The gun synchronizer used in P-39 and P-63 was a different type to those used in other American planes. It’s been a while since I read about it, but the details should be somewhere. Anyway those other types didn’t have as significant fire rate drop. I don’t think it was said why Bell used them. Perhaps the propeller axel took space from wrong spot or something.
About Japanese gun synchronizers I have never seen any real data. One book says something like “as low as 400rpm”, without noting where it is from. Also it’s about the lowest they think it could get. Unfortunately that 400rpm is taken as an absolute truth by some as it’s also in Wikipedia.
If the drop was so significant, there would likely be clear mentions about it in Japanese documents, pilot stories and US reports. In one American report there is a short mention about Ki-84s synchronizer. It was something along the lines “excellent” or “effective”. Nothing about issues. All IJA single engine fighters fired through propeller arc, so it would have made sense for them to develop very good synchronizers.
Synchronizers are truly the biggest mystery of all aircraft systems 🤔
Practically no real data available.
I think the general consensus is that synchronizers reduced RoF by roughly 25%.
While my personal biases view is that the electrically fired MG 151 only was slowed by 5-10%.
Christian Koll writes in his book that the B-20 cannon had a RoF of 750-850 RPM and 600 while synchronized.
I don’t think it would be any different with the ShVAK.
Ki-44 is very powerful but the fucked up rudder that likes to swing out a lot during dives and high speeds is enough to make me dislike it. Although “weaker”, I prefer the Ki-61’s much easier flying performance.
I’d like to share a source that offers a detailed explanation of the firing rate of propeller-synchronized machine guns. The original publication is a German aviation technology journal, which describes how the Rheinmetall 7.9mm machine gun was synchronized with a two-bladed propeller. Please note that my interpretation might not be entirely accurate, as my knowledge of German is limited, and some of the material is based on old Japanese text and technical terminology.
According to the source, the firing rate of a propeller-synchronized machine gun is mainly determined by two factors: trigger actuation time and cam delay. In wire-type synchronization gear systems, the trigger actuation time is approximately 0.017 seconds. This delay helps explain why synchronized machine guns often experience about a 25% reduction in their rate of fire.
A machine gun with a firing rate of 1200 rounds per minute fires one round every 0.05 seconds. However, with a synchronization gear that introduces a 0.017-second delay, one round can be fired every 0.067 seconds, reducing the rate to 895 rounds per minute.
The cam delay explains why the rate of fire varies depending on the propeller’s rotational speed. A synchronized machine gun set to fire at 900 rounds per minute achieves peak efficiency when the propeller rotates at 450, 900, 1350, 1800, or 2250 revolutions per minute.
Source: “Journal of the Society of Ordnance and Explosives.” Published by the Internal Section of the Department of Ordnance and the Society of Ordnance and Explosives, Faculty of Engineering, Tokyo Imperial University. 1938. pp. 625-626
Original source: Luftwissen, Bd. 4 (1937), Nr. 12.
From what I can tell, this is for a machine gun that can fire at 1200 rounds per minute.
But because of that “Steuerungszeit” which introduces a delay to fire the gun the maximum RoF can only be 900 RPM.
The delay comes from the fact that the gun is basically fired in single shots and the delay is the result of the time it takes from wanting to fire the gun to mechanically firing the gun.
Then there’s the “Wartezeit”, which decreases at higher RPM of the prop.
That’s because the slower the prop, the longer it stays in that danger zone, where the MG might hit the the prop.
If the prop is spinning at 900 RPM and the gun is going to fire at 900 RPM, once the gun is able to fire, it’s now synced with the prop and as long as there is no change to either system, the gun can fire without any additional delay, resulting in the highest possible RoF. Same for 450, 1350, 1800, 2250.
Which indicates that his was for a two bladed prop.
An electrical system and ammunition probably allows to greatly reduce the Steuerungszeit to fire the gun.
Thus reducing the maximum RoF only slightly.
No, to 900, because the gun isn’t firing full auto but basically single shots.
So instead of the mechanism running at full speed, every trigger pull is activated by the the synchronizer system which induces a short delay and prevents the gun from firing at it’s full RPM.
