The Bf110 was flying in 1936, the He100 was still a napkin waffe in October 1937, while the Bf109 was already adopted. The prototype was delivered in January 1938, but it started a mess and remained so IOTL through 1939. Without ASB intervention I don't see how it can get ready in time for 1940 in significant numbers, nor do I see anywhere it stated that it lived up to it's prototype performance without armor, ammo, and weapons/other equipment. It's range was no better than the Me109F and Fw190 and probably only available in significant numbers about the same time, i.e. after 1940 when it would be needed. Even without the Bf110 something else is going to absorb the resources spent on the Bf110 by 1939 when the proposed compromised 'production' He100 might start to be available to begin phasing in to production. As it was in 1936 the He112 was the He100 of the time and it wasn't the performer the He100 was.
At that point you're better off proposing the Fw187 instead, as getting the He100 in any version earlier would violate your OP restrictions. We can also write off the Me109Z early for that reason too for consistency, though technologically it was possible at the time if asked for (though it would be based on the E series air frame and engine rather than the 1941 OTL version being based on h F series), while the He100 still needed time to be technically ready. Unless I'm misreading the restrictions you put on us in the OP.
Resources spent on Bf 110 will be better spent on more Bf 109s early on, and on He 100 later on. He 112 was not He 100 of it's time - He 112 was underperformer. I'm not sure why do you mention the 109F, since it not just lagged behind the He 100, but it was also a problematic A/C with tails and wings detaching themselves under high G loads (later modified to remedy those shortcomings). The Bf 109G, with more weight and HP, was good for 700-1100+ km of range without drop tanks, and 1150-1950 km of range with 300 L drop tank, depending on power setting.
Anything that is in pipeline from 1936-40 is in for this time line, that includes He 100.
I'm okay with Fw 190 project if we speed up it, like retaining the small wing and having V12 to power it, though it will still be probably too late for the BoB, apart from token examples.
I propose cancelling the Bf 110 (and Fw 187).
Bf 109Z that uses Bf 109E as parts donor sitll has to do with blocky nose, deep radiators, strutted tail, fixed U/C - all drag-inducing items, this time x2. Still 400 L of fuel per engine, unless we think that asymetrical fuel load is a good thing.
Sure, but the production machine had a weight increase to make it dive capable, plus the ventral gondola, which added weight and drag. It compromised the design's speed and original purpose, which is not what happened with the transition to production models of the B25, B26, and A20.
A-20G-20 was the draggiest of the A-20s, featuring a turret for 2 HMGs, that also required fuselage widening. It was also the heaviest. Still with 1600 HP engines as it was the case with A-20 (no suffix).
B-25H (and most of earlier examples) also featured turret, 4 HMG blisters, each version got heavier. B-25 (no suffix) was without turret and protection. Engines remained the same from B-25 to B-25J.
B-26 was also without turret. Later versions have gotten a bigger wing, that also got bigger incidence, plus HMG blisters. Engines got several % of extra power, less than 5% extra above 12000 ft.
Having LMGs replaced by HMGs on most of hand-held positions will increase drag & weight.
Net result of all of this was a reduction of speed.
This might be a start of a good read.
We may be differing in our definitions of 'tactical' here, I don't mean it was CAS, rather this concept:
https://en.wikipedia.org/wiki/Tactical_bombing
It was supposed to be a speed bomber like the Mosquito with a limited payload to hit targets that were ideally engaged with 'light' bombs.
'Ideally engaged with 'light' bombs' - even if there was such a thing, a fast bomber that can lug both bigger and smaller bombs is a greater asset than a fast bomber that can carry just light bombs. As before, restricted bomb bay is a bug, not a feature, even the Germans tried and incorporated bigger and unrestricted bomb bays when He 177, Ju 288 and Do 217 were to replace He 111, Ju 88 and Do 17.
I'm not arguing it should be a Mosquito either, just pointing out that changing the aircraft from the OTL version with the liquid cooled Jumo engine means altering the aerodynamics as well as lowering the available power, raising the fuel consumption, and as result reducing OTL aircraft's range and carrying capacity. I don't necessarily think that would be a bad idea, just pointing out the trade offs that come with that move and that it would have consequences for the utility and survivability in 1940, which was already pretty bad in a contested air environment.
For take-off, Jumo 211A was making 1000 HP, Bramo 323P (2-speed S/C, as installed on Do-17Z from 1938 on) was also making 1000 HP. Installed 323P was lighter than Jumo 211A: 580 kg vs 615 kg + liquid cooling system.
