K-l Kugisho MXY7 Oka – data

Contemporaries Daimler-Benz Projekt E and Projekt F (Germany), Messerschmitt Me328C (Germany)


Varied. The Oka Model 11 and MXY7 K-l saw operational service. The Oka Model 22 was deployed but did not see action. The Oka Model 21 remained a single prototype. The Oka Model 43B prototype was incom­plete at war’s end. The Oka Model 33,43A and 53 remained designs only. The Oka Model 43 K-l Kai was too late to be issued to training units.


Kugisho MXY7 Oka (FE-N50)

The ‘N’ is assumed to signify ‘Navy’ as in the US Navy, thereby denoting the US Navy was evaluating this particular aircraft. This MXY7 was listed on a 10 March 101946 report allowing it to be released to aviation indus­try. On 1 August 1 1946, an inventory reported it at MAMA and by 18 Sep­tember 1946 was slated for the museum and storage at Park Ridge. No further trace of the MXY7 is known.

Kugisho Oka Model 11 (no tail number assigned)

One of a number of Oka aircraft taken to the US, this one, serial number 1049, was obtained by Edward Mahoney. It was restored and remains on display at his Planes of Fame Museum in Valle, Arizona.

KQgisho Oka Model 11

Bearing the serial 1018, this Oka is currently on display at the Marine Corps Base Quantico, near Triangle, Virginia.

Kugisho Oka Model 11

Originally this Oka was in the collection of the Victory Air Museum located in Mundelein, Illinois. It closed its doors in 1984 and the aircraft was sold off. It was last obtained by the Yanks Air Museum in Chino, California.

KQgisho Oka Model 11

Shipped to India in September 1947 by the No.4 Squadron of the Indian Air Force following their duties in Japan as part of the British Common­wealth Occupation Forces, the Oka is currently on display in the Indian Air Force Museum at Palam Air Force Station, New Delhi, India.

Kugisho Oka Model 11

Another Oka in England, this time displayed at the Fleet Air Arm Museum in Yeovilton, Somerset, UK.

Kugisho Oka Model 11

This example of the Oka is in the collection of the Museum of Science and Industry in Manchester, UK, with the registration number of LI 996.53.10. Since 1961, this Oka has passed through a number of muse­ums before it reached its current location.

Kugisho Oka Model 11

This Oka is housed in the collection of the Defence Explosive Ordnance Disposal School. The school is currently located in Chattenden, Kent, but is to be relocated to St. George’s Barracks, Bicester in Oxfordshire, UK.

Kugisho Oka Model 11

The fourth Oka in the British Isles is on display at the Royal Air Force Museum at Cosford in Shropshire. Prior to this, it was housed at the Rocket Propulsion Establishment in Westcott, Buckinghamshire.

KQgisho Oka Model 11

This, the only known genuine Oka in Japan (a replica is used at the Yasukuni Shrine in Chiyoda, Tokyo as well as the Oka Park in Kashima City, Ibaraki Prefecture), is currently housed at Iruma Air Base, a Japan­ese Air Self-Defence Force facility in Iruma, Saitama Prefecture. During the war it was at the IJA base Irumagawa Airfield.

KQgisho Oka Model 22

Restored and on display at the Smithsonian Air and Space Museum. KQgisho MXY7 K-l

With a serial number of 5100, the MXY7 K-l is housed in the Navy Museum at the Washington Navy Yard in Washington, D. C.

KQgisho MXY7 K-l

This trainer is currently on display at the National Museum of the United States Air Force, located on the property of the Wright-Patterson Air Force Base in Riverside, Ohio, which is just outside of Dayton, Ohio. At one time it was painted as an operational Oka but has since been returned to the orange colour scheme of a trainer.

KQgisho Oka Model 43 K-l Kai

At present, this trainer bearing the serial number 61 is in storage and unrestored at the Paul E. Garber facility.

