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Maeda Ku-6
Interest in airborne forces can be traced as far back as 1917 because they can provide several tactical advantages. Being air dropped, parachute troops can be deployed into areas not easily accessible by ground forces as well as bypassing defences meant to hinder or repel attacks from specific avenues of approach. Also, the ability to place troops anywhere on the battlefield requires the enemy to use assets to protect against such operations, thereby spreading defending forces thinner. Such advantages come at a cost, however. Airborne forces typically do not have the firepower of comparable ground forces nor the ability to remain independent for long before outside support must be obtained.
Airborne troops were used by all of the major warring powers in World War 2 and special equipment and weapons were created for use by these units in an attempt to provide them with heavier firepower. Artillery such as the US Army M1A1 75mm pack howitzer and the German 7.5cm LG 40 recoilless gun were air-droppable and the troops used modified or special small arms such as the US
M1A1 ,30cal carbine and the Japanese Type 2 Paratroop rifle. Despite such weapons, airborne forces were deficient in one critical area: armoured vehicles. The ability to provide airborne troops with armoured support such as tanks was one sought by all the warring powers and tank designs did emerge. The key problem was how to send in the tanks with the troops during an operation. One of the first solutions was the glider tank.
The Japanese would create and utilise airborne forces during World War 2. The IJA called their forces the Teishin Dan (Raiding Brigades) while the UN had the Rikusentai. Both would be used first in 1942 during the fighting in the Dutch East Indies. Unlike the Germans, British and Americans, the Japanese did not provide their paratroopers with a significant amount of specialised heavy weapons. In part, this may have been due to the fact that the Japanese parachute forces would rarely be used in their designated role. Instead, much of their fighting would be done as light infantry (much like the German Fallschirmjagers). Nevertheless, the IJA and UN were considering ways to improve the
striking power of their paratroopers and one such plan was a tank borne into battle on wings.
In 1943, the IJA set the wheels in motion to investigate a flying tank. The Army Head Aviation Office in league with the Fourth Army Research Department drafted the initial concept for the weapon. The aviation research section of Maeda was tasked with producing the wings that would form the glider portion of the weapon and the Army Head Aviation Office assigned the designation Ku-6 to the glider. The tank was to be designed and built by Mitsubishi and called the So-Ra (or Sora – Sha, literally ‘sky tank’). To ensure there was no confusion, the Army Head Aviation Office called the entire combination the Kuro-Sha (taking the ‘Ku’ from Ku-6 with ‘ro’ meaning 6 and the ‘Sha’ for tank).
Mitsubishi’s So-Ra was, due to the purpose for which it was intended, a tankette design. With a crew of two (driver/pilot and the com – mander/gunner), the So-Ra was to weigh 2,812kg (3.1 tons). The turret was set behind the driver/pilot compartment and was provided with three large, hinged ports to allow
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some measure of vision for landing. Armour was likely very light and was certainly less than the 6mm-12mm armour protection of the Type 95 На-Go light tank then being used by Japanese airborne forces. Three weapon fits were proposed for the So-Ra. The first was a 37mm cannon (such as the 37mm Type 94 used in the На-Go), the second consisted of a machine gun armament (either a light weapon like the 7.7mm Type 97 machine gun or a heavier calibre) and the third was a flamethrower. Power was to come from an air-cooled engine producing 50hp that was estimated to give the So-Ra a maximum road speed of 42km/h (26mph).
The glider portion, the Maeda Ku-6, has been interpreted in at least two ways since the original design is not known, the documents either having not survived the war or have yet to be discovered. One version shows the wings secured to the So-Ra at the hull, on either side of the turret, with a tail boom fitted to the rear of the tank. A horizontal stabiliser sat on top of the vertical stabiliser. The dri – ver/pilot moved the control surfaces via wires that ran into the tank. On the hull front was the tow cable attachment point. The second version has the So-Ra fitted with struts on the hull sides. Atop the struts was the main wing to which twin tail booms were fitted with a low mounted horizontal stabiliser connecting the vertical stabilisers. In essence, the So-Ra would hang below the wing. On landing, the tank would shed the wings and move into action with the paratroopers.
By 1945, the Ku-6 had been completed and Mitsubishi had produced a full scale mock-up of the So-Ra. Flight testing was conducted for a brief period and it is likely that the mock-up was used, suitably weighted to simulate the 2,812kg (3.1 tons) of an operational So-Ra. The So-Ra was to be towed by a Mitsubishi Ki-21 bomber. Tests soon showed the difficulty of the concept. The Kuro-Sha suffered from in-flight control problems, the driver/ pilot had poor vision and landing was extremely difficult. Another concern was that the So-Ra could not stand up to heavier and more powerful tanks. Any usefulness the Ku-6 may have possessed was minimised with the advent of the Kokusai Ku-7 Man – azuru (meaning ‘Crane’) glider that began development in 1942. First flown in August 1944, the Ku-7 was able to carry a 7,257kg (8 ton) tank within its fuselage which was more than enough to hold the 6,713kg (7.4 tons) of the На-Go light tank. With the Kuro-Sha’s problems evident, the 1JA terminated any further work on the Kuro-Sha favouring the Ku-7.
Contemporaries
Antonov A-40 (or KT for КгуГуа Tanka, flying tank) (Russia), Raoul Hafner’s Rotabuggy and Rotatank (UK), Baynes Bat (UK), John Walter Christie’s M1932 (US)
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Specifications are based on the second variation of the Kuro-Sha, with the So-Ra beneath the wing.
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Dimensions |
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Span |
21.97m |
72.1ft |
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Length |
14.96m |
41.9ft |
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Height |
2.98m |
9.8ft |
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Wing area |
59.99m2 |
645.83ft2 |
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Weights |
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Loaded (with the So-Ra) |
4,200kg |
9,2591b |
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Performance |
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Max glide speed |
174km/h |
108mph |
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Armament |
None |
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Type Tankette (So-Ra) Crew Two |
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Powerplant One 4-cylinder, air-cooled, gasoline engine developing 50hp at 2,400rp Dimensions
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In late 1942, the Koku Hombu was looking for a number of new aircraft types as improvements on those in service. These included a heavy fighter capable of conducting ground attack operations and a high-altitude fighter. Nakajima and Tachikawa were tasked with the latter, coming up with designs that would later result in the Ki-87 and Ki-94 respectively (see Pages 28 and 53). For the former, Kawasaki attracted the interest of the Koku Hombu with their multi-role Ki-102. However, Kawasaki’s design was not to go uncontested and the competition would come from a relatively small aviation company.
