Watanabe G11W (IJNAF Me210) What-if by Dizzyfugu

1:72 Kyushu G11W1-KAI (license-built Me210) with Igo-1-A-I glide bomb; ‘145’ of the Imperial Japanese Navy Air Force, 711th Kokutai; Sasebo (Kyushu/West Japan), early 1945 (Whif/modified Bilek kit)

Some background:<

The Messerschmitt Me 210 was a German heavy fighter and ground-attack aircraft of World War II. Design started before the war, as a replacement for the Bf 110. The first examples were ready in 1939, but they proved to have unacceptably poor flight characteristics due to serious wing planform and fuselage design flaws. A large-scale operational testing program throughout 1941 and early 1942 did not cure the type's problems. The design entered limited service in, but in Luftwaffe service the Me 210 was soon replaced by the Messerschmitt Me 410 Hornisse, a further, re-badged development of the Me 210 which rectified many of its shortcomings.

The type was, however, offered for license production, despite its flaws. In Europe the Me 210 was license-produced in Hungary (where 179 were built with the designation Me 210 Ca-1 from 1942). In Asia, the Imperial Japanese Army Air Force received one aircraft (Werksnummer 2350, a modified Me 210 A-2 which already incorporated many elements that would be integrated into the improved Me 410) bought in Germany for tests and delivered by U-boat. It was operated by the Testing unit of the First Tachikawa Air Army Arsenal. Despite its improvements the upgraded Me 210 did not find favor by the IJA, but the Imperial Japanese Navy became interested in the type because it would provide its land-based units with a versatile two-engine aircraft that could be adopted into a wide range of uses.

An agreement for license manufacture in Japan by Watanabe Tekkōjo, Kyūshū Hikōki K.K. (九州飛行機, Kyūshū Aircraft Company Ltd.) was signed by the Imperial Japanese Navy Aviation Bureau in late 1942. However, the IJN found the original Me 210 to be too complicated and heavy, and demanded changes that eventually led to the Kyushu G11W, how the license-built but much modified derivative was designated. The most important and obvious modification was the deletion of the original liquid-cooled DB 601 engines and their exchange with domestic air-cooled Mitsubishi Ha-102 14-cylinder radial piston engines. This required a re-design of the nacelles and of parts of the landing gear, as well as new engine mounts. The Ha-102s offered less power than the German DB 601 but provided net weight savings of almost 600 kg because the coolers and their respective ducting could be omitted, too.

Another weight-saving measure concerned the Me 210’s defensive armament, originally a pair of remote-controlled Ferngerichtete Drehring-Seitenlafette FDSL 131/1B barbettes on the fuselage flanks behind the cockpit. IJN officials were impressed by the engineering efforts behind this installation but had doubts about the weapons’ efficiency, its relative weight and reliability, so that the whole installation was rejected and deleted, too. Instead, two manually operated 7.7 mm (0.303 in) Type 97 aircraft machine guns were installed in simple ball mounts, operated by the rearward-facing navigator/radio operator. In service, these were frequently upgraded to 13.2 mm (0.520 in) Type 3 machine guns, though. The deletion of the motorized barbettes saved roughly another 400 kg, and with some other structural simplifications the reduction of overall weight could compensate for the slightly enlarged frontal area and loss of power induced by the radial engines, so that the G11W’s performance remained on par with the Me 210. As another side effect, due to a shift of the aircraft’s center of gravity forward, the G11W’s overall handling became less hazardous than the Me 210’s and the lower gross weight made the aircraft more responsive to control input.

Conceived as a fast bomber, the G11W’s offensive armament remained comparable with the German Me 210, with two light machine cannon and machine guns each in the nose, just Japanese weapons were mounted. The shallow bomb bay under the cockpit was retained, too, and could hold up to 1.000 kg (2.205 lb) of bombs. However, indigenous additions were plumbed hardpoints under the outer wings for 300 l drop tanks to extend range for long-range missions over the sea and for ferry flights in the PTO.

