Kawanishi N1K1 "Kyofu" 15-Shi Fighter Seaplane (K-20)

[Le Chat]

Hello,

I'm looking for a good drawing of the Kawanishi N1K1 Kyofu 1st prototype, with contra-prop. http://s478.photobucket.com/user/mokyme/media/Japanese%20Seaplanes/N1K1_kyofu_prototype_test-W-01.jpg.html

I have a drawing in the FAOW, but it seems to me crude.

I would built it in 1/48th scale from the Tamiya kit and I know that there are some differences comparing to standard models :
- larger spinner
- narrower cord fin
- narrower main float support
- no aerial mast (perhaps ?)
- different shape of cowl gun openings
- overall orange-yellow paint with cowl black and, perhaps, black paint under floats
and I think that's all.

Thank you very much.

Fabrice

 

[blackkite]

Hi! Kyofu. You can measure the size which you need.
Source : FAMOUS AIRPLANES OF THE WORLD No.124 KYOFU,SHIDEN, SHIDENKAI, BUNRINDO CO.,LTD. 5/1/2008,
ISBN978-4-89319-158-8
Japanese text says that the 1st prototype added large fillet at the wing root.(as you can see.)

 

[Le Chat]

Hello,

Thank you very much Blackkite ! I have the oldest FAOW # 53 :

http://i438.photobucket.com/albums/qq101/shigeko88/album%2027/faowblack531.jpg

So, the drawing shows not small fillet, but pics show large one. It will be more easiest to me to keep these large fillets at wing roots.

I suppose you read japanese. If yes, what colour was painted this 1st prototype ? I think that orange yellow is correct, but I found this built with a grey plane :

http://www.hyperscale.com/features/2000/rexrc_2.htm

Thank you.

Fabrice

 

[blackkite]

Hello,

Thank you very much Blackkite ! I have the oldest FAOW # 53 :

http://i438.photobucket.com/albums/qq101/shigeko88/album 27/faowblack531.jpg

So, the drawing shows not small fillet, but pics show large one. It will be more easiest to me to keep these large fillets at wing roots.

I suppose you read japanese. If yes, what colour was painted this 1st prototype ? I think that orange yellow is correct, but I found this built with a grey plane :

http://www.hyperscale.com/features/2000/rexrc_2.htm

Thank you.

Fabrice

Hi Le chat! Yes I can read Japanese because I'm a Japanese. Don't ask me about the color. It's my weak point. ;D
http://www9.plala.or.jp/fukugiya/72-064-kyofu.htm
This site says that,
"I thought that I would paint the experimental model of Kyofu yellow orange.
Then, since I heard that the experimental model of Kyofu carried out the first flight before from establishment of painting an experimental model in yellow orange at the time of the first flight, I painted the gray of SDE. "
Another site says that when Kyofu No.1 prototype meiden flight, strong vibration happened due to wing root stall, then lagre fillet added at the wing root immediately.

 

[blackkite]

Hi!
Kyofu at the Natinal Museum of the Pacific war.　Recent Maru magazine reported the detail of this aircraft.

http://www.pacificwarmuseum.org/

And other pictures.

 

[Winston]

Looks good indoors protect from the weather.

 

[blackkite]

Looks good indoors protect from the weather.

Yes it is!
Kyofu had a Kasei engine same as Raiden, but Kyofu did not have forced cooling fan.
Kyofu prototype and early production model did not have ram air intake for the engine at the front top of the engine nacelle.
Ram air intake and oil cooler are located in the engine nacelle for low drag, but perhaps this design did not work well. (low horse power and overheat?)
Kyofu late production model had ram air intake for the engine at the front top of the engine nacelle same as Shiden and Shiden-kai.

 

[blackkite]

These drawings are little strange compared with bottom actual Kyofu photo.

 

[blackkite]

Hi!

View: https://www.youtube.com/watch?v=bQ6YIUANJkQ

 

[SlickDriver]

I was over on the J-Aircraft org site and noticed that a member had posted a detailed set of drawing and pictures of a fuel purge system for the A6M2-N floats and was wondering if there was something similar for the N1K1 Kyofu.

 

[Winston]

Looking at FAOTW #53 I can't seem to find any drawing of the float. I think only the A6M2-N had this.

 

[blackkite]

I was over on the J-Aircraft org site and noticed that a member had posted a detailed set of drawing and pictures of a fuel purge system for the A6M2-N floats and was wondering if there was something similar for the N1K1 Kyofu.

Oh what a detailed information! Thanks a lot.
I will check N1K1 Kyofu float design.
Kyofu has shot down B-24(1/16/1944), and caused a damage to B-29(1/2/1945).

 

[windswords]

Here is what I have on the N1K1 prototype:

This matches the photo of the paint scheme used on the prototype

 

[windswords]

So, the drawing shows not small fillet, but pics show large one. It will be more easiest to me to keep these large fillets at wing roots.