(Note: The KQgisho Oka Model 11 displayed at the Wings of Eagles museum in Horseheads, NY, is a replica.)

The design and development of the Mitsubishi J8M1 SyCisui presented a challenge. Despite the information available to the Japanese on the Messerschmitt Me 163B, upon which the J8M1 was based, the concept of a tailless fighter, let alone a rocket powered one, was new and untested. What was required was a means to verily the design of the J8M1 and in doing so provide a way to train pilots who would be fly­ing a plane that was unlike any they had ever down before.

Therefore, Kugisho was given the task of cre­ating a glider that was to be a copy of the J8M1. The main purpose was to assess the flight char­acteristics of the tailless fighter given that the Japanese did not have extensive experience with such aircraft. Data collected from flying the glider would in turn be reviewed and applied to the J8M1 fighter prior to series pro­duction. In addition to serving as a proof of con­cept vehicle, the glider would provide the means to train new pilots in flying the aircraft since it was like no other fighter then in service in the 1JN and 1JA. By using the glider as a trainer, pilots could better transition to the J8M1 and therefore minimise operational mistakes.

Kugisho assigned the glider construction, called the MXY8 Akigusa (meaning ‘Autumn Grass’), to engineer Hidemasa Kimura. Kimura utilised wood with some cloth covered sur­faces in the design of the MXY8 and ensured that the glider was a near exact replica of the J8M1 in order to provide the most accurate flight data once testing got under way. By the close of 1944, the first MXY8 was finished and another two were nearing completion.

In December, the first MXY8 was taken to the airfield located in Hyakurigahara, which is about 79km (49 miles) northeast of Tokyo. It was here that the UN’s Hyakurigahara Air Group was stationed, operating in the defence of Tokyo. Also at the airfield was the 312th Kokdtai, a newly formed unit that was to be equipped with the J8M1 once it entered pro­duction. As such the 312th Kokutai was the per­fect group to begin testing the MXY8. The first flight, scheduled for 8 December 1944, was given to Commander One. Unfortunately, One was taken ill and was unable to fly so the mis­sion was assigned to Lieutenant-Commander Toyohiko Inuzuka. On the day of the flight, Inuzuka climbed into the cockpit of the MXY8 and once secure, a Kyushu K10W1 of the 312th Kokritai took the glider into the sky. At altitude Inuzuka was released from the tow plane and began his descent. After successfully bringing

MXY8 shown in the orange colouration as used on trainers and experimental aircraft.

the glider down, Inuzuka gave the MXY8 high marks, having found the handling and flight characteristics to be very acceptable.

The IJA, who were also slated to fly the J8M1 as the Ki-200, was provided with the second MXY8. Delivered to the Rikugun Kokuyijutsu Kenkyujo, the pilot selected to test the MXY8 for the IJA was Colonel Aramaki, and like Inuzuka, he felt that the MXY8 performed well. The only notable deficiency to be found by both Inuzuka and Aramaki was the tendency for the MXY8 to nose over into a dive. The third MXY8 to be built was delivered to the Naval Air Force.

The first MXY8 did not match the combat weight of the J8M1. To this end the UN wanted to modify the MXY8 so that it incorporated bal­last tanks which could hold enough water to fully simulate the combat weight of the J8M1 and be the definitive production model for use in training pilots. With the completion of the ini­tial three MXY8 gliders by Kugisho, a number of manufacturers were organised to begin the production of the revised ‘heavy’ MXY8 glider to meet the training needs of the 312th Kokutai and other units that would be flying the J8M1 and Ki-200. Maeda Kdkii Kenkyujo was tasked with producing the MXY8 for the UN and the MXY8 was to be built for the IJA by Yokoi KdkCi K. K. as the Ku-13.

