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The Greif (or Griffin) was a long-range twin engined bomber of the Luftwaffe. The troubled aircraft was the only heavy bomber built in large numbers by Germany during World War II. Aircrews nicknamed it the Reichsfeuerzeug (Cigarette Lighter of the Reich) due to the engines' tendency to catch fire in early versions.
An unusual feature of the airplane was the use of twin engines in each nacelle driving a single propeller. The insistence of this engine configuration by the Reichsluftfahrtministerium, (the German Air Ministry) stemmed directly from their determination that the aircraft should be capable of dive-bombing, a manoeuvre that is impossible in aircraft with four propellers, and also emblematic of the "Stuka mentality" pervasive in the Luftwaffe in the very late 1930s, which also badly influenced later bomber development programs, such as the ill-fated Bomber B program.
The paired engines had first been introduced on the single-propeller equipped Heinkel He 119 prototype reconaissance aircraft, to reduce drag where they worked well, but their tight installation in the He 177 led to considerable problems because of the poor packaging of the engine installations that caused oil leakage onto the hot exhaust manifolds on the two middle cylinder banks.
Starting with He 177 A-3, a slightly lengthened engine nacelle with a new choice of coupled-engine "system", the Daimler-Benz DB 610, was used to attempt to eliminate tendency for the engines to catch fire. This achieved only partial success and there were also problems with the transfer gearbox between the two engines and their shared propeller.
The insistence on the ability to dive-bomb also led to the need to strengthen the wing structure, leading to an increase in unloaded weight, producing the need to enlarge the undercarriage, in turn increasing further the weight and causing a decrease in speed, range and carrying capacity. The requirement to dive-bomb was never satisfactorily solved, and the He 177 was restricted to level and shallow dive attacks.
The overly ambitious design goals included an unrealistic requirement for a dive bombing capability, similar to the RAF's equally unrealistic requirement for catapult launching for the failed Avro Manchester heavy bomber. The attempt to reduce drag by coupling the engines, while theoretically sound, proved to be difficult in practice, leading to a history of engine failures not unlike that of the failed Manchester or that of the B-29, which had most of its defensive armament removed in order to lighten the burden on its engines and thus improve reliability.
Beset by many other technical difficulties in development and service, the plane had a troubled life. This was in part due to overly optimistic design requirements of long range, high speed, a large bombload, and even as a dive bomber. Though Goering forbade Heinkel to develop a version with four separate nacelles, Heinkel nevertheless produced prototypes of the Heinkel He 277 which was not produced in numbers.
The He 177's main gear arrangement can best be described as unbelieveably complex-there were four main gear struts, each with one large wheel, with the inboard and outboard retacting sets almost "meeting" under the nacelle of each of the twin coupled-engine systems when fully extended. A more conventional single-leg twin wheel arrangement for each main gear was not designed until the later He 274 and 277 prototypes were eventually built, and actually used on the sole example of the He 274, and a few developments that only existed as drawings actually had tricycle landing gear setups eventually being fitted to the He 277.
As example for these problem most resources cite a special situation regarding a night attack on England : 20 aircraft left, two failed to take off, 10 returned with burning or damaged engines and of the few that got to their target two were destroyed by enemy action. What most resources "forget" to cite is that these aircraft were brand new, just delivered about one week before and not even properly flown-in, the air unit just moved to a new airfield the day before and was missing lots of maintenance personnel and material.
The use of the He 177 was ended by the Emergency Fighter Program, which cancelled bomber production and operations and gave priority to defensive fighters in the final stages of the war.
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