Nodeo-Franvier
Airman 1st Class
- 121
- Jul 13, 2020
If the French already have a working motor cannon before 1935,how come the bf.109 didn't get one until late 1940?
Dewoitine D.501 motor cannon.
- Thread starter Nodeo-Franvier
- Start date
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Germans sorta also have had a working motor cannon, the MG 30C/L, aboard the He 112 (Jumo 210 engine), tested in Spain.
More seriously, it seems it had to do more about the engine than about the gun. HS 12 series of engines have had an 'empty' Vee, with induction manifolds running by the outer side of engine. That meant easy installation of guns of various sizes, the VK-105 engine (Soviet spin-off of the HS 12Y line) have had a 45mm cannon installed and worked well; granted, it was cracking the things around itself due to massive recoil.
DB 601A have had the blast tube running within the engine Vee, through which the guns were supposed to fire. Sems like that engine didn't liked that tube to be occupied with a cannon that fires; neither the Italians nor Japanese seem to take advantage of the possibility of the DB 601s to have the motor cannon.
Indeed, seems like the Germans finally managed to have the 601A 'agreeing' with the motor cannon by late 1940, aboard the 1st Bf 109Fs, a.k.a. the Bf 109F0 (zero).
More seriously, it seems it had to do more about the engine than about the gun. HS 12 series of engines have had an 'empty' Vee, with induction manifolds running by the outer side of engine. That meant easy installation of guns of various sizes, the VK-105 engine (Soviet spin-off of the HS 12Y line) have had a 45mm cannon installed and worked well; granted, it was cracking the things around itself due to massive recoil.
DB 601A have had the blast tube running within the engine Vee, through which the guns were supposed to fire. Sems like that engine didn't liked that tube to be occupied with a cannon that fires; neither the Italians nor Japanese seem to take advantage of the possibility of the DB 601s to have the motor cannon.
Indeed, seems like the Germans finally managed to have the 601A 'agreeing' with the motor cannon by late 1940, aboard the 1st Bf 109Fs, a.k.a. the Bf 109F0 (zero).
The MG FF 20mm was fitted to some Me 109E but most web sources say the gun overheated and even became damaged. Some sites say it vibrated too much. If the later is true it is odd because the MG FF had a relatively smooth recoil. It suggests problems in mounting the gun. The ideal is to attach it to the crank case. The problems were solved in the Me 109F but using the MG 151. The far more powerful C30 FLAK gun was successfully mounted on the He 112. Probably just a better design but as the He 112 received few orders it is little known about.
AFAIK Me 109F used either late model DB601N or DB601E, possibly better attachments for the gun.
Motor cannons were attached to the engine mountings, that was attached to the fuselage.
Unfortunately, the data on the He 112 that was tested with the big gun is sparse, the (only one?) aircraft being lost during the SCW.
Indeed, you're right, I've messed up the DBs.
Hispano-Suiza built their first motor-mounted cannon at the end of the First World War, so they had a long, long lead over the Germans! While the Germans were prohibited from building warplanes, the French continued to evolve the engines, mountings, and cannon to work together harmoniously. The Germans were playing catch-up. Also, remember that the early Bf109s had a completely different engine from the Bf109E and later, so a lot of progress that had been made was irrelevant. (Of course, the massive increase in power more than made up for the problems.)
Here's a coupla' pictures of a Hispano 12Y moteur-cannon engine on display at the Royal Armoury Museum in Brussels showing the cannon installation passing over the engine casing in between the cylinders, with its barrel through the RGB.
Hispano Motorcannon i
Note in this view from the rear the supercharger below the gun.
Hispano Motorcannon ii
Note in this view from the rear the supercharger below the gun.
Which weapon?
Hispano 12Y moteur-cannon engine...sorry. Btw, great pictures.
When looking at the D.500 on wikipedia, there is a description of G-force issues, "...5th Fighter Group led seven Dewoitine D.510s fighters on 04 November 1939 in a level head-on attack against an incoming formation of IJANF G3M bombers (Capt. Cen knowing from experience about the unreliability of the Hispano-Suiza HS.404 20mm autocannon under the g-forces of a diving attack, chose the level and direct head-on tactic); .."
