A Note on Engines

The Germans in some ways did very well with aircraft engines in the Second World War. Despite having less aero engine experience than the  British and Americans, they none the less managed to stay at rough parity with the Allies through the Second World War, with the Jumo 213 and the BMW 801 seeing constant development until war's end. The use of fuel injection rather than carburetors was an advancement over Allied designs, and the use of methanol as an aviation fuel additive was a clever fix to poor quality Axis fuel. At the same time, aero engines were yet another area where Germany was at a material disadvantage. The engines with the greatest performance couldn't be produced in anything like the numbers demanded, and metallurgy - especially in the creation of turbo and superchargers - was something that Germany's limited access to rarer metals couldn't help but suffer from. Both types of chargers cram extra air into engine cylinders to increase combustion, or at high altitudes increase the amount of air in a cylinder to stop power loss. Turbochargers are a turbine driven by exhaust gasses to create compression, while superchargers compress air via an engine driven by power off of the motor. Both have to work very close to the point of combustion, and thus experience *extremely* high temperatures; thus constructing working versions of a charger requires tight metallurgy skillz.

Until turbines arrive on the scene, aircraft engines came in two flavors: liquid-cooled and air-cooled radial. Liquid cooled aircraft engines are quite similar in mechanics to engines in cars today: they use liquid to manage waste heat. The performance was slightly better than a radial, but it came with a drawback that engine damage might cause the coolant to bleed out and render the engine (and often the airplane) nonfunctional. The radial was a series of pistons firing around a central crankshaft. While they gave away some raw output of liquid cooling they had a few advantages to the aircraft designer: first, they cooled themselves by air, and were thus could be lighter than a comparative liquid cooled V12. The air cooled aspect also made them less vulnerable to damage, as no vulnerable cooling fluid could leak away. Beyond that, radials sometimes took fairly incredible trauma and kept operating; radials could have their pistons shot off and still function, abet with a higher oil consumption.

All the combatants in the Second World War spent a lot of time and money trying to develop new engines. With Germany the evolution of existing designs happened kept pace, introducing new high powered piston engines went poorly. Several engines were scheduled to appear that would have the output for heavy, large aircraft just didn't, with many designs finding themselves canceled once the engine designers had based their projections on turned out to be vaporware.

This is especially important in the Nazi Amerika bomber projects, as the whole endeavor was impossible without engines of a very high level of reliability, power output, and power to ratio weight. The B-36 and the famous Hughes 300, the 'Spruce Goose', used six and eight Wasp majors, radial monster engines with an output that started at 2500 hp. America and Britain, despite their advantages, struggled in getting engines that past the 2000 hp mark - as a matter of fact, the Wasp Major and its supporting act in the monsters of internal combustion tour, the Wright R-3330, had delays and technical problems galore during World War 2. The Allies did manage to break the 2000 hp barrier - the slightly, lovably, mad British Napier H-24 could put out 2400 hp at low altitudes in 1944 - but this was not without a significant investment of blood, sweat, and tears.

My point is that the Nazis never had large engines that could manage this output - hence the linked engines debacle of the He 177. When looking at hypothetical Nazi Aircraft, one can gauge its plausibility simply by looking at the projected engine output - generally, anything above 2000 hp should be viewed as unlikely, especially as such an engine would have enormous pressure to go into a defensive fighter mid-1943 onward, assuming a minimal level of Black Gay Hitler. If those outputs stretch to the 3000 hp or above, our Black Gay Hitler curve approaches its Liberace point since we're now assuming a world where Jumo could develop and deploy Wasp Major-like engines successfully because the Third Reich defeated the Soviet Union and now rules everything west of the A-A line.
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