Further flight testing by the 312th Kokutai found that the MXY8 experienced aileron flutter at speeds above 295km/h (183mph) (as a side note, the same problem was encountered in the Messerschmitt МеІбЗА VI first prototype during testing). This and other minor problems were noted, analysed and corrected, and the flutter issue was resolved by closing the gap between the wing and the aileron (the Me 163A VI was rebalanced). In the meantime, the MXY8 was being flown by Naval Air Force pilots at the Kashiwa airfield in Chiba Prefecture. However, the pilots were less enthusiastic on the design, especially after a crash involving one of the gliders that severely injured the pilot. Regardless, the Kaigun Koku Hombu assessed all of the data from the test flights and formally approved the MXY8 on March 1945 and work proceeded with full production of the MXY8 and Ku-13 that continued until the end of the war.

Contemporaries Messerschmitt Me 163S, Heinkel He 162S (Germany)

Data is for the MXY8. The specifications also apply to the Yokoi Ku-13. No specific data is available on the MXY9 Shuka.

Type Proof of ConceplAraining Glider

Crew One













Wing area











Max glide speed


Max tow speed





Deployment Kugisho built the three prototype MXY8 gliders, Maeda constructed 44 to 54 MXY8 trainers while Yokoi produced 6 Ku-13 train­ers. A number of MXY8 gliders were operated by the 312th Kokutai.

No MXY9 was constructed and the project remained a design only.

Another version of the glider was investi­gated by the UN. Whereas the MXY8 was unpowered, the new version would have some means of propulsion. Designated the MXY9 Shuka (meaning ‘Autumn Fire’), the new design was to be an advanced trainer which, because it had the means to propel itself when it was airborne, would provide training with a modicum of power and offer longer flight times. It was envisioned that once training in the MXY8 was completed, pilots would transi­tion to the MXY9 for advanced training before moving to the J8M1 or Ki-200. The propulsion method proposed was the Tsu-11 thermojet. This was the same engine as used in the Kflgisho Oka Model 22 (see Page 70). However, the MXY9 was never

Given the expanse of the Japanese empire by 1942, the UN found that they had a need for a long range reconnaissance aircraft that could operate from land bases and fly at high speed to render it immune to interception. In the same year, the UN issued a 17-shi specifica­tion for just such a plane and Kugisho looked to provide the response.

The 1942 17-shi specification called for the aircraft to have a maximum speed of 667km/h (414mph) at 6,000m (19,685ft) along with a mission profile of long range recon­naissance. The speed requirement stemmed from the need to be able to avoid intercep­tion; the intelligence it gathered would be useless if the aircraft was shot down before it could return to base. The initial design, the R1Y1 Gyoun (meaning ‘Dawn Cloud’; other sources use Seiun, meaning ‘Blue Cloud’), bore the designation Y-30 and was to be developed around a new Mitsubishi, 24-cylin – der, liquid-cooled engine that was projected to produce 2,500hp. However, delivery of the engine was not expected to be rapid and in
order to proceed with the R1Y1, Kugisho decided to utilise two Mitsubishi MK10A radial engines. In so doing, the R1Y1 took on the appearance of the Kugisho P1Y1 Ginga and with the use of two radials and the result­ing drag imposed by them the RlYl’s calcu­lated performance was projected to fall below the 17-shi specification. Consequently, all work on the R1Y1 ended and the project was abandoned.

Even as Kugisho was working on the R1Y1, they were developing another design, the Y – 40, which was the result of an evaluation of the Heinkel He 119, two examples being pur­chased from Germany in 1940.

