Nakajima Kotobuki 3 9-cylinder air-cooled radial engine rated at 640 hp (470 kW)

[Texnuk]

Hello everybody! Dear Shinpachi ,

How and where can I read about Nakajima Kotobuki 3 9-cylinder air-cooled radial engine rated at 640 hp (470 kW). And in general, if there is more literature , manuals about other Japanese engines from other companies?

 

[bf109xxl]

And in general, if there is more literature , manuals about other Japanese engines from other companies?

 

[Shinpachi]

Kotobuki 3 is an informal copy of Wright Cyclone R-1820F with bore/stroke 146/160.
Dimensions: Length 1,170mm x Diameter1,280mm Weight 424kg
Drawings: not available

Hikari 1 is a formal copy of Wright Cyclone R-1820F with bore/stroke 160/180.
Dimensions: Length 1,129mm x Diameter 1,354mm Weight 450kg
Drawings: Type 94 550hp "Hikari prototype or Ha-8"

Type 94 550hp "Hikari prototype or Ha-8"

 

[bf109xxl]

Kotobuki 3 is an informal copy of Wright Cyclone R-1820F with bore/stroke 146/160.
Dimensions: Length 1,170mm x Diameter1,280mm Weight 424kg
Drawings: not available

Very strange. The book I mentioned above contains completely different information:

I would be very grateful for references to your sources. I can assume that the book may contain erroneous information, but I would like to see reliable confirmations.

 

[Shinpachi]

Not a difficult story.
The naming Kotobuki "寿" came from Jupiter as "寿" can be also read "Ju" in Chinese style.
So, Kotobuki engines had to be the Jupiter family but Nakajima copied Wright R-1820F without the formal license for Kotobuki 3 and pretended this was Jupiter family. But, in 1937 when Asahi Shinbun's Kamikaze-go flew to London for the world record. Wright doubted if this was a copy. Nakajima denied but, to avoid suspicion, formally acquired the production license from Wright and named it Hikari. So, Kotobuki 3 belongs to both Kotobuki and Hikari families in specifications.
Kotobuki models after model 3 would have belonged to Hikari family if bore/stroke had been 160/180 but they stayed at 146/160.

 

[Bretoal2]

Not a difficult story.
The naming Kotobuki "寿" came from Jupiter as "寿" can be also read "Ju" in Chinese style.
So, Kotobuki engines had to be the Jupiter family but Nakajima copied Wright R-1820F without the formal license for Kotobuki 3 and pretended this was Jupiter family. But, in 1937 when Asahi Shinbun's Kamikaze-go flew to London for the world record. Wright doubted if this was a copy. Nakajima denied but, to avoid suspicion, formally acquired the production license from Wright and named it Hikari. So, Kotobuki 3 belongs to both Kotobuki and Hikari families in specifications.
Kotobuki models after model 3 would have belonged to Hikari family if bore/stroke had been 160/180 but they stayed at 146/160.

By the beginning of the 1930s, many engineers around the world had understood that the dimensions of the Jupiter (146 x 190 mm) were outdated, seeing that it was necessary to reduce its excessive stroke, and that the future was in the Mercury (146 x 165 ). The Kotobuki goes in this direction, and even beyond, the stroke being reduced to 160 mm.

Which also demonstrates the interest of Japanese engineers in metric dimensions !

Furthermore, criticism of the Jupiter also focused on cylinder heads ("poultice heads"), experiencing numerous overheating problems (and which Bristol itself ended up in completely modifying them, with V-valves in forged and machined cylinder heads - which resulted in the Pegasus). We understand that Nakajima completely redesigned these cylinder heads, being or not being copies of Wright.

