Rikugun Kogiken Series

Kogiken Plan I – data (estimated)

Contemporaries Arado P.530 light bomber (Germany), Bell P-39 Airacobra fighter (US), Caudron C.670 light bomber (France), Farman N. C.223 heavy bomber (France), Messerschmitt Me 210 and 410 heavy fighter (Germany), Piaggio P. l 19 fighter (Italy), Potez 63 heavy fighter (France), Yakovlev Yak-2 light bomber (Russia).

Type Type A Heavy Fighter

Crew One

Powerplant One Nakajima Ha-4518-cylinder, air-cooled radial engine developing l,480hp for take-off and 1,460hp at 5,800m (19,028ft), driving a four-bladed metal propeller Dimensions Span Length Height Wing area 9.32m 8.71m 3.29m 14.59m! 30.6ft 28.6ft 10.8ft 157.1ft2 Weights Empty 2,291kg 5,0501b Loaded 3,140kg 6,9221b Performance Max speed 699km/h 434mph at 5,800m at 19,028ft Max range 599km 372 miles plus 1 hour Armament One 37mm Ho-203 cannon or one 20mm Ho-5 cannon and four 12.7mm Ho-103 machine guns

Kogiken Plan I – data

Type Type В Heavy Fighter

Crew One

Powerplant One Nakajima Ha-4518-cylinder, air-cooled radial engine developing l,480hp for take-off and l,460hp at 5,800m/19,028ft, driving a four-bladed metal propeller Dimensions Span Length Height Wing area 9.32m 8.86m 3.68m 14.59m! 30.6ft 29.1ft 12.1ft 157.1ft2 Weights Empty 2,295km/h 5,0591b Loaded 3,205kg 7,0651b Performance Max speed 699km/h 434mph at 5,800m at 19,028ft Max range 599km 372 miles plus 1 hour Armament One 20mm Ho-5 cannon, four 12.7mm Ho-103 machine guns and two 7.7mm Type 89 Model 2 machine guns

Without doubt, war often provides for rapid advancements in military technology. The key driver of this is the need for a weapon that is superior to those used by the opposition. In the majority of cases, improvements in weapons come about because one partici­pant fields a weapon that the other partici­pants have no answer for or cannot adequately counter with currently available weapons. This, then, spurs development of an equal or better weapon and the cycle repeats – an arms race! In some cases, devel­opment of a weapon does not result from actually encountering new developments on the battlefield. Instead, study of what could be encountered in the future, coupled with what can reasonably be advanced in terms of technology, provides the required emphasis for development – in essence, an attempt to second-guess likely developments so that if and when they manifest themselves the answer will already be in place. It was the lat­ter that prompted the IJA’s Rikugun Kokugi – jutsu Kenkyujo to initiate a series of studies and plans for a host of aircraft suitable to meet different roles.

In the summer of 1941, Kogiken (a con­traction of Kokugijutsu Kenkyujo) formed a group headed by aeronautical engineer Lieu­tenant Commander Ando Sheigo. The task put to Sheigo and his group of engineers was to study Japanese aviation technology in terms of what was possible at present and in the near future. In addition, some effort was to be spent on reviewing the aircraft technol­ogy of other countries. From the results of these studies, the group was to assemble and draft proposals for aircraft to fill various roles that could take advantage of future innova­tion. In all there were four roles or classes of aircraft the Kogiken group had to produce designs for: heavy fighter, light bomber, heavy bomber and reconnaissance. There was a fifth class, that of high speed, but meth­ods to achieve high speed aircraft were often
incorporated into designs in the other four classes. In addition to Kogiken, the IJA’s two biggest aircraft providers, Tachikawa and Kawasaki, were also invited to participate in some of the studies and tender their own designs.

A central theme in all of the Kogiken air­craft was the use of only a select group of engines. The two most prominent were the Nakajima Ha-45 and the Mitsubishi Ha-211-II, both of which were 18-cylinder, air-cooled radial engines. At the time of the Kogiken study, these engines were still in develop­ment but were expected to be operational in the very near future. Another factor concern­ing the engines was that, in some cases, the designs were built around the ability to replace the radial power unit with an inline engine without significant modifications. The primary inline engines were the Daimler – Benz DB601 and DB605. The former was licence built in Japan as the Kawasaki Ha-40.

By the close of September the designs were nearing completion. Since there were no performance requirements or specifica­tions applied to any of the classes of aircraft, this essentially left the engineers and designers with free rein to come up with aircraft they thought would be suitable for the roles. In many cases this led to aircraft concepts that featured, at least for the Japanese, unconventional mechanisms and approaches. Each aircraft was designated as a plan with each plan grouped by their respective class.

