Junkers Ju 188
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The Ju 188 Rächer (Avenger) was a German World War II high-performance medium bomber from Junkers, the planned follow-on to the famed Ju 88 with better performance and payload. It was produced only in limited numbers, due both to the presence of improved versions of the Ju 88, as well as the deteriorating war condition and the resulting focus on fighter production.
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[edit] Background
In 1936 Junkers submitted proposals for the Ju 85 and Ju 88 into competition for the new standardized Luftwaffe high-speed tactical bomber, known as the schnellbomber. The two designs were almost identical, differing only in that the Ju 85 used a twin-rudder and the Ju 88 a single fin. At the same time they offered modified versions of each as the Ju 85B and Ju 88B, again similar to the original designs, but using an "egg shaped" forward fuselage that was essentially one large window. The new design offered somewhat lower drag, and better visibility. At the time this was considered too radical, and eventually the Ju 88A with its simpler fighter-like cockpit won the contest.
By 1939 the original Ju 88 had itself evolved with considerably more window area, but in a fashion that was not well streamlined. The Reich Air Ministry (RLM) was in the process of ordering a "second generation" bomber in a project known as Bomber B, but this was extensively delayed due to the non-delivery of the large 2,500 hp (1,838 kW) class engines the designs relied on. Although Junker's own Ju 288 was currently leading the contest, there was no delivery date on the engines and the Ju 88B project was re-submitted as a stop-gap measure. For this version they used the latest Ju 88A-1 airframe as a baseline, but added the new Junkers Jumo 213 engine, which had recently started bench testing and was expected to deliver 1,500 hp (1,103 kW).
The RLM wasn't impressed with the new design, as it offered only small improvements over the existing Ju 88A's then in service. However they did suggest that Junkers continue with the prototype work anyway, but asked that they consider fitting the design with the BMW 139 radial engine instead. This engine was cancelled only a few weeks later, and all designs based on it moved to the newer and more powerful BMW 801.
[edit] Prototypes, Ju 88B-0
The prototype Ju 88B V1, D-AUVS, flew for the first time with the 801A/B engines in early 1940. The fuselage was identical to the Ju 88A-1, which presented a problem: with the extra power, 1,600 hp (1,190 kW), the design could now carry considerably more load than the small bomb bay could fit. An additional external shackle was then added to each wing well outside the engines, although using the rack would seriously hamper performance.
During the summer a pre-production run of ten Ju 88B-0 based on the pre-production Ju 88A-4 airframes were delivered. The A-4 used a longer wing for better altitude performance, just over 65 feet (20 m) as opposed to the 60 foot (18 m) span of the earlier A series, but attention to streamlining and new "pointy" wing tips kept drag to about what it was earlier. The airframe changes moved the center of gravity slightly, so the glazed "cockpit" area was made slightly longer to re-balance the aircraft, while also offering better visibility for other members of the crew.
Service tests were all successful, and the pilots generally lauded the new cockpit design. However the RLM still remained unconvinced that the small improvement in performance over the existing A-5's and future A-4's was worth investing time in. Instead the pre-production models were modified as long-range reconnaissance aircraft by removing the guns, bombsights and external bomb shackles, and fitting fuel tanks into the bomb bay.
Several of the airframes were retained by Junkers for further development. One of these was fitted with the slightly updated 801C engines and a small power-operated turret on the extreme top of the cockpit mounting a MG 131 machine gun.
[edit] Ju 188
By 1942 it was becoming clear that the Ju 288 wasn't going to be ready any time soon, and at the same time the Ju 88's were increasingly at the mercy of a rapidly improving RAF and Soviet VVS. The RLM finally decided that even the small gains in performance in the Ju 88B were worth considering, and asked Junkers for a series of upgrades as the Ju 188.