I suppose you read japanese. If yes, what colour was painted this 1st prototype ? I think that orange yellow is correct, but I found this built with a grey plane :

http://www.hyperscale.com/features/2000/rexrc_2.htm

Thank you.

Fabrice

I have a pic of a gray N1K1 that says it is the third prototype. If that's correct I would assume that the first two prototypes were the standard orange-yellow color:

 

[Stargazer]

...

 

[blackkite]

Thanks my friends for very rare items.

Japanese wikipedia says that

One Kyofu fighter was rushed into a battle with F6F in Chiba-prefecture Tate Yama in February 16, 1945.
Caused a damage to F6F was reported as a result of the fight competition. This was the only military gain Kyufu mentioned to an enemy fighter.

 

[airman]

There are any information and data about N1K2 proposed large version of Kyofu ?

 

[blackkite]

Hi!

http://roswitha.jp/[10]shinden@kyoufu@.html

At the Smithsonian Institution's Paul E. Gerber Facility in Washington, Maryland, USA

 

[blackkite]

『[太平洋戦争博物館/米テキサス]強風11型』

National Museum of the Pacific War. Fredericksburg, TX.340 East Austin StreetFr…

ameblo.jp

 

[Aurum]

...large version of Kyofu ?

large/larger version — what do you mean?

 

[Arjen]

@Aurum
From Japanese Aircraft of the Pacific War by René J Francillon, Putnam 1987.

The curtailment of the Kyofu production in favour of the Shiden, its land-based development, prevented the realization of an advanced floatplane version, the N1K2, which was to have been powered by a 1,900 hp Mitsubishi MK4R Kasei 23.

 

[airman]

@Aurum
From Japanese Aircraft of the Pacific War by René J Francillon, Putnam 1987

Ok, so it never were realized a project .

 

[blackkite]

Hi! We can see Kyofu laminar flow wing (LB wing) designed by Ichiro Tani through these pictures.

Photos of rare Japanese NIK Kyofu seaplane

Unrestored parts of a Japanese NIK Kyofu aircraft, codenamed Rex by the Allies, are stored in a National Naval Aviation Museum warehouse at Naval Air Station Pensacola on Thursday, March 14, 2019. Only 97 NIK Kyofu aircraft were manufactured and this is one of only 3 still in existence. Currently, t

www.pnj.com

 

[blackkite]

View: https://www.youtube.com/watch?v=5iif-JZJRgg

 

[blackkite]

Engine and fuselage shape
The Mitsubishi Kasei (output: approximately 1,500 hp) was used as the most powerful engine available at the time. Although the Kasei had a large output, its diameter (1,340 mm) was relatively large for a fighter, and it was expected that the nose, where the engine was located, would be the widest part of the aircraft, as in a normal single-engine fighter. Kawanishi therefore focused on a spindle-shaped fuselage shape similar to that of the Raiden, which also had the Kasei. At the time, wind tunnel experiments at the Naval Arsenal showed that for a fuselage with the same maximum cross-sectional area, it was more advantageous to have the maximum area closer to the center of the fuselage in terms of reducing drag, and the spindle-shaped fuselage was an application of this. In order to achieve the spindle shape, the engine was placed closer to the center of the fuselage and the front of the cowl was narrowed, and the propeller shaft was extended to accommodate the resulting clearance from the engine to the front end of the cowl. This was the same procedure as the Raiden, but the aircraft was not equipped with an engine cooling fan to compensate for the air flow rate from the narrow cowl opening.

 

[blackkite]

Main wing
The main wing for the Kyofu was a mid-wing configuration that had less interference resistance with the fuselage and was less likely to be hit by water splashes during takeoff. A laminar flow wing was also adopted as the wing shape. A laminar flow wing is a wing shape that delays the turbulent transition of the airflow over the wing and reduces air resistance, and it was expected to be effective in increasing speed. At the time, various shapes of laminar flow wings were researched and were also used on several military aircraft (such as the P-51 and the Saiun), but the one adopted for the Kyofu was the LB-type laminar flow wing invented by Professor Ichiro Tani of Tokyo Imperial University (now the University of Tokyo). The maximum thickness position of a normal wing's cross section is around 30% of the wing chord, but the maximum thickness position of the LB-type laminar flow wing is at about 40% of the wing chord, which makes the pressure gradient positive and expands the area where the airflow flows stably (the wing of the Shiun is also an LB-type laminar flow wing). In order for a laminar flow wing to be effective, the wing surface must be very smooth, but there is also a view that it may have been difficult to achieve the necessary precision with the machining technology of the time . The Kyofu that required high speeds also meant high wing loading, and in order to balance takeoff and landing performance, the wing root angle was an unusually large 4 degrees for a fighter, and on the first flight, as soon as the flaps were retracted, turbulence from the wing root stall struck the horizontal stabilizer, causing vibrations. As a countermeasure, the fillets were enlarged.

