Synchronized MG fire through propeller arc.

[windhund116]

Did the Germans and Japanese use a similar device to synchronize their MG gun fire through the prop arc? Was it a mechanical device (like a cam) or an electrical device (like a distributor)? What about similar Allied applications?

Are there any good references for these devices? Thanks!

 

[A.G. Williams]

Did the Germans and Japanese use a similar device to synchronize their MG gun fire through the prop arc? Was it a mechanical device (like a cam) or an electrical device (like a distributor)? What about similar Allied applications?

Are there any good references for these devices? Thanks!

This is a general survey of synchronisation in both World Wars: http://quarryhs.co.uk/Synchro.pdf

The WW2 Luftwaffe used two different kinds of synchronisation: the 7.92 mm MG 17 used percussion priming, but this was electrically controlled; when the pilot pressed the firing button, the synch system decided when it was safe to fire, and sent an electrical signal to the gun, which released the firing pin.

The 13 mm MG 131, plus the 15 mm and 20 mm MG 151E used electrical priming: it worked like the percussion one above, except that the electrical signal did not release a firing pin, it sent an electric pulse through the primer which fired it instantly. This was the best synchro system in service, providing the shortest lock times and therefore the highest rates of fire.

I don't know about the Japanese system but I think it was a mechanical WW1-era type. Certainly the rate of fire of the Browning-pattern 12.7 mm Ho-103 and 20 mm Ho-5 was much reduced in synchro installations.

 

[tomo pauk]

<snip>

Cheers, Tony

 

[windhund116]

This is a general survey of synchronisation in both World Wars: http://quarryhs.co.uk/Synchro.pdf

The WW2 Luftwaffe used two different kinds of synchronisation: the 7.92 mm MG 17 used percussion priming, but this was electrically controlled; when the pilot pressed the firing button, the synch system decided when it was safe to fire, and sent an electrical signal to the gun, which released the firing pin.

The 13 mm MG 131, plus the 15 mm and 20 mm MG 151E used electrical priming: it worked like the percussion one above, except that the electrical signal did not release a firing pin, it sent an electric pulse through the primer which fired it instantly. This was the best synchro system in service, providing the shortest lock times and therefore the highest rates of fire.

I don't know about the Japanese system but I think it was a mechanical WW1-era type. Certainly the rate of fire of the Browning-pattern 12.7 mm Ho-103 and 20 mm Ho-5 was much reduced in synchro installations.

Thanks! Electrical timing would also seems to be less likely to wear out and cause malfunctions --- compared to 100% mechanical (cams, etc).

Also, I have read that many of the Japanese aces (both Navy and Army) liked the cowl gun over the wing gun placement. Even, with the slower rate of fire, due to the synchronizing mechanism.

 

[GrauGeist]

Many pilots favored MGs that were fuselage mounted because weapons firing from the aircraft's centerline weren't limited to "convergence" like wing mounted weapons were.

 

[windhund116]

Many pilots favored MGs that were fuselage mounted because weapons firing from the aircraft's centerline weren't limited to "convergence" like wing mounted weapons were.

Does wing convergence add to the difficulty in a deflection shot?

Thannks!

 

[GrauGeist]

Convergence did factor considerably.

The MGs (or cannon) were set to converge at a certain distance and if you were short or long on your target, you weren't landing hits to full effect.

Aircraft like the P-38 or Me262, were going to land a solid pattern from all guns because it's MGs weren't limited to a short/long factor. Basically, what was in the reticle was going to get the full deal.

Also, having 4, 6 or 8 MGs on the wings provided a considerable amount of firepower that cowl-mounted weapons couldn't match, but unless the target was in the convergence zone or on the same "plane" as your aircraft, then the you'll only land some hits.
In other words, if your banking on your target and they are close to level to the horizon a bit out side of your convergence, your rounds will pass above and below them unlike a centerline setup.

 

[windhund116]

Convergence did factor considerably.

The MGs (or cannon) were set to converge at a certain distance and if you were short or long on your target, you weren't landing hits to full effect.

Aircraft like the P-38 or Me262, were going to land a solid pattern from all guns because it's MGs weren't limited to a short/long factor. Basically, what was in the reticle was going to get the full deal.

Also, having 4, 6 or 8 MGs on the wings provided a considerable amount of firepower that cowl-mounted weapons couldn't match, but unless the target was in the convergence zone or on the same "plane" as your aircraft, then the you'll only land some hits.
In other words, if your banking on your target and they are close to level to the horizon a bit out side of your convergence, your rounds will pass above and below them unlike a centerline setup.

Thanks. Seems the deflection shot, at speed and G's, is quite an art.