G11W serial production started in 1944, but the establishment of the type’s production line at the Kyushu plant was delayed and indigenous aircraft designs had received priority, so that the work’s capacity was never fully exploited. Only limited numbers of the new multi-purpose baseline aircraft, the G11W1, were delivered to frontline units, primarily to fill operative gaps.Most were adapted to special missions, though, and this led to a wide range of modifications of the equipment and even of the basic airframe. Beyond the original fast bomber/attack role many G11Ws were re-equipped as G11W1-C heavy fighters; their bomb bays were filled with more guns, and some late aircraft even received on-board radar to convert them into night fighters (called G11W1-S), even though the type’s maximum altitude was not sufficient to intercept the fast heavy B-29 bombers. Instead of additional forward-firing guns in the bomb bay these machines were frequently outfitted with an extra pair of forward up-firing Type 99 20 mm cannons behind the cockpit, in the space where the Me 210 formerly carried its motorized gun barbettes. A small number of G11Ws were furthermore outfitted with cameras in the bomb bay, lost their offensive gun armament, were lightened wherever possible, and used for tactical reconnaissance (as G11W1-R).

A special role the G11W was adapted for, too, was the attack of enemy ships with newly developed guided air-to-surface weapons, including missiles and glide bombs. These machines were typically baseline bombers and were designated G11W1-KAI which had a reduced offensive armament (typically the light machine guns in the nose were deleted) to compensate for additional radio equipment to control guided air-to-surface weapons. One of the few weapons that found its way into operational use on board of G11Ws was the Mitsubishi Igo-1-A, also known as Mitsubishi Ki-147 within the IJA. Developed along its sister projects of Kawasaki Igo-1-B and Tokyo Imperial University designed Igo-1-C, the Igo-1-A was a simple, visually guided, and radio-controlled glide bomb propelled by a Toku-Ro Model 3 solid-fuel rocket booster, which provided 240 kgf of thrust for up to 80 seconds.

The Igo-1-A’s design began in 1944 and it was developed in a hurry, probably with engineering support from Germany. The weapon resembled a classic torpedo with wings and tail surfaces. The Igo-1-A had an overall weight of 1.400 kg (3,083 lb), including an 800 kg (1.762 lb) HEAT warhead from a No. 80 standard bomb, a length of 5.77 m (18 ft 11 in) and a wingspan and wing area of 3.60 m (11 ft 10 in) and 3.60 m² (38.6 sq ft), respectively. Test trials were already carried out from a modified Kawasaki Ki-48 light bomber in late 1944 and quite successful. Launched at an altitude of 5.000m (16,000 ft) the Igo-1-A demonstrated a maximum effective range of about 11 km (7 miles), and the rocket boosters allowed an even higher range. However, effectively aiming the glide bomb into a major ship target beyond this distance turned out to be impossible. Despite its many deficiencies the weapon was quickly refined into the operational Igo-1-A-I, which had a modified configuration to make it better suited for aircraft operations. In this form the weapon was ordered by the war ministry and adopted by both IJA and IJN. The Igo-1-A-I’s planned standard mother aircraft were IJA’s Kawasaki Ki-102 heavy fighter and the IJN’s G11W. In both cases, a single glide bomb was carried under the fuselage on a massive pylon, in the case of the G11W its protruded from cut-outs in the bomb bay doors.

Beyond the simple radio guidance, more sophisticated means of target acquisition were under development, too, primarily to make it possible for the bomber to turn away after dropping the weapon without having to continue observing the target or even having to fly over it. One direction was a television seeker and a transmitter on board of the guided bomb and a viewing device on the carrier aircraft. Images of the target were transmitted via a VHF transmitter to the image receiver in the guided aircraft, which could be used by the bombardier for target control and flight path directions. The most important part of the television camera was a compact image pickup tube (a super iconoscope). It converted the optical image provided by a lens into electrical signals, with which the transmitter built into the bomb was modulated and the HF signal was fed to an amplifier with an antenna for transmission. The picture consisted of 441 lines with 50 picture changes according to the interlaced method. In the carrier aircraft, the gunner observed the monitor on which the image recorded by the camera was reassembled into a television image. The combination of transmitter, transmitter output stage and TV receiver was built and tested in only a small number, though.