The first class, the heavy fighter, had four main designs, all Kogiken creations. Two were for a single-engine aircraft while the other two were twin-engine concepts. The first was the Kogiken Plan I Type A heavy fighter. Outwardly it was a fairly conventional aircraft. It used low mounted, thin laminar flow wings but in order to reduce drag the Ha-45 engine was placed within the fuselage, along the aircraft’s centre of gravity. This, in

per. Both were twin-engine designs and fitted with the Ha-21 l-II radial although the Ha-145 and the Kawasaki Ha-140 12-cylinder, liquid cooled inline engine were also considered. At this time, the latter was a projected develop­ment of the Ha-40 engine, which as noted was a licence-built version of the German Daimler-Benz DB601A. They each carried a crew of two. The Kogiken Plan I Type A Long Range Heavy Fighter carried an armament of one 20mm Ho-5 cannon and two 12.7mm Ho-103 machine guns in the nose with a rear firing Ho-103 for the second crewman. The Kogiken Plan I Type В Long Range Heavy Fighter was identical to the Type A but fea­tured a slightly different weapon fit. It retained the two forward firing Ho-103 machine guns but would either add a second Ho-5 in the nose or swap both Ho-5 weapons for two 30mm cannons, perhaps based on the 30mm Ho-155 that would eventually

Kogiken Plan V – data
evolve from the Ho-5. A variation of the Type B, the Plan II Long Range Fighter, had a slightly redesigned wing that reduced the wing area from 44.99m2 (484.3ft2) down to 41.99m2 (452ft2). A final variation, the Plan III Long Range Fighter, reduced the crew glaz­ing and fitted a remote controlled Ho-103 machine gun in the tail.

The light bomber plans would feature an approach that would not be repeated in sub­sequent Japanese designs. The Kogiken Plan II Light Bomber used two airframes con­nected by a wing centre section. The vertical stabilisers were connected by a single hori­zontal stabiliser. The pilot and crewman sat in a cockpit on the left airframe while a third crewman had a station in the right. The main landing gear retracted outwards into the outer wing panels. Buried in each airframe was a Nakajima Ha-39, 18-cylinder, water cooled radial engine that developed l,760hp

Kogiken Plan V – data

Dimensions
Span	14.23m	46.7ft
Length	10.63m	34.9ft
Height	3.71m	12.2ft
Wing area	26.59m2	286.3ft2

Armament

One 7.7mm Type 89 machine gun, one 12.7mm Ho-103 machine gun and fourteen 50kg (110 lb) bombs, eight 100kg (220 lb) bombs, two 250kg (551 lb) bombs or one 500kg (1,1021b) bomb

Kogiken Plan I Type A – data

Type High Speed Heavy Bomber

Crew Four

Powerplant

Four Mitsubishi Ha-21 l-II 18-cylinder, air-cooled radial engines, each developing 2,100hp driving a four-bladed metal propeller

Dimensions Span 826.33m 6.4ft Length 19.78m 64.9ft Height 5.09m 16.7ft Wing area 88.00m2 947.2ft2 Wing loading 219.7kg/m! 45 lb/ft2 Power loading 2.76kg/hp 6.1 lb/hp Weights Empty 12,540kg 27,6451b Loaded 19,340kg 42,6371b Useful load 6,800kg 14,9911b Performance Max speed 684km/h 425mph at 8,500m at 27,887ft Cruise speed 515km/h 320mph at 8,500m at 27,887ft Climb 3 min 9 sec to 3,500m (11,482ft) 6 min 3 sec to 5,000m (16,404ft) Max range 3,000km/l,864 miles

Armament

Two 7.7mm Type 89 machine guns, one 12.7mm Ho-103 machine gun and up to 1,500kg (3,306 lb) of bombs

Armament One 7.7mm Type 89 machine gun, three 12.7mm Ho-103 machine guns and up to 1,500kg (3,3061b) of bombs

and drove a four-bladed propeller via an extension shaft. It was proposed that a sur­face evaporation cooling system be used which consisted of a network of piping that would take the steam produced by the engines as the water circulated through them out into the wings where the cooler air would condense the steam back into water that was then recycled through the engines. The main benefit from this method of cooling was that it allowed for a more streamlined fuselage which increased air speed. Typical of early
war Japanese light bombers, the armament was light consisting of two 7.7mm Type 89 machine guns. For bombs, a regular payload of 300kg (661 lb) could be carried with a max­imum of 400kg (881 lb).

The Kogiken Plan III Light Bomber was basically identical to Plan II. The main change was the replacement of the Ha-39 engines with the Ha-45 and the latter were situated deeper into the fuselages requiring a.83m (2.7ft) long extension shaft. Without the com­plex cooling system of Plan II, Plan III was

smaller, lighter and faster. In addition, the canopy for the third crewman was made flush with the fuselage and was provided with a ventral fairing to facilitate bombing or reconnaissance duties. The propellers were fitted with ducted spinners to help cool the engines. The Kogiken Plan III Revised Light Bomber was a version of the Plan III but with the Ha-45 radials placed in a conventional fashion in the nose – the ducted spinners were left out. Another light bomber, the Kogiken Plan V Light Bomber, shared a simi­larity to the Plan III Revised but whereas the twin airframes were of the same length, the Plan V had the right airframe shorter to the point that the propeller spun behind the one on the left airframe. The canopy for the pilot and second crewman was also length­ened. The Kogiken Plan V Revised Light Bomber broke away from the previous designs. The twin airframe scheme was dropped and an engine was placed in a large nacelle in each wing. The Ha-211-II engine was specified but the Ha-45 could also be used. The crew was reduced to two and the armament was dropped to a single 7.7mm Type 89 machine gun while the bomb pay – load was lowered to 250kg (551 lb).