Well, if the prop RPM matches the firing rate of the gun, it can always fire without delay.
But slight changes and you are back of having short firing pauses inbetween the shots.
So the 900 RPM will never be reached practically.
The best way to increase the RoF would be to reduce the Steuerungszeit, as the delay is very short when the prob spins at high RPM and only has a minor effect on the actual RoF.
Ye I agree with that. 400 RPM would be the lowest possible.
One thing to note is that Japan used 30% safety margin for the mechanically synchronized nose cannons.
Ki-43-I with its 2 blade props would have higher rate. Ki-43-II & Ki-43-III would be having a lower fire rate due to the 3 blade props. Ki-84 would be the lowest firing with its Ho-103.
One thing about them is that the nose mounted army cannons use HE, so they had to put extra measures, like the engine armor on Ki-61-I tei.
What is considered is that Ho-103 in this game has the constant 900RPM regardless of the installation, no way it’s right. And the whopping 950 RPM for Ho-5, literally double that of nose mounted Ho-5 in 4 bladed configuration.
By using Logitech G hub. I recently tried modelling the correct fire rate for the guns. By putting 10 milliseconds push-pull delay and a variable span between the cycle.
Ki-43-I with 700RPM, Ki-43-II with 600RPM, Ki-84 with 400RPM seemed reasonable to me. Though it’s based on my broad guessing.
Type 97 7.7mm machine guns on naval aircraft are also stated to have a rate of around 600 - 700RPM.
Despite the non-constant fire rate, having that much variance on the fire rate means it’s actually affected by the propeller’s condition more than the inconsistency. Firing 1000 rounds and the luck would be almost certainly negated, so the cause for that 100RPM difference is the props. Not specifically the number of the blades but the revolution per minute.
About P-39, yeah it’s a total exception from any other installation methods.
I read somewhere that prototype hurricane used hydro… what is that, sonic pulse thing…? To sync the guns. That’s pretty cool. Mg151 and Mg131 have the Electrical primer for the ammo, and most other guns of German heritage used Electric signals to time the firing. So they are less affected by the mechanical delay per shot. That’s why Mg131 still has the high fire rate in the cowl mounted configuration, and MG 151 is able to be fired through propellers even though they are mounted in the wing roots. This is to just inform the players visiting here, not trying to correct anyone. I think having these things modelled in this game would be pretty cool. Though the gun firing sounds are specific to that fire rate of the guns and they can’t really be optimized for different fire rate, since all the “Loop” audio files are in the length of that specific time span between each firing. M4 37mm cannons and alike use singular file for both single fire and automatic, and these sounds play fine in automatic firing, so all guns with variable fire rate can be formatted that way. If they are to make a change, that is.
Japanese 50 cals and 20mm utilize HE rounds of high filler contents, so that even for 50 cals they needed extra safety margin with the already aging mechanical synchronization system. That’s what I’m guessing as the explanation for such low fire rate in the nose.
Aw shucks, it’s really weird that others can’t see the pre-edited post. I just changed the line “can’t optimized” to “can’t be optimized” since that’s the correct way of saying things. That’s all.
The following three types of HE bullets were used in the Ho-103
Italian-made HE rounds
Ma-102 (made in Japan, without fuse)
Ma-103 (made in Japan, with fuse)
Ma 103 was already in production in 1941 and Ma 102 in 1942. Therefore, it is almost certainly incorrect to say that Ma 102 was put into service in 1944.
Incidentally, the Ma 103 seems to have changed from a mechanical fuse to an air fuse around 1944, so there is a strong possibility that you are confusing that information.
The Ma 102 has 2.70 g of explosive and 1.05 g of incendiary.
The Ma 103 has 0.5 g of explosive and 1.0 g of incendiary.
Both are based on primary Japanese sources.
postscript
There seems to have been a translation error, which has been corrected.
Ma-102 is 50:50 PETN/RDX and Ma-103 is RDX.
I could not find any Japanese documents, perhaps they were disposed of, but they are clear from the U.S. military survey data.
