The Ki-87 was developed in response to American B-29 Superfortress raids on the Home Islands. It followed up on earlier research by Nakajima and the Technical Division of Imperial Army Headquarters into boosting a large radial engine with an exhaust-driven turbo-supercharger, which had begun in 1942, well before the B-29 raids began.[1] The efforts of the Technical Division of Imperial Army Headquarters eventually culminated into the Tachikawa Ki-94-I, while the Ki-87 was developed as a fall-back project, using less stringent requirements.[2][3] Nakajima started in July 1943 with the construction of three prototypes, to be completed between November 1944 and January 1945, and seven pre-production aircraft, to be delivered by April 1945.[3] The Technical Division of Imperial Army Headquarters made itself felt during the development of the Ki-87 prototype when they insisted upon placing the turbo-supercharger in the rear-fuselage, and from the sixth prototype the Nakajima fighter was to have that arrangement.[4][5] The Ki-87 had a Curtiss P-40 Warhawk-like undercarriage, as space in the wing was needed for ammunition for the wing-mounted cannon. The 90° rearwards retracting undercarriage was to provide that needed space.[1][6]
Construction was delayed due to problems with the electrical undercarriage and the turbo-supercharger, and the first prototype was not completed until February 1945; it first flew in April, but only five test flights were completed, all with the undercarriage in the extended position.[6][7]
A further variant, the Ki-87-II, powered by a 3,000 hp Nakajima Ha.217 (Ha.46) engine and with the turbo-supercharger in the same position as the P-47 Thunderbolt, never went further than the drawing board
Specifications (Ki-87 prototype)
Another photograph of the first Ki-87 prototype, showing to advantage the turbo supercharger.
Data from Japanese Aircraft of the Pacific War;[6] Japanese Army Fighters, Part 2;[7] Famous Aircraft of the World, first series, no.76: Japanese Army Experimental Fighters (1)[10]
General characteristics
Crew: 1
Length: 11.82 m (38 ft 9.375 in)
Wingspan: 13.423 m (44 ft 0.5 in)
Height: 4.503 m (14 ft 9.312 in)
Wing area: 26.00 m² (279.860 ft²)
Empty weight: 4,388 kg (9,672 lb)
Loaded weight: 5,633 kg (12,416 lb)
Max. takeoff weight: 6,102 kg (13,448 lb)
Powerplant: 1 × Mitsubishi Ha.215 (Ha.44/11) eighteen-cylinder air-cooled radial four-blade, 1,789 kW (2,400 hp)
Performance
Maximum speed: 697 km/h (379 kn, 433 mph)
Cruise speed: 470 km/h (254 kn, 292 mph)
Service ceiling: 12,855 m (42,175 ft)
Wing loading: 216.6 kg/m² (44.3 lb/ft²)
Power/mass: 0.317 kW/kg (2.3 kg/hp; 5.2 lb/hp)
Armament
Guns: 2 × 30 mm (1.18 in) Ho-105 cannons in the outer wing panels and 2 × 20 mm synchronized Ho-5 cannons in the wing roots
Bombs: 1 x 250 kg (550 lb) bomb under fuselage
