Junkers Ju 288
| Ju 288 | |
|---|---|
| |
| Sole Ju 288A prototype (Ju 288 V5) with Junkers Jumo 222 engines and ducted spinners | |
| Role | Advanced bomber Bomber B design competitor |
| National origin | Germany |
| Manufacturer | Junkers |
| First flight | 29 November 1940 |
| Number built | 22 |
| Developed from | Junkers Ju 88 |
The Junkers Ju 288, originally known within the Junkers firm as the EF 074, was a German bomber project designed during World War II, but which only ever flew in prototype form. The first of 22 development aircraft flew on 29 November 1940.
Design and development
Prior to the opening of World War II, the Luftwaffe bomber force was primarily aircraft of limited performance, some originally developed with civilian uses in mind as well. The only truly modern design in the inventory was the Ju 88, the first purposed-designed schnellbomber. Although it outperformed the collection of other designs in service, it had numerous problems of its own. Perhaps most notable among these was its very small internal bomb bay that forced it to carry some of its load externally, slowing performance.
Junkers had been experimenting on paper in its engineering departments with a variety of improved models of the Ju 88 since 1937, powered by the planned Jumo 222 multibank gasoline engine, or Jumo 223 inline multibank diesel of greatly increased power of at least 1,500 kW/2,000 HP apiece. No serious work was undertaken on these versions, but after Heinrich Hertel left Heinkel and joined Junkers in 1939, the EF 074 design was submitted to the RLM in May 1939 as the Junkers corporate entry in the RLM's Bomber B design competition.
The EF 074 entry was essentially a scaled-up Ju 88, sharing its general layout and most of its fuselage and wings with extensions in various places. The nose was completely redesigned to follow the strongly developing preference (as with the He 111P and -H's revised cockpits) in German aviation firms for a more streamlined "stepless cockpit", having no separate windscreen panels for the pilot and co-pilot. This layout allowed cabin pressurization to be more easily implemented. All of the defensive armament was meant to be remotely controlled — in one proposal, comprising a remotely operated rear-facing dorsal turret at the rearmost end of the cockpit glazing, and two remotely operated "flank" turrets on the rearwards sides of the fuselage just forward of the empennage, otherwise each resembling the FDSL 131 units of the Me 210 – the exclusive use of remotely operated turrets for the Ju 288's defensive firepower allowed them to be located in useful positions, as well as eliminating "breaks" in the fuselage pressurization. The fuselage was expanded along its length to allow for a much longer bomb bay — somewhat as had been done with the Dornier Do 217 then in development itself — that would allow for an 3,630 kg (8,000 lb) payload to be carried internally, eliminating the need to carry ordnance on outside hardpoints. Performance would be greatly improved over the Ju 88, both due to the all-internal bombload and the greatly improved power.
Accordingly the RLM sent out the specifications for Bomber B in July 1939, the Ju 88 retroactively becoming the second aircraft to be designated Bomber A in the Luftwaffe's existence. (The original usage, dating from June 3, 1936, was the specification for what became the He 177). The Bomber B program aimed at replacing all of the medium bombers in the Luftwaffe inventory with a new design based on the EF.74 or something with equal performance. Bomber B was intended to have even better speed than the Ju 88, high-altitude cruising with a pressurised cockpit, heavier defensive armament, range allowing it to cover any point in the British Isles, and a massive 4,000 kg (8,820 lb) warload, double that of the earlier generation bombers. A number of companies returned proposals, but these were to some extent a formality, the EF.74 had already been selected as the winner, and of the rest of the designs submitted, only the Focke-Wulf Fw 191 and Dornier Do 317 progressed even as far as prototypes, with the Henschel Hs 130 even coming under consideration as a late entrant.
Work began on building prototypes soon after, and the first example was completed by mid-1940. Power was supposed to be supplied by two 24-cylinder Jumo 222 six-bank, four cylinders per bank, over-1,500 kW output class powerplants, but problems with the Jumo 222's development — as with almost every new concept for over-1,500 kW output, reciprocating aircraft engines then underway in the Third Reich — meant the first prototypes flew with BMW 801 radial engines, instead. The first flight-quality 222s did not arrive until October 1941, and even at this point it was clear they were nowhere near ready for full-scale production. When it became apparent the 222 was not likely to become a viable powerplant, in May 1942, Junkers proposed replacing them with the much heavier Daimler Benz DB 606s instead, the very same 1.5 tonnes-apiece, twin-crankcase "welded-together engines" that Reichsmarschall Hermann Göring complained about some three months later, regarding the He 177's own endless powerplant troubles.