The He 119 was an attempt to create a fast, unarmed reconnaissance aircraft whose high speed would enable it to avoid interception and elude pursuit. To accomplish this, the He 119 used radical concepts to minimise drag and thus enhance speed performance. A pair of Daimler-Benz DB 601 engines coupled together drove a single propeller shaft. The engines were placed in the rear of the He 119
fuselage with the shaft running forward, through the middle of the cockpit, spinning a four-bladed propeller in the nose. To cool the paired powerplants, the He 119 used a wing surface evaporation system in which steam from the engines was circulated through the wings where it cooled and condensed back to liquid where it was pumped back to the engines. To cool the engines when on the ground or during take-off and landing (due to the lack of sufficient airflow across the wings at such times), a supplementary radiator was installed under the forward fuselage. The He 119 VI first prototype attained a top speed of 565km/h (351mph) at 4,500m (14,765ft). Unfortunately, Heinkel was forced into adding armament to the He 119 but this was done in a very minimal fashion. The V2, with a full functional bomb bay, was able to reach speeds of up to 585km/h (363mph) at 4,500m (14,765ft). The V4 was used as a record breaker, briefly holding the record for speed with a 1,000kg (2,2051b) payload on a closed 1,000km (621 mile) circuit with the average

speed of 504.97km/h (313.78mph). Later the V4 was wrecked in a crash during an attempt to better that time. The record was set on 22 November 1937 and the successful aeroplane was listed as the ‘He 606’. The V3 was built as a float-plane, intended to best the 1,000km (621 mile) seaplane speed record. Ultimately, the V5 through to the V8 would be the last He 119 aircraft built because the Luftwaffe showed no further interest in the aircraft.

Following testing in the summer of 1938, a delegation from the UN was able to inspect the He 119 at Marienehe in Germany. The Japanese were most impressed by the range offered by the He 119 as well as its speed. Of interest were the coupled DB601 engines. After reporting their positive findings, nine technicians from the Dai-Ichi Kaigun Кбкй Gijutsu-sho flew from Japan to Germany to study the He 119 further. Commander Hideo Tsukada arranged to obtain the manufactur­ing licence for the He 119 and also the pur­chase of the He 119 V7 and V8. Both aircraft were crated for shipment and sent to Japan arriving in May 1940. Reassembled at Kasum – igaura, KQgisho began flight trials under the leadership of Major Shoichi Suzuki. During the brief trials, one He 119 was lost to landing gear failure (the He 119 used a special, retracting telescopic oleo leg in order for the long landing gear to fit into the wings). In the end plans to manufacture the He 119 in Japan did not come to fruition.

Although the He 119 was rejected, the study of this aircraft resulted in the development of the Y-40. Like the He 119, the Y-40 was to be a fast, unarmed two-seat reconnaissance air­craft using coupled engines placed within the fuselage behind the cockpit and driving a pro­peller via an extension shaft. The UN’s 18-shi specifications for a long range reconnais­sance aircraft were based on the Y-40.

The Y-40 project, by now called the R2Y1 Keiun (meaning ‘Beautiful Cloud’), was led by Commander Shiro Otsuki and his design team made good progress. The Keiun was to be equipped with two Aichi Atsuta 30 engines coupled together in a combination known as the Aichi [Ha-70] 10. The 24-cylinder, liquid – cooled [Ha-70] 10 was rated at a maximum of 3,400hp and drove, via the extension shaft, a 6-bladed propeller. The Keiun did not use the same method of cooling as the He 119. Instead, it relied on air intakes and a radiator bath underneath the fuselage, and it also dif­fered from the He 119 in that the Keiun used a tricycle landing gear system and was not a tail sitter.

By the fall of 1944, the war situation for Japan was deteriorating. With the loss of terri­tory to the advancing Allies, the UN no longer saw a need for a long range reconnaissance aircraft. Following the defeat of the Japanese in the Marianas Islands (following Operation Forager), the fate of the Keiun was all but sealed. The UN had no need for such a plane as existing designs would be adequate for the dwindling Japanese holdings. In addition, the need for fighters and bombers was rather more urgent than reconnaissance aircraft.