Reason I've suggested re-engining the Ju 87 with 323 is not beacuse the 323 was a wonder engine, but because that way we still have more than useful short-range dive bomber, while having enough of engines to support the early start of Ju 88 program where each bomber will obvoiusly require two engines.
If you can get a hit. That's the problem with the low rate of fire for both the Italian 13mm and the MG/FF, plus for the FF there was the issue of the low muzzle velocity/poor aerodynamic shape rounds (and low weight of the grenade rounds, which means it loses velocity even more quickly than standard bullets) and of course the poor drum magazine capacity of the design in 1940. That's ok to a degree for slow aircraft like bombers (depending on the defensive firepower) or the Shturmovik or when getting lucky and bouncing an enemy fighter, but there is a reason the Luftwaffe switched to the much heavier MG151/20 ASAP when it became available. Besides the Italian 13mm was slightly heavier than the MG FF, so no savings there, while being substantially less damaging than the MG FF with a slightly higher ROF and muzzle velocity. That said it was probably just enough better than the MG FF due to the lighter ammo and belt feed for 1940 that it would be an advantage to use instead, but that advantage would be gone as soon as the MG151 appears.
People were getting hits, even with 540 m/s slow MG FF, even on fighters or small bombers or recons. Many made themselfs aces.
Italian HMG fired at 700 rpg 'free', that makes it 100 rpg faster than the American BMG before 1940. Much better were Belgian HMGs (advertising RoFs of 1000-1200 rpg), Soviet DSHK is not used as aircraft HMG, German MG 131 is not available until way too late. I'm not trying to save on weight vs. MG FF(M), the cannon was already lightest available.
MG 151 is too early for 1940, and it it was no easy fit in confines of the Bf 109, meaning just one per Bf 109 unless we want to pay drag & weight penalty of the gondoly weapon. The DB 601A didn't agreed well with motor-cannon until Autumn of 1940 anyway.
Italian HMG will be much more damaging than 7.5-9mm MG.
Luftwaffe still needs to shoot down Allied bombers trying to bomb German columns.
The thing is since we are talking about optimizing what is available in 1940 for the threats having multiple fast and flat firing MGs of a larger caliber than OTL MGs with an OTL off the shelf cartridge that could work in a modified, existing Luftwaffe MG and not only saved on weight, which would improve maneuverability and speed, but also increase ammo capacity and firing time in the air it would be an improvement. After all the RAF did bag thousands of Luftwaffe aircraft in 1940 with .303 rounds, as their 20mm cannons weren't available except in tiny numbers during part of the BoB. The proposed 9mm round would be even more effective than their 7.7mm bullets, due to higher velocity and having a higher explosive content (IIRC the British didn't field an explosive 7.7mm round), while not being overall that much heavier, certainly not as heavy as a 13mm cartridge. Plus you could have two of them for the weight of 1x Italian 13mm. 6x 9mm high velocity MGs would be as effective if not more than 8x .303.
I hear you loud & clear. I'd still pick 4 x Breda 12.7 for the Bf 109s, or 2 x 12.7 + 2 x MG FFM (with at least 90 rd drums) for 1940.
I'm not exactly sure what weapon you're referring to there to be able to comment on it.
As to the Luftwaffe's use of the MG151 vs 151/20, they did use both throughout the war. The 20mm was preferred for killing heavy bombers like the B17 because of their capacity to absorb punishment...which is not an issue in 1940 given the aircraft the Luftwaffe was facing from France and Britain. Plus if really needed the 'destroyer' or whatever they field in it's place/role can carry the 20mm cannons. SE fighters can carry the 9mm MGs and upgrade to the heavier guns as the MG151 becomes available.
I'd avoid anything under a HMG.
LW used perhaps zero 15mm cannons on Fw 190s, and again zero on Bf 109s bar F1 and F2. 15mm cannons represented perhaps 1% of all guns/cannons on dive bombers, night fighters or attack A/C, if even as much?
MG 151 is no drop-in replacement for LMGs, not even for MG 131s. A fighter with two 20 mm cannons is not picky when it is about targets.
Considering they withdrew the Stukas in August, but not He111s through the entire campaign, it is clear that the medium bombers were much more surviveable in contested airspace, especially when you consider the He111 was the primary bomber used in the campaign.
The 2-engined jobs were indeed more survivable than Ju 87s.