Synchronisation

[spicmart]

Why wouldn't the American and British fighters not equipped with synchronized guns firing through the prop circle? I read that there were technical issues but apparently all other
big nations managed to solve that. The Russian fighters had only fuselage mounted guns and the Japanese partly.

 

[varsity07840]

American aircraft that saw combat with synchronized guns: SBD, TBD, TBF, F2A-3 P-35A, P-36, P-39, P-40B &C, P-43A, P-63, A-36A

 

[spicmart]

American aircraft that saw combat with synchronized guns: SBD, TBD, TBF, F2A-3 P-35A, P-36, P-39, P-40B &C, P-43A, P-63, A-36A

Oops... But the main late war fighters weren't.

 

[A.G. Williams]

Why wouldn't the American and British fighters not equipped with synchronized guns firing through the prop circle? I read that there were technical issues but apparently all other
big nations managed to solve that. The Russian fighters had only fuselage mounted guns and the Japanese partly.

Mainly, the introduction of multi-gun armament (6 or 8 MGs) which meant that most of the guns would have had to be mounted in the wings anyway, due to lack of space in the fuselage. Also, sync systems were an added cause of unreliability, as well as reducing the rate of fire. So it made sense to keep things simple and put all of the guns in the wings.

 

[glennasher]

It's a lot easier to shoot trap with a shotgun rather than a rifle.
Wing mounted guns gave a bit more leeway and didn't require quite as much precision in aiming. While the wing guns could be regulated to hit "more or less" in one small area, they usually weren't regulated that way, to make it easier to hit the opposing aircraft.
Then, add the factors noted above, less reliability for synchronised gun, and lower rates of fire, and wing guns just make sense.
Concentrated fire IS, of course, more effective, but it's only effective if you can HIT, if you can't hit, you got nuthin'.

 

[GrauGeist]

American aircraft that saw combat with synchronized guns: SBD, TBD, TBF, F2A-3 P-35A, P-36, P-39, P-40B &C, P-43A, P-63, A-36A

While it didn't see much in the way of aerial combat, the SOC was armed with a cowl-mounted .30 MG.

 

[Admiral Beez]

Why wouldn't the American and British fighters not equipped with synchronized guns firing through the prop circle? I read that there were technical issues but apparently all other big nations managed to solve that. The Russian fighters had only fuselage mounted guns and the Japanese partly.

Unlike the Japanese whose fighters were often armed with only two fuselage-mounted machine guns, the British went for eight guns. No point in having two of them synchronized to the propeller and six of them not.

Of course when they wanted to the Brits could mount synchronized guns as well as anyone else, with two of the Gloster Gladiator fighter's four machine guns being fuselage-mounted and thus in synchronization with the propeller. AIUI, the Boulton Paul Defiant's turret could fire straight forward safely through the propeller. Outside of fighters, the British had sychcronizsed machine guns on the Fairey Swordfish and Albacore, Vickers Vildebeest, etc.

 

[pbehn]

There is no free lunch, synchronised guns are generally forward of the CoG so create a CoG issue as ammunition is used, they have a reduced rate of fire and take up space. On a Spitfire or Hurricane they would probably have eaten into what little fuel they had to start with. 8 mgs in the Spitfire and Hurricane were based on taking down a bomber of the time with a two second burst. From the start of 1941 British preference was for 20mm cannon, the Spitfire disguises this because it retained 4x mgs for a long time. The Hurricane Whirlwind Typhoon Tempest and Mustang Mk1 all had cannon as did the Beaufighter and Mosquito.

 

[Admiral Beez]

From the start of 1941 British preference was for 20mm cannon, the Spitfire disguises this because it retained 4x mgs for a long time. The Hurricane Whirlwind Typhoon Tempest and Mustang Mk1 all had cannon as did the Beaufighter and Mosquito.

It's a good point on cannons. I do not believe the British ever synchronized a cannon. Did anyone have cannons synchronized with the propeller?

EDIT, the Russians did, Synchronization gear - Wikipedia

 

[tomo pauk]

It's a good point on cannons. I do not believe the British ever synchronized a cannon. Did anyone have cannons synchronized with the propeller?

EDIT, the Russians did, Synchronization gear - Wikipedia

So did the Germans, eg. on Fw 190 with MG 151/20 in the wing roots. Japanese Ho-5 could also fire synchronized.

 

[GrauGeist]

The Defiant's turret had a limited angle of depression when firing foreward, so as not to hit the prop.

Also, the early Hurricane did have MGs firing through the propeller arc (see attached - dated 1938), but that was soon remedied.

 

[tomo pauk]

The Defiant's turret had a limited angle of depression when firing foreward, so as not to hit the prop.

Also, the early Hurricane did have MGs firing through the propeller arc (see attached - dated 1938), but that was soon remedied.

Dave - is that a factory drawing?