Manshukoku Hikoki Seizo K. K. – the Manchurian Aeroplane Manufacturing Company Ltd., and better known as Manshu, a contraction of the kanji ‘Man’ in Manshtikoku and ‘Hi’ in Hikoki-was founded in 1938. Man – sliu was a subsidiary of Nakajima Hikoki K. K. and produced the Nakajima Ki-27 (code – named Nate by the Allies) and the Nakajima Ki-84 [Frank) for the company. Manshu would produce few of their own designs and only one ever saw service, the Ki-79
advanced trainer. Manshir’s main plant was located in Harbin in the Japanese puppet state of Manzhouguo. On learning of the Koku Hombu’s desire for new aircraft, Manshu sought to put together a proposal to meet the fighter requirement. The company assigned their two best men to the project, engineers Noda and Hayashi, and what resulted was an aircraft that was far from the conventional types Manshu had worked on in the past.
The aircraft was a single-engine fighter with a pusher, twin-boom configuration. The heart of the plane was to be a Mitsubishi Ha-211-III 18-cylinder, air-cooled radial engine fitted within the fuselage and behind the cockpit. The four-bladed propeller, situated at the very rear of the fuselage, was driven by a 2m (6.5ft) long extension shaft. In order to maintain a well streamlined airframe no air scoops were used; instead, flush inlets were fitted along the top of the fuselage behind the canopy. To increase the flow of air to the engine, a fan driven by the engine was installed. Flush outlets forward of the propeller completed the air circuit across the
engine. The thin wings were mounted low and on each wing was a boom that ended in an ovoid vertical stabiliser. A single, high mounted horizontal stabiliser connected the two tails.
A tricycle landing gear system was used, the nose gear retracting backwards into a wheel well that ran underneath the cockpit. Each of the two main wheels retracted into their respective tail booms. As the aircraft sat very high off the ground, the pilot had to access the cockpit via a hatch in the nose wheel well. If the pilot had to bail out, he had two choices. He could leave in a conventional fashion, but had to contend with both the twin tails and horizontal stabiliser along with the propeller. Manshift recommended that the pilot egress through the hatch out of the bottom of the aircraft. This method allowed the pilot to avoid being dashed on the tail but still had to contend with the propeller. Nevertheless, the chances of lowering the nose gear, sliding down and out through the hatch in a stricken plane were slim and Manshu were aware of this flaw in the design. The canopy was a bubble type that afforded an excellent field of view. For weapons, two Ho-5 20mm cannons and one Ho-204 37mm cannon were installed in the nose. Due to the short length of the fuselage, the barrels for the cannons, especially the Ho-204, protruded out from the nose.
Once the preliminary design for the fighter had been completed, Manshu submitted it to the Koku Hombu. Despite the unorthodox approach, it was accepted as the Ki-98 and work was allowed to proceed. Interestingly, the Koku Hombu rejected Tachikawa’s Ki-94-I that was similar in concept to the Ki-98. With approval in hand, the draft for the Ki-98 was finalised by July 1943. Work then commenced on a wooden mock-up that was completed in December. Design work continued into the beginning of 1944 further refining the Ki-98. A scale model of the aircraft were constructed and sent to Japan for wind tunnel testing at Rikugun Kokugijutsu Kenkyfjjo. Unfortunately for Manshu, the worsening war situation saw some of their personnel called into service or shifted to other departments and this, coupled with a plethora of design revisions, saw work on the Ki-98 slow down. Nevertheless, wind tunnel tests showed excellent results and Manshu began to make the preparations to construct the first prototype.
In the spring of 1944, the Koku Hombu instructed Rikugun Kokugijutsu Kenkyfijo to tell Manshtj that the Ki-98 should be adapted to serve as a high-altitude fighter. This they did, sending Manshu suggestions for design changes to the Ki-98 to make it suitable for the new role. On receiving the news Manshu had to substantially alter its initial design to meet the new demands. With strained manpower and resources, the mandated changes set the Ki-98 program further back and scuppered plans to build the prototype.
One of the most important changes was the need to fit an engine with a turbosupercharger resulting with the Ha-211-III being replaced by the Mitsubishi Ha-211 Ru which incorporated this feature. As the turbosupercharger was exhaust driven it required the appropriate additional piping, which, of course, was not originally included. The new engine was therefore larger than the original and this made it necessary for the fuselage to be lengthened and slightly widened. As the new propeller had a larger diameter, the twin booms had to be moved further apart to accommodate the blades and, by extension, the wings had to be reworked as well. Finally, the airframe had to be strengthened to support the heavier weight. Another alteration was to offer the pilot a more suitable way to bail out of the aircraft. Given the extreme difficulty in having to drop the nose wheel to gain access to the well hatch, the revised Ki-98 incorporated explosive bolts that shed the tail unit to allow the pilot to exit more conventionally. The weapon fit remained unchanged.
With the new specifications in hand, the Ki-98 design was reworked and redrafted but it would not be until October 1944 that the redesign was completed to be followed by a mock-up of its revised fuselage. Manshu expected to have the first prototype finished and ready for flight testing by early 1945. These plans were dashed following a US bombing raid on Manshift’s Harbin factory on 7 December 1944. It was not until January 1945 when work commenced on the Ki-98. Despite Manshu attempts to increase the pace of construction work, progress still lagged.
At the start of August 1945, the fuselage, wings and the tail booms were completed and were ready to be assembled. However, on 8 August 1945, the Soviet Union declared war on Japan and initiated its invasion of Manzhouguo the next day. With the Manzhouguo Imperial Army and the Japanese Kwantung Army unable to stem the tide of Soviet forces, Manshu ordered all relevant documentation including models, mock-ups, jigs, tools and the incomplete Ki-98 to be destroyed to prevent the aircraft and information on it being captured by the Soviets.
