Heinkel He 177 - Engine Difficulties

Engine Difficulties

The tendency of the DB 606 engine to ignite became increasingly serious as the test programme progressed and many of the He 177 A-0s were destroyed in accidents or engine related causes. The DB 606 engine had first been introduced on the Heinkel He 119 and later used on other aircraft such as the Messerschmitt Me 261 where they functioned as intended, but the extremely tight cowlings on the He 177 led to considerable problems, the most common being in-flight engine fires and engine overheating. There were several reasons for the flammability of the DB 606 engine, one of which was the common "central" exhaust manifold, serving a total of twelve cylinders, on the two inner cylinder banks of the engines, which became excessively hot and caused the usual accumulation of oil and grease in the bottom of the engine cowling to catch fire. When the pilot throttled back there was a tendency for the injection pump to deliver more fuel than was required by the engine, in addition to which the injection pump connections leaked. In order to restrict the aircraft's weight, no firewall had been provided, and the DB 606 was fitted so close to the main spar - to the point that the rear two-thirds of the component powerplants' engine blocks were located behind the wing's leading edge - that there was insufficient space for the fuel/oil pipelines and electrical leads. The engine was frequently saturated by fuel and oil from leaking connections. At high altitude, the oil tended to foam due to a badly designed oil pump, and in this condition it circulated in the engines, its lubricating qualities being severely reduced. Insufficient lubrication resulted in the disintegration of the connecting rod bearings which could burst through either one of the component engine crankcases, puncturing the oil tanks which poured their contents on to the hot central exhaust pipe collector. The tightly packed nature of the "power system" engine installations on the He 177A, with the extreme rearwards location of the component engines in their nacelles placing them mostly behind the wing's leading edge, also led to very poor access to the engines as well as very poor ventilation. As a result of these factors, as well as a lack of routine maintenance in the field, the DB 606 powerplants easily caught fire in flight. The effort to create an adequately powerful engine for the He 177 by mechanically coupling pairs of lower-power engines, while theoretically sound, proved to be difficult and time consuming to perfect, leading to numerous engine complications especially on the initial production models.

Reichsmarschall Hermann Göring, angered at the apparent slowness with which the He 177 was having its powerplant problems researched and solved late in August 1942, responded thus to one Oberst Edgar Petersen's report (the Kommandeur der Erprobungstellen) on the He 177's powerplant troubles, remarking on the unusual engine configuration, and the difficulty of maintenance access, of the DB 606"s:

Why has this silly engine suddenly turned up, which is so idiotically welded together? They told me then, there would be two engines connected behind each other, and suddenly there appears this misbegotten monster of welded-together engines one cannot get at!

— Hermann Göring

Starting with the He 177 A-3/R2, a modified engine nacelle with a new engine, the Daimler-Benz DB 610 which consisted of a pair of Daimler-Benz DB 605's, was used to eliminate the tendency for engine fires. With the introduction of the DB 610 came several improvements including the relocation of the engine oil tank, the lengthening of the engine mountings by 20 cm (8 in), the complete redesign of the exhaust system which also facilitated the installation of exhaust dampers for night missions, and the setting of a power limitation on the engines which resulted in greater reliability. These modifications, supposedly numbering 56 of both major and minor varieties, were successful as far as eliminating engine fires were concerned, but other minor problems with the transfer gearbox between the two component engines of each "power system" and their shared propeller remained.