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Considering this a bit more the best bet for a quick dirty night fighter is probably trying to stick turbo Allisons onto an A -20 airframe.
The wright R-2600 seems to have trouble with having a high altitude version although this is inferred by no high altitude version ever making it to production.
Switching to turbo-Allisons on the A-20 gives up take-off power although by not carrying bombs this may help the weight-take off problem. Guns and ammo have to be kept to well under 2000lb though
Since the 1325hp turbo Allison shows up in P-38s in Feb/March of 1942 it seems viable and at any altitude much over 13-15,000ft is going to give more power than the R-2600s. Perhaps the larger engine nacelles of the A-20 (you still need to fit the original wheels/tires) offer space for a better intercooler set up than the wing leading edges of the P-38 so the A-20 night fighter won't have the problem with engine restrictions that some of the mid P-38s had?
P-38 isn't big enough to hold the very early radars without playing with the fuselage although it didn't have to wait as long as it did to get the navy radar pod.
If the Army and Douglas had got off the stump perhaps the A-26 nightfighter could have showed up earlier but you still have the engine problem for high altitude performance and the A-26B empty weighed with a few hundred pounds of a P-61B empty and the P-61 already had two stage engines.
The Turbo P-61 has a bit of a problem in that the performance numbers for the P-61C need the R-2800-73 (same engine used in P-47M) engine so as good as that option may be it doesn't do any good until Fall/Winter of 1944.
Using the -21 engine out of the P-47B/C does increase the power at altitude but also picks up the weight of the turbo system (a P-61C picked up about 2000lbs in weight over a P-61B), perhaps an early version with lower powered engines doesn't need the bigger props used on the P-61C? or can save some weight other places?
Simply pulling the turret of the P-61 doesn't change a whole lot, 3-5mph in speed and with about 800lbs for the turret and 500-620lbs for .50 cal ammo (on a 30-31,000lb airplane clean) it does what for climb? Smaller fuselage will help but that takes longer once the drawings are finished for the big fuselage (when do you ditch the the turret in the planning stage?)
How about the turbocharged R-1830 aboard the A-20? The engine is rated for 1200 HP in the P-43 from the get go (1940-41?), vs. 1150 HP for the V-1710 prior early 1942? Drag would equalize speed, but weight would be a bit on Twin Wasp's side.
Hmm- how about A-26 plus two stage engines? The wing was smaller (540 sq ft vs. 664) and of 'faster' profile - laminar flow wing; should push such an A-26 to 400 mph?
How about turbo engines, like the ones used on the P-47C/D, whose increased weight would be compensated via deletion of turret?
I have no idea of the reasoning but Ford never made a two stage R-2800 (although many of the engines they made were turboed) while Nash Kelvinator never made a single stage R-2800 and they built 2692 R-2800s in 1943 and 9259 R-2800s in 1944.
This was one of the major curses of the Ta154 project, also. Once they got past the engine supply issues, they discovered that the wings tended to delaminate....wood as a whole does not lend itself well in the field...
Maybe but the Twin Wasp dead ends, nowhere to go so you need a second fighter soon or redo the A-20 engine installation a second time.
the 1200hp versions were 20mph slower than the 1600hp versions at the lower altitudes. With the turbos you might split the difference at medium/high altitudes. more drag than the base Twin Wasp version. The extra guns and radar antenna will not help. Classic turbo trade off, slower below 15,000ft, about tied between 15,000 and 20,000 and faster above 20,000ft. The 1600hp version might still have over 1000hp at 19,000ft although it is fading fast.
The speeds/performace for the 1200hp versions are often for a weight of 15,030lbs.
And we start getting into the armament question. The original 1200hp DB-7s carried eight or twelve .303 guns in nightfighter roles. The .50 cal weighs about 3 times what a .30 or .303 does and the ammo is about 5 times heavier per round. A lot of the P-70s used four 20mm cannon, either in the nose or in the belly pack but as far as I know they used 60 round drums. Rather limits firing time even if the installation is a lot lighter than the 200 round belts used in the P-61( and they often flew with reduced ammo)
[re. 2-stagers on A-26:] It might, depends on altitude. You want two stage engines you need the inter-coolers and it is not really the weigh of the inter-coolers but the drag. Unless you have doors/flaps to seal off them when you aren't using them.
Here we get back into the timing thing. Late model P-47D engines are going to give you a lot more power high up and a lot more power down low. Early P-47 engines are going to give more power up high and zip (no) extra power for take-off or down low.
WHEN do you want it? and you have to start planning not only the aircraft but engine production and allocations up to year before the planes show up in squadrons in more than handfuls. Once you are tooled up and ready to go new, improved dash numbers of similar engines can be introduced with little trouble but switching from single stage to two stage is a bit harder. I have no idea of the reasoning but Ford never made a two stage R-2800 (although many of the engines they made were turboed) while Nash Kelvinator never made a single stage R-2800 and they built 2692 R-2800s in 1943 and 9259 R-2800s in 1944. Chevrolet and the P&W Kansas City plant both come in in 1944 with single stage R-2800 C series engines, having never built a B series engine.
WWII Canada was a huge aluminum exporter. IMO Canada should have been designated primary producer for the aircraft which would have allowed aluminum construction.
Let British furniture manufacturers build something else such as gliders, landing craft or PT boats.