But Otsuki and Kugisho did not let the Keiun fall by the wayside. In late 1944, KQgishd approached the UN and informed them that the R2Yl’s airframe was readily adaptable to other roles, including that of a fast attack bomber. To heighten the interest, it was proposed that the [ Ha-70 ] 10 engine be replaced with two Mitsubishi Ne330 axial – flow turbojets, each of the engines being slung under the wings in nacelles. The fuse­lage space vacated by the Aichi engine would be replaced with fuel tanks. For weapons, the aircraft would carry one 1,800kg (7641b bomb) and have a cannon armament in the nose. With the introduction of the Ne330 engines, the maximum speed was expected to be 495mph, superior to the projected 720km/h (447mph) top speed of the Aichi engine model. With these advantages in mind, the UN approved that work should begin on designing the R2Y2, the turbojet powered Keiun which was sometimes referred to as the Keiun-Kai, as well as per­mitting the R2Y1 to be completed as an air­frame demonstrator to test the handling characteristics.

In April 1945, the first prototype of the R2Y1 was completed and moved to Kisarazu in Chiba Prefecture to begin flight testing. Initial taxi trials, conducted by Kugisho test pilot Tereoka, showed that the nose wheel had a bad shimmy when in motion and the Aichi engine was prone to overheating. The latter was either due to a lack of airflow through the radiators and inlets during taxi tests or through a poorly designed cooling system. Nevertheless, despite the problems testing of the Keiun continued.

On 8 May 1945, Lieutenant-Commander Kitajima, another Kugisho test pilot, took the Keiun on its first flight. Kitajima noticed that the oil temperature was rising rapidly and he cut short the flight, landing the Keiun before the engine suffered damage. Mechanics and engineers continued to try and solve the cool­ing problems, but a few days later the engine caught fire during ground testing, completely destroying the power unit. Then before the Keiun could be returned to KQgishd to receive a new engine, the aircraft was destroyed by a US bombing raid.

Even before the destruction of the first R2Y1, a second was being constructed and design work for the R2Y2 was underway.

Contemporary sources show no less than four versions for how the R2Y2 may ultimately have appeared. The first had the Ne330 engines in underwing nacelles. The second version showed the two engines buried within the fuselage with wing root air intakes and narrow jet nozzles. The third removed the wing intakes and replaced them with a nose intake, but it retained the narrow noz­zles. Finally, the fourth was similar to the third save that the engine nozzles were larger. The first design is considered by most to be the ini­tial R2Y2 concept while the other three are subject to debate. In part, this is due to the fact that the Japanese had very little time to explore various installations of turbojets in airframes. The easiest means to place turbo­jets on aircraft was by using nacelles and this was seen in the Nakajima Kitsuka, Nakajima Ki-201 Karyu and proposed KQgisho Tenga and Kawanishi K-200.

Even the Germans with their turbojet expe­rience did not fully understand the effects of a long nose intake feeding a high perfor­mance jet buried in a combat fighter’s fuse­lage. Messerschmitt, when they began to study how to start the P. l 101 second genera­tion jet fighter, catalogued the obstacles that needed to be overcome. They included the effects of engine operation on the fuselage integrity, ensuring the nose intake was prop­erly positioned and shaped for maximum air­flow, making sure the intake tube was made as smooth as possible to minimise air restric­tions, how to protect the rear of the aircraft from the heat generated by the exhaust thrust, the effects of reduced airflow on thrust due to flight angles and more. The Germans were at least able to devote some time to investigating these problems and providing solutions to them. This was time however, that the Japanese simply did not have. Up until the construction of the P. l 101 VI and the planned Focke-Wulf Та 183, all of the wartime jet designs flown by the Luftwaffe had nacelle mounted turbojets. The Japan­ese may not have been made fully privy to the latest German jet engine technology as it per­tained to long intakes before the war ended. It is within reason to suggest that the R2Y2 with the wing root intakes could have been under consideration since it would be a logi­cal development, especially since such intake arrangements were not entirely new. The third and fourth designs may or may not have been post-war conjecture.

