Large gun Me 109

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Z

Zmauky

Airman 1st Class
120
59
Jul 15, 2007
We all know about the Yak-9T and K where the cockpit and pilot were moved back approx. 0.4 m to install the 37/45 mm gun.


And the Japanese example would be the Ki-61-II where the engine was moved forward so that they could replace the 12.7mm with 20mm guns.


Ultimately, it wasn't (too big) problem for the Czechoslovaks and the Spaniards to rearrange the wing structure and insert the MG 13.1 / 20 mm Hispano into the wings themselves (not the underhang nacelles).


Would a heavier and much more specialized Me 109 with, say, 1x37 mm in the fuselage and 2x MG 131 in the wings or 5x20 mm (3x fuselage + 2x wings) be a viable bomber destroyer in 1942-1944?
And would such a thing be constructively feasible at all?
 
Zmauky said:
Would a heavier and much more specialized Me 109 with, say, 1x37 mm in the fuselage and 2x MG 131 in the wings or 5x20 mm (3x fuselage + 2x wings) be a viable bomber destroyer in 1942-1944?
And would such a thing be constructively feasible at all?
Click to expand...
What kind of 37mm are you suggesting?
 
Actually I didn't really think about the details or play with the 3d models, I thought more about the concept. But if a barrel of bk 37 (ie flak 36) fits in the DB 605, it's ideal, but also the 30 mm MK 103 is already a pretty big *** gun that we know goes through.
 
Well you can already see how a Bf109 with engine cannon required the breach area to come into the cockpit:



Let's do a quick comparison:

GunMG 151/20MK 108 cannonBordkanone 3,7
Calibre20mm30mm37mm
Typical Gun Length1.766 m1.057 m3.75 m
Typical Gun Weight42.7 kg58 kg295 kg
ApplicationsBf-109GBf-109GJu-87G

Now while these are obviously just taking existing data endnote allowing for any optimisation, I still think it shows that trying to put a typical German wartime 37mm cannon into the Bf-109 would be challenging in terms of gun size and weight without some sort of serious engineering.
 
Zmauky said:
And would such a thing be constructively feasible at all
Click to expand...
Nope.
Not and have much 109 left.



Please note that the feed tray will hold up to 12 rounds. Each cartridge case is (not including projectile) is 263mm long and that is 118mm longer than the cartridge case for a US M4 gun used in the Aircobra.

This is a huge gun and even with a little re-engineering (changing the area where barrel meets the perforated tube, or changing the diameter of the tube (70mm) of the tube going through the engine there is a lot of gun in back of the engine. The Germans did NOT mount the gun to the engine. The gun was mounted to the fuselage and the gun barrel went through the tube/tunnel in the engine.
The British 2pdr gun used on the Hurricane used cartridges 158mm long,
The Soviet gun used a cartridge case 198mm long.
 
A new-ish gun will be required, with a less powerful ammo than what the 37mm Flak was firing. Probably as powerful as what the post-war N-37?
My 1st suggestion is the 30mm ammo for the MK 103 necked-out to 37mm. Sorta-kinda what happened to the MG 151/15 -> MG 151/20; call it MK 103/37; yes, the motor-laffete version is needed so it can fit within the confines of the Bf 109. MV might go to 650-700 m/s with the standard HE shell, and to 750 m/s with the 500g M-shell?
Another suggestion is the scaled-up MK 108, with the much longer casing vs. diameter ratio than that the MK 108 ammo had, so the propellant weight is good enough to propel the shell at, at least, 650 m/s. Also the longer barrel is required, but again much shorter barrel than what the 37mm Flak had.

Good thing here is that German 37mm was with one of the lightest shells - surely a shortcoming in the ground defence role, but it allows for a less heavy and bulky gun.

I wouldn't bother with MG 131s by 1943 - fit the MG FFM in the wings instead; at 700 m/s for the M-shell, the ballistics will be a good match for our mid-power 37mm. By 1943, the belt fed version of the FFM was available IIRC.
MTT's schematics of the Bf 109 with MK 103 don't show the cowl guns installed (unlike when the MK 108 is installed as motor cannon), so we might even wind up with the lower drag.

