TYPE: High speed fighter project

ACCOMMODATION: Pilot only

POWER PLANT: One Daimler-Benz DB 601A liquid-cooled engine, rated at 1,159 hp

PERFORMANCE: No data available

COMMENT: Every aircraft creator seeks to reduce drag in their designs. The more drag, the slower the aircraft moves through the air due to the resistance. Drag cannot be completely removed from a design, but even in the early years of aviation various methods for minimizing drag were investigated and many different solutions were tried.
Not surprisingly, such applications were valued by those providing the military with aircraft and in Japan, prior to the outbreak of hostilities with the US, the Dai-lchi Kaigun Kok[ Gijutsu-sho (Yokosuka Naval Air Technical Arsenal, Kugisho) would study such efforts in an attempt to produce fast flying aircraft.
With the war clouds looming on the horizon, the seeds planted by the air racers of the 1920s and early 1930s were germinating in the aircraft used by the air forces of the major powers. Designs by Curtiss for the US Army Air Force were influenced by the Curtiss racers while the retractable landing gear of the 1920 Dayton Wright RB racer would become a hallmark of Grumman aircraft such as the F2F. In Great Britain, R. J. Mitchell would draw heavily from his experience designing Schneider Trophy racers to build the Supermarine Type 300 which would eventually evolve into the Supermarine Spitfire.
On 26 April 1939 German test pilot Fritz Wendel flew to a new world speed record of almost 469 mph with a Messerschmitt Me 209. The Me 209 was solely designed to break speed records and was a completely separate aircraft from the Messerschmitt Bf 109 that entered service with the German Luftwaffe at that time. It shared only its Daimler-Benz DB 601 liquid-cooled engine with the Bf 109.
Consequentially, Japan sought to produce racing aircraft and planes designed to beat world speed records. In 1938, a group of designers sought to produce a high-speed aircraft to challenge the world air speed record. Once war had broken out this aircraft, called the Ken lll, was soon taken over by the Imperial Japanese Army (IJA). Redesignated the Ki-78, its development was continued under Kawasaki. During this time, it may have been the Imperial Japanese Navy (IJN) who decided to conduct its own studies of high speed aircraft with Kugisho assigned the task of doing so. Whether the studies were initiated in response to the IJA’s own high-speed aircraft project is unknown but the prevalent aircraft design philosophy of both the IJN and the IJA prior to the war was of speed, agility and range at the expense of fire- power, durability and protection.
Kugisho examined over half a dozen aspects of aerodynamics in order to produce data on what would be needed to realize an aircraft capable of significant speed. One leading point of research was the main wings. The shape of a wing is one of the more critical aspects of aircraft design. Factors such as wing loading, expected air speeds, angles of attack and the intended use of the aircraft all influence how the wing is shaped. For high speeds, a low aspect ratio wing is often considered. Typically, these are short span wings with the benefits of higher maneuverability and less drag. In addition, having a backward sweep to the wing also lowers drag. The drag most associated with wings is termed induced drag, which is caused by wing tip vortices that change how the air flows over the wings. This change results in less and less lift which then requires a higher and higher angle of attack to compensate and, from this, induced drag results. Elliptical wings offer less induced drag than more conventional straight wings. However, low aspect ratio wings are more prone to larger vortices because they cannot be spread out across a longer wing.
Kugisho’s study on wing shapes was the likely result of testing various airfoils in a wind tunnel to determine their effectiveness and record the results. Another aspect Kugisho engineers reviewed were the merits and flaws of using either an inline or a radial engine and how each type reduced the form drag. In both cases the engineers drew up two concept aircraft and each made use of streamlining. Streamlining is the process of shaping an object, in this case, a fuselage, to increase its speed by reducing the sources of drag.
One concept used the German 1,159hp Daimler-Benz DB 601A, a 12-cylinder, inverted-V, liquid-cooled, inline engine. This engine would be license built for the IJN as the Aichi AEl Atsuta (the ‘A’ stood for Aichi, ‘E’ for liquid-cooled and ‘l’ for first liquid-cooled engine.  Atsuta was a holy shrine in Aichi Prefecture) and for the IJA as the Ha-40, before it was renamed the [Ha-60] 22.
The second concept aircraft (Kugisho High-Speed Aircraft Project with NK-1B) used a 1,000hp Nakajima NKlB Sakae 11 which was a 14-cylinder, air-cooled, radial engine. This engine was a license version of the French Gnome-Rhone l4K Mistral Major (in engine nomenclature, the ‘N’ was for Nakajima, ‘K’ for air-cooled, ‘1’as the first air-cooled engine, while the ‘B’ was for the second version of the NKl; Sakae means prosperity in Japanese).
Kugisho would use the same basic airframe for the engine study. It consisted of a well streamlined fuselage with the pilot mounted in a cockpit set behind the wing and just forward of the vertical stabilizer. This style was found in a number of racing aircraft such as the American GeeBee Rl and Geebee Z. Both aircraft used a standard tail-sitter configuration for the landing gear. The concept equipped with the DB 601A engine had a fuselage shape that was not unlike the Kawasaki Ki-61 Hien (“Swallow”, codenamed “Tony” by the Allies) which would appear in prototype form in December 1941 . The wings were mounted low on the fuselage. The fuselage appearance was due to the inverted-V engine which, by design, offered lower height, weight and length when compared to more conventional engines.
By contrast, the concept using the Nakajima NKlB had a more ovoid fuselage shape, the result of the height of the radial engine. To maintain the aerodynamic streamlining a large spinner was used. Also, in contrast to the DB 601A equipped design, the wings were mounted mid-fuselage.
Kugisho would not produce any direct prototype aircraft from either concept. lnstead, results of the various studies were likely kept available as reference for engineers to access as a means of obtaining data on the aerodynamic problem. Perhaps Kugisho in hindsight considered themselves fortunate to not have expended additional expense and effort in producing working prototypes given the failure of the IJA’s Kawasaki Ki-78, a program that lingered on into 1944 and never met its design goals (Ref.: Dyer III, Edwin M.: Japanese Secret Projects, Experimental Aircraft of the IJA and IJN 1939-1945, Midland Publishing, Hersham, U.K., 2010).