Another guidance method for anti-ship weapons used a heat-seeker. The idea behind the concept was simple and resulted in one of the first fire-and-forget weapons: a bomb with a heat-sensitive seeker head, which would, when locked onto its ship target, steadily correct the bomb's flight path from constant deviations, without external guidance. This concept was based around the idea that a steam-powered (battle) ship would produce a distinct heat signature and therefore an easy target - esp. at night, in good contrast to the colder sea around and with no sun interferences which could jam or distract the sensor. The seeker head used a bolometer, a device for measuring radiant heat by means of a material having a temperature-dependent electrical resistance, to home in on its target. Deviations from the ideal flight path (with the strongest recognized temperature signal) would cause tail rudders to correct the flight path, so that the bomb would follow a zig-zag path during its braked dive from about 2.000 m launch altitude. Tests were made with a target float on which a huge fire burned, but with appallingly poor results at first, because there was no way to confirm whether the seeker had locked onto the intended target upon launch or not. However, the heat-seeker was constantly improved, including a transmitter to control the bolometer’s readings and confirm its correct input, and it was expected to be ready for service in late 1945. Another novel guidance concept used the shock waves of a battleship’s firing guns to attract/guide a missile or guiding bomb without the need to actively control it.

None of these more sophisticated guidance measures made it to the operational Igo-1-A-I glide bombs, though. Until the end of hostilities, approximately 180 missiles were built and launched against Allied ships, but only with highly limited success and many carrier aircraft lost to AA fire and Allied air supremacy.

General characteristics

Crew: 2

Length: 11.41 m (37 ft 4 1/2 in) w/o Igo-1-A guidance antenna

Wingspan: 16.3 m (53 ft 6 in)

Height: 4.2 m (13 ft 9 in)

Wing area: 36.2 m² (390 sq ft)

Empty weight: 7,069 kg (15,584 lb)

Max. takeoff weight: 9,705 kg (21,396 lb)

Fuel capacity: 2,500 L (660 US gal; 550 imp gal) in four wing tanks

Powerplant: 2× Mitsubishi Ha-102 (Army Type 100) 14-cylinder air-cooled radial piston engines, 810 kW (1,080 hp) each for take-off and 787 kW (1,055 hp) at 2,800 m (9,186 ft), driving 3-bladed all-metal constant-speed propellers

Performance

Maximum speed: 580 km/h (360 mph, 310 kn) at 6,700 m (21,980 ft); 507 km/h (315 mph, 274 kn) at sea level

Cruise speed: 400 km/h (250 mph, 220 kn) at 4,000 m (13,123 ft)

Range: 2,000 km (1,200 mi, 1,100 nmi) with internal fuel; 3,102 km (1,927 mi, 1,675 nmi) ferry range

Service ceiling: 8,900 m (29,200 ft)

Rate of climb: 9.083 m/s (1,788.0 ft/min)

Time to altitude: Climb to 6,000 m (19,700ft): 11 min

Armament: 2× 20 mm (0.787”) Type 99 cannon with 120 RPG and 2× 7.7 mm (0.303”) Type 97 aircraft machine guns with 500 RPG in the nose, plus 2× flexible/manually operated 7.7 mm (0.303”) Type 97 aircraft machine guns with 500 RPG firing backwards (often replaced with 13.2 mm (0.520”) Type 3 machine guns and 200 RPG).

Shallow bomb bay under the cockpit for 2× 500 kg (1,100 lb), 2× 250 kg (550 lb) or up to 8× 50 kg     (110 lb) bombs; 2× underwing hardpoints for a single 250 kg (550 lb) bomb or a 300 l drop tank each    Total in- and external ordnance of 1.500 kg.

The kit and its assembly

This project had been lingering on my to-do list and in The Stash™ for quite a while, because it’s a combination of leftover parts from previous builds. The inspiration was based in real life, though: the German Me 210 was actually tested in Japan, and I wondered what a serial production/service aircraft could have looked like – primarily only livery-wise.A Bilek me 210 had, long ago already “donated” its FDL 131 weapon stations (to a modified He 115 floatplane), and after that it also lost its inline engines/nacelles and underwing radiators to a Germanized Ki-46III (the Gotha 146 B-1), leaving only the kit’s core. Since the Arii Ki-46III’s engines and respective nacelles were also left over the plan began to take shape to create a “Japanized” Me 210 with radial engines, as if the airframe had been adapted to local needs/preferences. And this is what became the Kyushu G11W1.

