Dornier Do 17

The radial variants

Despite its success, owing to shortages in the supply of the Daimler-Benz engine, the production Do 17M was fitted with the Bramo 323 engine, with the corresponding reconnaissance aircraft, the Do 17P, being powered by BMW 132Ns to give better range.

The supply of the DB 600 remained extremely limited as production was soon switched over to the fuel-injected DB 601, which was reserved for the Messerschmitt Bf 109 and Messerschmitt Bf 110 fighters. Therefore, production versions of the basic Do 17M model airframe were fitted with the new Bramo 323A-1 Fafnir engines of 670 kW (900 hp), which gave reasonable performance and raised the bomb load to 1,000 kg (2,200 lb). The resulting Do 17 M-1 was produced in small numbers and operated until 1941.

The prototypes for the M-1 series were Do 17M V1 (Werk Nr 691) and Do 17M V2 (Werk Nr 692) which were tested with bomb loads of a medium bomber. The third prototype, Do 17M V3 was evaluated as a fast bomber. The M V1 was fitted with two Daimler Benz DB 601 inline engines while the M V2 and M V3 had the Bramo 323 A and D respectively. The Ministry of Aviation favoured the widespread use of the DB 601, but demand for the DB 601s in fighter aircraft and the lack of production forced the use of the Bramo.

The Do 17 M-1 started its service as a medium bomber and was able to carry 2,200 lb (1,000 kg) of bombs. It was equipped with two air-cooled Bramo 323 A-1 or A-2. The defensive armament consisted of two, and later three, MG 15 machine guns. The first was operated in an A-Stand pod operated by the navigator through the windshield. The position was allocated 370 rounds of ammunition. The rearward firing B-Stand was operated by the radio operator and allocated 750 rounds. The rear position in the lower fuselage was allocated 375 rounds in a C-Stand pod. The Do 17M could carry a bomb load of either 20 SC50 50 kg (110 lb) or two SC250 250 kg (550 lb) bombs or 10 SC50 and a single SC250 bomb. The speed of the M was superior to that of the E variant. The Do 17M could reach 420 km/h (260 mph) at altitudes of 3,500 m (11,500 ft) and could achieve a maximum service ceiling of 5,790 m (19,000 ft) and a range of 850 nautical miles (1,570 km).

Reconnaissance aircraft based on the M-1, the under-surfaces of the wing were covered with duralumin and it had a wider engine axis and longer engine nacelles. The demand for a reconnaissance aircraft based on the M-1 led to the development of the P-1 variant.

The L version would not be able to enter production with the DB 600 owing to its use in the Bf 109, and the Bramo engine was rather thirsty on fuel and left the M models with too short a range for reconnaissance use. BMW 132N radials of 865 PS were selected instead, which had lower fuel consumption for better range. Another two prototypes with DB 600 engines were produced as the Do 17R-0, but did not enter production. During reconnaissance missions the P-1 was armed with four MG 15s in the A, B and C—Stands. One machine gun was located in the rear of the cockpit, another in the lower rear Bola mount, one facing forward through the windscreen and the other in the nose glazing. In earlier variants the B-Stand (the gun position in the upper rear cockpit) was open to the elements, but the P-1 now provided an enclosed bulb-shaped mount protecting the radio operator from the weather.

The P variant had similar features to the Do 17M-1, with added blind flying and camera equipment for reconnaissance work. The Do 17P-1 was powered by two BMW 132N radial engines with a maximum performance of 865 PS (853 hp (636 kW) each. The machine was fitted with several radio variations. The FuG IIIaU radio (Funkgerät), the PeilG V direction finder (PeilG - Peilgerät) and the FuBI 1 radio blind-landing device (FuBI - Funkblindlandegerät). The crew of three communicated with each other via the EiV intercom (EiV -Eigenverständigungsanlage). The P-1 was equipped with either Rb 20/30 and Rb 50/30 or Rb 20/18 and Rb 50/18 cameras. The P-1/trop was fitted with filters and protection for the cameras. The cameras were controlled remotely by the crew from the cockpit.