TYPE: Interceptor, fighter. Project

ACCOMMODATION: Pilot only

POWER PLANT: One Nakajima NK-1B “Sakae” radial engine, rated at 1,100 hp

PERFORMANCE: No data available

COMMENT: On 26 April 1939, a German Messerschmitt Me 209 V1 set a new world speed record of almost 469 mph. This relative small Me 209 was a completely new aircraft and not to mistake for a replacement of the Messerschmitt Me 109, entering service with the Luftwaffe at the same time. Its only purpose was to set a new speed record.
Impressed by that speed the Imperial Japanese Navy Air Force authorized the Yokosuka Naval Air Technical Arsenal, Yokosuka also known as Kaigun Koku Gijutsusho or Kugisho to propose several designs of similar aircraft. In a complete reversal from previous Japanese Navy requirements priority was given speed, rate of climb, and maneuverability.
One design was built around a Nakajima NK1 “Sakae” radial engine, one of the most powerful engines available in Japan at that time. Another design proposed by Kugisho was the Kugisho (Kugisho High-Speed Aircraft Project with DB 601A), powered by a Kawasaki Ha-40 liquid-cooled engine derived from the German Daimler-Benz DB 601A. A more powerful variant of this engine was installed in the world record-breaking Messerschmitt Me 209 V1.
Although calculations and designs were in an advanced stage none of the Kugisho projects were realized
Noteworthy is the fact that the Imperial Japanese Army Air Force had similar projects, e. g. the Kawasaki Ki-60.

TYPE: Interceptor. Project

ACCOMMODATION: Pilot only

POWER PLANT: One Kayaba Model 1 ramjet engine rated at 750 kp thrust at 457 mph and four solid fuel rocket boosters for take-off, rated at 7.200 kp thrust

PERFORMANCE: 559 mph (estimated)

COMMENT: The Kayaba “Katsuodori” (“Booby Gannet”) was the result of the endeavor to design a single-seat, ramjet-powered interceptor-minded platform which utilized a short, tailless fuselage configuration with swept-back wing main planes. The cockpit would be held well-forward and offered exceptional vision for the pilot. The mid-mounted main planes were affixed ahead of midship with each tip capped by small vertical stabilizers. The ramjet propulsion system was buried within the tubular fuselage and a rocket-assist scheme (consisting of four externally-held rocket pods) was to be used. The rocket pods were installed under the wing roots and jettisoned once their usefulness had run out. Having achieved the required speeds, the aircraft would then continue on under ramjet power with a flying window of about 30 minutes being estimated. To aspirate the ramjet, the nose section featured an air intake. No conventional undercarriage was provided. Instead the aircraft would glide back home powerless and land on a belly-mounted skid. The ramjet under consideration for the project became the Kayaba Model 1 which promised 750 kp thrust output.
Since the aircraft never achieved prototype form, performance specifications were estimated and this included a maximum speed of 560 miles per hour with a rate-of-climb around 11,000 feet-per-minute. The latter would prove a good quality to have in interception sorties. The service ceiling was listed at 49,215 feet
As an interceptor attempting to tackle very large, slow-moving (but well-defended) targets, it was seen to arm the fighter appropriately through 2 x 30mm Ho-301 series cannons – this was a suitable arrangement to counter even the high-flying and technologically advanced Boeing B-29 “Superfortress” which had made its presence known since mid-1944. The cannons would have been embedded in the sides of the nose.
Design work on the “Katsuodori” progressed into 1943 and plans were underway to begin construction of a working prototype for the following year. However, Japan’s fortunes in the war had worsened into 1944 and the attention of authorities turned to more viable military weapons such as the Rikugun (Mitsubishi) Ki-202 “Sharp Sword”, based on a rocket-powered interceptor developed by Mitsubishi as Ki-200 “Shusui” for the IJAAF and J8M-1 for the IJNAF on the basis of the German Messerschmitt Me 163 “Komet” (Ref.: 24).