Kawasaki – data Type High Speed Heavy Bomber Crew Four to Five Powerplant Two Kawasaki Ha-140 24-cylinder, liquid-cooled inverted V engines, each developing 1,350hp driving a four-bladed metal propeller Dimensions Span 19.17m 62.9ft Length 14.87m 48.8ft Height N/A Wing area 48.00m2 516.6ft2 Wing loading I99.69kg/m! 40.9 Ib/ft2 Power loading 3.40kg/hp 7.5 lb/hp Weights Empty 6,170kg 13,6021b Loaded 9,590kg 21,1421b Useful load 3,420kg 7,5391b Performance Max speed 580km/h 360mph at 6,000m at 19,685ft 610km/h 379mph at 7,500m at 24,606ft Cruise speed 400km/h 248mph at 7,500m at 24,606ft Climb N/A Max range 3,000m 1,864 miles Armament Two 7.92mm Type 98 machine guns, one 12.7mm Ho-103 machine gun and up to 1,000kg (2,2041b) of bombs

In the heavy bomber class, only one stan­dard heavy bomber design was completed by Kogiken and this was the Kogiken Plan VI Heavy Bomber. The fuselage was conven­tional and was reminiscent of the solid nosed Junkers Ju 88 bombers although the Plan VI had longer glazing over the compartment for the crew of four. The similarities ended there. Set into each wing was a nacelle that housed two engines driving two propellers in a push- pull configuration. Originally Ha-45 radial engines were planned but the Ha-211 -II was the engine of choice. The design could have been adapted to take the forthcoming Mit­subishi Ha-214 18-cylinder air cooled radial or the Kawasaki Ha-201 which was made from two Ha-40 12-cylinder inline engines mounted in tandem and was under development at the time. Defensive armament was light consist­ing of a single 7.7mm Type 89 machine gun and a 12.7mm Ho-103 machine gun. A vari­able bomb load could be carried depending on the mission. A slight variation of the Plan VI increased the wing area to 69.99m2 (753.4ft2).

There was far more activity in the high speed heavy bomber category. Here, Tachikawa and Kawasaki made proposals as well as Kogiken. The Kogiken Plan I Type A High Speed Heavy Bomber was similar to the Plan IV Heavy Bomber but was larger. Instead of a conventional empennage, the Plan I Type A used a horizontal stabiliser ending in rounded vertical stabilisers. The glazing for the four man crew was longer and the fuse­lage was more streamlined. The same engine and engine arrangement was used but the nacelles had a slightly improved shape. For defence, two 7.7mm Type 89 machine guns and one 12.7mm Ho-103 machine gun were fitted and a maximum bomb load of 1,500kg (3,3061b) could be carried. The Kogiken Plan I Type В High Speed Heavy Bomber was basi­cally identical save it was larger and had a longer range. The final design from Kogiken, the Plan II High Speed Heavy Bomber, was slightly smaller and lighter than the Type В but added a fifth crew member and beefed up the defensive armament to three Ho-103 machine guns and one Type 89 machine gun.

The Kawasaki High Speed Heavy Bomber was the smallest of all the designs in the class. Consequently, its performance was less and carried a lighter bomb load and defensive armament. Instead of the Ha-211-II engines it used two Ha-140 24-cylinder, inverted V inline engines, which again were two Ha-40 engines placed in tandem. It was also unique in using the 7.92mm Type 98 machine gun in its defensive armament fit. Tachikawa’s designs, the Plan 1, Plan II and Plan III High Speed Heavy Bombers, were all variations on the same theme with minor differences

Tachikawa Plan I – data
Type	High Speed Heavy Bomber
Crew	Six
Powerplant	Four Nakajima Ha-14518-cylinder, air-cooled radial
engines, each developing 2,000hp driving a four-bladed metal propeller
Dimensions
Span	24.47m	80.3ft
Length	17.67m	58ft
Height	4.45m	14.6ft
Wing area	85.00m2	914.9ft2
Wing loading	223.61kg/m2	45.8 lb/ft2
Power loading	3.49kg/hp	7.7 lb/hp
Weights
Empty	9,540kg	21,0321b
Loaded	19,000kg	41,8871b
Useful load	9,460kg	20,8551b
Performance
Max speed	684km/h	425mph
	at 9,300m	at 30,511ft
Cruise speed	480km/h	298mph
	at 9,300m	at 30,511ft
Climb	N/A
Max range	4,899km	3,044 miles

Armament Two 7.7mm Type 89 machine guns, one 20mm Ho-5 cannon and up to 1,500kg (3,3061b) of bombs

Tachikawa Plan II – data

Type High Speed Heavy Bomber

Crew N/A

Powerplant Four Nakajima Ha-14518-cylinder, air-cooled radial engines, each developing 2,000hp driving a four-bladed metal propeller Dimensions Span 28.49m 93.5ft Length N/A Height N/A Wing area 80.00m2 861.1ft2 Wing loading 223.61kg/m2 45.8 lb/ft2 Power loading 3.31kg/hp 7.3 lb/hp Weights Empty N/A Loaded 17,900kg 39,4621b Useful load N/A Performance Max speed 694km/h 431mph at 9,300m at 30,511ft Cruise speed 490km/h 304mph at 9,300m at 30,511ft Climb N/A Max range 5,049km 3,137 miles Armament Up to 1,000kg (2,2041b) of bombs

between them. The key changes from the Kogiken plans were the engines used. The Plan I and Plan II bombers used four Ha-145 radials while the Plan III used only two of the Mitsubishi Ha-211MB 18-cylinder, air-cooled radial engines. Of all the designs, the Tachikawa Plan I had the largest crew com­pliment at six men.

