What-if Kyushu J7W3 ‘Shinden-Kai’ by DizzyFugu

1:72 Kyushu J7W3 ‘Shinden-Kai’; aircraft “(A-343-)15”, 343th Kokutai/301st Hikotai, Imperial Japanese Navy, piloted by CPO Yishida Masaoka; Matsuyama AB (Shikoku/Takanawa peninsula, Japan), early 1946 (Whif/modified Hasegawa kit)

Some background:

In 1943, the IJN issued an 18-shi specification that included the requirement for a new interceptor. Japanese aircraft tasked with interception roles had by this time begun to be eclipsed by the newest Allied fighters and the IJN sought to ensure their edge was main-tained. Three contenders submitted their designs, and it would be Kyūshū's that was the most radical of them all: the J7W Shinden. The Kyūshū J7W Shinden (震電, "Magnificent Lightning") was a World War II Japanese propeller-driven fighter plane with wings at the rear of the fuselage, a nose-mounted canard, and a pusher engine. Developed by the Imperial Japanese Navy (IJN) as a short-range, land-based interceptor, the J7W was a response to Boeing B-29 Superfortress raids on the Japanese Home Islands. 

The man behind the Shinden ('Magnificent Lightning') was Captain Masaoki Tsuruno, a member of the Technical Staff of the IJN. Tsuruno conceived an interceptor that made use of a configuration rarely seen at the time of his design work, a design with canard fore planes. Canards were not a new concept, even in 1943. They were seen as far back as 1910 with a Gabriel and Charles Voisin design and later a Bleriot tail-first aircraft had incorporated canards. Tsuruno felt canards could offer a num-ber of advantages such as reducing the chances of stalling, improved controllability and maneuverability and easing some construction concerns such as the engine installation and control linkage arrangements. Tsuruno also believed the design could easily be retrofitted with a turbojet, when suitable engines became available, and the radical J7W was originally designed as a jet aircraft. At this time, the Shinden was known as the X-18. His ideas were worked out by the First Naval Air Technical Arsenal (Dai-Ichi Kaigun Koku Gijitsusho), which designed three gliders, designated Yokosuka MXY6, featuring canards. These were built by Chigasaki Seizo K. K., and one was later fitted with a 22 hp Semi 11 (Ha-90) 4-cylinder air-cooled engine.

By the time Tsuruno's initial layout for the Shinden was complete the IJN had already issued its late 1943 18-shi specifications for three classes of aircraft. The first of these covered an air superiority fighter (18-shi Ko), the second for an interceptor (18-shi Ōtsu) and the third for a night fighter (18-shi Hei). For the 18-shi Ōtsu competition, both Nakajima and Kawanishi had submitted designs: the single-engine J6K1 Jinpu ('Squall') and the twin-engine J5N1 Tenrai (or 'Heavenly Thun-der') respectively. These entries were based on the rather sparse directives of the specification which called for a top speed of 665km/h (413mph), a climb to 8,000m (26,246ft) in nine minutes and the ability to carry at least two 30mm cannons. To go with these two projects, Tsuruno introduced the X-18  to the IJN as a third competitor.

The feasibility of the canard design was proven by both the powered and unpowered versions of the MXY6 by the end of 1943, and the Navy were so impressed by the flight testing, they instructed the Kyushu Aircraft Company to design a canard interceptor around Tsuruno's concept. Kyushu was chosen because both its design team and production facilities were relatively unburdened, and Tsuruno was chosen to lead a team from Dai-Ichi Kaigun Koku Gijitsusho to aid Kyushu's design works. The aircraft was officially designated J7W; in the IJN designation system, "J" referred to land-based fighters and "W" to Watanabe Tekkōjo, the company that oversaw the initial design.

The construction of the first two prototypes started in earnest by June 1944, stress calculations were finished by January 1945, and the first prototype was completed in April 1945. The Shinden would carry four Type 5 30mm cannons. The Type 5, while heavier than the earlier Type 2 30mm gun, possessed a higher rate of fire at 500 rounds per minute and had a higher muzzle velocity. Each cannon was provided with 66 rounds. With less than eight seconds of 30mm rounds per gun, one hit would be sufficient to cripple and shoot down a fighter or bomber, therefore there was little ammunition to waste. Therefore, there were two Type 1 7.92mm machine guns, one on either side of the gun camera, in front of the nose. The purpose of these guns was not offensive but to serve as a ranging weapon for the cannons. Upon lining of his target, the pilot would fire a short burst from the machine guns. If the rounds struck the target, he would fire a burst from the cannons and be reasonably assured of a hit, thereby conserving the precious cannon ammunition. Each Type 1 was provided with 75 rounds of ammunition in a saddle drum magazine. For payload, the Shinden had a modest bomb carrying capacity of 120kg (264 lb).