 

[Texnuk]

I have some other information, dear Shinpachi... but somewhere nearby...) There are so many sources, so many opinions.
The Nakajima Ha-1 Kotobuki (寿, "Longevity") was an aero-engine developed by Nakajima. It was a radial piston developed under licence from the Bristol Jupiter.
Design and development
In 1917, Chikuhei Nakajima set up the "Airplane Institute" at Ojima Town in Gunma Prefecture. In 1918 they built their first airplane; the "Nakajima Type 1" with a U.S.A. made engine. In 1920 the company sent Kimihei Nakajima to France to study European advances, and in 1922 started their own engine factory in Tokyo. This led to production of engines based on the Lawrence A-3 two-cylinder air-cooled horizontally opposed engine.
At the time the Lawrence was an oddity. Most air-cooled engines at that time were rotary engines using cylinders that rotated together with the propeller, but Kimihei overheard that an engine with good cooling capability with fixed cylinders was being developed in England. He observed the English Gloster Gamecock fighter with its Bristol Jupiter engine, which was an advanced design for the era with an automatic adjustment device for tappet clearance, spiral piping for even intake distribution, and a four-valve intake and exhaust system. He acquired a manufacturing license for the Jupiter in 1925. In 1927, after inviting two production engineer instructors from the Bristol company,the Jupiter Type 6 of 420 PS and Type 7 of 450 PS with a turbocharger were put into production at the Nakajima factory.
After studying the Pratt & Whitney Wasp 9-cylinder radial, Nakajima tried to combine the good points found in Jupiter design with the rational design of the Wasp. Nakajima then produced a series of engine types, named "AA", "AB", "AC", and "AD", as engineering exercises. The next engine design, the "AE", was innovative, with a bore of 160 mm and a stroke of 170 mm.
Prototypes were made and performance tests were done, but this engine was not adopted due to its very complex engineering. Nakajima continued testing different cylinder designs. In 1929, the "AH" design, with bore and stroke of 146 × 160 mm and a total displacement of 24.1 L, was completed. This was to be the final version of this basic engine design.
In June 1930 the first prototype of was completed and it passed the durability test for the type approval in the summer. Then flight tests were started using a Nakajima A2N carrier plane. Nakajima had designed the first Japanese originally designed air-cooled 9-cylinder engine, the 450 PS "Kotobuki". In December 1931, this engine was approved and adopted by the Navy as the Ha-1 Ko for the Type 97 carrier fighter. The engine was named, in connection with the Jupiter engine, "Kotobuki".
The "Kotobuki" engine was improved and developed into the "Hikari (light)" engine with the bore and stroke expanded to the limit of the cylinder (160 × 180 mm for a displacement of 32.6 L), with the power was increased to 720 PS. The "Hikari" was used in Type 95 carrier fighters and Type 96 Carrier Attack Plane.
In search of more power the basic design was extended into a 14-cylinder 2-row engine, the "Ha-5 Ha-41 Ha-109" series.
I found the information today. But as you understood me well Shinpachi, I am interested in general views -drawings. "thanks.

Bristol Jupiter VII on display at the Shuttleworth Collection

The first Pratt & Whitney Wasp

 

[Shinpachi]

Almost answers are in my translation "Engine History of Nakajima Aircrat."
This is almost primary source.

Data Base: Japanese Aircraft Engines

Seems like a good place to put these manuals, I don't have the first one but does talk about engine oils, superchargers and other stuff.

ww2aircraft.net

 

[Bretoal2]

