Aircraft design, models used, armament etc.

England should license the Merlin as soon as possible

renatohm said:

England should license the Merlin as soon as possible

? to whom?

US.

Engines: So far I'm not proposing any change to the original TFW proposal to concentrate on the Merlin and Hercules engines. Both engines were historically developed to produce over 2,000 hp, which is enough until turbines become available. Where jets are concerned, I would also continue to back both horses, with one company focusing on Whittle's centrifugal designs and another on the axial flow type.

Armament: here I have changed my mind. The original TFW proposal was to get FN to develop a compact Browning HMG around the Vickers 12.7 x 81 round (as in the Japanese Ho-103) to plug the gap between the .303 Browning and the 20mm Hispano.   However, I have gone off the Hispano: it was too late when it was needed most (the BoB) and was always an awkward beast not well suited to wing or turret mounting. So I would choose an Oerlikon instead - at about the same time as the British were being shown the Hispano (much more impressive performance than the early-30s Oerlikon), Oerlikon were thoroughly revamping their aircraft guns to reduce weight and increase their rate of fire. These guns had been developed for years, and could have been bought off the shelf in good time to equip RAF fighters before the war (with a belt feed being developed in parallel). 

The question is: which Oerlikon? There were three performance levels, all of them firing the same 128g HE shell: the FF (20 x 72RB, 600 m/s, 500 rpm, c.24 kg); FFL (20 x 101RB, 750 m/s, 490 rpm, 33 kg); and FFS (20 x 110RB, 830 m/s, 470 rpm, 39 kg). For comparison, the Hispano Mk II fired a similar shell at 880 m/s and at 600 rpm,  but weighed 50+ kg (it needed a strengthened mounting, which was extra). The RAF was originally interested in the biggest Oerlikon (the RN and USN bought a heavy-duty AA version firing the same ammo), but the FFL has some advantages, in that the MV and trajectory were very similar to the .303 Browning, helpful in mixed-armament installations, and the Japanese showed that the gun could be speeded up to 620 rpm (and 720 rpm right at the end of the war). Later, a streamlined M-Geschoss Ausf.C type of shell would reduce the weight and boost the MV. The light weight and low recoil would also be valuable. 

So, I'd go for the Oerlikon FFL initially, but in parallel with that start developing a more advanced and powerful gun of 25mm calibre. Not a Hispano type or a revolver, but a Gast twin-barrel job (the British had an example of the Gast MG to study). A RoF of around 2,000 rpm should be feasible initially, with the ammo firing a 200g shell at 900 m/s. 

autogun said:

but the FFL has some advantages, in that the MV and trajectory were very similar to the .303 Browning, helpful in mixed-armament installations,

Good choice. 4 guns initially and 4 guns with belt feed and improved rate of fire later. I suspect the 303s were a sop to their ego more than being useful. It might be simpler to stick with 20 mm so the pilots return rather than poke about with an inadequate armament.

There was a practical benefit of mounting a couple of .303 Brownings alongside the cannon, especially before a belt-feed was introduced (so the wing-mounted cannon were limited to using 60-round drums): one .303 could be loaded with the B Mk IV day-tracer/incendiary, which left a smoke trail all the way to the target, while another could be given the Dixon incendiary which ignited on impact, the bright flashes indicating hits. So the pilots could open up with the MGs and not fire the cannon until the .303s were hitting, thereby saving cannon ammo.

For the Germans, what about drop tanks for the 109 in the BoB and Norway?

autogun said:

There was a practical benefit of mounting a couple of .303 Brownings alongside the cannon, especially before a belt-feed was introduced (so the wing-mounted cannon were limited to using 60-round drums): one .303 could be loaded with the B Mk IV day-tracer/incendiary, which left a smoke trail all the way to the target, while another could be given the Dixon incendiary which ignited on impact, the bright flashes indicating hits. So the pilots could open up with the MGs and not fire the cannon until the .303s were hitting, thereby saving cannon ammo.

The Oerlikons fire slower so they get about 8 seconds. They have a much better tracer than 303 and hitting is not in doubt because of the explosions and bits flying off the target aircraft.

hobbes154 said:

For the Germans, what about drop tanks for the 109 in the BoB and Norway?

Yes, that sounds reasonable. I know that they did use these at some point, but obviously later. Anyone have any stats on the extra range they provided?