The Heinkel He 277 was a four-engine, long-range heavy bomber design, originating as a derivative of the He 177, intended for production and use by the German Luftwaffe during World War II. The main difference was in engine configuration. Rather than using two fire-prone Daimler-Benz DB 606 "power system" engines, each of which consisted of side-by-side paired Daimler-Benz DB 601s and with each DB 606 "power system" weighing 1.5 tonnes apiece — or two of the similar DB 610, each of which used a pair of DB 605 engines in a similar "twinned" configuration on later He 177A airframes (the A-3 model and onwards), the He 277 was meant from the outset to use four BMW 801E 14-cylinder radial engines,〔Griehl & Dressel 1998, p. 196〕 each mounted in an individual nacelle and each turning a three-blade, four-meter diameter propeller. The design was never produced, and not a single prototype airframe was ever completed, owing both to the deteriorating condition of the German aviation industry late in the war, and the competition from other long-range bomber designs from other firms, competing for Germany's increasingly scarce aviation production capacity. Although not specifically intended for it at first, partially due to the time-frame in the spring of 1942 in which its ultimate niche was requested for by the RLM, the He 277 design essentially became Heinkel's entry in the important trans-oceanic range ''Amerika Bomber'' competition, struggling to compete against both several other designs from rival firms in the competition for a truly trans-oceanic ranged bomber for the Luftwaffe, and Germany's own rapidly degrading ability, from Allied bombing damage to its aviation plants, to produce military aircraft of any sort.
==The "He 177B" versus He 277 controversy==
For many years after the war, a substantial number of aviation history books and magazine articles that dealt with late World War II German military aviation developments consistently stated that ''Reichsmarschall'' Hermann Göring, early in World War II, was becoming so frustrated by the 177A's ongoing engine problems, caused by the twin DB 606 "coupled" powerplants selected for the He 177A design in the pre-war years, that he forbade Ernst Heinkel from doing any work on a separately four-engined version of the 177 airframe, or even mentioning a new "He 277" design with four separate engines – by one account, in the late autumn of 1941 – until Heinkel brought the disagreement directly to Adolf Hitler, who supposedly not only approved of calling the new, separately engined version of the 177 the "He 277", but overruled Göring's prohibition on working on the design (previously called the "He 177B" by Heinkel as a "cover designation" to hide its existence from Göring, and the RLM.)
Statements by Göring himself in August 1942 in response to ''Oberst'' Edgar Petersen's reports on solving the serious problems with the original Heinkel He 177A's powerplants, however, seem to directly contradict elements of the oft-repeated story, as those statements seem to show that Göring thought that the He 177A actually had four separate engines, and in late August 1942 Göring derisively labeled the He 177A's coupled engine arrangements, the 1.5 tonnes-apiece DB 606 and DB 610 "power systems" at that time as monstrous ''zusammengeschweißte Motoren'', or "welded-together engines",〔Griehl & Dressel 1998, pp. 52–53〕 in his complaints about the He 177A's ongoing engine difficulties, and was anxious to see a truly four-engined version of Heinkel's heavy bomber fully developed and in production.
Facts that could have fostered the origin of the post-war aviation book storyline about the "He 177B"/He 277 controversy were that the RLM, in listing the He 177 development projects that they approved of the Heinkel firm doing work on as of February 1943 — six months after Göring's recorded engine complaint statements, and 18 months after the first-ever consideration by the RLM for any He 177 proposed variant to have four "individual" powerplants, as the paper-only "He 177H" high-altitude predecessor to the later He 274 in October 1941,〔Griehl & Dressel 1998, p. 177〕 only included the He 177 A-5 heavy bomber, A-6 high-altitude bomber, A-7 long-range version, and the "He 277" itself, defining the February 1943 date as the earliest reliable date of any official German government mention of such an "He 277"-designated aircraft, as this date also indicates the time by which the RLM had issued the Heinkel firm the ''8-277'' airframe design number for the project.〔Griehl & Dressel 1998, p. 179〕 The RLM was also expecting, during the late spring of 1943 — about one year after the mid-Spring 1942 ''Amerika Bomber'' proposal first arrived in Göring's offices — that a trio of He 277 V-series prototype aircraft, and construction of ten pre-production He 277A-0 series service test machines were to be completed, as well as "progressive development" of the still-unbuilt and unfinalized design, were anticipated as coming from Heinkel's Schwechat southern plant complex in Austria.〔Griehl & Dressel 1998, p. 104〕 The initial starting place for the He 277's fuselage design had been meant to originate with the last "coupled-engine" proposed variant of the He 177 itself, the long-range A-7,〔 which itself was to be the basis for a four-engined variant of the ''Greif'' as the He 177A-10, then redesignated the He 177B-7 in the late summer of 1943, as both the A-7 and B-7 had omitted the manned rear dorsal turret of the earlier A-series versions for lighter weight.〔 The considerable changes in the He 277's overall design philosophy evolved after the ''Amerika Bomber'' proposal's emergence in May 1942, from the changes in the He 277's general arrangement proposal drawings during that time period. The original proposal, which was meant to use the He 177A-7's fuselage as the starting point, evolved into designing a dedicated, new and wider He 219-general pattern fuselage layout for the 277 from the Spring 1943 timeframe onward, which would be more capable of using a tricycle undercarriage then gaining favor with a few German aviation designers, even with the 277 not known to have been specifically considered by the RLM in the earlier timeframe for the ''Amerika Bomber'' proposal.
The main factor that seemingly required the lower-drag "coupled" powerplant format for the He 177A, the diving attack mandate by the RLM, which Ernst Heinkel vehemently disagreed with since the original ''Greif's'' beginnings in the late 1930s, was rescinded by Göring himself some five months ''before'' the "He 277's" earliest-known February 1943 RLM approval date. The Heinkel firm started work on the He 177B as a straightforward, separately four-engined development of the 177A under the B-series designation at least as early as the late summer of 1943, when official Heinkel documents began referring to the He 177B, evidenced from an August 1943-dated, (Heinkel factory-created general arrangement ''Typenblatt'' drawing of the He 177 V101 being labeled with the ''8-177'' RLM designation for the entire line of ''Greif'' airframes, and "B-5" elsewhere in the drawing's title block ), as a fully RLM approved development of the original He 177 aircraft line,〔Griehl & Dressel 1998, p. 166〕 and not in any way directly related to the entirely separate He 277 advanced bomber design project, which by the summer of 1943 was considered to be Heinkel's ''Amerika Bomber'' aviation contract contender. The first development of the original He 177A to fly with four "individual" engines – using a quartet of He 219-style annular radiators to cool its likely-unitized Daimler-Benz DB 603 powerplants – was the second He 177B prototype, the He 177 V102, on December 20, 1943.〔Griehl & Dressel 1998, p. 163〕
In total, there were three separate efforts, the movement toward which had been initiated by Ernst Heinkel as early as November 1938, to develop "true four-engined versions" of the A-series ''Greif'': the He 177B, which culminated in four prototype examples being built, with three getting airborne before the war's end; the He 274, of which only two prototypes were started before the end of World War II and completed and flown in France after the war's end; and the He 277, for which only a few airframe parts had been in the process of completion, with no completed prototypes at any time, before or after the end of the war.
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