 

[blackkite]

Flap
To gain an advantage in maneuverability, especially turning ability, in combat with land-based and carrier-based aircraft, Kawanishi developed an automatic air combat flap that automatically operates the Fowler flaps at the optimal angle according to speed and load. This was a unique invention by Kawanishi that enables automatic adjustment of the flaps using a container filled with mercury (a type of manometer (liquid column pressure gauge)) to detect dynamic pressure and load. The Kyoufu had a relatively large wing loading to achieve high speed, but this automatic air combat flap succeeded in giving it turning ability that could keep up with the Type 2 floatplane fighter, which had a smaller wing loading. The device installed on the Kyoufu was a prototype, and a more complete version was installed on the Shiden.

 

[blackkite]

Floats
The floats consisted of a main float under the fuselage and auxiliary floats under both wings, similar to the type 2 seaplane fighter. The main floats were supported at the front by a V-shaped strut with a small angle, and at the rear by a thin, wide strut in the axial direction, each designed to reduce air resistance (this is the opposite of the strut arrangement on the type 2 seaplane fighter. Initially, the auxiliary floats were considered to be retractable like those on the Shiun, but after the troubles with the Shhiun, they were made fixed to avoid complicating the mechanism.

‹•—

 

[blackkite]

Propeller
Contra-rotating propellers on Kyofu's prototype
The prototype used a contra-rotating propeller with two propeller blades, just like the Shiun, to eliminate the deflection of the aircraft caused by the spiral propeller wake. This made takeoff and landing on water easier, and the maneuverability and directional stability were good, and it was very well received by test pilots. However, it was not possible to eliminate the poor maintainability and oil leakage caused by the complexity of the propeller reduction gear, which was also a problem with the Shiun, so the mass-produced model was switched to a normal three-blade propeller. However, in the early production model, a gap was left where the second propeller was supposed to be, giving the propeller spinner a distinctive appearance of protruding forward from the cowl opening.
In addition, in later production models, the collective exhaust pipe was changed to a thrust-type single exhaust pipe, and the front end of the cowl was extended, and the rear of the propeller spinner, which had redundant space as a remnant of the contra-rotating propeller, was covered by the cowl.
The left torque of the Kasei engine, with a takeoff output of 1,460 horsepower, was so strong that the foot bar had to be operated with considerable force to counteract it, making takeoff and landing on water difficult.

 

[Justo Miranda]

Some additional info here

 

[Justo Miranda]

Post-2

 

[Justo Miranda]

Post-3

 

[blackkite]

Effectiveness of Air Combat Flaps
The Naval Aviation Technical Arsenal's Aircraft Department conducted experiments with air combat flaps from December 1942 to February 1943. Data was obtained by recording the course of the flight with a motion picture theodolite and using a self-recording accelerometer. The experimental altitude was 2,000m. The weight of the strong wind during the experiment was 3,500kg, and the wing loading was 148.9kg/m2. When air combat flaps were used, the turning radius was reduced to 70% - 80% of the normal. There was no reduction in turning time. The diameter of the loop was reduced, and the time required to loop was also reduced.

Turning
When Kyufu approached at 148 knots and a loop was performed, the load was 3.3G, the turning radius was 180m, and the time required was 15.5 seconds.

In contrast, when approaching at 151 knots with flaps at 19 degrees, the load was 4.1G, the radius was 140m, and the time was 14.5 seconds.

Somersault
When approaching at 190.5 knots without flaps, the loop diameter was 305m with a maximum load of 3.4G. It took 11 seconds to reach the top of the loop, with a speed of 105.4 knots, a load of 1.65G, and an altitude difference; of 437m (from the point of approach to the top of the somersault). The time required to complete the loop was 23 seconds, the altitude difference was -111 m (from the approach point to the bottom of the somersault), and the speed was 184.5 knots.

In contrast, when approaching at 189.4 knots and with flaps at 19 degrees, the loop diameter was 250 m and the maximum load was 4.0 g. The time to reach the top of the loop was 9.5 seconds, the altitude difference was 398 m (from the approach point to the top of the somersault), the speed was 95.5 knots, and the load was 2.0 g. The time to complete the loop was 17.5 seconds, the altitude difference was 95 m (from the approach point to the bottom of the somersault), and the speed was 142 knots.

There was an altitude difference of 200 m between when the air combat flaps were used and when they were not used, and the speed reduction was quite large when the air combat flaps were used.

 

[blackkite]

Operation and Evaluation
The Kyoufu was officially adopted on December 21, 1943, but by that time the Battle of the Solomon Islands had already been decided by the US military victory, and Japan was on the defensive, advocating the absolute defense of its national defense sphere, and the field for this aircraft, which was developed for the purpose of invading islands, had almost disappeared. Despite this situation, at the same time as its adoption, the Kyoufu was deployed to seaplane units deployed on Ambon Island in Indonesia and Penang Island off the west coast of the Malay Peninsula, and although the number was small, it was reported that it shot down B-24s and their patrol aircraft type PB4Ys and B-29s. In anti-bomber combat, it seems that the tactic of dropping a time-detonated 30 kg bomb from above the enemy aircraft and damaging it by the explosion was often adopted. Meanwhile, in mainland Japan, it was deployed to the Sasebo Air Group and the Otsu Air Group (Lake Biwa) and was assigned to air defense duties, but had almost no combat record.[8] It was also used as a direct cover for Operation Kikusui No. 1.

