Dornier Do 17Z: The main variant
The Dornier Do 17Z series was the most recognised and mass-produced variant, and saw more combat service than
the E-U types. The type was modified as a result of combat experience during the Spanish Civil War. The
forward fuselage was redesigned, with the cockpit area being "dropped", or extended further to enable a rear
firing gunner position to be installed, and the canopy extended aft, until it was nearly parallel with the
leading edge and wing root.
To test the design, the Do 17S and Do 17U were produced, both to be powered by the DB 600 power plants.
However, a call for all DB 600 series engines to be reserved for fighters led to the variants being fitted
with Bramo Fafnir 323 A radial engines. The bomb load was increased to 1,000 kg (2,200 lb) and a fourth crew
member was added. It proved to be underpowered, so Bramo 323 P engines were then fitted. Only three Do 17S
and 15 Do 17Us were built. With the updates, the Dornier, with a full bomb load, had a combat radius of 322
km (200 mi). Later variants, in the Do 17 Z-3, Z-4 and Z-5, which were fitted with cameras, dual trainer
controls and flotation aids (for maritime operations) respectively, still could not solve the problems
with range and bomb load.
At first, a batch of Z-0s were built with the Fafnir for testing, the DB 600 again proving to be too hard to
obtain. These were quickly replaced with the Z-1 model, which added another gun for the bombardier, but the
additional weight of the nose and guns meant the bomb load was reduced to 500 kg (1,100 lb). The Luftwaffe,
not being satisfied with the test outcome of the Z series, immediately ordered performance and design studies
to increase the overall performance of the bomber. These resulted in very optimistic speeds and altitudes for
all future Z variants, especially for the Z-5 aircraft. Planned performance altitudes of up to 7,620 m
(25,000 ft) at a maximum speed of 418 km/h (260 mph) with an aircraft weight of 8,100 kg (17,900 lb) were
planned. Unfortunately, production aircraft never reached these optimistic performances during the service
career of the Do 17Z. At 7,740 kg (17,060 lb), the heavy Do 17Z-1 used two Bramo 323 A-1 engines with
self-sealing fuel cells in the fuselage and wings. The crew of four consumed approximately 20 bottles of
oxygen during long flights above 3,700 m (12,100 ft). The Do 17Z-1 had a speed of 352 km/h (219 mph) at
1,100 m (3,600 ft). However, the performance of the Bramo 323s did not permit the Do 17 to reach
416 km/h (258 mph) at 3,900 m (12,800 ft) and level flight when fully loaded. Range of the Z-1 at
ground level was 635 nmi (1,176 km) while at 4,700 m (15,400 ft) this increased to 850 nmi (1,570 km).
This gave an average range of 400 nmi (740 km). The introduction of the Bramo 323P increased
subsequent performance in the following sub variants.
Dornier Do 17Z
This was addressed in the major production model, the Do 17 Z-2. The Z-2 mounted the new 323P-1 version of the
Fafnir with 746 kW (1,000 hp), which was specifically tuned to the performance needs of the Do 17 by
decreasing supercharger power at lower altitudes and thus improving low-level performance. The increase in
takeoff power allowed the bomb load to be increased from 500 to 1,000 kg (1,100 to 2,200 lb). However the
combat range with a full 1,000 kg (2,200 lb) bomb load was a very short 330 km (210 mi). The armament was
further upgraded by adding another pair of guns firing out of the sides of the upper part of the pod, but
as the three guns were all fired by a single gunner, only one of them could be fired at a time. From May
1940, 422 Do 17 Z-2s flew with Kampfgeschwader 2, Kampfgeschwader 3, Kampfgeschwader 76 and
Kampfgeschwader 77. The upgrades of the Z-2 had its overall weight increased from 17,600 to 17,920 lb
(7,980 to 8,130 kg). After heavy losses of Do 17s during the Battle of Britain it was decided to
replace the MG FF cannon with the more powerful MG 151/15. Losses had mounted in spite of an increase of
up to eight machine guns in some Dorniers. The standard MG 15 machine guns were retained. These features
were present in the next variant the Z-3.
The Z-3 formed part of the bomber versions of the Z series, it was, however, also used as a reconnaissance
aircraft by the staff flight of the particular unit. The engines and the general equipment were identical to
the Z-2 standard; however two cameras — the Rb 50/30 and Rb 20/30 - were incorporated into the crew entry
hatch. A handheld camera was issued to the crew to validate the success during bombing missions. Autopilot
equipment was added later. The Z-2 and Z-3 were identical visually, and could only be distinguished from
each other by the altered crew hatch on the Z-3. Owing to spacing problems because of the added camera
equipment, the ammunition supply was reduced from 44 to 42 magazines. The power plant of the Z-3 was
upgraded to the Bramo 323P-2. The Bramo P-2 remained the engine of all the remaining Z series variants.
The Z-4 was designed as trainer. Although nearly identical to the Z-2 and Z-3, it featured several equipment
changes optimised for blind flying training. The four-seat aircraft had a single control column with dual
steering, which was achieved by a jib protruding to the right. Rudder pedals were in front of both seats.
