I was watching an old WW II movie the other day (Tora Tora Tora if you must know), and this question popped into my head. Many of the fighters had one propeller in the front, and it seemed that the machine guns were firing from directly behind the propeller. How did this work? Why didn’t the bullets chew the propeller apart?
The nose-mounted machine guns had a synchronizer (a WWI invention) that prevented them firing whenever a prop blade was in the way.
Which reduced the ouput of those guns, but nose guns don’t have the convergence problems of guns spread out in the wings so accuracy and fire concentration were improved.
A few, like the P-39 and Fw190 (neither of which was in the film), had hollow propeller shafts that allowed guns to fire right through the center of the hub. That also prevented recoil effects from interfering with aiming.
Some pre-synchronizer-gear WWI designs simply had deflector plates on the propeller blades to protect them.
Just to add extra trivial details:
The original design in WWI was by the Dutch aircraft designer Anthony Fokker (working for the Germans). It was called the “Fokker Synchronised Machine Gun”, or occasionally referred to as an ‘interrupter mechanism’.
The French, I think, came up with the deflector plates that ElvisL1ves mentions. The Germans managed to capture one of their planes, and then not long after, Fokker’s synchroniser was in service.
The big improvement, alluded to in previous posts, was that the airplane became a point-and-shoot weapon. You could chase another plane, and shoot it down. Prior to this, they either had to have a second crewman to operate the gun, or just plain overload the pilot with work. (It’s hard enough to fly a plane in a dogfight… aiming and operating a machine gun make s it even more fun.)
There are other solutions too, like putting the guns somewhere else, (but then it’s harder to hit things, because you have to adjust for the position of the guns.)
Keep in mind that the “Zeros” in Tora! Tora! Tora! Were AT-6 Texan trainers in drag and they never had any real gunx to begin with. The originals did have fuselage mounted guns though.
That got me wondering, did we (Yanqui imperialist running dog 'murricans) have any planes in WWII that used syncronizers to fire through the propellor arc? I thought we phased them out in the thirties but I could be wrong. Are there any I’m overlooking?
I can’t resist the hijack, I say it was Sam Colt who perfected the “point and click” interface decades before they mounted a Mauser in a Messerschmidt.
I know, I know but the alliteration sounds better. 
To my knowledge the Focke-Wulf 190 never used a through-the-prop-shaft cannon, as did the more common Bf109.
All the Fw190 versions I have seen have two 13mm machine guns mounted on top of the engine cowling, and 20 or 30mm cannons on the leading edges of the wing roots.
- Lat
If we did they didn’t last long. I believe that there were a few Curtis P-26’s(!!!) still in use in the Philippines at the time of Pearl Harbor and they might have used synchronized guns, but that’s about it.
Actually I think that the advantage of having the guns mounted close together to mitigate the convergence problem for wing mounted guns is overrated. I know that wing mounted guns are boresighted to converge at some range, maybe 300 yards(?), but they are only about 20 ft. apart. It seems to me that in actual use the dispersion caused by vibration and airframe flexing during maneuvers would make that convergence sort of trivial.
It isn’t trivial, but it is less important with .50 cal machine guns than with cannon.
20 and 30mm cannon have a much, much higher effective range, and therefore convergences were pretty important (20mm can knock down a plane easily at 1000 yards).
With .50 cal basically the closer the better. Within 200 yards they would chew up just about anything. It is important to note also that not all of the machine guns (four in the early war, later six, eight in the P-47) weren’t aligned to converge at the one distance, but rather each pair was aligned, giving the pilot multiple distinct points ahead of him in which he got concentrated firepower.
- Lat
Well, it was the Boeing P-26 and not the Curtis. A natural mistake that I think you will all agree could have happened to anybody.
Here is a 3/4 front view and a formation of them.
Actually, they weren’t flown by US pilots in WWII, but by Philippine AF pilots.
Thanks David. I hadn’t considered they’s still have planes like those but it wasn’t like the defense budget was huge in the late thirties. It’s nice to have someone around who knows these things first hand. Studying WWII is just a hobby for most of us, very different for you. Also thanks for what you and your comrades did for us.
It is almost impossible for people to believe how primitive by today’s standards, was the technology of WWII.
The Fw-190 D and the Ta-152 varian did use that arrangement.
But you’re right in general, most 190’s did not. I should have been more specific.
The P-26 did see action briefly in the defense of the Philippines. One is credited with a Zero kill, as I recall.
I don’t want to run this into the ground, but …
All of the interviews with fighter pilots I’ve ever seen emphasized that success against another fighter comes from finding someone who is flying along with head up and locked, sneaking up behind, getting as close as possible and pulling the trigger. Sure, the guns have to be boresighted but out in front someplace will do.
All of them say that you rarely see the guy who shoots you down. Deflection shots, those where you have to pull a lead, are rare and not often sucessful unless your plane is greatly superior to the other guy’s. There are a couple of reasons for this; equally matched planes can pull about the same number of g’s and pilots, likewise, can stand the same acceleration without blacking out. So, when the guy goes into his hard turn you simply can’t pull enough g’s to get a lead. Sustained “dogfight” type encounters are brief, a minute or three and invariably wind up in a Lufberry Turn usually resulting in a draw. Both of you are pulling max acceleration, in any plane, and the other guy is on the opposite side of the circle and you are looking almost straight “up” at him.
Most successful deflection shots, according to the interviews, are accidental such as in a melee where somebody suddenly appears, crossing in front of you and you pull the trigger.
I would think that good boresight is most important for ground strafing where you have time to get a bead on the target which is either stationary or moving slowly.
What’s the difference between “cannon” and simple “buwettes”? I had the idea as a kid that the “20 mic mic” actually exploded, but I can’t really imagine that being the case.
Actually, you are correct ** Cardinal ** . 20mm shells can contain an explosive charge, while most .50 Caliber bullets are simply jacketed lead.
There were still a bunch early on, but superseded rapidly by later models with wing-mounted guns, or replaced by later marques:
Navy
F2A Brewster Buffalo (Midway)
(The prototype F4F Wildcat and F4U Corsair both had guns that fired through the prop arc, but the production models were wing-only.
Army
P-35 Seversky (Philippines)
P-36 Curtiss (Pearl Harbor, etc.) Managed to shoot down some Zekes.
P-39D, P-400 Bell (Guadalcanal) 2-.50-cal in nose, 4-.30cal in wings.
P-40B Curtiss (Pearl Harbor, etc.) Later models had wing-only.
P-43 Republic (Chinese AF) Quickly obsoleted by P-47
A-36 North American (North Africa) Attack version of P-51 had 2-.50 cal under engine and 4-.50cal in wings.
DAMN YOU UNCASTUART! 
The hamsters ate my post where I listed the same planes as you. Once there´s a topic where I can show off and I´m so unlucky as to be beaten to post a reply :mad:
OK, cool down Ale… I still have something to defend my honour…
The SBD Dauntless had nose guns too.
The French inventor was a man named Roland Garros, on whom more information can be found here.
The main fault, and the reason that his plane was captured by the Germans, was that the vibrations from the bullets being deflected eventually adversely effected the engine of the plane forcing him to land behind enemy lines.
Anthony Fokker was brought to examine the captured plane, and was not impressed (seeing the inherent problem), but it got him to thinking about the synchronizer that he eventually invented.
Fokker, a Dutchman (and thus technically neutral), was asked to demonstrate his new invention but couldn’t bring himself to actually shoot down a plane. Oswald Boelcke instead was the first to give it a try. It was a resounding success, and gave the Germans an upper hand for quite a while.