On February 16, 1945, off the coast of Tateyama, Chiba Prefecture, the Kyofu entered the battle by interrupting an F6F engaged in combat with a Zero-type carrier-based fighter, and after a dogfight, it was reported that it had destroyed one. This was the only victory Kyofu had achieved against an enemy fighter.

In the end, the aircraft missed its scheduled appearance, and the A6M2 floatplane, which was supposed to be a stopgap, ended up playing a more active role. However, it could be said that it was precisely because of these circumstances that Kyofu became the basis for the Shiden. The Navy at the time also realized thatKyofu was not suited to the times, so the number of orders was greatly reduced from the planned number, but this made Kyofu concerned about the slump in the business and prompted the development of the Shiden, a land-based version of the Kyofu. The Shiden inherited the features of the original aircraft, such as laminar flow wings and automatic air combat flaps, and showed its final fighting spirit at the end of the war.

Only Kawanishi produced the Kyofu, and a total of 97 aircraft were produced, including prototypes. Of these, about 31 survived at the end of the war. All aircraft produced were classified as the Kyofu Type 11, but there are said to have been plans to develop a derivative model, the Kyofu Type 22, which incorporated the Shiden Type 21 as a seaplane.
(Source Japanese wikipedia)

 

[airman]

Operation and Evaluation
The Kyoufu was officially adopted on December 21, 1943, but by that time the Battle of the Solomon Islands had already been decided by the US military victory, and Japan was on the defensive, advocating the absolute defense of its national defense sphere, and the field for this aircraft, which was developed for the purpose of invading islands, had almost disappeared. Despite this situation, at the same time as its adoption, the Kyoufu was deployed to seaplane units deployed on Ambon Island in Indonesia and Penang Island off the west coast of the Malay Peninsula, and although the number was small, it was reported that it shot down B-24s and their patrol aircraft type PB4Ys and B-29s. In anti-bomber combat, it seems that the tactic of dropping a time-detonated 30 kg bomb from above the enemy aircraft and damaging it by the explosion was often adopted. Meanwhile, in mainland Japan, it was deployed to the Sasebo Air Group and the Otsu Air Group (Lake Biwa) and was assigned to air defense duties, but had almost no combat record.[8] It was also used as a direct cover for Operation Kikusui No. 1.

On February 16, 1945, off the coast of Tateyama, Chiba Prefecture, the Kyofu entered the battle by interrupting an F6F engaged in combat with a Zero-type carrier-based fighter, and after a dogfight, it was reported that it had destroyed one. This was the only victory Kyofu had achieved against an enemy fighter.

In the end, the aircraft missed its scheduled appearance, and the A6M2 floatplane, which was supposed to be a stopgap, ended up playing a more active role. However, it could be said that it was precisely because of these circumstances that Kyofu became the basis for the Shiden. The Navy at the time also realized thatKyofu was not suited to the times, so the number of orders was greatly reduced from the planned number, but this made Kyofu concerned about the slump in the business and prompted the development of the Shiden, a land-based version of the Kyofu. The Shiden inherited the features of the original aircraft, such as laminar flow wings and automatic air combat flaps, and showed its final fighting spirit at the end of the war.

Only Kawanishi produced the Kyofu, and a total of 97 aircraft were produced, including prototypes. Of these, about 31 survived at the end of the war. All aircraft produced were classified as the Kyofu Type 11, but there are said to have been plans to develop a derivative model, the Kyofu Type 22, which incorporated the Shiden Type 21 as a seaplane.
(Source Japanese wikipedia)

then with four cannon of 20 mm instead 2 gun of 7,7 mm and two 2 cannon of 20 mm.

 

[airman]

https://www.cgtrader.com/3d-models/aircraft/historic-aircraft/kawanishi-n1k2-kyofu-rex - other speculative 3d models of enlarged version of Kyofu Type 22. I like this reconstruction.

 

[Justo Miranda]

Kawanishi N1K1-J Shiden​

With a mid-mounted wing and laminar flow aerofoil, the Shiden was designed at the end of 1941 to replace the Zero as standard carrier-based fighter of the IJN.

The choice was based on the mid-wing designs of the American naval fighters Wildcat and Buffalo that, at that time, looked better equipped to operate from aircraft carriers. The Shiden also considerably improved the roll rate compared to other low-wing designs.

However, while the American airplanes had a belly retractable undercarriage, the Shiden main legs retracted within the wing, as it happened with the Zero. This solution was to be problematic because the structure of the wing – originally designed for a floatplane – lacked the resistance to stand the impacts of deck landing.

