The Kawasaki Ki-78 (KENsan III) began its development as a high-speed research aircraft intended challenge air speed records of the 1930s. All-new wings were devised to trial various load factors at speed and the program was given life through a 1938 initiative under the direction of the Aeronautical Research Institute of the University of Tokyo and the aircraft manufactured by Kwasaki Kokuki Kogyo K.K. Only one flyable examples was ever completed as World War 2 (1939-1945) disrupted the project and forever changed its fortunes.
The design incorporated a sleek fuselage, devoid of any unnecessary protrusions, with fine contouring throughout and clean lines throughout. An inline piston engine was selected to power the aircraft and this installed at the nose in the usual way. The cockpit, lightly framed, was set at midships. A raised dorsal spine blocked any useful views to the pilot's rear but this was not a combat aircraft. The empennage tapered elegantly to the rear to which a single rudder and low-set horizontal planes were fitted. The tail-dragger undercarriage was retractable with the two main legs sitting under the wings. The aircraft was constructed of all-metal including its skinning.
The smallest possible cross-section, coupled with a powerful engine, was selected for the aircraft. Overall length reached 26.5 feet with a wingspan of 26.2 feet and a height of 10 feet. Empty weight was 4,255lb against an MTOW of 5,070lb.
Power stemmed from the German Daimler-Benz DB601A V-12 inverted liquid-cooled inline piston engine of 1,550 horsepower. Additional power was had by the injection of water/methanol. Performance included a maximum speed of 435 miles per hour, a range out to 373 miles and a service ceiling of 26,000 feet.
The Ki-78 was picking up speed before World War 2 began and, with interest, authorities of the Imperial Japanese Army (IJA) moved to take over the Ki-78 project in full. Two prototypes were contracted for and work on the first began in September of 1941. The aircraft was completed in 1942 and recorded its first-flight on December 26th. Despite its good showing as a speedy mount, the Ki-78 held little military value and the program was ended in January of 1944. Just one aircraft was completed along with a sole mock-up. The second prototype lay incomplete before being scrapped.