Aviation of World War II
In July 1938, Kawanishi Kokuki KK was awarded a contract to build a four-engine naval flying boat to replace the H6K in the Imperial Japanese Navy. The 13-C specifications attached to the order required higher data than those of the British Short Sunderland or the American Sikorsky HRV5-1: the maximum speed was set at 440 km / h, the cruising speed was 330 km / h, and the flight range was up to 8200 km.
Design work under the leadership of Shizuo Kikahara began in August 1938. As a result of blowing the models in a wind tunnel and towing in the experimental pool, a high-wing plane of pure forms appeared. To achieve a given flight range, the designers of Kawanishi installed eight relatively small wing unprotected tanks and six large tanks in the hull on the aircraft. The fuselage tanks were equipped with a neutral gas pressurization system and were partially sealed. Moreover, in the event of damage to the tank, the fuel leaking into the fuselage could be pumped into an undamaged tank. The total capacity of the fuel system reached 17,040 liters, fuel accounted for 29% of takeoff weight.
The crew had good armor protection. The defensive armament was to consist of three 20 mm Type 99 Model 1 cannons in the bow, upper and rear turrets, 7, 7 mm Type 92 machine guns in two side blisters, two side windows and in the lower installation.
The engines were chosen 1530-horsepower Mitsubishi MK4A Kasei 11; 14-cylinder air-cooled stars. The first prototype H8K1 was ready on December 31, 1940. The first flight took place in January of the following year. During high-speed taxiing and on takeoff, the plane showed itself extremely unstable, and soon after raising the nose, fountains of spray began to pour in the propellers and rose above the wing. The experienced H8K1 was immediately returned to the factory. There, the contours of the lower fuselage were changed and another cheekbone was added, after which the aircraft was immediately returned for testing. Although handling on water was still worse than that of the H6K, overall it improved markedly, and other characteristics were much higher. At the end of 1941, after military trials, the fleet authorized the start of serial production of the aircraft under the designation Marine Type 2 Flying Boat, Model 11 H8K1.
By this time, two more pre-production boats with modified hulls were built and flown; the second of them had an increased keel, which became a model for production vehicles. H8K1 Model 11 production aircraft were equipped with Mitsubishi MK4A Kasei 11 or MK4V Kasei 12 engines. The armament consisted of two 20 mm Type 99 Model 1 cannons, one each in the nose and tail turrets and four 7, 7 mm Type 92 machine guns. The aircraft could carry two 800 kg torpedoes or eight 250 kg bombs, as well as depth charges. The first combat sortie of the H8K1 took place on the night of March 5, 1942, when two aircraft from Kokutai Yokohama, having risen from Vautier Atoll (Marshall Islands), refueled from submarines and bombed Pearl Harbor. Since the weather was bad over Honolulu, the results were nil. Soon such raids had to be stopped due to the fact that the American fleet occupied the Frigate Shoals Islands, which were refueling from submarines. However, as an oceanic reconnaissance H8K1, the good protection of the crew, tanks and powerful weapons, combined with high speed, turned out to be very successful, allowing it to stand up for itself in battle with fighters.
The sufficiently high performance of the Model 11 was improved when the 1850-horsepower Mitsubishi MK4Q Kasei 22 engines equipped with a water injection system were installed on the H8K2 Model 12. The installation of Kasey 22 engines in modified nacelles was tested on an experimental H8K1. Improvement of flight characteristics made it possible to launch a model with Kasei 22 engines from the 17th aircraft. The keel was changed again. In all other respects, the aircraft did not differ from the H8K1. The high power of the engines made it possible to increase the takeoff weight from 31 to 32.5 tons, and the capacity of the fuel tanks to 18 880 liters. The armament was modeled on the first prototype aircraft, in addition, the 7, 7 m machine gun could be used through the side windows in the cockpit. Due to such powerful weapons and the highest speed among flying boats, this plane, in the opinion of allied pilots who collided with it, was the most difficult of all to shoot down. Gradually, the Type 2 Type 12 Flying Boat replaced the older Type 97, becoming the main long-range reconnaissance fleet. Some of the aircraft of the latest series received locators. The flying boat was used until the surrender of Japan.
Armament: three 20-mm type 99 model 1 cannons in the nose, upper and tail turrets (in the nose and tail turrets), 7.7-mm type 92 machine guns in the lower installation, in the side hatches and in the cockpit (in side blisters, lower and upper units); 2x 800 kg torpedoes or up to 2000 kg bombs
The first prototype aircraft, after using it as a prototype H8K2 with Kasey 22 engines, was converted into a transport version of the boat. The high fuselage made it possible to install two decks inside it. The lower deck ran from the bow to the rear step, and the upper deck ran from the wing to the tail. Accommodation was provided for 29 passengers or 64 soldiers. The armament was reduced to one 13 mm Type 2 machine gun in the forward turret and one 20 mm Type 99 Model 1 cannon in the stern. Installation of the lower deck required a re-arrangement of the fuel system: the fuel supply was reduced to 13,414 liters. After successful tests, the vehicle was transferred to the operational headquarters of the fleet in Yokosuka, where it was used as a liaison. The aircraft was put into production under the designation Marine Type 2 Seiku (Clear Sky) Transport Flying Boat or H8K2-B. A total of 36 H8K2-B were produced from 1943 to 1945, which were used in the transport units of the fleet.
Even at the beginning of work on the boat, it was planned to install removable stabilizing floats, but then this was abandoned to save weight. However, in 1943, an idea appeared to increase the speed of the H8K. Two experimental boats with Kasey 22 engines were equipped with retractable floats in 1944. They were actively tested. The armament of the new H8K3 was similar to that of the H8K2, but the side blisters were replaced by hatches; later, a similar revision was made to the serial H8K2, and the upper turret became removable. In 1945, these two boats were re-equipped with engines of Mitsubishi MK4T-V Kassey 25b with a capacity of 1825 hp. The aircraft were renamed H8K4 Model 23. But neither this model nor its transport version H8K4-b Model 33 were launched into production: the fleet needed fighters and he instructed Kawanishi to focus on the production of N1K2-J Syden.
A total of 167 H8Ks were produced, much less than the English Sunderlands or the American Catalin, but the Japanese boat proved to be one of the most outstanding naval aircraft in the world throughout the war.
H8K1 : designation of three prototypes and 14 first production aircraft with MK4A engines.
H8K1-L : designation of the sample after converting it into a transport aircraft with an MK4Q engine.
H8K2 : variant with MK4Q engine, enhanced weaponry and surface target detection radar; 112 vehicles were built under the designation Navy Type 2 Flying-Boat Model 12.
H8K2-L : a transport aircraft based on the H8K1-L model; could accommodate from 29 to 64 passengers; had less powerful weapons; launched into production under the designation Navy Type 2 Transport Flying-Boat Seiku Model 32 (Seiku - clear sky); built 36 cars.
H8K3 : Designation of two prototypes with retractable stabilizing floats at the wing tips. The dorsal rifle tower acquired a cylindrical shape and became removable. This option did not go into production.
H8K4 : new designation of the prototype H8K3 after the installation of Mitsubishi MK4T-B Kasei 25b engines (Mitsubishi MK4T-B Kasei 25b) with a capacity of 1361 kW (1825 hp); was not put into production.