To solve this issue, the joint of the main legs with the wings had to be positioned near the fuselage and, therefore, the legs were not long enough, and the propeller hit the ground. The Kawanishi designers were specialised in floatplanes and have no experience with retractable undercarriages; hence they tried to solve this problem with telescopic legs of great mechanical complexity, like those of the P-47 American fighter. When the Shiden was operational in February 1944, Japan had lost most of their aircraft carriers and almost all its naval pilots with experience on deck landing.

The airplanes of the IJN continued to operate from the ground bases, but the airdromes conditions were quite poor. A stripe of pounded earth and a few hastily built sheds on a remote tropical island were incompatible with the sophisticated mechanics of the Shiden.

The first airplanes of the 401st. Kokutai arrived at the Takao (Formosa) airdrome on August 31, 1944. Their mission was to intercept the B-29 airplanes based in Chengdu (China) on their route to Japan. The operation was a failure. Despite themselves, the Japanese pilots discovered that their maximum speed at an altitude of 6,000 m was almost the same than the cruising speed of the B-29 at 9,000 m. They simply could not intercept them. When the alarm was sounded with advance enough, the Shiden tried to climb up to 9,500 m to perform just one frontal attack, facing the intense fire of dozens of the B-29 heavy machine guns. Besides, they could not afford the additional weight of an extra detachable fuel tank and had just fuel enough to return to base.

Another unpleasant surprise revealed the low performance of the brakes, something that should not be extremely important over aircraft carriers although it was vital in an earth stripe under rain. To stop the airplane the pilots acquired the habit of getting out of the landing strip, to brake over the loose earth on the sides, with disastrous consequences for the delicate telescopic mechanism of the legs. The efficiency of next take off was seriously hindered as the legs incompletely retracted within its housing under the wing, thus considerably reducing the airplane speed and making of landing a very dangerous exercise.

Engines also failed. Originally designed for the 91-octane fuel available in 1941, they had to work with 87 octanes, or even sometimes mixed with a volatile oil extracted from pine tree roots that lowered the fuel to 85 octane. It was so contaminated with impurities that American Jeeps that used this fuel during occupation suffered engine failures.

The Nakajima NK9H Homare 21 engine was not easy to start at tropical temperatures and its cowling design was not adequate for efficient refrigeration. During climbing the cowl air control flaps should be fully opened to avoid an excessive heating of the cylinder heads, generating a considerable drag. The Homare also lost power above 7,000 m at a fast rate; although it has been designed to generate 1,990 hp with 85 octane, it actually was able to only generate 1,800 hp.

The Shiden was at its most efficient in fighting at medium and low altitude, thanks to its automatic flaps and powerful weapons. It performance equalled that of the Hellcat and Thunderbolt airplanes, being slightly below the Mustang and Corsair models.

The Shiden was however very useful defending the airdromes of Formosa and Luzon against the strafing operations of the American naval fighters. But it was incapable to defend its own bases to the south of Kyushu against the B-29 offensive during the spring of 1945.

During the last days of December 1944, the 402nd Kokutai, based in Marcott (Luzon) was converted into a suicide unit to perform attacks against US landings on Mindoro Island. By the beginning of January, the Squadron received 12 Shiden of the N1K1-Jb model that were able to transport two bombs of 250 kg under the wings and one 400 litres detachable fuel tank under the fuselage. On January 2, when they were ready for take-off, they suffered an attack by P-47 airplanes destroying eight Shiden. The four remaining machines were used to perform raids against Allied ships in the Lingayen Gulf during the following days.

Meanwhile, the technicians of the Yokosuka naval test centre had reached the conclusion that neither the Kawanishi N1K1-J Shiden nor the Mitsubishi J2 M3 Raiden were right to fight against the B-29 airplanes. They recommended the manufacturing of the N1K2-J Shiden KAI, an improved version of the Shiden, as a land based standard fighter for the IJN. It was a painful decision, considering that there were over 1,000 units of Shiden and 566 of Raiden already manufactured.

By August 1944 both models, together with the Yokosuka D4Y Suisei, the Nakajima B6N Tenzan and the Aichi B7A Ryusei, were allocated to the Kokoku Heiki Go.1 programme of reforms that had the objective to optimize the design of these airplanes for kamikaze missions. They installed supports for the new RATO rockets, developed by the IJN for take off from their light aircraft carriers, and one bomb of 500 to 800 kg.

The N1K1-J KAI-Ko was the first modified version of the Shiden. It had a Toku-Ro.1 Type 2 rocket, with 600 kg peak thrust and 30 seconds of life, under the rear (strengthened) fuselage. Its objective was to help the airplane taking off from short airstrips when heavily loaded. Another addition was the installation of a launch device for one anti-ship bomb Number 50 model 2 of 507 kg under the central section of the fuselage.

The concept seemed outdated in 1945 and it was considered to provide the Shiden with the new rocket booster package developed by Kugisho. Aerodynamically adapted to the Shiden belly, it contained four Toku-Ro.1 Type 1 rockets with 600 kg peak thrust and 10 seconds of life, two Toku-Ro.1 Type 2 rockets and a Number 80 Model 2 anti-ship bomb, fixed and without any tailfin.

