The first lessons learned by Stuka outfits during the Polish campaign clearly demonstrated to the Luftwaffe command that Junkers Ju 87 was in need of a major upgrade. Junkers engineers were directed by Technical Department officials to find ways to improve Ju 87’s fire power and to increase its bomb load, operational range and speed performance in level flight.
The key elements in achieving those goals appeared to be the use of a more powerful engine and aerodynamic modifications of the airframe.
Junkers Ju 87 D (Dora)
The initial work on the new Stuka model began in the spring of 1940. In May 1940 the new variant received its official designation: Junkers Ju 87 D. Originally the aircraft was to be equipped with a Jumo 211 F engine, but delays in its development sent Junkers engineers searching for an available replacement. They chose Jumo 211 J-1 powerplant, which was also being developed at that time. It was a 1,420 Hp, twelve cylinder inline unit with liquid cooling. Because the new engine was as much as 40 cm longer from its predecessors, the cowling had to be lengthened and redesigned. An improved engine cooling system was also introduced at the same time. Oil radiator was placed under the lower part of the engine fairing and two engine coolant radiators were added under the wing’s center section, near the trailing edge. The aircraft was also fitted with a new cockpit canopy, which was tested on a Ju 87 B (W.Nr. 2291).
Jumo 211 J-1 engine was mated to a Ju 87 B-1 airframe (W.Nr. 0321, D-IGDK) in October 1940. Flight testing of that configuration lasted for several weeks and was marred by frequent malfunctions of the powerplant. Ju 87 V21 (W.Nr. 0536, D-INRF), the first prototype of Ju 87 D model, was rolled out in March 1941. Flight test program of the Jumo 211 J-1 powered aircraft was carried out at Dessau between March and August 1941. In August 1941 Jumo 211 J-1 engine was replaced by a Jumo 211 F powerplant. During one of the early flight test sorties of the new powerplant, an in-flight separation of the propeller occurred at 1,420 rpm setting. After repairs, the aircraft was transferred to Rechlin test and evaluation facility on September 30, 1939. After another series of tests the machine was officially accepted by the Luftwaffe on October 16, 1941. The aircraft was subsequently used as a test bed for powerplant and cooling system tests. In February 1942 the bomber returned to Dessau for installation of new radiator fairings. The prototype was eventually taken on strength by a frontline unit on September 14, 1943.
The second prototype, Ju 87 V22 (W.Nr. 0540, SF+TY) was originally scheduled to be completed by the end of 1940. However, due to problems with the powerplant, the aircraft was not ready to begin its flight test program until May 1941. It was handed over to the Luftwaffe on November 10, 1941. Flight test program results were so far satisfactory both to Junkers staff and to personnel at Rechlin. Thanks to unusually cold November of 1941, some cold-start engine trials could also be run, which demonstrated that engine start procedures, even in extremely low temperatures, were straightforward and did not cause any malfunctions of the powerplant.
The prototype returned to Dessau at the beginning of 1942 for additional stability testing and some minor modifications of its Jumo 211 J-1 engine, following which it was sent back to Rechlin. On August 20, 1942 the aircraft was lost during one of the test sorties when it crashed into lake Müritzsee. The crew, Fw. Hermann Ruthard and a civilian employee of Rechlin test center, were killed in the crash. Probable cause of the accident was carbon monoxide poisoning of the crew and their subsequent loss of consciousness.
The third prototype, Ju 87 V23 (W.Nr. 0542, PB+UB) was completed in April 1941 and sent to Rechlin a month later. That particular example was a benchmark for Ju 87 D-1 production model. Continuing delays in Jumo 211 J-1 deliveries grounded the next prototype: Ju 87 V24 (W.Nr. 0544, BK+EE) could not be finished before August 1941. Upon its completion, the aircraft was promptly sent to Rechlin. The prototype was soon returned to Dessau after an accident in which it suffered damage to the fuselage. After repairs, the machine was once again delivered to Rechlin test and evaluation center in November 1941. Having completed the flight test program, the bomber was handed over to a combat unit.
