View Full Version : Why was the KI-61KO made?

08-02-2005, 05:49 AM
I can not figure out why this plane was made. The early Japenese planes (zero) were more agile had better fire power and seemed every bit as fast.

So, what was the reasoning behind the KI-61KO?


08-02-2005, 06:16 AM
-its an Army plane. Zero is Navy
-it should be fast - actual its ~40km/h too slow in game. and it was sure faster than the standart Army fighter Ki-43II http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif
- im comparison to the main Army fighter of that time , the Ki43II with two 12,7mm guns, it has a better armament
- its max dive speed is with over 800km/h IAS very good !
-it gave the real P-40 and P-39 pilots over NewGuinea some thoughts http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif
-the whole Ki61 series was a very important plane for the japanese Army , ~3000 build

08-02-2005, 06:19 AM
"Initial deliveries were made in February 1943 to the 23rd Dokuritsu Dai Shijugo Chutai at Ota, which acted as a conversion and training unit. The Hien initially entered combat in April 1943 when the 68th and 78th Sentais were transferred to the New Guinea theatre of operation. The aircraft subsequently appeared in every theatre in which the Japanese Army was involved. The Ki-61 immediately proved itself to be better suited for combat against its heavier-armed Allied opponents than was the Ki-43 Hayabusa. Although it was not as maneuverable as the earlier Ki-43, the Ki-61 had heavier armament, good armor protection for the pilot, and self-sealing fuel tanks. The Hien could be pushed over into a 45 degree dive very rapidly, and its diving performance was far superior to that of any other Japanese fighter. Its high diving speed worked to advantage against Allied fighters which relied on hit and run attacks from higher altitudes. In defensive operations, the Hien was especially difficult to counter, since the aircraft seldom offered a good target. When engaged in combat at a disadvantage, it could often escape by going into a half-roll followed by a dive, or else it would turn in and under the opposing plane, often getting in a deflection shot. The Hien completely outclassed the Curtiss P-40 in most combat encounters, unless the Allied fighter was being flown by the most experienced of pilots. The Hien was well-liked by its pilots and respected and feared by its opponents. However, the Ha-40 engine proved to be a maintenance headache, especially in the prevailing hot and damp weather of the New Guinea theatre. Main-bearing failures and oil-system faults were the primary problems. In addition, the power ratings of individual Ha-40 engines would vary greatly from one example to another, owing to poor quality control during manufacture. "


08-02-2005, 07:16 AM
the ki-61ko is favorite plane ^_^ it maybe not as manoverable as zero but can still easily outturn american plane and spitfire most importatnly can dive with hellcat, wildcat if need ^_^

08-02-2005, 08:05 AM
The answer quite simply is that the Ki-61 was a further development in the evolution of planes....

If you'll notice, all others of the Japanese at the time they were developed were "Radial" engined planes. Inline or V engined more compact allowing for a more streamlined shape. You'll also notice all other nations had made the move to them to a great degree....So though not new technology, it was the next step to try.

In truth the Ki-61 was a very advanced plane over the zero in many regards....The most important being Speed/Armor....What remained lacking was armament.......However, In truth by it's "prototype release" for combat (and I say prototype as it had not had it's bugs worked out till the 1d)....It was already outdated.

As to the Zero in relation...Well besides the Army/Navy differences (whole other topic)...The Ki-43 could out maneuver/climb the Zero....The Ki-61 was just slightly less agile then the Ki-43.......However, at this stage of combat fighter evolution WWI type dogfighting was long gone...Zoom and boom the new doctrine, where something like 90+% of all kills are made in a single pass.....So the Ki-61 was to catch up to that way of fighting.

Ki-61 innovations....
Unibody construction (body actually supported the engine not a frame wrapped in sheet metal like a 109)
Better Pilot armor
Better self sealing AND bullet "proofing" on fuel tanks.
Wing evaporation cooling systems.
Gyroscopic sights (very late model testing)
Modular construction...1d on

Trouble is, by late 42/43 the Japanese were playing catch-up with inline engine technology...Time was not on their side to experiment.

08-02-2005, 10:25 AM
but when you compare the Ki-61 to something like the Ki-84 or the N1K2-J Kai in late war the 61 really lacks a little...