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Contemporaries Arkhangelskiy BSh (Russia), Saab 21 (Sweden), Vultee V.78 (US), Bel! XP-52 (US) Performance specifications are estimates based on Manshu’s projections.
Deployment None. The only prototype was never completed and was destroyed to prevent capture. |
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Mitsubishi Ki-73 – data
Contemporaries
Consolidated Vultee XP-81 ‘Silver Bullet’ (US), North American P-5 ID ‘Mustang’ (US), Lavochkin La-11 (NATO codename Fang) (Russia), Westland Wyvem (UK)
Specifications
Outside of the intended engine and the aircraft’s role, specifications on the Ki-73 are unknown
Deployment
None. The Ki-73 never advanced past the concept stage.
In 1943, the Koku Hombu issued a specification for a fighter capable of operating for long distances in order to act as an escort for bomber formations. Despite the defensive weapons Japanese bombers carried, they were still vulnerable to interception. If a fighter had the extended range, it would be able to protect the bomber formations by being able to engage enemy interceptors and allow as many bombers as possible to survive and deliver their bomb loads. It was this desire that fuelled the Koku Hombu to issue their specification and from which Mitsubishi would build the aircraft to meet it.
Mitsubishi’s Tomio Kubo, along with engineers Kato, Sugiyama and Mizuno, began the investigation on how best to meet the specifications. They settled on using a single engine design and the heart of it would be the Mitsubishi На-203-II engine. This was a 24-cylinder, horizontal-H, liquid-cooled engine that was projected to generate 2,600hp. The На-203-II was chosen due to its horizontal-H configuration – in essence, two flat engines placed one on top of the other and geared together (a flat engine is one in which the pistons move horizontally). Each flat engine had its own crankshaft. Although horizontal-H engines have a poor power-to-weight ratio, they offer the advantage of being more compact, which made the На-203-II the ideal choice for the aircraft, now designated the Ki-73.
Unfortunately, Mitsubishi was having a very difficult time with the На-203-II. In fact, because of the relative complexity of the hor
izontal-H design the engine experienced near constant problems during its development. Ultimately Mitsubishi was unable to overcome these difficulties and abandoned the На-203-II. Due to the delays and eventual cancellation of the engine, Kubo’s Ki-73 design was abandoned even before he and his team could produce a mock-up, let alone a prototype. Even though the Ki-73 went nowhere, Allied intelligence was aware of this new project. Information obtained from various sources, including captured documents, led intelligence officers to conclude that the Ki-73 would see service. As such, in 1944, the Ki-73 was assigned the codename Steve. As it was, no Allied pilot would ever encounter the Ki-73 in any form.
What Allied pilots might have encountered had the war gone on would have been the Mitsubishi Ki-83. Not discouraged by the Ki-73’s demise, Kubo would go on to design the twin – engine Ki-83 to meet Koku Hombu’s specification. The result was a highly capable aircraft that would have provided a challenge to Allied air power. However, only four Ki-83 prototypes were built before the end of the war.
Very little is known to show what the Ki-73 looked like. The artwork depicted for the Ki-73 in this book is based on an interpretation of the Ki-73 printed in Richard Bueschel’s 1966 book Japanese Code Names. The illustration was based on the Ki-83 on the assumption that Tomio Kubo would have used aspects of the Ki-73 in the Ki-83. Steve is shown here in the markings and colours of the 101st Sentai.
Altitude is a major factor in an engine’s performance and, by extension, the aircraft as a whole. Known as density altitude, the higher the altitude, the less dense the air. The effects of this manifest themsleves in lower wing lift, a reduction in propeller efficiency and reduced horsepower output from the engine. As such, a plane that was not designed to operate in such conditions suffers accordingly. The Koku Hombu sought an answer to the problem and Nakajima looked to provide the solution. The result was the Ki-87.
In mid-1942, the Koku Hombu drew up a set of specifications for a high-altitude fighter. These called for a plane capable of operating at high altitude, heavily armed with a maximum range of 3,000km (1,864 miles) and capable of 800km/h (497mph). Examination of the specifications called into question the viability of meeting such performance expectations. After deliberation, they were revised. The role remained the same but the speed requirement was dropped entirely to the point that no mention was made at all for a minimum or maximum speed. The range requirement was adjusted to one hour of loi
ter flight time in addition to a half hour of combat flight time up to 800km/h (497 miles) from the airfield that the aircraft operated from. Finally, a heavy armament requirement called for two 30mm cannons and two 20mm cannons.
With these new specifications, Nakajima was contracted in November 1942 to produce three prototypes and seven pre-production aircraft for the IJA. The prototypes were to be completed between November 1944 and January 1945 with the pre-production planes finished between February and April 1945. The design of the Ki-87 was headed by Kunihiro Aoki.
Nakajima initially selected the Nakajima [Ha-44] 11 18-cylinder radial engine as the heart of the Ki-87. The [Ha-44] 21 (known also as the Ha-219 Ru) was also considered but the [Ha-44] 11 would be the engine used in the first prototype. Both engines were rated at 2,400hp and each used a turbosupercharger that would maintain and enhance the engine’s power output at altitude. A turbosupercharger is an air compressor used to force air induction to the engine. It does this by
having a turbine and a compressor linked together via a shared axle. Engine exhaust spins the turbine which in turn spins the compressor which draws in outside air, compresses it and then directs the air to the intake manifold of the engine. This compressed air, delivered at high pressure, results in more air reaching the cylinders for combustion. The net effect of this is that at higher altitudes where the air is thinner, the turbosupercharger allows the engine to function as if it was at a lower altitude where the air is heavier and thus engine performance is not adversely affected. A benefit of this is that because the air is thinner at higher altitudes, there is less drag on the aircraft and since the turbosupercharger preserves the horsepower of the engine, overall speed is improved.