The tropical variant of Ju 87 D-1 model was to be based on the fifth prototype, Ju 87 V25 (W.Nr. 0530, BK+EF). The airframe was completed in early March 1941, but it sat in the assembly building until July 1941 waiting for its Jumo 211 J-1 powerplant. It finally made its first flight in the summer of 1941 as the first example of Ju 87 D-1/trop. On September 12, 1941 the aircraft went to Rechlin for testing of its Delbag dust filter. The first mention of Ju 87 D-1 full-scale production goes back to 1940 when an initial order for 495 examples was placed with Junkers with deliveries scheduled between May 1941 and March 1942. In early February 1942 Technical Department of the RLM increased the order to 832 Ju 87 D-1 aircraft. Weser plant was to deliver the entire batch. Never-ending problems with Jumo 211 J engines caused delays in delivery schedules. The first two production aircraft were to be ready in June 1941, but Karman company, responsible for the manufacturing of upper fuselage sections, did not deliver the required components on time. The first production example was assembled on June 30, 1941. The optimists among the RLM officials still believed that in July 1941 48 Ju 87 D-1s would roll off the assembly lines. The reality turned out to be completely different. Only the first production aircraft was finished in July, after the damage it suffered while still in the factory had been repaired. In the face of all that trouble, the RLM staff and Junkers management, who granted Weser license rights to build Ju 87 D-1s, continued to be optimistic. Everybody believed that initial production delays would be gone by the end of September 1941. However, production problems continued to stack up until all hopes for improvement had to be abandoned. Not a single Ju 87 D-1 rolled out of the Bremen assembly buildings in August 1941. It was not until September that Weser finally managed to deliver first two production examples to the Luftwaffe. Both aircraft were sent to flight test centers.
October and November 1941 saw the completion of 61 Ju 87 D-1s, although they had to wait for their first flights until December 1941 due to horrible weather conditions at Lemwerder at that time. All aircraft were subsequently delivered to frontline units.
Ju 87 D-1 was a two-seat, single engine, low wing design of all-metal construction and featured conventional, fixed landing gear. The semimonocoque, all metal fuselage had oval cross section. The fuselage consisted of two sections joined by rivets. Load-carrying, duralumin skin panels were attached by standard, round-headed rivets in areas of greater load exposure, while counter-sunk rivets were used in places carrying lesser loads. Fuselage construction consisted of 16 frames connected by stringers and featured four spars in its forward section going back to frame 7. The first frame was a bulkhead and engine firewall. Additional strengthening spars in the forward fuselage served as attachment points for the belly bomb crutch assembly.
The cockpit was placed in the fuselage center section between frames 2 and 6. It was covered with a fully glazed, four-piece canopy made of laminated or organic glass, which provided excellent all-around visibility. The sliding canopy sections featured locks with emergency jettison capability. The crew were protected by a roll-bar mated to an internal armored partition. The windscreen was made of 25 mm armored glass. Additional protection for the pilot came in the form of armor-plated seat, protective 10 mm armor plate behind the seat’s headrest and 5 mm armor plating on the cockpit’s floor. The radio operator in the rear cockpit was protected by 5 mm armor plating on the floor and an additional armor plate placed between fuselage frames 5 and 6. Armored GSL-K-81 rear gun mount holding MG 81 Z machine gun provided additional protection. The cockpit floor, just forward of the pilot seat, featured a small window equipped with metal blinds for visual acquisition of ground targets prior to entering a dive. A first-aid kit in a metal container, accessible only from the outside, was stowed in a compartment behind number 8 fuselage frame.
A three-section inverted gull wing featured two main spars and was of all metal construction. Its characteristic flattened “W” shape was achieved by attaching two dihedralled outboard sections to the anhedralled center section. The wing had a trapezoid planform with rounded wingtips. The wing’s center section was permanently attached to the fuselage structure. Two coolant radiators were placed under the wing’s center section. Outboard wing sections were attached to the center section with for universal ball joints designed by Junkers. The aircraft featured stressed sheet duralumin skins. The wing was equipped with two-piece wing flaps behind the trailing edge of the center and outboard sections. The flaps and single- piece, trimmable ailerons were attached to the wing by patented Junkers support devices. Ailerons were operated mechanically, while flaps featured hydraulic actuation. All elements of the wing’s mechanization were covered with smooth duralumin skins. The aileron-flap system was a unique Junkers design called Doppelflügel, or “double wing”. That arrangement was technologically simple and the slotted flaps and ailerons increased the system’s effectiveness. Automatically actuated, slotted dive brakes were placed under the wing, near the number 1 wing spar. Those devices were used in automatic dive recoveries.