08-02-2005, 11:13 AM
Originally posted by Snow_Wolf_:
but when you compare the Ki-61 to something like the Ki-84 or the N1K2-J Kai in late war the 61 really lacks a little...

and when you compare a P-40 to a P-51 the P-40 lacks a lot.....evolution http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

08-02-2005, 11:36 AM
Originally posted by Snow_Wolf_:
but when you compare the Ki-61 to something like the Ki-84 or the N1K2-J Kai in late war the 61 really lacks a little...

Yes, but we are talking a mid war vs late war design. You can not make a comparison. Compared to the pace of development of the pre-war years, a year during the war was like a light year. A plane designed even six months later was bound to be radically different and theoretically better.

08-02-2005, 11:43 AM
I was just reading up on this bird last night. Its the next plastic model I am going to build, so I did a little preliminary research. The engine is derived from the Daimler-Benz DB 601, but lightened and otherwise modified. Kawasaki had been building aircraft with inline engines since the early 1930's, influenced by the head desinger, a Dr. Vogt, who would later return to Germany later in the decade. His students carried on his design tradition at the company.
When the Allies first encountered the Hien (Swallow) over New Guinea they were very surprised. Intelligence had thought that it was the anticipated license built Bf-109 as they knew that the Japanese had obtained all the necessary licenses and blueprints. A code name of "Mike" was proposed for this aircraft (licensed Bf-109). But the aircraft had different lines although a strong influence of the Axis aircraft using the DB601 engine. Therefore it was thought to be a design knock-off of the Macchi M.C. 202 and the code name of "Antonio" was set aside for it. When it was determined it was not, the code name of "Tony" was selected.
It's a very interesting aircraft, although its performance in this game is not up to historic standards.

08-02-2005, 01:07 PM
Originally posted by MichaelMar:
I can not figure out why this plane was made. The early Japenese planes (zero) were more agile had better fire power and seemed every bit as fast.

So, what was the reasoning behind the KI-61KO?

The Ki-61 can't be really compared to the Zero...the Japanese Navy and Japanese Army were in a very high level of competition. They had their own planes, their own weapons, bullet standards, bombs, and everything. The Betty is a Japanese Navy medium bomber (but operating from land bases)...the Japanese Navy operated the Sally bomber which was supposed to do essentially the same role but it was Japanese Army.

Ki-61 should be compared to the Ki-43 Oscar. In comparison to the Oscar, the Ki-61 was much better armed, better protected, much faster, and more importantly...could dive with American planes who were used to being able to dive out of combat and escape. Evolution.

08-02-2005, 02:05 PM
Originally posted by VW-IceFire:
Ki-61 should be compared to the Ki-43 Oscar. In comparison to the Oscar, the Ki-61 was much better armed, better protected, much faster, and more importantly...could dive with American planes who were used to being able to dive out of combat and escape. Evolution.

Actually, you almost can't even compare it to the Oscar as just like in the U.S. it would have been Vaught(sp?), Grummen, Republic, Bell, etc...

In Japan it was Kawasaki, Nakajima, Mitsubishi, etc...So different paths and proposals made by different companies all wanting "contracts"....So various concepts tried by various companies....The Ki-84 the evolved Ki-43......

Odd...funny how "business as usual" worked exactly the same for both sides http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

08-02-2005, 08:32 PM
The army realized in 1939 that the traditional Japanese aircraft design philosophy wasn't going to cut it when it got thrumped by Soviet fighters in Manchuria. I'm sure the exploits of the Germans over Poland and France along with contemporary fighter designs from the US and Europe also had something to do with the change in focus from manueverability at all costs to heavy, fast, well armoured fighters.

When it came to splitting what meagre reasources Japan had the Army always came out on top because of its greater political influence. I'd bet that the Navy and the Army both started seeing the light in 39 but the Army was really the only branch in any position to do anything about it.

As telsono has already said, the Kawasaki company had been looking at inline engines since the early 20s when its chief designer was Vogt. This had actually agravated the Japanese army until if found itself in need of a "modern" fighter more in line with the design philosophies of Germany, England and the US.

