Further Development-The Heinkel He 177B
Due to continuing problems with the DB 606's configuration, much development work was being done in order to rectify engine complications, including a complete redesign of the original He 177, primarily through newer wing designs and layouts to accommodate them, intended towards the creation of a four-engined version of the Greif's airframe. The first occurrence of such concerns over the coupled-engine vs. four separate engine issue for the He 177 emerged in mid-November 1938, as Ernst Heinkel had requested that he wished for two of the requested eight He 177 prototypes to be fitted out with four individual engines in place of the coupled-engine arrangements, eventually specifying that the V3 and V4 airframes get four individual Junkers Jumo 211 engines each in a November 17 in-plant corporate meeting - the same exact type and number of engines actually used for the first flights of the Me 264 V1 strategic bomber prototype's first flights in late December of 1942. Ernst Udet was also critical of the coupled DB 606 powerplant choice for the He 177 from before the war's start, with Göring adding his input from his own frustrations with the seemingly interminable engine problems delaying the introduction of the He 177A into service. Göring was reported as stating in August 1942:
I had told Udet from the start that I wanted this beast with four engines. This crate must have had four engines at some time! Nobody had told me anything about this hocus-pocus with welded-together engines.
— Hermann Göring
Nearly four years after Herr Heinkel had unsuccessfully requested two of the prototype He 177 V-series airframes to be built with four individual powerplants, the RLM's requirement for the He 177 to perform diving attacks was finally rescinded in September 1942 by Göring himself, and with that decision finally rendered, Heinkel's design work on the pair of "separately" four-engined versions of the He 177A, the A-8 and A-10, collectively renamed the He 177B in August 1943 were then able to progress, meant to be powered with four individual Daimler-Benz DB 603 engines on new longer-span wings, with each liquid-cooled DB 603 fitted with a Heinkel He 219-style annular radiator right behind the propeller for engine cooling. This task was accomplished in a considerably later timeframe than British aircraft designer Roy Chadwick had done in similarly converting the Avro Manchester. The Manchester, like the A-series Greif (with its coupled DB 606s and 610s) had depended on two very powerful and quite troublesome 24-cylinder powerplants, the British Rolls-Royce Vulture, but by 1941 had been redesigned with four Rolls-Royce Merlins, as the Avro Lancaster.
By August 1943 much of the detail work for the He 177B series aircraft was well on its way to completion, and Erhard Milch eagerly approved the creation of three He 177B prototypes, designated He 177 V101 to V103, from his statement on August 10:
The He 177A-4 and A-5 will be produced as before. The He 177B-5 will be tackled with vigor. It will be built in series as soon as possible.
— Erhard Milch
The B-5's first-built prototype, the He 177 V101, was converted from a mid-production He 177 A-3 airframe (number 535550, with Stammkennzeichen of NN + QQ), the V102 being converted from the eighth He 177 A-0 production prototype aircraft (which required lengthening to the He 177A-3 and later fuselage specification), and the V103 being converted from an existing, early production He 177 A-5 airframe, with all three airframes initially retaining the production 177A-style single vertical tail surfaces. The V101 was uniquely fitted with a small-area matching vertical pair, one per side, of so-called pivoting "drag rudders" mounted a short distance in from the horizontal stabilizers' tips, directly inline with the inner engine nacelles, to simulate "engine-out" conditions. Each of the pivoted "drag rudders" had their area divided equally above and below the plane of the stabilizer. Because of the 177A-style single-tailed V101 prototype having increasingly serious stability problems with higher airspeeds in its flight testing, the second prototype, the V102, was both the first He 177B example to fly with the quartet of DB 603 engines on December 20, 1943 in combination with a brand-new empennage of twin tail configuration, fitted to it during the early autumn of 1943. When the V102 was tested later that autumn while still flying with its A-series wing and powerplants before its own pair of B-series "four engine" wing units were ready, the new twin vertical tails gave the V102 significantly better in-flight handling when compared to the original He 177A's single tail design, except during the landing approach when the Fowler flaps were extended during its own initial flights with the twin tails in November 1943. By late February 1944, as the USAAF's Big Week strategic bombing campaign against Nazi Germany was initiated, at a meeting held at the Wiener Neustadt military airfield, visited by Erhard Milch, fellow guests Oberst Edgar Petersen and Oberstleutnant Siegfried Knemeyer each had a chance to fly the now four-engined V102 prototype after the B-series set of wings had been fitted, with Knemeyer stating that he could not believe a four-engined heavy bomber could possess the "excellent handling qualities" the V102 machine displayed. The only verifiable wartime photograph that exists today of any of these He 177B prototypes in an intact condition is one of the V101, parked outdoors on a foggy German airfield, most likely the Heinkel-Sud factory airfield at Schwechat. One additional surviving photo that is known to exist, showing what looks like an He 177B-series prototype from the right side with a production-style A-series single vertical tail surface set, and bearing the Stammkennzeichen code of NE+OD, does not match any item of the surviving documentation for the four known 177B-series prototypes ordered, built or flown before the end of the war.
