German strategic bomber design during WW2.
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 its engines. While the He 177 used four engines in two coupled pairs which proved troublesome, the He 277 was intended to use four unitized BMW 801E 14-cylinder radial engines, in single nacelle installations.
The design was never produced and no prototype airframe was completed. The deteriorating condition of the German aviation industry late in the war and the competition from other long-range bomber designs from other firms, led to the design being cancelled.
Designation.
For many years after the war, some aviation history books and magazine articles stated that "Reichsmarschall" Hermann Göring, early in World War II, was becoming so frustrated by the 177A's problems with its twin DB 606 "coupled" powerplants, that he forbade Ernst Heinkel from doing any work on a 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 version of the 177 the "He 277", but overruled Göring's prohibition on working on the design (which Heinkel referred to as "He 177B" as a "cover designation" to hide its existence from Göring, and the RLM.)
Statements by Göring in August 1942 in response to "Oberst" Edgar Petersen's reports - in his capacity as the "Kommandeur der Erprobungstellen" ("commander of all Luftwaffe test stations"), at "Erprobungsstelle Rechlin" - on solving the serious problems with the original Heinkel He 177A's powerplants, seem to directly contradict elements of that narrative. ,The 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 DB 606 and DB 610 "power systems", as monstrous "zusammengeschweißte Motoren", ("welded-together engines",) He was anxious to see a four-engined version of the bomber developed and in production. The earliest-dated initiative to be undertaken by Ernst Heinkel himself to trial a true "four-engined" design format for the original He 177 dated back to 17 November 1938, before the construction of the He 177 V3 and V4 prototype airframes had even been started, when Heinkel had personally asked the RLM to set aside the He 177 V3 and V4 airframes for a trial installation of four separate unitized Junkers Jumo 211 powerplants to overcome the concerns that the RLM "Technischen-Amt" technical department's director Ernst Udet and Heinkel had expressed about the RLM's specific dive-bombing priority for the He 177A, but was turned down for the trial fitment. However, several publications listed the He 177B and He 277 as separate designs, including Nowarra (1972).
The erroneous assertion in some post-1945 aviation publications about He 177B being a cover designation for He 277" could have been due to the fact 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 Heinkel conceived the paper-only "He 177H" high-altitude predecessor to the later He 274 in October 1941, 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 RLM mention of He 277, as this date also indicates the time by which the RLM had issued the Heinkel firm the "8-277" number for the project. The RLM as of late spring of 1943 anticipated that three He 277 V-series prototype aircraft, and construction of ten pre-production He 277A-0 series service test machines would come from Heinkel's Schwechat southern plant complex in Austria beginning in 1944.
The He 277's fuselage design had been meant to originate with the last proposed "coupled-engine" variant of the He 177, 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 (redesignated He 177B-7 in the late summer of 1943). The considerable changes in the He 277's overall design philosophy evolved after the "Amerikabomber" requirement’s emergence in 1941, from the changes in the He 277's general arrangement proposal drawings during that time period, especially after Heinkel had worked out the earlier P.1064 project in 1942 for a six-engine strategic bomber. 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.
The main factor that seemingly required the lower-drag "coupled" powerplant format for the He 177A, the dive bomb attack mandated by the RLM (and which Ernst Heinkel had vehemently disagreed with from the late 1930s) was rescinded by Göring five months before approval of the "He 277's" by the RLM in February 1943. Heinkel 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, and not in any way directly related to the entirely separate He 277 advanced bomber project, which by the summer of 1943 was considered to be Heinkel's "Amerikabomber" 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.
In total, there were four 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 unbuilt He 179 with four Jumkers Jumo 211s; 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 the project’s cancellation in May 1944.
Design features.
The general arrangement "Typenblatt" drawings that Heinkel's firm was developing for the He 277 by mid-1943 show an advanced design of heavy bomber, with a 133 square meter area (1,431.6 sq. ft.) "shoulder mount", 40 meter (131 ft 3 in) span wing design, four separate BMW 801E powerplants of 1,471 kW (2,000 PS, 1,973 hp) output each at take-off, with each engine turning a propeller of up to four meters in diameter.
The fully retracting undercarriage considered for the design was to be either conventional or nosewheel landing gear, with main gear assemblies of twinned wheels on each unit, retracting into the inner engine nacelles (forward when combined with the nosewheel but rearwards for a conventional gear arrangement). Heinkel had designed a retractable tricycle undercarriage-equipped in late 1939 for the Heinkel He 280 jet fighter prototype, and followed that with the Heinkel He 219 night fighter.
