Kawanishi heavy flying boat projects (K-120, K-200, etc.)

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The K-60 was a flying boat planned by the Imperial Japanese Navy. "K-60" was the prototype number given to a future aircraft in the Navy's Practical Aircraft Prototype Program, and some sources say it was called the "17-shi Large Flying Boat," while others say it was not given a military name.

In June 1939, the Imperial Japanese Navy, under its "Practical Aircraft Prototype Plan for 1939 to 1942," planned the development of the K-60 by Kawanishi Aircraft as a successor to the 12-shi Large Flying Boat (later known as the Type 2 Flying Boat). At the time, the K-60 was intended to be a four-engine aircraft with a 2,000 hp engine. However, in the 1941 draft of the "Practical Aircraft Prototype Plan for 1941 to 1944," the plan was revised to a super-large aircraft with 4,000 hp twin engines.

The Imperial Japanese Navy General Staff required a maximum speed of 519 km/h (at an altitude of 5,000 m), a practical ceiling of 10,000 m, and a range of 9,260 km or 10,733 km. In response to this, the Imperial Japanese Navy Aviation Headquarters prepared four proposals between June and September 1941, using Mitsubishi Heavy Industries' ME2A "Nu" liquid-cooled H-type 24-cylinder engine (takeoff power 2,500 hp), the ME3A "Wa" engine (takeoff power 5,000 hp) which consisted of two Nu engines connected in parallel, or the "Ken-2" air-cooled double-row radial 18-cylinder engine (takeoff power 2,400 hp).

The first plan was to equip four Wa-type engines.
The second plan was to equip two Nu-type engines and two Wa-type engines.
The third plan was to equip four Nu-type engines.
The fourth plan was to equip four Ken-2-type engines.(Nakajima HA-44)

Of these, the first plan was deemed the most optimal, regardless of budget and manufacturing capacity, and was therefore approved.
Subsequently, in 1941, Kawanishi was also ordered to prepare a basic design. However, numerous technical issues arose, including the impossibility of completing the Nu-type flying boat. Furthermore, due to changes in the intended uses of flying boats based on combat experience during the Pacific War and a shortage of materials, development was halted at the end of 1942 (Showa 17).
After the first plan was selected, the Imperial Japanese Navy Aviation Technical Arsenal planned to complete the first aircraft in March 1945 (Showa 20), and Kawanishi planned to complete the first aircraft at the end of September 1945.

The first design for the K-60 was an ultra-large aircraft with a wing area 2.5 times larger and a gross weight nearly 3.9 times that of the HK2 Flying Boat. While the Navy did not provide any specific specifications, Kawanishi envisioned it as a transport aircraft between the Japanese mainland and the south.

The main wing was designed to feature laminar flow aerofoils on the outer wings, and suction and blowing devices were used to control the boundary layer. This would reduce the increased air resistance of the wing due to the inclusion of both the engine and cooler within the wing, and the engine's forced-cooling fan would spurt cooling air aft, improving performance. Other plans included the use of laminated wood propellers and takeoff-accelerating rockets.

The K-60 was said to be the largest Japanese flying boat ever designed, but its development was kept strictly secret, so no detailed documentation remains.

Specifications (First Proposal/Planned Values)
Source: "The Story of the Giant Aircraft," pages 119-122.
• Length: 43.24 m
• Wingspan: 60.0 m
• Wing area: 400.0 m2
• Weight: 61,500 kg
• Gross weight: 120,000 kg
• Engine: Mitsubishi Wa-Go liquid-cooled 48-cylinder (5,000 hp at takeoff) x 4
• Maximum speed: 561 km/h
• Cruising speed: 370 km/h
• Practical ceiling: 9,950 m
• Range: 11,038 km
• Armament:
• Two 20 mm twin machine guns
• One 13 mm machine gun
• Eight 7.7 mm machine guns
• 8,000 kg bombs or torpedoes

Source : Japanese wikipedia
 
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