The 2,130 hp Mitsubishi MK9D (Ha-43) radial engine and its supercharger were installed behind the cockpit and drove a six-bladed propeller via an extension shaft. Engine cooling was to be provided by long, narrow, obliquely mounted intakes on the side of the fuselage. It was this configuration that caused cooling problems while running the engine while it was still on the ground. This, together with the unavailability of some equipment parts, postponed the first flight of the Shinden. The aircraft turned out to be agile but not easy to fly. The Shinden was found to have a relatively fast landing speed at 240km/h (149mph), its massive propeller and extension shaft caused substantial torque pull to the right and the aircraft had the unpleasant tendency to drop its nose at any speed. Especially bringing the Shinden down safely was not a simple task.

However, even before the Shinden took flight the IJN was desperately in need of a high-performance interceptor. The Kawanishi J6K1 Jinpu failed to show any improvement over the Kawanishi N1K2-J Shiden-Kai (meaning 'Violet Lightning', known to the Allies as George) and the Nakajima J5N1 Tenrai was proving to be a disappointment by the time flight trials commenced in July 1944. With the failure of these two entries for the 18-shi specification, the IJN ordered the J7W1 Shinden into production in May 1944 and in so doing made the type the only canard configuration aircraft to achieve this status during World War 2. By September 1944, the production plans had been formulated with Kyūshū's Zashonokuma factory expected to turn out 30 Shindens per month while Naka-jima's Handa plant would produce 120 Shindens each month. While serial production was ramped up, work on the J7W airframe continued: the propeller-driven aircraft were soon improved to get rid of the handling issues: the front canards were placed at 7.5° positive incidence, the center of gravity was adjusted and the extension shaft for the propeller pointed 3° to the right and 4.5° down from the zero thrust line.

In parallel, work on a more potent jet-powered version, as originally envisioned, continued, the  J7W2 Shinden-Kai. This was to be the turbojet-equipped version of the Shinden. The already available Ne 12B engine was rejected as its power was considered too low to effectively propel the aircraft. In any case, work was by this time under way on the Kügishō Ne 20 turbojet that was based on the German BMW 003A engine, the only turbojet built and flown in a Japanese aircraft so far: the Nakajima Kitsuka. Two of these engines were proposed to power the J7W2 but mounting them required a substantial redesign of the rear hull. A J7W2 prototype had been converted from a J7W airframe by April 1945, but it soon became clear that the aircraft was underpowered - it never got from the ground and only made high-speed taxiing tests, before it was destroyed in a bomb raid. However, the aircraft provided some valuable information to refine a jet-powered version of the Shinden. For instance, the original narrow air intake slits turned out to be ineffective, and the canards had to be enlarged to improve balance and control.

Another variant of the Siden-Kai was the J7W3, and this aircraft was to use the Ne 130 turbojet, also based on the BMW 003A, which was being developed by Ishikawajima-Shibaura. The Ne 130 was to have produced nearly double the thrust of the Ne 20, and this promised to be sufficient to exceed the propeller-driven J7W's performance and warrant further development. Together with the data gathered from the J7W2 the resulting aircraft retained the Shinden's core airframe but underwent considerable detail modifications. The most obvious difference were new air intakes on the wing roots, leading in constant diameter ducts to the engines that were now housed in more organic and aerodynamically more efficient nacelles that ran along the fuselage flanks. The tail section was also extended, ending now in a pen nib fairing that moved the center of gravity further back and improved aerodynamics. The canards and therewith wing area was increased. To save internal space the landing gear was shortened, resulting in smaller wells. The freed space was used for two additional 125 l wing tanks and an increased ammunition load of 90 30 mm rounds per gun. Due to the expected high speed and frontline experience with the J7W's arrangement, the two Type 1 7.92mm machine guns were deleted. Since the landing gear was shorter and there was no propeller anymore to protect, the twin fins' shape was also changed: they became taller while the lower halves were reduced in size, and their overall area was slightly increased to improve longitudinal stability. Most of the wings and the hull remained untouched, even though the different engine arrangement allowed an additional 450 l tank in the fuselage behind the cockpit, which remained unmodified, too. 

