Dornier Do 217 - Development and Design - Focus On A Heavy Bomber

Focus On A Heavy Bomber

At the end of August 1938 arguments against the floatplane version arose in favour of a land based aircraft to serve as a torpedo bomber in the Battle of the Atlantic, with its more numerous potential applications, were accepted. At the beginning of January 1939 the RLM stopped all work on the marine dive bomber version, as its estimated performance was not adequate. On 8 July 1939 Dornier issued a manufacturing specification for a Glide-Bomber version for full maritime use. It was to be equipped with BMW 801 engines. In contrast to the earlier description of the design, the Do 217 E had a new nose and the nose, cockpit rear, and ventral positions carried one MG 15 each. The design was to carry a maximum bomb load of two SC 500 and two SC 250 bombs. It was also possible to carry a torpedo or aerial mine. A dive brake was fitted to the tail to deploy during anticipated dive bombing missions. These features increased the design's weight to 10,500 kilograms (23,000 lb). Dornier had intended the speed to be in the region of 530 kilometres per hour (290 kn).

Superficially a scaled up Dornier Do 215, and initially powered by the same engines, the Do 217 was actually considerably larger and totally different in both structural and aerodynamic design. The first prototype (the Do 217 V1) flew on 4 October 1938, but crashed seven days later during a single-engine flying test. The aircraft had been piloted by Rolf Koeppe, a flight commander at Rechlin. A Dornier mechanic, Eugen Bausenhart was also on board. It was found to be underpowered and was not manoeuvrable when compared with contemporary bombers. Instability was a problem at first, but modifications such as fixed Handley-Page Leading edge slots along the leading edges of the vertical stabilizers to help to improve flight stability.

The second prototype flew on 5 November 1938. After arriving at Friedrichshafen in June 1939, further evaluations were scheduled to take place. Plans were made to install Daimler-Benz DB 603 engines to enable the aircraft for high-altitude reconnaissance. This meant the fitting of a pressure chamber. When Daimler-Benz failed to supply the engines, development came to a standstill. On 29 October the RLM ordered the aircraft to be scrapped, or a new use found for it. A third prototype flew on 25 February 1939 with Jumo 211A engines in place of the DB 601s. On 15 August 1939 and 23 January 1940, the aircraft was flown to Rechlin where it was tested in night flying trials. A number of the flights were to assess the performance of the new Siemens navigation aids under development. At the same time, Dornier also carried out fuel jettisoning and drop tank trials using 900 l external tanks. As with the Do 17, the test team tried several tail configurations with the Do 217 V3. Single, double and triangular assemblies were tried. These designs were used in the Do 217 M-3, M-9 and Dornier Do 317.

The same units were used on the fourth prototype V4 which flew in April 1939 at Friedrichshafen and Rechlin. The Jumo proved to be the best, and the designers deemed them to be essential if the desired performance was to be achieved. In February 1941, the V4 began trials with the dive brake which was installed in the tail. This was to satisfy a demand for the Do 217 to conduct dive bombing missions. It also was fitted with a brake parachute to test the ability of the Dornier to conduct short landings. The parachute brake was also considered in use as a dive brake. The V5 prototype was fitted with them and flew in June 1939. Later it was retested with DB 601s and was the third of six aircraft given the official designation Do 217 A-0. The Jumo 211 B-1 was used in the V5 prototype. But in September 1939 the water pump and entire cooling system failed. On 28 April 1940 the DB 601 A-1s were fitted.

The V6 prototype was powered by Jumo 211B engines, but was also tested with DB 601s. The V7 was tested with BMW 139 engines but their use was never taken beyond the prototype stage. The V8 was given BMW 801 engines, which became the fixture for the entire E series. The Do 217A and C series were only built in small numbers. Owing to this the following D and F types never advanced beyond the design stage.

There was a desire for the Do 217 to be capable of performing dive bombing, so it was therefore fitted with a tail-mounted dive brakes, with dorsal and ventral panels that were hinged at the rear of the tail extension they emerged from. This could not be made to function adequately in the early models however, and was omitted until the Do 217 E-2 entered service. When this mark reached service, use of the dive brake was found to sometimes overstrain the rear fuselage, so it was often removed.

The production specifications were ratified on 8 July 1939, with the ultimate goal of the Do 217 having the capability of flying maritime and land operations armed with glider-bombs. The four-seat aircraft was adaptable to both land and maritime operations wherein the tactical emphasis was on bombing from a 50-degree dive angle, and it had a maximum speed of 680 kilometres per hour (370 kn). In contrast with earlier specifications for a modified version of the Do 17M, the proposed Do 217E had a new nose section design in which the A-Stand position was armed with a MG 15 machine gun. Additional MG 15s were to be located in the B and C-Stands. The design teams configured the bomb bay to carry two SC 500 and 250 bombs or four SC 250 bomb loads. In addition a LMB II aerial mine, or an F5 Torpedo could be loaded. Instead of the dive brakes being installed under the wings as on the R variant, it was placed on the tail of the aircraft. The design was tested in the E-1 and became the blue print for all subsequent sub-variants. The E-1 carried strengthened wing and tail structures to deal with the upgraded armament increased the aircraft's weight.

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