darryl]

Thanks Tony,

I hadn't caught the other thread ("ANOTHER Sync question" should have sufficed to warn me if I had a brain!!).

I am not an engineer's bootlace I'm afraid so I can't explain why the theory doesn't translate directly to an unaffected RoF, but I accept that it doesn't. (STILL trying to figure exactly why the Camel was tail heavy, that is enough for me.)

I wonder why the Lewis gun's "variable" firing rate precluded it from synchronisation if the gear was the limiter? I am afraid I am much better at how it flys than how it shoots.
Suitably chastened :'(



MikeW,

Sorry, my knowledge of "interupter" type gears is nil. But as you say, the "slop" in the system must have been large. There is a large amount of blue sky between the whirling blades but it is not a contention I would seek to prove with my hand!!

very best regards

Darryl

[TonyWilliams]

Darryl,

The Lewis couldn't be synchronised because it fired from an open bolt; that is, the "gun ready" position was with the bolt held back to the rear and no cartridge in the chamber. Pressing the trigger (or getting the synchroniser gear to send a "fire" signal) therefore resulted in the bolt moving forward, collecting a cartridge from the magazine, chambering it and then firing it. This whole process took too long for the kind of accurate timing necessary for synchronisation.

The Vickers and Maxim types fired from a closed bolt, with the cartridge already in the chamber, so all that the trigger did was release the firing pin.

Tony Williams
Author: "Rapid Fire: The development of automatic cannon, heavy machine
guns and their ammunition for armies, navies and air forces"
Details on my military gun and ammunition website:
http://www.quarry.nildram.co.ukMilitary gun and ammunition discussion forum:
http://forums.delphiforums.com/autogun/messages/

[Darryl]

Thanks again Tony,

living and learning....


Off topic, the BREN. Did that fire from a closed bolt. I believe that a weapon is generally more accurate where it does. I have often heard the criticism that the BREN was TOO accurate for a machine gun. A strange comment, unless you want to spray lead everywhere, in which case the Mark 1 Hands should be able to do the spreading? But a common comment from WW2 and after guys I talked to.


regards

Darryl

[TonyWilliams]

I don't have a reference to hand but I believe that the Bren almost certainly did fire from a closed bolt.

Incidentally, at least two WW2 aircraft guns could be synchronised despite firing from an open bolt. This was made possible by maintaining a separate control of the firing pin release, so that pressing the trigger just chambered the cartridge; the firing pin was then released by the synchronising gear.

One of these guns was the MG 17, the other was the British .303 Browning. All other Brownings fired from a closed bolt, but the British cordite propellant was more heat-sensitive than US powders so a cartridge would "cook off" if left in a hot chamber. The .303 Browning therefore had to modified to fire from an open bolt, but it kept the separate firing pin release (not a lot of people know that )

The Lewis had no separate firing pin control, it fired as the breech closed.

Tony Williams
Author: "Rapid Fire: The development of automatic cannon, heavy machine
guns and their ammunition for armies, navies and air forces"
Details on my military gun and ammunition website:
http://www.quarry.nildram.co.ukMilitary gun and ammunition discussion forum:
http://forums.delphiforums.com/autogun/messages/