By the time the J7W3 entered hardware stage its intended powerplant also had made progress: this became the Ne 130-II, an improved design that was more reliable and produced 10.76 kN (2,420 lbf) / 10,000 rpm / sea level. Its weight was only 649 kg, and it featured one extra compressor and turbine stage for higher thrust, only lengthening the engine by 303 mm (11+15⁄16 in) overall compared to the original Ne 130. With these more advanced engines the J7W3 became a fighter to be reckoned with, offering a performance comparable with the German Messerschmitt Me 262 twin jet fighter. 

However, in dire need for an interceptor that could cope with the incoming American high-flying B-29 bombers, the IJN repeated the J7W’s hasty decision and ordered the J7W3 into production even before the first prototype took to the air in July 1945, and a quota of twenty Shinden-Kai a month was given to Kyushu's Zashonokuma factory, while 120 J7Ws from Nakajima's Handa plant were to be produced until production was supposed to fully switch to the J7W3 towards 1946. It was estimated some 1,086 Shinden could be produced in total between April 1946 and March 1947.

General characteristics:

    Crew: 1

    Length: 10,80 m (35 ft 4 1/2 in)

    Wingspan: 11.11 m (36 ft 6 in)

    Height: 3.42 m (11 ft 2 1/2 in)

    Wing area: 21.8 m² (234 sq ft)

    Empty weight: 3,795 kg (8,367 lb)

    Gross weight: 6,473 kg (14,271 lb)

    Max takeoff weight: 7,130 kg (15,719 lb)   

Powerplant:

    2× Ishikawajima Ne 130-II axial-flow turbojets, developing 1,100 kg (2,400 lb) of thrust each.

Performance:

    Maximum speed: 900 km/h (560 mph, 490 kn)

    Range: 1,050 km (650 mi, 570 nmi)

    Service ceiling: 11,450 m (37,570 ft)

    Rate of climb: 20 m/s (3,900 ft/min) at max weight of 7,130 kg (15,720 lb)

    Wing loading: 300 kg/m2 (61 lb/sq ft)

    Thrust/weight: 0.31

Armament:

    4× 30 mm (1.181 in) Type 5 cannon with 90 RPG

    Underwing hardpoints for 4× 30kg (66lb) or 4× 60kg (130lb) bombs or 2x 125l drop tanks

The kit and its assembly:

This fictional what-if project is a personal but somewhat history-based interpretation of what could have been, inspired by the J7W2 model/conversion that Hasegawa offers for its propeller-driven J7W Shinden kit, turning the latter (outwardly) into a jet-powered version. As mentioned in the background above, the J7W was originally envisioned as a jet-powered interceptor, but at a time when no suitable engine was available or even on Japanese drawing boards yet. So, it was – as an interim solution – modified to accept a radial engine with a pusher propeller, but with the perspective to switch again to a jet powerplant later. Over time the Ne-20 jet engine was developed, which was a simplified adaptation of the German BMW 003 – an axial design and rather slim. But it was experimental at best and not very powerful or reliable. It was used and flown on the Nakajima J9N Kikka, though, but even with two of these engines the aircraft was rather underpowered and far from an effective fighter airplane, let alone a fast interceptor .

When you then take a look at Hasegawa’s conversion offer (which only consists of a different end plate with a nozzle cone instead of the prop) for a J7W2 jet version of the Shinden, it’s IMHO bullsh!t because 

a) a single indigenous jet engine like the Ne-20 and even its more powerful derivatives would never have had enough power to let the J7W airframe perform like an interceptor, let alone fly at all, and 

b) the potential engine size/shape, which would rather reflect a centrifugal engine with a much bigger diameter. The shape and size of the air intakes would also leave some doubts. 

Another factor that speaks against the Hasegawa “proposal” is the fact that there was and is apparently no reliable design sketch or layout for a re-jet-engined Shinden.