In the reconnaissance class, three primary designs emerged, all by Kogiken. Each of them simply followed trends set in the fighter and bomber classes. The Kogiken Plan IV

Reconnaissance Plane was essentially the Kogiken Plan III Revised Light Bomber adapted for the reconnaissance role. Not sur­prisingly, the Kogiken Plan IV Revised Recon­naissance Plane was derived from the Kogiken Plan V Revised Light Bomber. The Kogiken Plan VIII High Speed Reconnais­sance Plane was based on the Kogiken Plan VI Heavy Bomber but had a highly stream­lined fuselage with nearly flush glazing over the crew compartment. As was typical of early Japanese reconnaissance aircraft the

defensive armament was extremely light for all of these planes.

None of the Kogiken aircraft would be con­structed. In part, this was due to the designs using technology that was either in develop­ment or not yet available. Another factor was the unorthodox nature of many of the aircraft drafted – one might liken the Kogiken aircraft to the results of a brainstorming with minimal restrictions on what might be deemed possi­ble. Nevertheless, the study was not a wasted effort and it is certainly reasonable to pre­

sume that the information provided valuable data and worthwhile methods for subse­quent IJA aircraft. For example, the Kawasaki Ki-64 would use the Ha-201 coupled engine with a surface evaporation cooling system. Another example was the Kawasaki Ki-88 which was to use a fuselage-buried Ha-140 engine that drove the propeller via an exten­sion shaft. The Mitsubishi Ki-46-III (code – named Dinah by the Allies) may have also benefitted from some of the aerodynamic streamlining studies done by Kogiken.

In 1939, a specification was drawn up that called for an aircraft capable of conducting long range reconnaissance and it was Tachikawa that answered the call to provide such a plane. However, the resulting Ki-74 would find itself both a victim of development delays and the changing fortunes of war.

In the spring of 1939, the Koku Hombu issued a specification for a long range reconnais­sance aircraft that could muster a range of 5,000km (3,107 miles) and a cmise speed of at least 280mph. The reason for this request was to provide a plane capable of operating from bases in Manchuria and flying to the west of Lake Baikal. The lake, the deepest in the world, is located north of Mongolia, near the southern Siberian city of Irkutsk. Certainly the intent was to monitor Russian and their allied Mongolian forces, especially in the face of Japanese defeats at the Battle of Lake Khasan in 1938 and the Battle of Khalkhin Gol in 1939, both at the hands of the Soviets. Tachikawa submitted a proposal to meet the

Koku Hombu’s specifications, drawn up by the design team led by Dr. H. Kimura. The ini­tial design for the Ki-74 was drafted in 1939. To achieve the required performance, Kimura selected two Mitsubishi Ha-214M radial engines. Each engine developed 2,400hp and would drive a six-bladed pro­peller. It was the pressure cabin for the Ki-74 that would be the stumbling block to finalis­ing the design.

Even before the Ki-74 was conceived, work on developing a pressure cabin for use in high-altitude aircraft was being conducted by Tachikawa. The purpose of such a cabin was to maintain air pressure for the crew when operating at altitudes in which the outside air pressure is much lower and the air thinner. Cabin pressurisation is desired for aircraft fly­ing higher than 3,048m (10,000ft) and doing so provided the crew with a much more com­fortable working environment that did not require the use of oxygen and flight gear to protect against the cold. It also prevented
conditions like hypoxia, barotrauma and alti – tude/decompression sickness. Two designs were built that would test pressure cabin con­cepts. The first was the Tachikawa Ki-77. Conceived as a plane to make a non-stop flight from Tokyo to New York, work on the Ki-77 began in 1940. For the Ki-77, Dr. Kimura utilised a sealed crew cabin but one which was not pressurised. The belief was that the cabin would keep in the oxygen but in testing it failed to meet expectations and the crew had to wear their oxygen masks constantly. With the poor showing of the Ki-77 cabin, Tachikawa tested a fully pressurised cabin in the Tachikawa SS-1. The SS-1 was a modifi­cation of the Army Type LO transport which itself was a licence built version of the Lock­heed Model 14 Super Electra (codenamed Thelma by the Allies). Work on the SS-1 also began in 1940 and the one and only example was completed in May 1943 with subsequent testing providing excellent data on pres­surised crew cabins.

The research into pressure cabins and the construction of the Ki-77 and SS-1 delayed the Ki-74 project so badly that work on it was halted; once it became obvious that the cabin for the new plane would not be ready the entire project was shelved. No prototype was produced.