The main crew accommodation of the He 277 consisted of a heavily glazed and "greenhouse"-framed clear view "stepless" cockpit, a common feature of many late-war German bomber airframes and new designs. Immediately aft of the heavily glazed nose, the cockpit glazing over the crew seating and pilot accommodation-enclosing upper section that was blended with the nose glazing's contours, protruding above the 277's forward dorsal fuselage decking level, with a rearward extension atop the fuselage that faired-in the forward upper dorsal turret's forward surface, extending rearwards to just forward of the inner engine cowls. The fuselage outlines themselves were deep, and almost slab-sided in cross-section, with its general sideview profile lines being strongly reminiscent of the He 219. This similarity with the 219 even extended to the depictions of the He 277's fuselage-mounted defensive armament emplacements as proposed by Heinkel, with one forward and two aft-facing "steps" along the slightly rounded dorsal and ventral surfaces of the fuselage, much like the smaller night fighter's earliest prototypes had, for the 277's manned aft dorsal and remote aft ventral turret defensive weapons mounts — the aft ventral emplacement being moved rearwards by roughly two meters, in comparison with the early He 219V-series prototypes, to accommodate the aft end of the He 277's bomb bay. The twin tail empennage assembly of the He 219 night fighter was also a likely inspiration for the 277's own similar unit, that added aerodynamic stability when compared to the 177A's single vertical tail — proven to be true from the first flights of the He 177B-series' four-engined He 177 V102 twin-tailed prototype from late December 1943 onwards — and made mounting a powered traversable defensive tail turret easier. Provision was shown on the Heinkel "Typenblatt" general arrangement drawing for four underwing hardpoints, two per wing panel on either side outboard of the engines, potentially allowing external ordnance loads or drop tanks to extend the bomber's capabilities or range.
A May 1943 Heinkel factory document showed possible offensive bombload configurations and flight consumable (fuel, etc.) weights for the He 277, two differing bomb bay sizes (interior dimensions of 1.5 x 7.5 meters for the tailwheel version, and 1.75 x 7.0 meters for the tricycle undercarriage version) were considered. The latter within a 1.90 meter wide fuselage. The lightest warload of six 500 kg (1,100 lb) SC 500 bombs for each bomb bay configuration, gave the tricycle-geared, 1.9 meter exterior width wider-fuselage version, considering a larger load (12,200 kg/26,895 lb) of fuel, a possible stated maximum range of , equalling the potential range capability of the earlier-designed Me 261, an indicator of what could have been achieved had the 277 been in full consideration from its beginnings for the "Amerikabomber" design competition.
Armament.
As envisioned the defensive armament was in five turrets; two manned, and the other three remotely operated. A remotely operated "Fernbedienbare Drehlafette" (FDL) 151Z turret with twin 20 mm MG 151/20 cannon was in the "chin" position under the aircraft's nose. Along the top of the fuselage were a remotely operated FDL 151Z in the forward dorsal and a manned "Hydraulische Drehlafette" (HDL) 151Z in the rear dorsal position; each turret with two MG 151/20 cannon. Underneath the rear fuselage, just to the rear of the bomb-bay was a remotely operated ventral turret with two more MG 151/20 cannon. The gunner for the turret would lay prone, facing rearwards in a starboard-side offset position with a slightly protruding ventral blister-like gondola for the gun sight. In the end of the tail was a manned "Hecklafette" (HL) 131V turret with four 13 mm MG 131 heavy machine guns. The "Hecklafette" four-gun turret was planned to be used on some of the other "Amerikabomber" airframes, Heinkel's proposed developments of the He 177A airframe, and a projected "C-version" of the He 219 night fighter. This increasing demand for an advanced gun turret that had not even been produced by Borsig (the firm responsible for it), beyond a small number of test units and engineering mockups led to an alternative twin-cannon "HL 151Z" version with a single MG 151/20 cannon each side of the turret. Only a few ground test examples of the twin-cannon variant tail turret had been produced by March 1944. One of these twin-cannon experimental tail turrets was mounted on an He 177A airframe for testing. Some sideview line drawing depictions of purported "He 277" aircraft, usually in the same aviation history volumes that purveyed the erroneous "He 177B/He 277" storyline, also show what could be an early He 177A-7-based depiction of the later "Amerikabomber" competitor bearing the He 177A's "Cabin 3" standard cockpit