Japan’s World War II Tailless Aircraft

During the early days of World War II, the Imperial Japanese Navy and Army’s Air Forces had minimal interest in the development of a tailless configuration airplane. This dramatically contrasted with the view held by their main ally, Nazi Germany, who had experimented with tailless aircraft for several years. The lack of effort by the Japanese Navy, the one service viewed by most observers as the forerunner in military aviation in Japan, did not imply that the Army would follow them. Indeed, the Army quickly started a crash design program in late 1939. Because of the lateness of their start, the Japanese Army top brass knew that they needed to set up a program that could achieve in a short time, and with a dwindling financial resource base, maximum results.

The HK1 with a rudder but no tailplane. (photo, via author)

Efforts by the Imperial Japanese Army concentrated on the glider designs of the Kayaba Works Corporation, as well as the Mitsubishi Company’s tailless aircraft designs, which copied the German Messerschmitt Me 163 rocket fighter concept. The Kayaba designs were first conceived to collect data on tailless airplane configurations. Many designs were submitted by engineers inside Kayaba and outside consultants. The most promising design program was the HK1. The HK1 was the brainchild of a brilliant, albeit, obscure Japanese engineer, Dr. Hidemasa Kimura. He based his design on the concept of Kumazo Hino, the pioneer aviator who was the first person in Japan to fly a plane – performing the feat in the spring of 1910. Initial tests on the HK1 design were promising and lead the Japanese Army to sponsor an aircraft concept program – the first step in establishing a development and production program for a military aircraft. Working closely with Kayaba’s Chief Developing Designer, Dr. Shigeki Naito, Kimura designed and constructed a tailless test model aircraft. The model, designated the KU2, was extensively tested between early November 1940 and May 1941.

The KU2 with wingtip rudders. (photo, via author)

After the test phase of the KU2 was over, Dr. Kimura, with the assistance of another brilliant Japanese engineer, Joji Washimi, began to work on a more advance design in the spring of 1941: the KU3 was born. The KU3 was a two-system experimental model, it had no vertical control surfaces and the edges of its wings were cranked, incorporating sections of different angles of sweepback. The KU3 had three-control surfaces arrayed along the trailing edge of each wing. The KU3 made 65 test flights before the only built model crash landed in late 1941.

The KU3, showing it’s cranked wing. (photo, via author)

Kimura wasn’t done with tailless aircraft. He took the data recollected on the KU3 program and used it to built the first Japanese powered tailless aircraft, the KU4. At this moment time was running out for Japan and Kayaba had not shown sufficient concrete results to merit further investment of resources. Japan’s limited resources were needed in other areas. The tide of war had turned against the Empire. The KU4 program was terminated by the Army as soon as the drawings were on the table. This marked the end of any official Japanese-funded research on a tailless aircraft design. Then in 1944, the appearance of America’s massive B-29 bombers in the skies over Japan’s Home Island changed the equation. The Japanese Army, now with the complete support of the Navy, re-started the tailless aircraft program. The need for a high flying interceptor plane to take out the B-29s became imperative. The Army knew time was running out, and so turned to the Germans for help. They knew that any aircraft development program would take years to produce a serviceable plane, and in the case of a radical design such as a tailless aircraft, the development process could take at least a decade. With this situation on their minds, the Japanese Navy leadership decided that the only route available to them was to copy the only successfully operational tailless design program in the world, Germany’s Me 163 Komet rocket fighter. The Mitsubishi Company, using German supplied Me 163 Operational Manuals as well as a Walter HWK 109-509 rocket engine, was selected for the job of interpreting the data given by the Germans. They promptly went to work on a design for the new tailless airplane. In a matter of only months, thanks to the assistance of German engineers, Mitsubishi produced a test version of what they thought would be the next great Japanese plane. The J8M-1 Shusui (Swinging Sword) was unveiled in late December 1944. Mitsubishi built first a glider version for data collection purposes. It first took to the air around mid January 1945 and was subsequently placed in full prototype production mode. Two prototypes models were designated for the two services, the previously mentioned J8M-1 for the Navy and the Army’s Ki-200.

Two MXY-8 training gliders. (photo, via author)

Pilots started taxi-run practices with the J8M-1 gliders at Kashima Air Base in the spring of 1945. Rigorous testing and practice runs were made at Kashima by Navy pilots in preparation for the day when the Walter rocket engines would be fitted on the J8M-1 and the aircraft could take-off under their own power. The first powered J8M-1, fitted with the Walter engine, first took to the air on the morning of June 7th, 1945. A catastrophic engine failure shortly after takeoff resulted in a massive crash and subsequent explosion. The test pilot was killed instantly. This crash and the end of the war just two months after, spelled the end of the minimal Japanese attempt of acquiring a tailless fighter. The J8M-1 never entered assembly line production status, and the next generation Ki-202 advanced fighter never made it off the drawing board. When the Allies entered Japan in August 1945, they discovered, to their relief, a crude tailless program, a program that was doomed before it could takeoff.

– Raul Colon

More information:
wikipedia: Kayaba tailless gliders
The Mitsubishi J8M Shusui
wikipedia: Mitsubishi J8M

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