The Heinkel HD 28 was a reconnaissance seaplane developed in Germany in the 1920s for export to Japan.

It was a conventional single-bay biplane with equal-span, unstaggered wings and three cockpits in tandem.

The rudder extended below the line of the lower fuselage, and there was a large ventral fin fitted.

The rearmost cockpit incorporated a ring mount for a gunner.

A single example built by Heinkel and supplied to Aichi as a pattern aircraft, given the designation Aichi Experimental Three-seat Reconnaissance Seaplane, for possible production in Japan, but was rejected due to problems with the engine and also failure to meet performance and weight reduction targets.