A sizable portion of the aircraft’s forward fuselage was taken up by the [Ha-44] 11 engine assembly and the large turbosupercharger was fitted to the starboard side of the fuselage, just ahead of the cockpit. To cool the engine, a sixteen-bladed fan was mated to the four-bladed, constant speed propeller, turning at 150 per cent of the propeller speed.
The engine reduction gear ratio was set at 0.578. As the Ki-87 was designed for high altitude operation, the pilot was to be provided with a pressurised cockpit (though the prototype was not equipped with one).
For weapons, Nakajima kept to the specifications mounting a 20mm Ho-5 cannon in each wing root, synchronised to fire through the propeller, and a 30mm Ho-155 cannon in each wing to the outside of the main landing gear wheel wells. Ammunition was stored in the inner wing near the fuselage. Hydraulic pressure was used to load the cannons and they were fired by electrical triggers. If required, provision was made to carry a 250kg (551 lb) bomb or a drop tank along the centreline. Because of the heavy weapon fit and to ensure enough room for the self-seal – ing wing fuel tanks, Nakajima designed a landing gear arrangement that was rare in Japanese aircraft development – the main landing gear struts would retract backwards and the wheels would rotate 90° to fit flush into the wheel wells.
Given the task the Ki-87 had to perform, Nakajima provided a degree of protection for the pilot in the form of 66mm thick, bullet proof glass in the front of the canopy and back protection via armour plate 16mm thick. To extend the range of the Ki-87, two 300 litre (79 gallon) drop tanks could be fitted under each wing beside the landing gear wells. The pilot could jettison them via electrically controlled releases and these could be used in conjunction with centreline payloads.
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As work progressed on the Ki-87, the IJA saw fit to change the design by insisting that the turbosupercharger be placed in the rear of the fuselage beginning with the third pre – production Ki-87. Nakajima protested against
Contemporaries Sukhoi Su-1 (Russia)
Because the Ki-87 was not flown to its full ability, the performance statistics are estimates made by Nakajima.
Type High-Altitude Interceptor
Crew One
Powerplant One Nakajima [Ha-44] 11,18-cylinder, air-cooled radial developing 2,400hp for take-off, 2,200hp at l,500m/4,920ft, 2,050hp at 6,000m/l 9,685ft and 1,850hp at 10,500m/34,450ft and driving a constant speed, 4-bladed propeller
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Span |
13.41m |
44.0ft |
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Length |
11.79m |
38.7ft |
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Height |
4.48m |
14.7ft |
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Wing area |
25.99m! |
279.8ft2 |
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Wing loading |
216.29kg/m! |
44.3 lb/ft2 |
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Power loading |
2.35kg/hp |
5.2 lb/hp |
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Weights |
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Empty |
4,387kg |
9,6721b |
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Loaded |
5,632kg |
12,4161b |
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Maximum |
6,100kg |
13,4481b |
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Performance |
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Max speed |
707km/h |
439mph |
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at 11,000m |
at 36,090ft |
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Endurance |
2 hours |
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Climb |
14 min 12 sec to 10,000m (32,810ft) |
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Ceiling |
12,855m |
42,175ft |
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Dimensions |
Armament
Two 30mm Ho-155 cannons, Two 20mm Ho-5 cannons and provision for one 551 lb bomb
Deployment
None. Only one Ki-87 was completed and test flown with two others incomplete before the war ended.
Survivors
Nakajima Ki-87 (FE-153)
This was the only Ki-87 to fly, having the serial 8701. Captured at the IJA air base at Chofu, the Ki-87 (nicknamed ‘Big Boy’ by the men who saw the large aircraft) was crated and shipped to the US, appearing on 10 March 1946 at MAMA Under restoration for the museum, the Ki-87 was soon moved to Park Ridge. However, after 1 May 1949 (the last written report documenting the aircraft) all trace of the Ki-87 disappeared, a likely victim of the cutter’s torch.
Nakajima Ki-87 (FE-155)
It has been surmised that FE-155 was, in fact, a typographical error made on a later report concerning FE-157 (see below). On the flip side, it may be that the FE-155 entry was a correction and that FE-157 as listed on the earlier report was designated in error. In either case, only two of the Ki-87 aircraft reached the US.
Nakajima Ki-87 (FE-157)
FE-157 was, most likely, the second of the two remaining Ki-87 prototypes found incomplete when the war ended. Listed as FE-157 on 10 March 1946 at MAMA, the plane would later reappear on a 1 August 1946 report as FE-155 and was located at the AOAMC in Newark, New Jersey.
No further trace of this Ki-87 exists after the August report and the aircraft was most probably scrapped.
the change but could do little to sway the IJA on the matter. In addition, the third prototype Ki-87 would have a reduction gear ratio set at 0.431 and the seventh pre-production Ki-87 was to feature a cooling fan that spun faster to facilitate enhanced engine cooling.
Despite the worsening war situation, Nakajima was able to complete the first prototype, c/n 8701, by February 1945 rolling it out from their Ota Plant. Problems with the electrical system that operated the landing gear and difficulties with the turbosupercharger delayed flight testing. It was not until April 1945 that the Ki-87 was able to take to the air. Due to the issues with the landing gear, Nakajima forbade the test pilot from retracting the main gear lest it fail in the up position, thereby damaging or destroying the Ki-87 with the resultant belly landing. This, however, prevented any chance of a thorough evaluation of the Ki-87’s top speed and full manoeuvrability. Consequently, there was no attempt to monitor and collect performance data. During the five flights the prototype did make, the pilot
reported good handling characteristics and it was thought that the Ki-87 was superior in comparison to the Nakajima Ki-84 Hayate (Gale).
Even as testing of the Ki-87 was underway with work continuing to meet the IJA turbosupercharger position requirement, Nakajima designers developed the Ki-87-II. Replacing the [Ha-44] 11 would be the Nakajima [Ha-46] 11 (known also as the Ha-219) that could provide 3,000hp. The turbosupercharger was situated in the belly of the fuselage as demanded by the IJA. Performance estimates showed a 4 per cent increase in speed compared to the Ki-87.
