Kawasaki Ki-91 Long Range Heavy Bomber Project

[blackkite]

Hi! I believe this is a trace of original drawing. This drawing is from Kawasaki designer Takeo Doi's book.
50 years memory of aircrafts design by Takeo Doi, Kantosha, ISBN4-87357-014-X C0053 P2890E

 

[PlanesPictures]

Thank you very much. Every iteration of drawing has "ïmprovements" of its new author and therefore I prefer original drawings although in poor quality. As sample I attach drawing of Dornier P252-2. Red lines is some new clear improved drawing. But some parts are totally out

 

[lark]

In my humble opinion,the windtunnel model of the Ki-91 forms
a solid basis also as background for drawings...

 

[blackkite]

Hmmm...

Hi! Kawasaki Ki-91 long range heavy bomber
Length ： 33.35 m
Height ： 10.00 m
Span ： 48.00 m
Wing area ： 224.0 m²
Aspect ratio : 10.3
Wing cross section ： Laminar flow wing
Empty weight ： 34,000 kg
Gross weight ： 58,000 kg
Maximum speed ： 570 km/h (at 10,000 m)
Service ceiling ： 13,500 m
Time climb to 8,000 m: 20minutes 30seconds
Range ： 9,000 km(with 4ton bomb)
Over 10,000km(without bomb)
Engine ： Mitsubishi HA214Ru turbo charged air cooling radial 18cylinders（2,500 hp × 4）
Propeller ： constant speed, 4 blades, diameter 4.4 m
Fuel ：27,500ℓ(the wing contained almost fuel)
Crews ： 8
Armaments ： 20 mm cannon × 9、Bomb : 8,000 kg(max)

The line which connect inner and outer propeller spinner top in the 3 side view is parallel to the wing leading edge line, but the wind tunnel test model's same line is not parallel to the wing leading edge line.

http://matever.com/archives/ct01complete/_91_1144.html

 

[Jemiba]

The line which connect inner and outer propeller spinner top in the 3 side view is parallel to the wing leading edge line, but the wind tunnel test model's same line is not parallel to the wing leading edge line.

Well spotted, blackite ! And comparing modeland drawing, there ae other differences, too, although some of them
may be caused by the photo of the model not being a precise plan view, although it sems to be. To be fair, the
draughtsman may have used other sources, too (or even other models ?), which may show some details diferently.
But I agree to lark, that the most authentic source probably is the wind tunnel model.

 

[PlanesPictures]

Yes, it is my way in similar case, too. Wind tunnel model as base and to check useful details on other sources. 3D modeling is as spy job. Plus you have to find compromise between not absolutely precise top/side/front views

 

[blackkite]

Many thanks my dear Jens and Jozef. There were some differences between wind test model and most reliable three side view drawing. ???
Hmmm...Mystery.

 

[PlanesPictures]

Did we have all clear similar with Fugaku versions? I wanted to render it but I had problems to collect right sources

 

[Jemiba]

The most authentic sources we have, may have been amongst those blueprints, posted by blackkite
here for example http://www.secretprojects.co.uk/forum/index.php/topic,14582.msg196372.html#msg196372.
But certainly we are still in a "mine field" here, especially as different versions and stages of the design may
be mixed up, I'm afraid.

 

[Stargazer]

I'm not sure the question is so much whether one is more "authentic" than the other. Both the plans and the wind-tunnel model originate from the company.


It's just that there can be variants in the plans, but not many wind-tunnel models. The tunnel stage is usually an indication that the design has attained its most developed form and is ready for tests.

 

[Jemiba]

What I meant with "authentic" in this context, was just, that although we see those
typical "old fashioned" blueprints, we shouldn't be too sure, that they don't just stem
from the fund of requisits made for the TV drama (for example !) mentioned by blackkite !
About wind tunnel models, there often is a stage in the development, where a lot of different
models are used, for determining the best basic configuarion, just remember our Junkers EF/
EFo thread. How many models were used to find out the final layout for the Ju 287 ?
When this stage is finished, the model in most cases remains unchanged, because the details,
that often need changes for during all those teething troubles (fillets for fins and wings for example)
probably were too small to be tested in the wind tunnel with reliable results, I think.
Unfortunately, in the case of the Fugaku there seem no models to have survived. Maybe for the
mentioned early stage there just was no need, becus of the quite conventional layout ?

