The Dornier Do 17 is a twin-engined light bomber designed and produced by the German aircraft manufacturer Dornier Flugzeugwerke. Large numbers were operated by the Luftwaffe throughout the Second World War.
The Do 17 was designed during the early 1930s as a Schnellbomber ("fast bomber") that was intended to use its speed to outrun opposing fighter aircraft. It was a lightly built aircraft, possessing a twin tail, "shoulder wing" and typically powered by a pair of Bramo 323P radial engines. The first prototype made its maiden flight on 23 November 1934, and it entered regular service with the Luftwaffe three years later. Sometimes referred to as the Fliegender Bleistift ("flying pencil") or the Eversharp, the Do 17 was a relatively popular aircraft among its crews due to its handling, especially at low altitude, which made the type harder to hit than other German bombers of the era.
During 1937, the Do 17 made its combat debut during the Spanish Civil War, where it operated as part of the Condor Legion in various roles. Along with the Heinkel He 111, it was the main bomber type of the Luftwaffe at the start of the Second World War. The Do 17 was used extensively throughout the first half of the conflict, seeing action in significant numbers in every major campaign theatre as a front line aircraft. As such, it was deployed during the Polish Campaign, the Norwegian campaign, the Battle of France, the Battle of Britain, and Operation Barbarossa amongst others. Its usage continued unabated up until the end of 1941, when its effectiveness and usage was curtailed by its limited bomb load and range capabilities.
Production of the Do 17 ended in mid-1940 in favour of the newer and more powerful Junkers Ju 88. The successor of the Do 17 was the much more powerful Dornier Do 217, which started to appear in quantity during 1942. The type was not withdrawn at this point; instead, the Do 17 continued to serve with the Luftwaffe during the latter years of the conflict in various secondary roles, including as a glider tug, research, and trainer aircraft. A considerable number were transferred to other Axis-aligned nations, including the Finnish Air Force, Bulgarian Air Force and the Spanish Air Force amongst others. Only a few aircraft are known to have survived the war and none are intact as of the twenty-first century.
Development In 1932, the Ordnance Department (Heereswaffenamt) issued a specification for the construction of a "freight aircraft for German State Railways", and a "high speed mail plane for Deutsche Luft Hansa".Dressel and Griehl 1994, p. 25. Dornier began work on the design on 1 August 1932.
When the Nazis took power in 1933, Hermann Göring became National Commissar for aviation with former Luft Hansa employee Erhard Milch as his deputy, soon forming the Reichsluftfahrtministerium (RLM, Reich Aviation Ministry). The Ministry of Aviation designated the new aircraft Do 17, and on 17 March 1933, just three months after taking office, Milch gave the go ahead for the building of prototypes. At the end of 1933, the Ministry of Aviation issued an order for a "high speed aircraft with double tail," and for a "freight aircraft with special equipment," in other words, a bomber. The original design (the Do 17 V1) configuration in 1932 had sported a single vertical stabilizer, and Dornier continued developing that model. The Do 17 was first demonstrated in mock-up form in April 1933. The "special equipment" was to be fitted later, to disguise its offensive role.Griehl 2005, p. 2.
In April 1934, the Dornier works at Friedrichshafen began project "definition." During this month, the defensive armament was designed and the bomb release mechanism details ironed out. Production of these prototypes began on 20 May 1934 and, on 23 November 1934, the Do 17 V1, with a single fin and powered by a pair of BMW VI 7.3 motors, took off on its maiden flight. Testing was delayed by a series of accidents, with V1 being damaged in landing accidents in February and April 1935. The twin-tailed V2 (powered by low-compression BMW VI 6.3 engines) first flew on 18 May 1935 and was evaluated together with the V1 by the Ministry of Aviation at Rechlin in June. During the tests, the single fin proved to be only marginally stable, resulting in the V1 being modified with a twin tail. The aircraft was destroyed in a crash after an engine failure on 21 December 1935.Green and Swanborough 1986, pp. 42–43. The V3, also fitted with a twin tail, was originally planned to be powered by Hispano-Suiza 12Ybrs engines, but as these were unavailable, it was fitted with BMW VI 7.3 engines like the V1 and flew on 19 September 1935.Green and Swanborough 1986, p. 43. The V1 prototype remained the only built machine with the single stabilizer.
It is claimed that, unlike the Heinkel He 111 series, whose military use was planned from the start, the Do 17 V1 was contracted as a fast six-passenger mail plane to compete with the smaller Heinkel He 70 monoplane.Nowarra 1990, pp. 4–5. It has been suggested that it was rejected by Luft Hansa, as the cramped cabin was too uncomfortable for passenger use and the operating costs were too high for a mail plane.Nowarra 1990, p. 4. According to the story, the three prototypes remained unused in the Dornier factory in Lowental for almost six months, until Flugkapitän Untucht of Luft Hansa came across them. After receiving permission to fly one of the machines, he proceeded to put it through an almost stunt flying routine. After landing, he said that "the machine is as nimble as a fighter, give it more lateral stability and we'll have a high speed bomber!" Untucht's comments prompted Dornier to redesign the tail unit and revived interest in the type.Nowarra 1990, p. 5.