The Ki-61 would have been a fantastic early war airplane. It was far more advanced than the Me109E and P-40 and had just as much room to grow as either design. Unfortunately the project was started way to late and instead of advancing the plane sort of stagnated. The Army realized that they had a quality fighter but the inline engine was just too much to deal with in the heat of the Pacific and resources were shifted to more advance designs like the Raiden and Ki-84.

IMHO, the ki-61 could have been one of the best fighters of the war and could have easily surpassed the performance of even the best me109s if its power plant had been upgraded, but there was no one really working on inline engine development in Japan like there was in the Allied countries and Germany so the plane's development stopped for all intents and purposes and it fought most of its career with a hopelessly out of date engine.

08-02-2005, 10:47 PM
Also bear in mind that the IJAAF asked Daimler-Benz to tailor the engine specifications for the KI 61 for mid altitude operation. It's critical altitude is very similar to the P40's. The Technical Air Intelligence Center manual of Japanese aircraft lists it's maximum speed as 361mph @ 15,800ft. (Cannot be achieved in game). Whereas they estimate the top speed of the "Tony II" with the stillborn Ha 140 (DB 605 copy, 1440hp at WEP) as 423MPH @ 28,000ft.

The overall design was not lacking, just the powerplant.


08-03-2005, 12:11 AM
Actually I have "begun" to learn tonight they were not copies.....simply used for concept. In actuality there was even a Navy version I have been informed used on the "Judy" called an "Atsuta Model 21"....(vs. Ha40)....The Model 21 was "more" similar to the DB601, yet none of the 3 were alike.

Sadly, as the Ha140 had trouble getting fully into production, that was when the Ki-100 came into existence...The slow deliveries of the fighter intolerable, and so the "Desperation Fighter" was born to utilize the remaining engineless fuselages.......

(know I'm still learning all this myself so don't take it for gospel)...

Information relating to the engines above from the extensive work of Mr. J. Long....His reports stunning and of which I'm grateful for his generous patience.

08-03-2005, 05:41 PM
"Sadly, as the Ha140 had trouble getting fully into production.."

He, he, that's an understatement, the factory where they were being produced was pounded into rubble by American heavy bombers.

08-03-2005, 07:25 PM
I read an article many years ago about the Hein. It was developed to beat the P-40, and in this it was successful. The Japanese even tested it against a captured P-40. But by the time it got into service it was up against P-51's, P-38's, F4U's, and F6F's. So it's ability to handle a P-40 was no longer relevant. It pretty much sums up Japanese advances during the war: too little, too late.


08-04-2005, 02:20 AM
It is NOT too slow in game- according to William Green's "Warplanes of the Second World War: Fighters Volume 3" the Ki.61 had a top speed of 346 mph TAS at approximately 16,500 ft. At 5000 metres the Ki.61 achieves 420 kph IAS in level flight in PF- which is approximately 346 mph TAS.

A plane which IS undermodelled as far as top speed is concerned is the F2A-2 which should be as fast as the Ki.61- but isn't. Same goes for the B-239 and Buffalo Mk. 1, which are also modelled with insufficient top speed (though they were not as fast as the F2A-2).

08-04-2005, 04:23 AM
so what ??
well, Rene Francillion in "Japanese Aircraft of the Pacific War" has the Ki-61-Otsu at 368mph ore 592km/h at 4860m TAS !
thats also the speed given in the game object viewer.
in game the plane is flying as max 570km/h TAS. (did a new test , with more patience http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif )

oleg said, he would look behind it.

and this is a Hien topic, no Brewster topic. lot of planes have percformance that are not following books we all have read................. and even such books are stating different datas - as you see here ! http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

08-04-2005, 04:52 AM
~S~ All
Knowing the Japanese ability to copy anything it is a good bet that the KI-61 is nothing but a knockoff of the HE-112 of which the Japanese took possesion of 30 of them between 1937-38.




08-04-2005, 04:58 AM
they not look that similar especially when compare those two profile side by side, maybe inspired by but I doubt copy.

"368mph" is most quoted speed figure i blieve it what see most often I

08-04-2005, 05:42 AM
The KI61 was an entirely Japanese/Kawasaki design. There is absolutley no resemblence in it's structure, only a passing similarity in the engine cowling area because of the DB based engine.

And every top speed figure I've ever seen puts it's speed at or above 360mph.

