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How about just four .303 in the nose and tons of ammunition? The concentrated fire of four .303 should kill anything flying in 1940.
In practice, the .303 MGs proved disappointing in the BoB, which is why the RAF was so desperate to fit cannon even before they were ready. Luftwaffe bombers made it back to base with as many as 300 bullet holes in them.
No need for changing the goal post, you didn't asked for ammo supply (Oerlikon was offering belt-fed cannons for RAF years before ww2; Shvak was belt-fed) or firing rates to match LMGs (cannons have shells that offer order or two of magnitude better effect on target than LMGs). You claimed that there were no reliable cannons (and HMGs) in 1940 - and that was not the case.
More analysis needed to take a range of factors into account (no doubt there have been BoB comparisons done elsewhere on this forum). For example, the RAF planes were mostly agile fighters which were hard to hit, the Luftwaffe mainly bombers, slower and easier targets. The Luftwaffe fighters' cannon were also relatively low-velocity with different ballistics from their MGs (of which they had only two).The Luftwaffe lost 2376 aircraft in the BoB mostly to .303 armed fighters, the RAF lost 1250 aircraft to mostly cannon armed fighters.
The British developed belt-fed cannon as a matter of urgency - they used drum-feeding at first simply because that was all that Hispano-Suiza had developed, so the British had to make do with drums until the Chatellerault belt-feed was available in 1941.The most common cause of jamming in both the .50 Browning and virtually all the cannons was caused by the ammunition belt, if belt felt cannons worked the British German and Japanese armed forces would have used them, like I have already said, the MG FF/M wouldn't even work with the drum. The RAF was doing trials as far back as 1937 to replace the .303's but couldn't get any of the HMG or cannons, not to mention their ammunition to work reliably enough, stick to the .303's but fast track cannon development
The British developed belt-fed cannon as a matter of urgency - they used drum-feeding at first simply because that was all that Hispano-Suiza had developed, so the British had to make do with drums until the Chatellerault belt-feed was available in 1941.
"stick to the .303's but fast track cannon development" was exactly what the British did.
I was thinking more for this scenario. Four .303 with a generous inclusion of incendiary rounds might do the trick. Did any IJA/N aircraft ever return with 300 bullet holes? I think this unlikely.In practice, the .303 MGs proved disappointing in the BoB, which is why the RAF was so desperate to fit cannon even before they were ready. Luftwaffe bombers made it back to base with as many as 300 bullet holes in them.
More analysis needed to take a range of factors into account (no doubt there have been BoB comparisons done elsewhere on this forum). For example, the RAF planes were mostly agile fighters which were hard to hit, the Luftwaffe mainly bombers, slower and easier targets. The Luftwaffe fighters' cannon were also relatively low-velocity with different ballistics from their MGs (of which they had only two).
I always thought the Hispano belt feed mechanism was made by Martin Baker?.
I was thinking more for this scenario. Four .303 with a generous inclusion of incendiary rounds might do the trick. Did any IJA/N aircraft ever return with 300 bullet holes? I think this unlikely.
It may have been made by them and/or final development made by them but the basic design came from France, the Chatellerault feed. The plans were actually gotten out of Paris in May of 1940?
The British developed belt-fed cannon as a matter of urgency - they used drum-feeding at first simply because that was all that Hispano-Suiza had developed, so the British had to make do with drums until the Chatellerault belt-feed was available in 1941.
"stick to the .303's but fast track cannon development" was exactly what the British did.
I was thinking more for this scenario. Four .303 with a generous inclusion of incendiary rounds might do the trick. Did any IJA/N aircraft ever return with 300 bullet holes? I think this unlikely.
The reason that I have a particular fondness for the mid-sized Oerlikon FFL, apart from its light weight, is that the MV was around 750 m/s, about the same as the .303s, which means the trajectories would be very similar. With a mixed cannon/MG armament, it would therefore be possible to have half the .303s loaded with the B. Mk IV (Buckingham) incendiary/tracer which ignited on firing, leaving a smoke trail on the way to the target, the other half loaded with B. Mk VI Dixon/De Wilde incendiaries which flashed on impact with the target, indicating hits. One firing button could operate the MGs, one the cannon. So the pilot would open fire on the target with the MGs, zeroing in with the tracers until the sparkles of hits became visible, then pressing the other button to fire the cannon. That should (in theory anyway) minimise the quantity of wasted cannon ammo.The trouble is not the guns, the trouble is hitting the target, 7-9 seconds of cannon ammo means 99% of pilots hit nothing but open air, at least the .303's have effective tracer and rounds to burn, 12 guns with every 5th a tracer means at least the pilots see were they are missing which will help them learn to lead the target
The most common cause of jamming in both the .50 Browning and virtually all the cannons was caused by the ammunition belt, if belt felt cannons worked the British German and Japanese armed forces would have used them, like I have already said, the MG FF/M wouldn't even work with the drum. The RAF was doing trials as far back as 1937 to replace the .303's but couldn't get any of the HMG or cannons, not to mention their ammunition to work reliably enough, stick to the .303's but fast track cannon development
Four .303s is OK but hardly devastating. cutting guns to increase ammo may be counterproductive
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A Whirlwind with 20mm cannon and drum feeds has about 6 seconds of firing time.
A Whirlwind with 20mm cannon and 120 round belt feeds has about 12 seconds of firing time.
A Whirlwind with twelve .303s and 500rpg has about 25 seconds of firing time.
A Whirlwind with four .303s and 1500rpg has about 1 min and 15 seconds of firing time.
It just has to shoot as each target 3 times longer
Several USN pilots made ace in a day using F6Fs with six .50s with about 30-32 seconds of firing time.
To get 30 seconds of firing time with the guns on target (in effective range) calls for quite a number of minutes of combat time (firing passes) and fuel/engine temperature pilot state may start to become issues.
Early in WW2 RAF combat reports indicated that one aircraft was shot down for every 4,500 rounds of .303 fired. Even before the war, in November 1938, tests had already produced the conclusion that the introduction of a weapon of at least 20mm calibre was urgent.
(both from Flying Guns WW2)
The reason that I have a particular fondness for the mid-sized Oerlikon FFL, apart from its light weight, is that the MV was around 750 m/s, about the same as the .303s, which means the trajectories would be very similar. With a mixed cannon/MG armament, it would therefore be possible to have half the .303s loaded with the B. Mk IV (Buckingham) incendiary/tracer which ignited on firing, leaving a smoke trail on the way to the target, the other half loaded with B. Mk VI Dixon/De Wilde incendiaries which flashed on impact with the target, indicating hits. One firing button could operate the MGs, one the cannon. So the pilot would open fire on the target with the MGs, zeroing in with the tracers until the sparkles of hits became visible, then pressing the other button to fire the cannon. That should (in theory anyway) minimise the quantity of wasted cannon ammo.
The Luftwaffe did not have this advantage as their 7.9mm MGs had a high MV, the 20mm MG-FF a relatively low one. This also applied to the IJN fighters with the Oerlikon FF (Type 99-1); they did not introduce the FFL (99-2) until later.
MG FFM certainly worked.
'If the belt fed cannons worked' - they worked, too, once belt feed was designed and produced.
Belt feed did indeed work yes but not till years later, hence the reason the A6M Bf109 Spit MkV all used drums.