This would not stop an ambitious model kit builder to try a personal interpretation, and effectively one that is more plausible than Hasegawa’s own rather lazy attempt. This eventually led to “my” J7W3, which took some inspiration from the very good and exhaustive description of the J7W in Edwin D. Myer’s book “Japanese Secret Projects (1)”. It discusses the potential engine options – which were all axial flow powerplants – and also suggests that there would have been some considerable hardware changes to the J7W airframe, like a modified tail section, a lowered/simplified landing gear, and therewith also different fins.

The basis became a standard Hasegawa J7W – and I had actually procured resin copies of the company’s own J7W2 conversion parts. However, I made considerable conceptual changes. The central difference was the decision to mount a pair of axial flow engines in the real hull, and I had resin upgrade parts for the twin J47 gondolas’ rear end for Hasegawa’s 1:72 B-47 kit in The Stash™. One of these was implanted into the J7W's slightly shortened tail/engine bay, adding length so that the aircraft’s center of gravity might be kept. Being much wider and flatter than the original radial engine I decided to add bigger air intakes, too, and to delete the original “slits” behind the cockpit. These were sanded away and replaced with the intakes from an Italeri BAe Hawk trainer, mounted relatively low in front of the wing’s leading edge. They look a bit modern (esp. because of their boundary layer gaps to the fuselage) but were simply perfect in size and shape. The ducts connecting the new intakes and the side-by-side engines were then sculpted with 2C putty and PSRed into the rest of the hull.

The cockpit was taken OOB, but I decided to modify the canards and give them more shape. I initially experimented with swept surfaces, but that did not look plausible and so I “just” mounted elevators from an Intech P-51 kit. Another mod was made to the landing gear: while the OOB struts and wheels were used, all parts were shortened and the respective wells were reduced in length/size accordingly, what moved the front leg forward and the main landing gear inwards, reducing track width. With less ground clearance and for a different look I also replaced the fins on the wings’ trailing edge – not an easy task, but I eventually found a pair of vintage elevators from an Airfix 1:72 F-86D kit, which were slightly modified and now occupy the original fins’ places. They are taller now, have less depth, and the lower section under the wings was dramatically shortened, too. That shape was inspired by an illustration in Edwin D. Myer’s book, and it looks quite plausible.

Another small mod was the replacement of the molded gun barrels with bits from hollow steel needles.

Painting and markings: 

I considered a lot of potential options, including a bare metal finish, an improvised camouflage over that, or even highly exotic or speculative schemes (e.g. in all-over IJN grey-green or a very pale grey). In the end I settled for a simple/conservative IJN green/grey livery for land-based aircraft. Boring, yes, but the aircraft itself was already so exotic that I wanted to keep the looks more standard, and therewith more convincing.

However, I built the paint up so that aluminum would shine through here and there, and I painted upper surface areas in different shades of dark green (including ModelMaster’s IJN Dark Green and Humbrol 2, 195 and 239). The underside was painted with Humbrol 40 (Light Gull Grey), and the low waterline became quite wavy.

The cockpit tub was painted in a yellowish green (a mix of Humbrol 63 and 226) while the landing gear wells were initially painted with aluminum and received a coat with translucent bright blue lacquer, simulating aodake iro. The landing gear struts became glossy black.

The model received a light black ink washing, thorough post-panel shading in various mixed shades of dark green on the upper surfaces, plus dry-brushing with silver to simulate flakes paint here and there. The exhaust fairings were painted with Revell 91 (Iron metallic) and treated with graphite to provide them with an uneven and more metallic/burnt shine. 

Markings came mostly from a PrintScale Kawanishi N1K kit, with typical late-war IJN markings. The yellow ID bands on the wings' leading edges were created with generic decal material (TL Modellbau) instead of trying to mask and paint them. Stencils were mostly taken from the Hasegawa J7W's OOB sheet. Finally, the model was sealed with a sheen acrylic varnish (a mix of semi-gloss and matt Italeri varnish) and the wire antenna, made from black heated sprue material, was added.

A project that I had had on my agenda for a long time, and I am happy that I eventually tackled it – and it turned out better and more plausible than expected! Despite the hand-sculpted air ducts/engine fairings the aircraft’s outlines do not look too fantastic, and the new tail section makes the Shinden look pretty fast, if not elegant. The shorter landing gear also suits the aircraft well, and I think that sticking to the classic green/grey IJN livery was the right move, because it suits the Shinden well and just underlines its “serious” origins as a real but undocumented development project.