08-04-2005, 07:38 AM
Actually though similar in shape the cowling area was radically different and much more advanced......

Like I said above it was a Uni-body sort of construction, the fusalage sheet metal actually supporting the engine where the BF109 used an actual tubular frame and connecting rods with simply a sheet metal skin wrapped around it....

The Ki-61 only had a light cover over the top and bottom for access....as seen below......Text and leaders in far bottom right pointing to the motor mount screw location....


08-04-2005, 08:32 AM
Originally posted by NS38th_Aristaus:
~S~ All
Knowing the Japanese ability to copy anything it is a good bet that the KI-61 is nothing but a knockoff of the HE-112 of which the Japanese took possesion of 30 of them between 1937-38.




The He100 was sold to the Japanese Navy not the Army and for the most part they never shared anything. The He100 was to be used as a template for a new land based fighter for the Navy. The production equipment necessary to establish the production line never arrived from Germany and the Japanese production of the plane never started. Some of the info I've read hints that the overall design concept of the Ki-61 was influenced by the He100 but given their radical differences in construction and appearance and the fact that the Navy and Army didn't share resources or information, I doubt it was the case.

08-04-2005, 12:10 PM
Ki 61 II with Ha140 (1475hp) had max. speed about 610 km/h. Even with with addition of let's say MW50, Ki61 II would hardly fly faster then 640 km/h. Still rather slow for 44/45.
It would be really interesting how would Ki61 fare against VVS 43/44 fighters..

08-04-2005, 01:17 PM

* The confusion of the Ki-61 with German and Italian fighters had some basis in the aircraft's origins. Between 1923 and 1933, Kawasaki Aircraft Engineering Company's head designer was a German named Dr. Richard Vogt, who returned to Germany in 1933 to take a similar position at the firm of Blohm und Voss. Not surprisingly, Kawasaki continued to be strongly influenced by Dr. Vogt's beliefs after he left, particularly a faith in the merits of liquid-cooled inline engines. This made Kawasaki something of a heretic among Japanese aircraft manufacturers, who preferred air-cooled radials.

In March 1938, Kawasaki signed an agreement with Daimler-Benz of Germany for manufacturing rights to the liquid-cooled inline engines then under development by the German firm. In April 1940, a Kawasaki engineering team visited Daimler-Benz in Stuttgart to obtain plans and samples of the DB-601A engine, then being used in the Bf-109.

The Kawasaki engine team managed to increase the take-off power of their version of the engine to 875 kW (1,175 HP) and reduce its weight slightly. The engine was put into production in November 1941. It was designated the "Ha-40", or "Army Type 2", though it would be later redesignated the "Ha-60" in a combined Army/Navy nomenclature.

In the meantime, certain officers at the Air Headquarters of the Imperial Japanese Army (IJA) were very interested in the new fighters powered by liquid-cooled engines being developed in Britain, the USA, the USSR, Germany, and France. The Japanese Army also had unpleasant experiences in air combat against Soviet Polikarpov I-16 fighters during the beating the Japanese took from the USSR in a border clash over Manchuria in the summer of 1939. This experience suggested that the single-minded focus on agility above all that characterized Japanese fighter design doctrine might need to yield to a focus on speed and improved armor protection and firepower.

* In February 1940, the IJA initiated work with Kawasaki on two single-seat fighters based on the DB-601A derivative engine: a heavy interceptor, designated the "Ki-60", and a general-purpose fighter, designated the "Ki-61". Kawasaki decided to build the Ki-60 first, and the design team, under Kawasaki chief designer Takeo Doi and his deputy Shin Owada, constructed three prototypes of the interceptor in 1941.

The Ha-40 engine was not available at that time, so the three aircraft were powered by sample DB-601A engines obtained from Germany. The Ki-60 was a low-wing monoplane, with plenty of power and heavy armament by Japanese standards. The first and second prototypes had two 12.7 millimeter (0.50 caliber) Ho-103 machine guns mounted on the nose in front of the pilot and two 20 millimeter Mauser MG-151 cannons, one mounted in each wing, for a total of four guns. The third prototype had four 12.7 millimeter guns.