However, towards the close of 1941, the Ki-74 project was resurrected in order to investigate the possibility of adapting the design to suit the role of a long range, high alti­tude bomber and reconnaissance platform. One such bombing mission envisioned was against the United States. To meet such a requirement, adjustments had to be made to the initial reconnaissance-only Ki-74 design. Armour was incorporated along with self­sealing fuel tanks. In addition, the appropriate apparatus for bombing was introduced. Finally, the initial Ha-214M radial engines were replaced by two Mitsubishi Ha-211-І radial engines, each producing 2,200hp. Once the redesign was completed it was pre­sented to the Koku Hombu who approved it in September 1942 ordering three prototypes.

It was not until March 1944 that the first Ki-74 prototype was completed, but the other two aircraft were ready soon afterwards. The latter two aircraft differed from the first Ki-74 only in the fact that they used the Mitsubishi Ha-211-І Ru engines that incorporated turbo­superchargers. With the completion of the authorised batch of three aircraft, flight testing of the Ki-74 began. Handling was considered acceptable but the Ha-211-І and the Ha-211-І Ru engines were proving to be temperamen­tal and prone to mechanical problems. A fur­ther thirteen pre-production aircraft were ordered, but due to the severe problems with the engines it was decided to replace them with Mitsubishi Ha-104 Ru radials. While the Ha-104 Ru was more reliable it also developed less horsepower, in fact only 2,000hp.

Tachikawa Ki-74 (FE-2207)

This example was at MAMA in storage as listed on the 1 August 1946 manifest. It was later slated for transfer to the Park Ridge storage facility in September 1946 but no further trace of FE-2207 remains and was most likely scrapped,

Tachikawa Ki-74 (FE-2208)

Like FE-2206, this Ki-74 was housed at AOAMC on 1 August 1946 and met the same fate.

Tachikawa Ki-74 (FE-2209)

FE-2209 was the third Ki-74 kept at AOAMC and joined the previous two aircraft on the scrapheap.

The Ki-74 as built was a mid-wing mono­plane. The pressure cabin made up the majority of the front of the aircraft with the bomb bay underneath. The use of the pres­sure cabin necessitated smaller window arrangements (as opposed to more conven­tional glazing) and the flight deck was offset to the port side of the fuselage. The aircraft had a crew of five which consisted of the bombardier, pilot, co-pilot, navigator/radio operator and gunner. All were housed within the cabin with the bombardier in the nose, the pilot and co-pilot on the flight deck and the navigator/radio operator and gunner in stations behind the flight deck. Because the Ki-74 was expected to operate at high – altitude where interception would be diffi­cult, the plane carried a very minimal arma­ment consisting of a tail mounted 12.7mm Ho-103 machine gun that was fired by the gunner via remote control. Although the Ki-74 was not a dedicated bomber, it carried a payload of 1,000kg (2,205 lb) of bombs which was comparable to IJA bombers then in service.

As construction commenced on the pre – production Ki-74s, plans were formulated to put them to use. When a number of Ki-74s had been built, they were to be assembled into shotai (a flight comprised of three air­craft) and massed to conduct bombing mis­sions against the US airbases in Saipan from which B-29 Superfortresses operated.

While the bulk of the Ki-74s were con­structed as bombers and reconnaissance platforms, another task was proposed. With much of the communication between Japan and Germany severed by the Allies, especially by sea, a plan was made to use a Ki-74 for non-stop flights to and from Germany. In 1944, the fourth pre-production Ki-74 was removed from the line and underwent modi­fications to allow it to accomplish such a feat. Higher powered На-211-I-Ru engines were utilised and fuel was carried to enable the air­craft to fly up to 12,000km (7,456 miles) – suf­
ficient to fly from Tokyo to Berlin. In addition, all non-essential equipment was removed and the flight deck was reallocated to the middle of the fuselage and lengthened. The modified Ki-74 would never make such a flight as Germany surrendered to the Allies before it could make the first attempt. The fif­teen Ki-74s were never to see combat, in part because the flight testing of the twelve remaining pre-production aircraft was not completed before the end of Japan’s part in World War 2.

Prior to the end of hostilities, two further variants of the Ki-74 were proposed. The first adapted the Ki-74 to a transport role but this was soon discarded. The second was the Ki-74-II which would have been a dedicated bombing platform. As such, the Ki-74-II was a redesign which showed some big differences to the Ki-74. The foremost alteration was the pressure cabin which was smaller and kept forward of the wings within the fuselage. This allowed for a deeper bomb bay that was needed to carry the planned 2,000kg (4,4101b) bomb load. Due to the heavier weight, the operating range was estimated to be 7,144km (4,439 miles) (in comparison to the 8,000km/4,971 miles of the Ki-74). Because of the heavier bomb load, the Ki-74-II was to be supported on a twin tyred front landing gear. The wings for the Ki-74-II were to be more slender than the Ki-74 for high-altitude operation and instead of the sin­gle tail mounted machine gun, two machine guns or cannons were to be used. Two Mit­subishi На-104-Ru engines would power the bomber, but like the transport concept, the Ki-74-II was abandoned and did not advance beyond the design stage.

Thanks to its long development history the US was aware of the Ki-74. The main thing they did not know was the role. Thinking that the Ki-74 was a fighter it was assigned the codename Pat. It was not until May 1945 that the true role of the Ki-74 was discovered and so the codename was changed to Patsy.