Unfortunately for KQgisho and the UN, the R2Y2 would never be brought to full produc­tion. With the end of the war, the second R2Y1 prototype remained incomplete and the R2Y2 would forever remain a design board aircraft.

Kugisho R2Y Keiun – data


Messerschmitt Me 509 (Germany), Tupolev Tu-91 (NATO codename Boot) (Russia), Messerschmitt P. l 100 (Germany)

The specifications in parenthesis are for the R2Y2 with the underwing turbojets.

Type Long range reconnaissance aircraft (attack aircraft)

Crew Two

Powerplant One Aichi [Ha-70] 10,24-cylinder, liquid-cooled engine developing 3,400hp at take-off and 3,100hp at 3,000m/9.845ft, driving a 6-bladed metal propeller (two Ne330 axial-flow turbojets developing l,320kg/2,9101b of thrust each)




















Wing area






Wing loading


48.8 lb/ft2




Power loading


5.2 lb/hp



7.1 Мір














Fuel capacity

1,555 litres

411 gallons


3,218 litres

850 gallons


Max speed



at 10,000m

at 32,81 Oft




at mean sea level, estimated

Cruise speed



at 4,000m

at 13,125ft

Landing speed








1,950 miles



788 miles


10 min to 10,000m (32,810ft)


7 min to 10,000m (32,810ft)








None (one 800kg/l,764 lb bomb and a battery of forward firing cannon)


Concerning the three other R2Y2 jet variants with internal engines, little is documented and much is open to conjecture. In some instances, the wing span, length, height and wing area are listed as being the same for the R2Y1 but the speed is given as being a maximum of 800km/h (497mph).


None. One prototype of the R2Y1 was built and flown while the second R2Y1 prototype was unfinished by the end of the war. The R2Y2 stayed on the design board.

Of the many Japanese experimental aircraft of World War 2, perhaps none is more of a mystery than the Kugisho Tenga. The Tenga (which can mean the Milky Way as one trans­lation of the kanji) was to be a first for Japan: a turbojet powered bomber. To realise this ambition as quickly as possible, the Japanese intended to use one of their latest and best bomber designs – the Kugisho P1Y Ginga (‘ginga’ also means Milky Way) – as the basis for the Tenga.

If one examines the aircraft available to the Japanese during the war, the distinct lack of a medium bomber quickly becomes evident. Whereas most of the warring powers oper­ated medium bombers (for example, the Martin B-26 Marauder, the Junkers Ju88 or the Vickers Wellington), the Japanese were very late in bringing such aircraft to the front. The IJA brought the Ki-67 Hiryti medium bomber into service in 1944 and so the UN looked to the Kugisho P1Y Ginga as their answer to the need for a medium bomber.

Development of the Ginga began in 1940 as the Dai-Ichi Kaigun Kokti Gijutsu-sho’s attempt to meet a 15-Shi specification for a medium bomber capable of high speeds, the ability to conduct low-level bombing and tor­pedo missions, and the capability to perform dive bombing. With Tadanao Mitsuzi and Masao Yamana at the helm the Y-20, as the Ginga was called at this stage, emerged as an aerodynamically clean, mid-wing, twin – engine design. Despite its relatively small size, the Ginga had fourteen fuel tanks (of which only eight had some protection from battle damage), a modicum of armour for the pilot (which consisted of a 20mm thick plate behind his head), a light defensive armament of a 7.7mm machine gun in the nose and in the rear of the cockpit, and the ability to carry a single 800kg (1,764 lb) torpedo or two 500kg (1,1021b) bombs. With the two Nakajima Homare 11 18-cylinder, air-cooled radial engines developing 1,280hp each, speed was estimated at 556km/h (345mph).

The first prototype was completed in August 1943 and flight testing began shortly afterwards. Test pilots found that the Ginga possessed excellent speed and also dis­played good handling qualities. Ground crews on the other hand had anything but good things to say about the aircraft. The Homare 11 engines and the hydraulic system used in the Ginga were a constant mainte­nance hassle, requiring far more time and effort to maintain than was considered rea­sonable. So bad were the problems, the IJN postponed its acceptance of the aircraft.