_____________________ _________________ _______________________

spec metric english
_____________________ _________________ _______________________

wingspan 10.5 meters 34 feet 5 inches
wing area 16.2 sq_meters 174.4 sq_feet
length 8.47 meters 27 feet 9 inches
height 3.7 meters 12 feet 2 inches

empty weight 2,150 kilograms 4,740 pounds
loaded weight 2,750 kilograms 6,063 pounds

max speed at altitude 560 KPH 348 MPH / 303 KT
service ceiling 10,000 meters 32,800 feet
_____________________ _________________ _______________________

Flight tests began in March 1941 and showed that the Ki-60 was too unmaneuverable and didn't meet its speed and climb requirements. Various tweaks to improve the aircraft failed, and so the Ki-60 was abandoned.

* The experience was valuable, however. Design work on the Ki-61, whose development had been proceeding in parallel with the Ki-60 since December 1940, incorporated new features derived from the lessons learned by the Ki-60 program:

* Aerodynamic refinements were added.

* The wing was increased in size and length to improve maneuverability.

* The fuselage was slimmed down to improve speed.

* Armament was reduced by replacing the two 20 millimeter guns in the wings with either two 12.7 millimeter Ho-103 guns or two Type 89 7.7 millimeter (0.303 caliber) guns.

* Fuel capacity was increased, as required by offensive fighter operations, which dictated longer range than required by an interceptor.

* The landing gear track was widened to allow use from primitive forward airfields.

The first prototype was rolled out in early December 1941, and its performance proved excellent. Eleven more prototypes were delivered to the IJA for intensive trials. The Ki-61 was pitted against other Japanese fighters, as well as against the Messerschmitt Bf-109E-3, of which two had been bought by the IJA from the Germans, and the Curtiss P-40E, several of which had fallen into Japanese hands after the capture of the Dutch East Indies.

While test pilots were a little skeptical of the new aircraft at first, pilots with combat experience appreciated the Ki-61's self-sealing fuel tanks, heavier armor and armament, and fast diving speed. The air combat tests showed the Ki-61 to be faster than all its adversaries, and easily out-maneuvered all of them except the Japanese Nakajima Ki-43 ("Oscar").

The 13th Ki-61, a production prototype, was delivered in August 1942. The IJA gave the green light for production, and the fighter began to roll off the assembly line, with 34 delivered by the end of 1942. The type was formally known as the "Army Type 3 Fighter Model 1 Hien", or "Ki-61-I".

The production machines differed from the prototypes only in tweaky details. Initial production consisted of two variants: the "Ki-61-Ia", with two 12.7 millimeter guns in the nose and a 7.7 millimeter gun in each wing, for a total of four guns; and the "Ki-61-Ib", with 12.7 millimeter guns in both fuselage and wings. These aircraft could be fitted with two 200 liter (53 US gallon) drop tanks.


* The Hien entered combat in the spring of 1943 in the New Guinea war zone, covering New Guinea, the Admiralty Islands, New Britain, and New Ireland. The new Japanese fighter caused some pain and consternation among Allied pilots, particularly when they found out the hard way that they could no longer go into a dive and escape as they had from lighter Japanese fighters. 5th Air Force Commander General George Kenney found his P-40 Warhawks completely outclassed, and begged for more P-38 Lightnings to counter the threat of the new enemy fighter.

The Ki-61 demonstrated only a few teething problems in field use, such as a tendency towards engine overheating during ground running under tropical conditions. However, despite the heavier armament, it still didn't have the punch to easily knock rugged and well-armed Allied bombers out of the sky.

The Kawasaki designers had forseen this problem. The Japanese Ho-5 20 millimeter cannon wasn't available at the time, but the Japanese obtained 800 Mauser MG-151/20 20 millimeter cannon from Germany in August 1943, and modified 388 Ki-61-I airframes on the production line to carry the German weapons in place of the two 12.7 millimeter wing guns. The cannon had to be mounted on their sides to fit into a wing, with an underwing blister for the breech, and some reinforcements were added to the wing to absorb the heavier recoil.

* Once the Ho-5 cannon became available, Kawasaki designers then reversed the arrangement of the guns, putting the 20 millimeter cannon in the nose and the 12.7 millimeter guns in the wings. While they were making these modifications, they also made a few changes to streamline manufacturing and simplify field maintenance.