The defensive armament and bomb racks were reduced, or in most cases omitted to reduce weight.
The Z-5 was similar to the Z-3 with a weight of 19,000 lb (8,600 kg). Designed as an anti-shipping aircraft,
the Z-5, was fitted with flotation cells in the fuselage and engine nacelles in case it was forced down on
water. Usually the flotation devices took the form of inflatable bags stored in the rear of the
engine nacelles and in bulges on either side of the nose, just behind the front glazing.
Later variants of the Z model were developed. The Z-6 was to be a reconnaissance aircraft, although it was
only built as a prototype. During the war only a few were converted from existing combat variants. The type
was selected for weather check flights. It was identical to the Z-1/Z-2 variants, but offensive armament was
omitted and extra fuel cells fitted. This increased the fuel load to 2,890 l (578 Imperial Gallons). As
flights required higher altitude, the oxygen supply was increased from 20 to 24 bottles. For long-range
flights over water, the larger dinghy of the Z-5 with its updated emergency escape equipment was mandatory
during operations. The Z-6s were also used for night fighter operations. Some of the few converted Z-6s had
the Ju 88C-6 nose installed and were equipped with machine guns and cannons. The nose proved to be
unsatisfactory, and it was redesigned. In the tip of the new nose was an infrared spotlight which was
soon made redundant after the introduction of Lichtenstein radar which was fitted to some of the Z-6.
The Z-8 Geier was not produced. It was intended as a ground attack aircraft and reached the first planning
phase but was given up due to lack of performance and protective armour allocation against anti-aircraft
artillery. An increase in armour would have meant a decrease in speed which would have exposed the aircraft
further to enemy fire.
The Z-9, which was fitted with special bomb release equipment, and delayed release gear for low-level attack
missions. Its purpose was to suppress enemy air defences. Therefore, it was designed to fly over anti-aircraft
positions and drop Butterfly Bombs, an early form of cluster bomb munitions. This could only be done with
air superiority, as the Z-9 was unarmoured. The airframe and equipment was identical to the Z-1/Z-2 version.
Only the bomb bay was altered to accommodate 16 bomb-dispenser systems. The maximum weight of the Z-9 was
7,800 kg (17,200 lb). The design did not reach serial production.
After bomber production ended in 1940, the Z model was modified with a "solid" nose from the Ju 88C, fitted
with one 20 mm MG FF cannon and three 7.92 mm MG 17 machine guns, to be used as night fighters.
Three prototypes were converted from existing Z-series airframes to the Do 17 Z-7 Kauz I ("screech-owl")
configuration. The standard Z-7 was fitted with Bramo 323P-1 radial engines and had a crew of three
airmen. In comparison to the standard bomber version, the fuel load arrangement was altered by
subdividing into cells. Two cells were in the wings, with a capacity of 770 litres (154 imperial gallons)
each. A third cell was placed in the bomb bay within the main fuselage, having a capacity of 895 litres
(179 imperial gallons). The oxygen supply for the three man crew was reduced to nine bottles, as
intercepts at high altitudes were not anticipated. Add-on armour in the form of heavy steel plates was
bolted to the nose bulkhead to protect the crew against frontal fire. Originally, it was planned to
completely armour the crew compartment. This idea, was given up again as the increased weight would have
reduced flight performance of an already slow aircraft. The ammunition loads for the three 7.92 mm
MG 17s amounted to 3,000 rounds and 400 rounds of ammunition for the 20 mm MG 151 cannon (although
some Do 17Z bombers carried a single 20 mm for ground attack missions).
Later, the design was further modified to the Do 17 Z-10 Kauz II, the solid nose now containing an infra-red
searchlight for the Spanner Anlage infrared detection system. The infrared lamp in the nose was used to
illuminate the target while the display unit in the windshield made the reflection visible to the pilot.
The Z-10 was armed with four 7.92 mm MG 17 machine guns grouped above the IR light and two 20 mm
MG FF in the lower nose. The crew could reload the 20 mm cannons' drum magazines internally. The Z-10
contained an IR searchlight (Spanner-Anlage) for the Spanner infrared detection system. A single Kauz II
was equipped with and tested the Lichtenstein radar.
Only 10 of these Kauz II designs were converted from existing Z-series airframes. The Spanner system proved
to be essentially useless and many Z-10 were left without any detection system. At least one Z-10, coded
CD+PV, was used as a flying test bed to help developing the early low-UHF band B/C version of the
Lichtenstein radar system in late 1941–1942. When the Z-10 was stripped of all non-night fighter equipment,
it had a maximum weight of 7,300 kg (16,100 lb). Armament fit was similar to that of the Z-7, with an
added MG 17 and an additional 1,000 rounds of ammunition in the nose section. Defensive gun positions
included the B and C stand, each equipped with a single MG 15.
, 1979, Airlife Publishing Ltd., Shrewsbury
, 1977, Salamander
Books Ltd., London