 

[blackkite]

Did we have all clear similar with Fugaku versions? I wanted to render it but I had problems to collect right sources

Hi! It's clear that we can't find survived official drawing for final Fugaku shape which determined by all Japan Fugaku comittee(member : the IJA, the IJN, Nakajima, Mitsubishi, Kawanishi, etc) still now. So it's impossible to render reliable final Fugaku shape.(I believe that final Fugaku had a slanting cocoon type pressurized cabin( B-29 like wind shield), turbo charged eigines, remote controlled turrets and dropable main tires.)
But I believe that we get reliable Fugaku candidate official drawing recently. I think it's better to construct 3D image for this candidate.

 

[CherryBlossom]

Hi!

Hello blackkite, long time no speak!

I was just wondering, what bomber is that behind the J7W in the artist impression? Is that the G8N or Ki-91?

( http://www.secretprojects.co.uk/forum/index.php/topic,16914.msg200260.html#msg200260 )

Would love to see a picture of the Ki-91 under construction if such exists.

 

[windswords]

CherryBlossum,

If you don't mind me answering, that is a G8N. As far as I know they did not ever make the Ki-91, so it was just a "paper project".

 

[blackkite]

CherryBlossum,

If you don't mind me answering, that is a G8N. As far as I know they did not ever make the Ki-91, so it was just a "paper project".

Yes I think so,too.

 

[CherryBlossom]

CherryBlossum,

If you don't mind me answering, that is a G8N. As far as I know they did not ever make the Ki-91, so it was just a "paper project".

Thanks for your reply Wind,

I have looked at different sources they state the Ki-91 began construction but was never finished. Some proof of the partial construction is something i would be interested in.

Do you know what sources say it was a paper project?

 

[windswords]

No not really. Just that I've never seen a picture of a prototype or even a partial construction. According to Ed Dyer's book Japanese Secret Projects a wood mockup was made and inspected by the JAAF in May 1944. The book also says that construction of a prototype was began but the factory was bombed by the Americans in February 1945 which severely damaged the project. With the war situation worsening the project was abandoned to concentrate on fighters.

 

[blackkite]

Japanese wikipedia says that
"Ki-91 full scale mockup inspection by the IJA were held in May and April 1944. The result of the mock up inspection was good. A factory for experimental productions of Ki-91 was completed in June 1944, installation of making jig began after factory completion.
Completion of No.1 experimental aircraft with pressurized cabin was scheduled in June 1946, completion of No.2 experimental aircraft with pressurized cabin was scheduled in March 1947.
But the Japanese mainland bombing by U.S. forces increased the violence from these days, and inevitably, an assembly plant in Gifu for this aircraft also changed the production system because the thing which becomes a target of bombing was expected. But the environment for the development of this aircraft aggravated because of delay of new large power engine with turbo charger, and lack of the fuselage material in particular, the aluminum alloy.
It was obvious by deterioration of the war that it was the situation to concentrate energy on production of interceptor and special attack aircraft than strategic bomber
Development cancellation of this aircraft was considered by the IJA and experimental production cancellation of Ki-91 was dictated in February 1945.
When cancellation, the design had ended until the stage of the 60%.
Further, every materials which Ki-91 need were gathered in experimental production factory in Gifu when cancellation."

 

[Stargazer]

Thanks a lot for this valuable info, folks, although I do believe it would be put to better use in a dedicated Ki-91 thread...

 

[blackkite]

I hope that Ki-91 full scale mockup pictures are still survive somewhere in Japan now and we will see these pictures near future.

http://alternathistory.org.ua/proekt-tyazhelogo-bombardirovshchika-91-kawasaki-ki-91-yaponiya

 

[CherryBlossom]

No not really. Just that I've never seen a picture of a prototype or even a partial construction. According to Ed Dyer's book Japanese Secret Projects a wood mockup was made and inspected by the JAAF in May 1944. The book also says that construction of a prototype was began but the factory was bombed by the Americans in February 1945 which severely damaged the project. With the war situation worsening the project was abandoned to concentrate on fighters.

