Aviation of World War II
The Do-217M at the Soviet Scientific Research Institute. Our specialists had an opportunity to examine the Messerschmitt DB 603A engine in detail. Single-engine Bf 109G and K variants had different DB 605 modifications with the same 35.7-liter cylinder volume. Thanks to increased piston stroke and cylinder bore, the total cubic capacity of the more powerful 603 engines increased to 44.5 liters. This engine became heavier (from the DB 605A's 745 kg) to 962 kg and its size increased. Problems concerning the reliability of the DB 603A assemblies and aggregates, as well as design changes, were of particular interest because Soviet engine designers headed by B. Ya. Klimov continued to refine the powerful VK-107A engine (displacement of 42.7 liters) even after combat actions ceased.
It turned out that the Daimler Benz engineers had changed the crankshaft, spark plugs, and the design of the main bearing oil feed; they made the propeller reduction gear casing longer. Engine control became more automated through introduction of a single control lever. The Germans managed to establish precise cross coupling among the main DB 603 operating parameters: rpm, supercharge, fuel-to-air ratio, ignition advance, and impeller rotational speed. In addition, the engine was fitted with automatic units controlling the fuel pump and the supercharger hydraulic clutch. Moreover, the engines operated quite well, without signs of pinking, vibration, and malfunctions. They compared favorably with VK-107A in spooling up, transition from one power setting to another, and start-up at low temperatures.
The focus on German power plants continued when a Do 217M aircraft fitted with two DB 603 engines underwent testing. Except for its powerful engines, the captured bomber generally did not impress leading Air Forces Scientific Research Institute specialists. Its maximum speed of 477 km/h could not be considered sufficient either for the end of the war or for early 1946 when it was first flown in the USSR (lead engineer Engineer-Major P. I. Kuzmin, pilot Lieutenant Colonel V. I. Zhdanov). The Dornier also lagged behind the domestic Tu-2 in rate of climb (it took 15-5 minutes to climb to 5000 meters) and service ceiling (7750 meters). Its defensive armament was less effective as well.
At the same time, the upper DL-13I/ID semi-mechanized gun turret was interesting. It had electrical drive allowina it to move weapons horizontally 360° at a constant speed. This turret was better than the Soviet "purely mechanical" UTK-1 mounted on I1-4 and Li-2 aircraft. However, in general, the defenses were weak and it was almost exclusively confined to performing night missions. In January 1946, study of the Dornier ended.
* - without radar antennas.
** - the nose 7.9-mm twin MG 81Z machine gun was quite often replaced with 13-mm MG 131.
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