Like the Italians, the Japanese were slow to enter the field of the ‘modern’ monoplane fighter with an all-metal structure, low-set cantilever wing, retractable main landing gear units and an enclosed cockpit. This resulted in large measure from the strong approval of pilots, of both the Imperial Japanese any and navy air services, for the biplane in its late form with moderately good performance but excellent agility, of which the latter was seen as essential for success in the dogfighting type of air combat, also enhanced by an open cockpit to provide the pilot with very good fields of vision. Both services also appreciated the well-established procedures for the maintenance of lightweight fighters, especially on aircraft carriers with their limited flight decks, hangar area and stores supply.
Yet the performance advantages of the monoplane configuration could not be ignored, so there appeared monoplane prototypes such as the Kawasaki Ki-5 with a cantilever wing of the inverted-gull configuration and the Nakajima Ki-11 with a wire-braced wing, in each case with open cockpits and fixed main landing gear units whose legs were enclosed in long-chord fairing. These paved the way to the first cantilever monoplanes to enter Japanese service as the Mitsubishi A5M for the navy and Ki-27 for the army.
Early in 1935 the Nakajima company began, as a private venture, the design a fighter intended to incorporate the latest Western innovations. Designed by Shigenobu Mori under the overall supervision of two Dewoitine engineers, Roger Robert and Jean Beziaud, the new fighter received the Imperial Japanese army air service designation Ki-12 (otherwise Experimental Fighter). Strongly influenced by the Dewoitine D.510 and based on the basic airframe of the Ki-11, the Ki-18 was a low-wing monoplane with the powerplant of one Hispano-Suiza 12Xcrs water-cooled V-12 engine rated at 670 hp (499.5 kW).
The Ki-12 was of all-metal construction with a semi-monocoque fuselage of oval section carrying the pilot’s open cockpit in line with the trailing edges of the wing roots. The flying surfaces comprised a cantilever tail unit and a low-set cantilever wing. The tail unit comprised single horizontal and vertical surfaces, the former including a tailplane carrying elevators with trim tabs, and the latter a fin (extended forward by a dorsal fillet into the pilot’s headrest) carrying a rudder with a trim tab. The port and starboard halves of the dihedralled wing extended from the lower sides of the fuselage, were tapered in thickness and chord to their rounded tips, and carried over virtually the full span of their trailing edges outboard ailerons and inboard split flaps. The airframe was completed by the tailskid landing gear, which included hydraulically operated main units designed to retract inward into wells in the underside of the wing roots and lower fuselage. The Ki-12 was the first Japanese aeroplane with retractable main landing gear units.
The engine was located in the nose inside a full cowling, drove a three-blade metal propeller of the fixed-pitch type and fitted with a spinner, and was cooled by a frontal radiator. As might have been expected in a prototype of this period powered by an imported French engine, the fixed forward-firing armament echoed French practice of the time: a 20 mm Hispano-Suiza HS-9 cannon was installed between the engine’s two cylinder banks to fire through the hollow propeller shaft, and two 0.303 in (7.7 mm) machine guns were fitted in the leading edges of the wing outboard of the disc swept by the propeller.
Not agile enough
The prototype of this sophisticated fighter was completed in October 1936 and, in its initial flight trials, revealed excellent performance. The prototype was evaluated competitively against the Kawasaki Ki-28, Mitsubishi Ki-18 and Ki-33, and Nakajima Ki-27. Despite its high level of performance, however, the Ki-12 lacked the agility still sought by the fighter pilots of the Imperial Japanese army air service and therefore was not ordered into production. The contract went instead to the Ki-27. Another factor which militated against the Ki-18’s production was its French engine and cannon: Japan feared that Hispano-Suiza would not grant production licences for these, and was adamantly opposed to reliance on an engine and cannon which would otherwise have to be imported in large numbers.
Having already appreciated that its private-venture prototype might be too advanced for the service, Nakajima had already launched, again as a private venture, a programme to create a less sophisticated fighter, the PE with fixed main landing gear units and a Japanese radial engine, which was the basis for the highly successful Ki-27, and the elegant Ki-12 came to be looked upon more as a design exercise than as a serious contender for service orders. As a result, the Ki-12’s full performance envelope was not explored in full, and the data therefore include manufacturer’s estimates.
Nakajima Ki-12 Experimental Fighter
Accommodation: pilot in the open cockpit
Fixed armament: one 20 mm Hispano-Suiza HS-9 fixed forward-firing cannon in a moteur-canon installation to fire through the hollow propeller shaft, and two 0.303 in (7.7 mm) fixed forward-firing machine guns in the leading edges of the wing
Disposable armament: none
Equipment: standard navigation equipment, plus an optical gun sight
Powerplant: one Hispano-Suiza 12Xcrs liquid-cooled V-12 piston engine rated at 670 hp (499.5 kW) for take-off
Internal fuel: not available
External fuel: none
Dimensions: span 36 ft 1 in (11.00 m); area 182.99 sq ft (17.00 m²); length 27 ft 2.75 in (8.30 m); height 10 ft 10 in (3.30 m)
Weights: empty 3,086 lb (1400 kg); normal take-off 4,189 lb (1900 kg)
Performance: maximum level speed 259 kt (298 mph; 480 km/h) at at optimum altitude; cruising speed 200 kt (230 mph; 370 km/h) at optimum altitude; climb to 16,405 ft (5000 m) in 6 minutes 30 seconds; service ceiling 34,450 ft (10500 m); range 432 nm (497 miles; 800 km)