TYPE: Interceptor fighter. Project

ACCOMMODATION: Pilot only

POWER PLANT: One Ishikawajima Ne-130 turbojet engine, rated at 900 kp thrust

PERFORMANCE: No data available

COMMENT: The concept of Kyushu J7W1 unique canard configuration was due to designers of the Technical staff of the Japanese Navy. From the onset of that project it was envisaged to replace the rear-mounted Mitsubishi Ha-43 air-cooled radial engine, which drove a six-blade pusher propeller, with the new turbojet engines under development at that time.
Following some initial work on that concept, the staff of Dai-Ichi Kaigun Koku Gijitsusho (First Naval Air Technical Arsenal) designed a glider to test the aircraft’s handling qualities at low speeds. Three prototypes of the MXY6 were built for the Navy by Chigasaki Seizo K.K. and these all-wood gliders with moderately swept wings supporting tall tail surfaces inboard the ailerons began flight trials in autumn of 1943.
Although the “Shinden” was expected to be a highly maneuverable interceptor, only two prototypes were finished before the end of war. And of course the turbojet engine powered Kyushu J7W2 was never realized, it didn’t even reach the drawing board (Ref.: 24).

TYPE: Fighter. Project

ACCOMMODATION: Pilot only

POWER PLANT: One Ishikawajima Ne-230 axial-flow turbojet engine, rated at 885 kp thrust

PERFORMANCE: Data not available

COMMENT: The availability of more sophisticated turbojet engines in the closing stage of the Pacific War brought the Japanese aircraft industry to plans to design completely new turbojet fighters, such as Nakajima Kikka, Nakajima Ki-201 Karyu (Fire Dragon), and Rikugun Ki-202,  or to provide newest piston engine designs with turbojets. Examples are the conversion of the Kyushu J7W1 Sinden (Magnificent Lightning) into the Kyushu J7W2 with one Ishikawajima Ne-130 turbojet engine, the Yokosuka R2Y1 Keiun (Beautiful Cloud) with two Ishikawajima Ne-330 turbo jet engines, and Mitsubishi J4M-1 Senden (Flashing Lightning). This twin-boom fighter project, powered by a Mitsubishi MK9D radial engine, driving a six-blade pusher propeller was redesigned to a much smaller aircraft, also in twin-boom configuration, but powered by one Ishikawajima Ne-230 axial-flow turbojet engine, that was expected to give 885 kp thrust. But the end of the hostilities brought all work on this Mitsubishi J4M-2 Senden-Kai project to a halt.

TYPE: High performance interceptor fighter. Project

ACCOMMODATION: Pilot only

POWER PLANT: One Mitsubishi Ha-43 radial engine, rated at 1,650 hp at 26,247 ft, driving 6-bladed metal constant speed pusher propeller

PERFORMANCE: 470 mph at 26,247 ft

COMMENT: To provide the Imperial Japanese Navy with a land-based high-performance interceptor aircraft, Mitsubishi designed the J4M Senden (“Flashing Lighting”) or Navy Experimental 17-Shi Otsu B Type Interceptor Fighter Senden. It was to have been a single-seat, twin-boom, low-wing monoplane with a central nacelle housing an unstepped cockpit and a 2,130-hp Mitsubishi MK9D (Ha-43) radial engine behind the pilot driving a six-bladed pusher propeller rotating between the booms. The booms were to extend aft from the leading edge of the wing and were mounted below the central nacelle. The aircraft was to have had tricycle landing gear and an armament of one 30-mm and two 20-mm cannon. Design of the initial J4M1 version ended when the Navy put its support behind the competing Kyushu J7W fighter. So the J4M project did not proceed beyond the design stage. The Allies nonetheless assigned the J4M the reporting name “Luke” during World War II.(Ref.: 23)