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Army (and Boeing, among others) had been working on successors to the B-17 with Boeing alone going through at least eight different 'paper' aircraft. Boeing designs 316, 322, 333A, 333B, 334, 334A, 341 and finally the 345 which was the basis for the B-29 and was submitted to the Army in May of 1940. After engineering studies, wind tunnel models and full size mock ups and prototypes ordered the Army orders 250 production B-29s in May of 1941, 4 months before the first single stage Merlin production engine is delivered by Packard. Back in Sept of 1940 (end of the daylight BoB?) The Army was ordering B-17Es with eight .50 cal guns and single .30. At high altitudes they could outrun and out climb Hurricane Is . And again with a nominal range of 2000 miles with a 4000lb bomb load there was no possible single engine fighter that could escort them when they started rolling off the production lines in Sept of 1941.
Now at some point the level of technology did get to a point where a single engine fighter could perform the escort mission but that wouldn't be until 1943.
The 2 stage mechanical supercharged R-2800 wasn't really the answer. It wasn't enough lighter or more compact compared to the turbo R-2800 used in the P-47 to make up for the 350-400 less hp at 22,000ft and up.
A long range fighter was very much within the scope of UK technology from mid-30s on, more so than it was the case for any other country, but a firm separation between FC and BC, reinforced by 'will get through' mantra, meant it will never, or too late came to frutition.
I don't know if it was "intentional" but the Spitfire and Hurricane were no more short legged than another European fighter of the time.
Sorry Tomo but it wasn't possible in 1930s. It was possible in 1942. The question was when it became possible.
As mentioned above it was fuel and engines, The Merlin III gave 880hp for take-off with 87 octane fuel. Even if the British had gone to constant speed props sooner that is not enough power to get a fighter with the capability of a 400 mile escort mission (roughly 1200 miles 'nominal range') out of a standard British Airfield. Yes, "technically" the British could have made the airfields bigger pre-war but financially it was another story. Initial specification for the Stirling bomber called for operating out of a 500yd field.
A Merlin III went 1375lbs, A Merlin XII went 1420lbs, The Merlin X and XX went 1450lbs for 1280hp take-off. Late model 20 series engines went 1475lbs and were allowed 1610hp for take-off using 18lbs of boost. Merlin 61 weighed 1640lbs and was rated at 1280hp for take-off. Merlin V-1650-7 weighed 1715lbs and had 1490hp for take-off using 15 1/4lbs boost on 100/130 fuel. The power to weight ratios of the powerplants (and the fighters) changed dramatically in just 4-5 years. Where was the 'tipping" point at which a long range fighter (which is a very imprecise phrase, a P-40C was long range fighter compared to a Spitfire MK I) became feasible?
And the question isn't just about take-off, it is about providing a fighter that is good enough to actually fight the enemy interceptors over their home territory. Which the Bf 110 wasn't able to do. You may not need to shoot down the enemy at a 5 to 1 ratio but you need to disrupt his attacks on the bombers and keep his interceptors busy. If your escort fighter is bigger and heavier and using roughly the same engine you are in trouble.
Now you just need a design team that is clued into engine (and fuel) development enough to rapidly respond with a good design and get it into production in months rather than the normal 2-3 years (or 4 years). You also have to compromise on certain things. The US army in 1942 wanted high speed, high altitude and long range. What they got was the Fisher P-75.
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Deliberately designing (requesting) a slower, poorer climbing, larger turning radius aircraft that had more range than it's contemporaries in the mid to late 30s would not have gone over well. It didn't go over well when the British got their hands on the early P-40s. They promptly shuffled them off to fight the Italians. Early P-40s having 35-60% more internal fuel than a Spitfire (depending on self sealing tank set up) and provision for the 52 gal drop tank? With drop tank the P-40 had nearly double the fuel of an early clean Spitfire.
The early Allison was good for 1040hp at 15,000ft which wasn't that far off form the Merlin IIIs 1030hp at 16,750ft.
In other words sticking a Melrin III in Tomahawk would have done almost nothing for altitude performance.
How bad the RAF wants the long range fighter (yes, we know they don't want it)? Lengthening 1/5th of take off lanes by extra 200 ft (70 yards?) to accomodate the longer ranged fighter should be cheaper than to produce bombers that Germans will make the practice shooting of.
The Merlin I/II/III was hardly a tipping point as the British were well aware that the Jumo 210 was Kestrel class engine and that the Germans would be working on something better in short order (if not already, Germans didn't put out press releases unless it put them in a favorable light). The French already had 860hp Hispano engines and were working on improving them. Germans were displaying 950hp DB engines in international flying meets in mid 1937.The tipping point is achieved once Merlin I/II/III is available. It provieds twice the power of what Jumo 210 was doing. Another tipping point is achieved with Merlin XX, that does not have peer in LW service before late 1941, when DB 601E is finally cleared for 2700 rpm.
Mentioning the Bf 110 was to show that it is not enough just to have some sort of fighter show up. The fighter has to able to put up a creditable fight which the 110 could not. BTW the armament in the 110 was no heavier than what you are proposing. 4 LMG and 2 light cannon aren't much different in weight than 8 LMGs and and lighter than 12 LMGs. It rather depends on ammo carried.Didn't I've alredy stated that Bf 110 was not ideal for the job? Keep things simple - 1 or 2 (in German case) crew members, 8-12 LMGs, either Merlin or DB 601, not too big and that's it. RAF has advantage in engine power at altitude at least by late 1941.
True but then the P-47N, the Merlin Mustang and the P-38 were not designed to be escort fighters. They were adapted from existing designs which means they managed to avoid some of the unrealistic "wish list" type requirement/s that bedeviled many new aircraft.Not every long range fighter was a lemon like P-75. Talk P-47N, Merlin Mustang, P-38, P-82, Hornet.
By the time P-40C is available, the Merlin 45 is around (the Merlin XX even earlier), so let's stick that one. No wonder P-40C was a worse performer than Spitfire V, at 15000 ft it has 300 HP less and admitedly greater weight.
edit: the Spitfire with 20-30 gals extra is a better bet
P-40 was not the only long range aircraft with humble power, let's take a look on the Ki 61, granted a mid-war aircraft, but using an engine of less power than Merlin III or the early V-1710.
The fact that escorting fighters are already at 15-20 kft, cruising at 250 mph puts them in advantage vs. defendes that need to climb 1st to get there - altitude and speed advantage counts for something. The defending side can call up the fighters that are nearby, say those at Ruhr area, while those around Hamburg, Munich or Berlin can't help. Makes things interesting - 500 bombers and 200 escorts vs. 250 defenders?
Many of you guys keep talking about the "myth of the self protecting bomber". I'm not really sure why this is considered a "myth". In 1940 there at most, 2 countries in the world that would be capable of intercepting B17's with any real hope of success, the Germans and maybe the British. As was pointed out above, the B17E could actually outrun and outclimb a Hurricane, and a 1940 model Spitfire with 8 303 LMG's would't really excite me when trying to attack a plane that has 8 50's to shoot back at me with,................