08/31/2012. When, by late 1937, the Junkers Ju 88 prototypes had eliminated possible rivals for a production contract, Junkers were already considering a replacement for this aircraft. Their most favored design for a new medium bomber went under the project designation of EF 73, and its advanced features included a pressurized cabin and remote-controlled defensive armament.
Submitted to the RLM, the EF 73 project did not itself obtain a development contract but was used as a basis for formulating the so-called Bomber B specification which was issued late in 1939 to Arado, Dornier, Focke-Wulf, and Junkers. Originally, major requirements were that the B medium bomber type should have a maximum speed of 373 mph (600 kmh) and carry a 8,820 lb (4,000 kg) bomb load to any part of the British Isles from French or Norwegian bases. For power, there were to be two engines of the 24-cylinder liquid-cooled type, such as the Junkers Jumo 222 or Daimler-Benz DB 604, being developed for the 2,500 hp class.
Under the guidance of Heinrich Hertel, Junkers' original design was then brought up to date and then modified again in accordance with the wishes of the RLM technical department. By the end of May 1940, cockpit and fuselage mockups had been inspected at Dessau and a contract was issued for the construction of prototypes under the designation Ju 288. (Unusually, this designation did not connect the type in any way with the Ju 88 or the later developments, Ju 188, 388, or 488.) Already, in February 1940, however, Junkers had begun the construction of the Ju 288 VI with an optimism born out of being instrumental in formulating the official specification.
The other designs competing with the Ju 288 were the Focke-Wulf Fw 191 which later received a development contract, the Dornier Do 317 which was put on low priority development, and the Arado Ar 340 which was eliminated. Of the four designs, the Ar 340 was the most radical in appearance: twin tail booms extended from the engine nacelles but were not connected at the rear by a tailplane; instead, each boom had its own vertical fin and rudder with a half-tailplane attached to the outside. This left a central fuselage with a clear rear field of fire for the armament. Another aircraft, which was developed at first unofficially to the Bomber B specification, was the Henschel Hs 130 C.
The elegantly proportioned all-metal Ju 288 was straightforward in layout, being a twin-engined shoulder-wing monoplane with twin fins and rudders, but it had many ingenious features. Typically German was the accommodation of the three crew members in close proximity in a glazed nose cabin, this being pressurized and enclosed beneath a bulged, glazed framework. Since the specification called for dive-bombing ability, dive-brakes were fitted to the upper and lower surfaces of the wing trailing edges, and it was proposed to fit an evaporative engine cooling system in the leading edges of the wing outer panels. The planned armament comprised a rear-firing remote-controlled single-gun barbette on each side of the fuselage. Each main leg of the fully-retractable tailwheel undercarriage had twin wheels and the main legs retracted backwards into the engine nacelles.
In the spring of 1940, the Ju 88 V2, D-ASAZ, and Ju 88 V5, D-ATYU, were modified to flight test components for the Ju 288 such as the nose section, vertical tail surfaces, dive-brakes, wing leading-edge coolers, and also ducted airscrew spinners. A Ju 288 static test airframe was also available in the same year. Finally, the Ju 288 V1, D-AOTF, made its first flight in January 1941. It was powered by two 1,600 hp BMW 801MA air-cooled radial engines, because the more powerful designated engines were not ready, and had a revised layout of gun barbettes, there being one just behind the cabin and one below the rear fuselage, but the barbettes were dummies.
This prototype was joined by the Ju 288 V2, D-ABWP, in the early spring of 1941, and the Ju 288 V4, D-AACS, in the summer. All these prototypes were powered by BMW 801 engines (as were the first prototypes of the Focke- Wulf Fw 191 competitor early in 1942), and it was not until 8 October, 1941, that the Ju 288 V5 was flown with the first available Junkers Jumo 222 engines, although these were not developing their full power. Each engine drove a four-blade airscrew with a ducted spinner extending to the diameter of the engine nacelle, but these spinners proved unsuccessful.