Despite the problems production got mov­ing and design changes saw the machine guns replaced with Type 99 Model 1 20mm cannons and 13mm Type 2 machine guns. Other changes included revised engine cowl­ings, replacing the retractable tail wheel with a fixed wheel, moving from flush riveting to flat-head riveting, incorporating a bullet-proof panel in the windshield and also replacing the Homare 11 engines with the Homare 12 which could produce l,825hp.

After these modifications, the IJN finally accepted the P1Y1 Ginga bomber into ser­vice. But the type was still nagged by prob­lems, notably the Homare 12 engines which rarely produced the horsepower they were rated for. Such issues delayed the Ginga entering combat until the spring of 1945. Even though the Ginga would see battle for a mere six months the design nevertheless proved to be a capable medium bomber and one which the Allies respected when they encountered it. When the Allies first heard of the plane they thought it was a heavy fighter and assigned the codename Francis to it (after Francis ‘Fran’ Williams of the Material Section of the Directorate of Intelligence, Allied Air Forces, Southwest Pacific Area). However, when the Ginga was finally spotted after 1943, it was realised that it was a bomber and the name was changed to the feminine version of Francis – Frances.

The Ginga was developed into several vari­ants and there were plans to use the bomber as a carrier for the Oka Model 21 and Oka Model 22 suicide aircraft. Kawanishi built a night-fighter/intmder version as the P1Y2-S, which entered service with the IJN as the Kyokko (meaning ‘Aurora’) in the summer of 1944. The Kyokko was fitted with Mitsubishi Kasei 25a l,850hp, 14-cylinder radials

because the Homare 12 could not be assem­bled fast enough to meet demand. Weapons included two forward oblique mounted 20mm Type 99 Model 2 cannons firing upwards and the nose cannon was removed. First flown in July 1944, it was found that the Kyokko did not perform well at the high alti­tudes where the Boeing B-29s roamed. This revelation was so disappointing that the upward firing cannons were removed and the Kyokko returned to its bomber role as the Ginga Model 16 (P1Y2). Nakajima also built a similar night-fighter version as the P1Y1-S Byakko (which meant ‘White Light’). The Byakko fared little better than the Kyokko and did not see service. Other modifications and plans included upgrading the engines to the Homare 23, Kasei 25c or the Mitsubishi MK9A,

the idea of an attack model with ten to sixteen forward firing 20mm cannons and using steel and wood in the aircraft’s construction. The most interesting was the P1Y3 Model 33. This version was to be built from the ground up to carry the Oka and would have had a special bomb bay to accept the Oka Model 21 or 22 with increased wing span and an enlarged fuselage. The P1Y3 never left the drawing board.

With the Ginga’s success in terms of per­formance, it’s easy to see why there was interest in converting it to turbojet power. The concept of the Tenga was certainly real. But outside of the name and the basic intent to replace the radial engines with turbojets, nothing else is known. Therefore, one has to review other designs to make assumptions on what kind of task the Japanese might have faced in making the Tenga a flying reality.

The first point to consider would be that the Kugisho Ne 20 turbojets, then in production for use in the Nakajima Kitsuka, would not have been sufficient to provide the Tenga with any meaningful speed if mounted one per wing. One Ne20 produced 487kg (1,074 lb) of static thrust and two could propel the Kitsuka to 623km/h (387mph), which was not particularly significant over conventional high-performance propeller driven aircraft. The Kitsuka was a much lighter aircraft and a twin turbojet Tenga using Ne20s would not have been feasible.

