as i understand it, fighter plane technology had to evolve mid-way during the war; from short- to medium-range, low- to medium-altitude pursuit/interceptor planes fighting over battlefields, enemy airfields, and carriers; to long-range, high-altitude fighting, revolving around bomber strikes deep into enemy territory. by 1943, a lot of excellent planes in the first set that have evolved through several variants from 1940 have gone obsolete. they just can't fight above 27,000 feet and loiter long enough to either escort or intercept flying fortresses. i can rattle off the following (forgive inaccuracies): spitfire mk 9 focke wulf 190D p-47 me-109F a6m6 zero shiden kai p-51 a-c the fighter planes developed for the new air war would include the p-38, the raiden, p-51D, ta-152, me-262, later variants of the spitfire, plus models that came too late like the p-51H and the a-7 reppu just how do those two types differ mechanically, and how difficult is it to develop a variant from the first to the second?
WWII was fought by fighters that either existed or were under development at the beginning of the war. All of the types evolved during the war and improved, but of your list only the Fw 190D, the P-51B/C, and the Spitfire were major changes in that they were re-engined. The P-38 which you list as "new" first flew in 1939. The major change in the P-51 was from the Allison engined P-51A to the Merlin engined P-51B/C in early 1943. The P-51D was not as large a change as it added the bubble canopy and six guns over the B/C version. The bubble canopy actually made the center-of-gravity issue with the fuselage fuel tank worse than it was in the B/C versions, although was an overall improvement. The Fw 190D "long nose" changed from a radial engine to an inverted V12 which gave greater high altitude perfomance. The Spitfire first flew in 1936 and was continually upgraded to keep it competitive with later Marks shifting from the Merlin engine to the Griffon. The Spitfire was a good basic airframe that lent itself to continual improvement.
so aside from the engine changes you made, what are things a high altitude fighter needs? a pressurized cockpit, of course. for the engine, is liquid cooled better? do you need turbo-chargers? what about auxilliary tanks for NO2 and pure oxygen? thanks.
The only large scale production combat aircraft that I know of that had a pressurized cockpit and crew space was the B-29. I am pretty certain the remainder were not. Turbosuperchargers were required for performance at high altitude so as to provide enough oxygen for combustion in the engines.
For some unexplainable reason the Spitfire didn't take well to drop tanks, the narrow track undercarriage may have had something to do with that, so it was never very long legged. High altitude bombing was mostly an European trend, as Japan didn't have anything like the massive AA defences Germany had the B29 soon switched to low altitude raids, most Japanese fighters had poor high altitude performance and limited firepower, a terrible combination to counter B29s at high altitude but there were so few of them left that the switch was possible without too much risk. In Europe the ground support war had a huge importance up to the very end, the USSR fielded an impressive number of planes but the high altitude types were a very small percentage of that. Even early in the war there was a kind of "parallel air war" between German very high altitude recon planes and bombers and Spitfires that were "stripped down" in order to have a chance to catch them. Had the high altitude threat increased in size there were high altitude variants of the Spitfire ready to go into mass production, but there never was a need for them. A high altitude fighter needs a lot of things, a supercharger for sure, otherwise the engine output will drop dramatically, a large wing span is also useful, a pressurized cockpit is really need only for very high altitudes, otherwise an oxygen mask may be enough. The bombers had the same limitation, given the armament layout of the B24 and B17 pressurizing them was close to impossible. More than from short ranged low medium to long range high altitude the evolution of fighters could be traced by engine power and firepower, early models had around 1000HP and rifle calibre machine guns, with some HMG and "first generation" 20mm cannons, mid war saw the disappearance of the rifle calibre MG, and an increase of the number of cannons, with engines in the 1500HP range, the more powerful engines compensated for the additional weight. To bring down a four engine bomber you needed a lot of firepower, so Axis fighters went to 2000HP and 30mmm guns. Allied late war planes didn't have to deal with massed bomber attacks so could afford a lighter armament in favour of more fuel to get range. There were of course exceptions where exceptional designs like the P 51 or Yak 3 remained competitive despite having significantly less engine power than their adversaries.
For high altitude you need a different prop blade angle...and a wing config that allows for the thinner air...basically a larger wing area. (or go much faster ie: more air across the wing per second) You need a turbo charger...you need plenty of oxygen.
What did planes use NO2 for at that point in time? Certainly they needed oxygen which had it's own problems (my uncles B-24 was almost lost because a green copilot lit a cigarette while they were at altitude and he had his oxygen mask on.).
Pressurized cockpit: As Slipdigit said, only the B-29 had one. Even modern fighters are not pressurized as battle damage and pressurization systems don't play well together. Liquid vs Air Cooled engines: Each type has advantages and disadvantages, but related to high altitude performance, one isn't inherently better than the other. The P-51 is known for its high altitude performance, but Hub Zemke who flew both types in combat considered the P-47 a better fighter above 25,000 feet. Turbochargers: the short answer is yes - or a mechanical supercharger. Any normally aspirated engine loses power as it climbs and the oxygen level decreases. Your ubiquitous Cessna engine is approved to run continuously at 75% rated power. However, it will only make 75% power up to about 8,000 feet. At 12,000 feet it will only make about 55% power. Turbo-superchargers or mechanical superchargers pressurize the incoming combustion air and allow the engine to make full power to higher altitudes. A turbocharger and a supercharger accomplish the same thing but drive the compressor by different means. Early WWII fighters tended to have single stage, single speed superchargers (or turbos) and suffered a drop in power at altitude. Later designs were multi-stage, multi-speed which increased the available power at altitude. If i remember correctly, the Merlin in the P-51 would produce full power to about 27,000 feet. There are some links to information on superchargers in this thread: http://www.ww2f.com/topic/57952-p-51-question/ Tanks for NO2: I assume you mean Nitrous, N2O? The Germans used a nitrous system for War Emergency Power, but the allied generally used a water injection system for WEP. Tanks for Oxygen: The aircraft had an oxygen system to supply oxygen masks worn by all aircrew anytime they were above 10,000 feet.
I thought exhaust driven turbochargers were able to spin faster the higher the plane climbed due to decreased air pressure that the exhaust pressure had to push against. The mechanical supercharges were linked to engine speed. So the turbos got better the higher they got. Not sure about this though. Anyone have any more info on this?
Yes, that is correct. Also, the exhaust driven turbo did not rob the engine of horsepower to drive the supercharger. But turbos had their own problems in WW2. In some detail...Super vs Turbo http://www.pacificaviationmuseum.org/pearl-harbor-blog/superchargers-and-turbochargers
