The Kayaba Ku-4 was a research aircraft built in Japan in 1940 to investigate the possibilities of tailless aircraft designs. It followed designer Hidemasa Kimura's successful Ku-2 and Ku-3 designs for the Imperial Japanese Army. While these previous aircraft had been gliders, however, the Ku-4 was to be powered by a pusher engine. It had a low, swept wing, and like the Ku-2, fins at the wingtips.

Ku-4
Role	Research aircraft
National origin	Japan
Manufacturer	Kayaba Industry
Designer	Hidemasa Kimura
Status	Cancelled project

Work on the prototype was well advanced by April 1941, but the following month, Kimura's relationship with the Army soured following the crash of the Ku-2. The Ku-4 was canceled, and Kimura eventually received only ¥17,000 of the ¥200,000 that had been promised for the development of his tailless designs.