Question on M.S.406

[elbmc1969]

All three of these were 2-pitch, manually controlled props?

Came across this in a SHDDA listing: Moteurs Hispano-Suiza 12Y, réducteur pour hélice à pas constants et circulation d'huile : plans.
Dated 1937-1938.

So, a constant speed prop was well under development before 1940 for the 12Y (not just the 12Z for the D.520). Don't know if it couldn't be retrofitted to the M.S.406 or if prop production was just running too far behind to devote any to the 406s.

MINISTERE DE LA DEFENSE SERVICE HISTORIQUE DE LA DEFENSE Centre des archives de l'armement et du personnel civil SERIE 2 K 3 1085 2K3 1 à 9 Archives de l'établissement d'essais de moteurs du service technique de l'aéronautique d'Orléans-Bricy 1926-1949 Inventaire n° 1085 2K3 Version de novembre 2015 Par Sylvain Lebreton Chef du département des archives de l'armement Châtellerault 2015

Document 1085 2K3 3

[Yeah, another dumb error with me talking about the 12Z ...]

 

[Greyman]

For what it's worth, recorded rates of fire from Hispano guns in firing trials. Various Spitfires, various front mounting units.

Recorded rates of fire of Hispano Mk.II cannon:
600, 610, 625, 535, 595, 665, 594, 530, 660, 660, 530

I got a chuckle when I did the math: average rate of fire? 600.36 rounds per minute

Recorded rates of fire of Hispano M.2 cannon:
660 & 680

Recorded rates of fire of Hispano Mk.V cannon:
720, 750, 725, 750, 750, 690, 730, 765

 

[elbmc1969]

For what it's worth, recorded rates of fire from Hispano guns in firing trials. Various Spitfires, various front mounting units.

Regardless, the D.520 and VG-33 were not significantly better armed than the M.S.406. The Germans, of course, abandoned the twin MG-FF/Ms despite the destructive Minengeschoss shells and went with a hub-mounted MG151/20 (after briefly using the MG-FF/M in the propeller hub. This certainly indicates that the M.S.406's armament wasn't far off the mark. Certainly, it would have been outclassed by early 1941, but it was fine for the May-June campaign.

 

[tomo pauk]

Regardless, the D.520 and VG-33 were not significantly better armed than the M.S.406. The Germans, of course, abandoned the twin MG-FF/Ms despite the destructive Minengeschoss shells and went with a hub-mounted MG151/20 (after briefly using the MG-FF/M in the propeller hub. This certainly indicates that the M.S.406's armament wasn't far off the mark. Certainly, it would have been outclassed by early 1941, but it was fine for the May-June campaign.

Replacement of two MG FFMs by single MG 151/20 was not universally welcomed in Luftwaffe. Even though MG 151/20 was a very good wepon. Galland insisted and got two MG FFMs for his '109F special', as well as replacement of two MG 17s with two MG 131s.
We can also recall that MG FFM was used aboard Fw 190s by some two years.
But, at any rate, having a working cannon in a fighter in 1940 was certainly a plus; problem the MS.406 had was low performance, rather than a perceived lack of firepower.

 

[Shortround6]

The MG 151 cannon in the 109's propeller, after they finally (after several years) got the MG/FF to work in that position with an acceptable level of reliability, had several advantages over the MG/FF.
1. much greater ammo capacity.
2. higher rate of fire, around 700rom vs 500rpm (at best?)
3, higher velocity making deflection shooting easier. (the MG 151/15 was the champ but the MG 151/20 fired shells (non mine) 18% faster than the MG/FF with a corresponding reduction in flight time).

As far as the Ms 406 argument goes. 60 rounds is 60 rounds. you have 60 rounds of 20mm ammo. the 109E-3 had 110-120 rounds depending on how full the drums were even if they weren't mine shells.
1 or 1.5 seconds extra firing time for the slower firing cannon isn't that big a deal. How many pilots succeeded using their last 1-2 seconds of ammo? Not saying that a few didn't get a kill that way but it wasn't a huge factor.

 

[elbmc1969]

To be clear, I was only responding to the assertion that the M.S.406 was underarmed. The accusation certainly doesn't make sense in comparison to the D.520, which only added two more MAC-34s.

We can also recall that MG FFM was used aboard Fw 190s by some two years.

For space reasons, not because it was a desirable weapon. Mixing the ballistics of three weapons was really, really sub-optimal.

In any case, a side issue, and you're definitely right that having a cannon was better than not.

