The gun synchronizer

[HomeBoy 1]

I didn't want to hijack the other thread where I brought this topic up (http://forum.combatace.com/index.php?showtopic=44498) so I decided to start this new one.

 

I have been puzzled by the fact that the B.E.2c in OFF has a fuselage mounted forward Lewis gun that obviously fires through the prop (i.e. is synchronized). I was unaware that there were any Lewis guns configured this way so I started Googling. I found this fascinating article:

 

http://www.flightglobal.com/pdfarchive/vie...20-%201391.html

 

The relevant excerpts follow.

 

There was apparently experimental success with synchronizing the Lewis. The problem with the Lewis had to do with the mass of the round and the acceleration necessary to get the bullet going. This delay apparently made synchronizing the Lewis difficult . (I've always wondered about that!). Anyway, here is the excerpt:

 

 

It is possible that success was delayed because the standard machine-gun used in British aircraft was the drum-fed Lewis, and all the early experiments were conducted with it. It suffered from two disadvantages: it could fire only a limited number of rounds before having to be reloaded, and the masses which had to be accelerated in the gun were so heavy that the fitting of any kind of purely mechanical interrupter or synchronizing gear was a difficult matter. (A synchronizing gear for the Lewis gun was in fact designed by Sergeant-Mechanic Alkan of the French air service and fitted experimentally to a few R.F.C. aircraft in the spring of 1916

 

So, having a synchronized Lewis gun on the B.E.2c in OFF is not far fetched I suppose. Very interesting.

 

Also, Condor and I were discussing how the synchronizing gear actually worked. Neither of us had studied this, we were just being smarty-pants. I don't know a lot of detail of the workings of machine guns except to know that guns like the Lewis, Maxim, Parabellum use the gas expelled from the round just fired to load the next round as well as actually fire that next round. Condor seemed to think that a synchronizing gear would effectively "release the trigger" (i.e. stop the gun from firing) when the propeller blade passed across the gun's path. I was arguing that perhaps a semi-automatic gun (my only personal example is my 1911 pistol which of course is semi-automatic and certainly existed at the time) would work better in this application such that the teeth of a gear would "pull the trigger" and there would simply be teeth missing in the appropriate places where the prop blade was. In other words, Condor was saying the synchronizing gear "stops the gun from firing when the prop is in the way" and I was saying the synchronizer "makes the gun fire when the prop is not in the way." Well, apparently we were both right! :yes: Here is the relevant excerpt:

 

The Vickers device was a form of link motion which, in effect, made the airscrew fire the gun when a blade was not in a position to be struck by a bullet. This stamped it as a synchronizing gear, different in principle from the Fokker interrupter gear in which the gun was prevented from firing when the airscrew blades were in the line of fire

 

So, apparently, the idea I had was basically how the Vickers synchronizing gear worked and Condor's idea was how the Spandau worked.

 

Pretty cool stuff!

[Bullethead 12]

I have been puzzled by the fact that the B.E.2c in OFF has a fuselage mounted forward Lewis gun that obviously fires through the prop (i.e. is synchronized).

 

I've been curious about this, too. I was just figuring it was unsyncrhonized and relying on luck, which the RNAS did in some cases :).

 

There was apparently experimental success with synchronizing the Lewis. The problem with the Lewis had to do with the mass of the round and the acceleration necessary to get the bullet going. This delay apparently made synchronizing the Lewis difficult . (I've always wondered about that!).

 

I've always heard a different story....

 

The Lewis was gas-operated like the modern M249, where there's a hole in the barrel that allows expanding gas behind the bullet to come back up a separate tube and push the bolt open. A gas-operated weapon has to be carefully balanced to work at all in an unmodified state because its bolt has to open at exactly the right time after firing, when the gas pressure is enough to fully operate the mechanism. If the bolt opens too soon or too late, there isn't enough pressure for full operation. The bolt will only go part of the way back and then the spring will carry it forward again. This almost always fails to load the next round and can quite easily cause the spent case to jam in the works instead of ejecting cleanly. Anyway, this timing of the mechanism requires that a gas-operated weapon's bolt has a carefully controlled mass, its springs have carefully controlled strengths, the gas outlet in the barrel has to be in a specific place, and has to be the correct diameter.

 

The problem with synchronizing a gas-operated weapon is that this requires attaching some sort of extra parts to the existing mechanism, and the mass and spring tension changes the dynamics of the system. This requires redesigning the entire mechanism and/or gas system to account for these changes, which is usually not possible within the other constraints of the system, or is at least not practical. IOW, you have to design what is essentially a whole new gun. This is why, throughout history, there haven't been AFAIK any synchronized gas-operated weapons. They've all been recoil- or blowback-operated.

 

So, apparently, the idea I had was basically how the Vickers synchronizing gear worked and Condor's idea was how the Spandau worked.

 

Note that these 2 approaches produce very different results.