The sole Ju 88E-0 was modified with several additional guns, another MG 131 firing rearward just below the turret, one firing forward through the nose, and the twinned MG 81Z in the ventral bulge firing rearward. Two other airframes had their engines and outer wings removed to act as testbeds for water ditching, as it was planned to use the 188 in long overwater flights against British shipping. A second 188 test airframe was also built up from another 88A-4, this one including larger tail surfaces to provide more directional control at higher altitudes, a feature also used on future Ju 88 models. Originally known as Ju 88V44, this airframe was later designated Ju 188V1.
October 1942 the program was given the go-ahead to start planning for production. A second prototype was delivered in January, which moved the outer bomb shackles to a position inboard of the engines. Both started testing the dive bombing system installed in the 88A-4 in February. The RLM then asked for another change, allowing the aircraft to mount either the BMW 801 or Jumo 213 engines as a complete "power egg" that would simply be bolted on and hooked up. Concerns about the Jumo 213, now years overdue, were offset by this engine's better altitude performance, so it made sense to delay the aircraft slightly if that meant it could switch to the 213 as soon as they became available. To allow both versions to use the same propeller, BMW modified the gearing on the 801D series to run at the same RPMs as the Jumo, resulting in the 801G/H.
[edit] Ju 188A & E
The Ju 188 was designed to be fitted with either the 1,750 hp (1,287 kW) Jumo 213A or 1,730 hp (1,272 kW) BMW 801G/H engines without any changes to the airframe. It was originally intended that both would be known as A models, but the naming was later changed: the Ju 188A model powered by the Jumo, and the Ju 188E with the 801.
The first three production Ju 188E-1 machines were delivered with the BMW engines in February 1943, another seven in March, and eight in April. A conversion testing unit was formed up in May, and after testing were attached to an operational unit. By the end of the year 283 aircraft had been delivered, and two new factories were added to the production effort. Most operational machines differed from the prototypes only in having a 20 mm MG151/20 cannon in the nose and dorsal turrets in place of the 13 mm MG131. The Ju 188E-2 was built as a torpedo-bomber.
Although the A and E models were to have been delivered at the same time, the Jumo engine was still having difficulties getting into production. Nevertheless the first Jumo powered Ju 188A-1 versions were shipped only shortly after the BMW versions, albeit at a much slower rate. By the time delivery rates were finally picking up in late 1943 the Jumo was available in a new MW50 "boosted" version that delivered 2,100 hp (1,544 kW) for takeoff. With this engine the plaers were known as the Ju 188A-2, and started deliveries in early 1944. This was matched with the 801G/H series engines in the E model, geared to match the RPM range of the Jumo and thus be able to run the same propeller.
A modified version mounting a small FuG 200 Hohentwiel sea-search radar set under the nose and shackles for a torpedo for naval strike missions was delivered as the E-2, and with the Jumo as the A-3. The only other difference was the removal of the outer pair of wing bomb shackles.
For all its good points, the Ju 188 was only a small improvement over the Ju 88 it was supposed to replace. The bombload and bomb-bay was no larger than the earlier plane, so although it could handle a larger load by mounting externally, doing so hurt performance. Even then the performance was rather poor considering all the effort – only 325 mph (523 km/h) or less. One has to wonder about the German armament designers as well, the fancy dorsal turret had only one gun in it, yet they retained the single-gun flexible position only a few centimeters away from it. In the meantime the various projects to finally provide the plane with real tail armament were all abandoned.
Delivery problems of the Jumo were never entirely sorted out, and the only model to be built in large numbers were the E series with the 801. Even then so few were available that they were generally given out to Ju 88 units, who flew them on "special" missions where the longer range or better performance would be helpful.
[edit] Ju 188C
It was planned all along to skip over a "B model" to avoid confusion with the original Ju 88B, but in the original planning the A and E models would both be called A's. The Ju 188C would thus be the next model in line.
The C series was built to the extent of a single example, by modifying one of the few A-1 machines. To this they added the new power-operated FA 15 turret in the tail. The turret mounted two 13 mm MG 131 machine guns, aimed with a double-periscope (top and bottom) system mounted in the cockpit.