Dornier was then ordered to produce the V4 prototype. Some sources state this differed from the V3 in that the passenger portholes were removed and the single fin was replaced with two smaller ones.Goss 2005, p. 7.Munson 1983, p. 296. Photographic evidence demonstrates the V3 had twin stabilizers from the start of its construction.Griehl 2005, p. 12. The tests of the "twin-tailed" V4, V6 and V7 prototypes were positive and more prototypes like the V8 emerged as the forerunner of the long-range reconnaissance version, while the V9 was tested as a high-speed airliner.Dressel and Griehl 1994, p. 26. The V9 machine was still flying in 1944.
During 1937, the Do 17 made a high-profile public debut in Zürich at the International Military Aircraft Competition. By this time, bomber squadrons of the Luftwaffe were already being equipped with the first two productions models, the Do 17E and F. During 1938, both these versions were flying combat missions in the Spanish Civil War.
Design The forward fuselage had a conventional stepped cockpit, with a fully glazed nose. Early variants were labelled the "flying pencil" owing to its sleek and continuous "stick-like" lines. As a result of the lessons learned in the Spanish Civil War, the cockpit roof was raised and the lower, or bottom half, of the crew compartment was a typical under-nose gondola or "Bodenlafette" (abbreviated Bola) this inverted-casemate design ventral defensive armament position was common in German medium bombers. The Bola was extended back to the leading edge of the wings where the lower-rear gunners position and upper-rear gunner position were level with each other.Goss 2005, p. 12. As with contemporary German bombers, the crew were concentrated in a compartment.
The cockpit layout consisted of the pilot seat and front gunner in the forward part of the cockpit. The pilot sat on the left side, close up to the Plexiglas windshield. One of the gunners sat on the right seat, which was set further back to provide room for the MG 15 machine gun to be traversed in use. The Do 17 usually carried a crew of four: the pilot, a bombardier and two gunners. The bomb-aimer also manned the MG 15 in the nose glazing and Bola-housed rear lower position. The two gunners operated the forward-firing MG 15 installed in the front windshield, the two MGs located in the side windows (one each side) and the rearward firing weapon. The cockpit offered a bright and panoramic view at high altitude.Goss 2005, p. 25.Goss 2005, pp. 24–25. The standard ammunition load was 3,300 rounds of 7.92 mm ammunition in 44 double-drum magazines.Griehl 2005, p. 6.
The wings were of a broad area and had a span of with a straight leading edge which curved in a near-perfect semicircle into the trailing edge. The positions of the wing roots were offset. The leading edge wing root merged with the top of the fuselage and cockpit. As the wing extended backwards, by roughly two thirds, it declined downwards at a sharp angle so that the trailing edge wing root ended nearly halfway down the side of the fuselage increasing the angle of incidence.Wrobel 2008, page not numbered after p. 93. Schematic drawing in Appendices: "Sheet 1". This design feature was used on all future Dornier bomber designs, namely the Dornier Do 217.Griehl 1991, p. 57. The trailing edge was faired into the round fuselage shape. The engine nacelle was also faired into the flaps. The extreme rear of the nacelle was hollow and allowed the flap with an attached vertical slot to fit into the cavity when deployed.Goss 2005, p. 20.
The fuselage was long. It was thin and narrow, which presented an enemy with a difficult target to hit. The fuselage had twin vertical stabilizers to increase lateral stability. The power plant of the Z-1 was to have been the Daimler-Benz DB 601 but, owing to shortages from priority allocation for Bf 109E and Bf 110 fighter production, it was allocated Bramo 323 A-1 power plants. The Bramos could only reach at . The limited performance of the Bramo 323s ensured the Do 17 could not reach at in level flight when fully loaded.Griehl 2005, p. 5. The range of the Do 17Z-1 at ground level was ; this increased to 1,370 km (850 nm) at . This gave an average attack range of . The introduction of the Bramo 323P increased the Z-2 performance slightly in all areas.
The Dornier had self-sealing fuel tanks to protect fuel stored in the wings and fuselage. This reduced the loss of fuel and risk of fire when hit in action, and often enabled the aircraft to return. Twenty oxygen bottles were provided for crew use during long flights above . Communications usually consisted of FuG X, the later FuG 10, navigational direction finder PeilG V direction finder (PeilG - Peilgerät) and the FuG 25 IFF and FuBI 1 blind-landing devices. The crew communicated by EiV intercom. A primitive autopilot device, the Siemens K4Ü, was installed and could maintain bearing using the rudder's control surfaces.
The bomb bay had four bomb racks, the No. 5 for SC50 bombs and two ETC 500 racks to carry heavier loads of up to each. A Lotfe A, or B bombsight was issued together with the BZA-2 aperture (a modernised optical lens system). The bomb bay allowed two options, one was to carry four bombs for a load of , which reduced aircraft range. With half the maximum load, ten bombs, additional fuel tanks could be placed into the forward part of the bomb bay to increase range. The bomb aimer aimed the bombs via the Lotfe (A, B or C 7/A, depending on the variant) bomb sight which was in the left side of the nose compartment directly under and forward of the pilot.Keskinen and Stenman 1999, pp. 6–7. When fully loaded, the Z-1 weighed .
Variants Early Daimler-Benz-powered variants
The initial production variants were the Do 17E-1 bomber, which was tested with two Daimler-Benz DB 600, and Do 17F-1 reconnaissance aircraft, powered like the early prototypes with BMW VI engines, which entered production in late 1936. The first Luftwaffe units converted to the Do 17 in early 1937.Green 1967, pp. 142–144.