Ultimately, the Ki-87’s design team failed to overcome the problems with its engine. Because they were unable to solve difficulties with both the turbosupercharger and the [Ha-44] 11 as well as the temperamental landing gear system, the Ki-87 would make no more test flights. When hostilities ceased the other two prototypes remained incomplete and the Ki-87-II was still on the drawing board.
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By 1945, Japan was reeling from one defeat after another in the face of the Allied advance. With the possibility of an Allied invasion looming in the minds of Japanese military leaders and planners, several means to repel the invaders were considered, investigated, and in some cases, allowed to proceed towards a finalisation. One of the ideas developed was to use aircraft for shimbu (suicide) missions against the invasion fleet. Airworthy aircraft of any type were to be thrown against Allied shipping. In order for the missions to succeed, wave attacks were envisioned, involving scores of aircraft. Sheer numbers would ensure successful hits on naval ships and landing craft even in the face of heavy anti-aircraft fire and combat air patrols. Even one aircraft that struck a ship had the potential to cause significant damage. Such mass attacks, however, led to the conclusion that the available pool of aircraft would quickly be depleted. Thus, it was clear that an airplane had to be designed that could be built rapidly to swell the number of aircraft available for these shimpu missions. It was Nakajima that would provide one answer.
On 20 January 1945, the 1JA issued specifications for an aircraft that could be built by semi-skilled labour, would use very few war critical materials, had the ability to accept any radial engine with a 800hp to 1,300hp rating, was easy to maintain in the field, was able to carry at least one bomb and had a maximum speed of at least 340km/h (211mph) with landing gear and 515km/h (320mph) without landing gear. Nakajima was tasked with making the specifications a reality and engineer Aori Kunihiro was assigned the project. Kuni – hiro would have assistance from the Mitaka Kenkyujo (Mitaka Research Institute) and Ota Seisakusho K. K. (Ota Manufacturing Co Ltd).
Because semi-skilled workers would be used to build Kunihiro’s aircraft, the Ki-115 Ко was simplicity itself. The fuselage used a steel
structure with steel panelling and centre sections with tin used for the engine cowling. The tail was made of wood with fabric covering while the slightly swept wings were of metal with stressed skinning on the outer wing surfaces. The И-115 Ко could accept a variety of radial engines and to simplify the installation only four bolts were used to secure the engine to the fuselage. The Nakajima [Ha-35] 23 (Ha-25) radial engine was used on the prototype Ki-115 Ко and would be found on the subsequent production aircraft. The pilot was provided with an open cockpit with simple instruments and controls. A crude aiming sight was provided as well. The landing gear could be jettisoned after take-off, had no suspension outside of the balloon tyres and was made out of pipes. For weapons, the Ki-115 Ко carried only a single bomb and this was held in a recess under the fuselage between the wings. The heaviest bomb that could be carried weighed 800kg (1,7641b) and the bomb had no provision for release from the cockpit.
In March 1945, the prototype of the Ki-115 Ко, called the Tsurugi (which means ‘sword’ or ‘sabre’), was rolled out and flight testing commenced. As soon as the trials had started problems began to surface. The landing gear contributed to poor ground handling and this was compounded by the poor view afforded the pilot. Once in the air, the flight characteristics of the Ki-115 Ко were anything but stellar and even skilled test pilots had some difficulty in flying the aircraft, let alone a pilot with minimal training. Nevertheless, given the mission of the Ki-115, flight trials continued while modifications were investigated to improve the aircraft. By June 1945, the initial flight testing was completed. Two further changes were made to the Ki-115 Ко and this involved adding suspension to the landing gear and including auxiliary flaps to the inboard trailing edge of the wings. Production
models of the Ki-115 were to be fitted with two solid-fuel rockets, one under each wing. The purpose of the rockets was to boost the speed of the aircraft during the final, terminal dive on the target. With the Ki-115 Ко deemed acceptable, Nakajima began production of the Tsurugi at both their Iwate and Ota plants. The IJA anticipated that 8,000 aircraft per month would be assembled from production lines scattered throughout Japan.
Even with production underway, steps were being taken to further simplify the Ki-115. To save on precious metals, the wings of the Ki-115 Ко would be replaced with wooden versions and the wing area increased. To better address pilot vision, the cockpit would be moved forwards. The version of the Tsurugi was to be designated the Ki-115 Otsu. A variation of the Ki-115 Ко was the Ki-115-III (also known as the Ki-115 Hei). The only two modifications was the provision of a bomb release and cockpit being moved even further forwards. But even these models would not be the end because the Ki-230, a further development of the Ki-115, was also investigated.
The UN, having learned of the new plane, became interested in the Ki-115 and sought to produce it for themselves. To facilitate this, Nakajima provided Showa Hikoki K. K. (Showa Aeroplane Co Ltd) with two Ki-115 Ко aircraft. In UN service, the aircraft was to be called the Toka, meaning Wisteria. Showa was to adapt the design to accept any number of UN radial engines from older, refurbished motors to ones then in current service.
By the time the war ended, Nakajima had only been able to produce 104 of the Ki-115 Ко (22 from the Iwate plant and 82 from the Ota plant) and none would be used in anger. Neither the Ki-115 Otsu, КІ-115-ІІІ or the Ki-230 would be constructed, remaining forever as design board projects. Likewise, Showa had no time to produce the Toka.
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PHOTOGRAPHS BY TIM HORTMAN |
Survivors
Nakajima Ki-115 Ко Tsurugi (FE-156)
One of four captured at Nakajima’s No. l plant in Ota, Gunma Prefecture, this Ki-115 Ко (serial 1002) was listed on the MAMA 1 August 1946 report as being in storage and was moved to Park Ridge in September 1949. Lucky enough to survive the scrap heap, the Ki-115 Ко is currently in storage, unrestored and in poor condition at the Paul. E. Garber facility in Suitland-Silver Hill, Maryland (pictured left).
Nakajima Ki-115 Ко
Apparently another surviving Ki-115 Ко is being restored in Japan but there are few, if any details, on who is restoring the aircraft nor the history of the Ki-115 involved.
