The so-called "NK-1b fighter" (I don't found this designation in Japanese sources) was one of many research studies done by Kugisho engineers under the generic term Shisei-ki Kugisho Seino Suisan (Kugisho Prototypes Estimated Performance, 試製機空技廠性能推算) or Seino Hyojun in short (Performance Standard, 性能標準). These research studies was done permanently for almost every type of aircraft used and planned for use by the IJNAF. These was not the detailed projects ready for prototyp built but rather studies for future demands of aircraft performance. Seino Hyojun was used by Kaigun Koku Honbu and Gunreibu for preparation of an appropriate specifications, which was later send to aircraft manufacturers.
One of these Seino Hyojun, dated 19 March 1941, was about future carrier fighter (Kansen). They called for following parameters: engine 15-Shi Ru-Go (十五試ル号), wingspan 12.5 m, length 10.0 m, wing area 24.8 sq. m, take-off weight 3100 kg, max loaded weight 3250 kg, wing loading 125 kg per sq. m, max speed 639 km/h (345 knots) at 6000 m, flight endurance 1-2 hours at max speed, range 2315 km (1250 Nm), take-off distance 70 m with wind from head 12 m/s, armament (1st variant) 2x20 mm (120 rounds of ammunition) and 2x7.7 mm (800 rounds) or (2nd variant) 2x20 mm (120 rounds) or 1x20 mm motor cannon (120 rounds) and 2x13 mm (300 rounds), necessary equipment - short-range (185 km, 100 Nm) or long-range (926 km, 500 Nm) radio, radio direction finder. 15-Shi Ru-Go (十五試ル号) engine was in fact Nakajima NK9 Homare (誉), then in prototype stage.
Regards,
LAW