The two Type 2 rockets were used in RATO configuration during take off while the two central Type 1 rockets were used to gain speed when confronting the defence fighters of the US Fleet. The two forward Type 1 served to provide a 60 km speed increase during the terminal dive over the Allied ships, thus reducing the time of exposure to the 40 mm Antiaircraft Artillery.

The 20 mm guns were removed from the ‘KAI-Otsu’ to reduce weight, leaving the two type 97 machine guns of 7.7 mm that were installed behind the engine as the only armament to defend from the Allied fighters. It had been ascertained that the kamikaze pilot could better estimate distances and angles for an optimal impact if the tracer bullets were shot during the terminal dive.

By the end of 1944, both the conventional and suicide version of the Suisei started to use I.S.R. type rockets of 12 cm to distort the aiming of the AA Allied gunners during the terminal dive. These rockets had been originally developed for Antiaircraft Artillery usage, with incendiary pellets and shrapnel warhead, in imitation of the German Föhn. They could be mass shot from a square matrix or one by one from iron tubes similar to the German W.Gr 21. The Suisei carried two or four tubes under the wings, something that was generalized for all the airplanes of the Kokoku Heiki Go.1.

Four Shiden had been already modified by the end of the war, but they were preserved to counteract the invasion of Kyushu and never went into operation.

Kawanishi N1K2-J Shiden KAI​

Designed in the spring of 1943 to succeed the Shiden, the Kawanishi N1K2-J Shiden KAI was its simplified version with a more reliable and similarly powerful engine that was 222 kg lighter. A total number of 23.000 parts were removed and it had a lower wing and simpler undercarriage.

These changes improved the chances to compete against the B-29 airplanes, although its armament of four 20 mm guns was somehow insufficient to destroy these gigantic machines. Thanks to the use of Type 3 Number 6 Mark 27 Model 1, with 60 kg rocket bombs - launched from rails installed under the wings - but also through ramming attacks, the Shiden KAI was able to shoot down some of the Superfortress.

On 7 April the B-29 42-63512 was rammed over Tokyo by a KAI of the 301st Kokutai. Between 18 April 18 and 11 May 1945 the Shiden KAIs of the 343rd Kokutai performed 120 interception operations against the B-29 that were striking the kamikaze bases of Oita, Tachiarai, Kanoya and Chiran, to the South of Kyushu. On April 22, two KAIs of the 407th Kokutai shot the belly of an unidentified B-29 at 8,000 m over Kanoya. The bomb bay exploded as a result and the three airplanes were destroyed.

On 5 May two B-29 bombers, with numbers 42-65305 and 44-69899, were shot down by Shiden KAIs of the 343rd Kokutai over Oita, one by the rocket-bombs and the other by ramming. On May 7, the 42-63549 and the 44-69887 B-29 were also destroyed over the same place and following same pattern of attack.

During the combats of these days, three KAIs of the 343 rd Kokutai were shot down by the machine guns of the B-29 bombers, seven by forced landing and fifteen by bombing. At medium altitude fighting, the KAI was more efficient than the Shiden, a serious opponent to the Mustang under 4,000 m and to the Corsair at low level. On June 22, 1945 one KAI of the 343 rd Kokutai rammed the Corsair FG-1D BuNo.88441 in a fight over Amami Oshima.

A total of just 428 Shiden KAIs were manufactured to be used by the elite units. The KAI was too valuable to be used in suicide missions, but during the Okinawa battle the IJN lost 29 aircrafts against the U.S. Navy fighters while escorting kamikaze groups.

By mid-1943, the effective blockade by the U.S. Navy Submarine Force began to strangle the Japanese economy and the aeronautical industry was particularly affected by increasing shortages of high aviation fuel and light alloys. On 8 September, Nakajima, Tachikawa and Mansyu were instructed by the IJA to use wood and steel as aluminium substitutes in the manufacture of the Hayate fighter.

In the version Ki.113, designed in the fall of 1944, Nakajima used steel in as many sub-assemblies as possible, but the excessive weight of the new airframe caused the abandoning of the project after the completion of the prototype early in 1945. Kawanishi proposed the construction of the N1K5-J, a steel version of the Shiden-KAI with 13.92 m extended wingspan, powered by one Mk 9A engine, but the project was dismissed because of excessive weight.

 

[Justo Miranda]

Kokoku Heiki​

In August 1944 the Japanese Technical Office Kaigun Koku Hombu published the specifications for the project Kokoku Heiki (Empire Weapon). It required the manufacturing of three classes of suicide airplanes that carrying a bomb of 800 kg would be capable of attacking the invasion fleets.

Kokoku Heiki Go.1 was a transformation program of existing naval airplanes to optimize their use in suicide missions. Based on the experience acquired with the Zero and the Val, the proposal was to modify the Kawanishi N1K1-J Shiden, the Mitsubishi J2M Raiden, the Yokosuka D4Y Suisei, the Nakajima B6N Tenzan and the Aichi B7A Ryusei.