Building the Me 210 core went straightforward. The openings for the gun barbettes were filled, and as an alternative defensive armament I added mounts for single, hand-held machine guns that were fitted into the inside of the backward-facing flat glass panels of the rear cockpit section. Simple and effective.

Things became more demanding with the new radial engines and their respective nacelles from the Ki-46. The original nacelle fairings on the Me 210 wings had been completely cut away, leaving gaps in the wing surfaces, so I completed the new engines first, including their own nacelle extensions, and tried to trim them down so that they’d slip over the wings’ leading edges and upper/lower surfaces, attempting to minimize PSR. That turned out to be easier and more effective than expected – the Ki-46 nacelles just covered the gaps, and only the nacelles’ curvature for the upper wing surfaces had to be adjusted. The nacelles could be slipped over the Me 210 wings like gloves! The propellers were taken OOB, but – as usual – modified with long metal axles to make the spin freely and insert them once the whole model had been painted/finished. The landing gear was taken over from the Me 210 kit, I just had to scratch mounts for a stable hold of the struts inside of the new nacelles.

The Bilek Me 210 kit itself is …mediocre. Details are all a bit clumsy, and the fit of major parts (esp. of the ventral section that includes the bomb bay and the wing/fuselage intersection on both sides) is really poor. Nothing matched, and the whole thing required PSR on every seam.

Since the aircraft’s paint scheme would be quite simple (see below), I decided to add some special equipment, namely a Ki-148 glide bomb (an A&V resin “kit” from the Czech Republic, upgraded with some extra bits), and a PE guidance antenna (left over from an MPM Boulton Paul Defiant night fighter) on the nose, inspired by real Japanese radar systems of the model’s era.

Even though I wanted to add a pair of drop tanks under the outer wings, taken over from a Ki-61, I eventually left them away because the glide bomb would have eaten away almost all of the Me 210's ordnance load capability of 1.5 tons.

Painting and markings

This became intentionally “dry”, because many late-WWII IJN aircraft received very simple paint schemes, mostly with green upper surface and grey undersides. This concept was also applied to the G11W, even though I went a step further and tried to create the impression of a hastily camouflaged bare metal aircraft (only with grey-green fabric-covered rudders). For this purpose, the model received an initial overall coat with Tamiya XF-16 (Flat Aluminum). Once dry, the upper surfaces were unevenly painted with Tamiya XF-11 (IJN Green,). To break the look up a little and add more Japanese flavor I painted the engine cowlings in anti-glare black-blue, mixed from Humbrol 85 and a little 15, and the propellers were painted with red-brown primer (Humbrol 160 for the blades, 186 for the spinners).

The cockpit interior was painted in a yellowish green (“bamboo”) tone, mixed from Humbrol 83 and 80, while the landing gear wells and the inside of the engine cowlings were painted with aodake iro over the white aluminum basis – actually a clear blue acrylic paint was used. The landing gear struts were painted in semi-gloss black.

The Igo-1-A was a bit challenging, because there is only little visual evidence about this weapon’s livery. A b/w picture I found suggests an overall light grey paint scheme (probably only a test weapon, though). I rolled with that with an overall basis of Humbrol 147 (FS36495), but to add some excitement I painted war head in grey and added triangular black markings to the wings to help identify the bomb’s direction for the guiding WSO in the mother ship.

The G11W's markings became minimal, just six Hinomaru (those under the wings without white contrast border), the tactical unit code as well as the "registration plate" on the tail, and - as the only extraordinary marking - a yellow fuselage band.

After some more weathering and wet-sanding on the surface the model was sealed with a shiny mix of matt and semi-gloss acrylic varnish, and some soot stains around the guns and the exhaust stubs were added. I also added some oil traces behind the engines' cooling louvres with Tamiya's Smoke.