In 1991, two other Ki-115 aircraft were reported to be found in Japan, one in Kanda and the other in Koganei. Who has them and in what condition is neither known nor confirmed.
Nakajima Ki-230 – data (estimated)
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Dimensions Span Length Height Wing area |
39.69m 8.47m 3.29m 13.09m2 |
1.8ft 27.8ft 10.8ft 141.0ft2 |
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Weights |
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Empty |
1,700kg |
3,7471b |
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Loaded |
2,400kg |
5,2911b |
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Performance |
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Max speed |
557km/h |
346mph |
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at 2,800m |
at 9,185ft |
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Range |
1,199km |
745 miles |
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Ceiling |
6,500m |
21,325ft |
The Ki-201 depicted here sports the colours of the 244th Sentai, one of the more successful Japanese home defence air units.
As a result of the development of the Nakajima Kitsuka for the UN, Japan’s first turbojet – powered aircraft to fly (see Page 114), Nakajima was in the position of being the leader in the fledgling jet aircraft field. Seeking to expand on that position, Nakajima took it upon themselves to offer a jet that would be superior to the Kitsuka. This was to make the most of what little data was received from Germany on the Messerschmitt Me 262. With the Kitsuka under development for the UN, Nakajima provided the IJA with their proposal for what was to be the definitive Japanese version of the Me 262, the Ki-201 Karyu, the Fire Dragon.
Depending on the source, the IJA was or was not interested in developing its own jet aircraft. However, evidence supports the fact that the IJA wished to have its own jet-powered fighter or was looking to have an option should the Ki-202 and fighter variant of the Kitsuka not meet their expectations. In October 1944, the Japanese embassy informed the Germans that the IJA would be the producer
of the Me 262 and requested reports and projections for the production of 100 and 500 aircraft a month. It was known that the wartime manufacturing capability of Japan could not produce an exact copy of the Me 262 and adaptations would have to be made to accommodate Japanese capabilities. Nakajima sought to provide that answer.
The genesis of the Ki-201 took place on 12 January 1945 with the formation of the design team led by Nakajima engineer Iwao Shibuya. Unlike the Kitsuka project, from the outset Shibuya designed the Karyu as a fighter. In addition, Shibuya realised that the aerodynamics of the Me 262 had been tested and felt assured that by applying as much of the design of the Me 262 into the Karyu as was possible would result in an aircraft that would need minimal testing before production was started. This idea was shown to good effect in the development of the Mitsubishi J8M Syusui.
Shibuya had the same access to the Me 262 information as the UN. It consisted of sketches
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Imperial Japanese Army |
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DANIEL UHR |
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Contemporaries |
Messerschmitt Me 262A-la (Germany), Avia S-92 |
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Turbina (Czechoslovakia) |
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Type |
Fighter |
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Crew |
One |
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Powerplant |
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Two Ne 230 axial-flow turbojets rated at 885kg (1,951 lb) of static thrust each; later, two Ne 130 axial-flow turbojets rated at 908kg (2,0021b) of |
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static thrust each |
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Dimensions |
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Span |
13.68m |
44.9ft |
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Length |
11.49m |
37.7ft |
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Height |
4.05m |
13.3ft |
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Wing area |
23.96m2 |
258ft2 |
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Weights |
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Empty |
4,495kg |
9,9101b |
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Loaded |
7,021kg |
15,4781b |
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Overload |
8,492kg |
18,7221b |
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Performance Max speed |
812km/h |
504mph |
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(Ne 230) at 10,000m |
at 32,808ft |
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845km/h |
525mph |
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(Ne 130) at 10,000m |
at 32,808ft |
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Landing speed |
161knVh |
1 OOmph |
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Max dive speed |
l,006km/h |
625mph |
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Take-off distance |
945m |
3,100ft loaded |
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1,588m |
5,209ft in overload |
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Range at 60% thrust |
987km |
613 miles |
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at 7,995m |
at 26,230ft |
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Fuel capacity |
2,200 to 2,590 litres 560 to 684 gallons |
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Climb |
(Ne230) 6 min 54 sec to 6,000m (19,685ft) (Ne 130) 6 min 17 sec to 6,000m (19,685ft) (Ne 230) 14 min 56 sec to 10,000m (32,808ft) (Ne 130) 13 min 15 sec to 10,000m (32,808ft) |
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Ceiling |
12,000m |
39,370ft |
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Armament |
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Two Но-155-II 30mm cannons and two Ho-5 20mm cannons; one 1,763 lb bomb or one 1,102 lb bomb; proposed Navy version to be fitted with two Type 5 30mm cannons and two Type 99 20mm cannons |
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Deployment |
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None. The prototype Ki-201 was incomplete by the close of the war. |
and drawings of the Me 262A-1 and little else. Whereas the Kitsuka only bore a superficial resemblance to the Me 262, Shibuya’s design would seek to match the Me 262 as much as possible. Shibuya and his team may have had little, if any, contact with the Kitsuka developers despite being in the same company. The first draft of the Karyu nearly matched the dimensions of the Me 262. However, it featured a straight wing as opposed to the swept wing of the German jet. This was quickly changed and the revised Кагуй was larger and heavier than the Me 262, but replaced the straight wing with a gently swept wing.
Initial design work, including wind tunnel testing, was completed in June 1945. For all intents and purposes, the Ki-201 was a larger derivative of the Me 262. That it was bigger and heavier than the German jet may point to adaptations the Japanese had to make in order to produce the Кагуй. For example, the Japanese did not have the experienced fabricators to make the thin, sheet steel used in the nose of the Me 262. The result was that the KaryO’s nose had to make do with duralumin which was heavier. In addition, it is certain that the Кагуй incorporated simplifications to accommodate production by semi-skilled labour and construction using less critical war materials. The latter was borne out by the intense interest by the Japanese in obtaining the German process for making plywood (and likely the bonding glues as well) which the Germans used in their aviation industry because, although Japan was lacking in aviation metals by the close of the war, they had ample access to wood.