Kokoku Heiki Go.2 should be a suicide bomber propelled by two centrifugal turbojets TsU-11, Ne-12 or Ne-30. Nakajima’s proposal was to manufacture the Maru-Ten whereas Yokosuka/Kugisho proposed the R2Y2 Keiun and the Tenga.

Kokoku Heiki Go.3 should be a conventional and easy to manufacture airplane, using non-strategic materials and designed to allow the installation of several types of reconditioned surplus engines. Kawanishi proposed the Tokko-Ki, Nakajima the Tsurugi, Sowa the Toka and Tachikawa the Ta-Go.

Kokoku Heiki Go.1



Kawanishi N1K1-J Shiden​

With a mid-mounted wing and laminar flow aerofoil, the Shiden was designed at the end of 1941 to replace the Zero as standard carrier based fighter of the IJN.

The choice was based on the mid-wing designs of the American naval fighters Wildcat and Buffalo that, at that time, looked better equipped to operate from aircraft carriers. The Shiden also considerably improved the roll rate compared to other low-wing designs.

However, while the American airplanes had a belly retractable undercarriage, the Shiden main legs retracted within the wing, as it happened with the Zero. This solution was to be problematic because the structure of the wing – originally designed for a floatplane – lacked the resistance to stand the impacts of deck landing.

To solve this issue, the joint of the main legs with the wings had to be positioned near the fuselage and, as a consequence, the legs were not long enough and the propeller hit the ground. The Kawanishi designers were specialised in floatplanes and have no experience with retractable undercarriages; hence they tried to solve this problem with telescopic legs of great mechanical complexity, similar to those of the P-47 American fighter. When the Shiden was operational in February 1944, Japan had lost most of their aircraft carriers and almost all its naval pilots with experience on deck landing.

The airplanes of the IJN continued to operate from the ground bases, but the airdromes conditions were quite poor. A stripe of pounded earth and a few hastily built sheds on a remote tropical island were incompatible with the sophisticated mechanics of the Shiden.

The first airplanes of the 401st. Kokutai arrived at the Takao (Formosa) airdrome on August 31, 1944. Their mission was to intercept the B-29 airplanes based in Chengdu (China) on their route to Japan. The operation was a failure. In spite of themselves, the Japanese pilots discovered that their maximum speed at an altitude of 6,000 m was almost the same than the cruising speed of the B-29 at 9,000 m. They simply could not intercept them. When the alarm was sounded with advance enough, the Shiden tried to climb up to 9,500 m to perform just one frontal attack, facing the intense fire of dozens of the B-29 heavy machine guns. Besides, they could not afford the additional weight of an extra detachable fuel tank and had just fuel enough to return to base.

Another unpleasant surprise revealed the low performance of the brakes, something that should not be extremely important over aircraft carriers although it was vital in an earth stripe under rain. To stop the airplane the pilots acquired the habit of getting out of the landing strip, to brake over the loose earth on the sides, with disastrous consequences for the delicate telescopic mechanism of the legs. The efficiency of next take off was seriously hindered as the legs incompletely retracted within its housing under the wing, thus considerably reducing the airplane speed and making of landing a very dangerous exercise.

Engines also failed. Originally designed for the 91 octane fuel available in 1941, they had to work with 87 octanes, or even sometimes mixed with a volatile oil extracted from pine tree roots that lowered the fuel to 85 octanes. It was so contaminated with impurities that American Jeeps that used this fuel during occupation suffered engine failures.

The Nakajima NK9H Homare 21 engine was not easy to start at tropical temperatures and its cowling design was not adequate for efficient refrigeration. During climbing the cowl air control flaps should be fully opened to avoid an excessive heating of the cylinder heads, generating a considerable drag. The Homare also lost power above 7,000 m at a fast rate; although it has been designed to generate 1,990 hp with 85 octanes, it actually was able to only generate 1,800 hp.

The Shiden was at its most efficient in fighting at medium and low altitude, thanks to its automatic flaps and powerful weapons. It performance equalled that of the Hellcat and Thunderbolt airplanes, being slightly below the Mustang and Corsair models.

The Shiden was however very useful defending the airdromes of Formosa and Luzon against the strafing operations of the American naval fighters. But it was incapable to defend its own bases to the south of Kyushu against the B-29 offensive during the Spring of 1945.

During the last days of December 1944 the 402nd Kokutai, based in Marcott (Luzon) was converted into a suicide unit to perform attacks against US landings on Mindoro Island. By the beginning of January the Squadron received 12 Shiden of the N1K1-Jb model that were able to transport two bombs of 250 kg under the wings and one 400 litres detachable fuel tank under the fuselage. On January 2, when they were ready for take off, they suffered an attack by P-47 airplanes destroying eight Shiden. The four remaining machines were used to perform raids against Allied ships in the Lingayen Gulf during the following days.