The tailplane was of an all-metal design with smooth, duralumin skins. The vertical fin had a trapezoid shape and featured a rudder operated by steel control cables. Trimmable horizontal stabilizer with neutral dihedral had a rectangular planform and was braced by steel tube struts with duralumin fairings. The elevator was actuated by a system of push-rods. Both rudder and elevator were aerodynamically and mass balanced and featured trim tabs.
Conventional, fixed landing gear with a tail wheel provided good ground handling. The single-strut main landing gear was attached near number 1 wing spar at the junction of the wing’s center and outboard sections. KPZ main landing gear struts manufactured by Kronprinz featured a fork and oleo shock absorbers with additional spring damping. The main wheels were covered by characteristically shaped fairings, one of Stuka’s most recognizable features. A set of 840x300 mm tires was mounted on the main landing gear wheels. Recommended operating pressure for the tires was 0.25 MPa. The aircraft had hydraulic drum brakes on the main wheels which used F1- Drucköl brake fluid. The tail wheel assembly was attached to a horizontal frame placed between fuselage frames 15 and 16. The wheel was attached to a Kronprinz strut and fork which was spring-damped. The tail wheel strut had a 360° free-castoring capability. The tail wheel rim was designed to accept a 380x150 mm tire with recommended operating pressure of 3 to 3.5 atm. The tail wheel could be locked for take-off, landing and in-flight by means of a control cable running to the cockpit. Technical inspection of the landing gear was recommended after every 500 cycles. The aircraft was also equipped with a tail skid to protect the empennage during emergency landings. For winter operations the aircraft could be equipped with skis in place of landing gear wheels. The kit consisted of a set of three skis with plywood fairings. The main skis were 3,780 mm long, 1,025 mm wide and 519 mm high. The tail ski dimensions were 1,005x440x200 mm respectively.
The powerplant was a Junkers Jumo 211 J-1 engine developing 1,420 Hp. It was a twelve cylinder, inverted “V” unit with a two-stage supercharger and fuel injection. The engine featured a 60 degree cylinder angle and had a 35 l working capacity. Each cylinder was 150 mm in diameter, had a piston stroke of 165 mm and produced a 6.5:1 pressure ratio. A dry engine weighed in at 660 kg. The powerplant sat on the engine mount attached at four points to the firewall. Engine start could be performed using a combination hand and electrical inertia starter, which could be activated either by hand-cranking or by a ground power source. Engine cooling was provided by a 1:1 mixture of water and ethylene glycol with 1.5 percent addition of Schutzöl 39 anti-corrosive fluid. Coolant overflow tank had a capacity of 18 l and was placed on the left side of the engine mount. Two pumps controlled the proper coolant flow. The heat was dissipated through a pair of radiators mounted under the wing’s center section, close to the trailing edge. The counter-clockwise rotating engine drove a clockwise rotating VS 11 propeller with 20° adjustable pitch. The propeller’s diameter was 3,260 mm and it was redlined at 2,250 rpm.
Lubrication system included an oil radiator mounted in the lower part of the engine cowling and connected to the compressor intercooler. The main oil tank had a capacity of 55 l, although in practice only 35 l was used. The tank was mounted in the forward, lower section of the fuselage, just behind the firewall. Two additional 31 l tanks were placed in the upper part of the fuselage behind the firewall and one more 27 l tank was placed directly above the engine. Oil circulation was maintained by an engine-driven, geared oil pump. Three different types of oil were used for lubrication: Stanavo 100, Aero-Shell Mittel or Intava-Rotring.
The fuel system consisted of four self-sealing wing tanks. A pair of 260 l tanks were built into the wing’s center section, while the outboard sections of the wing housed two 160 l tanks. Each tank had to be fuelled separately. The aircraft’s fuel installation had a provision for two additional 300 l drop tanks under the wings. In operational environment the drop tanks were filled with 295 l of fuel each. The system featured an engine driven fuel pump and two auxiliary KNP 16A electric pumps in the main fuel tanks. The fuel used was B4 type 87 octane ethyl gasoline. A small tank of ether gasoline used in cold engine starts was placed in the forward section of the fuselage. Fuel consumption at sea level was 310 l per hour, 305 l per hour at 2,500 m and 320 l per hour at 5,000 m. Fuel load of 760 l resulted in flight endurance of 2 hrs. 15 min. The use of drop tanks increased total fuel capacity to 1,370 l and extended the aircraft’s endurance to over 4 hours.