I have some other information, dear Shinpachi... but somewhere nearby...) There are so many sources, so many opinions.
The Nakajima Ha-1 Kotobuki (寿, "Longevity") was an aero-engine developed by Nakajima. It was a radial piston developed under licence from the Bristol Jupiter.
Design and development
In 1917, Chikuhei Nakajima set up the "Airplane Institute" at Ojima Town in Gunma Prefecture. In 1918 they built their first airplane; the "Nakajima Type 1" with a U.S.A. made engine. In 1920 the company sent Kimihei Nakajima to France to study European advances, and in 1922 started their own engine factory in Tokyo. This led to production of engines based on the Lawrence A-3 two-cylinder air-cooled horizontally opposed engine.
At the time the Lawrence was an oddity. Most air-cooled engines at that time were rotary engines using cylinders that rotated together with the propeller, but Kimihei overheard that an engine with good cooling capability with fixed cylinders was being developed in England. He observed the English Gloster Gamecock fighter with its Bristol Jupiter engine, which was an advanced design for the era with an automatic adjustment device for tappet clearance, spiral piping for even intake distribution, and a four-valve intake and exhaust system. He acquired a manufacturing license for the Jupiter in 1925. In 1927, after inviting two production engineer instructors from the Bristol company,the Jupiter Type 6 of 420 PS and Type 7 of 450 PS with a turbocharger were put into production at the Nakajima factory.
After studying the Pratt & Whitney Wasp 9-cylinder radial, Nakajima tried to combine the good points found in Jupiter design with the rational design of the Wasp. Nakajima then produced a series of engine types, named "AA", "AB", "AC", and "AD", as engineering exercises. The next engine design, the "AE", was innovative, with a bore of 160 mm and a stroke of 170 mm.
Prototypes were made and performance tests were done, but this engine was not adopted due to its very complex engineering. Nakajima continued testing different cylinder designs. In 1929, the "AH" design, with bore and stroke of 146 × 160 mm and a total displacement of 24.1 L, was completed. This was to be the final version of this basic engine design.
In June 1930 the first prototype of was completed and it passed the durability test for the type approval in the summer. Then flight tests were started using a Nakajima A2N carrier plane. Nakajima had designed the first Japanese originally designed air-cooled 9-cylinder engine, the 450 PS "Kotobuki". In December 1931, this engine was approved and adopted by the Navy as the Ha-1 Ko for the Type 97 carrier fighter. The engine was named, in connection with the Jupiter engine, "Kotobuki".
The "Kotobuki" engine was improved and developed into the "Hikari (light)" engine with the bore and stroke expanded to the limit of the cylinder (160 × 180 mm for a displacement of 32.6 L), with the power was increased to 720 PS. The "Hikari" was used in Type 95 carrier fighters and Type 96 Carrier Attack Plane.
In search of more power the basic design was extended into a 14-cylinder 2-row engine, the "Ha-5 Ha-41 Ha-109" series.
I found the information today. But as you understood me well Shinpachi, I am interested in general views -drawings. "thanks.
View attachment 772488
Bristol Jupiter VII on display at the Shuttleworth Collection
View attachment 772489
The first Pratt & Whitney Wasp

As I said above, the Jupiter VII is a second generation Jupiter, with "V" (not parallel) valves in a forged and entirely machined head. The Wasp had cast aluminium cylinder heads.

 

[bf109xxl]

Not a difficult story.
The naming Kotobuki "寿" came from Jupiter as "寿" can be also read "Ju" in Chinese style.
So, Kotobuki engines had to be the Jupiter family but Nakajima copied Wright R-1820F without the formal license for Kotobuki 3 and pretended this was Jupiter family. But, in 1937 when Asahi Shinbun's Kamikaze-go flew to London for the world record. Wright doubted if this was a copy. Nakajima denied but, to avoid suspicion, formally acquired the production license from Wright and named it Hikari. So, Kotobuki 3 belongs to both Kotobuki and Hikari families in specifications.
Kotobuki models after model 3 would have belonged to Hikari family if bore/stroke had been 160/180 but they stayed at 146/160.

Thank you very much for the explanations. But still references to sources would be highly appreciated.
I tried to compare the drawings. Honestly, the drawing you cited is much more similar to the P&W R-1340 than the Wright R-1820F.
Unfortunately, the quality of the Wasp drawing available to me is not sufficient for a definite conclusion, nevertheless some details speak in favor of Kotobuki's kinship with this particular engine.

 

[Shinpachi]

But still references to sources would be highly appreciated

 

[Texnuk]

Here is my source-https://military-history.fandom.com/wiki/Main_Page
There is another book, I downloaded it today. Boring and uninformative.

Bill_Gunston_Bill_Ganston_-_World_encyclopedia_of_aero_engines.2006