Nakajima Ki-115 Tsurugi

As the Pacific War progressed, it became increasingly apparent that Japan's wartime fortunes were declining and that the country would resort to increasingly desperate measures to attempt to stall the Allied advance and the ambition to hinder, if not prevent, a successful invasion of Japan itself. To this end, kamikaze tactics were embraced, sacrificing pilots and their aircraft in an attempt to damage their opponents.^[4][5] Initially, obsolete combat aircraft and trainders were assigned this role, however, officials within the Imperial Japanese Army Air Service (IJAAS) recognised that there were not enough aircraft, even including obsolete ones, to fulfil the number of kamikaze attacks that the service intended to perform in the long term. Accordingly, it was decided it was decided that purpose-built sacrificial aircraft should be produced quickly in anticipation of an Allied invasion of Japan.^[4] While the Imperial Japanese Navy (IJN) preferred exotic propulsion, such as rocket motors and jet engines, for its suicide aircraft, the Imperial Japanese Army (IJA) favoured more conventional propulsion.^[5]

Accordingly, on 20 January 1945, the Nakajima Aircraft Company was instructed by the IJA to design a dedicated aircraft for performing suicide attacks; such an aircraft would have to be affordable and simplistic to manufacture, easy to both maintain and fly, and be able to carry a single bomb. It was also to possess a maximum speed no less that 340 kmph (211 mph) with the landing gear deployed, and that it should be jettisonable (as there was to be no landing) to attain no less than 515 kmph (320 mph); power was to be provided by an air-cooled radial engine.^[4][7]

The design team, which was augmented using personnel drawn from the Mitaka Research Institute and the Ota Manufacturing Co. Ltd, was headed by Aori Kunhiro. From the onset, it was planned for the aircraft to be suitable for production by semi-skilled labourers and therefore be relatively simple wherever practical to do so.^[4] Furthermore, it was designed to be constructed from "non-strategic" materials, primarily wood and steel. The wings were entirely composed of metal, complete with a stressed-skin outer surface, the fuselage structure comprised steel while the engine cowling was made of tin.^[4] The tail surfaces has a wooden structure and a fabric exterior. An open cockpit was positioned just above the trailing edge of the wing; a recessed crutch on the underside of the fuselage's centreline accommodated a single 800 kg (1,764 lb) bomb.^[4]

The cross section of the fuselage was circular and not elliptical, common to many aircraft of this size and type, as such a fuselage was easier to manufacture. The Ki-115 featured an austere instrument panel, featuring flight instruments, rudder pedals, a joystick type control column, and a place for a radio. Flight controls included both ailerons and elevators and (in production versions) flaps. The aircraft was fitted with a basic welded steel tubular undercarriage. As a weight-reduction measure, the main legs of this undercarriage were jettisonable.^[8][9][1] The Ki-115 was designed to be able to use any engine that was in storage for ease of construction and supply and to absorb Japan's stocks of obsolete engines from the 1920s and 1930s. The initial aircraft (Ki-115a) were powered by 858-kilowatt (1,151 hp) Nakajima Ha-35 radial engines. It is not known if any other engine was ever actually fitted.^[4]

On 5 March 1945, only two months after work commenced on its design, the prototype Ki-115 performed its maiden flight and flight testing commenced that same day.^[6][5] Partially due to the rapid pace of development, its performance was underwhelming. In particular, testing revealed the aircraft's crude undercarriage to possess unmanageable ground-handling characteristics, leading to it being rapidly redesigned to incorporate shock absorbers.^[11] Following a period of testing, the first production aircraft was fitted with the revised undercarriage, as well as a pair of rocket units, which may have been used to assist with take-off,^[1] or may have been fired to boost the aircraft's terminal acceleration towards its intended target.^[2][3]

The Ki-115 demonstrated very poor take-off and landing performance and could not be safely flown by anyone other than experienced pilots; these factors heavily contributed to the multiple fatal crashes that occurred during testing and training.^[2] While the IJAAS launched a training programme involving the Ki-115 in late June 1945, it was quickly abandoned due to the rate of fatal accidents occurring; instead, a redesign of the aircraft was ordered.^[5][2] It was around this time that the Imperial Japanese Navy Air Service (IJNAS) approached Nakajima, having taken an interest in the type, and requested a variant of the Ki-115 be produced for their own operations.^[12] At one point, the Japanese High Command had plans to construct some 8,000 Ki-115s each month at workshops all across mainland Japan.^{[citation needed]}

The Surrender of Japan ended the conflict in August 1945, before any Ki-115s were ever delivered to combat units, and thus no offensive missions were actually flown by the type.^[3][13]

• Ki-115 Prototype: Single-seat suicide attack aircraft. prototype version, tested during early 1945.^{[14][unreliable source?]}
• Ki-115 Tsurugi: Single-seat suicide attack aircraft, production version.
• Ki-115b Tsurugi: Single-seat suicide attack aircraft. proposed version using larger wooden wing, none built.^{[14][unreliable source?]}
• Ki-230: Single-seat suicide attack aircraft. projected version, none built.^[3]

Of the 105 examples produced, two airframes are known to exist.

• Ki-115 1002 is on display at the Pima Air & Space Museum in Tucson, Arizona, and is on loan from the National Air and Space Museum.^{[15][16][failed verification]}
• Another, once displayed as a gate guardian at Yokota Air Base, was since 1952 turned over to Japanese authorities and is reportedly at a Japanese museum.^[17]

Data from Japanese Aircraft of the Pacific War^[3]

General characteristics

• Crew: 1
• Length: 8.55 m (28 ft 1 in)
• Wingspan: 8.6 m (28 ft 3 in)
• Height: 3.3 m (10 ft 10 in)
• Wing area: 12.4 m² (133 sq ft)
• Empty weight: 1,640 kg (3,616 lb)
• Gross weight: 2,580 kg (5,688 lb)
• Max takeoff weight: 2,880 kg (6,349 lb) with 800 kg (1,764 lb) bomb
• Powerplant: 1 × Nakajima Ha-35 Model 23 14-cylinder air-cooled radial piston engine, 840 kW (1,130 hp) for take-off

980 hp (730 kW) at 6,000 m (20,000 ft)

• Powerplant: 2 × solid rocket attack boosters (optional)
• Propellers: 3-bladed fixed-pitch metal propeller

Performance

• Maximum speed: 550 km/h (340 mph, 300 kn) at 2,800 m (9,200 ft) with undercarriage jettisoned
• Cruise speed: 300 km/h (190 mph, 160 kn)
• Range: 1,200 km (750 mi, 650 nmi)
• Wing loading: 208 kg/m² (43 lb/sq ft)
• Power/mass: 0.322 kW/kg (0.196 hp/lb)

Armament

• Bombs: 1 × 250 kg (550 lb), 500 kg (1,100 lb), or 800 kg (1,800 lb) bomb

Aircraft of comparable role, configuration, and era

• Mitsubishi A6M7
• Nakajima Ki-43-IIIa
• Yokosuka MXY-7 Ohka
• Kokusai Ta-Go

Related lists

• List of aircraft of Japan during World War II
• List of military aircraft of Japan