I have the book as well, its a dam shame about it.

It reminds me of the Ki-98 and Ki-119, I just wish to see some photos of them!

But otherwise i have another question; The Ki-91 was supposed to have 12 x 20 mm cannons according to various sources. However, In artist impressions and the drawings, you find it difficult to see where the remaining two go. I think if i recall correctly, the far-rear turret housed 4, but again i cannot see them on the impressions/drawings. Do you know why this is?

 

[blackkite]

Hi!
I think 20mm cannon were 10.
Some Japanese source says that each fuselage side had a 20mm cannon.
But I can't confirm it.

http://military.sakura.ne.jp/ac/ki91.htm

武装(armament) ２０ミリ機関砲(20mm cannon)×１２（連装銃座(coaxial machine cannon)（機首(nose)、前方下部(front under)、上部(upper)、後方下部(aft direction under)、尾部(tail)）５、
胴体側面左右各１(fuselage left and right side had one cannon each)）、爆弾(bomb)４，０００kg～８，０００kg搭載

 

[Winston]

http://military.sakura.ne.jp/ac/ki91.htm

武装(armament) ２０ミリ機関砲(20mm cannon)×１２（連装銃座(coaxial machine cannon)（機首(nose)、前方下部(front under)、上部(upper)、後方下部(aft direction under)、尾部(tail)）５、
胴体側面左右各１(fuselage left and right side had one cannon each)）、爆弾(bomb)４，０００kg～８，０００kg搭載

In "The Xplanes of Imperial Japanese Army & Navy 1924-45" the armament is listed as 20mm x12 but in the drawing there are only x10. :-\

 

[blackkite]

Hi!
The engine was Mitsubishi Ha214 Ru(HA42-21 Ru or MK10 or A18) with turbo charger.
This engine has 4 kinds of name in the thing which should be marvellous.　Crazy! ;D
Take off power was 2,500hp each.
RU means turbo charged engine.
Ha214's base was the Kasei 14 cylinders air cooling engine.
Ha214 was a 18 cylinders air cooling engine.
Ki-91 engine nacelle shape is very clean same as Mitsubishi Hiryu's engine nacelle.
We can't see ram air intake for engine and air intake for oil cooler.
Perhaps Ha214-Ru engine had a forced cooling fan.
Perhaps Ki-91's engine was same as Mitsubishi 4-shiki heavy bomber Hiryu Ki-67-Ⅱ's engine.

Of course A18 engine had many delivatives for example, A18A,B,C,D,E.
(1) Single stage two speed mechanical supercharger type ; A18A?
(2) First stage turbo charger+second stage two speed mechanical supercharger type ; A18B?(Ha214 ru?)
(3) Single stage three speed mechanical supercharger type ; A18C?
(4) Vulkan coupling drive first stage supercharger+second stage two speed mechanical super charger type(for pusher) ; A18D?
(5) Vulkan coupling drive first stage supercharger+second stage two speed mechanical super charger type(for tractor) ; A18E?

 

[blackkite]

Hi! Larger images.
There is no window for sight in the rear turret under the fuselage. ???
I can see some turret shape in existing images.

https://forum.warthunder.com/index.php?/topic/337549-kawasaki-ki-91-%E3%82%AD-91/

 

[blackkite]

Hi! May be the original drawings?

サービス終了のお知らせ

blogs.yahoo.co.jp

 

[blackkite]

Impresssive Ki-91 model. How about wing root shape?
I can't find any information about this model.

サービス終了のお知らせ

blogs.yahoo.co.jp

 

[blackkite]

Hi! Larger image.

https://www.reddit.com/r/Warthunder/comments/ane24q

 

[TerryM76]

Saipan B-29 base received several Japanese aircraft attack. And some B-29 were destroyed without Ki-91.
Japanese aircraft which attack Saipan B-29 base were the IJA's Mitsubishi type 97 bomber(９７式重爆撃機), the IJN's Mitsubishi type 1 bomber(一式陸上攻撃機) and Mitsubishi Zero fighter(零式艦上戦闘機) from Iou island(硫黄島). They were all Mitsubishi's aircrafts.