 

[PAT303]

From the start of 1941 British preference was for 20mm cannon, the Spitfire disguises this because it retained 4x mgs for a long time

The RAF stayed with the four .303's, two loaded with AP and two with incendiary because they were still very effective guns and gave a shotgun effect on the target, it wasn't until the Mk14 gunsight allowing for more precise aim came into being that they changed to two .50 browning's. For the average pilot wing mounted guns with their inherent greater pattern made sense over tightly packed centerline guns.

 

[pbehn]

The RAF stayed with the four .303's, two loaded with AP and two with incendiary because they were still very effective guns and gave a shotgun effect on the target, it wasn't until the Mk14 gunsight allowing for more precise aim came into being that they changed to two .50 browning's. For the average pilot wing mounted guns with their inherent greater pattern made sense over tightly packed centerline guns.

There were all sorts of reasons, others were the extra weight affecting performance at altitude and heating two cannon in a thin wing at altitude.

 

[GrauGeist]

Dave - is that a factory drawing?

To the best of my knowledge, Tomo.
Within a year of that date, the Hurri would go through several more changes, including the fitment of a three-bladed prop.

 

[nuuumannn]

The Defiant's turret had a limited angle of depression when firing foreward, so as not to hit the prop.

The Defiant could actually shoot of its own prop since it didn't have interruptor gear and the guns could be lowered to zero degree elevation facing forward, as well as a switch within the turret itself that the gunner could switch over firing to the pilot, that is, if the pilot was so inclined to want to shoot off his own propeller...

 

[Koopernic]

Why wouldn't the American and British fighters not equipped with synchronized guns firing through the prop circle? I read that there were technical issues but apparently all other
big nations managed to solve that. The Russian fighters had only fuselage mounted guns and the Japanese partly.

Reginald Mitchell, who designed the Spitfire argued that cowling guns and even motor guns invariably thicken the fuselage and thereby increase drag.

The US did us ultrasonic mechanism to synchronise 0.5 guns. I think maintenance was an issue.

The Germans simply perfected their mechanisms. They used electrically ignited primers to ignite the propellants instead of percussion which greatly simplified the syncrhisation issues.

 

[GrauGeist]

The Defiant could actually shoot of its own prop since it didn't have interruptor gear and the guns could be lowered to zero degree elevation facing forward, as well as a switch within the turret itself that the gunner could switch over firing to the pilot, that is, if the pilot was so inclined to want to shoot off his own propeller...

Seriously, the turret had a limit to it's foreward depression.

The gunner could rotate the turret directly forward and transfer firing control of the guns to the pilot, with the guns firing along each side of the cockpit canopy; this was rarely done as the turret's minimum forward elevation was 19°
(Colin Sinnot - The RAF and Aircraft Design 1935-1939)

Plus:

The principal armament of the aircraft is its powered dorsal turret, equipped with four Browning machine guns.
The Brownings were electrically fired and insulated cut-off points in the turret ring prevented the guns firing when they were pointing at the propeller disc or tailplane.
(Michael Bowyer - Aircraft Profile No. 117: The Boulton-Paul Defiant)

 

[nuuumannn]

Seriously, the turret had a limit to it's foreward depression.

No, the guns could be lowered to face directly forward, but I guess he couldn't fire them because of the electrical cut-offs (missed that), which meant they wouldn't fire until they were angled at 19 degrees.

http://www.tangmere-museum.org.uk/wp-content/uploads/2012/04/Defiant-2.jpg

https://upload.wikimedia.org/wikipedia/commons/c/c9/15_Boulton_Paul_Defiant_N3377_(15812158966).jpg

Dangit, I thought it was funny that the pilots had the option of shooting through their own prop Roland Garros style!

 

[Shortround6]

A problem with synchronization is lock time + barrel time.

Lock time is from when the signal to fire the gun is sent to when the primer initiates combustion. You may find other definitions. Like the time from sear release to firing pin striking the primer. This depends on the weight of the firing pin, the length of the firing pin travel and the strength of the firing pin spring. It also depends on lubrication (cold oil slows it down.

Barrel time is from when the primer initiates combustion to the projectile leaving the barrel. This can be more variable than lock time as not all primers burn at the same intensity or speed. Not all powder charges are distributed uniformly in the cases so flame propagation varies from one shot to the next. Generally the larger the case/charge the bigger this problem is.
The speed of the flame in the solid gunpowder may be fairly uniform but the air spaces between the powder granules can vary a lot and the amount of flame from the primer varies leading to varying amounts of the powder being ignited during the primers burn.
This has not a lot to do with the actual velocity of the projectile.

Lock time is why the Oerlikon guns were never synchronized. For them when you released the sear you were not releasing the firing pin, you were releasing the breech block to start moving forward, stripping a round out of the feed mechanism, chambering it and firing as the bolt was still moving forward. There was simply too much variation to successfully time the exit of the projectile from the barrel to coincide with the absence of a prop blade in front of it.

The German electric primers took most of the lock time out of the problem and were a lot less temperature sensitive in that the electrical contacts didn't really vary the results with temperature (no freezing)