The machine featured a 24 V electrical system powered by a 2,000 W Bosch engine-driven generator and a 7.5 Ah lead-acid battery. The system powered all radio equipment, as well as bomb sight and cockpit illumination, instrument panel lights, navigation lights and an external flood light mounted between ribs Id and Iia of the port wing. The system was protected by a set of circuit breakers on a control panel placed on the right side of the front cockpit.
Oxygen system consisted of a set of two breathing regulators for the crew, which provided proper breathing mixture depending on the altitude. Oxygen was fed from 18 spherical tanks with separate regulators, which were grouped into six sets of three tanks. Total system pressure was 15 Mpa and all oxygen tanks were refilled through a single-point input valve under the wing.
Radio equipment consisted of a two-way FuG VIIa communication unit operating at frequencies between 2,500 and 3,750 kHz mounted in the rear cockpit. FuG VIIa radio set included an S6b transmitter, an E5a receiver and a U4b 24 power inverter. A copper wire antenna ran from a mast on the canopy to the top of the vertical fin. An EiV 1a intercom provided internal communication between crew stations. The aircraft was also equipped with an FuG 25 IFF unit with its dedicated blade antenna under the fuselage and a Peil G IV, V or VI radio ranging device with a rotating PRE 4 goniometric antenna in a Plexiglas-covered dorsal compartment behind the rear cockpit.
The cockpit was fitted with a set of flight and engine control instruments, as well as aircraft systems controls placed on the front and side instrument panels. A Walther signal gun was stowed on the left side of the cockpit, under the front section of the canopy.
One of the most notorious elements of the Ju 87 D-1 optional equipment were two (sometimes one) externally mounted sirens, which emitted a horrifying wail during dives. The sirens were attached to the upper part of the main landing gear fairings and were powered by ram-air spinners. The spinners were electro-pneumatically actuated and stopped. The spinners’ drag decreased the aircraft’s airspeed in level flight, so in frontline use the sirens were often left behind. Tropical variants, designated Ju 87 D-1/trop, were equipped with sand filters, additional wing machine gun seals and sported dessert survival kits, similar to kits carried by Ju 87 R-2/trop models. In addition, the top part of the canopy was equipped with sun shades.
Offensive armament consisted of a pair of 7.92 mm Rheinmetall-Borsig MG 17 machine guns mounted in bays near the outboard wing sections. The aircraft carried a supply of 1,000 rounds of ammunition per gun. An MG 17 weighed in at 10.2 kg, had a theoretical rate of fire of 1,200 rounds per minute and muzzle velocity of 755 m/sec. The guns were charged by an electro-pneumatic system. 15 Mpa constant system pressure was provided by compressed air from a set of 1 liter tanks. Gun aiming was aided by a Revi C/12 D reflex sight illuminated by a 15 W bulb.
Offensive armament could be augmented by six MG 81 Z machine guns carried in two WB 81 A or WB 81 B pods (WB – Waffenbehälter)1 mounted on the underwing weapons stations. Each pod was designed to carry 1,500 rounds of ammunition. WB 81 As had a 15 degree downward muzzle deflection, while WB 81 Bs featured neutral gun deflection. Each pod weighed 140 kg without ammunition and 180 kg with a full supply of ammunition. In the Luftwaffe lingo the pods were called Gießkanne, or “watering cans”.
The radio operator manned the aircraft’s defensive armament – twin 7.92 mm Mauser MG 81 Z (Zwilling)2 flexible machine guns with a supply of 1,000 rounds of ammunition per barrel. The MG 81 Z gun weighed 12.9 kg, had a theoretical rate of fire of 3,200 rounds per minute and muzzle velocity of 705 to 875 m/sec. The gun was mounted on a GSL-k 81 Z gun mount in the rear cockpit.
On the fuselage centerline there was a universal Schloß 1000/500 XI B bomb rack which could accept either a 500/XII C bomb ejector for 250 or 500 kg bombs, or a 2000 XIII type ejector for 1,000 or 1,800 kg weapons. A special crutch was used to swing the bomb clear of the propeller disc during bomb release in a dive. Two additional weapons stations were located under each wing. Those could be used to attach a Schloß 1000/500/IX B bomb rack with a 500/XII C ejector for a 250 kg bomb, or two ETC 50/VIIIe ejectors for 50 kg bombs. A total of 592 Ju 87 D-1 examples were built with serial numbers from W.Nr. 2000 to 2600.