The He 177B was also intended to introduce a slightly enlarged, somewhat more aerodynamic fully glazed nose, first meant for use on the production A-7 version, that could incorporate a remotely controlled power chin turret at the front of its Bola for forward ventral defense, mounting either a pair of MG 131 machine guns or MG 151 cannon, but the new nose design was only tested on the fifteenth He 177 A-0 production prototype, without the chin turret, and was never fitted on any of the He 177B prototypes, which used the standard "Cabin 3" He 177A's well-framed nose. No photographs of this new nose design are known to have survived the war and only drawings exist of it in modern archives. The remaining defensive armament generally remained similar to the He 177A, particularly the twin dorsal gun turrets for the He 177 B-5, with the aft manned dorsal turret being deleted on the planned He 177 B-7 (as on the He 177 A-7) to reduce weight, and a fully powered manned Hecklafette HL 131V tail turret, carrying a quartet of MG 131 machine guns, was intended for installation on the prototypes and would have been standardized on the production aircraft, but never went beyond the mockup and working prototype stage, with a pair of the prototype tail turret units documented as being fitted to the He 177 V32 and V33 A-series DB 610-powered prototype airframes for trials. The cumbersome four-strut main landing gear of the A-series was retained intact for the B-series prototypes, even though their height, meant to allow clearance for the A-series' pair of large four-blade propellers, was not changed - the outer edge of the DB 603's inner engine nacelle/wing surface juncture was located right at the "centreline" of each of the twin pairs of A-series main gear strut locations, on all four of the B-series prototypes.
The first flights of the He 177B prototypes, starting with the He 177 V102 on December 20, 1943 occurred between late December 1943 and early January 1944 in the vicinity of the Vienna-Schwechat airfield, at the firm's Heinkel-Süd southern production facility, where an additional prototype, the V104, whose purpose was to be the "finalized" production prototype for the He 177B-5, and also meant to be a twin tailed prototype like the earlier V102, was being completed by order from the RLM, converted from an early production He 177 A-5.
However, from April 23 through July 1944, repeated Fifteenth Air Force bombing raids on German aircraft production facilities in Vienna destroyed the airworthy V103 and the incomplete V104 at the Floridsdorf and Zwölfaxing satellite plants of the Heinkel-Süd complex during a July 8 raid, setting back plans of producing any series examples of the B-5 version. Arado Flugzeugwerke, which had been the major subcontractor for the A-series Greif airframes, at that time was itself fully involved with the production of its own, much more advanced Arado Ar 234B turbojet-powered reconnaissance-bomber, and was not able to handle the anticipated demand from Heinkel to produce the B-5 by October 1944. The Arado firm would not have been able to have started the He 177B-5's production for another month (November 1944) from its own focus on the Ar 234B. The last known official accounts of the whereabouts of the two He 177B prototypes that escaped heavy bombing had the V101 still at the Heinkel-Süd plant's airfield at Schwechat near Vienna, and the V102 also there at Schwechat as late as February 1945, after damage sustained from a bad landing in April 1944 while evading one of the initial USAAF 15th Air Force raids on the area, which had kept it from being flown north to the Luftwaffe's well-known, central Erprobungstelle test facility at Rechlin for safety. It is possible, from some accounts, that the V101 prototype might have survived until at least February 1945 (as the V102 had) before it was scrapped, as at least a pair of photos of what is stated as the wrecked V101 place it at Cheb in May 1945, and allegedly showing that the V101 had even been test-fitted with a quartet of Junkers Jumo 222 engines, if verified, would conflict with Heinkel records as to the V101 having been scrapped. One of the Czech photos does show what is thought to be the V101 with four bladed propellers instead of its earlier three-blade units used with its four DB 603 engines, a combination of prop type and powerplant also used for the Fw 190C fighter prototype.
The adoption of the Emergency Fighter Program in early July 1944 dealt the final blow to the entire He 177B development program, with the Heinkel He 162 jet fighter being the only new Heinkel aircraft design that would be allowed into production.
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