Undercarriage difficulties
The Ju 288's intricate main landing gear system's design proved to be troublesome, possessing twin vertical members directly behind a single oleo strut, for each pair of twinned wheels mounted to a uniquely-attached main oleo strut unit to which the twinned wheels were mounted. This single-tube oleo strut was pivoted off the lower end of the twin-member, "Y-shaped" retraction strut assembly, and was rotated in the vertical plane about this single attachment in a rearwards direction during retraction of the maingear unit, separate from the twin-member unit to help "shorten" its stowed length within the engine nacelle. This distinctive type of design required the oleo strut's freely-moving top end to physically rotate downwards and aftwards during retraction, operated by a lever and gear-sector system mounted on the portside of each main gear assembly, with its upper end anchored to the firewall's rear surface, through an arc of over 270º from its position when the main gear was fully extended. The stowed position of the oleo strut ended up orienting it aftwards within the rear of the engine nacelle, and placing the wheels' axle location just ahead of and above the oleo strut's pivot point when fully retracted. Such a complex main gear design, with only the single pivoting retraction point for its oleo struts taking the primary stress of touchdown, was likely only one of the many potential sources of trouble causing the Ju 288's main gear units to repeatedly collapse on touchdown.[1]
Lack of a clear combat role
As these technical difficulties were being addressed, the lack of a well-defined strategic bombing doctrine — which effectively ceased to exist within the Luftwaffe by June 1936, with the untimely death of General Walther Wever, the main proponent for such a capability — meant the mission and purpose of the Ju 288 remained nebulous throughout its development. As an interim measure, RLM ordered the Junkers Ju 188, which was a fairly minor upgrade of the original Ju 88 incorporating the basic cockpit design of the never-produced Ju 88B. Work continued on the 288 throughout, but in 1944 the project was finally abandoned as Luftwaffe priorities became more intensely focused on homeland defence.
Operations
Although the 288 never even reached production status, let alone official operational service, the aircraft did see limited combat duty. In 1944, following the cancellation of the 288 programme, the surviving A and C series prototypes were hurriedly fitted with defensive armament and equipment and deployed as reconnaissance bombers on the Western Front. Very few missions were flown, owing to the scarcity of aviation fuel and spare parts, and the unresolved problems with the aircraft's powerplant and undercarriage. It is believed that the 288s were attached to the same unit operating the small number of Ju 388 reconnaissance planes that saw service; the loss of much of the relevant documentation at the end of the war means precise facts about the 288's brief combat career will always remain elusive.
Variants
- Ju 288A - first seven prototypes with BMW engines
- Ju 288B - seven prototypes with slightly enlarged airframes and better defensive armament
- Ju 288C - final eight prototypes (of which only four were completed) with two Daimler-Benz DB 606 or 610 "power system" engines. This version was selected for serial production in 1944, but the programme was abandoned before that could take place.
- Ju 288D - mock-up of a Ju-288C with improved tail armament
- Ju 288G - design for an anti-ship version armed with a 355.6 mm (14 in) recoilless cannon
Specifications (Ju 288B)
Data from [citation needed]
General characteristics
- Crew: 4
Performance
Armament
- Guns:
- 4 × 13 mm (.51 in) MG 131 machine guns
- 1 × 15 mm (.59 in) MG 151 cannon or 20 mm MG 151/20 cannon
- Bombs: 3,000 kg (6,610 lb) of bombs
See also
Related development
Related lists
- List of World War II military aircraft of Germany
- List of bomber aircraft
- List of German aircraft projects, 1939-1945
References
- Notes
- ^ Sengfelder, Günther (1993). German Aircraft Landing Gear. Atglen, PA USA: Schiffer Publishing. pp. 175–177. ISBN 0-88740-470-7.
The Ju 288's landing gear was most innovative in its design. A Y-shaped bearer was mounted in the engine nacelle with its upper arms hinged. At the bottom end of this bearer was the shock absorber leg, which was likewise hinged. Two double-brake wheels, with (metric) size 1015 x 380 tires, were mounted on the cross-axle. During the retraction cycle a folding strut was raised by a hydraulic jack. The bottom part of the folding strut drew the Y-bearer upwards. Functioning via a lever-and-gear arrangement, a pushrod positioned parallel to the Y-bearer acted upon another gear segment mounted to the oleo leg's hinge pin and rotated it about this as the Y-bearer was drawn upwards.
- Bibliography
- Hitchcock, Thomas H. Junkers 288 (Monogram Close-Up 2). Acton, MA: Monogram Aviation Publications, 1974. ISBN 0-914144-02-2.
External links