The MG 151 cannon in the 109's propeller, after they finally (after several years) got the MG/FF to work in that position with an acceptable level of reliability, had several advantages over the MG/FF.
1. much greater ammo capacity.
2. higher rate of fire, around 700rom vs 500rpm (at best?)
3, higher velocity making deflection shooting easier. (the MG 151/15 was the champ but the MG 151/20 fired shells (non mine) 18% faster than the MG/FF with a corresponding reduction in flight time).

Yep, yep, yep, and yep. No arguments there, even if it doesn't directly relate to the question of the Bf109E-3 and early -4's armament compared to the M.S.406.

I suspect that getting rid of the wing guns improved roll rate, along with other things. And dang, the increase in ammo capacity made up for everything.

As far as the Ms 406 argument goes. 60 rounds is 60 rounds. you have 60 rounds of 20mm ammo. the 109E-3 had 110-120 rounds depending on how full the drums were even if they weren't mine shells.
1 or 1.5 seconds extra firing time for the slower firing cannon isn't that big a deal. How many pilots succeeded using their last 1-2 seconds of ammo? Not saying that a few didn't get a kill that way but it wasn't a huge factor.

Particularly the fire before that last burst is less effective than the competition. That said, at least if you can sight in with the MGs, you can get a lot more out of that last burst than you otherwise would.

From Lundstrom's The First Team, the Wildcat pilots seem to have done a lot of damage with their final bursts, often because they were finishing off damaged aircraft or were firing from shorter range than before. There were probably other factors. OTOH, if you can just hit and kill the target with your second burst, you're better off all around.

Incidentally, I see that the D.520 had switches that were apparently selectors for the cannon and each wing's machine guns. (The could be for charging, I suppose.) Anyone know if this is correct? Did the M.S.406 have selectors?

 

[tomo pauk]

For space reasons, not because it was a desirable weapon. Mixing the ballistics of three weapons was really, really sub-optimal.

In any case, a side issue, and you're definitely right that having a cannon was better than not.

I agree that mixing 3 wepons with different ballistics was sub optimal, and certainly having extra firepower is a good thing (provided one does not over-do it). OTOH, ballistics of MG 17 and MG FFM were not that different.
Space reasons did not prevented instalaltion of MG 151/20 inn outer wing position (they were installed there from Fw 190A-6 and on in factory, even the MK 108 was), but probably it was the case of not having enough of MG 151s.

 

[Shortround6]

I am afraid the whole using machine guns to sight in for the cannon thing is something of a myth.
Not saying it wasn't put forth as a technique at the time or tried, just that it isn't going to work very well.
You have the different ballistics thing going on, that is different times of flight to the same distance needing different amounts of lead. You also have the problem of any tracer or impact system, it tells you where you should have been aiming around a 1/2 second ago or so (depending on range) .

 

[elbmc1969]

I agree that mixing 3 wepons with different ballistics was sub optimal, and certainly having extra firepower is a good thing (provided one does not over-do it). OTOH, ballistics of MG 17 and MG FFM were not that different.

Not talking about that so much as the ballistic differences between the MG FFM and the MG 151/20.

Space reasons did not prevented instalaltion of MG 151/20 inn outer wing position (they were installed there from Fw 190A-6 and on in factory, even the MK 108 was), but probably it was the case of not having enough of MG 151s.

Sure, but engineering solutions evolve over time, and what people are willing to put up with evolves over time. The MG 151/20s in the outer wings just took more engineering effort, and the engineers may not have been able to come up with an acceptable solution in the time available. They had to get the 190 into flight testing and then into production. Then you go back an improve things after the initial release to production. I've seen this with all sorts of engineering.

 

[tomo pauk]

Not talking about that so much as the ballistic differences between the MG FFM and the MG 151/20.

Ballistic differences were similar when in is about MG 131 and MG 151/20, a set-up often found on German fighters. Or MK 108 vs. MG 151/20 or MG 131, again a frequent occurance.

Sure, but engineering solutions evolve over time, and what people are willing to put up with evolves over time. The MG 151/20s in the outer wings just took more engineering effort, and the engineers may not have been able to come up with an acceptable solution in the time available. They had to get the 190 into flight testing and then into production. Then you go back an improve things after the initial release to production. I've seen this with all sorts of engineering.

The engineers were replacing one cannon with another, admitedly longer (that goes mostly into the air anyway) and heavier, and again with a bigger one (MK 108). They are not trying to stick a jet engine on it, or a swept wing (although there were proposals about those, too).