It would have needed some of the pro­jected advances in the Ne 20’s development to come closer to reality to provide the Tenga with a meaningful system of propulsion. The Ne 30 turbojet was expected to generate up to 850kg (1,873 lb) of thrust (better than the Ger­man BMW 003 turbojet rated at 800kg/l,7631b) while the Ishikawajima Nel30 was projected to produce 900kg (1,9841b) of static thmst, comparable to the Junkers Jumo 004 engine. The Nakajima Ne 230 and the Mitsubishi Ne 330 were esti­mated to be able to produce 885kg (1,951 lb) and 1,300kg (2,8661b) of thrust respectively with the Ne 230 sacrificing thrust for a lighter weight.

It is said that the Ne 30 would have been the initial choice to power the Tenga had it been available. In comparison, the German Arado Ar234B jet bomber used two Jumo 004 engines. It was similar in size to the P1Y1, the notable differences being a smaller wing span, the loaded weight was nearly 680kg (1,5001b) lighter and the Ar234B had far less wing area. Together, the two Jumo 004 engines could move the Аг 234B at speeds up to 742km/h (461mph). Certainly, two Ne30 engines would not have provided such a speed when mounted to the P1Y1 but it would have been the logical starting point. Quite possibly, RATO units may have been needed to boost the Tenga off the ground. Clearly the Ne 130 would have been a better selection and with the Ne330, the Tenga would have enjoyed a noticeable speed improvement. Problems with the develop­ment of the Ne 30 engine are cited as a reason for the Tenga project being cancelled. Indeed, the Ne 30, an off-shoot from the Ne 12 program, never advanced, being surpassed by the Ne 20, Ne 130, Ne 230 and Ne 330 devel­opments.

But could the basic airframe of the Ginga be used with radial engines replacing with turbojets? It may have been attempted had the Tenga advanced in design. Even changing the radials for turbojets would have necessi­tated fairly significant adjustments in the wings to accommodate them but at least redesigning a wing to accept turbojets is a simpler task than redesigning the entire aircraft.

However, if one examines the history of combat aircraft, you would be hard pressed to find a conventional combustion engined bomber switching to jet power merely by changing the engines and adjusting the wings. For instance, not even among the dozens of jet bomber projects undertaken by the Germans did a piston-engined bomber switch its engines for turbojets without heavy modifications, if at all. One such example was the Messerschmitt Me 264 which used four Junkers Jumo 9-211 radial engines when the first prototype was flight tested. However, the proposed four turbojet engined version bore little resemblance to the original design.

Perhaps the only notable propeller to tur­bojet design created by adaptating an existing airframe was the Russian Tupolev Tu-12 whose heritage was owed to the Tu-2, one of the premiere Soviet light bombers. Built from 1941 through 1948, the Tu-2 possessed fast speed, excellent agility and had a substantial weapon fit and bomb carrying capacity. When Tupolev answered the call to produce a jet bomber, he took the Tu-2 as the basis for his Tu-12. He used the fuselage, wings and tailplane of the Tu-2 and adapted them to suit the installation of two Rolls-Royce Nene-1 tur­bojets and the higher speeds that would result. Although one can certainly see the lin­eage of the Tu-2 in the Tu-12, the aircraft still required a general redesign to cope with the new engines and the associated handling characteristics and was not simply a case of swapping the radial engines for turbojets. The design of the Tu-12 began in 1946 and the first flight took place in June 1947.

It is not unreasonable to conclude that the initial Tenga designers may have tried to utilise as much of the Ginga as possible, offer­ing the benefit of an airframe already in pro­duction with proven airworthy characteristics. This would have reduced development time when the need for such a bomber was most urgent. It would have also served as a starting point for aerodynamic testing. Still, when one reviews the jet bomber proposals of other nations, the num­ber of piston engine to jet engine concepts can be counted on a single hand. For the majority, the jet bomber was designed from the ground up instead of being adapted from an exisiting aircraft. The designers of the Tenga may have come to the same conclu­sion had they had the opportunity to continue their work. If so, the final Tenga design and prototype may have borne little resemblance to the Ginga with which it shares its name.

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