 

[A.G. Williams]

A few comments:

At the start of the Pacific war, the Japanese Navy pilots had another reason for favouring their cowling -mounted MGs rather than the wing-mounted 20mm cannon: the Type 99-1 cannon were Oerlikon FF which had a muzzle velocity of only 600 m/s, much lower than the MGs. So it was more difficult to hit the target with the cannon, due to the slow time of flight and steeper trajectory. It also meant that the cannon and MG fire could only be set to converge at one point. Furthermore, the drum magazines for the cannon only held 60 rounds, so they preferred to preserve the cannon ammo, to use only when they were unlikely to miss.

Later on, the IJN changed to the Type 99-2 cannon which was the Oerlikon FFL; this raised the MV to 750 m/s which was about the same as their MGs, so they could use the MGs for "sighting", and fire the cannon when the MGs were hitting. Also, they later developed first a 100-round drum and then a belt feed for the cannon. Incidentally, unlike the Army's Browning-pattern Ho-103 and Ho-5, the Type 99s could not be synchronised (which also applied to the Allied Hispano).

About convergence distances: the US planes with six (or eight) wing-mounted .50s often spread them e.g. the inner pair of guns might be set to converge at 100m, the middle pair at 200m, the outer pair at 300-400m, thereby providing a reasonable density of fire at all ranges. Conversely, the RAF found the Hispano to be so destructive that they later deliberately spread the fire of 4-cannon layouts, to improve the chance of a hit (the problem with concentrated fire being that most pilots did not hit with all guns, they missed with all of them).

The chances of a hit in deflection shooting was improved considerably with the introduction of gyro sights, although the Luftwaffe seemed to have problems getting these to work, the Allies relied heavily on them from 1944 on.

Incidentally, I have read that the Luftwaffe reckoned that a centre-line gun (e.g. mounted on the engine to fire through the propeller hub) was worth about 1.5x as much as the same gun out in the wing, because of the improved hit probability.

 

[macharvard]

Hey, Tony. Welcome to the forum. It's been a long time since the days of allaboutwarfare!

Doug

 

[A.G. Williams]

Hey, Tony. Welcome to the forum. It's been a long time since the days of allaboutwarfare!

Doug

Hi Doug, I don't even recall what that was...

 

[fastmongrel]

The only WWII British fighter that used synchronization was the Gladiator. It used a Constantinesco Hydraulic system that utilised supersonic wave pulses to fire the gun.
George Constantinescu - Wikipedia

 

[A.G. Williams]

The only WWII British fighter that used synchronization was the Gladiator. It used a Constantinesco Hydraulic system that utilised supersonic wave pulses to fire the gun.

Your description is correct, but the use of sound pulses rather than hydraulic pressure to send the firing signal meant that the CC system was called "hydrosonic".

 

[GrauGeist]

The Hurricane *almost* had two cowl mounted MGs (plus one MG in each wing) but was changed to all wing mounted weapons before it reached production.

 

[windhund116]

The Hurricane *almost* had two cowl mounted MGs (plus one MG in each wing) but was changed to all wing mounted weapons before it reached production.

Was this because of the layout of the non-inverted V-12 which many British fighters used? Unlike the Germans, that used a lot of inverted V-12 design and maybe had more room for MGs in the cowling?

 

[GrauGeist]

Was this because of the layout of the non-inverted V-12 which many British fighters used? Unlike the Germans, that used a lot of inverted V-12 design and maybe had more room for MGs in the cowling?

The original design for the Hurricane called for the fitment of the Goshawk engine, which was changed to the PV-12 (early Merlin), both of which were V-12s.
I don't recall exactly were they intended to fit the MGs, but I suspect they may have been installed in the "cheek" position of the lower cowling, much like the early Mustang/P-51/A-36 types had, which as you may recall, had the Allison V-12.

 

[Greyman]

They were beside the pilot, next to his thighs.

 

[windhund116]

Always thought it was interesting how the Japanese Kawasaki Hien Ki-61II KAI-a variant and the Ki-100 had armament of two Ho-5, 20mm cannons in the nose --- firing through the propeller. And two 50-caliber Ho-103 MGs in the wings. Not sure of any other fighters, in WW2 with this setup. Maybe the cannons in nose was a suggestion put forth, by their combat aces?

 

[fastmongrel]

Hurricane prototype

It's not easy to see the mounted machine gun but it's at the level of the engine crankcase just to the left. You can see the perforated barrel jacket.

 

[taly01]

Japanese Kawasaki Hien Ki-61II KAI-a variant and the Ki-100 had armament of two Ho-5, 20mm cannons in the nose --- firing through the propeller.

As the Ki-61 used a DB601 clone it could have an engine cannon like Me109 did, but neither did the Italian Macchi 202/205 DB601 engine fighters. A single 20mm centreline engine cannon seems better than twin synchronised slow cowl 20mm and lighter.