In the summer of 1942, the Koku Hombu was formulating specifications for a fighter that supported a heavy armament and could operate at high altitude. After settling on the specifications, the Koku Hombu approached Tachikawa and Nakajima and asked each firm to produce a design to meet these requirements.

The specifications for the fighter included a maximum speed of 800km/h (497mph) and a range of 3,000km (1,864 miles). The Koku Hombu knew the demands were high, per­haps even impossible to obtain, and so asked Tachikawa and Nakajima to put forward pro­posals to meet the demands. But they handi­capped Tachikawa by allowing Nakajima to ignore the range requirement. As such, Naka­jima could concern themselves with making their design fast without worrying about how far it could operate. Undeterred, Tachikawa’s designers set about the task of coming up with a concept that would achieve what the Koku Hombu asked for. What resulted was a departure from the conventional.

It was decided that two Mitsubishi Ha-211 Ru (Ha-43 Ru), 18-cylinder, air-cooled radial engines should be used placed in the fuse­
lage in a push-pull configuration. The key advantage this offered was a reduction in drag over a more conventional, wing mounted engine arrangement. Secondly, the centreline thrust symmetry of the aircraft would be maintained in case of engine failure which, in turn, allowed for nearly no loss of control. Each engine was to drive a four – bladed propeller. A twin-boom arrangement was mated to the low mounted wings. For weapons, a 30mm Ho-155 cannon was fitted
into each wing while a 37mm Ho-2044 can­non was situated directly below the Ho-155, installed in the tail boom. If required, the КІ-94-І would be capable of carrying up to 500kg (1,1021b) of bombs. The Ki-94-1 was to use a pressurised cockpit for the pilot and fea­tured a tricycle landing gear.

Once the Ki-94-1 was finalised, construction began on a wooden mock-up to be com­pleted in October 1943. Tachikawa then invited representatives from the Koku

Hombu to visit and inspect the Ki-94-I. On inspection and review, Tachikawa was to be disappointed when the design was rejected outright. The Koku Hombu inspectors found the Ki-94-l to be too unorthodox, too complex to build and that Tachikawa’s performance estimates were optimistic.

Tachikawa, however, did not give up on the Ki-94-I and reworked the aircraft into a heavy fighter that was designated the Riku-

gun Kogiken Ki-104. To boost the armament, two 57mm Ho-401 cannons were added. Unfortunately, this design was also rejected. With the rejection of the high altitude fighter and the subsequent heavy fighter revision, Tachikawa finally abandoned the Ki-94-1. Tachikawa did not wish to let Nakajima’s design against the high altitude fighter speci­fications, the Ki-87, go unchallenged. The result was the Ki-94-II.

MUNEO HOSAKA

Contemporaries

Focke-Wulf Fw 190 VI8/Ш (Germany), Focke-WulfTal52H (Germany), Mikoyan-Gurevich MiG-3D (Russia), Mikoyan-Gurevich 1-220 and 1-230 series (Russia),Yakovlev 1-28 (Russia), Poiikarpov ITP(M-2) (Russia), Yakovlev Yak-3PD and Yak-ЗТК (Russia)

Because the КІ-94-ІІ was never flown, the specifications are based on Tachikawa’s estimated performance.

Type High-Altitude Fighter

Crew One

Powerplant One Nakajima [Ha-44] 13 (Ha-219), 18-cylinder radial engine, developing 2,450hp for take-off, fitted with a Ru-204 turbosupercharger, driving a constant speed, four-bladed metal propeller Dimensions Span 13.99m 45.9ft Length 11.97m 39.311 Height 4.60m 15.1ft Wing area 27,99m! 301.3ft2 Wing loading 230.45kg/m2 47.21b/ft! Power loading 2.63kg/hp 5.8 lb/hp Weights Empty 4,690kg 10,3401b Loaded 6,450kg 14,2201b Performance Max speed 720km/h 447mph at 10,000m at 32,808ft Range 2,200km 1,367 miles Climb 17 min 38 sec to 10,000m (32,808ft) Service ceiling 14,250m 46,751ft Armament Two 30mm Ho-155 cannons, two 20mm Ho-5 cannons and either two 30kg (661b) air-to-air rockets or one 500kg (1,1021b) bomb

Deployment

None. One prototype was completed with a second under construction when the war ended.

In October 1943, the Koku Hombu rejected Tachikawa’s radical, twin engine, twin – boom, push-pull fighter, the company’s answer to the Koku Hombu’s request for a high-altitude fighter. Tachikawa was told the Ki-94-I was unconventional, complex and its estimated performance specifications were optimistic. The rejection left Nakajima’s Ki-87 the sole contender for the specification, something Tachikawa was not going to let happen.

Soon after the rejection Tachikawa utilised the same specifications given to Nakajima to plan a revised design. Whereas Tachikawa had to meet the Koku Hombu’s 3,000m (1,864 mile) range requirement and a 800km/h (497mph) maximum speed, Nakajima only had to contend with meeting the speed max­imum. Unbridled by the range issue, Tachikawa engineers went about the task of producing a design capable of matching and exceeding the Ki-87.