 

The thing to remember is that a prop blade passed in front of the muzzle way more often than the gun fired. For instance, a 2-bladed prop turning at 1200rpm has a blade passing in front of the muzzle 40 times per second, but the gun's rate of fire is only about 8 rounds per second.

 

Now, with an interrupter, the gun is just allowed to fire naturally except when the mechanism stops it at those times when the position of the blade and the gun's mechanism happen to correspond. This has a relatively small impact on the gun's rate of fire.

 

With a synchronizer, OTOH, the engine is effectively pulling the trigger about 5 times faster than the gun's mechanism can cycle. Thus, much of this is wasted and then sometimes when the gun is ready to fire, the mechanism won't let it. As a result, synchronizers cause a greater reduction in the gun's rate of fire. Also, while the rate of fire of both systems is somewhat dependent on prop RPM, this has a greater effect on the synchronizer, to the point where it's unsafe to fire the gun at certain RPMs.

 

Or so I've heard it. I could be wrong.

[HomeBoy 1]

Great insight Bullethead. Can always depend on you for that!

 

Wasn't the Vickers and Spandau also gas operated? I thought they were. According to the research I've done, the Vickers had a rate of fire of 450-600 rnds/min opposed to 400 for the Spandau. Obviously the synchronizer issue you (quite logically) present must have been dealt with in such a way as not to impede rate of fire too much unless that rate of fire is wrong or is the non-synchronized version, something like that.

 

It is called a "synchronizer GEAR" which obviously means that the 40:8 ratio you refer to is handled with gearing. That is not a difficult ratio to gear so I can see how they might do that. It still seems like a difficult problem to solve because of the range of RPMs the gun would have to deal with. At idle, the engine maybe turns 200 RPM (just guessing) and at full throttle we might see 1800 RPM (again just guessing). Gearing would take care of some of that but that kind of range certainly would make this a pretty tricky thing.

 

Thanks for the education here. This is really fascinating and I'd love to understand this stuff better.

 

<S>!

-mark

Edited July 17, 2009 by HomeBoy

[HomeBoy 1]

I found this diagram at this web site: http://wapedia.mobi/en/Interrupter_gear

The author claims it is the original design of the Spandau lMG 08. It looks a little too simplistic to me. Is that cam wheel geared? It would obviously have to be. Besides, this design is a synchronizer not an interrupter which was the Spandau design anyway, right? To further the confusion. The gun in the diagram could not (or should not) be a machine gun (fully automatic) but would need to be a semi-automatic in order to function properly in this configuration. Most machine guns have a semi-automatic mode so I suppose that isn't too much of a problem.

 

This is probably more confusing then helpful. It is however, exactly the idea I had as I sat with my 1911 imagining how I might go about firing that gun through a propeller.

 

Edited July 17, 2009 by HomeBoy

[Bullethead 12]

Wasn't the Vickers and Spandau also gas operated? I thought they were.

 

No, both of them (and the Parabellum used by German observers) used the Maxim recoil operation system. Gas pressure has nothing to do with this. The recoil force from firing immediately shoves back the bolt and barrel, which are this point are firmly locked together. This is basically storing the recoil energy until the bullet leaves the muzzle, by which point the recoiling parts hit a catch that stops the barrel and unlocks the bolt. The bolt thus flies back furhter, changes out the ammo, and then springs forward again.

[HomeBoy 1]

I see your point Bullethead.

 

I was (incorrectly) considering all those guns you mention as "gas operated" from the standpoint that the recoil is being created from the gas blowing the breach backward. I understand "gas operated" really means that there is an actual gas tube involved, etc. Sorry for that confusion.

 

BTW, it seems that the little booklet that came with my Springfield 1911 refers to the extraction and reloading mechanism as "gas operated." That's probably what corrupted my thinking.

Edited July 17, 2009 by HomeBoy

[Hasse Wind 46]

Interesting thread. I have a book with a picture of the real Fokker interrupter mechanism, but I don't have a scanner so unfortunately I can't post it here. The book is very good, Fokker Flugzeugwerke in Deutschland 1912 - 1921 by Peter M. Grosz & Volker Koos. (You'd think I work for those guys - I end up advertising their book in almost every thread!)

[RAF_Louvert 101]

I find it interesting that the article did not specifically mention the Swiss engineer Franz Schneider who designed and patented an interrupter in July of 1913 for LVG, but rather his collaboration with Anthony Fokker 18 months later, (and referred to him as "Hans"). And also of note was Raymond Saulnier's patented gun synchroniser of April 1914, and the fact that the French military chose to ignore it. Imagine if the Saulnier N's and Parasols had been the first in the air with synhronized guns firing through the props.

 

By the way, I have posted this before, but this seems like a good place to offer it again. Here is the illustration of the Lewis Airplane Type from my 1918 original Savage Arms service booklet for this weapon.

 

 

 

And, because I am always happy to share this sort of thing with folks who are interested, here is a link to the full-sized scan I put together and cleaned up so that it is suitable for framing.