Note that I'm not the fan of 500 m/s muzzle velocities, as it was the case with MK 108.
 
tomo pauk said:
My 1st suggestion is the 30mm ammo for the MK 103 necked-out to 37mm. Sorta-kinda what happened to the MG 151/15 -> MG 151/20;
Click to expand...
Won't work, unless the dimension specs most sources have are wrong.

The case is too skinny.

I am not a fan of the 500m/s velocity either but the problem is the basic premise, Putting a large gun in the 109 is going to be a problem. You are going to have a lot of the same problems the Yak-9T had with recoil, rate of fire and so on. The Soviet gun was roughly twice as powerful as the 37mm gun used in the P-39.
 
Shortround6 said:
Won't work, unless the dimension specs most sources have are wrong.

The case is too skinny.
Click to expand...
We might be better off with a bit bigger, bespoke casing and the accompanying breech.

You can note that I was suggesting the cartridge of the power close to what the N-37 had, not the NS-37 that fired the full-power cartridge. Keeps both the recoil and the gun size down.
Rate of fire similar to the MK 103 (ie. of about 400 rd/min) is still very useful to bringing down the bombers. Perhaps 3 hits required?
 
Don't we just give Z Zmauky a couple of the prototype MK112 and let him go play?
MK112 being the 55mm version of the Mk108 (weight about double the MK108 and has an intermediate muzzle velocity of ~600m/s) 55mm being picked as that was the size the RLM determined that 1 hit would destroy a B-17.​

I suppose if we wanted to keep a couple designers away from eastern front, we could have them design a 3.7cm version.

I was just surprised the Czechoslovaks and the Spaniards to rearrange the wing structure and insert the MG 151/20 mm and magazine into the wings. That they fit Hispanos left me questioning Messerschmitt's design ability... (I also had to triple check Tony's numbers, in Flying Guns WWII, that the Hispano Mk. V and MG 151/20 were basically the same weight. (OK, the Hispano fires with much more energy, but I had it in my head that the German Wonderwaffe was much lighter.)
 
The MK 108 was very good at what it did or what they were trying to do.
The gun went about 60kg as you know. It was fast firing but each shell had a bit less ME (42,000 J) than a 20mm Hispano (48-50,000 joules)
The US M4 37mm was about 96kg (and ??for braces/brackets/mounts) and fired very slowly with a 608g shell at 610m/s. Energy was 113,000 Joules and while muzzle energy is not exactly related to recoil energy/force it is sort of an indicator.
The Soviet NS-37 had 285,000 joules and fired at 240-260rpm which is one reason it weighed 160-170kg.
The post war N-37 had 175,000 joules and fired at about 400-430rpm and weighed 103-105kg.
But post war guns often had different steels, different gun powder and different expected barrel or gun lives before replacement. Things changed during the war for some countries.
The German 37mm AA gun was rather pedestrian in it's ballistic performance. But AA guns needed to be sturdy and long lived compared to aircraft guns.
Soviet late 1930s 37mm AA gun

had nearly similar ballistics to the NS-37 aircraft gun but used a larger cartridge case and fired slower.

If somebody could have come up with a 30mm gun that fired at around 500rpm with a MV of 600-650 that might have been a very good choice. With 2-3 times the rate of fire you get a much better chance of hit/s even if each hit is only 1/2 as destructive.
The big 37mm also have a rather low effective rate of fire as the recoil throws the whole plane around so much that only a few shots can be fired before the pilot has to stop firing and get the aircraft lined up again.
 
Do a XP-37 or F4U Corsair and move the cockpit aft, and move the 88 gallon fuel tank forward, closer to the CoG, with area relieved for the cannon receiver

And since that make the pilot visibility even worse, this is the result


The fix is in. Me-109 gets a heavy cannon, and better take-off and landing characteristics
 
don4331 said:
(OK, the Hispano fires with much more energy, but I had it in my head that the German Wonderwaffe was much lighter.)
Click to expand...
How much lighter is the question
Hispano specifications often cheat. They give you the weight of the 'bare' gun. Great if you want to stick a drum on the Hispano V. Not so great if you want to use a belt feed which was 4-5kg. Of course the 60 round drum for a Hispano was about 10.8kg.
 
Thanks for the answers, and apologies for the pause in the discussion, RL is getting in the way. As an idea for a single engine destroyer with a big gun I think it has room but the bk 37 is definitely a big no. Not so much in overall dimensions, but in the size of the shutter. If I didn't confuse the dimensions, cockpit should move back at least 1.2 meters. (and I think that raising it upwards would result in a grotesquely too high cabin).