At the end of 1941, the Ju 288 V2 was flown in comparative trials with the
Ju 88 V16, D-ACAR. Up to this stage, the purpose of the prototypes had been development of the Ju 288 A production aircraft, which was to carry a bomb load of 11,025 lb (5,000 kg), but, although the prototypes were giving high performance, various faults and bad handling characteristics indicated that a redesign was needed.
Thus, the planned Ju 288 A was abandoned in favor of the Ju 288 B production version, which had increased span and wing area, an enlarged tail assembly and a larger cabin for a crew of four, but, because of increases in structural and equipment weights, it was necessary to reduce the bomb load to 6,615 lb (3,000 kg). The first prototype with the new wing for the Ju 288 B was the V6, which flew in November 1941; the V7, although it also had the bigger wing, differed in using again the BMW 801 radial engine. The Ju 288 V8 had the smaller wing planned for the Ju 288 A but the taller fins planned for the Ju 288 B and was flown with Junkers Jumo 222 engines.
The first full prototype for the Ju 288 B was the Ju 288 V9 (VE+QP) which flew in May 1942. This prototype had Junkers Jumo 222 engines and dorsal and chin barbettes but no armament. Armament, in the form of a single 0.591 in (15 mm) MG cannon, was fitted in a remote-controlled tail barbette for the
Ju 288 V3 in the summer of 1942, but this prototype, like the V2, suffered an undercarriage failure. With the lagging development of the Junkers Jumo 222 engine and the abandonment in 1942 of the Daimler-Benz DB 604 engine, prototypes continued to be flown with other engines.
The Ju 288 V10 appeared with two 1,810 hp BMW 810TJ radials with exhaust-driven superchargers, while the V11 appeared with two 2,600 hp Daimler-Benz DB 606 24-cylinder liquid-cooled engines. The DB 606 consisted of a coup led pair of DB 601 engines and was an interim solution to the problem of providing more than 2,000 hp from one unit for one airscrew. Three more prototypes for the Ju 288 B were flown, and sufficient Junkers Jumo 222 engines were obtained for these, but before the end of 1942 this planned production version had been abandoned in favor of the Ju 288 C production version.
The Ju 288 C was designed specifically for the DB 606 engine, since it offered the requisite power and some hope of sufficient deliveries. Some structural strengthening of the aircraft was also undertaken, and the planned armament comprised a remote-controlled barbette at the fuselage chin, forward dorsal and aft ventral positions. By about August 1942, the first two prototypes for the Ju 288 C, the Ju 288 V101 and V102, were ready. All the barbettes were fitted to the Ju 288 V 103 (DE+ZZ) which flew in the spring of 1943, and this prototype had the more powerful (2,900 hp rating) DB 610 engines as did the next three prototypes flown in the summer of 1943.
The DB 610 was of the same configuration as the DB 606 but consisted of a coupled pair of DB 605 engines. Serving as a test bed for the Ju 288 program, the Heinkel He 177 V11 had been fitted with a pair of DB 610 engines and was flown at Dessau. Although used in the Heinkel He 177 bomber, the various coupled engines worked on by Daimler-Benz had reduced power-to-weight ratios and reliability and were but a stop-gap solution for the Ju 288. In any event, by mid-1943, the whole Bomber B program had been cancelled because of difficulties and an unwillingness to commit effort and scarce material to a new bomber at a time when thoughts were turning more towards defense.
Although the Ju 288 prototypes had a bad record in terms of accidents and development difficulties, the type had been steadily improved and was giving a high performance by the time the contract was cancelled. Thus, Junkers considered it worthwhile to complete two more of the partially-built prototypes for research purposes, and these, the Ju 288 V107 and V108, were flown from July 1943.
By the summer of 1944, when flight testing finished because of strict control on fuel supplies, only a small number of the Ju 288 prototypes were still serviceable but some of these were issued for operational use. Each aircraft had special armament in the form of a single 1.97 in (50 mm) BK5 (KWK 39) cannon in a pod beneath the fuselage. This large weapon had a weight of 1,190 lb (540 kg), a barrel length of 9 ft 11.625 in (3.04 m) and could, theoretically, empty its 22-shell magazine in half a minute. Thus equipped, the Ju 288s were probably intended as bomber-destroyers.