This new variant was designated the "Ki-61-I KAIc" (where "KAI" was for "kaizo", or "modified") was 19 centimeters (7.5 inches) longer than its predecessors, and also featured a detachable rear section; a fixed tailwheel instead of the earlier retractable tailwheel; stronger wings; and stores pylons outboard of the main landing gear, allowing it to carry two 250 kilogram (550 pound) bombs.

_____________________ _________________ _______________________

spec metric english
_____________________ _________________ _______________________

wingspan 12 meters 39 feet 4 inches
wing area 20 sq_meters 215.3 sq_feet
length 8.94 meters 29 feet 3 inches
height 3.70 meters 12 feet 2 inches

empty weight 2,630 kilograms 5,800 pounds
loaded weight 3,470 kilograms 7,650 pounds

maximum speed 590 KPH 366 MPH / 318 KT
service ceiling 10,000 meters 32,810 feet
range 1,800 kilometers 1,120 MI / 975 NMI
_____________________ _________________ _______________________

The Ki-61-I KAIc went into production in January 1944 and ultimately replaced production of all earlier models in August 1944. A few "Ki-61-I KAId" bomber interceptors were also built in late 1944. These aircraft featured two 12.7 millimeter guns in the fuselage and a 30 millimeter Ho-105 cannon in each wing. Total production of all subvariants of the Ki-61-I was 2,654, with the Ki-61-I KAIc accounting for over half that number.

KI-61-II / KI-100 / KI-64

Even before the Hien saw combat, the IJA had been pressing Kawasaki for an improved version of the same aircraft. To this end, Kawasaki engineers focused on an improved version of the Ha-40 engine known as the "Ha-140", which was expected to have a take-off power of 1,120 kW (1,500 HP).

The first prototype of the new variant, the "Ki-61-II", flew in August 1943. Ten more prototypes were ordered. They featured a wing with 10% more area, and an improved canopy to provide better rear visibility, but the Ha-140 development program ran into troubles, and only eight of the prototypes were fitted with engines. Even then, they suffered from engine troubles, structural failures due to weaknesses in the new wing, and handling problems.

In an attempt to fix the problems, after delivery of the eighth Ki-61-II prototype the ninth prototype was extensively modified during manufacture. The extended wing was replaced with the original Hien wing, the fuselage was lengthened, and the rudder area increased. The result was the "Ki-61-II KAI", with initial flight of the prototype in April 1944. It was followed by 30 more prototypes. As long as the temperamental Ha-140 engine worked properly, the Ki-61-II KAI proved to be a promising interceptor, with a fast climb rate and good high-altitude flight characteristics.

Despite the problems with the engine, the military situation was increasingly desperate, and so the Ki-61-II KAI was put into production in September 1944. Two versions were produced, one designated "Ki-61-II KAIa", with 12.7 millimeter guns in the wings and 20 millimeter cannon in the nose, and the other designated "Ki-61-II KAIb", with four 20 millimeter cannon.

374 Ki-61-II KAI airframes were built and 99 of them fitted with engines. Then, on 19 January 1945, US Army Air Forces B-29 Superfortresses turned the plant at Akashi that was producing the Ha-140 engine into cinders and rubble. That abruptly ended concerns over the reliability of the Ha-140 engine, but left 275 airframes sitting around without powerplants.

* However, in November 1944 concerns over the availability (or lack thereof) of the Ha-140 engine had led the Munitions Ministry to request that Kawasaki redesign the Ki-61-II KAI to use another engine. Company engineers performed a lightning design effort to mate the fighter to the 1,120 kW (1,500 HP) Mitsubishi Ha-112-II 14-cylinder double-row air-cooled radial engine. The engineers inspected the radial engine installation of a sample Focke-Wulf FW-190 fighter obtained from Germany and, in an example of interservice cooperation that was far more the exception than the rule between the Imperial Japanese Army and Navy, took advantage of Navy efforts to use the Ha-112-II.

The first prototype conversion of three took to the air on 1 February 1945. Sometimes improvisations work poorly, sometimes they work surprisingly well, and the new variant demonstrated excellent performance. The rest of the engineless Ki-61-II KAI airframes were then converted to the new fighter type, which was designated the "Ki-100-Ia". They retained the armament of the Ki-61-II KAIb, consisting of 12.7 millimeter guns in the wings and 20 millimeter guns in the fuselage.

