Editing Luftwaffe (section)

===Engine development===
[[File:Daimler Benz DB 610.jpg|thumb|right|A restored DB 610 "power system" engine, comprising a pair of DB 605 inverted V12s – the top of its central space-frame motor-mount structure can be seen.]]
By the late 1930s, [[airframe]] construction methods had progressed to the point where airframes could be built to any required size,<ref>founded on the all-metal airframe design technologies pioneered by [[Hugo Junkers]] [[Junkers J 1]] in 1915</ref> especially in Germany with aircraft like the [[Dornier Do X]] flying boat and the [[Junkers G.38|Junkers G 38]] airliner. However, powering such designs was a major challenge. Mid-1930s aero engines were limited to about 600 hp and the first 1000 hp engines were just entering the prototype stage{{snd}}for Nazi Germany's then-new Luftwaffe air arm, this meant liquid-cooled inverted V12 designs like the [[Daimler-Benz DB 601]].<ref>Mantelli-Brown- Kittel-Graf 2019 pp. 23–24.</ref>

Nazi Germany's initial need for substantially more powerful aviation engines originated with the private venture [[Heinkel He 119]] high-speed reconnaissance design, and the [[Messerschmitt Me 261]] for maritime reconnaissance duties. To give enough power in each engine installation, Daimler-Benz coupled two DB 601 engines as single "power system" with the propeller gear reduction housing across the front ends of the two engines. The combined powerplant, known as the DB 606, gave {{convert|2,700|PS}} maximum output in February 1937, for a total weight of around 1.5 tonnes.<ref name="weldedtogether-606">{{harvnb|Griehl|Dressel|1998|p=224}}</ref>

Daimler-Benz's was at the same time developing a 1,500 kW class [[X engine|X-configuration]] engine design resulting in the twenty-four cylinder [[Daimler-Benz DB 604]] (four banks of six cylinders each). Possessing essentially the same displacement of {{convert|46.5|L|in3}} as the initial version of the liquid-cooled [[Junkers Jumo 222]] multibank engine, six banks of four inline cylinders apiece instead; coincidentally, both the original Jumo 222 design and the DB 604 each weighed about a third less (at some {{convert|1,080|kg|lb|disp=or}} of dry weight) than the DB 606. The DB 604's protracted development was diverting valuable German aviation powerplant research resources, and with more development of the "twinned-[[Daimler-Benz DB 605|DB 605]]" based DB 610 coupled engine (itself initiated in June 1940 with a top output level of {{cvt|2950|PS}},<ref name="weldedtogether-606" /> and brought together in the same way – with the same all-up weight of 1.5 tonnes – as the DB 606 had been) giving improved results at the time, the Reich Air Ministry stopped all work on the DB 604 in September 1942.<ref>{{cite book |last1=von Gersdorff |first1=Kyrill |last2=Schubert |first2=Helmut |title=Die deutsche Luftfahrt: Flugmotoren und Strahltriebwerke. |language=de |year=2007 |publisher=Bernard & Graefe Verlag |location=Bonn |isbn=978-3-7637-6128-9}}</ref> Such "coupled powerplants" were the exclusive choice of power for the [[Heinkel He 177 Greif|Heinkel He 177A ''Greif'']] heavy bomber, mistasked from its beginnings in being intended to do moderate-angle "dive bombing" for a 30-meter wingspan class, heavy bomber design – the twin nacelles for a pair of DB 606s or 610s did reduce drag for such a combat "requirement", but the poor design of the He 177A's engine accommodations for these twin-crankcase "power systems" caused [[Heinkel He 177#Engine difficulties|repeated outbreaks of engine fires]], causing the "dive bombing" requirement for the He 177A to be cancelled by mid-September 1942.<ref>{{harvnb|Griehl|Dressel|1998|p=54}}</ref>

BMW worked on what was essentially an enlarged version of its highly successful [[BMW 801]] design from the [[Focke-Wulf Fw 190]]A. This led to the 53.7-litre displacement [[BMW 802]] in 1943, an eighteen-cylinder air-cooled radial, weighing {{convert|1530|kg|abbr=on}} matching that of the 24-cylinder liquid-cooled inline DB 606; and the even larger, 83.5-litre displacement [[BMW 803]] 28-cylinder liquid-cooled radial, which from post-war statements from BMW development personnel were each considered to be "secondary priority" development programmes at best.{{Cn|date=December 2023}} This situation with the 802 and 803 designs led to the company's engineering personnel being redirected to place all efforts on improving the 801 to develop it to its full potential.<ref>{{cite magazine |last=Fedden |first=Sir Roy |date=6 December 1945 |title=German Piston-Engine Progress |page=603 |magazine=Flight Magazine |location=London, UK |publisher=Flightglobal}}</ref> The BMW 801F radial development, through its use of features coming from the 801E subtype, was able to substantially exceed the over-1,500 kW output level.{{sfn|Christopher|2013|pp=80–81}}

The twinned-up [[Daimler-Benz DB 601]]-based, 1,750 kW output DB 606, and its more powerful descendant, the 2,130 kW output DB 605-based DB 610, weighing some 1.5 tonnes apiece, were the only 1,500 kW-plus output level aircraft powerplants to ever be produced by Germany for Luftwaffe combat aircraft, mostly for the Heinkel He 177A heavy bomber. Even the largest-displacement inverted V12 aircraft powerplant built in Germany, the 44.52-litre (2,717 cu. in.) [[Daimler-Benz DB 603]], which saw widespread use in twin-engined designs, could not exceed 1,500 kW output without more development. By March 1940, even the DB 603 was being "twinned-up"<ref name="weldedtogether-606" /> as the 601/606 and 605/610 had been, to become their replacement "power system": this was the strictly experimental, approximately 1.8-tonne weight apiece, twin-crankcase DB 613; capable of over 2,570 kW (3,495 PS) output, but which never left its test phase.{{Citation needed|date=January 2021}}

The proposed over-1,500 kW output subtypes of German aviation industry's existing piston aviation engine designs—which adhered to using just a single crankcase that ''were'' able to substantially exceed the aforementioned over-1,500 kW output level—were the DB 603 LM (1,800 kW at take-off, in production), the DB 603 N (2,205 kW at take-off, planned for 1946) and the BMW 801F (1,765 kW (2,400 PS) engines. The pioneering nature of jet engine technology in the 1940s resulted in numerous development problems for both of Germany's major jet engine designs to see mass production, the [[Junkers Jumo 004|Jumo 004]] and [[BMW 003]] (both [[Axial compressor|axial flow]] designs), with the more powerful [[Heinkel HeS 011]] never leaving the test phase.{{sfn|Christopher|2013|p=74}}