Meanwhile, the technicians of the Yokosuka naval test centre had reached the conclusion that neither the Kawanishi N1K1-J Shiden nor the Mitsubishi J2 M3 Raiden were right to fight against the B-29 airplanes. They recommended the manufacturing of the N1K2-J Shiden KAI- an improved version of the Shiden – as a land based standard fighter for the IJN. It was a painful decision, considering that there were over 1,000 units of Shiden and 566 of Raiden already manufactured.

By August 1944 both models, together with the Yokosuka D4Y Suisei, the Nakajima B6N Tenzan and the Aichi B7A Ryusei, were allocated to the Kokoku Heiki Go.1 programme of reforms that had the objective to optimize the design of these airplanes for kamikaze missions. They installed supports for the new RATO rockets, developed by the IJN for take off from their light aircraft carriers, and one bomb of 500 to 800 kg.

The N1K1-J KAI-Ko was the first modified version of the Shiden. It had a Toku-Ro.1 Type 2 rocket, with 600 kg peak thrust and 30 seconds of life, under the rear (strengthened) fuselage. Its objective was to help the airplane taking off from short airstrips when heavily loaded. Another addition was the installation of a launch device for one anti-ship bomb Number 50 model 2 of 507 kg under the central section of the fuselage.

The concept seemed outdated in 1945 and it was considered to provide the Shiden with the new rocket booster package developed by Kugisho. Aerodynamically adapted to the Shiden belly, it contained four Toku-Ro.1 Type 1 rockets with 600 kg peak thrust and 10 seconds of life, two Toku-Ro.1 Type 2 rockets and a Number 80 Model 2 anti ship bomb, fixed and without any tailfin.

The two Type 2 rockets were used in RATO configuration during take off while the two central Type 1 rockets were used to gain speed when confronting the defence fighters of the US Fleet. The two forward Type 1 served to provide a 60 km speed increase during the terminal dive over the Allied ships, thus reducing the time of exposure to the 40 mm Antiaircraft Artillery.

The 20 mm guns were removed from the KAI-Otsu to reduce weight, leaving the two type 97 machine guns of 7.7 mm that were installed behind the engine as the only armament to defend from the Allied fighters. It had been ascertained that the Kamikaze pilot could better estimate distances and angles for an optimal impact if the tracer bullets were shot during the terminal dive.

By the end of 1944, both the conventional and suicide version of the Suisei started to use I.S.R. type rockets of 12 cm to distort the aiming of the AA Allied gunners during the terminal dive. These rockets had been originally developed for Antiaircraft Artillery usage, with incendiary pellets and shrapnel warhead, in imitation of the German Föhn. They could be mass shot from a square matrix or one by one from iron tubes similar to the German W.GR 21.The Suisei carried two or four tubes under the wings, something that was generalized for all the airplanes of the Kokoku Heiki Go.1.

Four Shiden had been already modified by the end of the war, but they were preserved to counteract the invasion of Kyushu and never went into operation.

Kawanishi N1K2-J Shiden KAI​

Designed in the spring of 1943 to succeed the Shiden, the Kawanishi N1K2-J Shiden KAI was its simplified version with a more reliable and similarly powerful engine, and 222 kg lighter. A total of 23.000 parts were removed and it had a lower wing and simpler undercarriage.

These changes improved the chances to fight the B-29 airplanes, although its armament of four 20 mm guns was somehow insufficient to destroy these gigantic machines. Thanks to the use of Type 3 Number 6 Mark 27 Model 1, with 60 kg rocket bombs - launched from rails installed under the wings - but also through ramming attacks, the Shiden KAI was able to shot down some of the super fortresses.

On April 7 the B-29 42-63512 was rammed over Tokyo by a KAI of the 301st Kokutai. Between April 18 and May 11, 1945 the Shiden KAIs of the 343rd Kokutai performed 120 interception operations against the B-29 that were striking the kamikaze bases of Oita, Tachiarai, Kanoya and Chiran, to the Shouth of Kyushu. On April 22, two KAIs of the 407th Kokutai shot the belly of an unidentified B-29 at 8,000 m over Kanoya. The bomb bay exploded as a result and the three airplanes were destroyed.

On May 5, two B-29 bombers, with numbers 42-65305 and 44-69899, were shot down by Shiden KAIs of the 343rd Kokutai over Oita, one by the rocket-bombs and the other by ramming. On May 7, the 42-63549 and the 44-69887 B-29 were also destroyed over the same place and following same pattern of attack.

During the combats of these days, three KAIs of the 343 rd Kokutai were shot down by the machine guns of the B-29 bombers, seven by forced landing and fifteen by bombing. At medium altitude fighting, the KAI was more efficient than the Shiden, a serious opponent to the Mustang under 4,000 m and to the Corsair at low level. On June 22, 1945 one KAI of the 343 rd Kokutai rammed the Corsair FG-1D BuNo.88441 in a fight over Amami Oshima.

A total of just 428 Shiden KAIs were manufactured to be used by the elite units. The KAI was too valuable to be used in suicide missions, but during the Okinawa battle the IJN lost 29 aircrafts against the U.S. Navy fighters while escorting kamikaze groups.