When looking at the D.500 on wikipedia, there is a description of G-force issues, "...5th Fighter Group led seven Dewoitine D.510s fighters on 04 November 1939 in a level head-on attack against an incoming formation of IJANF G3M bombers (Capt. Cen knowing from experience about the unreliability of the Hispano-Suiza HS.404 20mm autocannon under the g-forces of a diving attack, chose the level and direct head-on tactic); .."
Temperature was not a problem. On the contrary, when the H.S.404 was installed in the wings of the MB152, there were problems with freezing. There were also problems with the wings being much less rigid than the motor mount.
The motor cannon was used with both the 12X and 12 Y engines of various sub-types (the "c" suffix indicated cannon until the French starting numbering versions instead of coding them). The guns used were the HS-7 and HS-9 (versions of the Oerlikon FF built under license) and the H.S.404 (designed because Marc Birkigt hated paying licensing fees with a passion).
While the HS-9 seems to have been reliable, the H.S.404 had numerous problems that had nothing to do with the engine mounting. The most biggest problem was the spring in the 60-round drum, which was simply too long to maintain consistent pressure from 60 rounds down to 1. Some escadrilles loaded as few as 30 rounds to prevent loading jams, which reduced firing time to unacceptable levels. (I don't have any information about the reliability of the HS-7, which was well out of service by WWII.)
The Soviets don't seem to have had significant problems with their cannons mounted on the Klimov M-100 (license-built 12Y) or its later developments (VK-105 series).
A.G. Williams
Airman 1st Class
- 182
- Oct 10, 2020
The HS 7 and 9 were actually versions of the big Oerlikon in 20 x 110RB calibre, not the little FF.
There was a little-known halfway stage in between the Oerlikon and the HS 404, from Scotti. This used a delayed-blowback system similar in nature to the HS 404 only with rotary bolt locking instead of locking flaps. The 20 x 110 ammunition developed for it was also a half-way house: it retained the sloping shoulder of the Oerlikon case but adopted a rimless base rather than rebated. At least one example of the case survives, helpfully stamped "20 mm Scotti 1933". No details of the performance are known.
Tony, was this the same as the Scotti AA gun that the Dutch got? (Having the second batch arrive unexpectedly on May 14, 1940 was ... weird.) Commando Supremo page on the Scotti 20mm: Scotti Cannone-Mitragliera da 20/77 | Comando Supremo
Was the Scotti actually installed in any French aircraft? I haven't seen any references to it.
The AA gun used 12-round trays, although it was designed for the Oerlikon's 60-round drums. I assume that this was for handiness, possibly related to balance. An aircraft weapon would obviously use the drum.
Was the Scotti actually installed in any French aircraft? I haven't seen any references to it.
The AA gun used 12-round trays, although it was designed for the Oerlikon's 60-round drums. I assume that this was for handiness, possibly related to balance. An aircraft weapon would obviously use the drum.
A.G. Williams
Airman 1st Class
- 182
- Oct 10, 2020
No, the Scotti 20 mm AA gun was designed around the same 20 x 138B ammunition as the Breda AA guns.
I don't think that the Scotti 20mm aircraft gun (of which there were at least two types in different sizes, firing different ammunition) was ever used, although Chinn mentions some sales.
The flat 12-round trays used by the AA gun were the same as those used in the Breda AA gun, in the interests of simplifying logistics
No, just mentions them. As I understand it, the differences between them were down to the mounting points, which varied according to the installation. They were basically an earlier version of the FFS, but heavier and slower-firing. As far as I know, no-one but the French used the big Oerlikon in an engine mounting.
fastmongrel
1st Sergeant
You can see the compromises involved in designing an engine to fit a cannon if you compare the HS to the Merlin in the background. The Merlin between the cylinders is crammed with induction piping and the supercharger is much bigger. The Merlin could shift a hell of a lot more air and fuel.
Getting off-topic here, but you have to understand that the 12Y was at least a half-generation behind the Merlin, which had nothing to do with the cannon.
The 12Y couldn't use a larger supercharger because it was power-limited by its very light crankshaft (completely machine from a single metal bar), which was right on the verge of excessive flexing.
The 12Z managed 4 valves per cylinder but still fit the cannon. The 12Y had only 2 valves partly because it was an evolution of the 12X, partly because redesigning the cylinder heads and adding the additional valves was a big deal and would have delayed the 12Y too much, and a lot because the 12Y was power-limited as noted above. This meant that it couldn't benefit as much from a 4-valve design without other, extensive, changes. (The 12Z had all of those changes.)
Back to cannon, please!
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