Mentioning double powerbanks :
The German WW2 bomber Heinkel He-177 ‘Greif’ (‘Griffin’), was the only Axis bomber (apart from the four engine Italian Piaggio P108, that hardly has seen production), capable of matching the capacities of planes like the Allied B-17 or Lancaster. Its power system was ‘four engine’, but in order to use it as a dive bomber too (another mad idea of Hitler), two coupled engines drove one four blade propellor.
The He-177 featured some novelties, like remote controlled machine gun turrets (such as would be installed on the American B-29), in order to save the weight and space for gunners, and to increase the structural strength of the hull.
The coupled engines were however a nightmare for maintenance (too cramped space), and had a problem with dissipating heat trough the exhausts. Undesired building up of heat in the engine nacelles caused mixtures of oil spills and dirt to catch fire easily, leading to many deadly accidents with the aircraft.
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