Knowing that the Koku Hombu would likely reject anything out of the ordinary in concept, a more conventional approach was taken. The man behind the revised aircraft was Tatsuo Hasegawa. Retained from the Ki-94-I was the pressurised cockpit for the pilot but everything else was redesigned. The new project used a standard configuration for a single-engine, all-metal fighter to ensure acceptance by the Koku Hombu. The power – plant selected for the plane was the Nakajima [Ha-44] 13 (Ha-219), 18-cylinder radial engine that was rated at 2,450hp. The engine was equipped with a fan cooled, exhaust driven Ru-204 turbosupercharger that was situated
on the underside of the fuselage. Originally, it was planned that a six-bladed propeller should be used. However, testing showed that when in operation a blur was created by the spinning prop, obscuring the pilot’s for­ward vision. Therefore, a four-bladed pro­peller was selected. For weapons the aircraft had a similar cannon armament as the Ki-94-I, but this was downgraded to two Ho-155 30mm cannons and two Ho-5 20mm cannons with one of each calibre cannon fit­ted into each wing. The wings were a typical laminar flow-type with the cockpit situated behind the trailing edges of the wings. As the dimensions show, the new design was fairly large by Japanese standards, even supersed­ing Nakajima’s Ki-87 in size.

With the drafts completed, Tachikawa presented them to the Koku Hombu. After review, the design was accepted as the Ki-94-II and Tachikawa received the order to produce a static test airframe, three proto­types and 18 pre-production aircraft. As soon as approval was received for the Ki-94-II, work began on the construction of the first two prototypes with the first to be completed by 20 July 1945. However, this date would not be met as delays in production caused the program to fall behind schedule which, in turn, delayed the final completion of the first Ki-94-II.

Tachikawa scheduled the first flight for 18 August 1945. However, on 15 August 1945, the war ended for Japan and the Ki-94-II was pre­vented from making any flights. The end of the war meant that the second prototype was never completed.

MUNEO HOSAKA

MUNEO HOSAKA

It was only after January 1945 that the Japan­ese were given access to the very latest Ger­man jet technology. Prior to that, access came only after German equipment had achieved operational status. Thus, in the beginning of 1944, the Japanese were made aware of the Messerschmitt Me 262 jet fighter and Me 163 rocket-powered interceptor long after they were flying. Consequently, it was not long before official requests for data came from Japanese representatives in Berlin. In the subsequent negotiations the Germans were told that only the IJA would be building the Japanese version of the Me 262, the Nakajima Ki-201 Karyu, the development of which began in January 1945. But even before this, the IJA began to formulate jet designs of its own, spurred by the release of technical information by the Germans.

In late 1944, the IJA initiated a study for a sin­gle engine jet fighter and the task was given to the Tachikawa Dai-Ichi Rikugun Kokusho.

The IJA’s Captain Hayashi and Captain Yasuda assembled and led two teams to research the concept and begin design. The one restriction imposed was the requirememt for at least a half hour’s endurance. At this time, only the Ne 12 series of turbojets was available. The Nel2, a development of an earlier project called the Ne 10, was found to be too heavy. A lighter model, the Ne 12B, was produced in limited numbers until the Ne 20 turbojet was first tested in March 1945. This engine proved to be superior to the Ne 12B.

The problem facing both Hayashi and Yasuda was that performance and endurance on a par with a twin engine design had to be achieved using only a single power unit. With the Nel2B unacceptable, both of these looked to the projected developments of the Ne20. These included the Ishikawajima Nel30, Nakajima Ne230 and the Mitsubishi Ne 330 turbojets because they were expected to produce improved thrust over the Ne 20.

With at least the basic dimensions of the tur­bojet in mind, each team got to work drafting their designs for the jet fighter. Two concepts emerged from both teams towards the mid­dle of 1945.

Hayashi’s team took the turbojet and placed it inside the fuselage near the tail. The fuselage was to be fairly slender in shape with the cockpit forward of the low mounted wings which were to be placed about mid-fuselage. The aircraft was to have a nose intake with the turbojet’s exhaust being vented out through the tailpipe or rear of the fuselage. Yasuda’s group took the turbojet and placed it on top of the fuselage. As opposed to Hayashi’s more slender aircraft, the Yasuda design had a shorter and wider fuselage. As a result of the engine being on top, this eliminated the pos­sibility of a conventional tail stabiliser arrange­ment and thus each tailplane ended in a vertical stabiliser. Yasuda felt that with the engine outside the fuselage, the nose could then be used to carry armament allowing for improved and concentrated accuracy. Yasuda’s design was very reminiscent of the Heinkel He 162 Volksjager.

At this juncture, the Volksjager will be dis­cussed briefly. The He 162 was designed as a fighter that could be built quickly with semi­skilled or unskilled labour, using few war crit­ical materials and only a single turbojet. This enabled the He 162 to be turned out more quickly than the more complex Me 262 then in service. The He 162 began with the Volk­sjager competition, but as Heinkel had the inside track with Deputy of the Reich Ministry of Armament and War Production, Karl-Otto Saur, who also happened to be the managing director for Heinkel, the study for the He 162 was already underway. By the time the other competing designs were submitted for the competition, the mock-up of the He 162 was already under construction. Little surprise the contract for the Volksjager went to Heinkel in September 1944. On 6 December 1944, the He 162 VI flew for the first time.