Wish I had noticed this part ot the thread a few years ago. Do you know when the last Japanese air attack occurred on Saipan B29 base? My father was stationed on Saipan during last year of the war. One of his duties was guarding the fresh water supply. He passed last year and he often spoke about his time on Saipan but made no mention of any air attcks.

 

[blackkite]

The first japanese attack on Saipan Island was completed on November 2, 1944, when nine Japanese Army Air Corps heavy bombers were launched and three were unreturned, but there was no damage to the U.S. military. In addition, the Japanese Luk army and the Japanese Navy jointly attacked the airfield in Saipan as a retaliatory attack on November 27, three days after Tokyo's first air raid. Two four-type heavy bombers of the Second Independent Squadron, led by Major Norinori Shinkai of the Japan Army Air Corps, bombed Isley Airfield (renamed by the U.S. Army than athletes), and the battle results were damaged by four aircraft, and both type 4 heavy bombers were brought back alive. Next, 12 Zero Fighter steams of the first shield corps led by lieutenant Kenji Omura of the Japan Navy Air Corps, machine-gun shot five B-29 swept through Isley Airfield, and also shot down one of the P-47 that had intercepted, but m Zero Fighter was all unreturned. Major Shinkai's second independent squadron also destroyed four B-29s in a night attack on December 7, damaging 23 aircraft. The last attack was at Christmas in 1944, when he first sprayed a tin-foiled imitation paper (electric probe, now a chaff), deceptiond radar, and then attacked Saipan and Tenian with a clever attack of simultaneous entry of high and low, defeating four B-29s, 11 aircraft are damaged. The Japanese army's attack on an airbase in the Mariana Islands completely destroyed or wrecked 19 B-29aircraft, damaging 35 aircraft, and 245 U.S. military casualties.

 

[TerryM76]

Thank you for the response. If I recall correctly, my father did not arrive on Saipan until after January 1945. I need to research his military service history further.

 

[blackkite]

Perhaps your father was a very lucky man same as my father.
Those were small but brave counterattack by Japanese aircraft.

 

[blackkite]

Hi! Wind tunnel test model and engine larger images.

Engine ： Mitsubishi HA42-21 (HA214Ru) air cooling radial 18cylinders with turbocharger and forced cooling fan.（2,500 hp × 4）

Picture of the Day - Miscellaneous

WWII 1938 Japanese Soldiers Playing Baseball North China Original Wire Photo | eBay

ww2aircraft.net

 

[blackkite]

Hi! I compare the model and the official drawing.

 

[blackkite]

I compared the wind tunnel test model and the official three side view drawing about the plan view of the Ki-91 bomber.
As a result, it turned out that they did not completely match.
Therefore, I compared the wind tunnel test model and the official three side view drawing for the case where the fuselage length was assumed to be the same and the case where the main wing width was assumed to be the same.
Assuming that the length of the fuselage is the same between the wind tunnel test model and the official three side view drawing, the engine spacing is the same, the horizontal tail width is the same, and the turret diameter is the same. Therefore, this assumption is likely to be correct.
In this case, the main wing span of the wind tunnel test model is 8.4% larger than the official three side view drawing.
As a result of the wind tunnel test, it is possible that the main wing width was reduced.

 

[windswords]

Balackkite,

In regards to the Mitsubishi HA42-21 (HA214Ru) you mentioned earlier:

Did the Japanese ever create a reliable turbo super charger? I think I read somewhere that they lacked the skill to work with or possesion of metal alloys to make adequate turbine blades that could hold up to prolong use, similar to the problems encountered with the Kikka's jet engines.

 

[iverson]

Balackkite,

In regards to the Mitsubishi HA42-21 (HA214Ru) you mentioned earlier:

Did the Japanese ever create a reliable turbo super charger? I think I read somewhere that they lacked the skill to work with or possession of metal alloys to make adequate turbine blades that could hold up to prolong use, similar to the problems encountered with the Kikka's jet engines.