Performance was roughly the same but engine reliability was vastly improved. The Ki-100 was in fact an excellent fighter, a nasty customer for Allied aircraft to deal with while being surprisingly comfortable and easy to fly, an important consideration when experienced Japanese pilots were in increasingly short supply.


A batch of 118 new-production Ki-100s were then built, incorporating an all-round vision canopy, tested on a modified Ki-61-II KAI, and given the designation "Ki-100-Ib".

Work was then done to add a turbosupercharger and water-methanol engine boost to the Ki-100 to provide improved high-altitude performance. The first prototype of this variant, designated the "Ki-100-II", flew in May 1945, with two more prototypes completed before Japan's surrender ended plans for production.

_____________________ _________________ _______________________

spec metric english
_____________________ _________________ _______________________

wingspan 12 meters 39 feet 4 inches
wing area 20 sq_meters 215.3 sq_feet
length 8.82 meters 28 feet 11 inches
height 3.75 meters 12 feet 4 inches

empty weight 2,525 kilograms 5,567 pounds
loaded weight 3,495 kilograms 7,705 pounds

max speed at altitude 580 KPH 360 MPH / 315 KT
service ceiling 11,000 meters 36,000 feet
normal range 1,400 kilometers 870 MI / 755 NMI
_____________________ _________________ _______________________

* As Allied forces pushed in the bounds of Japan's overextended ocean empire, the Hien fought in the South Pacific, in the Philippines, on Okinawa, and finally in defense of the Japanese home islands themselves. Some Hien units also served on in China and on Formosa.

The home defense units operating on Japan used a mixed bag of Ki-61 variants, essentially anything they could get their hands on. The most famous of these units was the 244th Sentai (Fighter Group) under Japanese ace Major Tembico Kobayashi. Major Kobayashi encouraged his men to perform frontal attacks on B-29s and press their assaults to close range, even ramming if that was what was needed. Major Kobayashi set an example by fighting with almost suicidal determination.

By this time, the Hien was outclassed by American Mustangs and other late-model US fighters. In fact, when attacking B-29s Hiens often had to be protected by Ki-100s. Operations faded away as planes and pilots continued to fall in combat and fuel and spare parts dried up. By the end, the home defense units were no longer capable of posing a real threat to the Americans.

Of the 3,159 Hiens built, not many survived the war. Several were evaluated by the Americans and one was presented back to Japan by the US Air Force later. This was the only surviving Hien as of the mid-1960s. American aircraft restorer Kermit Weeks has a Ki-61 airframe in slow process of restoration.

* The Ki-61 wasn't the only fighter design to be powered by the Ha-40 inline engine. Kawasaki also experimented with an unusual twin-engine design conceived by Takeo Doi in 1939 and approved for prototype development in October 1940 as the Kawasaki "Ki-64".


The Ki-64 had both engines in tandem, straddling the cockpit and driving a single contra-rotating prop system with twin three-bladed props. The combined engine was known as the "Ha-201", and generated 1,755 kW (2,350 HP) take-off power. It featured an unusual steam cooling system with radiators in the wing and flap surfaces. The front engine used the right wing for cooling, while the rear engine used the left wing. The Ki-64 had a vague configurational resemblance to the Hien, though it was larger.

_____________________ _________________ _______________________

spec metric english
_____________________ _________________ _______________________

wingspan 13.5 meters 44 feet 4 inches
wing area 28 sq_meters 301.4 sq_feet
length 11.03 meters 36 feet 2 inches
height 4.25 meters 13 feet 11 inches

empty weight 4,050 kilograms 8,929 pounds
loaded weight 5,100 kilograms 11,245 pounds

max speed at altitude 690 KPH 429 MPH / 375 KT
service ceiling 12,000 meters 39,400 feet
range 1,000 kilometers 620 MI / 540 NMI
_____________________ _________________ _______________________

One prototype was finished in December 1943, but the rear engine caught fire on the fifth test flight. The aircraft made an emergency landing and survived. However, it was never repaired and the project was abandoned in the middle of 1944.