The Heinkel He 177 Greif (Griffin) was a long-range heavy bomber flown by the Luftwaffe during World War II. The introduction of the He 177 to combat operations was significantly delayed, by both problems with the development of its engines and frequent changes to its intended role. Nevertheless, it was the only long-range, heavy bomber to become operational with the Luftwaffe during the war. The He 177 had a payload/range capability similar to that of four-engined heavy bombers used by the Allies in the European theatre.
Work on the design began in response to a 1936 requirement known as Bomber A, issued by the RLM for a purely strategic bomber. Thus the He 177 was intended originally to be capable of a sustained bombing campaign against Soviet manufacturing capacity, deep inside Russia.
In contrast to its heavy payload and very wide, planform, the specifications called for the design to have only two very powerful engines. To deliver the power required, the He 177 needed engines of at least . Engines of this type were new and unproven at the time. The Daimler-Benz DB 606 power system that was selected, in conjunction with its relatively cramped nacelles, caused cooling and maintenance problems, such that the powerplants became infamous for catching fire in flight, and contributing to the He 177 gaining nicknames from Luftwaffe aircrew such as Reichsfeuerzeug ("Reich's lighter") or Luftwaffenfeuerzeug ("Air Force lighter").
The type matured into a usable design too late in the war to play an important role. It was built and used in some numbers, especially on the Eastern Front, where its range was particularly useful. It is notable for its use in mass raids on Velikiye Luki in 1944, one of the late-war heavy bombing efforts by the Luftwaffe. It saw considerably less use on the Western Front, although it played a role during Operation Steinbock (the "Baby Blitz"), against the UK in 1944.
Design and development
General Walther Wever had long been an advocate of strategic bombing and pressed the Luftwaffe to develop a dedicated long-range bomber for the role of attacking the Soviet Union's factories in the Ural Mountain area. This concept met significant scepticism within the Luftwaffe, and by 1936 this "Ural bomber" program had delivered two rather uninspiring designs, the Dornier Do 19 and Junkers Ju 89.
Wever continued to press for new designs for this role, and the Reichsluftfahrtministerium (RLM) finally released a new specification for what they called Bomber A on 3 June 1936. This called for a significantly more advanced design with higher speeds, longer range and larger payloads. This was also the same day that Wever was killed in an air crash, and the design lost its only politically powerful champion.
The specification required the plane to carry a bomb-load of at least 1,000 kg (2,200 lb) over a range of 5,000 km (3,100 mi), with a maximum speed of not less than 500 km/h (311 mph) at altitude. In addition to outperforming, by a considerable margin, any bomber then in service, the design's speed was intended to allow it to outrun any contemporary fighter, the so-called Schnellbomber concept.
On 2 June 1937, Heinkel Flugzeugwerke received instructions to proceed with construction of a full-scale mock-up of its Projekt 1041 Bomber A. Heinkel Flugzeugwerke's estimated performance figures for Projekt 1041 included a top speed of 550 km/h (342 mph) at 5,500 m (18,050 ft) and a loaded weight of 27,000 kg (59,500 lb). In order to achieve these estimates, Ernst Heinkel's chief designer, Siegfried Günter, employed several revolutionary features.
Engines
The He 177 required at least a pair of 2,000 PS (1,973 hp, 1,471 kW) engines to meet performance requirements. No engine in the German aviation power-plant industry at that time developed such power. A four-engine version would have been possible with engines like the Daimler-Benz DB 601 but the four-engine layout would impose higher propeller drag to the detriment of performance in dive bombing. The use of only two counter-rotating propellers on a heavy bomber offered many advantages, such as a substantial reduction in drag, reduction of dive instability and a marked improvement in maneuverability. The eight initial V-series prototypes, and the larger number of A-0 pre-production models of the He 177, displayed an airspeed and maneuverability comparable to many heavy fighters of the time.