 

 

Lewis Airplane Type MG Illustration (very large)

 

Cheers!

 

Lou

 

 

 

.

Edited July 17, 2009 by RAF_Louvert

[Bullethead 12]

[quote name='HomeBoy' date='Jul 17 2009, 02:42 PM' post='316653'BTW, it seems that the little booklet that came with my Springfield 1911 refers to the extraction and reloading mechanism as "gas operated." That probably what corrupted my thinking.

 

What's an M1911 Springfield? I have an M1903, which was actually built as in 1944, and it's a bolt-action rfile using the Mauser mechanism.

[HomeBoy 1]

What's an M1911 Springfield? I have an M1903, which was actually built as in 1944, and it's a bolt-action rfile using the Mauser mechanism.

 

1911 GI spec (A1) 45 pistol. Sorry I didn't make that clearer.

 

I'd love to get a M1903. I love those old bolt action rifles.

[HomeBoy 1]

Don't need to have the cam wheel geared, as long as the cam follower is spring loaded. This mechanizm would only be utilized on a rotory engine, with the cam wheel physically connected to the rear of the rotating mass.

 

The Inlines or the V's used a cable just like an automotive speedometer, like a distributer or an oil pump, they all run off the camshaft

 

Hmmm. I think I understand how that could work. The trigger push rod would just wack away at the trigger but only when the trigger was actually ready to be pulled would it actually fire. The spring loaded cam follower would prevent damage when the trigger was not ready. Using this very simple method would also allow the gun to fire as fast as it can possibly be fired too. I could also see where the gun might not fire but one time as the trigger is getting hammered with all those presses and never get a chance to "recover" from the first firing. Apparently that is not a problem.

 

Thanks for clearing that up. I'm getting a real education here!

[Bullethead 12]

1911 GI spec (A1) 45 pistol. Sorry I didn't make that clearer.

 

OH!!!!! That's usually called a Colt, not a Springfield, which is what threw me :). IIRC, the design was by Browning when he was working for Colt, but Colt got the credit and thus it was known, even if other companies and armories made clones of it during wartime.

 

That old .45 is a very nice weapon, specifically designed to drop a drug-crazed native his tracks before he could get close enough to stick a spear into you. The older .38 Special service round just lacked that kind of knock-down power, and the even wimpier 9mm Parabellum so common today is a total joke in this regard. There was a great wailing and gnashing of teeth when the US, for political NATO reasons having nothing to do with combat effectiveness, switched from the .45 to the 9mm in the 1980s.

 

Fortunately, in my war, we were equipped in large part from prepositioned supply ships that had been packed in the 1960s, so were STUFFED with .45s. Not just the M1911, but also the M3 "greasegun" SMG. Too bad there weren't any Tommyguns in there, too, but we were just glad to have anything in .45 APC, and plenty of ammo for them. These things came in VERY handy when we had to clean out all the by-passed bunkers after ther war was officially "over".

 

The ideal handgun is, of course, the original Star Trek phasor. No mess, no smell, no body to hide--the guy just turns blue and disappears. Failing that, if you ever have to use a pistol in earnest, you want something that will put a hole in the target large enough to reach through with a beer stein, and will knock the guy down long enough for him to bleed to death regardless of how much PCP is in his system. If your pistol's caliber isn't .45 or above, you'd better throw a grenade or, failing that, run away.

 

The M1911, like the fast majority of automatic pistols, is actually blowback-operated. Again, gas pressure has nothing to do with it. Nothing at all locks the bolt to the breech, so the recoil force immediately starts shoving the bolt backwards. This isn't a problem, however, because the barrel is so short that the bullet is gone before the breech opens.

 

I'd love to get a M1903. I love those old bolt action rifles.

 

I have never shot a more accurate rifle. With iron sights, you're dead if I see you up to about 1000m away. Plus, if somehow you get closer, and I can beat you into jelly with it :).

[HomeBoy 1]

OH!!!!! That's usually called a Colt, not a Springfield, which is what threw me :)

....

 

Yup. Well, I said Springfield because it is a Springfield Armory. There are so many 1911 variations that it's getting difficult to just say 1911 anymore and people understand what you mean. I guess I could have said 1911 ACP made by Springfield Armory but hindsight you know.

 

One thing I do know, finding ammo for this thing right now is not the easiest thing to do and when you do, it's close to 50 cents a round! Even reloading my own is near 40 cents. Outrageous. I just bought 200 rounds of that crappy Blazer non-reloadable stuff and paid $106 after taxes and shipping! Crazy. I'm shooting my .22 mostly these days cause I can't afford anything else. :yes:

[Bullethead 12]

I'm shooting my .22 mostly these days cause I can't afford anything else. :yes:

 

Although I have an externsive arsenal, I'm saving it against the day the Revolution comes. In the meantime, I keep my hand in with black powder, plus I practice my atlatl throwing. Need any dart points? I can provide :).