This modification would have greatly improved defensive firepower, always lacking on German designs, but reliability was so poor it was decided to abandon the system.
[edit] Ju 188D & F
In early 1944 it was decided to focus on reconnaissance versions of the A and E models The airframe was modified with the removal of the bomb aimer and the forward gun, and additional fuel cells were added to extend the range to 2,110 miles (3,400 km). The Ju 188D-1 was otherwise similar to the A-1, and the Ju 188D-2 fitted nose radar for naval reconnaissance. Similar conversions of the E models were the Ju 188F-1 and Ju 188F-2.
[edit] Ju 188G & H
One problem with the Ju 88 that carried into the 188 was the lack of internal room for bomb storage. Both carried the majority of their bombload on the outside of the plane on racks under the wing, where it greatly effected performance. This was to have been addressed in the G and H models, which extended the fuselage downward for more room with the addition of a wooden pannier.
This modification also left enough room at the tail to fit a manned turret in place of the C model's remote-control one. However this system proved to be just as limited as the remote-control FA 15, being so small that only gunners could fit into it, and had basically no ability to escape in an emergency. The RLM rejected the design and planned on mounting the FA 15 even if it was unreliable. Oddly, the designs still had the nose area extended under the plane for a rear gunner, when this would no longer be needed and its removal would have greatly cleaned up the lines of the plane.
With the Jumos now being sent to fighter production, the Ju 188G-2 was to use the 801 only, with the reconnaissance conversion known as the Ju 188H-2. Neither entered production before the war ended.
[edit] Ju 188R
In the summer of 1944 three E models were modified as night fighters with the addition of radar and either four 20 mm MG 151/20s or two 30 mm MK 103s in the nose. However the added visibility of the 188 was not useful in the night role, and as the added drag of the radar washed out any speed difference, so the Ju 188R-0 was not ordered.
[edit] High-altitude versions
In 1943 it was planned to upgrade the entire lineup with even more wing area and a pressurized cockpit for high-altitude work. A single basic airframe would be offered in three versions, the Ju 188J heavy fighter, Ju 188K bomber, and the Ju 188L reconnaissance version. All three did away with the under-slung gunner's compartment, leading to a cleaner nose profile, and the bomber and recce versions mounted their loads in a long pannier under the middle of the plane instead of the deeper fuselage of the G and H models.
Simpler versions of these with no defensive armament and even longer wings became the Ju 188S fighter and Ju 188T intruder. With Jumo 213E-1 engines 2,100 hp (1,544 kW) at take-off and 1,690 hp (1,243 kW) at 9,500 m (31,400 ft), the Ju 188T could reach 700 km/h (435 mph). Operating at this altitude, the Ju 188S could carry only 800 kg of bombs.
Before any of these could start production, the entire lineup was renamed the Ju 388, the vastly improved performance warranting this change in name.
[edit] Specifications (Ju 188E)
General characteristics
- Crew: 5
- Length: 15 m (49 ft 1 in)
- Wingspan: 22 m (72 ft 2 in)
- Height: 4.4 m (14 ft 7 in)
- Wing area: 56 m² (603 ft²)
- Empty weight: 9,900 kg (21,825 lb)
- Loaded weight: 14,500 kg (31,967 lb)
- Powerplant: 2× 1 BMW 801G-2/H-2, 1,272 kW (1,730 hp) each
Performance
- Maximum speed: 499 km/h (310 mph)
- Range: 2,190 km combat (1,360 miles)
- Service ceiling: 9,500 m (31,170 ft)
- Wing loading: 258.9 kg/m² (53.0 lb/ft²)
- Power/mass: 0.175 kW/kg (0.106 hp/lb)
Armament
[edit] Related content
Related development
Designation sequence
Ju 186 - Fw 186 - Fw 187 - Ju 188 - Fw 189 - Fw 191 - Ao 192
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