The initial idea was to see if it was possible to design a single-engine zestorer (on the Me 109) that could shoot down a four-engined bomber in one pass. Or at least shoot it from a distance greater than defensive weapons. Of course in the historically available framework.
For now, it seems to me a more realistic version is 3xMG 151/20 in the fuselage (with the motor moved forward by approx. 15 - 20 cm to to make room for them instead of 7.9/13.1 mm ala Ki-61-ii) and 2xMG 151/20 in the wings. The heavy weight of the weapons should probably be compensated by smaller amounts of ammunition, but on the other hand, how much is needed for one attack. On the other hand the 5x20mm should be pretty devastating.
And maybe with the CG moving forward we can cram bigger tanks/MW50 ect into the rear of the hull.
 
Three MK 108s (one in prop, one in each wing)

3 times 600rpm equals 30 rounds per sec times 330G per shell equals 9.9kg of shells per second.

Five MF 151/20s (one in prop, two in cowl, one in each wing.)

5 times 720rpm equals 60 rounds per second times 104 G per shell (average) equals 6.21kg of shells per second.

Adjust rate of fire as you see fit. Adjust shell mix for the MG 151/20 ( I used 50/50) as you see fit.
Three MK 108s are going to get a LOT more HE into the target.
Soviet NS-37 fires about 2.94kg per second (at 240rpm)

BTW four 20mm Hispano Vs will fire 6.14 KG per second but their shells don't carry the same amount of HE as the German mine shells.
 
I like the MG 112 idea, although unfortunately it is a little too late for the 1942-43 timeframe. I agree that 3x MG 108 is almost an ideal variant, only that's MG 108 started to appear by the end of 1943 and in nacelles which are a degraded of the flaying characteristics. Only with the late K variants did they do projects to push them into (wooden ?) wings. I was thinking more about something similar to the Yak-9T or K where they crammed a big gun into the plane without losing (too much) performance.


The Me 109 and the weapons in the wings is a strange story. I seem to remember reading somewhere that Willy was not happy with the idea of anything that would disrupt the basic function of the wing, i.e. lift. And something else about the his reaction when they showed him Buchon with Hispano in the wings in Spain. On the other hand, from Me 109E model had radiators and starting with D (?) guns in the wings ( and only one Gallands F special had guns "in" wing ). But if I didn't mix up the pots, MG FF didn't go through the main spar, as well as, of course, the underwing gondolas. And even those tests with RZ rockets did not touch the structure. I am not sure about the projected MG 108 in the wings of the later 109K variants. But the fact is that in S-199s with MG 131s and Buchon with Hispanos they had to insert auxiliary spars.
Probably the best solution (as suggested by tomo) would be to extend the carrier box me 109 (on which engine and landing gear we're attached) and simply spread the wheels and get places for weapons in the wing roots, it seems like a win-win situation.
 
A slightly different option that achieves a similar effect might be to try to fit a 30mm MK 101 (or later MK 103) cannon pod (similar to that actually used on Hs129 - see below) on the centreline:





This could penetrate 75 mm of armor at 300 m range. Weight/dimensions compared to the BK 3,7:

GunMK 101MK 103Bordkanone 3,7
Calibre30mm30mm37mm
Typical Gun Length2,592 m2.335 m3.75 m
Typical Gun Weight139 kg141 kg295 kg
ApplicationsHs 129B-2/Bf110 C-6Hs 129B-2Ju-87G
 
According to the information I have:
Bf.109V8 was 1st to receive MG17s in wings and it pointed out need for beefing up wing;​
Bf.109C-1 being the production version with strengthened wing and 2 - LMG in wings. That there isn't box magazine, but rather the belt is laid out in single layer to wing tip and back is...interesting.​
Bf.109C-3 replaces the MG17s with MG FF (and drum magazines).​
​
And the cutaways in books I have absolutely show the guns going through the main spar for C-E.
They also show additional cross bracing (I won't call it a spar) so the MG FF​
Interestingly, the lateral bracing in the flaps is right behind the gun position as well.​
​
Modifying Bf.109 to move the landing gear outward has major structural and production implication (sort of like my tricycle Sea Hurricane) you'd be better off starting with clean sheet design.
 
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