 

[Shortround6]

Simply not true compared to its contemporaries in the May-June campaign. It was facing Bf109E-3s and -4s, which had two MG-17s in the nose (synchronized) and two MG-FFs in the wings. Importantly, these were not MG-FF/Ms, so no Minengeschoss. That makes a huge difference in destructiveness. The H.S.404 (and even the HS-9 in the early production M.S.406s) had a much higher rate of fire and muzzle velocity than the MG-FF, which meant that it hit much harder. The French 20mm cannons and the MG-FF were all drum-fed with 60 rounds (often reduced to 55 rounds in service). The MG-FFs had more total firing time, but that was because of their low rate of fire, so it's not an advantage

Unfortunately the German MG/FF was used for only a short time and tends to get overlooked or lumped in the MG/ FFM. The Mine shell seems to hog all the attention/glory.

The MG/FF was supposed to use a 134 gram projectile (4-6 grams heavier than a Hispano Projectile) at 600M/S velocity. This is about 17-19 grams heavier than the non mine shells fired by the MG/FF and MG 151/20. It also had a slightly higher velocity but only about 15M/S worth compared to the MG/FFM. It does mean the old MG/FF cannon had about 20% more kinetic energy at the Muzzle than the MG/FFM firing non mine shells.
Now a big difference could be that the old shells may have had up to 10 grams of HE per shell, there is no real reason to think they had much less as most other shells of their size/weight and type held about 10 grams. The lighter 115-117 gram shells used in the MG/FFM did hold much less HE, but mostly because they devoted a fair amount of internal space to the tracer element. I don't believe they ever made a mine shell (at least in 20mm ) with tracer.
The MG/FF may have been fairly comparable to the Hispano as far as HE destructiveness goes on a shell for shell basis. The rate of fire was a nominal 520-540 rpm but actual rate of fire may have been a bit lower. At 500rpm a 55 round drum will last 6.6 seconds. A 700 rpm Hispano will go through 60 rounds in 5.4 seconds.
One could play the statistical game and say the Germans have 22% more firing time but in the real world 1 second isn't that big a deal, it certainly isn't enough for another firing pass for 99.99% of the pilots that flew in WW II.
How good (or bad) the fuses were on the French and German ammo at this time I have no idea. The British shortly after the Battle of France (or the BoB) had so much trouble with their 20mm HS shells exploding on impact (fuselage or wing skin) and not getting inside before detonating that they took to mixing in inert training projectiles (they called them ball rounds) in order to insure that some projectiles would get deep into an aircraft and cause damage there. Later they got improved fuses that detonated the shells several feet inside the aircraft.

 

[Greyman]

How good (or bad) the fuses were on the French and German ammo at this time I have no idea. The British shortly after the Battle of France (or the BoB) had so much trouble with their 20mm HS shells exploding on impact (fuselage or wing skin) and not getting inside before detonating that they took to mixing in inert training projectiles (they called them ball rounds) in order to insure that some projectiles would get deep into an aircraft and cause damage there. Later they got improved fuses that detonated the shells several feet inside the aircraft.

The early British fuzes (No.252) followed the design of French fuzes very closely, so I imagine they suffered the same issue.

On testing captured examples, early German 20-mm fuzes were criticized by the British as being as bad as their own with respect to detonating too early. This was in 1940, I'm not sure how things progressed from there. I know for sure the Luftwaffe, like the British, updated their fuzes several times.

 

[Shortround6]

Thank you. Perhaps the fuses were intended to function on fabric covered airplanes (or on both types of skinning) as there were still considerable numbers of fabric covered (or partially) aircraft in the late 30s?

 

[Greyman]

I haven't seen that specifically stated but I'd say it's a good bet. I've read evaluations of cannons as late as 1937 (25mm Hotchkiss) where the assessors made specific notes on how the rounds functioned on fabric.

 

[ThomasP]

I once read a write-up on the HS404 in UK service in WWII. It was quite clear about the different ROF. The 650-660 rpm was when the gun was fed from a 60-round drum magazine. The 600 rpm and less was when when using a belt feed system. Even when using a servo powered feed assist mechanism the ROF dropped by 10%-20% depending on the weight of the belt and the ergonomics of the installation. The write-up also stated that the belt-fed installations in the P-38E had a similar reduction in ROF compared to the original drum-fed installation in the P-38 and the standard installations in the P-400 and P-39D-1.

 

[Glider]

All I can add is that the manual for the RAF 20mm mk II quotes it as having a rate of fire of 570 - 620 rpm