I don't believe so. I'm sure that the Japanese had the skills. But, fundamentally, they lacked the time to experiment and the economic strength to pursue all desirable powerplant developments at once. They had to prioritize those that offered the best return in the near term--air-cooled radials with modest levels of mechanical supercharging.

We tend to forget that Japan was a small, resource-poor economy--which was one of the reasons it went to war. And by the time of the Pearl Harbor attack, Japan had been at war in Manchuria and China for 10 years and had suffered badly at the hands of the Soviets in the Khalkin Gol fighting. So it already had immediate problems to address in the 1930s and could not give longer term development the same attention that even an underfunded USAAF could manage.

When war broke out, just as the Depression was ending, the USAAF could draw on the enormous engineering and production capabilities of its civilian aircraft, automotive, and electrical industries to address both short- and long-term objectives in parallel. It could also afford failures and take risks that Japan could not.

Given our interest in technical matters, I suspect that we give too little thought to the limits that history and economics place on technical solutions. Both Germany and Japan were relatively small, resource-poor countries that sought to become great powers through conquest. They both bet on short, lightning wars that would demoralize their enemies before their own resources ran out. But the USSR, Britain, and the USA were already comparatively big powers, and, to paraphrase George Bernard Shaw, God is on the side of the big economies.

 

[blackkite]

Hi windswords-san! Good question.
In 1943, the Ha 112-II Le single-stage two-speed super charged engine with a turbocharger developed by Mitsubishi was decided to be installed on the Type 100 reconnaissance aircraft, and the Army developed it as the Ki-46-IV. In December of the same year, the first prototype of the Ki-46-IV was completed. Developed on the basis of the Type 3 (Ki 46-III) without major remodeling, it succeeded in its first flight on January 12, 1944 at the Kakamigahara Army Airfield. As a result, a maximum speed of 630km / h / 10,000m was recorded, and the high altitude performance was improved by 50km / h or more compared to the Type 3 (Ki46-III).
After refurbishment and examination, it was planned to be put into practical use in February 1945 (Showa 20), but the war ended before mass production.

At 10:00 am on February 27, 1945, two Type 4 (Ki 46-IV) equipped with turbochargers took off from Nanyuan Airfield in Beijing and flew to Fussa's Tama Army Airfield. It took 3 hours and 35 minutes for the No. 1 aircraft and 3 hours and 15 minutes for the No. 2 aircraft from the takeoff in Beijing to the stop in front of the Fussa hangar. The actual flight distance was 2,250 km, with an average speed of over 700 km / h. The jet stream in the winter helped them to gain an advantage, but there was a problem during takeoff (the second aircraft took off again in Beijing. The first aircraft that took off waited for the second aircraft and turned over Beijing. Repeatedly lost time) and bad weather (Beijing weather on that day was powder snow and visibility was only about 2 km, it was a complete cloudy to the Korean Peninsula).When they landed at Tama Airfield, there was enough fuel in the tanks located front of the fuselage.

 

[windswords]

]

I don't believe so. I'm sure that the Japanese had the skills. But, fundamentally, they lacked the time to experiment and the economic strength to pursue all desirable powerplant developments at once. They had to prioritize those that offered the best return in the near term--air-cooled radials with modest levels of mechanical supercharging.

It seems that the Japanese were trying very hard to develop turbo superchargers. Experimental examples were tried on the aircraft such as the A6M4, C6N2, J2M4, Ki-100-II, Ki-46-IV, Ki-83, Ki-91, Ki-87, G8N and Ki-94-II. Now the experimental models had other issues but the already in production models should have reached production status. But they didn't. that tells me that their was something lacking in process or materials, engineering or resources. It's not like this was a last year of the war rush program. They started earnest supercharger work in 1943. As for the expermental models I do know that the American test pilots of the G8N bomber postwar said that the turbo supercharges never worked during their tests so they just switched them off. Maybe that was due to lack of maintenance on them prior to the Americans taking possesion but I suspect it was because the bugs were not yet worked out.

 

[Grey Havoc]

Materials would have been the major roadblock there, I would suspect. Possibly with a bit of bureaucratic infighting mixed in.