The Кагуй was initially slated to be fitted with Ne 230 axial-flow turbojet engines each rated at 85kg (1,951 lb) thrust. These were calculated to push the Кагуй at a maximum speed of 812km/h (504mph). However, it was also planned that once they became available, the Ne230 engines would be switched for the improved Ne 130 axial-flow turbojets. Projected to produce 908kg (2,001 lb) of thrust each, the calculated speed of the Кагуй with the Ne 130s was a maximum 852km/h (529mph).
For armament, the Кагуй was fitted with two Ho-155-11 30mm cannons and two Ho-5 20mm cannons. On the chance that the UN might acquire the Ki-201, provision was also made to use two Type 5 30mm cannons and two Type 99 20mm cannons. More notable was that the Кагуй was slated to be equipped with the Ta-Ki 15 airborne intercept radar. Used in conjunction with the Ta-Chi 13 ground control radar, the Кагуй could be guided to its targets by ground controllers with a 153km (95 mile) radius. Such a system would have been a benefit in low-light, night or poor flying weather interceptions. In addition to the cannon fits, the Кагуй was to be capable of carrying a 800kg (1,7631b) or 500kg (1,1021b) bomb.
With the initial progress of the UN’s J8M SyCisui program, which would provide the IJA with the Ki-200 and the subsequent IJA Ki-202 SyOsui-kai project, IJA interest in the Ki-201 looked to have waned. The result was delays in further developing the Кагуй. Nakajima wanted to have the final design of the Ki-201 completed by July 1945 with more advanced testing underway by August. The first prototype of the Кагуй was to be completed and ready for flight trails by December 1945, and in addition, a further 18 examples of the Ki-201 were to be built and delivered by March 1946.
Despite the delays, work commenced on the prototype. Nakajima’s Mitaka plant, which was located on the western edge of Tokyo, was the facility for the prototype Ki-201’s constmction. Regular production of the Ki-201 was intended to be carried out at the Kurosawajiri Research Works No.21 situated near Kitakami, in Iwate Prefecture, in Honshfl. The fuselage for the Кагуй was nearly complete when Japan surrendered on 15 August 1945. With the surrender, work on the Ki-201 ceased. It would be nearly 30 years before the next Japanese designed and built jet fighter would fly, this being the Mitsubishi F-l which first flew on 3 June 1975.
At the time the Ki-93 was conceived the war situation for Japan was dire. The mainland was suffering from near daily B-29 raids and looming on the horizon was the anticipated US invasion of Japan. A means to counter the B-29s as well as to attack Allied invasion ships was needed. The resulting Ki-93 would be a first and a last for Rikugun and Japan.
When Rikugun Kokugijutsu Kenkytijo began the design research for the Ki-93, the goal was to provide an aircraft that could provide a platform for anti-bomber operations and anti-shipping missions. In both cases the aircraft had to be able to absorb damage when flying in the face of interceptors, the defensive machine guns of the bombers, and the anti-aircraft weapons of ships.
Two versions of the all-metal Ki-93 were to be constructed. The first, the Ki-93-I Ко, was the heavy fighter that would combat bombers. The second was the Ki-93-I Otsu and this was the anti-shipping model. The Mitsubishi Ha-211 radial engine was consid
ered at first to power the Ki-93 but both models were ultimately powered by two Mitsubishi Ha-214 18-cylinder, air-cooled radial engines, each providing a maximum of 2,400hp. In order to give the aircraft a measure of survivability in the face of enemy fire, armour plating was used. The pilot was provided with five armour plates, each 12mm thick. Two plates were placed just forward of the cockpit in the nose, one on each side of the pilot and the fifth would protect his back. The front glazing was composed of 70mm thick bullet proof glass. The rear gunner was also protected by a 12mm armour plate, offering defence from rounds being fired at the Ki-93 from behind. Likewise, the fuselage fuel tanks were given a measure of protection from incoming fire via an 8mm thick armour plate. Each engine was also provided with armour plating in the nacelles. Should the armour protecting the fuel tanks be penetrated, each tank was self-sealing and, to prevent fuel fires, had an automatic fire
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MUNEO HOSAKA |
Contemporaries
Henschel Hs 129B-3/Wa (Germany), Messerschmitt Me410A-l/U4 (Germany), Tupolev ANT-46 (Russia), North American B-25G Mitchell (US), Bell YFM-1 Airacuda (US), Curtiss XP-71 (US), de Havilland Mosquito FBMMVIII (UK)
Type Heavy Fighter (Ki-93-1 Ко) and
Ground Attack Aircraft (Ki-93-1 Otsu) Crew Two
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Powerplant Two Mitsubishi Ha-214,18-cylinder, air-cooled radials, developing 2,400hp for take-off, l,970hp at l,500m/4,920ft and l,730hp at 8,452m/27,729ft; each engine drove a 6-bladed, metal propeller Dimensions
Armament One 57mm Ho-401 cannon with 20 rounds of ammunition, two 20mm Ho-5 cannons with 300 rounds of ammunition per gun and one 12.7mm Ho-103 machine gun with 400 rounds of ammunition (Ki-93-I Ко); One 75mm Type 88 cannon, one 12.7mm Ho-103 machine gun and two 250kg (551 lb) bombs (Ki-93-1 Otsu) |
Deployment
None. Two Ki-93 prototypes (one of each version) were produced but did not enter production before the end of the war.
extinguishing system. Finally, a defensive armament, consisting of a single 12.7mm Ho-103 machine gun was Fitted in a rear firing position to be operated by the second crewman.
The difference in the two versions was in the offensive weapon fits, both mounted in ventral gondolas. The Ki-93-1 Ко was equipped with a powerful 57mm Ho-401 cannon and this was backed up by two 20mm Ho-5 cannons (although one initial design did away with the two Ho-5 cannons and used a single 37mm cannon with 40 rounds of ammunition). It was anticipated that the Ho-401 cannon would inflict enough damage with a single hit to cripple or shoot down a B-29. The Ho-401 could fire 90 rounds per minute with a muzzle velocity of 518.2m/sec (l,700ft/sec). For the Ki-93-1 Otsu, the large 75mm Type 88 cannon was fitted. The weapon was an adaptation of the Type 88 anti-aircraft gun that had been modified for use on aircraft. Besides the Ki-93, this weapon was also used operationally in the
Mitsubishi Ki-109 (flown by the 107th Sentai). The Type 88 had to be hand loaded by the second crewman. In addition to the cannon the Ki-93-I Otsu would carry two 250kg (551 lb) bombs.
