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https://live.warthunder.com/post/524863/en/
"Kawanishi K-100
Kawanishi Kokuki K.K., founded in 1928, built its reputation on this flying boats and seaplanes. Aircraft such as the Kawanishi H6K (code-named ‘Mavis’) and the H8K (‘Emily’), the latter being considered the best flying boat of the war, were the pinnacle of Kawanishi’s work. And while the company continued to explore the boundaries of flying boat design, it dipped into the fighter realm, creating the potent and fearsome N1K-J Shiden (‘Violet Lightning’, Code-named ‘George’) from the earlier N1K Kyöfü (‘Great Wind’, code-name ‘Rex’) floatplane. But kawanishi would dip into another realm, that of bombers. Its first was the answer to a 17-shi specification for a bomber, and it was the Kawanishi K-100.
In 1941 the Kaigun Koku Hombu issued a 16-shi specification for a bomber to replace the Mitsubishi G4M (code-name ‘Betty’). There were two key components of the specification: a minimum speed of 580 km/h (361 mph) and a range of at least 7,340 km (4,598 miles). Mitsubishi was tasked with creating a bomber design to meet the 16-shi requirements and this would be the G7M Taizan (‘Great Mountain’). The initial G7M was a four-engine design by Kiro Honko, which was immediately rejected by the Kaigun Koku Hombu. The design was revised into a radical twin-engine departure from the norm by engineer Kijiro Takahashi. The powerplant was to be the Nu engine, which was a 24-cylinder, horizontal -H, liquid-cooled motor capable of 2,200hp. The design had more than a passing resemblance to the German Heinkel He 177 Greif. But Germany’s inability to export the machinery to produce the Nu engine spelled the demise of Takahashi’s G7M. Honjo took back the G7M reins and based his two-engine bomber on the G4M that he had designed back in 1937. By the time the mock-up of the G7M was completed in 1942, the projected performance was well below the 16-shi specifications. Also in that year the Kaigun koku Hombu issued a new 17-shi specification for a bomber, to which Kawanishi responded. The G7M now hat to compete with Kawanishi’s K-100. Mitsubishi was instructed to halt all further development of the G7M until such time as the K-100 could be evaluated.
Within Kawanishi, the K-100 was designated the KX-1, and, like the G7M, it was a twin-engine bomber design. But whereas the G7M was to use two Mitsubishi MK10A (Ha-42-11) 18-cylinder, air-cooled radials rated at 2,000hp each, Kawanishi elected to use the prototype Nakajima Mamoru-Kai (NK10A). This was an 18-cylinder variant of the standard 14-cylinder Mamoru engine (NK7A) and was projected to provide 2,300hp. Overall, the K-100 was smaller and lighter than the G7M but exceeded the G7M’s range projection as well as speed. In part, this came at the expense of defensive weaponry; Kawanishi planned to arm the K-100 with only three 20mm Type 99 Model 2 cannons, which was paltry compared to the G7M, which boasted six 13mm type 2 machine guns and two 20mm type 99 Model 2 cannons. The K-100 was a mid-wing design with a 0-degree dihedral on the inner wing surface and a 5-degree dihedral on the outer win portion. The overall wing aspect ratio was 7.3. The four-man crew was housed in the forward portion of the fuselage. It was proposed to make the tail turret remote-controlled so as to eliminate the need to house a gunner in the tail section. For offensive mission, a single 800kg (1,763lb) torpedo could be carried (which, incidentally, was the same war load capacity as the G7M). Fuel capacity was approximately 2,800 liters (739 gallons) with 240 liters (63 gallons) of oil. By the summer of 1943 Kawanishi had completed its initial design draft of the K-100 and presented it, along with the estimated performance measurements, to the Kaigun Koku Hombu for evaluation.
Unfortunately for Kawanishi, the Kaigun Koku Hombu felt that neither the G7M nor the K-100 would meet the 16-shi and 17-shi specifications. For the G7M, it was felt that the defensive armament was inadequately distributed, the estimated performance was little better than the G4M already in service, and that the Kaigun Koku Hombu was now looking to four-engine bombers to fulfil the specifications. For the K-100, the Kaigun Koku Hombu found that the payload capacity was not superior enough and that the decision to use only three cannons was too light a defensive weapon fit. Another problem with the K-100 was the choice of the NK10A Mamoru-Kai engine. The production Mamoru, as used in the Nakajima G5N Shinzan (‘Mountain Recess’, code-named ‘Liz’) and the Nakajima B6N Tenzan (‘Heavenly Mountain’, code-named ‘Jill’), was mechanically unreliable and rarely met its horsepower rating.
The Mamoru-Kai was even more problematic and Nakajima was not able to overcome the motor’s teething difficulties. Consequently, Nakajima cancelled further work on the Mamoru-Kai. This, then left the K-100 without a powerplant, and none of the available engine types offered any edge in terms of power. The K-100 like the G7M, also fell victim to the IJA’s lack of interest in twin-engine bombers to fulfil its specification requirements. With no further interest being shown by the Kaigun Koku Hombu in the K-100, Kawanishi shelved the project.
As a side note, some sources cite that the K-100 was given the IJN designation Kawanishi G9K Gunzan (‘Mountain Group’). There is no evidence to support this, especially in light of the quick termination of the K-100 project.
Kawanishi K-100 - data
Because the K-100 was never built, these specifications are estimated
Type Bomber
Crew Four
Powerplant
Two Nakajima NK10A Mamoru-Kai 18-cylinder, air-cooled radial engines developing 2,300hp, each driving at 4.5m (14.7ft) diameter, four-bladed, constant-speed metal propeller.
Dimensions
Span 21.6m 70.8ft
Length 15m 49.2ft
Height 6.07m 19.9ft
Wing Area 64.0sq m 688.8sq ft
Wing loading 210.9kg/sq m 43.2lb/sq ft
Weights
Empty 8,550kg 18,849lb
Loaded 13,500kg 29,672lb
Maximum loaded 16,000kg 35,274lb
Performance
Maximum speed 606km/h 376mph
Cruise speed 370km/h 229mph
Landing speed 145km/h 90mph
Climb 6min 16sec to 4,000m (13,123ft)
Range 5,556km (3,452 miles)
Ceiling 11,200m (36,745ft)
Armament
Three 20mm type 99 model 2 cannons, one 800kg (1,763lb) torpedo."