The He 162 used a light metal monocoque fuselage with a moulded plywood nose. The high-mounted wing was one piece, made of wood and plywood skinning with metal wing tips. The two tailplanes sported vertical sta­bilisers on their ends. Only four bolts secured the wings to the fuselage. A single BMW 003A-1 Sturm turbojet sat atop the fuselage just behind the cockpit and to help him aban­don the aircraft in an emergency, the pilot was provided with an ejection seat. For weapons, two MG 151 20mm cannons were fitted with 120 rounds per gun. The top speed of the He 162 was 905km/h (562mph) at 6,000m (19,690ft) with a 438km (272 mile) radius at full power.

In January 1945, Erprobungskommando 162 was created to field test the He 162 and on February 6 I/JG 1 was ordered to convert to the jet fighter. The He 162 was an unforgiving aircraft but in the hands of a skilled pilot it was an exceptional dogfighter. Pilots were told to avoid combat with Allied aircraft, however in late April and early May, I/JG 1 scored a hand­ful of aerial victories. This was tempered by the loss of 13 aircraft and 10 pilots, mostly due to accidents. The only other unit activated, the l.(Volkssturm)/JG 1 at Sagan-Kupper, never received their He 162 fighters and this was fortunate. The pilots of this unit were to only receive training in the He 162S, a glider version of the He 162 that had no engine, non- retractable landing gear and a rudimentary second cockpit for the instructor. After a few gliding flights, the untrained pilot was expected to fly the jet powered He 162 and the results would have been disastrous. A fly – able two-seat He 162 known as the Doppel – sitzer, fitted with a second cockpit for the instmctor at the expense of the cannons and ammunition, oxygen system and fuel capac­ity, was not completed by the end of the war in Europe.

On 15 April 1945, the Oberkommando der Luftwaffe approved the release of specifica­tions and production data for the He 162 to the Japanese. A delegation of UN officials studied the He 162 and visited Heinkel’s He 162 production line in Rostock, Germany. Impressed with the aircraft, the Japanese quickly requested technical data on the fighter. Of course, by this stage of the war for Germany there was no way that physical blueprints, production tools, jigs or a sample He 162 could be shipped to Japan. Instead, the only means available to rapidly send infor­mation on the jet was via wireless transmis­sion – i. e., radio. To help facilitate the transmission of the data, Commander Yoshio Nagamori used a datum line (a fixed, mea­surable line, used as a reference from which angular or linear measurements are taken) to measure the He 162 and transmitted the resulting dimensions to Japan. Only a portion of the data Nagamori sent was received in Japan.

Even though parts of the measurements for the He 162 made it to the Japanese mainland, enough was received to begin making use of the information, filling in the gaps, revising the design to suit Japanese production capa­bility and compiling the drafts needed to realise the aircraft. Even though the 1JN was the branch that obtained the He 162 data, it appeared that it would be the IJA who would produce it. In addition to developing the air­craft from the data, plans were made to begin production.

Whether Captain Yasuda and his team used the He 162 as their influence or arrived at a similar design by coincidence may never be known. But the IJA would reject Yasuda’s fighter and instead selected Captain Hayashi’s design for continued work. Per­haps it was felt that with the acquisition of the He 162, Yasuda’s design was redundant. With Hayashi’s aircraft approved, he and his team moved forward with refining the design and constructing a prototype. However, by August 1945 when hostilities ceased, none of the IJA’s jet programs were ready to fly. Neither Hayashi’s jet nor the Japanese version of the He 162 would progress past the initial design stage. Only the Nakajima Ki-201 ever made it to the construction phase which, by the end of the war, amounted to a single incomplete fuselage.

As a note, ‘Ki-162’ has been used by some as the designation for the Japanese produced He 162. There is no historical evidence to sup­port this although it is not without precedent, such as the case with the proposed Mitsubishi Ki-90 that was to be the Japanese version of the Junkers Ju 90. In addition, one may see the full name as the ‘Tachikawa Ki-162’. It is not unreasonable to believe that Tachikawa may have played a part in assessing the He 162 data given that the IJA had the Tachikawa Dai-Ichi Rikugun Kokusho and the Rikagun Kokugijutsu Kenkytijo (also at Tachikawa) at their disposal. Whether Tachikawa would have actually built the pro­duction Japanese He 162 is not known.

Tachikawa Ki-162 – data

Contemporaries

Blohm und Voss P.221/01 (Germany), Republic F-84 Thunderjet (US), Heinkel He 162 (Germany), Arado E.580 (Germany), BMW Strahljager I (Germany), Heinkel PJ073 (Germany), Henschel Hs 132 (Germany), Antonov SKh (Russia)

Specifications

Very little is known of the jet designs created by Yasuda or Hayashi and thus no specification information has surfaced. Likewise, since there was little time to act on the He 162 data, there is no information on what the specifications would have been for the Japanese version though it would not be unreasonable to conclude the dimensions and performance would have been similar to the German jet.

Deployment

None. None of the jet fighters got past the design stage.