Rikugun had Dai-Ichi Rikugun Kokusho, located in Tachikawa (which is about 24 miles from the centre of Tokyo), construct the Ki-93. The first prototype in the Ki-93-1 Ко configuration was completed by April 1945. In the same month the aircraft successfully took to the air making it the first Rikugun aircraft to be built and flown. However, further flight testing was hampered by the war situation, so much so that the test program was never completed. Despite the worsening conditions in Japan and delays with the flights of the first prototype the second aircraft in the Ki-93-I Otsu configuration was completed. However, it would never fly.
With the surrender of Japan, the Ki-93 would become the last heavy fighter and ground attack aircraft to be built during the war.
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DANIEL UHR |
The IJA was not satisfied with the Ki-200 (the IJA designation for the Mitsubishi J8M1 Syusui – See Page 96). They felt that the UN’s plans to adopt and adapt the Messerschmitt МеІбЗВ as the J8M1 would amount to the same, if not more, effort and development compared to creating a new design based on, but not a direct adaptation of, the Me 163B. Although the IJA attempted to make the IJN see their point – of-view, the IJN pushed aside such plans, forging ahead with their J8M program. Thus, the IJA took it upon themselves to design the better aircraft they had wanted from the outset.
The IJA saw a main flaw in the Ki-200 that resulted in aspects of the plane’s performance that they found unacceptable: the limited fuel capacity. Because of this, combat endurance was reduced and fuel was rapidly consumed by the KR10 (Toku-Ro 2) engine. Even with the UN’s proposed J8M2, which removed a Type 5 30mm cannon to make way for more fuel, the IJA felt that the endurance was still insufficient. Starting in 1945, Rikugun Kokugijitsu Kenkyujo began the process of developing the IJA’s own rocket aircraft using the Me 163B as a template. This development was in secret and the designation given to the aircraft was the Ki-202 Sytisui-Kai which meant ‘Autumn Water – Improved’.
The IJA took the obvious route and increased the fuel capacity by stretching the fuselage to make room for larger fuel tanks. They also planned to use an improved motor, but exactly what power plant depends on which source is referred to. Two main options appear. One was the KR10 as used in the Ki-200 that developed 1,500kg (3,3061b) of thrust, but with a secondary rocket added providing a further 400kg (881 lb) of thrust. The other motor was the KR20, which may also be known as the Mitsubishi Toku-Ro.3. The KR20 promised 2,000kg (4,409 lb) of total thrust and may have been fitted with a cruise chamber. This is a secondary combustion chamber which was typically mounted above or below the main combustion chamber. The purpose of having two such chambers is that the main one (or both if necessary) can be used for full power needs such as take-off and rapid ascent, while the cruise chamber has a lower thrust output and can be employed for normal cruise speeds once the plane is aloft and the main chamber shut off. The benefit of this is the conservation of fuel, allowing the plane to remain airborne and in action longer. Wartime Allied intelligence reports stated that the Germans had provided data to the Japanese on the Walther HWK 509C rocket motor which used a cruise chamber. If this was so, then the KR20 was most likely the Japanese development of the HWK 509C motor and the answer the IJA was looking for in extending the range of the Ki-202. Contemporary illustrations of the Ki-202 clearly show some form of a secondary means of thrust. As a stop-gap measure, the Ki-202 could have accepted the KR10 motor if problems arose with the development and production of the KR20 and thus any delays in flight testing could have been avoided.
Although the Ki-202 was larger than the Ki-200, no attempt was made to include a landing gear system. Like the Ki-200, the Ki-202 retained a central landing skid, tail wheel and would use the jettisonable wheeled dolly for take-off and ground handling. No provision for catapult launching is known to have been considered as a means to conserve fuel that would have been consumed during normal take-off procedures.
For weapons, the Ki-202 was slated to use two Ho-155 30mm cannons, one mounted in the each wing root, the same as the Ki-200.
Insofar as the larger size and motor, the Ki-202 was estimated to have an endurance of 10 minutes and 28 seconds, whereby the Ki-202 was calculated to achieve 5 minutes and 30 seconds. With a near doubling of the endurance time, this would have allowed the Ki-202 to remain in combat for a longer period or, at the least, extend its operational radius. It was projected that the final design of the Ki-202 would be completed by February 1945 with construction of the first prototype commencing shortly afterwards. The first test flight was scheduled for August 1945.
As it was, the Ki-202 design would remain just that, a design. When the war ended, no metal had been cut on the Ki-202 prototype nor was a mock-up even constructed. In part, the Ki-202 program may have hinged on the success or failure of the J8M1. The technical issues in producing the KR10 in a reliable form most likely stymied work on the KR20, which was to be the main powerplant for the Ki-202. The problems with the KR10 delayed flight testing of the J8M1 until July 1945 and even then, a fuel system failure caused the crash of the Syusui during its maiden flight. This set back the J8M1 further still and although the fuel system problem was corrected, the war ended before any further flights could be made. Had the J8M1 succeeded and the IJA version, the Ki-200, entered service, it is likely development of the Ki-202 would have rapidly proceeded and had it succeeded, the IJA would have offered it to the UN. If accepted, the designation would have been the J8M3.
Contemporaries
Messerschmitt Me 163C-la (Germany)
Type Interceptor/Fighter
Crew One
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Powerplant (planned) One Toku-Ro.3 (KR20) bi-fuel rocket motor producing 2,000kg (4,409 lb) of thrust with supplementary rocket or cruise chamber producing 400kg (8801b) of thmst
Armament Two Ho-155 30mm cannon |
Deployment
None. The Ki-202 did not advance beyond the design board.