Due to a shortage of night fighters, at least one Do 17P-1 was assigned to this role. A smooth metal sheet was installed in place of its glass nose and it was armed with three 20 mm (0.79 in) MG 151/20 cannons. The machine operated under Luftflotte 1.

The Do 17P-2 was identical to the P-1, with the additional installation of an ETC 500 bomb rack under the fuselage. These aircraft were designed for night reconnaissance. It is assumed that Dornier converted most, if not all, P-2 models from existing P-1 production aircraft.

Unlike the P-2, the Do 17R-1 did not see series production. The experiences of the Spanish Civil War proved that unarmed aircraft were easy prey for fighter aircraft. The R-1 was to be a fast long-range reconnaissance aircraft with two additional fuel cells inside the fuselage aft of the bomb bay. Two variants were suggested, the first (variant I) had a single Rb 50/30 and two Rb 20/30 cameras, while variant II had a third fuel cell to replace the rear Rb 20/30. The aircraft had a gross weight of 7,250 kg (15,980 lb) but could be overloaded to 7,500 kg (16,500 lb) in emergencies. The crew usually numbered three, but a fourth was added depending on the missions to be flown. To achieve a high performance at increased altitudes two DB 600 Gs were to be used. The power plants were tested in the Do 17R V1 prototype registered D-ABEE. The second, the R V2, registered D-ATJU, received the even more powerful DB 601 Aa engines. The power plant of the R-1s that did exist are not known.

The lessons from the Spanish Civil War had led Dornier's designers to incorporate more defensive machine guns. Battles with Soviet-built fighter aircraft had demonstrated that the Dornier was not as fast and invulnerable as was first thought. To cope with this, a completely new pod-like cockpit was designed to give the crew more room and better visibility. The roof was extended upward over the line of the fuselage, sloping down to meet it just in front of the wing. The dorsal gun was moved to the rear of the pod where it had a considerably better field of fire. Likewise, the floor was dropped under the fuselage as a Bola casemate-style defensive armament emplacement, and the ventral gun moved to the back of the Bola, allowing it to fire directly to the rear. The changes in the roof and floor made the whole front of the aircraft much larger. The rest of the airframe remained the same. The new cockpit design was nicknamed Kampfkopf (German: "Battle head").

Three S variant prototypes with the DB 600 G inline engines were tested. The S-01 (designation D-AFFY), 03 and 04 were flown. The inverted V-12 engines were constructed as the Do 17 S-0 reconnaissance version, but it did not go into production. An additional 15 Do 17 U-1 pathfinder models were built, similar to the S-0 but adding another crewman (taking the total to five) to operate the extra radio equipment. The U models were to fly ahead of other bombers on night missions, using the radio equipment to locate the target and drop flares on it. They were personally requested by KG 100 as experimental models for this role. The U-1 had a maximum speed of 265 mph (426 km/h) and a combat ceiling of 4,500 m (14,800 ft). The U-1 had a cruising speed of 384 km/h (239 mph) and a maximum reachable height of 5,700 m (18,700 ft), owing to the "rather low performance of the Bramo 323 A-1 engines". The three prototypes (U-01 - U-03) and twelve production aircraft were built by 1938.

Sources:
Gunston, Bill - The Encyclodepia of the Worlds Combat aircraft, 1976, Chartwell Books, Inc., New York
Brown, Eric, Captain - Wings of the Luftwaffe, 1979, Airlife Publishing Ltd., Shrewsbury
Gunston, Bill & Wood, Tony - Hitler's Luftwaffe, 1977, Salamander Books Ltd., London
Donald, David - The Complete Encyclopedia Of World Aircraft, 1997, Brown Packaging Books Ltd., London
Wikipedia - Dornier Do 17