Ju 87 D-2 was not a production model. Initially it was to be a dedicated tropical variant of Ju 87 D-1 equipped with Ju 87 B-2 landing gear and fuel installation compatible with two 300 l underwing auxiliary tanks. Because the basic Ju 87 D-1 could be quickly modified to a tropical standard, a decision was made to change the Ju 87 D-2’s application. It was now to be converted to a ground attack aircraft with additional armor protection for the crew. Flight testing of the proposed additional armor on a Ju 87 D-1 test bed showed that the aircraft’s level flight speed performance and operational ceiling were greatly affected, which prompted the Luftwaffe High Command to cancel the development of that Ju 87 derivative. That did not mean, however, that plans for beefed-up armor protection were abandoned all together. After some modifications to the original design, the extra armor protection was installed on all new Ju 87 D-1 production aircraft from February 1942 on; earlier production examples were also retrofitted with the same modification.
The next production version was Ju 87 D-3, which was in effect a ground attack derivative of Ju 87 D-1 equipped with even stronger protective armor. Apart from the cockpit armor modifications introduced in the Ju 87 D-1 model, the aircraft featured armored lower fuselage and cooling system lines. As a weight-saving measure, the RLM made a decision in May 1943 to discontinue siren installations in lieu of additional armor plates on both sides of the cockpit to better protect the crew from ground fire and flak. The new configuration was successfully tested at Rechlin and went into full-scale production.
Many other modifications were introduced during Ju 87 D-3 production run. Some of them focused on the fuel and lubrication systems (different diameter of fuel and oil lines), some other were introduced into the cooling system design. Early production aircraft had partially covered exhaust stacks, which were changed to fully exposed stacks in later examples. Wing-walk non-skid rubber matting was replaced with metal strips. In February 1942 engine cowling was strengthened. A special device limiting downward movement of MG 81 Z barrels was installed in March 1942 to avoid accidental damage to the horizontal stabilizers while firing the weapon. In May 1942 four coolant radiators support beams were added, which connected the wing spar to the armor plated bottom part of the radiators. A month later an extra piece of reinforced glass was added to the windscreen and the engine installation received an acetylene gas relief tube. August 1942 saw further modifications: fuselage frames 7 through 12 were reinforced, pitot tube assembly was modified and there were changes in the fuel injection system. An additional access panel in the engine cowling was added in September 1942 to allow the connection of a hot air duct. The main landing gear received a new wheel fork in March 1943, which was recessed by 90 mm. The use of a new fork also lengthened the main landing gear struts by 12 mm. In mid 1942 a Ju 87 D-3 was tested at Forschungsanstalt Graf Zeppelin in Stuttgart with experimental overwing personnel pods. The pods were mainly designed to insert covert agents behind enemy lines. Each pod could accommodate two people and was equipped with a parachute landing system. The pods were never used operationally.
In total by the fall of 1943 1,559 Ju 87 D-3s were produced in serial number blocks from W.Nr. 2600 to 3000, W.Nr. 1000 to 1500 and W.Nr. 4200 and above. In the fall of 1942 serial number blocks from W.Nr. 31100 to 31600 were introduced. The serial number system was changed in the spring of 1943 with the introduction of six-digit serials. Ju 87 D-3 were assigned serial number blocks from W.Nr. 100001 and from W.Nr. 110300 up. Out of 1,559 Ju 87 D-3s bulit, 599 examples were assembled at Weser’s Bremen plant and 960 rolled out the assembly lines at Berlin-Tempelhof.
Ju 87 D-4, based on the Ju 87 D-1 airframe, was a maritime variant. It was designed for shipping interdiction using not just bombs, but also torpedoes. Ju 87 V25/torp (torpedo) prototype was delivered to Travemünde test facility on December 16, 1941. It was a standard production Ju 87 D-1 airframe, W.Nr. 0530 (BK+EF), equipped with an underwing PVC 1006 B rack for a LT F-5w airborne torpedo. The prototype’s first flight had to be postponed until the end of December 1941 due to unfavorable weather conditions. After a series of tests at Travemünde, the aircraft was ferried to Grosseto, Italy for further trials. Flight test program went smoothly and the Luftwaffe began to show increased interest in the torpedo derivative of Ju 87 D. [...]
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